Ferdinand

Do retrofit ASHPs need larger pipes to the rads?

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Not quite the correct thread, but I'm having a minor heat pump debate this morning elsewhere with a couple of ASHP-sceptics (aka haters), including an engineer who says they have installed 5 and all are unhappy customers. 

 

We have installed 5 in domestic new build properties, all had a plant room to accommodate all the equipment required, the cost was between £15-£20,000, the users are disappointed with the heat provided so far and that will only get worse as the days get colder. Currently although we make more money out of ASHP we would never recommend them.

 

Another point to remember is heating in a Commercial setting. We do lots of boiler changes in School's. We did 4 this summer, all were changing old gas boilers for new. 

 

On a technical note a gas boiler will provide output at 80 degrees, an ASHP willprovide output at 30-40 degrees. Therefore the size of pipework in a house willhave to be changed from the standard 15mm to anything between 22mm to 42mm depending on the output of the ASHP and all the radiators will need to be changed to match the new pipework. Imagine having  42mm pipework running throughout your house. 

 

Now, the flow temperature thing is blather, as condensing boilers become far less efficient over 55C, and rads are recommended to have a max surface temp of 43C where vulnerable people (eg children) are around.

 

But the new 42mm pipework thing. Do ASHPs require new pipework? Really? I thought pipe systems had a tolerance for flow variation which would just allow say a single -> double rad change and an moest increase in the flow.

 

Can anyone comment?

 

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Round here all the schools and public buildings like swimming pools and leisure centres switched to biomass boilers about 10 years ago on the mistaken belief that was "green"

 

If your house needs radiators to run at 70 degrees to get enough heat into it, then you are going to be disappointed of you just swap the boiler for a heat pump and do nothing else.  A lot of these are piped in radial microbore systems so quite likely won't get enough flow for the radiators, assuming you have actually swapped them for larger ones. 

 

A lot of us keep saying, there is nothing wrong with heat pumps, but if you swap half the system without proper design then you ARE going to get disappointed customers and bad press for heat pumps.

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5 minutes ago, Ferdinand said:

But the new 42m pipework thing. Do ASHPs require new pipework? Really? I thought pipe systems had a tolerance for flow variation which would just allow say a single -> double rad change and an moest increase in the flow.

 

The ASHP will require new piping from the ASHP to the Buffer/UVC/Manifolds. I can't speak for all, but thought most domestic installations required 22mm.

 

Microbore pipes to radiators will need replacing through.

Regs next year set the max flow temp to 55° fro all new builds.

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18 minutes ago, IanR said:

Regs next year set the max flow temp to 55° fro all new builds.

 

 

That is a smart move by the Government because it creates a more viable pathway to ASHP conversion in future years and will also also encourage some house designers to improve insulation rather than increase radiator size. 

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Flow rate to rads is a function of the heat transfer and pump speed. I would just turn up the pump speed but the pipework won’t be a limiting factor. The pipework is just providing heat input.

 

The issue here @Ferdinand is the rate of transfer of heat to the room which is a function of the delta T between radiator surface temperature and room temperature. It is also psychological issue as people think radiators need to be “hot” to work. 
 

 

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1 minute ago, PeterW said:

Flow rate to rads is a function of the heat transfer and pump speed. I would just turn up the pump speed but the pipework won’t be a limiting factor. The pipework is just providing heat input.

 

The issue here @Ferdinand is the rate of transfer of heat to the room which is a function of the delta T between radiator surface temperature and room temperature. It is also psychological issue as people think radiators need to be “hot” to work. 
 

 

 

Cheers.

 

My thinking is leave the existing pipework in place, reduce the flow temperature, and replace existing rads with double stackers as the simplest solution if heat emitter area is a problem.

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4 minutes ago, Ferdinand said:

 

Cheers.

 

My thinking is leave the existing pipework in place, reduce the flow temperature, and replace existing rads with double stackers as the simplest solution if heat emitter area is a problem.


it is not even double stack. There is a table of delta-T compensation values that most rad manufacturers provide. Stelrad call them operating factors in their documents

 

 

https://www.stelrad.com/wp-content/uploads/2014/08/stelrad_technical_info.pdf

 

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We had a low temp radiator system running off a heat pump in our last house. Radiators were a lot bigger (surface area) compared  to the size required for gas/oil system. Pipework was IIRC 22mm ring with 15mm feeding each radiator.

 

Microbore would in my view need replacing.

 

 

 

The customer feedback above is I think a little misleading - unhappy with heat - what exactly do they mean? Are they are trying to use a HP system like a gas boiler only coming on for a couple of hours in the morning/evening?  Living with a low temp system is very different to a gas/oil rapid response system.

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1 hour ago, PeterW said:

It is also psychological issue as people think radiators need to be “hot” to work. 

Or a terminology one, they should be called convectors, not radiators.

 

I do hope that science lessons in schools start teaching this stuff, it is all very simple, little mathematics needed  and could make a huge difference.

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51 minutes ago, Ferdinand said:

Further to this, comments on this suggested table of increased pipe sizes would be interesting:

 

https://omnie.co.uk/heat-pump-pipe-sizing/

 

Can't really add a lot other than Nibe recommendation for the family of Heat Pumps I have, up to 16kW, is 22mm, although they do (and so did the installer) recommend a max 10m run. I did a longer run of nearly 20m and did choose to go with a pre-insulated 32mm.

