Jump to content


ebuild is sad to announce its closure - it has become too time and resource intensive to develop, manage and maintain.

However, ebuild will remain on-line in archive mode (ie no posting facilties) for several weeks so that users can use it as an information resource.

Sunamp PV vs Thermal Store Heat Loss Comparison


  • Please log in to reply
52 replies to this topic

#1 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 01:31 PM

Some may remember the standing heat losses that I found with our 260 litre thermal store (around 3.5 kWh/day as standard, reduced by about 1/3rd with extra insulation). There are some photos and thermal images in this thread here: http://www.ebuild.co..._40#entry120570 . Subsequently Steamy Tea went and did some tests and found that his hot water cylinder had broadly similar standing losses (recounted Here: http://www.ebuild.co...water-cylinder/ ).

I've now had the Sunamp PV installed as a direct replacement for the 260 litre thermal store for about a week and it has been charging whenever there has been any sun. Given my relatively low hot water use at the moment this means it is staying fully charged for long periods, exactly the conditions where thermal losses would be expected to be at their greatest.

Here's a reference photo that's roughly framed to match the thermal image camera shot:

Attached File  Sunamp PV Visual Image 1.jpg   18.41K   21 downloads
The pipes exit to the top right in this shot and the thermostatic mixer valve is within 50mm of the Sunamp, to minimise the length of hot water pipe. All the pipes are lagged and taped with Armaflex, so are difficult to pick out because the stuff is black.

Next, here is a thermal image taken from very roughly the same position. It is charged to maximum temperature (~75 deg C):

Attached File  Sunamp PV Thermal Image 1.jpg   16.51K   16 downloads

Note that the Sunamp PV case is at 18 deg C, slightly cooler than the rest of the house, as when the services room was overheating I added an extra MVHR outlet to this room to try and cool it down a bit. I'll probably remove this now, as it tends to cool this area a bit in the cold weather we're currently having (below zero last night, but the heating still hasn't come on and the house is at 21 deg C).

I'm incredibly impressed with this unit. It's sitting at around 75 deg C inside that case, yet very, very little heat escapes. It works just like a combi, if you turn a hot tap on it flash heats water to a high temperature, mixes it with cold at the external TMV on the right hand side to the set hot water temperature and delivers it to the hot water outlets.

There is a lot more discussion on this unit in this thread : http://www.ebuild.co...120#entry132061, but I felt that my experience as the "forum guinea pig" deserved a new thread for clarity. The discussion on the Sunamp PV starts at this point in a long running thread on batteries and energy storage and is worth a read, and it's worth looking at the thermal store thread I linked to earlier to see just how marked the difference is in the thermal images.

#2 ProDave

ProDave

    Self build in the Highlands

  • Moderators
  • 5,960 posts
  • LocationScottish Highlands

Posted 23 November 2015 - 01:42 PM

It would be very useful if you could actually measure the standing loss in KWh for a 24 hour period, just as you did with the thermal store.

#3 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 01:49 PM

I can try to, but the methodology would have to be very different, as I can't measure the internal temperature of the Sunamp PV. All I could do is replicate the test that Sunamp did, by turning the unit off, leaving it for 24 hours, then measuring how much energy it took to reach full charge again. My guess is that I'd get the same answer, around 600W, but I'll give it a go and see what happens.

#4 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 23 November 2015 - 01:56 PM

Have you given it a full work out yet.

Max flow rate
Time to depletion
Recharge time (though that is tricky with PV)

#5 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 02:03 PM

I've run a shower for 10 minutes, and it had no problem doing that. It reheats somewhat differently to a water tank, it seems, in that it seems to get hotter quicker, and then stays hot but absorbing more thermal energy over time. One consequence of this is that a short re-charge gives very hot water for a few minutes, before it then cools down again.

I'll run some proper tests on it when I have a bit more time and have wired in an energy monitor so I can see just what's going in to the unit.

In terms of every day performance it seems to do exactly what it's supposed to.

The one downside is that if you fitted one of these instead of a hot water cylinder in an air cupboard I doubt the airing cupboard would even get slightly warm.

#6 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 23 November 2015 - 02:12 PM

I like the image as it shows that the hot part is only just above ambient.

