I think I can see now how I can make this work without having to replace things i already have, so that’s great.
I have a few questions…
Given my 2 well insulated storage tanks, 280L for DHW and 120L for UFH, in summer I am using 5-8kWh per day to heat DHW for showers etc. Zero for UFH. In winter DHW is the same, but the UFH runs all day. I guess on average the UFH energy usage is around 20kWh per day.
if I were to install solar thermal (flat plate or evac tubes)
1) what size would be best for me?
2) How do I make use of solar thermal in the early morning?
My showers are used at 6.30am before the sun comes up! That’s when i use most of my DHW energy.
I (think) my GSHP will monitor the DHW tank, and when it drops below temp, will kick in. Won’t the solar come on later in the morning? Then I will still be using 4-5kWh on my GSHP to heat showers every day.
3) Would boosting the DHW temp in the day solve this?
I‘ve now got a DHW tank at 45°C (thanks for the tip @moojuiceuk nobody in the house has noticed yet!). I’m not sure i understand how the DHW tank temp monitoring works really What if I got the solar thermal to boost this to, say, 60°C during the day? The tank should only lose about 5°C overnight. As the tank is hotter the showers shouldn’t draw so much as they are mixed with cold to get the right temp. Assume the GSHP will kick in when the tank gets below 45°C.
4) Could I delay the GSHP triggering
I’m not sure I understand how the DHW tank temp works really, I understand heat rises in the tank, gets drawn from the top and cold gets fed in the bottom. I realise the cold water at the bottom will eventually mix to reduce the overall temp, but in the hour we have our showers, won’t we be using the hot water at the top? I think it’s a big enough tank to cover our early morning showers.
So, could I also stop the GSHP heating water in the morning unless I run out of hot water? Say we have guests and have 6 showers instead of 3, I’d need the GSHP to start if the Solar hasn’t kicked in yet. (Although, guests don’t get up at 6.30, so this may not be a problem
5) Can i do the same for UFH tank?
This currently stores at 35°C. I could just maintain that with solar thermal, or could I boot that to say 60°C then add a mixer to drop it down to 35 for feeding back into my UFH. This could reduce the GSHP operation at night.
Interested in your thoughts, it will help me decide if it is worth doing or not.