This seems to be one of the unluckiest weeks to draw in the on-call pool
for a technician. You see, over the Winter you have to respond to
no-heat calls much faster than a residence without cooling on Memorial
or Independence Day. I remember visiting homes many Festivus evenings
and getting the old clunker of a boiler running, without the swears from
"A Christmas Story". But, even over the last fifteen years, being on-call
has changed. If you were not able to barter your way out of this
holiday, you may experience a process similar to these:
We would always get that 4:30pm call of the old woman without heat on
Christmas Eve. Why the office staff hadn't left yet, I could never
figure out. Of course, this responsibility fell onto the on-call
technician. Hopefully, the local distributors and stock houses have yet
to close if you needed a part!
About 10-15 years ago, most technicians used to carry beepers. When
you were on-call, you got the pleasure of carrying two beepers and
living in fear of being confused for a drug dealer! When the beeper
went off -911, that dreaded buzz could have been confused for a lot of
things. But, in the back of your mind you knew exactly what it meant!
Luckily, those beepers were quickly replaced with Nextel service and
cell phones. We would instead carry two cell phones when we drew the
short straw over the holidays. The technicians where I worked always
set the most horrible, annoying ring tone on that on-call phone. So bad
that even my wife still can't forget the tone some 4 years later.
Lately, I have noticed more companies are opting for an answering
service. This provides a person for your customer to immediately talk
to, avoiding the situation where they would leave a message and start
dialing another company. I can see how this service would reduce the
frustration for a homeowner that is already uncomfortable without heat.
Still, waiting for that call back will seem like watching water boil,
all the while a potential confrontation brewing.
So, in the age of technology, how great would it be if you could
"FaceTime" with your customer? Video conferencing is quickly taking
over business meetings and would really translate well into the service
industry. How often has a customer screamed, swore, and threatened over
the phone, only to be oh so cordial when face-to-face. Seeing their
trusted technician would go a long way, particularly when they need to
talk them off of that cliff. The technician may be able to avoid an
evening trip on a holiday weekend when you may be paying for warranty
work anyhow. The technician could see the customer pushing the correct
thermostat buttons, or even see the error code on the furnace ahead of
their decision to strap on their boots.
Is anyone out there trying this approach? I understand not everyone
has an IPhone, but there are many tablets and phones that can
accommodate other providers. Is there another recipe that I did not mention? I never thought I would have been carrying
2 beepers at one time, so why not set yourself apart by using the
technology already in both of your fingertips?
A Successful Technician
I am sure I am not the first to write about this, but it doesn't change
expectations of homeowners or trade employers. Why is it that
millionaire ball players can be successful batting .300? A pitcher can
have thirty starts, win 20 games and could be named for the Cy Young?
Or that a successful quarterback can throw 20 touchdowns and 10
interceptions? The reason: they are much better than their peers.
Imagine, as an HVAC Tech, you got the diagnosis correct one-third of the time? For one, if your employer did keep you on the payroll the homeowner would not be calling you back! So what makes a good technician? Not the one winning the Cy Young, he only gets it right two-thirds of the time. Here is a short list that I find 'fits the bill', no matter how far along in the industry they are:
A clear understanding of the basics
If I need to explain what a multimeter is, or how to measure amps and what it means, we have a problem. This assures no batting title and no way I want this player on my team. It is not enough to know just how to take the measurement, the technician should know what they mean. This feeds into proper diagnosis, the first time. When working with any HVAC equipment, you should have a Physics 101 course under your belt as well. As much as I hated that mandatory course in trade school, it has helped me every day in every job I have had since!
When their license/certification expires
Knowing the expiration of their certifications and licenses shows some pride in their accomplishments and contribution to the industry. If they know the expiration, they will know the requirements to renew. The employer should not have to keep track of the minimum requirements for you to work in this industry, I am sure they have kids at home they need to worry about.
Punctuality & Initiative
It is not enough to be on time and in the proper dress, you need to know what you should be doing. Wouldn't it be great to have all the service tickets turned in (with payment), the truck cleaned and restocked, know where you are heading today, and where you could pick up parts if needed? A good technician that is successful in this industry makes all of this happen, before the Service Manager needs to tell them. As a Manager, listen to your techs as this is the way to identify the key players.
Knowledge is Power
There is nothing more powerful in this world than knowledge. I learned this week 2 of boot camp on Parris Island. Learning from those whom have done it the hard way. We had a saying in our platoon some 5 years later: "Work smarter, not harder". If you reach the point of frustration with equipment, or cannot diagnosis the problem in an hour, you likely do not know enough about what you are working on and need to call someone! This is what keeps good technicians engaged in our industry: the unknown. This is also how I figured out I need to keep up with changes in our industry. When you settle on the fact you do not know everything, you realize that attending the evening classes at local distributors has much more in it for the technician, not the company. You see, there may be tools you need to return if things don't work out with your employer, but knowledge will always go with you.
There is still new equipment coming out everyday, with new technology centering around efficiency and comfort. A lot of the old timers, eying retirement and more worried about quitting time, will not be attending these late night classes. Do not fall into this trap! Just because the they are content with their position and not being the best mentor, does not mean you need to follow in these footsteps. Our industry will be in dire need of qualified, engaged technicians in no time. Ones that can fill the unrealistic expectations set by homeowners and employers alike, making much less than ten percent of the worst pitcher in the league, but getting the diagnosis right 99% of the time!
Imagine, as an HVAC Tech, you got the diagnosis correct one-third of the time? For one, if your employer did keep you on the payroll the homeowner would not be calling you back! So what makes a good technician? Not the one winning the Cy Young, he only gets it right two-thirds of the time. Here is a short list that I find 'fits the bill', no matter how far along in the industry they are:
A clear understanding of the basics
If I need to explain what a multimeter is, or how to measure amps and what it means, we have a problem. This assures no batting title and no way I want this player on my team. It is not enough to know just how to take the measurement, the technician should know what they mean. This feeds into proper diagnosis, the first time. When working with any HVAC equipment, you should have a Physics 101 course under your belt as well. As much as I hated that mandatory course in trade school, it has helped me every day in every job I have had since!
When their license/certification expires
Knowing the expiration of their certifications and licenses shows some pride in their accomplishments and contribution to the industry. If they know the expiration, they will know the requirements to renew. The employer should not have to keep track of the minimum requirements for you to work in this industry, I am sure they have kids at home they need to worry about.
Punctuality & Initiative
It is not enough to be on time and in the proper dress, you need to know what you should be doing. Wouldn't it be great to have all the service tickets turned in (with payment), the truck cleaned and restocked, know where you are heading today, and where you could pick up parts if needed? A good technician that is successful in this industry makes all of this happen, before the Service Manager needs to tell them. As a Manager, listen to your techs as this is the way to identify the key players.
Knowledge is Power
There is nothing more powerful in this world than knowledge. I learned this week 2 of boot camp on Parris Island. Learning from those whom have done it the hard way. We had a saying in our platoon some 5 years later: "Work smarter, not harder". If you reach the point of frustration with equipment, or cannot diagnosis the problem in an hour, you likely do not know enough about what you are working on and need to call someone! This is what keeps good technicians engaged in our industry: the unknown. This is also how I figured out I need to keep up with changes in our industry. When you settle on the fact you do not know everything, you realize that attending the evening classes at local distributors has much more in it for the technician, not the company. You see, there may be tools you need to return if things don't work out with your employer, but knowledge will always go with you.
There is still new equipment coming out everyday, with new technology centering around efficiency and comfort. A lot of the old timers, eying retirement and more worried about quitting time, will not be attending these late night classes. Do not fall into this trap! Just because the they are content with their position and not being the best mentor, does not mean you need to follow in these footsteps. Our industry will be in dire need of qualified, engaged technicians in no time. Ones that can fill the unrealistic expectations set by homeowners and employers alike, making much less than ten percent of the worst pitcher in the league, but getting the diagnosis right 99% of the time!
Return Air Locations
When using ACCA's Manual T for register selection, there are several basic rules that are followed regarding location. Most guidelines revolve around room air circulation and stagnant air, as well as the equipment application (heating only, cooling only, or combination). Application is the largest determining factor when it comes to return air locations.
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Diagnosing Bypass Air
How is it possible to cool the air if it never passes through the evaporator? I think we both know what the answer is, it cannot happen. This tends to take place with improperly installed coils for A/C add-ons. But, cutting into the plenum to take a look is time consuming and for any mechanical company "time is money". Here is a way to be sure you should spend the time, just be prepared for what you will find!
The simplest way to know you have too much bypass air, air not being cooled by the evaporator through bypassing, is to measure the temperature drop and superheat of the system during operation. If you have measured low superheat and low temperature split, then you have too much bypass air.
When there is a large amount of bypass air, Technicians tend to see low suction pressures and start to add refrigerant. This will not fix the system! In fact, you will likely flood the evaporator and run the chance of slugging the compressor with liquid. You must measure the superheat and subcooling to verify proper refrigerant charge. Do not fall into the pressure trap. Since the air is not traveling through the evaporator, the heat is not being delivered to the refrigerant and therefore cannot absorb that heat. This tends to drive the evaporator temperature lower, equaling lower suction pressure. If you try to add refrigerant, you could go through an entire 30# cylinder and not change your suction pressure!
