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Balancing radiators with heatpumps

Air Source Heat Pumps (ASHPs)

Last Post by batalto 4 years ago

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Prunus

(@prunus)

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Joined: 5 years ago

Posts: 64

Topic starter 12/02/2022 8:57 pm

I think I need to balance my radiators, since there doesn't seem to be proper flow getting through some of them.

Various guides out there suggest to aim for a 12 degC difference between the flow and return temperatures. But heatpumps are supposed to have lower flow temperatures, which is why we oversize radiators. Does this 12C rule (which seems fairly commonplace) still apply, or should another differential be used?

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Derek M

(@derek-m)

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Posts: 4427

12/02/2022 9:10 pm

Posted by: @prunus

I think I need to balance my radiators, since there doesn't seem to be proper flow getting through some of them.

Various guides out there suggest to aim for a 12 degC difference between the flow and return temperatures. But heatpumps are supposed to have lower flow temperatures, which is why we oversize radiators. Does this 12C rule (which seems fairly commonplace) still apply, or should another differential be used?

Hi Prunus,

I know that Daikin recommend a delta T of 8C for radiators according to their manuals. Other manufacturers specify a 5C or 6C delta T.

I think that with heat pumps it is very much a balancing act, a reasonable delta T is required otherwise the heat energy is not going to be transferred from the heat pump to the heat emitters, but of course, the higher the delta T, then the higher the water flow temperature and the lower the efficiency.

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Prunus

(@prunus)

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Posts: 64

Topic starter 12/02/2022 9:17 pm

@derek-m Thanks. For the purposes of balancing, does it matter if the value is 12, or 8 or 5, as long as they're all the same? In other words, when balancing I aim to get as much deltaT out of the radiators as possible, and then step it back so that they're all doing the same (with the windows open so the rooms don't fight back by getting warm)?

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Derek M

(@derek-m)

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12/02/2022 10:06 pm

Posted by: @prunus

@derek-m Thanks. For the purposes of balancing, does it matter if the value is 12, or 8 or 5, as long as they're all the same? In other words, when balancing I aim to get as much deltaT out of the radiators as possible, and then step it back so that they're all doing the same (with the windows open so the rooms don't fight back by getting warm)?

Sorry Prunus, I should have made it clear, when the various manufacturers were referring to delta T. it was in relation to the water flow and return temperatures at the heat pump.

The purpose of balancing radiators, is not so much a matter of achieving a specified difference between the water entering, as against the water leaving, but to balance the heat energy supply to the heat loss, so that the room remains at the desired temperature. In an ideal world the radiators would be perfectly sized to match the room heat loss and balancing would not be necessary.

In the real world the practice is to calculate the heat loss, and then install the next size up radiator. The heat output from the radiator can then be adjusted down using the valves.

For the most efficient operation of a heat pump system, the heat emitters should be as large as possible so that they can still dissipate the required amount of heat energy, but at lower water flow temperatures. So the major limitation is set by the coldest room, the one with the smallest radiator output to heat loss, and hence requiring the highest water flow temperature. Once this room has been identified, its radiator valves should always be fully open, and then the valves on the radiators in the other rooms adjusted to achieve the desired room temperatures.

If there are large differences between rooms, then improvements in overall efficiency can be made by additional insulation and/or installing large output radiators.

It is not a quick and simple process balancing your heating system, but I think that you will find it to be beneficial in the long term.

👍

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Prunus

(@prunus)

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Posts: 64

Topic starter 13/02/2022 10:13 pm

I found this helpful:

https://www.heatgeek.com/balancing-heating-systems-the-ultimate-guide

Makes the point that what we really want is to balance the room temperatures, rather than the radiator temperatures, so this deltaT rule of thumb is a bit arbitrary in that context.

Meanwhile I have this radiator:

so things are very much not right (other radiators were more evenly about 32C, highest was 34C)

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batalto

(@batalto)

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Posts: 1092

14/02/2022 10:04 am

heres me just using the Mk. 1 hand to balance my rads

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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