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!

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Comment by tedkidd on May 18, 2012 at 5:36pm

ho boy, is this gonna turn into a top ten list?

Sellers oversize:

Because they're busy when it's zero or one hundred, and they can't spend uncompensated time fielding complaints or attempting to explain recovery to attention deficit disorder listening disabled clients who choose to leave equipment off until they get home...

Comment by Tom DelConte on May 18, 2012 at 12:28pm
Why hvac sellers oversize: so you can hold your daughter's wedding at home on a sweltering 95 degree F day! This was actually told to me by an hvac "sizer". He forgot to mention his profit!
Comment by Bob Blanchette on May 14, 2012 at 7:43pm

Could undersizing actually increase real world SEER beyond the ratings at the expense of being warm on the hottest afternoons of the year? Could blower speeds be increased during times of high demand to get a bit more sensible capacity out of the system? A 2 stage thermostat could easily engage a higher blower speed during times of high sensible demand. Once the sensible demand was satisfied the blower could drop back to low speed to work on the latent load. There's no reason equipment needs have a constant blower speed regardless of type of load.

Comment by Bob Blanchette on May 14, 2012 at 7:37pm

Tedkidd you are onto something. Unless the consumer participates in Time of Use pricing from the utility they are FAR better off with correctly sized equipment vs. a setback thermostat. In our area the local utility is giving price breaks for shifting use to off peak times (Peak is 2-7pm weekdays). Under the program electricity is  about 1/2 the standard rate during the "off peak" times, but about double during the on peak times. Under such a program a setback stat makes a LOT of sense...

Comment by tedkidd on May 14, 2012 at 11:43am

Nice post Chris, really nice response Steve!  

Let's not forget the HVAC guy's burden of completely unreasonable expectations and avoiding no pay highly time consuming complaint calls.  Homeowners get home to a 95f 90% home and want 70f 60% in 45 minutes.  And everyone telling homeowners that equipment not running saves money, so they do everything they can to keep the equipment from running, including throwing windows open at 75f 95%rh.  

Moisture is energy, and it is not moved quickly.  Not efficiently anyway.  I really feel this is an issue of design failure based upon operational ignorance and absurd expectation.  Discuss latent and psychometric curves - are you kidding me right now!?  Watch the prospect's eyes go foggy and lose the sale? Can't pay the mortgage if you don't sell.

Projecting savings that nobody measures or tracks is so absurd.  There is no verification.  No tracking of Realization Rates.  I have to agree with my buddy Phil - the best lie wins.  

So we may sell equipment with the appearance of high seer/eer, but the true efficiency may be more like a Prius with 18 cylinder engines and emergency brakes 1/3 on all the time so the homeowner can accelerate 0-60 in 6 seconds starting at the bottom of a hill.  After all, they don't call complaining about energy savings they don't track, they call when 0-60 takes 15 seconds.  

SEER and EER are about as much hooey as the rest.  Now you've got short cycling, throw in pressure releasing TXV's and what is really happening to SEER and EER...

Fast recovery and high efficiency are polar opposites.  Until we are willing to accept and teach this, take a stand against absurd, unmeasured "energy savings operational strategies"  and teach you can't have recovery and good latent management (mold avoidance, etc).  

We need to track realization rates.  We need to get stupid pet tricks out of the lexicon.  We need a way for people to see what absurd thermostat machinations ACTUALLY save (or cost!).  

Comment by Steven Lewis on May 10, 2012 at 11:50am

I agree with what you say.  Properly charged units perform better and last longer while using the minimum amount of electricity they can.  I will give you a reason why SEER came in. It had little to with improving efficiency by looking at EER alone.  What was happening was when there was a single number EER, rated at a specific temperature. some manufacturers were designing systems to meet the test and their performance went away if the temp (conditions it was operating in) changed.  This allowed some manufacturers to sell high EER systems at lower costs and that really misled the public's ability to make an informed decision.   SEER was the response to this and while it isn't perfect it does reflect a more real world application and has the effect of making manufacturers design equipment that performs in a wide range of temps.

Now to the actual design and charging of the systems you discussed on the micro channel systems that are starting to appear.  Correct charge is critical since their design will not allow the condenser coil to store refrigerant like the traditional systems.  These designs are being implemented to reduce the amount of refrigerant contained in the systems as well as having some size and cost advantages.  Charging "beer can cold" was only the lazy way to do it never the correct way. 

Another change is that most manufacturers are now designing equipment to 350 cfm per ton to start getting back the ability to dehumidify (latent heat) that has been a comfort issue in newer high efficiency systems. Old systems did that already by adding "airflow modifiers"    that means "crappy Duct Systems"

As long as people are involved in the design, application and service of heating and A/C systems I will never be out of work.  LOL

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