Ground-Coupled System Capacities
Since the entering fluid can be below 32°F. heat pumps sold for ground source closed-loop applications require an extended ratings design.
The ARI Standard 330-certified cooling capacity of heat pumps for ground source closed-loop use are published by the manufacturers 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 80°F dry bulb and 67°F wet bulb indoor coil entering air with 80°F temperature air surrounding the heat pump unit. The standard rating condition is 77°F water entering the heat pump at a flow rate in gallons per minute (gpm) 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.
In addition to the certified ratings, application cooling ratings are typically published with entering water temperatures from 40°F to 110°F entering air wet bulbs from 63°F to 71°F. Also, two added gpm water flows, one above and one below the certified gpm.
ARI also requires all certified models pass a 30 minute low temperature cooling test with entering fluid at 32°F at the certified gpm.
Beyond this, ARI requires all certified models pass a one hour maximum operating conditions test with 95°F dry bulb and 71°F wet bulb indoor coil entering air with 95°F air temperature surrounding the heat pump unit and entering water of 100°F at rated gpm water flow.
A four-hour insulation efficiency test is also required. No condensate must drip, run or blow off the unit casing with 80°F dry bulb and 75°F wet bulb indoor coil entering air and 50°F entering water.
The ARI-certified heating capacity for all models is stated at the standard heating condition of 70°F dry bulb and 60°F maximum wet bulb indoor coil entering air with 70°F air temperature surrounding the heat pump unit and 32°F fluid entering the heat pump at the water flow rate gallons per minute (gpm) as specified by the manufacturer.
In addition to the certified ratings, application heating ratings are typically published with entering fluid temperatures from 25°F to 80°F entering air dry bulbs of 60, 70 and 80°F.
Also, two added gpm water flows, one above and one below the certified gpm. ARI also requires all certified models pass a two hour maximum heating operating conditions test with 80°F dry bulb indoor coil entering air with 80°F air temperature surrounding the heat pump unit and rated gpm water flow at 75°F entering fluid. Heating tests done with a sodium chloride-water solution must indicate the exact percentage by weight or volume.
Additionally, all models must pass a low temperature heating operations test with 60°F indoor coil entering air and 25°F fluid entering at 90 percent of rated flow. After soaking for 10 minutes, the unit must start and run for a minimum of 30 minutes.
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 fluid pump effect of 0.8 watts per foot of head (approximately 25% pump efficiency total) is added to the measured power input. Furthermore, a pressure drop of 17 feet of water is added for the loop to determine the total pressure drop of the system for the pumping penalty. A typical ARI certified rating table of a nominal 4-ton ground source closed-loop heat pump might look like this...