Then you have to decide between real 8KW units where you can have problem with colder climates. I think in UK you will not have an issue but here in Winter temperature can get close to -10 to -15C and I guess 8KW would suffer badly and not sure if ii would be able to heat the place. 8KW is max. but until which temperature this is achievable ? 0C ? -5C ?
I think next time I will buy a pump I will ask manufacturer how low it can modulate
Hmm, actually I do this with thermostat. I’ve set hysteresis +/- 0.2C. So e.g. I’m running pump by weather curve but not less than 38C. So in case there is 10C outside and I have target temp set to 23C then thermostat command the pump to stop when indoor temp reach 23.2C with flow temp of 38C. Then it will start it when it decrease below 22.8. In warmer wetter the pump is off maybe for one or two hours so it’s pretty good. When I did not use thermostat it used water law and to achieve best efficiency the pump was cycling every few minutes like crazy. So maybe efficiency was a bit better but the components must suffered heavily.
So basically this is what you mean by pauses between cycles right ? Does this solution have some benefit over this one with thermostat ?
Hi Michael,
Yes, if switching on the thermostat, then the hysterysis will cause a welcome pause. The problem is when the unit cycles off when stat is on. e.g. when the heat load is low and the heat pump drops to the minimum, but the flow temperure creeps up. The unit has to stop. The ecodan seems to start only 4 mins after stopping. I never did make a module to help with this. My idea was to have a pause depenent on outside temperature.
Yes, Samsung does the same. The warmer the weather the more cycling observed. With my system it was really unbearable. In the past I’ve shared this screen - 8 cycles per hour:
Absolute craziness. Of course combined weather law + thermostat did not work properly because the pump always turned heat since water temperature was too high to keep up with target so I had to switch to pure thermostat regulation. In that way the pump never turn off and tries to keep as lowest LWT as possible. Often this is inefficient because compressor and FAN are running an minimal speed. Water law tries to optimize this but not in a very nice way.
Pause based on external temperature is good idea if you don’t have any other choices but I’ve found this thermostat is pretty good. I think every pump offers this kind of control. In colder weather usually the pump is running 24/7 so thermostat will not kick in and when there is hotter it will turn off the pump. Once indoor drops by 0.4C it will start it again. I had maybe 3 or 4 cycles per day. Problem is that man users won’t notice this and it’s definitely not good for a pump.
With my own experience with R410 twin rotary compressor there is alot of oil in the refrigeration lines. There is no oil seperator installed in the unit and no oil injection at the suction line respectively.The oil seperation of the compressor itself is very poor. At high revs alot of oil is circulating in the system. I planned a full rebuild of my heatpump next summer and installation of oil separator to monitor the effect of oil sepration on the whole system and efficiency values. After two years of explotation of my Atlantic Fujitsu HP and alot of learning I can surely state that the refrigeration cycle in these small AC/HP systems is not well ingineered for heating purposes.
