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Octopus design temperatures confusion

AndrewJ · 2025-02-04T18:34:09Z

I have a design from Octopus for my house and I'm a little confused about the design temperatures and how the ASHP would operate. As an example, the living room has a design temp of 21c, the bedroom is 18c and the sunroom is 16c. This is at their normal 50c flow temp at -3c. I'm trying to understand this with Octopus themselves of course but I know plenty here will have a system installed and operating where the design temperatures were different in rooms. My idea of comfortable is that the house is heated uniformly to 21c throughout during the day and (perhaps) set back to 18c at night. Notwithstanding the advice to sleep in cooler rooms at 18c, if my wife goes to bed and it's 18c at that time she is going to go absolutely thermonuclear and I'll catch it big-time. She's fine with 18 once she's under the duvet of course, and as long as it has warmed up in time for getting up. If the radiators are sized to these design temperatures, how can I possibly uniformly heat the house? If I, for example, heat the bedroom to 21c, won't the rooms of the house designed to 21c be overheated? So far Octopus said I can heat the house to whatever temperature I like, the stated figures are just "guarantees" for the coldest day of the year. I just don't seem able to get my head around it (HG created a design for every room to be 21c and that I can understand.) There's something I'm just not understanding as the majority of people are very happy with their Octopus install. I assume that it operates on weather compensation but how is this all controlled to normalise temperatures and how does it assure the house is properly warm on the coldest of days? Hopefully that lot is all clear - I thought I had educated myself on all this but I feel a bit thick right now!

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 5476

05/02/2025 10:46 am

Posted by: @andrewj

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If I want the room that is 16c to be held at 21c I could expect the other two rooms to be overheated (by 5c?) and the efficiency to fall through the floor. I don't even know how I would achieve this under a weather compensation set up

No to the first. You can reduce the temperature of the other rooms by adjusting the lockshield valves. You have to do this anyway because radiators are never perfectly sized. This is called balancing and is part of the installation process although, because it takes time (hours or days) to get spot on often needs to be finished by the homeowner of it is to be done properly.

However you are correct that there is an efficiency penalty because you will have to run at a higher flow temperature.

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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AndrewJ

(@andrewj)

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Joined: 2 years ago

Posts: 247

Topic starter 05/02/2025 12:27 pm

Posted by: @jamespa

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Posted by: @andrewj

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Posted by: @jamespa

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I suspect 60dc120 means 60cm high 120cm long double convector. SC single convector.

Do you know how single/double convector relates to Type 21 or Type 22? Does that relate to SC and DC respectively - sounds feasible?

Not exactly. Type 11 = 1 panel, set of fins, type 21 = 2 panels 1 set of fins, type 22 = 2 panels 2 sets of fins. Unfortunately SC could be 11 or 21 and DC could be 21 or 22. I just dont know the Octopus terminology.

You may be able to deduce it from the variants on the list, or alternatively from the output. Radiator output is proportional to deltaT to the power 1.3, and 1W = 3.41btu/hr so conversions could in principle be done, but it might be simpler to ask