#7 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 02:18 PM

View PostSteamyTea, on 23 November 2015 - 02:12 PM, said:

I like the image as it shows that the hot part is only just above ambient.

Yes, so by definition the heat loss has to be very low, just because of the very small temperature differential. It's an ideal height to sit on when working up there, but is doesn't feel the slightest bit warm unless hot water has just been drawn off (the hot water pipes are just under the lid insulation layer).

#8 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 23 November 2015 - 02:53 PM

So it doubles up as a naughty step when your in hot water.
Sorry, could not resist.

#9 Triassic

Triassic

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,239 posts
  • LocationCumbria

Posted 23 November 2015 - 03:00 PM

As this a long term test, how about logging power usage, PV versus mains input over a twelve month period?

#10 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 23 November 2015 - 03:02 PM

Did you manage to lift the lid and see how thick the insulation is?

Edited by SteamyTea, 23 November 2015 - 03:02 PM.


#11 declan52

declan52

    Advanced Member

  • Members
  • PipPipPipPip
  • 3,087 posts
  • LocationCo. armagh

Posted 23 November 2015 - 03:06 PM

Is the hotter pipe connection on the top right of the image what you expect it to be all the time. Or when you are having a shower etc and the water leaving the sunamp is much hotter will there be an even greater heat loss into the room. Going by the image there is near enough no heat leaking from the main unit so the weak point is the pipes. You have them all taped and insulated up so is it just an negligible amount of heat loss you are having. My thermal store has a lot of pipes in and out so I would say I lose more heat from these rather than through the actual tank.
Have you noticed any drop in pressure at all??

#12 gravelld

gravelld

    Regular Member

  • Members
  • PipPipPip
  • 655 posts

Posted 23 November 2015 - 03:15 PM

Great write up, thanks Jeremy. I read your blog about this a few hours ago and was about to post "can you post some IR images of the pipes" but you got there first!

This device is looking very promising. How do they avoid heat leaking out through the pipes? I didn't realise no return valves stop heat conduction.

Pipe losses are a massive part of HWC heat loss in my experience, lagged or not (mainly because lagging is so pathetically thin).

Edited by gravelld, 23 November 2015 - 03:15 PM.


#13 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 03:27 PM

Yes, most of the heat loss if definitely through the pipes, the case of the unit feels cool to the touch, despite being 2mm thick aluminium alloy. The warmth at the top right is because I'd drawn off hot water an hour or two before taking that thermal image. I deliberately connected the TMV as close as I could get it to the hot pipe outlet, to try and keep the length of hot pipe to an absolute minimum:

Attached File  Sunamp PV - TMV.JPG   33.75K   6 downloads

This also happened to leave the control in an easy-to-access position. Internally there are non-return valves in the circulation system that prevent thermosyphon circulation, I think, and this probably helps. The internal pipework is simple, yet clever, and uses no motorised valves yet retains isolation.

I could have taken photos with the lid off, but I'm a bit wary of breaching Sunamps rights. The vacuum insulation panels are pretty thin, though, thinner than I expected. But then the lambda value of these panels is around 0.004 W/m.K at the centre, so a fair bit better than aerogel as insulation, or over 5 times better than PIR.

Edited by jsharris, 23 November 2015 - 03:30 PM.


#14 SustainableJohn

SustainableJohn

    Member

  • Members
  • PipPip
  • 98 posts

Posted 23 November 2015 - 04:19 PM

Excellent write up as usual Jeremy. Many thanks for this.

Good to see the thermal image confirming the low heat losses (I want a thermal imaging camera of my own now!).

It will be interesting to see how the unit copes with demand in practice. It says the unit has a storage capacity of around 4 to 5 kWh and by my reckoning (just a quick calculation) the average shower (say 50 litres) would use about 2 kWh at a temperature of 45 degrees (that's heating water from a temp of 10 deg C and it would be just under 1.5 kWh from a temp of 20 deg C, or around 0.6 kWh for a starting temp of 35 deg C). So the Sunamp unit should be able to supply at least 2 showers by that reckoning and if you're using water preheated at 35 deg C then maybe a lot more?

Edited by SustainableJohn, 23 November 2015 - 04:21 PM.