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| Add-on Evaporator with Bypass Air (Submitted by a local MA Contractor) |
Since the air is not traveling through the coil, the air is not being cooled, and you will measure a low temperature split (Return Air Dry Bulb - Supply Air Dry Bulb). Typically, temperature split on a properly commissioned system can be anywhere from 10⁰F to 30⁰F. The actual target temperature split depends on the operating conditions and proper refrigerant charge. When I say you will see low temperature split, you will most likely be under 10⁰F. This is not going to cool the building, under almost any load.
Before spending the time cutting into plenums, redesigning systems, and cursing the installation crew, be sure to set the system up correctly. This means 350-450 CFM per ton of airflow (matched to the condensing unit), and an attempt to adjust the refrigerant charge. Then, if you find you still have low superheat and low temperature split, start cutting - cursing is really not needed and will not fix a thing!
Building Code: ACCA Manual S
For information regarding changes to ACCA Manual S, Click Here.
A seldom practiced design procedure, equipment selection, has been part of the International Residential Code for many years, and local MA/RI code at least since 2010. This critical step is the second part of residential system design, following a Manual J load calculation and prior to the Manual D duct design. I think confusion around the dated manual has contributed to lack of use and enforcement. Whether you are installing an air-conditioner, heat pump, furnace, or boiler, there is a definite maximum over sizing that is allowed under the code, based on ACCA Manual S.
If installing a furnace or boiler, you are allowed to oversize the equipment by 40% above the Manual J heat loss of the home. This is based on the net or output BTU/hr of the equipment. Of course, significantly over sizing equipment can lead to many mechanical and comfort issues, but a system could be oversized by 100% and not have it affect the AFUE!
When installing a heat pump, you can oversize the equipment by a max of 25% above the Manual J Heat Gain of the building. Under no circumstances are you allowed to size to the heating load, based on International and Local building codes. This means you will need supplemental heat to make up the difference between the heating output of the heat pump and the heat loss of the home at your design temperatures.
For A/C systems, some math is required. I could not hold your attention long enough in a blog to explain the how - we have a tough enough time during class, those who have attended can attest! Basically, you cannot oversize your A/C by more than 15% above the heat gain of the home. You will notice that they gave you some room for heat pumps to gain that extra output in heating. The problems with oversized equipment is only compounding as our ducts and homes get tighter with the new code. When we (not sure who "we" are) were ok with throwing energy into the attic, that oversized system worked - it blew cold air. But let me ask you this: Was it efficient cold air?
Since this Manual S was last updated in 1995, it does not limit how to select variable speed equipment, interpretation treating them and conventional as one and the same. A two-stage or multi-stage condenser is not what I mean here - there is a big difference with Variable Refrigerant Flow (VRF). Since the turndown ratio is so large with the updated ductless heat pumps, I would install a ductless system in my own home sized to the heating load knowing that the capacity will ramp down in the summer = I can still feel comfortable. Carrier, Bryant, and Whirlpool all have conventional split systems with this VRF technology. So, just because the code (Manual S) is outdated, should the homeowner suffer? Why does it seem like our industry is already ahead of the code the day it is adopted, and still not enforced?
A seldom practiced design procedure, equipment selection, has been part of the International Residential Code for many years, and local MA/RI code at least since 2010. This critical step is the second part of residential system design, following a Manual J load calculation and prior to the Manual D duct design. I think confusion around the dated manual has contributed to lack of use and enforcement. Whether you are installing an air-conditioner, heat pump, furnace, or boiler, there is a definite maximum over sizing that is allowed under the code, based on ACCA Manual S.
If installing a furnace or boiler, you are allowed to oversize the equipment by 40% above the Manual J heat loss of the home. This is based on the net or output BTU/hr of the equipment. Of course, significantly over sizing equipment can lead to many mechanical and comfort issues, but a system could be oversized by 100% and not have it affect the AFUE!
When installing a heat pump, you can oversize the equipment by a max of 25% above the Manual J Heat Gain of the building. Under no circumstances are you allowed to size to the heating load, based on International and Local building codes. This means you will need supplemental heat to make up the difference between the heating output of the heat pump and the heat loss of the home at your design temperatures.
For A/C systems, some math is required. I could not hold your attention long enough in a blog to explain the how - we have a tough enough time during class, those who have attended can attest! Basically, you cannot oversize your A/C by more than 15% above the heat gain of the home. You will notice that they gave you some room for heat pumps to gain that extra output in heating. The problems with oversized equipment is only compounding as our ducts and homes get tighter with the new code. When we (not sure who "we" are) were ok with throwing energy into the attic, that oversized system worked - it blew cold air. But let me ask you this: Was it efficient cold air?
Since this Manual S was last updated in 1995, it does not limit how to select variable speed equipment, interpretation treating them and conventional as one and the same. A two-stage or multi-stage condenser is not what I mean here - there is a big difference with Variable Refrigerant Flow (VRF). Since the turndown ratio is so large with the updated ductless heat pumps, I would install a ductless system in my own home sized to the heating load knowing that the capacity will ramp down in the summer = I can still feel comfortable. Carrier, Bryant, and Whirlpool all have conventional split systems with this VRF technology. So, just because the code (Manual S) is outdated, should the homeowner suffer? Why does it seem like our industry is already ahead of the code the day it is adopted, and still not enforced?
Humidification: Forced-Air Systems
Months fly by, and it is closer to Fall in New England. Soon most local Plumbing, Heating, and Cooling companies will be consumed with Fall maintenance programs. I remember spending countless hours a week dealing with humidifiers, whether it was the old Skuttle drum style, the Aprilaire bypass version, or even the steam models that have actually been improved over the years - particularly Honeywell's Truesteam. The one common theme that always arose was: What do I set the humidistat for? If you loyal readers remember, a while back I wrote a short blog about ASHRAE's Psychometric Comfort Zone. Based on this time tested theory, you can set the Relative Humidity (RH) anywhere between 30-60%! With scorched, or forced-air, systems it is desirable to keep the RH between 35-45% in order to prevent static buildup (ACCA Manual RS). But, every home is different. In order to properly sense the RH, most humidistats are located on the return duct. This may represent the RH at some point in the house, but not everywhere. So, what is the maximum RH that should be set? I say it depends on the windows - as visible condensation on the windows can cause many problems. There is a possibility of concealed condensation in walls, but if a vapor retarder is used and installed correctly, this should not happen in New England. As a Service Technician, we can only worry about the visible condensation. If concealed condensation is a concern, please contact a qualified Building Analyst!
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| Equation for Surface Temp. |
Visible condensation occurs on surfaces that have a temperature below the dew point of the air. This is why we get "dew" on the grass or my car most summer mornings. Or why an evaporator actually condensates during operation in our climate. The temperature of the coil (Evaporator Saturation Temp) is lower than the dew point of the return air. In order to find out the maximum RH prior to visible condensation, you should use this equation and a Psychrometric chart. You will need to know the indoor and outdoor design temperatures, and the u-value of the device calculating for. Since the weak point in most walls is the window, you should find the lowest u-value window in the conditioned space. If you were solving for a wall or ceiling, remember that the U-Value = 1/R-value, or the inverse.
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| .49 U-Value Window in MA |
For example, lets say your design temperatures were 0F (typical local outdoor) and 70F (2009 IECC and building code compliant indoor), with a window that has a .49 U-Value ( typical double pane, wood frame). Using the formula, you can determine the temperature of the window at design temperatures, in this case 48F. This correlates to a dew-point of about 47F. Then, use of your psychrometric chart (I am sure "there is an app for that") you can determine the max setting for your central humidifier is about 45% RH.
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| .36 U-Value Window in MA |
Control of this is very important for most new homes as this math with a Low-E window having a .36 U-Value may not yield any visible condensation until the relative humidity hits close to 60%! If technicians are using the old method of visible condensation, it may be too late for "insert issue here" (concealed condensation, mold, damage to paintings, pianos, etc) or I like to say the many possibilities of IAQ. In fact, did you know that just as much (if not more) bacteria, viruses, fungi, and mites grow above 60%RH as they do below 30%RH? (see ASHRAE Systems and Equipment Handbook, 2000) Not only does the static vanish between 35-45%, but so does the rest of the unwanted possibilities. Ever wonder why condensation builds in attic duct systems and supply registers during the winter? Check out the duct insulation and do the math...
Triple Evacuation vs. Deep Vacuum Method
Little did I know, call it that HVAC Tech's ignorant moment, there are actually two different types of methods of evacuating a system free from non-condensables. The Deep Vacuum and the Triple Evacuation methods are not one in the same. Maybe my confusion started because I kind of used a hybrid to maximize my time on the job site. Hopefully this could help you!
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Duct Gains: Why do we hate R-8?
Ever since the adoption of the 2009 International Residential Energy Conservation Code (IECC), duct sealing efforts have been tested using the total leakage or leakage to outdoors methods. It really is amazing how much duct gains effect the operation of your equipment and the comfort of your customer. The missing part of "duct testing" appears to be how well the ducts are insulated. Sure, you are required to use R-8 insulation on supply ductwork when located outside the building envelope, but how do we know it was installed correctly? We're not required to test like the duct leakage codes, so is a check in the box sufficient? How about we use some simple math to figure the gains, or lost capacities in cooling, and hold everyone to a standard - check out the equation below.
