Eco heating system for a 1926 solid walled suburban semi

[PhilRobinson]

We’re renovating a 1926 suburban 3 bed semi. Nothing flash, but we decided we’d try and make it as eco as possible on our limited budget. The first thing we did was asked for quotes from companies with names like “eco heat”, “green heating solutions” etc (these are just made up). They all suggested we install a gas combi, which was a bit disappointing. So we’ve found ourselves insulating external walls as we decorate and largely going it alone from a design POV. We now have a a small solar PV install on the roof, a 14kw sunamp heat battery and a pellet boiler and are working on how to integrate them so the pellet burner heats up the sunamp (in winter) and the sunamp then provides a ‘buffer’ of heat so the pellet burner doesn’t have to turn on too often.

In the course of all this, I made a little monitor/logger for the sunamp as we were surprised to find that in spite of being quite pricey, the sunamp has absolutely no indication of the state of charge or even whether its currently charging or not. This is the primary reason for signing up to buildhub; I’m hoping someone here knows more about working out the Sunamps state of charge from its temperature than I do.

 

 

[SteamyTea]

You have to define 'eco'.  It is a nonsense term otherwise.

 

Quite interested in your energy monitor though, care to post up more details?

Edited October 21, 2020 by SteamyTea

[PhilRobinson]

Very happy to… Basically, I’m trying to get it to report the charge state as a percentage.

I ran all the hot water out of my sunamp uniq12, then set it charging at a slow current and had the logger monitor the 3 cell temp. readings. In the graph the x-axis is time, y-axis is °C. The series shown is average temp of the 3 sensors. As you see, its non-linear but not half as much as you’d expect. (I expected the temp to stay at or around 58° for ages.) However; if you look at the temps of the individual cells, they do show a much greater non-linearity around the phase change temp. The relatively sane average graph results from the fact that the cells heat up at different rates so they’re not all phase changing at the same time. So this makes the logger able to calculate the charge reasonably accurately for the 3 cell sunamp, while it’s charging or discharging (similar things happen during a constant discharge).
However, my brother has a small sunamp which I think has only 1 cell (or maybe 2), so my simple algorithm which works out the charge % based on an average isn’t going to work so well for his. Also, in real life the temps seldom hit empty and/or full, and the cells are are constantly charging and discharging every time you turn the hot tap on or a radiator comes on, so it doesn’t work so well then either. So in practice, the logger can report the actual “charge” with some accuracy only in the top and bottom 20% or so. BUT, at least where you have multiple cells, I can’t help feeling that the differences between their temperatures must be telling me something useful about the charge state. I just can’t work out what. Does anyone know more about this than I do? Happy to post more graphs etc if anyone's interested.

 

[Nickfromwales]

Hi.
If you are using your single size 12 for DHW ( domestic hot water ) then do not even THINK about connecting it to your heating for exporting stored heat energy. That will run flat in very little time at all, leaving you with zero useful DHW capacity. 
By all means connect to the boiler to heat the SA but please check the MI’s as you will likely need a pipe stat / other means of detecting dangerously high input temps which could damage the PCM. Usual to see a pipe stat controlling a zone valve, and for that to be used to arrest flow to the SA in the event of a failure of the boiler stat eg loss of tempering and boiler goes to max temp.

[PhilRobinson]

15 hours ago, Nickfromwales said:

> Hi.
> If you are using your single size 12 for DHW ( domestic hot water ) then do not even THINK about connecting it to your heating for exporting stored heat energy. That will
> run flat in very little time at all, leaving you with zero useful DHW capacity. 

Well, in our little 3 bed semi it’s hours rather than minutes and it seems to me that’s a useful amount of down time for the boiler – pellet burners are horrendously inefficient if they have to cycle on and off a lot. I agree that if we let it run flat we’ll have no DHW, and that’s one reason why I want to get the logger to compute a charge state as accurately as possible so I can turn the boiler on again before it does.

> By all means connect to the boiler to heat the SA but please check the MI’s as you will likely need a pipe stat / other means of detecting dangerously high input temps
> which could damage the PCM. Usual to see a pipe stat controlling a zone valve, and for that to be used to arrest flow to the SA in the event of a failure of the boiler stat eg
> loss of tempering and boiler goes to max temp.

A pipe stat. and zone valve is indeed sensible; at the moment we have the boiler set to 72 and it never seems to overrun by more than a degree or two, but it would only take someone to set it to 85 by mistake…

Do you know what happens if the input temp _does_ get too high? The SA manual gives “Maximum constant heat source flow temperature when charging the heat battery” as 85°, which suggests that higher can be tolerated for as short time, but I may be reading too much into that ‘constant’. Thanks, P