Post and beam Posted September 9 Share Posted September 9 I have seen 32mm pipe pairs in 125mm, 140mm and 160mm so far. For a relatively mild Hertfordshire installation is it necessary to go for the thickest insulation or is this overkill. Dont want to skimp on this element. Link to comment Share on other sites More sharing options...
G and J Posted September 9 Share Posted September 9 How long a run are you looking at between the ASHP and the house? Link to comment Share on other sites More sharing options...
JohnMo Posted September 10 Share Posted September 10 32mm - how big is your heat pump? Is this under or a overground, inside or out? Link to comment Share on other sites More sharing options...
Dave Jones Posted September 10 Share Posted September 10 pipe size also dictated by flow rate and temp. Can be bad for efficiency to over/under size. Link to comment Share on other sites More sharing options...
Nick Laslett Posted September 10 Share Posted September 10 (edited) I previously collected a few good threads on this topic in the thread linked below. There is a HeatGeek video on YouTube about pipe diameter, I believe a higher flow rate/lower temp requires larger diameter. For the insulation question the length of pipe will be the biggest factor. Edited September 10 by Nick Laslett Link to comment Share on other sites More sharing options...
Post and beam Posted September 10 Author Share Posted September 10 (edited) 9 hours ago, G and J said: How long a run are you looking at between the ASHP and the house? 8 metres in a direct line so a little more than that to account for the Bends at each end to get up through the block & beam. Thats 8 metres to the manifold under the stairs. 1 hour ago, JohnMo said: how big is your heat pump? 7kW Vaillant Edited September 10 by Post and beam Link to comment Share on other sites More sharing options...
JohnMo Posted September 10 Share Posted September 10 2 hours ago, Post and beam said: 7kW Vaillant Sounds big pipe. I am doing about 16m each way to the 3 port valve and have used 28mm Hep2O, have it all in 25mm thick armaflex closed cell insulation, the underground parts is within 110mm flexible duct with the ends seals with stainless steel mesh and spray foam. Link to comment Share on other sites More sharing options...
Post and beam Posted September 10 Author Share Posted September 10 What is the detrimental affect of too big a bore pipe, if any ? Link to comment Share on other sites More sharing options...
JamesPa Posted September 10 Share Posted September 10 13 minutes ago, Post and beam said: What is the detrimental affect of too big a bore pipe, if any ? More heat loss because the water spends more time in the pipe Link to comment Share on other sites More sharing options...
sharpener Posted September 10 Share Posted September 10 (edited) 26 minutes ago, JamesPa said: More heat loss because the water spends more time in the pipe Right answer for the wrong reason! Assuming the flow temp is the same then the dwell time does not matter. The heat loss is more bc for a given delta T and insulation thickness (measured radially) there is more surface area to lose it through. 7kW Vaillant can put out 10kW under reasonable conditions so needs 28mm pipework. For 5C dT the rule of thumb says 22mm is good up to 6kW and 15mm up to 3. Edited September 10 by sharpener Link to comment Share on other sites More sharing options...
Post and beam Posted September 10 Author Share Posted September 10 Thanks. 28mm with perhaps a thick insulation layer then rather than a thinner insulated 32mm Link to comment Share on other sites More sharing options...
JamesPa Posted September 10 Share Posted September 10 1 hour ago, sharpener said: Right answer for the wrong reason! Assuming the flow temp is the same then the dwell time does not matter. That can't be the case so far as I can see. Consider the limit situation of static water in the pipe ( ie an infinitely large pipe). All the heat will be lost. Speed it up very slightly. Most of the heat will be lost and very little will reach the house. Unless I'm smoking the wrong substance of course. Link to comment Share on other sites More sharing options...
sharpener Posted September 10 Share Posted September 10 Rate of heat loss (in kW) is what you need to worry about, it is quantifiable as additional cost. OTBE this will be proportional to exposed surface area. Hence smaller pipework better. Temp drop of water in pipe will be proportional to heat loss, and multiplied by vol flow rate in l/hr /860 will equal the heat loss in kW. So temp drop inversely prop to flow rate for a given heat loss. Not in itself important assuming it is small compared with dT across the HP. Not directly a measure of heat loss hence not a measure of avoidable cost. Volume of pipework is however dead volume which we can assume has to be heated to flow temp once per cycle and mostly lost when HP stops. This is a direct function of pipe size, small pipe is better. Link to comment Share on other sites More sharing options...