#15 ferdinand

ferdinand

    Advanced Member

  • Member Blogger
  • PipPipPipPip
  • 1,031 posts

Posted 23 November 2015 - 04:40 PM

>I've run a shower for 10 minutes, and it had no problem doing that. It reheats somewhat differently to a water tank, it seems, in that it seems to get hotter quicker, and then stays hot but absorbing more thermal energy over time. One consequence of this is that a short re-charge gives very hot water for a few minutes, before it then cools down again.

That is exactly the profile to be expected if the phase change of the salt happens at around the temperature matching your ideal hot water temperature, and would give the best performance in terms of minimizing gas usage. So it sounds well-matched, giving the maximum percentage of availability at the best temperature.

Ferdinand

Edited by ferdinand, 23 November 2015 - 04:41 PM.


#16 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 04:57 PM

I'm sure you're right about the way the PCM works, it makes sense.

So far I'm struggling to find a downside to this unit, and my review is sounding a bit one-sided, as if I were being paid to do it! I can confirm that I did buy this unit from Sunamp, it isn't a trial or demo version, but a standard production item, albeit one from the very start of their production run. Sunamp are aware that I'll report performance warts and all, and to be fair they did offer to lend me a free review model for a year, but I declined on the basis that I wanted to be free to report performance free from any constraints.

#17 gravelld

gravelld

    Regular Member

  • Members
  • PipPipPip
  • 655 posts

Posted 23 November 2015 - 05:12 PM

View PostSustainableJohn, on 23 November 2015 - 04:19 PM, said:

It will be interesting to see how the unit copes with demand in practice. It says the unit has a storage capacity of around 4 to 5 kWh and by my reckoning (just a quick calculation) the average shower (say 50 litres) would use about 2 kWh at a temperature of 45 degrees (that's heating water from a temp of 10 deg C and it would be just under 1.5 kWh from a temp of 20 deg C, or around 0.6 kWh for a starting temp of 35 deg C). So the Sunamp unit should be able to supply at least 2 showers by that reckoning and if you're using water preheated at 35 deg C then maybe a lot more?
Why 45C? That's very hot, but I'm not sure if this is the temperature required in practice for a shower (i.e. after pipe losses before it gets to the shower).

Also warming up water from 10C seems pessimistic, our feed is still way above that...?

#18 declan52

declan52

    Advanced Member

  • Members
  • PipPipPipPip
  • 3,087 posts
  • LocationCo. armagh

Posted 23 November 2015 - 05:21 PM

So the only issue you have come across initially is the bleed screw. As yours is one off the first versions do you know if its been modified or maybe you get a custom tool supplied with it now.
Seems like an excellent piece of technology. Fair play to Andrew and his team.

#19 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 23 November 2015 - 05:26 PM

I measured our current shower several times to get a reasonable figure and it seems we like it at around 38 deg C. However, the lowest I can run the hot water and still get the thermostatic shower valve to regulate is 45 deg C, so that's the practical lowest normal hot water temperature. Even that is lower than the thermostatic mixer spec, as that supposed to require a 10 deg C differential, rather than the 7 deg C that it seems I can get away with.

Yes, the pump bleed screw access is a nuisance, but it would be very easy to supply a pressed metal key like the one I nicked from my hole punch set, in order to get around the problem. I can't see an easy way of re-jigging the internal layout as there isn't much space above the heat storage cells.

Edited by jsharris, 23 November 2015 - 05:27 PM.


#20 SustainableJohn

SustainableJohn

    Member

  • Members
  • PipPip
  • 98 posts

Posted 23 November 2015 - 05:33 PM

View Postgravelld, on 23 November 2015 - 05:12 PM, said:

Why 45C? That's very hot, but I'm not sure if this is the temperature required in practice for a shower (i.e. after pipe losses before it gets to the shower).

Also warming up water from 10C seems pessimistic, our feed is still way above that...?

In one part of his blog Jeremy said this - "We need hot water at between 42 and 45 deg C to deliver a shower at 38 deg C" and so I just took the 45 deg C as the worst case.

The 10 deg C was just my guess for the incoming temperature of mains water (probably pessimistic). Obviously Jeremy's system is different, but this was just a calculation for the average household that had a mains water supply. I did include some figures for starting temps of 20 and 35 deg C for comparison.