Sensible Btu/hr = CFM x Delta T x 1.08
So, based on this math, one can take a few simple temperature measurements and calculate the lost sensible capacities due to duct leakage and insulation. You should measure the temp of the air entering the return grille and at the unit to figure the return gain in sensible temperature. I would also recommend averaging the temp readings at the furthest supply register, an average supply register, and a close one to figure the delta T from the air exiting the coil or air handler. Do the same for an extensive return system.
When you start measuring, it is very scary what you start to find. As you can see, like the industry accepted national average, this system is losing 30% of the 3-ton capacity through it's well sealed, but poorly insulated duct system. Unfortunately, the method is not perfect since a hotter day in the attic could cause greater gains. But, that would be the time to sell duct sealing and insulation to the homeowner! Any of you energy auditors out there could probably comment on how much attic ducts effect home infiltration as well. So, why do we hate R-8 insulation? Is it really just the hassle of wrapping the equivalent of a blanket around the ducts? I don't recommend retrofitting a distribution system in an attic in the middle of July, but maybe it makes sense to offer to come back in the Fall? Please, don't just leave it be! Doing so makes it hard for this tree hugger to sleep at night!
Site Survey: Windows & SHGC
When completing your site survey for Manual J Load Calculations, significant time can (or should) be spent identifying window values. Did you know that most windows these days come with an NFRC rating, a tag located in the window jam that you can reference on NFRC.org? This identification number can tell you important details like window coatings, u-value, light transmittance, air leakage, and solar heat gain coefficients (SHGC). Not identifying the correct values can sway your load calculation thousands of Btu's per hour in both directions, in heating and cooling. Of course, the SHGC impacts the cooling load more heavily.
There are a few things that can influence the solar heat gain through a window or glass door. You can manage these gains by installing awnings and/or exterior shades, but the easiest way is to use windows with low SHGC values. Rated on a scale of zero to one, the lower the value than the less btu/hr gains from the suns rays make it into your home.
Using a leading load calculation software program, I was able to create a few scenarios to display the importance of spending the extra few moments at the customer's home during the sales process and site survey. When adding a 4'x6' bay style, facing south, vinyl frame, double-pane, and clear window, the cooling load was increased by a total btu/hr of 1,045. If spending the time to include the shading default of medium color blinds at 45 degrees, and an outdoor insect screen (50%), then the load of the window can be minimized to only 790 btu/hr.
If the contractor spent the extra few moments to identify the NFRC rating of the window, they may have been able to establish there is a low-e coating on this particular window. When including only the coating, not the blinds and insect screen, the cooling load of the window was minimized to just 688 bu/hr. You can see how missing this feature, multiplied by all of the windows in the home can contribute to improperly over-sizing equipment and IAQ issues like high humidity, etc. Also, this can change the system design process when selecting equipment and designing ductwork in the ACCA Manuals S and D. Or, maybe the window faces another direction, and this creates a spike in the "adequate exposure diversity" that could otherwise require zoning.
On the bright side, no pun intended, you can see how installing blinds and insect screens could deflect the sun's rays just enough to possibly make an uncomfortable room bearable under high loads. When a homeowner is uncomfortable in particular rooms, it always turns into an HVAC Contractor's nightmare to appease them. Instead of blaming the airflow, ductwork, or even system sizing, maybe you should look to those wide open skylights and bay windows. Sure, I like the sun, but sometimes you have to compromise in order to feel "comfortable" when it is 100F and sunny outside.
There are a few things that can influence the solar heat gain through a window or glass door. You can manage these gains by installing awnings and/or exterior shades, but the easiest way is to use windows with low SHGC values. Rated on a scale of zero to one, the lower the value than the less btu/hr gains from the suns rays make it into your home.
Using a leading load calculation software program, I was able to create a few scenarios to display the importance of spending the extra few moments at the customer's home during the sales process and site survey. When adding a 4'x6' bay style, facing south, vinyl frame, double-pane, and clear window, the cooling load was increased by a total btu/hr of 1,045. If spending the time to include the shading default of medium color blinds at 45 degrees, and an outdoor insect screen (50%), then the load of the window can be minimized to only 790 btu/hr.
If the contractor spent the extra few moments to identify the NFRC rating of the window, they may have been able to establish there is a low-e coating on this particular window. When including only the coating, not the blinds and insect screen, the cooling load of the window was minimized to just 688 bu/hr. You can see how missing this feature, multiplied by all of the windows in the home can contribute to improperly over-sizing equipment and IAQ issues like high humidity, etc. Also, this can change the system design process when selecting equipment and designing ductwork in the ACCA Manuals S and D. Or, maybe the window faces another direction, and this creates a spike in the "adequate exposure diversity" that could otherwise require zoning.
On the bright side, no pun intended, you can see how installing blinds and insect screens could deflect the sun's rays just enough to possibly make an uncomfortable room bearable under high loads. When a homeowner is uncomfortable in particular rooms, it always turns into an HVAC Contractor's nightmare to appease them. Instead of blaming the airflow, ductwork, or even system sizing, maybe you should look to those wide open skylights and bay windows. Sure, I like the sun, but sometimes you have to compromise in order to feel "comfortable" when it is 100F and sunny outside.
Heat Pump Break-Even COP's
How do you know if should upgrade your air-conditioner to a heat-pump and create a dual-source application during replacement this Summer? I personally always prefer the option of multiple fuel sources, particularly since energy prices have been all over the place during the last decade. Fortunately, based on average energy prices, there is some simple math to figure out if an aggressive assessment should be made for a dual-source heat pump application, based on equations from ACCA's Manual H: "Heat Pump Systems: Principles and Applications". First, you will need the average energy costs for the selected fuels, and then plug in the information into the equations below. This will provide your "break-even COP", or the point where operating the heat pump will cost the same as the furnace. You can then take the calculated Coefficient of Performance (COP) and see what temperature the heat pump will be operating at; the lower the better!
I did a little research for you, so lets insert the average annual prices into the Natural Gas, Oil, and Propane equations to see if the investment in a heat pump will make sense during replacement.
As you can see, if installing a 96% Natural Gas furnace, the Break-Even COP would be 6.8. Based on the Heating Performance Data for Goodman's most efficient DSZC18 Heat Pump, it would need to be above 65F for the cost to operate the heat pump to be cheaper than the Natural Gas Furnace (see data at bottom). Even if I installed an 80% furnace, the break even COP is still at 5.7, much too high to realize a savings.
Not all homes in MA are lucky to have access to a Natural Gas supply. There are more than enough Oil Tanks out there to keep the hundreds of delivery companies busy during most New England winters. As you can see in the equation for oil, a resulting break-even COP of 1.17 indicates a significant savings can be realized. Based on installing an extremely efficient 87% oil furnace and the same heat pump performance data, the heat pump would still be cheaper to operate as low as -10F. Of course, you must worry about the output of the heat pump at that low ambient, and in order to feel comfortable you will need to calculate the Thermal Balance Point.
If you decide to install a Propane tank you can realize the same efficiencies as the natural gas furnaces out there, but the increased costs in fuel/delivery could be even higher in than oil, even after including recent oil surges. As you can see, the break even COP for installing a heat pump add-on above a 96% Propane Furnace is only 1.07. This is even lower than the Oil application, proving the recommendation of a more thorough calculation into the Thermal Balance Point and investment costs for going to Dual Source.
With the recent technological advancements in the HVAC industry in controls and conventionally ducted VRF's like the Carrier GreenSpeed, break even COP's and Thermal Balance Points can be driven even lower. This makes Dual Source Heat pump applications more attracting to New England homeowners. Some contractors are still installing electric supplemental heat, hopefully in stages, for low-ambient operation. Although not any more efficient than the heat strips it replaced, the new heat pumps could save more than enough above the temperature of the defrost cycle to still be worth it. I would still prefer dual-source, you know these energy companies will not be leaving any money on the table over the long run!
With the recent technological advancements in the HVAC industry in controls and conventionally ducted VRF's like the Carrier GreenSpeed, break even COP's and Thermal Balance Points can be driven even lower. This makes Dual Source Heat pump applications more attracting to New England homeowners. Some contractors are still installing electric supplemental heat, hopefully in stages, for low-ambient operation. Although not any more efficient than the heat strips it replaced, the new heat pumps could save more than enough above the temperature of the defrost cycle to still be worth it. I would still prefer dual-source, you know these energy companies will not be leaving any money on the table over the long run!
Diagnosing Improper Fixed Orifice Sizes
I have found that this topic often goes unnoticed, or can be a guessing game out there in the field. Diagnosing improper fixed orifice sizes is actually a fairly simple, cut and dry procedure. First, I would argue for efficiency reasons, as well as ease of proper charging, you should just field install a TXV. Of course, when you are on the job site you don't want to spend precious time attempting to adjust refrigerant charge with the incorrect orifice. You would never be able to get the Superheat and Subcooling within proper parameters. The next best thing to field installing the TXV is actually installing the correct orifice to match the condensing unit - which is why they are shipped accordingly.
