Cycling of heat pump
I have a Fujitsu heat pump with two indoor units each in relatively small rooms. (For good or bad, this decision was made because I was not satisfied if only one room had a unit that sufficient heat could be transmitted to the second room and I wanted each room to have its own thermostat. I recognize that they are larger than I need but I did not see good alternatives) Currently both units are set on “minimum heat” (50 degrees F) because the rooms are not occupied for days at a time.
When the temperature outside is zero degrees F, my power consumption is as shown in the first attachment. The graph shows whole house power consumption but the pattern is clear. The compressor comes on and power jumps by about 800 watts. After about six minutes, power jumps by another 500 watts for about three minutes. Then power drops to almost nothing for three minutes, then the cycle restarts. The entire cycle lasts about 12 minutes.
When the temperature is warmer, around 35 degrees F cycling is much more rapid. The compressor comes on, (power up by 600w), runs for one minute, Then the compressor turns off and there is a small draw probably for the fan for a minute. Then there is nothing for four minutes. The cycle lasts only six minutes. Note that the scale is different on the second graph, with the top of the graph 1 kw vs 2 kw on the first graph.
It is interesting that the two units seem to operate in tandem, both on the same cycle, sharing the output of the compressor when it is running. They never seem to get out of synch.
I assume the unit would be more efficient if it ran longer cycles. Is there any way to increase the difference between the temperature at which they demand more heat and when they turn off? Is this the way they are supposed to work?
The graph comes from my new “Sense” power monitor that is supposed to tell me how much power various things in my house are using. After a month it has not yet recognized the heat pump but hopefully it will figure things out eventually.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part