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Effect of buffer tank or volumiser on heat pump system

bontwoody · 2023-11-20T18:52:25Z

Can someone please either confirm or put me right on the following: My understanding is that a buffer tank will introduce mixing of flow and return water in a system and causes its overall efficiency to reduce as a higher flow temeperature is needed. Do volumisers have the same effect? as an installer is telling my brother in law that it wont effect the efficiency and is there as a safe guard for the defrost cycle. I also thought that if you add up the volume of the radiators and pipes you could then say whether a volumiser was needed or not. Thanks in advance.

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Air Source Heat Pumps (ASHPs)

Last Post by DavidAlgarve 2 years ago

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Derek M

(@derek-m)

Illustrious Member Member

Joined: 5 years ago

Posts: 4425

19/05/2024 4:11 pm

Posted by: @davidalgarve

↑

Apologies for re-introducing this topic. I was persuaded by contributers on this forum, that I should remove the second CH pump and change the function of the buffer tank to use it as a volumiser.

I have forgotten how it was suggested that I should use the four connections on the tank in this configuration.

Existing connections are LHS: Top - From ASHP; Bottom - Return to ASHP RHS Top- To CH: Bottom - Return from CH

I think that you will find that the best location for a volumiser is in the return pipework to the heat pump.

It has also become apparent that some buffer tanks are directional, so have a look around the casing for any direction arrows.

The LHS bottom - return to ASHP pipe should be left as is. The LHS top - from ASHP pipe should be disconnected from the buffer tank and also the RHS top - to CH pipe should also be disconnected. A connection pipe should be used to connect these two pipes together, so that the flow from the ASHP goes directly to the heating system, bypassing the buffer tank. The remaining pipe connected to the RHS bottom - return from CH should be disconnect from its present position and connected to the LHS top. The two pipe connections that will now be without pipes will need to be plugged.

Once completed the water flow should be from the heat pump, direct to the heat emitters, with the return from the heat emitters going into the LHS top of the volumiser, then out of the LHS bottom connection back to the heat pump.

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DavidAlgarve

(@davidalgarve)

Reputable Member Member

Joined: 3 years ago

Posts: 246

20/05/2024 9:41 am

Thank you very much for reminding me, Derek. My installer of choice, here in Portugal, is rather sceptical so I have to be persuasive. I am attaching a photo of my tank and you will see that re-directing the CH return to the top left hand may be rather difficult. Is there any real difference if the CH return is connected to the top right? It seems to me to be almost advantageous for the flow to be across the tank in addition to top to bottom but I am in new territory here.

The other pipe from the 3 way valve goes vertically to my DHW tank.

Incidentally, there is no evidence that this Cordivari tank is directional

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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Derek M

(@derek-m)

Illustrious Member Member

Joined: 5 years ago

Posts: 4425

20/05/2024 12:11 pm

@davidalgarve

If the flow through the buffer tank is not directional then it should be possible to connect the CH return to the top RHS connection rather than the top LHS.

I forgot to mention that it will also be necessary to remove the secondary water pump and replace it with a connecting length of pipe.

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DavidAlgarve

(@davidalgarve)

Reputable Member Member

Joined: 3 years ago

Posts: 246

20/05/2024 4:18 pm

Many thanks Derek. That is what I will suggest and hope to report back in due course.

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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