Heat Pump
The same refrigeration cycle, reversed on demand, so one machine can heat and cool.
What it is
A heat pump is an air conditioner with a reversing valve. In cooling it rejects heat outdoors. In heating it does the opposite: the outdoor coil becomes the evaporator and absorbs heat from outdoor air, and the indoor coil becomes the condenser and releases that heat into the building.
How it works
Compressor: The compressor raises refrigerant pressure and temperature, so hot discharge gas leaves it in either mode.
Heating and cooling modes
Because the outdoor coil runs below outdoor temperature in heating, frost forms on it. A defrost control periodically reverses the system to cooling, energizes supplemental heat, and melts that frost before returning to heating.
What can go wrong
- A reversing valve that does not shift fully leaves the system underperforming in one mode.
- A failed defrost control leaves the outdoor coil iced over and capacity collapses.
- Supplemental electric heat staging on too early raises operating cost without a comfort benefit.
- Low charge shows up in heating first, because the outdoor coil has the harder job.
Field note
Supply air feels cooler
Symptoms
Practice & Mastery
- Heat Pump Troubleshooting Scenarios2
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