ASHP Advice: High Temperature vs. Low Temperature Heat Pump For Microbore

Graeme · 2024-04-25T20:22:41Z

Hi, I already have Solar Panels - about 150% of current usage. Battery and Eddi. Looking for advice on moving to a ASHP. We have a 4 bed house. 14 rads. House is 2006. In 2021 our gas usage CH&HW was 13411. EPC stated expected 12808. Wearing occasional jumpers and using Hive controls to only heat the rooms we were using reduced our usage to 7765kWh in 2023. Gas bill in 2023 was £788. So motivation is not simply financial. Main problem in moving to ASHP is we have (plastic) microbore. [Mars-thanks for the commentary in your bodgebuster]. Most installers want to provide us with a LT ASHP and replace the microbore, replace all the radiators and provide some more. Replacing the microbore would mean ripping up all the wooden floors upstairs and opening up all the walls downstairs. The disruption of ripping our house apart is simply not an option. Last winter we could generally get away with having only two or three radiators on at any one time (our bedroom radiator, hasnt been on in 6 years) and the gas boiler operating at a flow temperature of about 50C. but on really cold days raising it to 60C (and using immersion once per week for legionella). We are currently looking at a Daikin HT and peoples thoughts as to how that would fit into our position with microbore would be helpful. Primary concern is if costs increase significantly. G

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Air Source Heat Pumps (ASHPs)

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Derek M

(@derek-m)

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Joined: 5 years ago

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26/04/2024 8:06 pm

@jamespa

I fully agree with James that a HT heat pump will probably be no more costly to run than a LT heat pump when operating at the same LWT.

If the reason for installing a HT heat pump is because a LT heat pump would not be able to supply LWT at sufficiently high temperature to meet demand, then a HT heat pump is likely to be more expensive to run.

This is why improved insulation, larger heat emitters and other ways of lowering the required LWT should be the primary objective.

As I have stated repeatedly 'if you don't require the thermal energy in the first place, then it is not necessary to produce it'.

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Marzipan71

(@marzipan71)

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Joined: 3 years ago

Posts: 102

29/04/2024 12:07 pm

Hi - we have a Daikin 16kW HT ASHP installed which was the choice of our builder when we did our renovation. We heat around half the (300 sqm detached) house with 7 new aluminium radiators averaging 1.5kW each at T40, and half with wet UFH. The radiators have a mix of 10, 12, and 15mm copper piping which is connected to a Caleffi coplanar manifold which results in each radiator being on its own loop. Our LWT on the coldest days in winter is around 45C, and the house is a constant 21C in winter. The only time the system uses the HT functionality as far as I can see is the weekly legionnella cycle (to 60C). Total grid consumption for the year is around 11000 kWh with solar consumption adding around 5000 kWh. After four years of ownership, I think we probably could have gotten away with a LT system but we are happy with the HT system overall, skinny piping and all.

This post was modified 1 year ago by Marzipan71

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