| My 7kw unit can only possibly draw 900ish watt. 800 watt for the refrigerant pump, and about 100 watt combined for the two fans. This means even when I'd like it a little warmer on the coldest days, making the heat pump use more power isn't an option. A larger unit would have a bigger refrigerant pump and larger fans. This would result in us inadvertently leaving the unit on a higher heat setting more often. Also, a larger unit will be turning a larger pump and larger fans even when smaller would achieve the same outcomes. Mechanic losses. These two factors, human habit & mechanical losses, are, as I understand it, why you're generally better off having more small systems than one big system. We have three split systems, in addition to the 7kW unit at one end of the house, there are two 2.4kW units, one I'm each of the bedrooms we use. When one or more units aren't required they can be turned off. Another advantage of this setup is that it's extremely unlikely all three systems will breakdown simultaneously. Another issue with the larger units is they tend to be ducted, where the ducting is in a poorly insulated roof space, so there's additional heat losses there, and additional losses due to energy required to push air through the ducts. |
Your second argument is silly: a larger pump will surely take more energy to run but will run for less time. It’ll also wear out slower as it doesn’t have to work as hard unless you have drafts and it has to cycle on and off all the time. Generally having more capacity is always a good thing for mechanical things.