JamesPa Posted September 10 Share Posted September 10 (edited) Temp drop isn't completely irrelevant because it translates to the need for a higher ft which equals lower efficiency. 2-3% per degree. I have been idly thinking about the optimum strategy if the planners force me to put my heat pump 20m down the garden, which is still possible (planning inspector for my appeal against refusal of permission visited today, couldnt tell from his demeanour what the outcome will be). I have a feeling it's small pipes from heat pump to house, and big water pump at the end. At what point does pipe wall friction causing erosion of the pioe material become a problem in a long straight pipe with a swept bend either end? Obviously in this scenario pipe noise is irrelevant. Are the 'usual' recommendations of 1-1.5 m/s over cautious in this scenario? Edited September 10 by JamesPa Link to comment Share on other sites More sharing options...
sharpener Posted September 10 Share Posted September 10 53 minutes ago, JamesPa said: At what point does pipe wall friction causing erosion of the pioe material become a problem in a long straight pipe with a swept bend either end? Obviously in this scenario pipe noise is irrelevant. Are the 'usual' recommendations of 1-1.5 m/s over cautious in this scenario? There was this discussion including a link to an external erosion calculator here, that might help, took some finding again though! Link to comment Share on other sites More sharing options...
JamesPa Posted September 10 Share Posted September 10 3 minutes ago, sharpener said: There was this discussion including a link to an external erosion calculator here, that might help, took some finding again though! Thanks I saw somewhere else that pex is more tolerant of flow rate than copper. I'm looking at 8-9kW which is borderline 22/28mm. If I am forced to put the heat pump 20m from the house and could get the externally buried pipe down to 22mm or even 15) the resulting heat loss would feel much more tolerable, to the extent that I might be tempted to go this way even if not forced to. Link to comment Share on other sites More sharing options...
sharpener Posted September 10 Share Posted September 10 28 minutes ago, JamesPa said: I saw somewhere else that pex is more tolerant of flow rate than copper. Plausible. The Cu erosion mechanism seems to be removal of the CuO layer forcing it to be formed anew. This won't happen with PEX though; who knows whether mechanical/acoustic erosion of the parent material is more or less a problem? The material is softer but also has more internal damping. 35 minutes ago, JamesPa said: I'm looking at 8-9kW which is borderline 22/28mm. For my money it's significantly above my 6kW rule of thumb for 22mm. What do the detailed calcs show? My worked example was for intermittent HW use, your case is round the clock. Link to comment Share on other sites More sharing options...
JamesPa Posted September 10 Share Posted September 10 14 minutes ago, sharpener said: Plausible. The Cu erosion mechanism seems to be removal of the CuO layer forcing it to be formed anew. This won't happen with PEX though; who knows whether mechanical/acoustic erosion of the parent material is more or less a problem? The material is softer but also has more internal damping. For my money it's significantly above my 6kW rule of thumb for 22mm. What do the detailed calcs show? My worked example was for intermittent HW use, your case is round the clock. Heat Geek calculator does indeed say 6kW/22mm/0.9l/s, so pushing the rate to 1.5l/s (which is often recommended as max for Cu) would do 8-9. I wouldn't do this internally because of noise and fittings, but we are talking underground and swept bends so a different set of considerations. 9kW will be rare - never, most of the time more like 4kW. I have so far found little definitive about the max erosion limited rate for plastic pipes, which is disappointing because it has quite an effect if you need to remote a heat pump. Im still hopeful the planning appeal will come out in my favour, but cant resist thinking about a backup plan! Link to comment Share on other sites More sharing options...
sharpener Posted September 11 Share Posted September 11 18 hours ago, JamesPa said: pushing the rate to 1.5l/s (which is often recommended as max for Cu) would do 8-9. I wouldn't do this internally because of noise and fittings Assuming you mean m/s think you are being a bit conservative. For reasons already discussed I have got up to 17 l/min (as measured by Vaillant flow sensor) going through the original 15mm feed to the coil and, rather to my surprise, it doesn't make any flow noise at all despite lots of elbows. According to my old friend here that equates to 1.9 m/s. John Hearfield suggests 3 m/s max acceptable from noise POV. Re-reading my linked post I also found this from @JohnMo. That would give you 19 l/min in 22mm plastic so about 7kW. For 9kW you would want 25.5 l/min so 1.7 m/s, too high for plastic on his criterion which I assume is for erosion, maybe he can give you the source for this? On 15/02/2024 at 13:26, JohnMo said: As a side note Hep2O is only happy with 1.3m/s for hot water. Link to comment Share on other sites More sharing options...
