How to set the warm end of the weather compensation curve when it's not warm

Dockray · 2023-02-28T12:37:34Z

Hi, I am very new to all this! How do I set the warm end of the weather compensation curve when it’s not warm outside? We’ve got a Mitsubishi Ecodan 8.5kW with UFH (plus 2 radiators on the mezzanine). We live in a newly converted industrial building that is well insulated, it has big windows so we have good solar gain when it’s sunny but we live 400m above sea level on an exposed fell in The Lakes so we have a lot of wind wash. After commissioning, WC was left set at factory settings. I’ve watched the Heat Geek videos and read lots of threads on here and got the cold end of the curve set when it was minus two outside. We are now down to a flow temperature of 28* at -2 to give us an indoor temperature of 19.5. This month the heating COP is 3.4 and the DHW is 2.2. Now the weather is beginning to improve I am getting some cycling (but at other times the LWT & RWT appear to be nearly the same) so I’m guessing I need to alter the warm end of the curve or possibly the pump speed?? I've currently got the warm end of the WC curve at 20 degrees with an outdoor temperature of 10 degrees (because that is the highest the outside temperature has got so far) but it’s still cycling when the outdoor temperature gets above 7 or 8* (and I’ve got the room stats capping at 22* whilst I am trying to find the sweet spot, which is higher than I need). Our flow temperature seems to be lower than most people’s and I don't want to find I’ve got a low flow temp but something else in the system is working to keep the house warm - if this is even possible? I can’t compare energy usage as we now live in a different part of the country, in a different house, with an ASHP and UFH rather than gas CH and radiators. I’ve got SO many more questions but I’ll leave it at this for now. Until a few weeks ago I knew nothing about ASHPs so please go gently and simply with your replies. Thank you in advance.

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Air Source Heat Pumps (ASHPs)

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HarriUp

(@harriup)

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Joined: 4 years ago

Posts: 107

08/03/2023 5:30 pm

There was thread somewhere recently, which I can't find now, where someone had a DHW pump that was running continuously. That would be annoying but not a hindrance if the HW is always getting topped up after 10° drops, but if something like that was happening in your system after the end of a heating cycle then you would just end up with a tank of tepid water following a sizeable draw-off. It was easily fixed as the pump wiring had been connected to the wrong socket in the controller. It is worth checking if the pump is running when it should be off – just feeling if it is vibrating should be enough.

Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop
210l Mitsubishi solar tank
Solar thermal
3.94kW of PV

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Dockray

(@dockray)

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Joined: 2 years ago

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Topic starter 08/03/2023 9:37 pm

@harriup Thanks, I've found the thread and will check that because we didn't used to have a problem when the water was on all day, its only come to light since we've scheduled the DHW.

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