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Correctly Sizing a Capacitor
I don't know how many times a technician has said that they installed a part based on what was on their service truck. I have heard of technicians wasting money over-sizing contactors, cutting down air filters, and even using controlled substances to clear condensate drains! Of course, these scenarios all get the job done, but I would argue the many reasons why not to do these. The one thing that gets to me is when a technician doesn't verify they are installing the correct size dual run capacitor. Believe it or not, there is a simple method to figuring the correct size capacitor, without waiting on hold for the distributor's guru. Of course, you could use a multimeter that reads microfarads (uf), but this will only tell you if the existing capacitor is weak - not the correct size!
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Realistic Expectations and "The Occupied Zone"
How many times as a technician have you gone out to the same customer's home because of unrealistic expectations? Some homeowners expect air-conditioners to work like an ice box, want you to size them for their big party on Fourth of July weekend, and expect you to show up at the drop of a dime when it doesn't meet their impossible notion. Of course, this could be avoided by establishing a standard during the sales process or a little customer education. I liked to talk about "The Occupied Zone" and work in a little Radiant Asymmetry, using more layman's terms of course.
The occupied zone is a concept used in the design process to properly heat and cool spaces without a customer feeling drafts. As you can see in the picture taken from ACCA Manual RS: Comfort, Air Quality, and Efficiency By Design, the zone is 2' inwards from all walls and ceilings. ACCA Manual J: Residential Load Calculation, states the occupied zone is only 6.5' in height. This area near walls and ceilings is use to mix conditioned air with room air. In fact, this mixing is what cuts down on occupants feeling convective currents or drafts in the heating season.
Not only will occupants feel drafts, but they will feel what is termed as radiant asymmetry. This is the phenomenon (not really, just to a homeowner) of a warm or cold temperature. If the wall is colder than you are, the wall will be pulling radiant heat from you. This makes you feel cold, even if it is 70F in the room, hence the statement "a cold 70F". The best example I ever heard of this is the temperature at an ice rink. It feels cold when on the ice, but the air temperature hovers around 65F! Anyhow, have you ever wondered how much asymmetry is too much? ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy was nice enough to spell this out for us. As you can see, a warm ceiling is the number one device that occupants will find uncomfortable with only a 10-20F difference. This would of course happen during the cooling season, and with any luck on Friday afternoon just before that Summer, holiday weekend/family reunion, right? I can see this happening more often in Cape style homes since there are more ceiling/roof combinations and occupants are more than likely outside of the occupied zone. The only answer to this issue is proper home air sealing and insulation. It does not matter how oversized your air-conditioner is, it will not be able to overcome the laws of physics and radiation. This is just another reason to peer into the attic during your sales calls to verify the weatherization of the home and the thermal boundary. Don't set your install up for failure, and certainly establish some basic expectations with the homeowner. You don't want to leave this up to your technician on a holiday weekend, getting paid double-time for warranty work!
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| Occupied Zone - ACCA Manual RS |
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| ASHRAE Standard 55 |
Energy Efficiency Ratio (EER)
Energy Efficiency Ratio, or EER, is a way to exhibit how well an air-conditioner is operating based on the power being used. Most homeowners are of course familiar with SEER, the ratio across an entire season. Since SEER is tested at a "partial load", the EER is a more realistic number to use when figuring energy savings. AHRI tests their EER of residential air-conditioners using 400 CFM per ton of airflow at 95F Outdoors / 80F Indoors and 67F Wet Bulb. This compared to the SEER testing completed at 82F Outdoors and the same indoor conditions.
When using EER in the field, a technician can effectively calculate improvements made to systems being serviced using this simple equation:
Without getting too technical, the capacity can be calculated by using supply and return wet bulb readings, converted to enthalpy. Use the equation Q = (H2 - H1) x 4.5 x CFM. H2 being the Return Enthalpy and H1 being Supply. When calculating total power, use Power = Volts x Amps x Power Factor.
This will give a snapshot of the system based on the test conditions that day, or time of day. We know that in New England, if you don't like the weather to just wait five minutes, right? So, it is possible that a technician could have made an improvement to the a/c, but since the sun came out the EER may have still dropped. One would need to normalize the answers to a known point in order then compare apples to apples. This is where computers and tablets come in handy.
The above equation explains why there is a benefit to add refrigerant to an undercharged system. The capacity gained by correcting the superheat and/or subcooling will outweigh the additional watts used by the compressor. We all know that if we make the compressor work harder by introducing additional refrigerant, the amperage draw will increase during run load. As long as the EER rises, the customer will benefit. Adjusting refrigerant charge is not the only way to improve this ratio, you could also fix airflow issues, seal duct systems, or even reduce watt usage by replacing components like blowers with more efficient alternatives. In fact, then maybe the system will actually reach temperature and shut down. There really is no better energy savings than that, right?
When a technician overcharges a system, using the EER equation, you can see the condenser will use additional wattage without a benefit of additional capacity. It does not take much refrigerant to overcharge a high SEER condenser these days. I was working with a contractor just last week on a micro-channel unit. We removed 4 oz. of R-410A and reduced the subcooling from 20F to the correct 10F. This is the amount of refrigerant that could fit into a 6' charging hose! Be careful out there, it is amazing what you find when you start measuring the invisible!
When using EER in the field, a technician can effectively calculate improvements made to systems being serviced using this simple equation:
EER = Capacity (or Btu/hr) / Power (or Watts)
This will give a snapshot of the system based on the test conditions that day, or time of day. We know that in New England, if you don't like the weather to just wait five minutes, right? So, it is possible that a technician could have made an improvement to the a/c, but since the sun came out the EER may have still dropped. One would need to normalize the answers to a known point in order then compare apples to apples. This is where computers and tablets come in handy.
The above equation explains why there is a benefit to add refrigerant to an undercharged system. The capacity gained by correcting the superheat and/or subcooling will outweigh the additional watts used by the compressor. We all know that if we make the compressor work harder by introducing additional refrigerant, the amperage draw will increase during run load. As long as the EER rises, the customer will benefit. Adjusting refrigerant charge is not the only way to improve this ratio, you could also fix airflow issues, seal duct systems, or even reduce watt usage by replacing components like blowers with more efficient alternatives. In fact, then maybe the system will actually reach temperature and shut down. There really is no better energy savings than that, right?
When a technician overcharges a system, using the EER equation, you can see the condenser will use additional wattage without a benefit of additional capacity. It does not take much refrigerant to overcharge a high SEER condenser these days. I was working with a contractor just last week on a micro-channel unit. We removed 4 oz. of R-410A and reduced the subcooling from 20F to the correct 10F. This is the amount of refrigerant that could fit into a 6' charging hose! Be careful out there, it is amazing what you find when you start measuring the invisible!
Non-Condensables? Are you sure?
Non-condensables in a residential split air-conditioner can be, for most technicians, a pandora's box to diagnose. Fortunately, there is a simple process that can identify this condition without spending hours and hundreds of dollars in virgin refrigerant. I think we all are aware that R-22 has hit an all time high, so getting this right is more important than ever - if you want to retain your customer.
There are several ways air and/or water vapor can enter a sealed system. First, improper evacuation practices appear to be the most common these days. If you are not currently evacuating a system using the Triple Evacuation Method, I highly recommend it - along with the manufacturer of the equipment you are installing if you want to keep that warranty! So do a quick search on the web, read it, it's simple. Second, careless service by the technicians. When connecting your gauges to a closed system, be sure to purge the air (non-condensables) from your refrigerant lines. This seems like such an easy thing, but hurried technicians working in extreme conditions tend to make mistakes, particularly after a long week of such. The final way that I am aware of air entering a system is one with a leak, so bad that the suction line pulls into a vacuum, pulling air into the system. When a technician finds this situation, the first instinct is to add refrigerant and then diagnose the issue. There is a leak, do not knowingly vent refrigerant into our environment by adding! Use dry nitrogen to pressurize an empty system, then use the Triple Evacuation Method once the leak is fixed!
Non-condensables can cause many problems in a working system. The problems arise when that air settles in the condenser coil, taking up room and board without pulling it's weight! Since air cannot be condensed, it remains stuck there in the condenser or accumulator, increasing your head pressure. Since the area of your condenser becomes reduced for the refrigerant to reject heat, the head pressure elevates to compensate, now relying on temperature difference instead of surface area of the coil. When this happens, you will get higher discharge/condensing temperatures and reduced capacities. Based on the only value I could find over the years,"a 10 psi increase in condensing pressure will increase power consumption of compressors by 6%." ("Air Tech Notes". T. Quello, 2004) If there is enough air in there, you could cause the amperage of the compressor to raise to a point of internal overload.
If you think you have non-condensables in a working system, because some joker is keeping you gainfully employed, be sure to verify it is not any of the following conditions causing your high head pressure:
There are several ways air and/or water vapor can enter a sealed system. First, improper evacuation practices appear to be the most common these days. If you are not currently evacuating a system using the Triple Evacuation Method, I highly recommend it - along with the manufacturer of the equipment you are installing if you want to keep that warranty! So do a quick search on the web, read it, it's simple. Second, careless service by the technicians. When connecting your gauges to a closed system, be sure to purge the air (non-condensables) from your refrigerant lines. This seems like such an easy thing, but hurried technicians working in extreme conditions tend to make mistakes, particularly after a long week of such. The final way that I am aware of air entering a system is one with a leak, so bad that the suction line pulls into a vacuum, pulling air into the system. When a technician finds this situation, the first instinct is to add refrigerant and then diagnose the issue. There is a leak, do not knowingly vent refrigerant into our environment by adding! Use dry nitrogen to pressurize an empty system, then use the Triple Evacuation Method once the leak is fixed!
