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Mitsubishi Ecodan Air Source Heat Pump - Low Efficiency

  • 5 September 2022
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M.isterW
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Having multiple heating zones isn't straightforward with a heat pump. Have a look at this video to understand why https://youtu.be/zpTVIeUh04E.  

 

I think you've got two options. The first is to tweak your existing setup. You could reduce your heating flow temp as that should improve efficiency.

 

The second option is to turn on weather compensation. Set the thermostats to high and use the weather compensation controls to get the house temperature as you want it. This will only work if your rads are correctly sized for each room.

 

 

1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
juliamc
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You should try setting weather compensation which would mean you’re running at a much lower temperature (eg my leaving water temp is 35 deg at 6 deg outside). Open up all rad valves and turn up thermostats so they no longer control your three areas. Let the system balance out for a day, then turn down any radiator in a room that’s too hot eg bedroom. That way your heat pump is running continuously low and slow. 

E
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Thank you both for the feedback.I really appreciate your time.Do you know if it’s possible to set a command to the hydrobox to supply hot water of i.e 42deg to the buffer tank when the buffer tank’s water temperature falls below let’s say 35deg?

Thank you in advance

juliamc
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Sorry not me, I don’t have a buffer tank.

E
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Juliamc, the three thermostats should give info of the internal temperature to the hydrobox?

Should they be linked to the hydrobox in order to activate the weather compensation?

And how i will control the temperature of the 3 areas?

M.isterW
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I think your system is set up in an unusual way so the normal answers won’t apply. I’ll explain how I think your system is working and please correct me if it’s wrong.

 

You have two circuits. The first is the heat pump heating water and pumping it into the buffer tank. There’s a thermostat on the buffer that triggers the heat pump to switch on. You then have a second circuit that runs water from the buffer tank into the radiators. The room thermostats decide when this circuit switches on. I assume there’s a separate circulation pump on this circuit?

This means that the room thermostats aren’t controlling the heat pump in any way. They just tell the circulation pump on the second circuit to switch on (and maybe operate valves?).

 

If this is correct it makes it a bit more difficult to advise on efficiency improvements. I’m trying to work out if the normal weather compensation approach will work and as I’m not an expert (just an ethusiastic amateur) my brain keeps flipping from yes to no and back again.

 

Weather compensation changes the flow temperature from the heat pump based on the outside temperature. The idea is that you provide the radiators with enough heat to get the rooms to your preferred temperature and no more. In cold weather you need more heat to get the rooms to temperature so your flow temperature is higher. You don’t need room thermostats because the combination of correctly sized radiators and correct flow temperatures means the rooms will remain at the required temperature.

I think it might work if you change your heat pump to weather compensation mode and turn your room stats up full. You’ll need to adjust the compensation curve over a period of time to get the right temperatures. If you find one area of the house is getting too hot you could turn the stat for that area down but you should leave at least one zone on full or you negate the benefits of using weather compensation.

 

If you don’t fancy trying that, just turn the flow temperature for your heating down. That should improve efficiency (although probably not as much as using weather compensation).

1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
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Thank you M.isterW.Two circuits you are correct to that.On the buffer there is no thermostat.The circulation pump of the hydrobox very often pumps the water of the buffer tank to the hydrobox and with that way checks the water temperature inside the buffer.Suppose we have set 45deg for the water temperature and the hydrobox sees 42deg then the outside unit start working.I think here we have an issue.

For the second circuit you are correct there is another circulation pump which is activated by the thermostats.

I am trying to find out whether

A)is possible to give a command to the circulation pump of the hydrobox to start every let’s say 2 hours the check of the water temperature instead of 30min that is now  or

B)Increase the difference between the set water temperature (45deg) and the actual one in order the outdoor unit start working i.e 5-7 deg.So the outdoor unit to start working when a water temperature of 38deg is identified or

C)Just put a thermostat on the buffer as i have already done with the DWH tank and give a command when the the water temperature in the buffer is 38deg just warm it up to 45deg.

Do you know which of the above is feasible?

juliamc
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I don’t think I can add anything more here as I’m now v out of my depth ! Who designed your system @epolyzois ? 

Z
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I am at a similar situation trying to improve my setup as well so just reading along. I will refrain from asking anything specific to me to not litter this topic, but after reading posts here and reading up on heat geek and other channels, low and slow is the idea. 

 

If you manage to find your utopian curve that always works bang on at every temperature to always heat all the rooms at your desired temp like 22c, that means that heat pump never ever turns off (until winter ends that is), right? If that is the case, how much does that reduce your end of month electrical bill. I understand that the COP would be very high in this utopian case, but would the end of month bill be any lower assuming that the unit runs 24/7/30 versus a thermostat pulsing the valves and shutting the circuits?

 

I am asking this from the perspective of what I got now, when my stats shut my valves, my ashp does so aswell

E
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And what is your cop now zzzzz?

Z
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And what is your cop now zzzzz?

Heating exclusively:

2.64375 for November

2.40 for 2022 so far

 

New construction, Ecodan box

E
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How many thermostats you have, how many radiators and do you have also a buffer tank and if yes what size is it?

Z
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I have UFH, 3 stats (well actually its just smart home controllers that open/close valves on temperature targets), no buffer tank. Just a ecodan with an internal 200L tank (10kw)

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