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Towns water feed to air source heat pump system

Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 1 month ago

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DavidAlgarve

(@davidalgarve)

Reputable Member Member

Joined: 3 years ago

Posts: 246

Topic starter 04/05/2026 4:25 pm [#2979]

As installed, my system had a buffer tank which I had converted to a return-line CH volumiser.

It was badly done and I now plan to improve the pipework by putting the volumiser in the CH flow and reducing the number of multiplex elbows, all with the objective of improving flow.

The towns water feed to pressurise the system is still as original, i.e. to the middle of the buffer/ volumiser tank, (as diagram below) but I am uncertain if this is still the best point for the towns water pressurisation.

The DHW flow is from the 3 way valve and its return taps into the main return to the Ecodan.

Comments would be appreciated.

This topic was modified 1 month ago by Mars

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 5019

05/05/2026 8:32 am

Posted by: @davidalgarve

↑

The towns water feed to pressurise the system is still as original, i.e. to the middle of the buffer/ volumiser tank, (as diagram below) but I am uncertain if this is still the best point for the towns water pressurisation.

Ultimately I doubt it matters much because pressures will inevitably equalise. I would probably choose to put it upstream of valves just so there is no possibility of forcing a valve open, although even this isn't absolutely certain because there are of course two paths from any one place in the system to any other place.

Maybe someone else can come up with a reason why it would make a material difference, but I cant!

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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DavidAlgarve

(@davidalgarve)

Reputable Member Member

Joined: 3 years ago

Posts: 246

Topic starter 05/05/2026 3:09 pm

@jamespa Thanks James. As you say, the pressures should equalise.

I was contemplating teeing it into the return line to the Ecodan.

There does not seem to be the same need to pressurise the much simpler and shorter DHW circuit, but I suppose it can't be separated.

I do now see that I have no air bleed on the DHW heating coil circuit and this may need to be added.

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5019

05/05/2026 4:17 pm

Posted by: @davidalgarve

↑

DHW circuit, but I suppose it can't be separated.

I do now see that I have no air bleed on the DHW heating coil circuit and this may need to be added.

The DHW circuit cant be separated (well it could, you could use a plate heat exchanger, but why bother).

There needs to be an air bleed at every locally highest point. I guess it might well be possible to plumb a DHW cylinder so it (or some part of its pipework) isnt a locally highest point, but its tricky!

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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