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ASHP Cut-off Temperatures: What's Your Setting and is a Your Heating Still On?

Mars · 2024-04-16T15:15:32Z

I recently came across an interesting piece of information regarding air source heat pumps where the "accepted" ambient outdoor temperature at which ASHPs are designed to automatically turn off is 18C. Does anyone have this automated – ours isn't automated. If it is automated, at what ambient temperature does your ASHP shut down?

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Air Source Heat Pumps (ASHPs)

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HughF

(@hughf)

Noble Member Member

Joined: 3 years ago

Posts: 489

06/05/2024 10:30 pm

My system has been running 24/7 on weather compensation from last September until today when I fitted a thermostat.

I did think about just changing the weather comp curve to 20@20, but then the pump would still run.

My wife still has the heating on as of this evening, she wanted it at 24 in the lounge. I tweaked the low temperature end of the curve up from 35 to 37.5 to make the rads feel warm when she turns the stat up.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Mars

(@editor)

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Joined: 5 years ago

Posts: 3549

Topic starter 13/09/2024 9:53 pm

I imagine that for those of you with “automated” systems, your heat pumps must have kicked in this week with the chill in the air.

For the rest of us with more basic, older controls (like mine), when do you plan on switching your heat pumps on for heating? Or did you give in to the colder temperatures these past few days?

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Anonymous 5011

(@Anonymous 5011)

Joined: 3 years ago

Posts: 563

13/09/2024 10:31 pm

This year it been rubbish weather in Scotland, think we missed out on summer, it was too wet to get warm. Last year it was October before the heat went on, this year beginning of September - global warming doing it's thing - making Scotland colder! But it's let me fiddle with settings and PV pays for any mistakes and any higher electricity consumption.

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TechnoGeek

(@technogeek)

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Posts: 132

14/09/2024 6:31 am

@editor as my smart thermostat system is "on" all the time I guess you could class it as automated and yes it has kicked in in early mornings and a little at night this week.

In the wilds of Cambridgeshire we have had a couple of 3 - 5 degree nights but the temperatures this year have been frequently under par since the start of La Nina

5 Bedroom House in Cambridgeshire, double glazing, 300mm loft insulation and cavity wall insulation
Design temperature 21C @ OAT -2C = 10.2Kw heat loss
Bivalent system containing:
12Kw Samsung High Temperature Quiet (Gen 6) heat pump
26Kw Grant Blue Flame Oil Boiler
All controlled with Honeywell Home smart thermostat

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Suzy-shadow

(@suzy-shadow)

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14/09/2024 8:44 am

If heating shuts off for the summer but is still needed to heat hot water is that economical or expensive due to heating from cold?

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TechnoGeek

(@technogeek)

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Joined: 2 years ago

Posts: 132

15/09/2024 7:53 pm

@suzy-shadow Hi, Domestic hot water production is generally less efficient in itself. For example my combined heating and hot water efficiency is on average 4.3 COP. Hot water only production over the summer has been a COP of 3.6.

Is it more or less expensive? That is a difficult question to answer as it depends on tariff prices, hot water tank efficencies etc. In my case I find it cheaper to heat my 200 litre tank to 55 Celsius and take a hit on my COP value which all happens during a cheap electricity period in the night. This tank full in most cases lasts all day and costs on average 17p per day. If I made the COP value better by reducing the tank temperature then the hot water would possibly need 2 heating cycles in a day, 1 in the morning and another in the afternoon due to hot water running low, costing approximately 40p to 50p a day if that makes sense

Hopefully that helps answer your question