Slide 1
A heat pump moves existing heat using work
A heat pump uses work to move thermal energy from a colder source to a warmer destination. It transfers existing heat as well as adding its work input.
More to Read
This is why delivered heating can exceed the electricity supplied without violating energy conservation. The balance includes heat taken from air, ground or water outside the heated space.
Slide 2
Evaporation absorbs heat; condensation releases it
In a common cycle, refrigerant evaporates while absorbing heat and condenses while releasing it. A compressor and expansion device connect those conditions.
More to Read
Pressure changes alter the temperatures at which these phase changes occur. The cycle arranges the refrigerant to be colder than the source during absorption and hotter than the destination during release.
Slide 3
Delivered heat can exceed the work input
The heating coefficient of performance compares delivered heat with supplied work. A value greater than one is expected in useful operating conditions.
More to Read
If 1 unit of electricity drives the transfer of 2 units of source heat, 3 units reach the destination in the idealized balance. The resulting heating coefficient is 3.
Slide 4
A larger temperature lift generally needs more work
Moving heat across a larger temperature difference generally demands more work. Performance therefore changes with source and delivery temperatures.
More to Read
A heating system that can deliver comfort using lower-temperature water may improve heat-pump conditions. The whole building and heat-distribution design influence the result, not only the compressor model.
Slide 5
Fans, pumps and defrosting affect seasonal performance
Fans, pumps, defrosting and controls also consume energy. Seasonal performance reflects changing conditions across time.
More to Read
A laboratory rating at one temperature does not predict every day’s result. Comparing systems requires a consistent boundary that includes the equipment and operating pattern relevant to the application.
Sources
- Heat Pump Systems
US Department of Energy
- Decarbonizing Building Thermal Systems
US Department of Energy