Non-condensables can cause many problems in a working system. The problems arise when that air settles in the condenser coil, taking up room and board without pulling it's weight! Since air cannot be condensed, it remains stuck there in the condenser or accumulator, increasing your head pressure. Since the area of your condenser becomes reduced for the refrigerant to reject heat, the head pressure elevates to compensate, now relying on temperature difference instead of surface area of the coil. When this happens, you will get higher discharge/condensing temperatures and reduced capacities. Based on the only value I could find over the years,"a 10 psi increase in condensing pressure will increase power consumption of compressors by 6%." ("Air Tech Notes". T. Quello, 2004) If there is enough air in there, you could cause the amperage of the compressor to raise to a point of internal overload.
If you think you have non-condensables in a working system, because some joker is keeping you gainfully employed, be sure to verify it is not any of the following conditions causing your high head pressure:
- Clean Condenser Coil
- Proper condenser airflow
- Recirculation of condenser air
- Overcharged; Check Subcooling
- Turn off the condenser using the disconnect switch (you still need a call for cooling).
- Remove the wires to the compressor, so that only the condenser fan is operable.
- Apply voltage to condenser by turning disconnect back on. Only the condenser fan should run.
- Measure the temperature of the air entering the condenser.
- After a few minutes, use your Pressure/Temperature (PT) Chart for your selected refrigerant to identify the saturation pressure - based on the Condenser Entering Ambient.
- Your Liquid Line Pressure should equal the Saturation Pressure, based on the PT Chart. This is within a couple of degrees of the outdoor ambient, to allow for tool accuracy.
New England: HRV or ERV?
I remember installing some early version residential Energy Recovery Ventilators (ERV) and discovering a potential freezing issue. Also, if I used only a Heat Recovery Ventilator (HRV) than I would be drying the air during the Winter, and adding significant latent load in the summer. So, which one do I choose? The homes are tight enough these days to require mechanical ventilation, and I would much rather a balanced ventilation system that I can control.
An HRV works well for tight, moisture prone homes. This is because the unit can actually recover up to 85% of the exhaust air's heat, preheating the incoming fresh air. A small diagram from Honeywell shows how the air crosses paths on the core to cause this transfer, with as little as 10% contamination. Unfortunately, any ventilation in New England will reduce the indoor relative humidity in the Winter due to the cold, dry fresh air. This means that in the Summer, the very humid air can be tempered, but will increase the indoor RH and cause an increase in load on your air-conditioner. Since our part of the country sees approximately 2,500 run hours in heating, and only 500 in cooling, I would recommend installing an HRV on heating only equipment or tight homes with many occupants or latent load in the Winter. This means there was no need to install a humidifier!
For those homes with an air-conditioner, or concerns about moisture control (too dry in the winter), than I would always recommend an ERV. An ERV not only transfers the heat, but controls a small amount of moisture as well. This will not remove the need for a dehumidifer, but will certainly decrease the load caused by your ventilation efforts. Those old freeze-up problems I saw on the early systems were addressed years ago with more integrated controls that actually sense defrost. If the temperature in these units get below 20F in the Winter, the fresh air damper closes to increase the temperature of the core and avoid freezing! The most important feature of the ERV is the moisture transfer. For instance, if the hot, humid Summer air was to enter the home or central a/c unchecked, this would increase the latent load of the unit and create a situation where the homeowner may be uncomfortable and turn off their ventilation. By removing up to 80% of this load, there is little tax on the central a/c. ERV's are most cost effective in extreme climates like New England. I would also install an ERV in a climate like Miami, extreme latent loads year round. Just remeber, it is not the outdoor climate that determines which unit to install, it is the indoor climate of the home and possibly HVAC equipment that decides which system is best!
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| Honeywell HRV |
An HRV works well for tight, moisture prone homes. This is because the unit can actually recover up to 85% of the exhaust air's heat, preheating the incoming fresh air. A small diagram from Honeywell shows how the air crosses paths on the core to cause this transfer, with as little as 10% contamination. Unfortunately, any ventilation in New England will reduce the indoor relative humidity in the Winter due to the cold, dry fresh air. This means that in the Summer, the very humid air can be tempered, but will increase the indoor RH and cause an increase in load on your air-conditioner. Since our part of the country sees approximately 2,500 run hours in heating, and only 500 in cooling, I would recommend installing an HRV on heating only equipment or tight homes with many occupants or latent load in the Winter. This means there was no need to install a humidifier!
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| Honeywell ERV |
For those homes with an air-conditioner, or concerns about moisture control (too dry in the winter), than I would always recommend an ERV. An ERV not only transfers the heat, but controls a small amount of moisture as well. This will not remove the need for a dehumidifer, but will certainly decrease the load caused by your ventilation efforts. Those old freeze-up problems I saw on the early systems were addressed years ago with more integrated controls that actually sense defrost. If the temperature in these units get below 20F in the Winter, the fresh air damper closes to increase the temperature of the core and avoid freezing! The most important feature of the ERV is the moisture transfer. For instance, if the hot, humid Summer air was to enter the home or central a/c unchecked, this would increase the latent load of the unit and create a situation where the homeowner may be uncomfortable and turn off their ventilation. By removing up to 80% of this load, there is little tax on the central a/c. ERV's are most cost effective in extreme climates like New England. I would also install an ERV in a climate like Miami, extreme latent loads year round. Just remeber, it is not the outdoor climate that determines which unit to install, it is the indoor climate of the home and possibly HVAC equipment that decides which system is best!
Site Survey: Area-Weighted Average R-Value
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| R-Value Weighted Average Worksheet |
Due to the recent plunge into Spring (or more like Summer!) weather, most Residential HVAC Companies in New England have seen a fair amount of early season sales calls for air-conditioning. This quick changeover tends to spark some very interesting conversations around Load Calculations and Site Survey. One in particular tends to come up every year: Attic Insulation. Attic Insulation can be a tough R-Value to identify when out on a quick sales call, so it is important to take notes as to what you see. This way the Area-Weighted Average R-Value can be calculated prior to entering such details into your software. The first image is a blank worksheet to calculate this average R-Value, which is always more affected if you have a well insulated attic. I will walk through (2) examples to examine a properly insulated attic and one with poorly installed insulation.
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| Example #1 |
In my first example, I have a 920 Sq. ft. attic with 12" of blown-in fiberglass - a value of R-30. This value must be discounted for all of the other areas in that attic without the 12" of insulation. For instance, an uninsulated 2' x 2' access hatch. This wood has an R-2 value. The 2"x 6" rafters that have 6" of insulation above them have an effective R-17 (6" of insulation = R-15;Wood = R-2). As well as the (10) 12" x 12" supply and return registers/grilles, and 24" x 24" hall return I am about to cut-in and turn this ceiling into swiss cheese! Remember, we insulate our ducts to R-8 outside the building envelope for code (this attic is outside). When completing this worksheet, I need to figure the areas (in feet) of the devices being deducted from the entire ceiling in order accurately estimate the remaining ceiling area. In the first example, with perfectly installed R-30 insulation, we reduced the average value of this ceiling to an R-25! Doesn't sound tremendous, but this can affect your heat loss as well as your heat gain calculations.
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| Example #2 |
The second example uses poorly installed insulation. Sure, there was still 12" in some locations. But, did you know that just 2% voids in insulation can reduce that R-30 to only R-15? No offense to all the homeowners and "DIYers" out there, but this is why we hire licensed contractors - to get what you pay for! Since the starting value is so low, when weighting out the average and adjusting for the access hatch, rafters, and registers, the value is only reduced to R-14.5. When entering this into software, it will need to be R-15 anyhow.
So, finding the R-Value weighted average does not need to be done for every ceiling/attic, only the ones that were well insulated! If the insulation was not installed professionally, I would take an extra moment to probe around and discount the starting R-Value accordingly. Just don't take it for granted, see it with your own eyes - this means a trip to the attic on all of those sales calls involving a load calculation! Otherwise, you are doing the customer and your company a disservice!
TXV Hunting Season
If you didn't call out sick today from Spring Fever, you may be working on some air-conditioners sooner than later! It looks like it may actually reach 70F in New England and Service Managers will be looking to push the envelope when it comes to Maintenance. I used to try and fit in some early season cleanings and always had trouble in the mornings. You see, Thermostatic Expansion Valve (TXV) Hunting Season just opened and it is everyone's best guess if these units will work correctly come July.