 

But, this is new pipework that required as part of an ASHP Install. It's not ripping out existing to replace it. ie. a gas install doesn't have a unit outside, and if it's a combi it doesn't have a UVC, and probably doesn't have a buffer.

 

It's not really worth arguing with people that are comparing to Gas. Gas is off the table so is no longer an option. The comparison needs to be to low carbon heat sources. It's just not clear what's included in that group, apart from heat pumps and direct electric. I'm waiting to see if a door's going to be kept open for "hydrogen ready" boilers in the hope that there's going to be a step change in hydrogen production technology, with all the lobbying the gas industry is doing.

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8 minutes ago, IanR said:

 

Can't really add a lot other than Nibe recommendation for the family of Heat Pumps I have, up to 16kW, is 22mm, although they do (and so did the installer) recommend a max 10m run. I did a longer run of nearly 20m and did choose to go with a pre-insulated 32mm.

 

But, this is new pipework that required as part of an ASHP Install. It's not ripping out existing to replace it. ie. a gas install doesn't have a unit outside, and if it's a combi it doesn't have a UVC, and probably doesn't have a buffer.

 

It's not really worth arguing with people that are comparing to Gas. Gas is off the table so is no longer an option. The comparison needs to be to low carbon heat sources. It's just not clear what's included in that group, apart from heat pumps and direct electric. I'm waiting to see if a door's going to be kept open for "hydrogen ready" boilers in the hope that there's going to be a step change in hydrogen production technology, with all the lobbying the gas industry is doing.

 

I'm arguing on a very general forum, so it is about convincing several thousand third parties to keep open minds 🙂 . Quite a bit of proper-gander around from "UK Govt is evil" people, and ASHP skeptics.

 

Need to make sure I don't overegg my pudding.

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Think some of those pipe sizes are a bit big but agree with the principle 

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6 hours ago, PeterW said:

Flow rate to rads is a function of the heat transfer and pump speed

Does anyone know the approximate rate of water flow through a rad system?

It appears to me that the circulation on a loop is about 10 minutes when cold and all rads open for flow.. So normal pipes are not limiting the flow too much.

 

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3 hours ago, IanR said:

Gas is off the table so is no longer an option.

 

The boilers will be on sale for another 14 years.

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3 hours ago, saveasteading said:

Does anyone know the approximate rate of water flow through a rad system?

It appears to me that the circulation on a loop is about 10 minutes when cold and all rads open for flow.. So normal pipes are not limiting the flow too much.

 


Wilo Yonos 25/1-6 does around 3.3 cubic metres / hour on full so would expect it is closer to 2 on a normal setting. In 15mm pipe that would equate to around 3.2m/s flow rate. 
 

 

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Is there anything, from an energy transfer point of view, to not have larger pipework?

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I first looked into heat pumps about 12 months ago, then again 6 months ago. Concluded it wasn’t for me, largely due to insufficient government support making it far more expensive to install than a gas boiler. However the recent news has made me think about what I will do when the gas boiler we are about to install dies in 15 or so years’ time. The above discussion on pipe size seems focused on pipe size required for a rad based system. But what about in a house where insulation levels are okay ish and the whole house has been set up with 16mm diameter UFH pipes. On the ground floor these are laid at 180mm centres. Are there any changes I could make to my gas boiler installation now, that will make the switch to HP easier in 15 years’ time? E.g. oversizing the diameter of certain pipes? If so, which ones?

 

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Interested in hearting the replies for the post above 

 

my flow and return are 22mm but looking at ASHP connections inch and a quarter pipe is common.

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1 minute ago, TonyT said:

inch and a quarter pipe is common

BREXIT language is kicking in already.

 

I think I am going to invest in a company that makes metric to imperial adapters.

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the terms are still used interchangeably.  Oddly enough tho, true Imperial plumbing is still common in the South of Ireland...

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23 minutes ago, dpmiller said:

Oddly enough tho, true Imperial plumbing is still common in the South of Ireland

That is because, like Cornwall, it was never invaded by the Romans.

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1 hour ago, SteamyTea said:

BREXIT language is kicking in already.

 

I think I am going to invest in a company that makes metric to imperial adapters.

Can’t speak for anyone else but I regularly change between metric and imperial to describe fittings, connections and pipework.

 

l

 

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Using 28mm to run to manifolds and valves is good practice, keeping the runs under 10m is also worth doing which reduces flow restrictions. Other than that, anything less than 12kW should be happy on 22mm. 

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2 minutes ago, PeterW said:

Using 28mm to run to manifolds and valves is good practice, keeping the runs under 10m is also worth doing which reduces flow restrictions. Other than that, anything less than 12kW should be happy on 22mm. 

So are you saying that as long as I ask my plumber to use 28mm to connect from boiler to UFH system (I think that is what you were referring to when you said “manifolds and valves”) and I keep those 28mm pipes to 10m or less, it should be fairly straightforward to switch to HP? What about hot water requirements - any difference in the way a cylinder is connected when you switch to HP? What’s this I hear about buffers?

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