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Solar PV to heat water for central heating

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Comments

  • EricMears
    EricMears Posts: 3,286 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    Also the water in the second tank may have to be temperature controlled if its for floor heating (I don't have floor heating by water, but note most sources suggest a lower temperature than radiators)
    Our 'Heatbank' is used for both DHW and UFH and any water for either use tends to be extracted via a mixer valve so that there is no limit (apart from boiling point) on how hot the stored water can be.  AFAIK,  that's fairly typical of other UFH systems.
    NE Derbyshire.4kWp S Facing 17.5deg slope (dormer roof).24kWh of Pylontech batteries with Lux controller BEV : Hyundai Ioniq5
  • Freepost
    Freepost Posts: 219 Forumite
    Part of the Furniture 100 Posts Name Dropper Combo Breaker

    My thoughts on the motorised valves was that they would operate automatically, if the heat in the tank is at a low temperature then bypass the tank. Also, I had assumed that I could use just one motorised valve and a couple of non return valves on the other side of the tank.

    I am surprised that the DHW is at a temperature that could scold, can I ask, what temperature is the water in the tank?

    I think a "wee thread on the tanks" would be very interesting.

    One further point with regard to the water in the tanks, is this just standing water? Do you replace it every now and again?

    Regards

    F.


  • Forty years ago, I purchased a new home that had E7 wet central heating. At midnight, there was a very loud clunk as the contactor closed and a raft of immersion heaters started to heat a very large cylinder of water. This ‘heat’ store was then used to heat the water that was pumped around the wet radiator CH system. I am not sure that it was the greatest of design ideas.

    Would it work with my 6.35kWp array. Certainly, but it might have been a bit chilly on the 10 December last year when the total output was 350Wh!
  • EricMears
    EricMears Posts: 3,286 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    Freepost said:

    I am surprised that the DHW is at a temperature that could scold, can I ask, what temperature is the water in the tank?

    One further point with regard to the water in the tanks, is this just standing water? Do you replace it every now and again?

    Not sure if that was a question to me or someone else ?

    Although the temperature inside my Heatbank is usually far higher than that of most people's DHW,  it does not mean that there is any possibility of my DHW scalding anyone.  DHW in a Heatbank system is mans pressure (cold) water that has been passed through a heat exchanger and if necessary mixed with further cold mains water to supply a comfortable temperature at hot water taps.

    The stored water in a Heatbank system can be topped up if necessary but would normally sit there forever.  It contains the same additives that are used to protect radiator systms.
    NE Derbyshire.4kWp S Facing 17.5deg slope (dormer roof).24kWh of Pylontech batteries with Lux controller BEV : Hyundai Ioniq5
  • Freepost
    Freepost Posts: 219 Forumite
    Part of the Furniture 100 Posts Name Dropper Combo Breaker

    Hi Eric, my comments were in response to Solarchaser's explanation of how his system works but without a doubt the explanation that you have provided of your own system is very interesting and perhaps very similar to what Solarchaser has or is trying to achieve with his system.

    Regards

    F.



  • Solarchaser
    Solarchaser Posts: 1,730 Forumite
    Fifth Anniversary 1,000 Posts Name Dropper
    EricMears said:
    Also the water in the second tank may have to be temperature controlled if its for floor heating (I don't have floor heating by water, but note most sources suggest a lower temperature than radiators)
    Our 'Heatbank' is used for both DHW and UFH and any water for either use tends to be extracted via a mixer valve so that there is no limit (apart from boiling point) on how hot the stored water can be.  AFAIK,  that's fairly typical of other UFH systems.
    Fair doos, as I said I don't have water based ufh, so I just didn't know.

    Thanks for the confirmation 👍 
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 60Kwh storage
  • Solarchaser
    Solarchaser Posts: 1,730 Forumite
    Fifth Anniversary 1,000 Posts Name Dropper
    Freepost said:

    My thoughts on the motorised valves was that they would operate automatically, if the heat in the tank is at a low temperature then bypass the tank. Also, I had assumed that I could use just one motorised valve and a couple of non return valves on the other side of the tank.

    I am surprised that the DHW is at a temperature that could scold, can I ask, what temperature is the water in the tank?

    I think a "wee thread on the tanks" would be very interesting.

    One further point with regard to the water in the tanks, is this just standing water? Do you replace it every now and again?

    Regards

    F.


    Yeah sorry I misunderstood,  I thought you only meant one valve, so yeah one motorised and one check would be fine I think.

    I made the mistake of fitting only 1 check valve, so I now need to fix that.

    In regards to the tanks, right now it's a 72C, my plan is to store at 90C ideally.