I found out some interesting information about R-410A TXV's a few days back, and as always I am willing to share. When there was the big switch to 13 SEER and R-410A a few years ago, manufacturers actually adapted their TXV technology to work for the new pressure, rather than redesign their valves. Danfoss claims, based on independent studies, a TXV will save 15-26% when replacing a fixed metering device. When this changeover happened, hundreds of thousands of non-optimized valves were installed. These systems work just swell under a load, but when we are completing maintenance under less than desirable conditions, the TXV's tend to "hunt" and never let the air-conditioner reach a steady state. This can create some serious issues if liquid makes it back to the compressor, and I am sure we have all heard that wonderful sound on more than one occasion. Anyhow, if the valve does close entirely under low load, the system operates like a fixed metering device is installed - which we know are very load dependent. Emerson actually figured this out quite quickly, and in 2008 began to manufacture R-410A optimized valves called their C-Series. This valve made the unit reach steady state under low loads (little to no hunting), and actually requires less refrigerant. In turn, this lets OEM's create smaller coils. This valve actually made systems operate .5 SEER higher than ones without optimized TXV's. The biggest influence is early season maintenance and installations since technicians can actually get the refrigerant charge correct. When charging under low load, it is very simple for a technician to overcharge a system. The other day I was on a job site with a valve like this, and it was only 64F outdoors. At first, the TXV was hunting and we figured it was due to the low load, remember: TXV hunting season! When I saw the valve, I immediately recommended that the technician adjust and tighten the sensing bulb. Sure enough, the Superheat pegged at 8F, and now the subcooling was around 22F! This was actually due to a short line set, he knew better than to charge under such low load - even though he could have with these new valves.
There was a study completed two years ago by some physical engineers at Purdue that quantified a few points for undercharged units. Apparently, SEER and COP (for heat pumps) are not decreased until the units reach 70% or less of their recommended charge (Kim, Braun, Purdue University, 2010). This is the point when the TXV actually shuts down and acts like a fixed orifice. These units that reach 25% undercharged see a decrease in SEER by 16%, and on average will use $100 per ton, per year more than a correctly charged unit. But be careful here, don't overcharge a system and create problems come July. Verify the TXV bulb is tight, to the point you cannot move it by hand. Also, the bulb needs to be correctly installed and insulated, even if installed at the factory. Just because old TXV's used to hunt under low loads doesn't mean all of them will. Take the time to correctly diagnose the TXV operation before you add or remove refrigerant!
I found out some interesting information about R-410A TXV's a few days back, and as always I am willing to share. When there was the big switch to 13 SEER and R-410A a few years ago, manufacturers actually adapted their TXV technology to work for the new pressure, rather than redesign their valves. Danfoss claims, based on independent studies, a TXV will save 15-26% when replacing a fixed metering device. When this changeover happened, hundreds of thousands of non-optimized valves were installed. These systems work just swell under a load, but when we are completing maintenance under less than desirable conditions, the TXV's tend to "hunt" and never let the air-conditioner reach a steady state. This can create some serious issues if liquid makes it back to the compressor, and I am sure we have all heard that wonderful sound on more than one occasion. Anyhow, if the valve does close entirely under low load, the system operates like a fixed metering device is installed - which we know are very load dependent. Emerson actually figured this out quite quickly, and in 2008 began to manufacture R-410A optimized valves called their C-Series. This valve made the unit reach steady state under low loads (little to no hunting), and actually requires less refrigerant. In turn, this lets OEM's create smaller coils. This valve actually made systems operate .5 SEER higher than ones without optimized TXV's. The biggest influence is early season maintenance and installations since technicians can actually get the refrigerant charge correct. When charging under low load, it is very simple for a technician to overcharge a system. The other day I was on a job site with a valve like this, and it was only 64F outdoors. At first, the TXV was hunting and we figured it was due to the low load, remember: TXV hunting season! When I saw the valve, I immediately recommended that the technician adjust and tighten the sensing bulb. Sure enough, the Superheat pegged at 8F, and now the subcooling was around 22F! This was actually due to a short line set, he knew better than to charge under such low load - even though he could have with these new valves.
There was a study completed two years ago by some physical engineers at Purdue that quantified a few points for undercharged units. Apparently, SEER and COP (for heat pumps) are not decreased until the units reach 70% or less of their recommended charge (Kim, Braun, Purdue University, 2010). This is the point when the TXV actually shuts down and acts like a fixed orifice. These units that reach 25% undercharged see a decrease in SEER by 16%, and on average will use $100 per ton, per year more than a correctly charged unit. But be careful here, don't overcharge a system and create problems come July. Verify the TXV bulb is tight, to the point you cannot move it by hand. Also, the bulb needs to be correctly installed and insulated, even if installed at the factory. Just because old TXV's used to hunt under low loads doesn't mean all of them will. Take the time to correctly diagnose the TXV operation before you add or remove refrigerant!
MA/RI Code: Interior Design Conditions
Besides proper indoor air quality, comfort, and system sizing, there is one other important reason to size your heating and air conditioning equipment to the proper indoor design conditions: State Code! This is always a tough conversation with the homeowner. After all, the customer is always right, right? When I start to talk about state codes, I like to explain to those less concerned that this is the worst case allowed by laws in our state. Luckily for homeowners and quality contractors, these days that minimum is getting better. The 2006 and 2009 International Energy Conservation Code sets the minimum indoor design temperatures in cooling and the maximum indoor design temperature in heating. Notice the years? This is not new information, it is just finally being enforced. For the most part, as soon as something is enforced in this state, that is when contractors "embrace".
2009 IECC Section 302.1: Interior Design Conditions
- The interior design temperatures used for heating and cooling load calculations shall be a maximum of 72° (22°C) for heating and a minimum of 75°F (24°C) for cooling.
Why these temperatures you might ask? Please refer to the ASHRAE Psychrometric Comfort Zone. If you notice, there is no place in the Summer when sizing to 70F and any humidity level is comfortable. If your system was to actually reach 70F in a home during the summer, your customer will feel cold and clammy. You should always design to the ACCA Manual J cooling indoor design conditions of 75F and 50% Relative Humidity (RH). This will put you in the middle of that comfort zone with some room for "drift" on those above design days in mid August. If the unit cannot keep up, it will operate constantly, and it will still be comfortable in the conditioned space. Humans are much more sensitive to the relative humidity than the sensible temperature on the thermostat. ASHRAE was nice enough to publish some charts regarding their reasoning for 50%RH with respect to indoor air quality as well. Lo and behold the least amount of viruses, bacteria, mold, etc. grow between 30%RH and 50%RH! This is why we add humidifiers to forced-air furnaces in the Winter.
So, customer education to establish expectations is a must in today's equipment sales process. If you install a system to code, the very minimum required by state laws, it will not run the same as the old unit. We found it is much more efficient to properly size systems for homes, not homeowner lifestyles. Sure, you can give the customer what they want - but I am sure they would rather be comfortable, with a unit installed to code!
2009 IECC Section 302.1: Interior Design Conditions
- The interior design temperatures used for heating and cooling load calculations shall be a maximum of 72° (22°C) for heating and a minimum of 75°F (24°C) for cooling.
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| ASHRAE Comfort Zone |
So, customer education to establish expectations is a must in today's equipment sales process. If you install a system to code, the very minimum required by state laws, it will not run the same as the old unit. We found it is much more efficient to properly size systems for homes, not homeowner lifestyles. Sure, you can give the customer what they want - but I am sure they would rather be comfortable, with a unit installed to code!
MA: Completing a Total Leakage Duct Test
If you have not been asked to complete a duct test by your local Massachusetts Inspector, it is just a matter of time before you are surprised by this additional code requirement. Despite some push-back from city and town Inspectors, all of MA is required to test new or altered duct systems - with varying enforcement, and held to various degrees of leakage rates. All of MA adopted the 2009 International Energy Conservation Code (IECC) back in 2010. Some cities and towns wished to be eligible for the available funding from the Green Communities Act, and voted to adopt a Stretch Code - known to most contractors as the more stringent regulation. It pays to know which towns you are working in, and their permit structure, to avoid losing what could amount to be a significant part of your profit on these jobs.
If you are working in most of the cities and towns across the state, you are able to complete your own "Total Leakage Duct Test". If the town adopted the Stretch Code, third-party testing by a RESNET Certified HERS Rater will be required. This means that even if you went and got your certification, you could not test your own jobs in these towns anyhow. Don't worry though, a HERS Rater is needed to rate the home or addition, and their testing is not exclusive to your duct system. This means a rating is needed when a Building Permit is pulled, a change to a structural wall. In other words, if the testing does not fail due to your duct system, the general contractor will be paying for this rating. For all other cities and towns across MA, you can complete your own testing and no certification is needed. In fact, there are no certifying bodies for duct testing that I am aware of. Many organizations like BPI or RESNET will offer training, but no certification.
Anyhow, take a look at the attached document I created, I think it will help those that are just becoming involved with Duct Testing in MA. Also, please share your experiences with the local city and town requirements by commenting below - nobody likes to be surprised!
If you are working in most of the cities and towns across the state, you are able to complete your own "Total Leakage Duct Test". If the town adopted the Stretch Code, third-party testing by a RESNET Certified HERS Rater will be required. This means that even if you went and got your certification, you could not test your own jobs in these towns anyhow. Don't worry though, a HERS Rater is needed to rate the home or addition, and their testing is not exclusive to your duct system. This means a rating is needed when a Building Permit is pulled, a change to a structural wall. In other words, if the testing does not fail due to your duct system, the general contractor will be paying for this rating. For all other cities and towns across MA, you can complete your own testing and no certification is needed. In fact, there are no certifying bodies for duct testing that I am aware of. Many organizations like BPI or RESNET will offer training, but no certification.
Anyhow, take a look at the attached document I created, I think it will help those that are just becoming involved with Duct Testing in MA. Also, please share your experiences with the local city and town requirements by commenting below - nobody likes to be surprised!
Home Performance: Combustion Powered Ventilation?
