ShareThisA Case for Testing Heat Pumps: One Tech Staffer’s Experience
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Heat pumps are one of the many ways to heat and cool your home, but how do you know that the heat pump is operating at the most efficient level? It’s having a trained professional perform a heat pump commissioning test.
A very brief overview of the heat pump commissioning testing procedures:
- The air temperature and air pressure of the supply and return ducting are measured and recorded.
- Using a TrueFlow plate, the airflow is measured inside the furnace and must pass a minimum airflow rating. The TrueFlow plate measures the air pressure difference from one side of the plate to the other. The difference in pressure is then calculated into cubic feet per minute (CFM). The goal is 350 CFM per 12,000 btu’s of energy.
- Complete a performance check on the heat pump by connecting refrigerant gauges to the unit and verify the correct amount of refrigerant as per manufacturer specifications.
- If everything meets the minimum requirements of the manufacturer, the system passes.
A recent testing experience:
The minimum required air flow for this particular house was 1,750 cubic feet per minute (CFM) whereas the ideal airflow would be around 2000 CFM. The initial air flow test result was a dismal 684CFM. There were obviously some equipment and duct problems that the HVAC contractor would have to address to correct the situation. The refrigerant test would have to wait until the airflow issue was resolved. The amount of refrigerant added to a system depends on a correct amount of airflow across the indoor coil. The indoor coil is part of a heat pump system that is located inside the air handler. The coil itself allows air to travel through and “pick up” either hot or cold air. If this air flow is blocked the heat or cooling efficiency of the system is greatly diminished.
The success:
The HVAC contractor went back to correct some of the ducting issues and discovered a piece of plastic construction debris had blocked most of the duct. The plastic had actually draped itself over the indoor coil and restricted a large amount of air from passing through. The re-tested airflow came in at 1759CFM. That’s not great, but it does pass the minimum requirements for heat pump commissioning. The adjusted refrigerant charge on the heat pump was also in line with the manufacturer’s specifications. Without the verification, that piece of plastic would not have been detected, except through high energy bills and poor airflow. It would have taken a long time to heat and cool this 3000 sq.ft. house with only 39% of the minimum airflow.
How many heating /cooling systems are out there with poor airflow? Without testing nobody knows.
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