I took some measurements today. Clearly can see the rads and UFH aren’t losing 5c so makes sense why the main ASHP delta isn’t 5c

I’m finding it very difficult to balance the rads. Our house is a thin long house with the buffer tank in the middle. So I think the heating splits out left and right. 

I closed down the nearest rads and opened them up 1/8 -1/4 turn which is fine. The rads at the end of the house weren’t that hot but as soon as I opened them up, the other rads went much colder. Will have to tinker a bit and find the sweet spot I guess. I was balancing based on room temp rather than delta, as advised by Heat Geek. 

Said it on another thread, but worth checking if you have a low loss header and if that's causing losses from your system. It could easily be a culprit for high return temps.

Posted by: @batalto

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Said it on another thread, but worth checking if you have a low loss header and if that's causing losses from your system. It could easily be a culprit for high return temps.

you want the return to be relatively. lose to the flow temp though.. this increases radiator out put.

Your heat pump relies on a high  flow rate, don’t restruct it!

hugher delta Ts are good on condensing boilers, but so are lower delta ts..as long as flow is below dew point,

We don’t have a LLH but we have a large buffer tank. So I presume I’d the flow around the house to the rads etc isn’t enough the heat pump will still see a high enough flow rate it’ll just be from the buffer, so warmer. 

The issue I have is that when I try and open the radiators up a bit, the others go cold. It seems very difficult to get a good balance. Maybe due to the layout of the house. And the fact the original plumbing was rather bad. We have a mix of new copper and old plastic microbore. 

Any advice on next steps?  It was a decent 5c delta the last couple of years and all that’s changed in the balancing so I presume it’s that. 

Posted by: @benseb

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We don’t have a LLH but we have a large buffer tank. So I presume I’d the flow around the house to the rads etc isn’t enough the heat pump will still see a high enough flow rate it’ll just be from the buffer, so warmer. 

The issue I have is that when I try and open the radiators up a bit, the others go cold. It seems very difficult to get a good balance. Maybe due to the layout of the house. And the fact the original plumbing was rather bad. We have a mix of new copper and old plastic microbore. 

Any advice on next steps?  It was a decent 5c delta the last couple of years and all that’s changed in the balancing so I presume it’s that. 

a buffer serves the same function as a header as well as additional ones! 

If the pipe sizing is wrong then you are stuck with the substandard performance,

my bet is that too many rads are on 15mm a common scenario!

you won’t need to replace all 15mm, but 15mm should only serve a max of two rads, preferribly only one

@alec-morrow I don’t know exactly what pipework we have in all areas. I do know for example we have 2x 600x1599 rads in our lounge and 2 600x600 rads (all doubles) in our bedroom. These are fed by a 22mm but all branch off the same 15mm. 

not ideal but now we have real engineered wood floor down so difficult to amend. 

So we’re going to get UFH in our lounge with a separate feed. But that’s a big job for another year!

Posted by: @benseb

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We don’t have a LLH but we have a large buffer tank. So I presume I’d the flow around the house to the rads etc isn’t enough the heat pump will still see a high enough flow rate it’ll just be from the buffer, so warmer. 

The issue I have is that when I try and open the radiators up a bit, the others go cold. It seems very difficult to get a good balance. Maybe due to the layout of the house. And the fact the original plumbing was rather bad. We have a mix of new copper and old plastic microbore. 

Any advice on next steps?  It was a decent 5c delta the last couple of years and all that’s changed in the balancing so I presume it’s that. 

Try opening up all the valves fully, then gradually close the lockshield valve on the radiator in the warmest room. Allow room temperatures to stabilise before making any adjustments, and only adjust one room at a time. You may have to repeat the process until you get it right.

Also monitor the temperatures around the buffer tank to check for flow rate issues.

@alec-morrow yes sure, but you also want your system to push as much heat as possible. Losing heat back without using it is a crime and means you need higher flow temps. a LLH could be a prime suspect.

The trouble is you can’t force an emitter to loose heat, the rate of heat loss from an emitter is determined by physics. A consequence is cycling and the odd moment odd readings are picked up that alarm the amateur

so design engineers embrace cycling by make flow temps over shoot, so the shut down is fairly long.. needed by heat pumps and benefits a condensing boiler.

This machines have had billions spent on R&D and are excellent. They all design out client interference, meaning all you have to do is enjoy your heating assuming it’s installed on a system that meets design engineers expectation

if there is an issue the heat pump will advise you with a fault code!

If you aren’t an engineer haven’t you got other interests? 

@alec-morrow of course you cant, but the real issue that a LLH creates a short circuit between the house and pump. The pump will chug along all day and not realise there is any issue. It'll output lots of heat, which comes straight back and on the other side you get less heat which can be emitted. And your assumption of just turning it on and forgetting about it is, at least from what I've seen, incorrect. Many systems are not designed by actual engineers - and by that I mean people with actual qualifications and not John from down the road who is a plumber but calls himself a "Heating engineer". Most will simply pop in the system just like a gas boiler and they will usually follow the steps from a supplier. My system came from Freedom and they supply a Low Loss Header with it. Why? Because it removes the need for any actual engineering on the plumbers part. No need to work out flow rates or anything like that. Provide a LLH and you can put any pump you like on the house side. Its not an issue with the heat pump - its an issue with the house setup and no heat pump fault code provides that kind of thing. If anything having a LLH will mean you get less fault codes which you could use to identify issues because the pump isn't aware of what's actually in the house.

I hold a Masters Degree in Engineering, including the study of both thermodynamics and fluid mechanics. This I would wager is more of an insight than most "engineers" I've met. I wasn't aware this forum had gatekeepers on who could post what and about what. Nor did I realise you had assumed that role? Which topics do you feel I am free to venture an opinion on?

edit: typo

Agreed I definitely don’t think ASHP are “set and forget”, there’s a whole spectrum of issues that don’t get flagged by errors. 

I’m no engineer but between work and home we’ve had 7 ASHPs so I do know my way around them and can spot when things don’t look right. 

Posted by: @derek-m

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Posted by: @benseb

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We don’t have a LLH but we have a large buffer tank. So I presume I’d the flow around the house to the rads etc isn’t enough the heat pump will still see a high enough flow rate it’ll just be from the buffer, so warmer. 

The issue I have is that when I try and open the radiators up a bit, the others go cold. It seems very difficult to get a good balance. Maybe due to the layout of the house. And the fact the original plumbing was rather bad. We have a mix of new copper and old plastic microbore. 

Any advice on next steps?  It was a decent 5c delta the last couple of years and all that’s changed in the balancing so I presume it’s that. 

Try opening up all the valves fully, then gradually close the lockshield valve on the radiator in the warmest room. Allow room temperatures to stabilise before making any adjustments, and only adjust one room at a time. You may have to repeat the process until you get it right.

Also monitor the temperatures around the buffer tank to check for flow rate issues.

 

Thanks Derek. Yes I’d been working by locking them down and gradually opening up until they were roughly equally warm but I’ll try the other way around with them open fully and closing down the overly warm rooms. Or I guess if we find rooms not getting any heat them closing the closest ones to the buffer a bit til we get heat at the ends of the circuit. 

Ah the fun and games of retrofit. Our installer didn’t touch any of the rads or pipes!