This fortieth entry was published originally by JSHarris on the 30th October 2015 and received 787 views on the closed forum
Continuing on from the last entry, here’s some more detail about installing the Sunamp PV and the plate heat exchanger pre heat system. Here are a couple of photos of the way the plate heat exchanger, its circulating pump, flow switch and the 50mm layer of insulation was applied, before fitting the Sunamp PV in front of it:
The plate heat exchanger is insulated with 50mm of PIR foam all around and the pipe insulation has been fitted, to reduce heat loss and prevent condensation on the cold water pipes. The Sunamp PV will sit on the varnished ply base and be plumbed to the pipes just visible on the right hand side (the hot water pipe has a temporary flexi bridge hose across it at the moment, just visible at the top right). The white drain is for the overflow pipe (this can’t ever be at very high temperature, so plastic pipe should be OK).
The Sunamp PV arrived this afternoon, so after getting it off it’s pallet and unpacking it I took the opportunity to take a photo with it sat next to the thermal store removed last week:
The Sunamp PV is tiny in comparison with the thermal store, and I’m really looking forward to having more space in the services area. Things were very cramped with the extra insulation I’d added around the thermal store, so much so that I’d had to remove the 100 litre accumulator tank I had up there to provide water whilst the filtration system backwashes. There’s enough room now to reinstate that, which means I can switch the filtration system backwash time back to the afternoon, where the noise isn’t so noticeable and when there is a reasonable chance that we’d have excess PV power available to run the pump (it takes around 20 mins, with the pump running continuously at around 750W).
Here are some close up shots of the Sunamp PV:
It is exceptionally solid and well-made, with a really thick and robust outer casing, stainless steel fasteners and the appearance of being a high end industrial product, rather than the often flimsy stuff that’s aimed at the domestic market. Here’s a close up that shows the impressive thickness of the case, which seems to be powder coated alloy, about 2.5mm thick:
I should get it plumbed in next week, so by the end of the week may be able to give an initial view on its performance. Sadly PV generation has dropped off a lot over the past few weeks, as we enter the winter dip, so I won’t be able to give it a proper test until we get a nice sunny day. We do still see days in winter where we generate over 5 kWh, so I’m hopeful that we should be able to see how it performs solely with PV input once we’re through the current typically equinoctial succession of depressions and associated bad weather.
SustainableJohn 16 Nov 2015 05:31 PM:
I just wanted to thank you for producing this excellent blog. I have enjoyed reading it immensely.
I think you’re willingness to share your experiences (good and bad) and in such detail to help others is both commendable and refreshing. I have certainly learnt a great deal from what you have shared. Thank you.
Is there any update on how things are coming along with the Sunamp PV unit?
Just one question, if I may. I realise that passive house type construction is relatively thin on the ground in this country and therefore the various issues you have encountered are perhaps not very well documented elsewhere. But as I understand it, this type of construction has been around much longer in some other countries and I’m wondering whether the same issues have arisen elsewhere and, if so, what solutions they have come up with. Have you come across any such information regarding experiences in other countries? Is it just a case that they normally incorporate more conventional heating systems or perhaps geothermal (GSHP) as opposed to trying to incorporating PV and an ASHP? Just trying to get some idea before I launch into research of what happens elsewhere!
jsharris 16 Nov 2015 06:48 PM:
Thanks for the kind words.
I’ve had a week off with a stomach bug, but have plumbed and wired the Sunamp PV in today and should start testing it tomorrow.
I’ve been following passive house builds and issues for a fair time and it seems there isn’t really a common view on how best to provide the hot water system. Heating is really so negligible that it hardly needs a system, but I’ve found that having a heat re-distribution system in the floor slab is extremely effective.
