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Working With It - Selecting

Open-Loop Capacities

The ARI Standard 325 certified cooling capacity of heat pumps for ground water-source use are published by the manufacturer in their catalogs. ARI ratings cover units rated below 135,000 BTUH at ARI standard cooling rating conditions. Units above 135,000 BTUH may be rated but these ratings are not certified.

This standard allows reasonable comparisons between manufacturer's models. It can be used as a basis for estimating cooling energy use and annual cost, as covered elsewhere in this program, to help the consumer make a "better value" decision. Keep in mind actual water and air temperatures may vary by location from the standard condition.

For all models, the standard cooling condition is 80F dry bulb and 67F wet bulb indoor coil entering air with 80F temperature air surrounding the heat pump unit. Water flow rate in gallons per minute (gpm) are as specified by the manufacturer. Wet bulb temperature is a device for measurement of relative humidity and this standard indoor air condition is equivalent to 50 percent relative humidity.

For ground water-source use, the standard rating conditions are 50F low temperature and 70F high temperature water entering the heat pump. In addition to the certified ratings, application cooling ratings are typically published with entering water temperatures from 40F to 110F entering air wet bulbs from 63F to 71F. Also, two added gallon per minute water flows, one above and one below the certified gpm.

ARI also requires all certified models pass a one hour maximum operating conditions test with 95F dry bulb and 71F wet bulb indoor coil entering air with 95F temperature air surrounding the heat pump unit and 90 percent of rated gpm water flow at 75F water entering the heat pump.

A four-hour insulation efficiency test is also required. No condensate must drip, run or blow off the unit casing with 80F dry bulb and 75F wet bulb indoor coil entering air and 50F entering water.

The ARI-certified heating capacity for all models is stated at standard heating conditions of 70F dry bulb and 60F maximum wet bulb indoor coil entering air with 70F temperature air surrounding the heat pump unit. Water flow rate gallons per minute (gpm) are as specified by the manufacturer.

For ground water-source use, the standard rating conditions are 50F low temperature and 70F high temperature water entering the heat pump. In addition to the certified ratings, application heating ratings are typically published with entering water temperatures from 45F to 80F. entering air dry bulbs of 60, 70 and 80F. Also, two added gallon per minute water flows, one above and one below the certified gpm.

All certified models must also pass a one hour maximum operating conditions test with 80F dry bulb and 75F wet bulb indoor coil entering air with 80F air temperature surrounding the heat pump unit and 110 percent of rated gpm water flow entering the heat pump is 75F.

Additionally, all models must pass a four hour low temperature heating operations test with 60F indoor coil entering air and 45F water entering at 90 percent of rated flow.

Heating and cooling tests are run at 90 percent and 110 percent of the rated voltage. In calculating EER's or COP's a penalty for water pump effect is added to the measured power input.

 
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