JamesPa Posted September 11 Share Posted September 11 1 hour ago, sharpener said: Assuming you mean m/s think you are being a bit conservative. For reasons already discussed I have got up to 17 l/min (as measured by Vaillant flow sensor) going through the original 15mm feed to the coil and, rather to my surprise, it doesn't make any flow noise at all despite lots of elbows. According to my old friend here that equates to 1.9 m/s. John Hearfield suggests 3 m/s max acceptable from noise POV. Re-reading my linked post I also found this from @JohnMo. That would give you 19 l/min in 22mm plastic so about 7kW. For 9kW you would want 25.5 l/min so 1.7 m/s, too high for plastic on his criterion which I assume is for erosion, maybe he can give you the source for this? This https://www.pandhengineering.co.uk/advice/pipe-sizing-the-ciphe-loading-units-method#:~:text=According to figure 4%2C when,excess of 2.5 m%2Fs. seems to suggest up to 2.5m/s is acceptable in noise-insensitive locations, broadly consistent with John Hearfield (apparently) Confusion reigns! 20m of 22mm at 25l/min gives a head loss of 5m according to here https://www.plasticpipeshop.co.uk/Flow-and-Headloss-Calculator_ep_60-1.html So for out and back its 10m head loss; allowing for 5m internally that means a pump capable of sustaining a 15m head is required. 6m seems to be the norm, I wonder if 15 is even obtainable. Can you just run two pumps in series? 'Remoting' heat pumps seems to throw up questions that I haven't really thought about. Hopefully I wont have to if my planning appeal is allowed. Link to comment Share on other sites More sharing options...
JohnMo Posted September 11 Share Posted September 11 1 hour ago, sharpener said: maybe he can give you the source for this? Page 86 of the attached manual, top of second column of text. Hep2o_Parts_Users_Guide_Australia_2018.pdf Link to comment Share on other sites More sharing options...
JohnMo Posted September 11 Share Posted September 11 (edited) I am using 22mm plastic pipe from my UFH manifold (location of the diverter valve) to cylinder via CCT and additional pump. The pump on the ASHP delivers 1.5m³/HR doing hot water. From measuring flow temp temps, even with CCT pump at full speed I cannot get the same volume through the 22mm, as the ASHP delivers via 28mm. 28mm is circa 16 to 18m each way, the 22mm is about 10m each way. Just use 28mm like a sensible person would. Your pumping losses are going to more than your heat losses. Edited September 11 by JohnMo Link to comment Share on other sites More sharing options...
JamesPa Posted September 11 Share Posted September 11 (edited) 14 minutes ago, JohnMo said: Just use 28mm like a sensible person would. Your pumping losses are going to more than your heat losses. Thanks; that's actually the conclusion Im rapidly coming to, but faced with an unpleasant problem I like to explore alternatives even if unconventional to ensure convention isn't hiding untruths. A few years ago many people would have said (and some still do say) 'just put in a buffer tank like any sensible person would!'. Hopefully, as I say, the issue doesn't arise and my planning appeal is granted for a location close to the house. My (very) back of the envelope calculations using figures from a commercial twin pipe insulated system suggested a loss of order 300W and order 2-6% efficiency penalty if I need to remote it; not disastrous but not desirable either. Edited September 11 by JamesPa Link to comment Share on other sites More sharing options...
sharpener Posted September 11 Share Posted September 11 16 minutes ago, JamesPa said: So for out and back its 10m head loss; allowing for 5m internally that means a pump capable of sustaining a 15m head is required. 6m seems to be the norm, I wonder if 15 is even obtainable. Can you just run two pumps in series? Jon Cantor's calculator gives 395mbar for a single 20m run, so similar. Vaillant 5 and 12 HPs can do 560/550 respectively, the 7kW is the outlier at 440. Yes you can run pumps in series subject to the static pressure limit but better to use a multistage centrifugal which is essentially multiple series pumps on one shaft. 10 minutes ago, JohnMo said: Just use 28mm like a sensible person would. Your pumping losses are going to more than your heat losses. I think this is the correct answer if you are going to have such a long run. Link to comment Share on other sites More sharing options...
JohnMo Posted September 11 Share Posted September 11 57 minutes ago, JamesPa said: commercial twin pipe insulated system suggested a loss of order 300W Wasn't convinced the commercial twin pipe was that good, that's why I did my own, each pipe in its own 110mm duct with 25mm wall thickness insulation all around. Also penny's in the pound cost wise. So only has approx 15mm insulation horizontally. Although there is quite a bit vertical, think the losses would just go sideways. Link to comment Share on other sites More sharing options...
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