ASHP - Want to run 24/7 but continually calling for heat

mcwatson1974 · 2022-12-15T09:37:30Z

Hi all, first time poster, looks to be a great source of advice and assistance.I probably going to be answering a question that many others have asked, but I couldn't seem to find the specific answer that is applicable to my situation. The question in summary form: I want to run my ASHP in 24/7 mode by stats being high and flow rate being low, but when I tried this, ASHP used 3KW every hour all day as stats kept calling for heat. I assumed the low flow rate would mean the ASHP would calm down once the house got to the desired temp. Do I need to do something to tell the stats to stop calling for heat and just let the ASHP do its flow rate thing? The question but with more background or detail: My house was built in 2017, 4 bed chalet bungalow, around 260 Sq Mtrs. I had a 8KW Ecodan installed, 250l water tank, every room in the house is zoned with a Heatmiser Neostat for every zone. Have three manifolds serving the UFH, two for downstairs (can see in picture) and one is located upstairs to run upstairs. System has always badly struggled during winter (I acknowledge the obvious - that its colder and ASHP's aren't as efficient etc etc) but this year, it seems to be exceptionally bad, or maybe I'm just focusing on it more because of the increased electric costs, and/or the particularly heavy cold snap. I was running my system using the Neostats to call for heat but house has struggled to get up to temperature. So yesterday, I tried the theory of having all stats on high, and using weather compensator to keep the flow temp down at a level that the rooms don't over heat. Here lies the issue...... I ran this for 24 hours and I used the most power ever (90KwH, and the costliest day ever (£29). The house was far more pleasant temperature wise and I got the flow rate down to around 35c which considering I had it at 50c-55c before, was great. But the stats called for heat on every single zone all day for the whole day and so the ASHP was using 3KW for every hour, even when the house was ticking over at the desired temperature. Thus, I got the flow temp as I wanted it, I got the rooms warmed as I wanted it, but at the expense of highest cost and highest KwH usage. I really want to use the 24/7 theory but couldn't afford too. The ASHP just never calmed down or reduced usage once the house was all good, and I think this was because it was trying to respond to the call for heat all day. Any advice on what I'm doing wrong? (I went to attach a picture of my installation but message saying no more attachments allowed - maybe because I've just joined)

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HughF

(@hughf)

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Joined: 4 years ago

Posts: 489

16/12/2022 10:40 am

@oswiu the building regs from 5 yrs ago made no recommendations for air tightness, that has only just come in with the changes to part L.

The OPs house could easily be more leaky than my ‘46 end of terrace due to dot ‘n dab construction on blockwork.

I’d still like to know the construction method.

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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