    Water in the tanks is, yeah kinda standing, it's water with central heating inhibitor in it, and a central heating pump to run as a destrat pump circulating the water around the coils.... though so far that's not been needed, seems like I had a solution for a problem that didn't exist.
    I'll probably replace it every 5 years or so I guess.
    Stainless tanks, stainless coils and brass connections, so only risk of corrosion is the steel pump I think.
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 60Kwh storage
  • Heedtheadvice
    Heedtheadvice Posts: 2,677 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    I find this all very interesting, either that or I have envy and wish I had gone down a similar route when I too thought about a thermal store several years ago. That was on a much smaller scale as I have a lot less solar PV and as yet no batteries.
    (Expansion is now happening but it will be a while before I could do more work! Some of it was to help heat a greenhouse (getting very expensive now!!!) with a thermal store underground. Water was not feasable for several reasons so the cheap install was tubular heaters and lots of bricks making use of excess solar in springtime.)

    I take my hat off to you Solarchaser going through the research, design and installation yourself. I hope it works out well but you do seem to be going down the right track and have understood all the points made in threads (on here at least, cos I have not read your other forum posts but assume the same!) both those constructive and those casting doubt.

    Here are some point that just crossed my my so pass on for your consideration but I would bet you have them covered!!

    I note your comment about inhibitor. Have you taken precautions regarding frost protection? It may not be necessary but I am thinking of a possible rare and long event when there is a combination of problems such as an extended cold spell, a breakdown of power supply loss. Although the planet is warming generally we can still get events that result in electricity grid problems lasting several days and very cold snaps in my living memory where storage tanks could freeze. Could be a minimal and acceptable risk.

    I also did wonder about the need for destrat but whether you need it or not you have that covered!

    Do you have your thermal safety cut outs yet that you have mentioned. Interested to hear what temperature you have selected and (presuming auto reset types) what differential you have been able to find. You wrote that an operating temperature of 90C (?) was your aim and I wonder if that is too high? You will no doubt have the specs for all the bits in use but wonder if that is too high for water boiling to start around the heaters?

    I like the thinking behind the project overall but especially the positioning of the 'tank'. I had a smile thinking of how you could be hot stuff in bed if you had a leak (not personally!) but those safety consideration are priority. Under the lounge is goid though probably of minor benefit but use that benefit rather than totally loose the heat!

    Have you installed a drain for the odd occasions you need to empty and a drip tray to collect any spills?

    Hope you end up with a great system and I expect many others will be doing similar activities in the coming years.

  • Solarchaser
    Solarchaser Posts: 1,730 Forumite
    Fifth Anniversary 1,000 Posts Name Dropper
    Hi heedtheadvice,  thank you for your comments.

    I did start a thread here
    https://forums.moneysavingexpert.com/discussion/6377030/ditching-gas-going-electric-immersion-only-a-wee-project

    And I think that answers some of your questions, but to hopefully cover the others.
    Both tanks are linked together at their drain points and are connected to a water pump, which is then connected to some pex directed to outside the house, the idea being that if there is any kind of emergency I open both valves and pump the water out, as due to the depth the tanks are sitting, if they started to leak, there wouldn't be a gravity draining to outside, they would essentially sit in their own puddle.
    With this I've made a larger recess in the ground and directed each of the damp proof sheets to this recess, so that if they do leak I have a central point to pump out from.

    The tanks are apparently rated to 10 bar, I pressure tested everything at 3.5bar with full tanks, before then reducing to 1 bar as the running pressure.

    Every connection to the tanks is compression fittings, but each pipe join etc has been soldered, which is something I'd never done before, but taught myself /youtubed and then tested with a little test rig I made using a pressure tester and some valves so I could be sure of their integrity before fitting.
    I also bought a pipe bender and have used that where possible so as to reduce the noise and flow losses in the system That I'd get using standard 90 degree bends.
    The pumps both have valves both sides as I figure these are most likely to leak, so I need to be able to isolate them from the rest of the system.

    The thermal safety cut outs, well the immersion elements have 2, 1 which is the usual bimetallic (I assume) which cycles itself on and off when heating, however they also have a manual reset cut out as well, in theory they are set to 70c and 80c respectively,  but as with everything,  there is tolerances.
    The left side element has been more likely to trip the manual reset than the right side, so I've been mostly just using the right element. 
    I also put a very slight incline on the left side of the tank as heat rises (both elements in 500l tank are at bottom) and I wanted the central heating, which is on the left coil, to have the higher temperature if possible.

    As the water will be sitting at 1 bar guage (so 2bar Absolute) the boiling point is closer to 120C, and so should be fine at 90C, but I am finding that as I approach 70C the pressure is raising to 1.5Bar guage, which says I need to add more expansion vessel literage and thats a shame as my Google research suggested a 4% expansion in water, and this looks more like a 6% expansion,  but this falls back to when theories meet reality,  you need to go with the reality.

    I have not put any antifreeze in the system.
    I have to admit I went back and forward on this a few times, and the truth is I'm still not totally set on this, although the chances of freeze are super super small, due to the tanks being almost always above 40C and being very well insulated (100mm pir added after I'm finished playing) it is something that I'm still considering rather than inhibitor,  both from a freezing concern and also flow of water and also recognition of leaks.
    As I type this now I feel myself veering back to antifreeze 😳🤣
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 60Kwh storage
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