How is a properly sized and installed heat pump supposed to work?
mpd
| Posted in General Questions on
If you have a correctly sized and installed heat pump system does it run continuously at a low level providing just enough heating and cooling to match building losses? Or does it ramp up heating or cooling (possibly overshooting the desired temperature and then turn off, recirculating room air until the temperature falls/rises and it needs to heat/cool again?
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Replies
In correct operation, it should be ramping up and down to meet the heating/cooling loads. But if it does not have modulation capacity for the current load, it will cycle. Some heat pumps have a lot more modulation ability than others.
There is no one answer to your question.
Most conventional heat pumps sold do not have variable speed compressors so they simply are either on or are off.
Some conventional heat pumps have 2 speed compressors and they can be off, low or high.
A few conventional heat pumps have variable speed compressors and can operate in the way you described.
Most multi split systems have variable speed compressors and can operate down to 33% in the way you described.
Most miny split systems have variable speed compressors and can operate down to 10% in the way you described.
Their will always be conditions when the compressors minimum speed exceeds the heat needed and the unit will cycle on and off.
Overshooting the set point is almost never a comfort issue because it generally gets less than half a degree over the set point and half a degree under the set point and it is imperceptible to the humans.
Is cycling on and off a bad thing? Different people will have different opinions. When I look at the power usage graphs, I do not see any huge spikes at start up. I know the spike exists but its duration is so short it is almost irrelevant to power used. Is the equipment likely to be operational for more years if it is cycling VS modulating? The cycling equipment may have half the run time but 50 times more startups. Historically older systems all cycled and live long lives and running almost continuously is an unproven idea.
If anyone has seen a study for HVAC compressor life please post a link.
It is possible for the multi split systems to way overshoot when they must dump extra heat into heads not calling for heat as sometimes happens.
Walta