Posted by: @jamespa

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Presumably mixing of return water with flow water to the emitters (and thus a reduction of ft to emitters) will however still occur if the primary pump throughput is less than the secondary,

This could be mitigated by putting a one way check valve on the top input so that flow is only downwards. Can't think of any detrimental effects.

Posted by: @heatgeek

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This could be mitigated by putting a one way check valve on the top input so that flow is only downwards. Can't think of any detrimental effects 

Or of course not having a buffer at all! 

Would an installer that wants to fit a buffer unnecessarily because 'thats what we do' or because of warranty reasons be prepared to fit a three way buffer with a one way check valve.  I suspect this would be a tiny minority!

It's ab interesting thought experiment though.

Posted by: @heatgeek

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@heatgeek I kind of get it… but aren’t you still in the same situation of having excess flow temp water at the bypass entering the buffer at circa 23 LPM.

In so doing, raising the return temp and narrowing the DT… ergo prompting a raising of the flow temp and inducing the cycling.?

Only now there are 2 pumps?

(It isn’t like it’s just trickling into the buffer, is it? And the return pump will want to maintain the flow rate, for sure!)

Also on 4 port systems I’m not convinced that PWM pumps can cope with matching actual water flow rates, at variable speeds on either side of the hydronic circuits - since there is already believed to be a compromise or resistance to flow on the emitter side. Yet that’s possibly the very reason why buffers are being proposed. 

Is there a proper definition as to why buffer tanks are being specified and what exact problem is expected to be overcome?

Posted by: @sunandair

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buffer tanks are being specified

A buffer is a legacy issue, they were never used on gas boiler systems, but generally specified when fixed output heat pump came along. So unlike today's heat pump which modulates they had a fixed kW output and generally a fixed flow temp. Add to this a UK liking for zones, the heat pump didn't stand a chance of running well without one.

Today people are still obsessed with zones - so it's the easy choice for manufacturers and installers to add one. Plus more product to install and sell, more profit.

@johnmo yes I can believe that. It seems to be human nature to keep dong what we did before.

I’m really pleased to see that we’re starting to have a positive impact on homeowners who are getting smart about their systems. I received this email today from a homeowner, and based on our content they’ve declined an installer who was hell bent on fitting a buffer tank.

Here’s what they wrote:

“I’ve been watching your videos on YouTube, I have learnt so much!

We are moving house in the next couple of months and have an ideal opportunity to install a new heating system from scratch.

I have had a site visit and quote from an installer but they are telling me I will need a buffer in the system. When questioned why they replied:

'Your research seems very very high! We fit systems with buffers or a low loss header, never without either. The reason is because to keep a heat pump running efficiently, we need a higher flow rate than most heating systems require, so the heat pump satisfies the buffer and the buffer satisfies the space heating system. This stops the heat pump short cycling, short cycling is bad for efficiency and the life expectancy of the heat pump compressor will be compromised.'"

This kind of explanation should set off alarm bells for consumers everywhere. If the default answer from an installer is “we never fit a system without a buffer or LLH,” it usually means they’re designing to their own convenience (or they're just incompetent) rather than what’s best for the homeowner.

It’s fantastic to see homeowners pushing back and questioning these decisions!

Posted by: @editor

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'We fit systems with buffers or a low loss header, never without either.

@mars That response surely deserves a nomination for Turkey of The Year, for the company itself not for the specific installation.  It shows a company which either consistently does the wrong thing, or lies to its customers.  Either way it doesn't deserve to be in business unless it changes radically.