ASHP and Microbore

[Worcester]

Anyone retrofitted an ASHP where the installation (12 years old) used 100 microbore?

The house (large - 360m2 , built in 2001/2002 and needs 2 x 10kW heat pumps) has all radiators plumbed on 10mm microbore, we are going to have to increase the radiator sizes at each location so that we can run at 45°. Just wondered if, with the increased flow rate needed due to the lower flow temperatures anyone had succesfully retrofitted with 10mm microbore, and if so - what did you do? TIA

 

[wersolaruk]

What is manufacturers recommended size?

 

[Worcester]

They don't and won't !..

 

[wersolaruk]

Well I can only speak from systems I have designed and we spec 28mm off the pump, to 22mm spilit off manifold then down to 15 mm on the rads, but I have heard pumps be installed on 10mm to the rads, would need a good power flush and a magna clean rads may take a tad longer to heat, are you using triple panel rads?

 

[Worcester]

Yep, triple panel, most are currently double panel (and as usual are oversize for a normal boiler, and undersize for a HP), so we have to swap all the rads.

The house is in good order and don't really want to have to re-plumb all the rads. We always powerflush and add in a magnaclean anyway. If we have to replumb it all, then we have to..

Hence the question, anyone done one using the existing 10mm microbore? If you have what problems / snags did you hit and how did you resolve them?

 

[wersolaruk]

Well is the main runs in 22mm then I would say it should be fine, am a spark by trade and went down the easy route with the eco dan system there sizing software is good. I have spoke with other installer who have used 10mm on 22mm runs, if its 8mm I would not, as for snags your only problem could be flow especially if its a large property.

 

[jason121]

Pipe the heat pump thru a buffer tank. Let the radiators draw from the buffer. Think off two circuits. Hope this helps

 

[Worcester]

Main runs are in 28 then 22mm however there are 20 radiators in this place... hence we need 15kW of actual output - not peak rated output

 

[a1colly]

Flow rates are your biggest issue, best bet is to install a low loss header and then run a separate pump after it to handle the rads.

 

[Worcester]

@Jason121 thanks for that, realised that approach - @a1colly - the buffer tank will work as the low loss header

So flow rates won't be an issue from the heat pump(s) aspect, and I realised that. The question is is it practical to do it or with the higher flow rates around the radiators, will it end up being noisy and then the pump struggling with the increased flow pressures to achieve the higher flow rate?

 

[jason121]

speak to Graham at FREEDOM, I am not sure.

 

[Earthstore]

pocketpipe - Pipe Sizing, frictional calculation0

Frictional loss may be your big problem here, not sure if the link above is of any use to you, or something similar maybe?
What you may find is that running at such low temperatures is that the rads will take a very long time to warm up.

I would have thought that the Heatpump supplier should be able to help you the best though, they should have all the expertise....

 

[Greenday]

Does the rad circuit after the zone valve/s go to manifold/s and run mainly in 10mm or as commonly found run in 22mm/ 15mm and just reduced down to do the last few metres to the one rad.

Buffer with seperate pump to rad circuit would be the way we do it. We have used this method and had no problems with noise.

 

[Worcester]

Thanks Jason121, Earthstore and Greenday,

No zone valves and no room stat! - just a simple S plan on a timer and TRV's. At the moment can't see if there is any 15mm or whether it is straight into a manifold - more investigation work to do ... If it is as Greenday suggests it is only the last few meters in 10mm then that shoudl work OK...

Ironically the plumbers forum is full of people not nescessarily as helpful as they could be hence the postings here

So many thanks to all here - we're back there on Thursday so will see if we can do some digging around between the floor boards.

 

[Gavin A]

Main runs are in 28 then 22mm however there are 20 radiators in this place... hence we need 15kW of actual output - not peak rated output

so what's actually run in microbore then? is each rad run individually off the 22mm pipes?

I think you're going to need to be running the pumps at nearly double the pressure to get you the around 1/3 higher flow rates in the microbore you'd need to account for around 1/3 lower flow temps. Something like that anyway.

 

[solarsavings]

I can't think why any plumber would run the last few meters to all rads in 10mm. I guessing you'll find 28mm-22mm-distribution manifolds-10mm-rads.

It can be, and is done without a buffer. I don't use either. You will need to increase the pump(circulator) size (or two in series) to get the flow without the velocity=noise.

Tip: Make sure all the existing rads are getting hot top to bottom and note how long its takes to get an idea of the set up.

 

[The Solar King]

We used to run in 10mm from 22mm flow and return, either direct or from a manifold. For reasons discussed we now use 22mm F&R with 15mm branches to radiators.

As with so many things, plumbers take the line of least resistance (eg combi boilers) and end up fitting less than optimal systems.

If you use a hgh quality plastic pipe, you still have the installation benefits of microbore without all the disadvantages. Replacing the pipework would also give the opportunity to properly insulate it. The reduced heat loss does make a difference.