I’m not at all convinced that a GSHP would make any sense at all. The capital cost is massive and the energy requirement so minute that it would never make sense. You would be paying far more for the energy in capital, maintenance, repairs and replacement than you would by using direct electricity, and it’s barely sensible in terms of CO2, as I doubt that you’d recover the CO2 used to manufacture the thing with the tiny amount of saving from using it. A cheap and simple split air-to-air ASHP makes more sense, if it could be placed in the centre of the house. Such a unit would cost around £600 to £800 and provide all the heating and cooling needed, far more sensible really than the system we have.
Hot water is the key problem, without a doubt. There’s a need to get water at a usable temperature (42 to 45 deg C) at the outlets with the minimum heat wasted to the house. If I were doing things again I’d not bother running hot water to the kitchen, utility room, downstairs WC or bathroom hand wash basins, but would have run wiring in for instant electric water heaters. Very reliable and very energy efficient (because of the tiny heat losses). That then leaves just the high volume hot water requirement for the bath and shower, and there I’m hopeful that the Sunamp PV will provide a compact and efficient system, together with an inline electric booster heater if required.
SustainableJohn 17 Nov 2015 10:24 AM :
Sorry, I wasn’t very clear when I used the term ‘heating systems’. I was really referring to hot water heating and not space heating. I also wasn’t considering using a GSHP. Just thought that maybe other projects had used different systems (which might have had a different set of problems).
I think there is merit in your idea for using instant electric water heaters as although they cost more to heat a specific amount of water there are no standing losses from storage of hot water and no distribution losses from pipework (therefore the amount of water that you need to heat is reduced significantly). You have clearly shown that standing losses are a problem. Distribution losses must also account for a significant percentage of the energy when you consider the usual usage pattern at hand basins etc. We generally only run the water for relatively short periods each time and it takes time for that hot water to run through the system and for the pipework to warm up (wasting much more than the volume of water in the pipe before the water runs hot). Once we have finished with the basin all the hot water then stands in the pipework and all that heat is then dissipated within the house. As you have stated many times, these losses are clearly a problem in a passive house, particularly at times when you don’t need any heat gains (which is probably most of the year!).
In this paper that discusses issues with hot water system design in passive houses, the modelled system losses shown in the figure on page 5 are clearly much greater than the hot water heat demand itself:
Note – I don’t normally give too much weight to such papers because theory doesn’t always accurately model reality. But even this model shows how great the wastage is and reality is probably worse because insulation of cylinders and pipework etc is never ideal.
Some more information by the same authors in this presentation also:
Their solution seems to be better insulation of the cylinder, designing the system to have shorter runs and using smaller pipes. But even in their “best” case system the modelled system losses are virtually the same as the actual hot water used (i.e. 50% efficient). In the worst “UK basic” case the losses are almost double the hot water used (about 35% efficient). An inline water heater at the point of use then starts to compare favourably with what are normally considered to be more efficient hot water heating systems.
Sorry to hear about the stomach bug. Look forward to hearing more about the Sunamp PV in due course.
jsharris 17 Nov 2015 04:51 PM:
I’m just finishing the commissioning of the Sunamp PV, should be running hot water off in about five minutes (I hope!).
The good news is that is dead easy to install, the hardest part is getting at the internal pump bleed plug to get the air out, which ideally needs some sort of small flat key, as there’s no room in there to get even a dumpy screwdriver in.
SustainableJohn 18 Nov 2015 09:56 PM:
Great. Don’t suppose there’s been very much sun to charge it up from the PV.
lways seems to be the case with bleed plugs!
jsharris 18 Nov 2015 10:25 PM:
I’m pleased to say it fully charged this morning, just on PV. The good news is that the case was barely warm to the touch, almost at room temperature, so it looks like the vacuum insulation panels work very well indeed. I drew off around 50 litres of so of very hot water and all seemed to be work fine, it even recharged back to full in the very dull sunlight we had this afternoon.
Now I know all is OK I’ll get the pipe work lagged and taped up tomorrow, then it looks like, finally, the water system is completed.
SustainableJohn 19 Nov 2015 12:22 AM :
Sounds promising indeed.