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Grant Aerona3 with Octopus Cosy tariff

ASHP-Aerona · 2025-02-06T17:06:14Z

Grant Aerona3 13kW HPID 13R32I have a Grant Aerona3 ASHP and I am on Octopus Cosy tariff, with underfloor heating and room thermostats plus Grant HPIDTM4 programmer.As you probably know the Cosy tariff gives 3 periods of cheaper energy and one of more expensive energy.I would like to reduce my energy costs by turning off the ASPH from 16:00 to 19:00 when energy is more expensive.My installer insists that I should have the ASPH on constantly, so the programmer is doing nothing as it is set to Constant.Does this make any sense?

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Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 2 years ago

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 5457

08/02/2025 7:02 pm

Posted by: @uk_pete_2000

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Posted by: @jamespa

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Posted by: @uk_pete_2000

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Some where, someone said they had two HP. with this setup and some changes to the pipes, you could have one HP deal with DHW and CH and the other one just looking after the CH

Allows the best of both

You can (just like you can have two boilers) but unless you use vast amounts of dhw to the extent that the dhw is a material proportion of the total daily energy demand, there is not much point. Better just to tweak your settings to do whatever it is you want to do.

Most of the time your ashp has plenty of excess capacity assuming it's designed to cope with the standard requirements. If it is getting challenged on the coldest days because it is well matched to the demand, switch on the immersion during a cheap rate period. That will only be necessary for a handful of days per year.

Sorry I think you lost the point. The main question was about the CH turning off when DHW was being called for.

So having two HP, that person can have one looking after DHW & CH, while the other one just deals with CH. That way the house will always receive heat and the DHW request will not effect it.

Unless I completely misunderstood you (in which case apologies) I don't think I did lose the point.

If the dhw only needs to be on for a couple of hours a day it won't materially affect the house when the dhw turns the ch off, unless you live in a tent (or somewhere else with minimal insulation and minimal thermal mass).

If the dhw needs to be on for substantially more than that to satisfy the demand then it will materially affect the ch, but that then falls into my case where the dhw demand is a material proportion of the daily total demand.

EDIT - OK I look back and see you were referring to someone who already had 2 Heat pumps, which I hadn't realised. If they only need 1 then yes it could be replumbed this way. But if they only need 1 then why not replumb it this way and sell the other, unless its marginal and the DHW load is such that, including DHW, 1 isn't sufficient.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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