Is It Worth Insulating UHF Manifold Feeds/Returns

[MortarThePoint]

On another thread I think I worked out that there is little point in insulating domestic hot water pipes unless you have a circulatory system. Cold water pipes should be insulated to avoid condensation.

 

I've been wondering about UFH manifold feed and return pipes and did some calculations I thought were worth sharing:

 

I adapted the pipe insulation spreadsheet from the CheGuide.com. The table shows the amount of heat lost in the feed/return pipes. 'Recovery Factor' represents the usefulness of heat that is lost since it isn't truly lost, it is staying within the heated envelope, but in the wrong place. I intend to have a relatively uniform heat and so most of the heat will be 'recovered'. Various insulation scenarios are considered with the resulting annual cost of lost heat as well as the cost of the insulation (material only). The payback time for insulating PE 13 (e.g. ScrewFix) is just 3.4years. The payback time of upgrading from PE 13 to Phenolic 15 Shiny (e.g. Kooltherm) is 38years. That ignores interest/inflation. There is no consideration of the carbon costs, either of lost heat or insulation manufacture. 'Cost of heat' is based on £0.30/kWh electricity an a COP of 300% which is hopefully pessimistic, but who knows these days.

 

Not everything comes down to cost obviously, but using 13mm PE insulation looks to offer the best compromise for my system based on a relatively low 35C average flow/return temperature (e.g. 38C flow, 32C return). I hope to have lower temperatures than that, in which case the payback times go up higher. If however you run your ASHP flow temperatures at 65C, the payback time of upgrading to Phenolic 15 Shiny would be about 13 years.

Edited July 3, 2023 by MortarThePoint

[JohnMo]

I insulate all DHW heating flow and returns, but where it splits to go to UFH manifold I have left it uninsulated as it's useful heat.

[BadgerBadger]

I'm not sure I follow, the pipe length is 60m? This feels quite long for just UFH manifold feed and return?

[MortarThePoint]

32 minutes ago, BadgerBadger said:

I'm not sure I follow, the pipe length is 60m? This feels quite long for just UFH manifold feed and return?

I've got three manifolds: 2.5m, 8m and 15m from the low loss header. Doubling as flow and return gives a total of 5+16+30=51m. I pessimistically rounded up to 60m.

 

Payback times should be independent of length in this calculation.

[MortarThePoint]

Need to check building regs, but insulation looks mandatory:

https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/8.1/pipeinsulation.pdf

 

Part L:

 

What's draconian is the insistence on using 60C for the consideration. PE needs to be much thicker than Phenolic for he same loss so that 10mm figure rises to around 20mm for PE.

Edited July 4, 2023 by MortarThePoint

[MortarThePoint]

@Nickfromwales I'm going to route my UFH feed and return pipes through the ceiling void (~60mm high) to the manifolds. Flow temperatures are expected to be around 35C. Am I reading part L correctly that I wouldn't be able to use the 'standard' 13mm PE insulation the likes of Screwfix sell? With a low flow temperature, it doesn't make sense on paper to use phenolic, or 20mm thick PE. Appears that the regs disagree though.

[MortarThePoint]

Below is a table from BS 5422:2009 which assumes 60C pipe and 15C ambient. Looking at 28mm pipe it has a minimum thickness of 16mm for 0.035 W/m.K which is the best you can hope for from PE and 20mm for 0.040 W/m.K which is perhaps more realistic. At a 35C average flow/return temperature moving from PE13 to PE20 reduces the loss per metre by 20% from 3.8 W/m to 3.1 W/m, but both are massively under the maximum permissible heat loss of 10.07 W/m.

 

[JohnMo]

Toolstation do better pipe (thicker) than Screwfix, titled bylaw something.

[Nickfromwales]

11 hours ago, MortarThePoint said:

@Nickfromwales I'm going to route my UFH feed and return pipes through the ceiling void (~60mm high) to the manifolds. Flow temperatures are expected to be around 35C. Am I reading part L correctly that I wouldn't be able to use the 'standard' 13mm PE insulation the likes of Screwfix sell? With a low flow temperature, it doesn't make sense on paper to use phenolic, or 20mm thick PE. Appears that the regs disagree though.

I only use 9mm or 13mm in PH settings (9 on cold water and 13 on ‘hot’ heating / UFH) but I always use 25mm wall for DHW and DHW HRC. 

The grey stuff is cheap as chips so just fit 19mm and be above the standards. 
Remember that part L is a dogshit standard and nothing to ever be bragging about, hence the recommendation to go “overboard”.

Once you’re at the price point of 9mm or 13mm, you may as well go to 19mm. 
I’ve been looking into insulation for my current Passiv Haus project (as PH standard has just tightened its belt also) and there’s extremely little in it between the black neoprene (Armafalex / Armacell) stuff and the grey (Climaflex ) stuff, to the point that for the significant cost difference it makes better sense to me to go one size thicker and stay with Climaflex.

For DHW and DHW HRC runs I’ll stick to 25mm wall Climaflex and tape along the seams with the Armacell 3mm x 50mm adhesive ‘insulation tape’ for belt & braces.

[MortarThePoint]

2 minutes ago, Nickfromwales said:

Once you’re at the price point of 9mm or 13mm, you may as well go to 19mm.

 

I can happily do that for the DHW 15mm and 10mm pipes, but the void is too cramped for 19mm insulation on 28mm pipe unfortunately.

[Nickfromwales]

Just now, MortarThePoint said:

 

I can happily do that for the DHW 15mm and 10mm pipes, but the void is too cramped for 19mm insulation on 28mm pipe unfortunately.

Add a strip of 11mm OSB to the beams, then plasterboard? Or stick with 13mm. 
At 35mm and within the heated envelope means this is neither here nor there tbh, just make sure you fully fill the voids where the pipes exit up high, to stop convection losses from the room to the attic.

After that, I think you can relax.   

[Nick Laslett]

On 05/07/2023 at 10:01, Nickfromwales said:

I only use 9mm or 13mm in PH settings (9 on cold water and 13 on ‘hot’ heating / UFH)

 

Hi, @Nickfromwales, if I am understanding this correctly, I need to use 9mm insulation on the cold pipes going to shower and taps, etc.

 

Or is this only for Passive House?

 

I think I missed the need for insulating the cold pipes.

[SteamyTea]

Neoprene, as used in wetsuits, has a conductivity of 0.055 W/m.K.

You can buy 10mm by 600mm by 300mm for 22 quis on eBay.

 

Can't you wrap pipes in that.

 

You can get it thinner if the pipe diameter is small.

[Andehh]

Expanding foam around them?