Part Forty One – Hot Water At Last!

This forty first entry was published originally by JSHarris on the 21st November 2015 and received 1,244 views on the closed forum


After battling with a stomach bug for over a week, I finally managed to get the Sunamp PV in place and installed.

Installation was generally exceptionally easy, with only two areas that caused some challenges. The first was manhandling the sheer weight of the unit up stairs. It isn’t very heavy (around 75 kg) but it is small and very dense, meaning a two man lift is the bare minimum. The second challenge was getting at the pump vent plug when commissioning it. It’s set inside the top of the unit but very close to some adjacent pipe work, so a very marrow key is needed to get in and open it up – there isn’t enough space for a dumpy screwdriver. I happened to have a flat key that was intended to fasten the mandrel sockets on my hole punch set, and that proved ideal, so a suggestion is that such a key could be provided as a bleed screw tool.

Installation was simple, just connect the pre-heated warm water pipe to the cold inlet pipe at the top, connect the supplied thermostatic mixer valve to the centre hot water outlet pipe and attach a tundish and drain to the overflow pipe. The unit does not require a tundish, just a drain, as it only has a very small water capacity, so doesn’t fall within the Part G3 regulations (meaning DIY installation by a suitably competent person is fine). I fitted a tundish simply to give a visible indication if the PRV operated, as my drains are all internal and otherwise not visible. For the sake of £5 for a tundish it seemed daft not to fit one.

The thermostatic mixer is set to 50 deg C at the moment and the outlet connects directly to a 9.6 kW electric in line water heater that is set to come on at 42 deg C. This means that, for as long as the Sunamp PV can provide water above 42 deg C the electric inline booster heater won’t operate and waste electricity.

The electrical connections are very simple. The Sunamp PV comes with a 4 core heat resistant cable and is wired to earth, neutral, switched live via and isolator and switched live via an isolator and the PV diverter and bypass system.

Water is fed to the Sunamp PV via a plate heat exchanger that is fed with incoming cold water. The incoming cold water also feeds the cold side of the thermostatic mixer valve, to ensure that there is a high temperature differential to keep it regulating well. The plate heat exchanger can pre-heat the incoming water, typically to between 20 deg C and 30 deg C, which reduces the amount of heat energy the Sunamp PV needs to provide.

Here are some photos of the completed installation:



Having plumbed it and wired it, I had to commission it according to the MI’s. Really very easy, except for bleeding the pump. Turn on the water and check for leaks, waiting a while to be sure. Keep the power off. Unscrew the top lid, remove some foam insulation and taking care to not damage the vacuum insulation panels down the sides, insert a suitable tool into a very narrow gap and bleed the air from the circulating pump. I’d have liked to have taken photos of this bit, but was a bit concerned about giving away Sunamp proprietary information, so refrained. The pump is easy to get at, but has the water heater case and pipes running very close to where the shaft vent plug is situated. I couldn’t get enough purchase with a coin in the slot and there wasn’t space to get a dumpy screwdriver in there, so I first resorted to a small 1/4″ socket set with a wide screwdriver bit. This didn’t work as there’s not enough room to get more than about 1/10 turn at a time. After pondering for a while, I remembered that I had a metal hole punch kit with just the tool in it.

It’s the rusty thing at the bottom of this photo. After a bit of fiddling this did the job and with some kitchen roll placed under the pump to catch the drips the air was soon bled out OK.

Nest was to switch the power on and check the status lights, then switch the PV diverter to boost for 20 minutes to partially charge the Sunamp PV. When charging there is a very quiet hum as the circulating pump drives water past the slim inline heater and through the thermal storage cells. BTW, the internal design and layout is very neat and tidy, and looks to be extremely well engineered – none of the scrappy untidyness you see in a typical combi boiler.

After charging for 20 minutes and checking that the indicator lights were all correctly showing the status, I drew off a few litres of hot water. I have to say that the unit works extremely well, providing a high water flow rate (I could detect no difference between it and the old thermal store when the shower was running) and water at a surprisingly high temperature after just a 20 minute charge.

Since then I have left it running 24/7 and it is reliably charging solely from excess solar PV. We’re not drawing lots of hot water off yet, so I have the boost timer turned off, but in all respects is seems to meet or exceed it’s specification. One very interesting thing is that the case stays cool. It’s the right height to sit on, yet one doesn’t get a warm backside unless the pump has recently run to draw off hot water or charge the unit (the pump and pipework are near the top of the unit). I shall take some thermal images next week, and add then to this post, but the services room is remaining cool and there is no obvious indication that this little box is storing 5 kWh of thermal energy.

So far I’m very impressed indeed, and feel that there is a definite market for this device, in addition to it’s intended market as an adjunct to a combi boiler, perhaps together with some peripherals similar to mine to better suit it to a low-energy house wit no gas or oil hot water system.


ProDave 21 Nov 2015 03:44 PM:

 Interesting about the circulating pump running when the unit is charging.

 Does that come on automatically when it sensed input? And what sort of threshold, i.e would it come on on a dull day then say only 100W of spare pv is going into the unit?


 jsharris 21 Nov 2015 04:00 PM:

 From what I can tell (bearing in mind that I’ve not been sat next to it all the time) it seems that the circulating pump switches on as soon as the first pulse of excess PV is detected, and this also turns on the “PV detected” LED (the second one up from the bottom, the bottom one being “power on). There seems to be a pump over-run time, where the pump carries on running for a short time, in the anticipation that there will be more PV energy along soon. A system of internal non-return valves keeps this circulation wholly internal, so the water only runs through the heating element and the thermal storage cells.