I sat in a review class today prior to my Building Performance Institute (BPI) written exam, and I heard the first explanation I have ever seen as to how a basement would become more humid after replacing a furnace. So, I have to share with as many folks as possible in our HVAC field. You see, a Category I furnace: naturally vented and 80%+ AFUE, takes the needed air for combustion from the basement. Once burned, said byproducts go out the chimney; the draft (or draft inducer) pulling the needed combustion air, and with it moisture out of the home. What happens when a responsible contractor identifies an opportunity to save fuel and sells the homeowner a sealed combustion 95%+ AFUE furnace? Now, that combustion powered ventilator was removed from the basement, leaving the high moisture content air to sit there.
The solution? Add ventilation. But, one does not know what one does not test. How do you know if you actually need to add ventilation to a home that has had the natural conditions changed, and how long does that fan need to operate? During the retrofit furnace replacement, the HVAC Contractor more than likely changed the way the home performs as a system. If an air-conditioner was not working correctly you would have to send a technician out to test it, right? This is where a Home Performance Contractor, or Energy Auditor, could identify this ventilation need - or lack there of. You don't know what you don't test, and since you installed a sealed combustion furnace you are more than likely not going to kill anyone; but this does not mean you're not killing the house! There is some simple math that can be completed, coupled with a blower door test and you can know if you must add ventilation to the home.
I remember a lot of local HVAC contractors up in arms last year about BPI certifying heating professionals. Instead of complaining, I would highly recommend these guys jump on board. As an HVAC professional for all of my working life - granted that is "only" the last 15 years, I can contest that is is much easier for an HVAC technician to become a Building Analyst Professional than the other way around. There is some training involved, but believe it or not these guys have some real important information to share that just may save your business one day - or at least help you sleep at night! Check out their standards, easiest way to learn something new/free this week: http://bpi.org/standards_approved.aspx
The solution? Add ventilation. But, one does not know what one does not test. How do you know if you actually need to add ventilation to a home that has had the natural conditions changed, and how long does that fan need to operate? During the retrofit furnace replacement, the HVAC Contractor more than likely changed the way the home performs as a system. If an air-conditioner was not working correctly you would have to send a technician out to test it, right? This is where a Home Performance Contractor, or Energy Auditor, could identify this ventilation need - or lack there of. You don't know what you don't test, and since you installed a sealed combustion furnace you are more than likely not going to kill anyone; but this does not mean you're not killing the house! There is some simple math that can be completed, coupled with a blower door test and you can know if you must add ventilation to the home.
I remember a lot of local HVAC contractors up in arms last year about BPI certifying heating professionals. Instead of complaining, I would highly recommend these guys jump on board. As an HVAC professional for all of my working life - granted that is "only" the last 15 years, I can contest that is is much easier for an HVAC technician to become a Building Analyst Professional than the other way around. There is some training involved, but believe it or not these guys have some real important information to share that just may save your business one day - or at least help you sleep at night! Check out their standards, easiest way to learn something new/free this week: http://bpi.org/standards_approved.aspx
Dirty Socks in the Attic?
Last week I heard a great idea from a great HVAC contractor - the two kind of go together don't they? It is an easy answer to a common problem in our industry: the dirty sock syndrome. I have heard of many ways to avoid condensation forming over the winter in ducts and on coils, including but not limited to: operating your fan constantly, installing a fan cycling thermostat, and use of a UV light. Unfortunately, all of these solutions are not demand based, meaning they will operate whether they are needed or not. For those of you that know me, you know that I have crossed over to the dark side of Energy Efficiency - and I can't sleep at night if I installed one of these solutions. Don't get the wrong idea, these are solutions and will stop that smell first thing in the Spring. But, how much energy did it take to get you there, and how much was the total investment for the homeowner? What if I told you there was a simple fix that would cost you, the contractor, about $50? Got your attention?
In the Northeast we have a lot of boilers, and I mean a lot! Usually, this means a lot of ductwork must be added in the attic - for that all important conditioned air in the Summer. Unfortunately, this creates quite the "chimney effect" and phantom airflow issues all winter. Most homeowners are aware that they need to close the supply registers, but returns are often ignored since there is no easy way to close them. I used to use a white trash bag to cover the air filter, but you can see where this is leading when the homeowner forgets to call you for maintenance by late May. So, instead of closing off the registers, why not cycle the fan on a demand basis? Mold, mildew, and that dirty sock smell is created by condensation and standing water in the ducts and coils over the winter. In order for condensation to form, the relative humidity in the ductwork must reach 100% Rh, right? That is the humidity when it is raining outside, 100%. For sake of simple math, and to avoid the psychrometric conversation, I am going to leave out dew points and surface temperatures. The easiest solution there is to just insulate your ducts to code. Anyhow, if you install a De-humidistat to close the Fan circuit, or 'G' on your Integrated Fan Control, than the fan will cycle on (in most cases on your lowest speed) prior to condensation forming in your ducts and coils. The key point here is that it will then shut off when the humidity reaches the acceptable level that you set it for. So, you may get a short span of cool air being blown around that zone, but doesn't that beat the poor indoor air quality and men's locker room stink in the Spring? Not to mention less energy use (Kwh) to get you there!
Special thanks to Jeff Rossi of RER Fuel for sharing this week's tip. Jeff knows this works because it was a solution for his own house!
In the Northeast we have a lot of boilers, and I mean a lot! Usually, this means a lot of ductwork must be added in the attic - for that all important conditioned air in the Summer. Unfortunately, this creates quite the "chimney effect" and phantom airflow issues all winter. Most homeowners are aware that they need to close the supply registers, but returns are often ignored since there is no easy way to close them. I used to use a white trash bag to cover the air filter, but you can see where this is leading when the homeowner forgets to call you for maintenance by late May. So, instead of closing off the registers, why not cycle the fan on a demand basis? Mold, mildew, and that dirty sock smell is created by condensation and standing water in the ducts and coils over the winter. In order for condensation to form, the relative humidity in the ductwork must reach 100% Rh, right? That is the humidity when it is raining outside, 100%. For sake of simple math, and to avoid the psychrometric conversation, I am going to leave out dew points and surface temperatures. The easiest solution there is to just insulate your ducts to code. Anyhow, if you install a De-humidistat to close the Fan circuit, or 'G' on your Integrated Fan Control, than the fan will cycle on (in most cases on your lowest speed) prior to condensation forming in your ducts and coils. The key point here is that it will then shut off when the humidity reaches the acceptable level that you set it for. So, you may get a short span of cool air being blown around that zone, but doesn't that beat the poor indoor air quality and men's locker room stink in the Spring? Not to mention less energy use (Kwh) to get you there!
Special thanks to Jeff Rossi of RER Fuel for sharing this week's tip. Jeff knows this works because it was a solution for his own house!
Rules of Duct Design, Why?
I went many years as a Service Tech and never had a clue as to these rules. As a matter of fact I went years as a Service Manager, and quite a while as an Instructor, without seeing these all in one place. I had this problem with learning the hard way - who knew you could pick up a book (or read a blog!) and learn this so easy? If you haven't been able to tell, I am all for giving this type of information to those that need it; so please share with your service managers, techs, sales, and even the greenest of tin knockers.
Excess Air has moved to HVACProBlog.com! Read More
Excess Air has moved to HVACProBlog.com! Read More
Sleep through the Static
In my last post, Under Pressure, I talked about available blower static pressure and PSC motor maximums. But, what if you have correctly designed the ductwork and set up your airflow perfectly - only to get a call years later about an uncomfortable couple of rooms? A contractor in RI had just this problem a week ago, but he was armed with the knowledge of static pressure and the ability to measure it!
Last week I got a call from the contractor in RI with a couple of static pressure measurements that didn't sound quite right. He explained that during the recent cold spell, most of the rooms being fed by this unit were uncomfortable. He checked the static pressure in the supply duct and only had a .01" w.c. - almost nothing. Measuring before the add-on A/C coil, doing so by removing the high limit switch of the furnace, the tech was able to record a static pressure of .77"w.c.! Most coils have a pressure drop of .20"-.30"w.c. when clean. Since the pressure drop of the coil is .76" (.77 - .01), it was easy to determine that the clogged evaporator was the culprit. Since removing this 10 year old coil that was obviously never cleaned was so labor intensive, the tech was able to sell a new coil that will be compatible with DOE SEER minimums when the time comes to replace the condensing unit.
If the technician was never armed with the necessary tools and knowledge, it would have been easy to start replacing motors and searching for disconnected ductwork. After all, mechanical systems are much easier to fix when you know what the answers are. Static Pressure, like temperatures or amperage, is an invisible thing and we must have the right tools to even quantify them. Start measuring static pressure when commissioning the unit, and during maintenance. It really is amazing what you will find!
Static pressure is a simple measurement that can be taken with a static pressure probe and a dual-input manometer. I have seen guys out there still using magnahelics, u-tube and incline manometers. These mechanical means will give you the same answer - but I wouldn't use an abacus to do what I can with a calculator! Anyhow, the manometer you are using to measure gas pressure can be used for static pressure too, as long as the resolution is .01" w.c. (25 pascals) or better. With static pressure, we are able to see how much (or little) pressure is in the ductwork. We can also identify restrictions like clogged evaporator coils or hidden air filters. I once used a static pressure probe to locate a filter that had been insulated over and remained untouched for years! When measuring, I had a very low negative static pressure before the filter, and extremely high negative static after. This identified an abnormal restriction. Most pleated filters have a .12"-.15" pressure drop when clean.
