Maximal minisplit efficiency
A few things I have gathered reading here and elsewhere on mini-split efficiency
-A larger compressor, operating at the lower end of its range is more efficient. (But not too far down, as at some point, efficiency drops off again)
– The compressor still shouldn’t be too big, or short cycling can occur, reducing efficiency
– Maintaining a smaller temperature difference is easier, so higher COP
I live in an old, drafty, and poorly insulated farmhouse near Olympia, WA. Currently the main source of heat is wood stove, with space heaters used to supplement. Needless to say, the interior of the house experiences very large temperature swings, from being in the 40’s on frozen winter mornings, to well into the 80’s when the fire really gets cooking. Eventually the house will be well insulated and sealed up, but that’s some time off. In the meantime, I am looking to get a mini-split to help the house not be quite so cold when the wood stove isn’t going.
Here’s how I’d like to program the heat pump to operate:
Default: run at 25% speed always (25% being a proxy for max efficiency)
except when indoor temperature is less that 50°F , then use up to 75% of speed to get back to and hold 50°.
and use all available capacity to hold 40°
if the temperature reaches 80°, turn off, and only turn back on at 70°.
My goal with the above program is to get the highest COP most of the time as a baseline input of heat into the house. Trying to maintain a set point is a costly proposition, and I don’t mind a variety of indoor temperatures. The wood stove will be utilized when temperatures above what 25% of the heat pump’s output can generate are desired.
Turning off at 80° and only back on at 70° is to avoid short-cycling. A 10° range seems not short. And why 80°? If the heat pump ever managed to make the interior of the house 80° in the winter running at only 25% speed, it would be a gift I’d happily accept.
Is my theory correct here?
And is there any mini-split out there that can accept this kind of input? I can write some python code and program and Arduino if that’s what would be needed.
If direct control or limits on compressor speed would not be possible, perhaps it would work to write a program that continually moved the set point, keeping it 2° above the actual indoor temperature? Might that ‘trick’ the unit’s firmware into thinking it was close to it’s goal, and therefore run the compressor at a low speed?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part