This is the way a 4-port buffer should look like. The flow and return, go in the same direction.

What you have described occurring in your buffer is referred to as distortion. Distortion happens when the cooler return water mixes with the hotter flow water inside the buffer tank, potentially lowering efficiency. Ideally, the system should maintain clear separation between these temperatures (hot water at the top, cooler water at the bottom) but that doesn’t always happen in practice. Why? I have no idea. We are recording another episode of the podcast on Friday about buffers, so I will raise your case.

Very likely better still if it looks like this:

@iraknic the connection diagram you provide looks very like it might be A cause (not necessarily the only one) of your poor performance. My reasoning is that there will certainly be mixing of warmer-cooler water, not the separation by height which is how they are supposed to work.

You don’t say any more about your system, is it in a different thread? If you’ve recently had the system installed get your installer back pronto to fix it to the conventional piping. If you’ve not described your system elsewhere please do.

@jamespa i have 2 zones and 6 fan coils connected. I think a buffer tank is inevitable

Posted by: @iraknic

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@jamespa i have 2 zones and 6 fan coils connected. I think a buffer tank is inevitable

Maybe

With 6 fan coils you probably do need a volumiser (2 port buffer) because of low system volume, but fan coils alone aren't sofaik an argument for a buffer (why would they be?)

Do you really need 2 zones, and even if you do does that really require a buffer?  Not really any different to having a few rads on TRVs.

If you watch the video by @editor on this forum the installers who appear are pretty adamant that buffers are not needed in almost all domestic cases.  Installers who advocated for buffers declined to appear, I wonder why?

That said I agree that the way your buffer is plumbed is absolutely bound to causing problems, but if the installer is coming back maybe its an opportunity to get him to take it out altogether/turn it into a 2 port volumiser!

If the pipe work is connected as per your diagram, then you need to get the installer back and make them change it.

I would suspect it is more a flow problem and not having the two side balanced correctly.

If possible get 4 temperature guages, with probes, and attach them to each pipe into the buffer (about 3inch away from join). You will then get an idea of your flow temp around the pipes. If you only have one guage then place it on each pipe in turn (ashp out, ashp return, ch out, ch return). Making notes of each temp.

You are looking to get the ashp out to match the ch out (or within 1-2°).

If there is a larger temp difference, then look at the flow rate on both side. Your HP instructions should give you an idea of its flow rate. For the CH side you need to look at the pump and see what it's rated for (use the internet)

If one side is much greater, then you have a flow imbalance that needs correcting.

If flow the greater on the ashp then the ch, look at lowering the flow on hp, or increasing it on the ch side.

Note - ensure all emmitters are open and full flowing. It could be yhey have been turned down / off which has caused the imbalance

Why do buffers get such a bad press?  They aren't evil, they're just not properly designed.

I buffer should hold a volume of heat and absorb swings in heating demand.  Yes, running with weather compensation "low and slow" will help, but an ASHP will need to defrost in cold weather and then you're pumping cool / cold water into the feed to your radiators / underfloor heating.  A properly designed buffer can prevent the cold water getting into the house.

Most of the designs I've seen on here and other forums (and online shops) are really just very large low loss headers.  They have the primary return at the top, relatively small nozzles and no inlet distributor.  A properly designed buffer would have the primary inlet about 1/3 to 1/2 way up from the bottom, and have an inlet distributor to maintain stratification.  The "Large low loss header" design has too much turbulence inside which mixes everything up - you end up and tank of luke warm water.

It would be great to see a buffer design that has inlet distributors and can maintain stratification.  This design does exist but they tend to be very large and very expensive.  A smaller / cheaper option might be a good fit for homes with variable heat load.

Regards

Bob

Posted by: @bobtskutter

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Why do buffers get such a bad press?  They aren't evil, they're just not properly designed.

You have answered your own question, at least in part  In addition the pumps either side often aren't balanced properly so you get mixing, resulting in often a 5C drop flow to flow, and thus a 15% performance penalty.

Volumisers (2port buffers) solve the defrost problem if there is one and are (almost) idiot proof.

I don't doubt that in properly designed commercial applications they work well, but we are in the realm of domestic heating systems.

Posted by: @jamespa

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You have answered your own question

Yeh, I did really didn't I.

Regards

Bob

Posted by: @jamespa

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If you watch the video by @editor on this forum the installers who appear are pretty adamant that buffers are not needed in almost all domestic cases.  Installers who advocated for buffers declined to appear, I wonder why?

And it's happened again. We're recoding a second buffer tank episode tomorrow, and I've contacted scores of installers since the start of the year that I know install buffers (because I want to have a balanced conversation) and most have ignored my requests to come on the podcast and others have simply declined. But when I contact installers with a successful open-loop, buffer less installation track record they are more than happy to come on and speak.

Make of that as you will.

@editor Even though we can see a reason to remove them, there's also a reason to keep then.

I've found that they can help greatly in reducing defrosting time and also stop the house emmitters cooling down as they get feed cold water. It also help in stopping the pipes from freezing, if the ASHP is not producing heat.

Without the buffer and just using an open loop, all the cold water from both those activities would flow around the emmitters and cool the house down.

I'm now looking at using a 3 way buffer, with a valve. So when just running water around to stop the pipes freezing and during a defrost cycle the valve closes and send all the cold water around the buffer. Once defrosting has completed and heating resumes to the right flow temperature the valve reopens and goes towards the emmitters.