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| Dirty Coil Angle #1 (.76"w.c. pressure drop) |
Last week I got a call from the contractor in RI with a couple of static pressure measurements that didn't sound quite right. He explained that during the recent cold spell, most of the rooms being fed by this unit were uncomfortable. He checked the static pressure in the supply duct and only had a .01" w.c. - almost nothing. Measuring before the add-on A/C coil, doing so by removing the high limit switch of the furnace, the tech was able to record a static pressure of .77"w.c.! Most coils have a pressure drop of .20"-.30"w.c. when clean. Since the pressure drop of the coil is .76" (.77 - .01), it was easy to determine that the clogged evaporator was the culprit. Since removing this 10 year old coil that was obviously never cleaned was so labor intensive, the tech was able to sell a new coil that will be compatible with DOE SEER minimums when the time comes to replace the condensing unit.
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| Dirty Coil Angle #2 |
If the technician was never armed with the necessary tools and knowledge, it would have been easy to start replacing motors and searching for disconnected ductwork. After all, mechanical systems are much easier to fix when you know what the answers are. Static Pressure, like temperatures or amperage, is an invisible thing and we must have the right tools to even quantify them. Start measuring static pressure when commissioning the unit, and during maintenance. It really is amazing what you will find!
Under Pressure
A recent conversation with a high quality HVAC contractor reminded me that every piece of equipment (and people for that matter) has their limits. A 1/2 ton truck can only pull so much weight, a man can watch only so many movie award shows, and a Permanent Split-Capacitor (PSC) motor can overcome only so much static pressure. The conversation started centered around figuring the design friction loss for a newly installed unit. For those seasoned system designers, you should be aware that this very important number is traditionally figured prior to duct installation. Anyhow, in order to calculate the friction loss, one must know the available blower static pressure and the total equivalent length of the longest duct run. Here in lies the problem: How can a blower overcome more static pressure than it is "designed" for?
Most technicians have looked at furnace manufacturer data plates to write down model numbers and even find the required temperature rise. System designers usually peer over manufacturer ratings and instructions, long before the homeowner makes that last payment - never mind by the time a technician completes a service call. The issue is that many system designers and technicians overlook an important detail on every forced-air furnace's label: Maximum Total Static Pressure. This is the highest amount of restriction the motor can overcome before seeing performance issues, like frozen a/c coils for instance. When designing the system, and figuring the available blower static, it is most important to be able to deliver your design airflow (CFM) at half of an inch of water column (.50" w.c.) on medium speed. All PSC blower motors have manufacturer blower charts that generally end at .50" w.c. and have clearly labeled data plates stating this maximum restriction.
Sounds like a lot of pressure to go around, right? Well, the maximum is not all that is available. What if we added a new high efficient 4" or 5" pleated filter? This is a restriction in our airflow, and the higher the airflow the more of a restriction. In this particular example, we lost .20" w.c. for the air filter, when it is clean and new! Also, since there is ductwork on that furnace, why not add an evaporator for air-conditioning? That's right, another restriction and we lost .25" w.c. for this device. Oh, and don't forget the return grille, balancing damper, and supply register on that longest duct run. This added an additional loss of .09" w.c. Some quick math, even for the greenest of technicians, will show that we now have negative available blower static pressure (.50" - .20" - .25" - .09" = -.04"). This means there is no static to overcome any ductwork! Unfortunately, by this point all of the ducts are installed and the unit is operating - providing the much needed heat over the past week of single digit weather. So, it is determined that the ductwork is undersized and modifications are needed. This is usually quite the conversation to have with the homeowner, and do you think they will be paying to fix that ductwork? Good luck! The problem could have been found long before this point by installing equipment at or below it's limits. Technicians could find this issue much quicker by measuring total static pressure, or even measuring airflow for that matter. The problem is not that the ductwork is too small, it is usually the fact that it was designed using a different or incorrect friction rate. Electronically Commuted Motors (ECM's) can help deliver the airflow and comfort, but higher static (max should be .80" or less) translates to more noise and increased Kwh. Think about these things before setting your equipment up for failure! Remember: a PSC motor can only overcome .50" w.c. and most men have a (1) movie award show limit per year...
Most technicians have looked at furnace manufacturer data plates to write down model numbers and even find the required temperature rise. System designers usually peer over manufacturer ratings and instructions, long before the homeowner makes that last payment - never mind by the time a technician completes a service call. The issue is that many system designers and technicians overlook an important detail on every forced-air furnace's label: Maximum Total Static Pressure. This is the highest amount of restriction the motor can overcome before seeing performance issues, like frozen a/c coils for instance. When designing the system, and figuring the available blower static, it is most important to be able to deliver your design airflow (CFM) at half of an inch of water column (.50" w.c.) on medium speed. All PSC blower motors have manufacturer blower charts that generally end at .50" w.c. and have clearly labeled data plates stating this maximum restriction.
Sounds like a lot of pressure to go around, right? Well, the maximum is not all that is available. What if we added a new high efficient 4" or 5" pleated filter? This is a restriction in our airflow, and the higher the airflow the more of a restriction. In this particular example, we lost .20" w.c. for the air filter, when it is clean and new! Also, since there is ductwork on that furnace, why not add an evaporator for air-conditioning? That's right, another restriction and we lost .25" w.c. for this device. Oh, and don't forget the return grille, balancing damper, and supply register on that longest duct run. This added an additional loss of .09" w.c. Some quick math, even for the greenest of technicians, will show that we now have negative available blower static pressure (.50" - .20" - .25" - .09" = -.04"). This means there is no static to overcome any ductwork! Unfortunately, by this point all of the ducts are installed and the unit is operating - providing the much needed heat over the past week of single digit weather. So, it is determined that the ductwork is undersized and modifications are needed. This is usually quite the conversation to have with the homeowner, and do you think they will be paying to fix that ductwork? Good luck! The problem could have been found long before this point by installing equipment at or below it's limits. Technicians could find this issue much quicker by measuring total static pressure, or even measuring airflow for that matter. The problem is not that the ductwork is too small, it is usually the fact that it was designed using a different or incorrect friction rate. Electronically Commuted Motors (ECM's) can help deliver the airflow and comfort, but higher static (max should be .80" or less) translates to more noise and increased Kwh. Think about these things before setting your equipment up for failure! Remember: a PSC motor can only overcome .50" w.c. and most men have a (1) movie award show limit per year...
The Drop Light
Well, the mild Winter couldn't last forever in New England - and so starts all the panic phone calls from those that did not have their equipment maintained. I used to dread waking up on days like today, something about snow that brings out all the crazy homeowners. Don't get me wrong, companies I have worked for made plenty of money while I ran around like a chicken with my head cut-off. I used to do well selling maintenance contracts on the first snow day, and the first scorcher after Memorial Day too! Imagine telling a homeowner that if they had completed preventive maintenance back in October they wouldn't have had to call you today - and would have been much more comfortable when trying to roll out of that warm bed this morning. As a technician, I started out not finding the value in maintenance or service contracts. But, I firmly believe that is because no one showed me how to correctly service a furnace, heat-pump, A/C, etc. The old man I first carried tools for was more concerned that I knew how to wrap up his drop light than teaching me how to set a heat anticipator! I just didn't see what the big secret was and set out to find out on my own.
When you get right down to it there is much more to maintenance than changing the air filter and kicking the ductwork while mumbling to yourself that "it's still here!". A lot of companies out there have what we call "A" and "B" techs. The "B" techs tend to be the ones doing the maintenance and are viewed not as profitable as the "A's". But, completing proper maintenance can take quite the load off of your Service Departments on these first days of snow. How many times have you had to go back to homes on days like today under warranty because the system was just serviced? If you are starting to count any number above zero than it sounds to me like you showed your "B" techs how to wrap up a drop light! Don't leave it as a mystery with these guys, start making your service department profitable: invest in them. We're not talking about increasing hourly wages here, we're talking updated testing equipment and knowledge. Completing proper maintenance prior to the heating and cooling seasons will free-up your "A" techs to respond to the emergencies, and give your staff the ability to respond to new customers at a time like this. We all have to start somewhere, and believe me when I say I can wrap a drop light with the best of them!
When you get right down to it there is much more to maintenance than changing the air filter and kicking the ductwork while mumbling to yourself that "it's still here!". A lot of companies out there have what we call "A" and "B" techs. The "B" techs tend to be the ones doing the maintenance and are viewed not as profitable as the "A's". But, completing proper maintenance can take quite the load off of your Service Departments on these first days of snow. How many times have you had to go back to homes on days like today under warranty because the system was just serviced? If you are starting to count any number above zero than it sounds to me like you showed your "B" techs how to wrap up a drop light! Don't leave it as a mystery with these guys, start making your service department profitable: invest in them. We're not talking about increasing hourly wages here, we're talking updated testing equipment and knowledge. Completing proper maintenance prior to the heating and cooling seasons will free-up your "A" techs to respond to the emergencies, and give your staff the ability to respond to new customers at a time like this. We all have to start somewhere, and believe me when I say I can wrap a drop light with the best of them!
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