Posted by: @colin-g

↑

New to heat pumps and two issues.

1) when heating the leaving water the pump seems to be flat out until it reaches the required temp at which time is slows and consumption drops. That is all fine but it always heats the water beyond the target level - it overshoots - and this cannot be economical can it?
2) the Madoka controls the temp and turns on and off accordingly - it turns off at about 1.5 degrees over the target temp and once off it stays off until we are about 1 degree below the target. That means it is off for a couple of hours and the leaving water has cooled big time. The knock on effect is that when the pump kicks back in it is working very hard, especially during these very cold spells. I would have expected the pump to tick over at least keeping the leaving water at some sort of base temperature. Again, this does not seem economical.

 I believe a part of this might be due to modulation but I do to understand that aspect.

 Can I do anything to improve things or is an this just how it is?

 Thank you, Colin.

The problems you are experiencing are because you have an on - off type room thermostat controlling how the heat pump operates. If you wish to have the heat pump operate in a more consistent, more efficient manner, it will need to be adjusted for Weather Compensation operating mode, with the room thermostat set 1C above the desired indoor temperature.

@derek-m That is where I am trying to get to but something is wrong. Today the pump is drawing over 2kw in power to heat the house to 20 degrees. Consumption drops considerably once the leaving water has reached temperature but is back in ten minutes or so as the leaving water has cooled so much. There are those who say that is to be expected in extreme weather conditions like today (minus 1 at best a and freezing fog all day); the pump is less efficient when frosted up as air flow is more difficult. Counter intuitive really - a product designed to keep us warm is less efficient when it is cold. I note the booster heater was not turned on by the installer and wonder if this has anything to do with it?

Posted by: @colin-g

↑

@derek-m That is where I am trying to get to but something is wrong. Today the pump is drawing over 2kw in power to heat the house to 20 degrees. Consumption drops considerably once the leaving water has reached temperature but is back in ten minutes or so as the leaving water has cooled so much. There are those who say that is to be expected in extreme weather conditions like today (minus 1 at best a and freezing fog all day); the pump is less efficient when frosted up as air flow is more difficult. Counter intuitive really - a product designed to keep us warm is less efficient when it is cold. I note the booster heater was not turned on by the installer and wonder if this has anything to do with it?

All forms of heating systems are going to have to work harder and use more energy when the weather is cold.

Because heat pumps get most of there energy supply, free of charge, from the outside air, when the outside air is colder then there is less free energy available, so the heat pump has to work harder. Freezing fog is probably the worst operating conditions for an ASHP, lower free energy supply and increased likelihood of defrost cycling.

I cannot comment about the 2kW per hour usage, since I don't know the size of your heat pump, the type and size of your home, or the heat loss calculations and type and size of heat emitters.

deleted

@derek-mThank you. I can get that but what worries me is that it appears to be cycling. I am new to all this but the leaving water heats up to the desired temp and the pump then reduces its consumption significantly but only for 15 minutes or so as by that time then leaving water has cooled and the pump has to jump back in to heat it up. The house is not cold and this is happening when the indoor temp is 20 and the target is 21. Could that be the result if freezing fog? Certainly it was not doing this yesterday

deleted

Posted by: @colin-g

↑

@derek-mThank you. I can get that but what worries me is that it appears to be cycling. I am new to all this but the leaving water heats up to the desired temp and the pump then reduces its consumption significantly but only for 15 minutes or so as by that time then leaving water has cooled and the pump has to jump back in to heat it up. The house is not cold and this is happening when the indoor temp is 20 and the target is 21. Could that be the result if freezing fog? Certainly it was not doing this yesterday

During this cold weather I suspect the cycling will invariably be due to the heat pump defrosting. This is perfectly normal, and whilst undesirable, is nevertheless unavoidable.

@derek-m I haven't followed all this topic, but my Ecodan is defrosting once, or slightly more than once, per hour in this weather. I also thought it was cycling but after derek-m's posts, I checked and it is definitely defrosting (the Ecodan FTC controller shows this as the heating symbol turns white, and also per cathode-ray's post, the Flow temperature drops below the Return temperature).

@sliderule Yes it was defrost that was causing the concern. That was confirmed by my installer late last night and there is no evidence of that sort of behaviour this morning