EER, IEER, SEER, IPLV, HSPF… What do all of these efficiency terms REALLY mean
EER, IEER, SEER, IPLV, HSPF… You have probably seen all of these terms before and never even thought of what the heck they stand for, or why you would care to look at one over the other. In order to look out for the best interest of the building owner, however, it is important that all of us in the industry can articulate the differences to our customers to ensure the proper equipment is selected.
With the Department of Energy changes on the horizon, I thought I would take the opportunity to dive into what all of these efficiency terms REALLY mean, and what impact they have on end-users and the environment.
EER – (Energy Efficiency Ratio)
This value shows efficiency when operating at peak load capacity (when you could fry an egg on the sidewalk). Although it is a good reference, it can be a misleading representation if you live in a part of the country with seasons.
Defined as “the ratio of the cooling capacity of the unit (in Btu per hour) to the power input (in Watts)” – Energy.gov. This is calculated at 95/75 degrees DB/WB (AHRI Standard Rating Conditions).
IEER – (Integrated Energy Efficiency Ratio)
This value is more representative of the actual efficiency you will get out of your HVAC equipment. To calculate this value, efficiencies are reported at different loads (outdoor temperatures ranging from 65 to 95 degrees F) and then given weights to obtain an overall efficiency value. Surprisingly, the peak load efficiency only counts for 2 percent of the overall value! IEER is calculated as follows:
IEER = (0.02 * A) + (0.617 * B) + (0.238 * C) + (0.125 * D)
A = EER at 100% net capacity at AHRI standard condition (95 deg F)
B = EER at 75% net capacity and reduced ambient (81.5 deg F)
C = EER at 50% net capacity and reduced ambient (68 deg F)
D = EER at 25% net capacity and reduced ambient (65 deg F)
SEER – (Seasonal Energy Efficiency Ratio)
Calculated very similar to IEER above, however, this is more common for residential equipment.
IPLV – (Integrated Part Load Value)
More geared towards Chillers, but still calculated the same way, and gives a standard for real-world efficiency comparison. The formula from AHRI is below:
IPLV = (0.01A) + (0.42B) + (0.45C) + (0.12D)
A = COP or EER @ 100% Load
B = COP or EER @ 75% Load
C = COP or EER @ 50% Load
D = COP or EER @ 25% Load
So, if you are designing for a space with somewhat constant internal loads that are independent of outdoor air temperature, EER is a good indicator. These types of applications come about from time to time in commercial and industrial spaces so it is important to make sure to use the correct basis for comparison.
However, in the much more likely scenario that you live in a place with varying outdoor air temperatures and internal loads, IEER and SEER will be your best bet!