 I’m guessing that if excess PV doesn’t occur again for some time, then the pump turns off. When I took those photos on Friday the unit was fully charged, having had a pretty good day. The lights on the side (from the bottom up) are “power on”, “PV detected”, “Charging” and “Flow detected” (when hot water is being drawn off).

 There’s no indication in the manual of the threshold, but the pump is a very low power unit, only used to circulate water around a very small circuit inside the unit, so probably draws no more than around 20W or so.


 Sunamp 25 Nov 2015 07:12 AM :

 Hi Jeremy,

 Congratulations! Sorry its taken a few days to pick up on your report.

 We at Sunamp are extremely happy that you like our product and appreciate its design and build. Thanks very much for that.

 I see no problem with you publishing pictures of the hydraulic assembly in the top of the unit. Just don’t try taking a heat battery cell apart!

 Your problems with the bleed valve are well understood and appreciated, as is the “dense mass” handling issue, and I’d like to share our plans for dealing with them. We are in progress to a V1.5 design with revised and compacted hydraulics. This new design does two things that are beneficial to the above issues:

 The bleed valve should be easily accessible. No need for a special tool with the V1.5 (sorry it wasn’t ready for you – and props for your improvisation!)

  • The smaller hydraulic block lifts in and out – its mounted on push-fit flexible hoses. Then you can easily remove the heat battery cells (assuming the unit is cold and fully discharged at the time), and hence move each part separately. Nothing then weighs more than ~30 kg. Then re-assemble at point of install.
  • Additional improvements are planned to include:
  • Choose from 4 locations where the hydraulic connections enter and exit: Each end and each edge of the back.
  • An accessories catalogue – we’ll take your system components into account on this for non-gas properties.
  • I’ll get back to you and ProDave on the more technical questions abut thresholds ASAP.

 Again, really appreciate the success you’ve had and the fact you have taken the trouble to report it very thoroughly.

 Best regards

 Andrew Bissell, CEO, Sunamp Ltd


 jsharris 25 Nov 2015 08:55 PM:

 Thanks for the comments, Andrew. The Sunamp PV continues to work exceptionally well, I still cannot get used to the fact that, unlike the thermal store it replaced, it doesn’t seem to leak heat and always feels cool to the touch.

 The bleed valve was nothing more than a bit awkward, and not really a significant issue. I’m aware than some combi boiler integral pumps are self-bleeding, with a built in auto vent, so that may be an option.

 The idea of moving parts separately sounds great for those that need to fit the unit upstairs (as we have).

 I’ve yet to run the unit out of capacity, despite running 20 minute showers, as it seems that the combination of preheated water plus the fully charged Sunamp PV, plus the ASHP delivering around 5 to 6 kW is more than enough to deliver a couple of hundred litres of hot water. I doubt that the inline booster heater I have will be needed. It’s set to 42 deg C, with the TMV on the Sunamp PV output set to about 45 deg C, and so far the inline booster hasn’t ever come on.

 Some ASHP manufacturers make a hydronic unit that is very similar to the plate heat exchanger and flow switch I have made up. It might be worth looking at making such a pre-heat add-on at some stage for the Sunamp, as then you’d have a system that would be well-matched to any low energy home tha has an ASHP and a PV installation. It may not be a big market yet, but if we continue to try and push people towards building low energy homes then such a combination would be a pretty good hot water solution.


4 thoughts on “Part Forty One – Hot Water At Last!”

  1. Hi Jeremy,

    Sorry if this is already somewhere in your excellent site and I missed it. I saw your various notes on the improvement in heat loss with the Sunamp PV versus the thermal store, but I was interested in whether you have now quantified it. I’ve seen a quoted figure of something like 0.5-0.6 kwh per day from the Sunamp PV.

  2. Hi Jeremy,

    I was passed on your details by Sunamp as we are building a Passivhaus and are very interested in how we might integrate the system into it. We will have plenty of PV for charging when there is sun, however at other times it had been our intention to charge with an ASHP, although we understand that this would necessitate the use of a high temperature model, we had been intending to use th Ecodan range?

    We look forward to hearing from you.



  3. Hi Jeremy, I read with great interest your experiences with not just the Sunamp but your self build in general. It really is a great collection of your work. Do you have any updates on how the Sunamp is/has performed in recent years? My build will be without mains gas and as near passive status as budgets will allow. My concern with just having electric for everything is a constant supply of hot water as my family insist that a bath is “essential” in our dream home!
    The Sunamp PV set up sounds like a winner as we will be installing around 10Kw PV array in combination with ASHP and underfloor heating.
    Due to my no gas concerns I am thinking about localized outlet based instant electric heaters under sinks a) to cope with dead legs around the property b) not enough capacity to produce hot water.
    Both of these fears could be negated with the Sunamp PV from what I read?
    Many thanks

    1. Sorry for the delay, I’ve been a bit lax with updating this site, but intend to do a new entry specifically dealing with the Sunamp. The current position is that I’ve just taken out the Sunamp PV (not because of any problems) and as of yesterday just finished installing and commissioning a Sunamp UniQ 9 eHW. The Sunamp PV I had was an early model, almost a prototype, yet worked extremely well. The Sunamp provides “instant” hot water in the same way as a combi boiler, with an impressively high instantaneous heating power. The unit I’ve just fitted can deliver around 30 kW or more into the incoming cold water to flash it up to around 50 to 55 deg C. Provided the pipe runs to teh taps are reasonably short (I used a distribution manifold for both hot and cold to get good flow to all taps) then the delay before hot water arrives is pretty short.

      I’ve posted in a thread on Buildhub, describing the Sunamp UniQ installation and initial operation:

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