Working With It: Operating
Performance Ratings
Most manufacturers publish performance ratings on their various models. These ratings are usually specified by a model number at a fixed air flow in cubic feet from minute (cfm) with the following variables:
- Several fluid flow rates in gallons per minute;
- Entering fluid temperatures from 25 to 100 degrees;
- Entering air temperatures at 80 degrees dry bulb and 67 degrees wet bulb for cooling; and
- Entering air at 70 degree dry bulb for heating.
The following rating values are given for cooling for each of the above variables:
- Total capacity in Btu per hour;
- Sensible heat capacity in Btu per hour;
- Heat rejection to the loop in Btu per hour;
- Power input in watts; and
- Energy efficiency rating (EER), which is the total capacity divided by the power input, or Btu per watt.
Also, for each of these variables, the following rating values are given for heating:
- Total capacity in Btu per hour;
- Heat absorption from the loop in Btu per hour;
- Power input in watts;
- Coefficient of Performance (COP), which is the total capacity divided by the power input converted to Btu per hour, and multiplied by 3.412 Btu per hour per watt; and
- Performance includes provision for an antifreeze solution used at 35 degrees and below entering water temperatures, but not the pumping penalty for the antifreeze use.
It's important not to extrapolate from the data tables provided by the manufacturers. Extrapolation removes the data from the context and boundaries of the table, and is not a good engineering practice. This is why most manufacturers say that interpolation between ratings within a table is permissible, but extrapolation is not.
Other published data typically includes:
- Correction factors given for various other entering air conditions, dry and wet bulb, and other air flow ratings.
- The unit water pressure drop is also published for each flow rate, in either feet of water or pounds per square inch.
- Blower performance including fan motor brake horsepower and external static pressure capability.
- Electrical data on voltages and current draw.
- Physical data including operating weight and refrigerant charge.
- Hot water generating capacity.
Closed loop certification
Manufacturers of products certified by the ARI Standard 330 for ground-source closed loop heat pump equipment publish a capacity rating for each model, cataloged at the standard entering water rating conditions of both 77 degrees for cooling and 32 degrees for heating.
The cooling EER, heating COP and fluid flow for both is also published.
In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a penalty for the water pump effect of 0.8 watts per gallon per minute per foot of head is added to the measured power input. This approximates a 25 percent total pump efficiency.
In addition, a 17-foot pressure drop is added for the loop to determine the total pressure drop of the system for the pumping penalty.
The ARI Standard EER should not be confused with the SEER, or Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions.
Closed loop systems for use in Canada also should be rated in accordance with the Canadian Standards Association (CSA) and the Canadian Earth Energy Association (CEEA).
Open loop certification
Manufacturers of products certified by the ARI Standard 325 for groundwater-source heat pump equipment publish a capacity rating for each model, cataloged at the standard entering water rating conditions of both 70 and 50 degrees for cooling and heating.
The cooling EER, heating COP and fluid flow for both is also published.
In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a penalty for the water pump effect is added to the measured power input.
The ARI Standard EER should not be confused with the SEER, or Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions.
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Learn more about:
Working With It: Troubleshooting
Resources: Incentives & Financing
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Brochures and fact sheets
GeoThermal: Bringing Comfort to Your World
By Alliant Energy
[PDF format – 7 pages, 174kb]
