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How to balance a post buffer tank circulation pump?

Air Source Heat Pumps (ASHPs)

Last Post by Dunlorn 1 year ago

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Potatoman

(@potatoman)

Trusted Member Member

Joined: 2 years ago

Posts: 57

Topic starter 19/12/2024 10:54 pm [#1959]

Hi, has anybody managed to balance the circulating pump in the ASHP with the post buffer tank circulating pump, and if so how did you manage it. Thanks

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Transparent

(@transparent)

Famed Member Moderator

Joined: 4 years ago

Posts: 3157

20/12/2024 1:10 pm

@potatoman - follow what @ashp-bobba is describing to @netdonkey over on this other topic.

He's addressing a very similar issue!

Save energy... recycle electrons!

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4518

20/12/2024 4:08 pm

@potatoman, to balance a buffer system effectively, both flow rates and flow temperatures on the primary and secondary sides must align perfectly.

Modern air source heat pumps modulate their flow temperature based on the controller’s set point, and many also adjust flow rates to maintain a specific Delta T (temperature difference) on the primary side of the buffer. However, the secondary side is less straightforward.

The secondary pump may regulate flow using pressure control methods, but it cannot directly maintain Delta T due to factors like zone valves or TRVs adjusting flow dynamically. This means the flow to individual emitters isn’t always consistent, which can affect balancing.

Emitters are sized for specific mean flow and return temperatures, and changes in flow rate can shift the Delta T, altering radiator output. Without precise control or measurement of both flow and temperature on the secondary side, true balancing isn’t achievable.

While buffers aren’t inherently bad, they’re often less effective with modern inverter-driven compressors, which perform best in direct systems. Buffers work better with fixed-compressor units, where control is based on return temperatures rather than flow temperatures.

For your specific question, balancing would require synchronising both pumps through careful calibration and possibly additional controls or sensors on the secondary side. However, this level of precision is rarely implemented in standard installations.

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