Combining an air-water heat pump and solar thermal

[SteamyTea]

1 hour ago, bontwoody said:

I plan to DIY install the ST and connect it to a twin coil cylinder.

If it is a pressurised system you need G3 signoff.

 

 

[bontwoody]

53 minutes ago, SteamyTea said:

If it is a pressurised system you need G3 signoff.

 

 

Yes and yes, but doing the figures against a thermal store I still think its the better option. Another point I forgot to mention is the possibility of maxing out on the PV if you cant get DNO approval to go over 4kW. Id also like some battery storage but so far Ive had no luck in getting any installers to answer my queries about mixing up a 3kW FIT paying array with another new array and including some battery storage. I think Ill concentrate on the ST solar and improving insulation until the winter in the hope things calm down a bit. 🙂

[JohnMo]

If doing ST do a drain back system, look on eBay etc for an Alpha SolarSmart drain back system, comes complete with pump, drain back cylinder and plate heat exchanger.  You can take the water back to anywhere and the PHE it is certified for drinking water.

[bontwoody]

58 minutes ago, JohnMo said:

If doing ST do a drain back system, look on eBay etc for an Alpha SolarSmart drain back system, comes complete with pump, drain back cylinder and plate heat exchanger.  You can take the water back to anywhere and the PHE it is certified for drinking water.

 

I was curious about a drain back system, thanks Ill have a look for it 🙂

[Dillsue]

3 hours ago, SteamyTea said:

If it is a pressurised system you need G3 signoff.

 

 

Even if its a pressuried coil in an open vented cylinder??

[JohnMo]

Mine is going to open vented thermal store. Direct to top and bottom of store not via a coil.

Edited June 21, 2022 by JohnMo
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[SteamyTea]

6 minutes ago, Dillsue said:

Even if its a pressuried coil in an open vented cylinder??

I think that is okay. It is all about overall energy storage and modes of failure.

While the water in either a pressurised, or vented system contains the same energy, a pressure vessel fails much more rapidly, seconds rather than months usually. This allows a much greater power delivery.

Isn't a vented cylinder with isolation coils a thermal store.

Or do you mean an old system boiler type cylinder, the ones with the coil in the base and an immersion element at the top.

[scottishjohn]

system I had which worked very well was pressurised with an expansion vessel I never had a problem in 15 years 

the failure point was a stupid plastic auto air seperator valve which was mounted outside on the panels on garage roof  -which failed when a sensor went down and temp in system must have been close to 150c to melt the plastic 

or maybe it was other way round temp  these unregulated panels could have taken plastic air valve first and then kept rising until sensor failed

I obviously replaced that with a metal one and new sensor  and it ran for another 6 years till some tubes started to fail ,but to be fair they could have started to be damaged when it got over hot 

40tubes and 300litre tank is not big enough to abosrb all the heat the sun can throw at it, even in scotland --so If I go that way again it will be larger storage so I cannot boil the tank on any given day and keep away from silly temps 

yes it looks good seeing the panels knocking high temps ,but better to have larger storage and never get close to boiling 

you do not need water for DHW or UFH at anything like those temps 

 I was using a mixing valve on my tank so the whole tank could be max temp and then mix with cold on output fromDHW coil down to 55c

taller the tank  the better if taking dhw and UFH form same tank -as heat will always rise so DHW coil is at top of tank 

 ,or you could use 2 tnaks and divert as required ,especially if using solar PV to run an immersion heater  or heaters 

 

[Dillsue]

4 hours ago, SteamyTea said:

Isn't a vented cylinder with isolation coils a thermal store.

What I call our DHW tank is open vented with 3 separate coils. I suppose thats storing heat so could be called a thermal store but I guess youre talking about a space heating TS??

[SteamyTea]

27 minutes ago, Dillsue said:

so could be called a thermal store

I think they should all be called thermal energy stores, even my storage heaters.

Then sub dive them into vented, unvented, direct and indirect. Then the number if coils classed surface area.

[scottishjohn]

I maybe was not clear 

 the solar system was pressurised and also the 3 coil 300 litre tank was running on mains pressure 

so 3 coil and  unvented 

so from bottom to top 

 solar coil 

,ufh coil 

dhw coil 

 and lpg boiler connected to main volume of tnak at approx half way and top 

 only thing i would change is to have some sort of baffle inside to stop mixing effect of flow of lpg boiler when it came on ,so solarr part stays as low a temp as possible and can take any solar input there is 

if using pv+immersion heater there would be little stirring effect as that would be at the UFH coi level and the heat would just rise and would heat down from top  with no pump involved