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:

EER = Capacity (or Btu/hr) / Power (or Watts)

  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!

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:
  • Clean Condenser Coil
  • Proper condenser airflow
  • Recirculation of condenser air
  • Overcharged; Check Subcooling
  Then use this process to verify your unfortunate situation:
  1. Turn off the condenser using the disconnect switch (you still need a call for cooling).  
  2. Remove the wires to the compressor, so that only the condenser fan is operable.
  3. Apply voltage to condenser by turning disconnect back on.  Only the condenser fan should run.
  4. Measure the temperature of the air entering the condenser.
  5. 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.
  6. 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.
  This process works because of the Pressure/Temperature relationship and Dalton's Law of Partial Pressures: Total pressure of a mixture of gases is equal to the sum of their individual pressures.  For instance, if there was non-condensables in a system, your actual pressure will be higher than your supposed saturation temperature.  If your gauges were supposed to read 155# for R-22 because it is 85F outside, but instead they read 175#, then you have 20# of said non-consensable air.  This could increase compressor power consumption by as much as 12%!

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.

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!

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!