I bought a Heat Pump

Reed_Richards

shinytop said:

Thinking about it, @shinytop,  that energy usage is remarkably flat, in between the spikes.  If you had TRVs operating in parts of the house would you expect to see step changes or do they open and close the valve very gradually at around their set temperature without any hysteresis?     

shinytop

I don't know for sure but what I think would happen is that if I shut a couple of TRVs they would just close and the flow temp would rise in the remainder of the system for a while.  The ASHP may just smoothly modulate down but think the control system is a bit clunky and it might just stop, let the flow cool a bit and restart with a bit of a spike, a bit like it does after the HW cycle at around midday in the graph. 

Reed_Richards

Reed_Richards said:

I use a nighttime set-back on my heating controller.  For the sake of simplicity we'll say it is 21 C from 07:00 to 22:30 then 18 C overnight.  If the outside temperature is near 0 C it takes about 6 hours for the temperature to cool from 21 to 18 so the heat pump is off all that time.  That leaves 2.5 hour for my controller to get the temperature back up to 21 C in time for 07:00.  It will do this automatically if I set "Comfort Mode".  But to do this it has to make the water in my radiators hotter than is necessary to maintain a constant 21 C which means it will be running less efficiently.
   

I have been thinking about what I wrote above and I have realised it is wrong.  It could be true but it isn't for my heat pump nor most others.  That's because the water temperature that my heat pump uses is either set at a fixed temperature or a temperature determined by weather compensation.  So when it has to warm up the house it does not make the water in my radiators hotter, it just stays on for longer at the same water temperature.  There is no loss of efficiency.   

@shinytop has a Mitsubishi Ecodan which is one of the few ASHPs capable of Load Compensation but only if not used with a third party controller.  If they can use this feature it might lead to a loss of efficiency when warming up the house - but a faster response.   But it ought to achieve optimum efficiency when maintaining a constant temperature.  

Spies

Haven't looked through all the previous pages but I found this interesting https://www.automatedhome.co.uk/automated-home-2-0/automated-home-2-0-45-real-world-air-source-heat-pump-costs-for-full-year-energy-data-for-all-electric-house.html 

Apologies if already posted. 

Reed_Richards

Spies said:

Haven't looked through all the previous pages but I found this interesting https://www.automatedhome.co.uk/automated-home-2-0/automated-home-2-0-45-real-world-air-source-heat-pump-costs-for-full-year-energy-data-for-all-electric-house.html 

A frighteningly automated house in my opinion, and it looks to be about three times the size of a normal house.  I was surprised how much energy their heat pump uses in summer, by comparison with winter.  They must use masses of hot water.  

ccbrowning

Pretty cool. I can report on a similar albeit much smaller home in a couple of months. 

Martyn1981

Spies said:

Haven't looked through all the previous pages but I found this interesting https://www.automatedhome.co.uk/automated-home-2-0/automated-home-2-0-45-real-world-air-source-heat-pump-costs-for-full-year-energy-data-for-all-electric-house.html 

Apologies if already posted. 

That's impressive. I was quite shocked working through that article, firstlt what a great looking and very large property, then that it was heated by just an 11kW ASHP, and finally that their space heating and DHW come out at 5,345kWh, which even if at a COP of 3 to 3.5 is only 16k to 19k kWh pa. Shows what can be done if built to be efficient.

@ RR, yep weirdly high in the summer, perhaps 25kWh of DHW per day? Big roofs and big leccy demand scream big PV system to me (8-10kWp), probably cover most of their daytime demand including DHW for 6 months of the year.

shinytop

Reed_Richards said:

Reed_Richards said:

I use a nighttime set-back on my heating controller.  For the sake of simplicity we'll say it is 21 C from 07:00 to 22:30 then 18 C overnight.  If the outside temperature is near 0 C it takes about 6 hours for the temperature to cool from 21 to 18 so the heat pump is off all that time.  That leaves 2.5 hour for my controller to get the temperature back up to 21 C in time for 07:00.  It will do this automatically if I set "Comfort Mode".  But to do this it has to make the water in my radiators hotter than is necessary to maintain a constant 21 C which means it will be running less efficiently.
   

I have been thinking about what I wrote above and I have realised it is wrong.  It could be true but it isn't for my heat pump nor most others.  That's because the water temperature that my heat pump uses is either set at a fixed temperature or a temperature determined by weather compensation.  So when it has to warm up the house it does not make the water in my radiators hotter, it just stays on for longer at the same water temperature.  There is no loss of efficiency.   

@shinytop has a Mitsubishi Ecodan which is one of the few ASHPs capable of Load Compensation but only if not used with a third party controller.  If they can use this feature it might lead to a loss of efficiency when warming up the house - but a faster response.   But it ought to achieve optimum efficiency when maintaining a constant temperature.  

@Reed_Richards
Yes, my house warms up slowly in the morning with the radiators at the same temperature had they been on all night.  However, there is a slight loss of efficiency, at least with my ASHP.  When the actual flow temperature is a long way below the target, the ASHP works harder for a while to raise it. You can see this at 5am in my 6/12/21 graph above.  And according to the Mitsubishi databook, the COP is lower at these higher outputs.

I believe Mitsubishi's Auto Adaptation (Load Compensation) would do as you say and boost the flow temp to raise the room temperature. I would also think (I don't know) that it might do something a bit cleverer than just switch off and start again after the target room temp is reached.  I'm going to look into getting this working soon.       

Reed_Richards

shinytop said:

I believe Mitsubishi's Auto Adaptation (Load Compensation) would do as you say and boost the flow temp to raise the room temperature. I would also think (I don't know) that it might do something a bit cleverer than just switch off and start again after the target room temp is reached.  I'm going to look into getting this working soon.       

Load Compensation was a feature I had on my gas boiler in my old house.  Today was sunny and there was enough sun to raise the temperature in the rooms on the south side of my house by a degree or two.  Weather Compensation would not know about this but Auto Adaption would and could reduce the output water temperature whilst the sun was shining.  If the water temperature set by Weather Compensation was a bit too low or a bit too high then Auto Adaption should be able to correct this.  

shinytop

Reed_Richards said:

shinytop said:

I believe Mitsubishi's Auto Adaptation (Load Compensation) would do as you say and boost the flow temp to raise the room temperature. I would also think (I don't know) that it might do something a bit cleverer than just switch off and start again after the target room temp is reached.  I'm going to look into getting this working soon.       

Load Compensation was a feature I had on my gas boiler in my old house.  Today was sunny and there was enough sun to raise the temperature in the rooms on the south side of my house by a degree or two.  Weather Compensation would not know about this but Auto Adaption would and could reduce the output water temperature whilst the sun was shining.  If the water temperature set by Weather Compensation was a bit too low or a bit too high then Auto Adaption should be able to correct this.  

Yes it should and would also compensate when I use my log and coal burners.  As it is even when the thermometer says 25C the ASHP keeps running.  The more I think about this the more I want to get it up and running.