Posted By: welshboyI hope to run some underfloor heating directly from the big store and when the temperature of the store drops too low for the direct ufh to then extract the remaining heat via another heatx raising the temperature of the groundloop of our heat pump so it does not need to work as hard and is more efficient.

This is an interesting idea. I've not heard it mentioned before.

How does this work? Is there a heat exchanger on the GSHP's ground loop return fed from the 170l solar store? Does the GSHP's load loop feed the 1100l store or does it feed the underfloor heating directly? How is this controlled?

I guess the solar store becomes unuseable for underfloor heating below about 28 degrees. Is the idea to take the solar store down close to zero degrees? The GSHP's ground loop may operate close to or below zero degrees, have you thought about frost protection?

David

Posted By: welshboySolar plan- Stress plan - about to be installed .
Flow is routed through a heatx which thermosyphons heat to 170l .This 170l tank is part of the dhw and takes to part of the space heating. After the solar flow has routed through the heatx it goes into the 1100l store.
Inside the 1100l store there is a heatx which routes via a pump to the house ufh and radiators.

I'm not a plumber, but don't you need a diverter valve across the solar connections to the 1100l store?

There's a limit to how much power the first heat exchanger can take out of the solar flow & there's a limit to how much power the solar panels can put into the solar flow. Normally the output of this heat exchanger would go back directly to the solar panels. So whatever temperature you get out of the heat exchanger becomes the inlet temperature to the solar panels. As the temperature in the 170l DHW store goes up, so does the inlet temperature to the solar panels. The solar panels then add 10-20 degrees to the flow & send it back to the 170l DHW store again until the target DHW temperature is reached.

If you connect the 1100l thermal store in series with the 170l DHW store's heat exchanger then the inlet temperature to the solar panels will be roughly equal to the temperature of the 1100l thermal store. In other words, unless you do something to switch the heat exchangers then your DHW temperature will be limited to 10-20 degrees above the 1100l thermal store temperature.

David

<blockquote><cite>Posted By: davidfreeborough</cite><blockquote><cite>Posted By: welshboy</cite>Solar plan- Stress plan - about to be installed .
Flow is routed through a heatx which thermosyphons heat to 170l .This 170l tank is part of the dhw and takes to part of the space heating. After the solar flow has routed through the heatx it goes into the 1100l store.
Inside the 1100l store there is a heatx which routes via a pump to the house ufh and radiators.</blockquote>I'm not a plumber, but don't you need a diverter valve across the solar connections to the 1100l store?

There's a limit to how much power the first heat exchanger can take out of the solar flow & there's a limit to how much power the solar panels can put into the solar flow. Normally the output of this heat exchanger would go back directly to the solar panels. So whatever temperature you get out of the heat exchanger becomes the inlet temperature to the solar panels. As the temperature in the 170l DHW store goes up, so does the inlet temperature to the solar panels. The solar panels then add 10-20 degrees to the flow & send it back to the 170l DHW store again until the target DHW temperature is reached.

If you connect the 1100l thermal store in series with the 170l DHW store's heat exchanger then the inlet temperature to the solar panels will be roughly equal to the temperature of the 1100l thermal store. In other words, unless you do something to switch the heat exchangers then your DHW temperature will be limited to 10-20 degrees above the 1100l thermal store temperature.

David</blockquote>

"If you connect the 1100l thermal store in series with the 170l DHW store's heat exchanger then the inlet temperature to the solar panels will be roughly equal to the temperature of the 1100l thermal store. In other words, unless you do something to switch the heat exchangers then your DHW temperature will be limited to 10-20 degrees above the 1100l thermal store temperature."

That is the way it is planned.

I did not say but the 170l store linked to the heatpump and planned solar acts as a preheat store for another 170l dhw store in series.Ie Hot out from preheat store is feed for dhw tank.
Also the preheat store 170l is the dishwasher and washing machine feed.
Works ok.

I'm going to use a diverter valve for both solid fuel and solar input - 120L DHW tank first, then switch over to a pair of 180L tanks coupled together which I hope will act as a buffer for the radiators.

However, you can arrange solar to heat your DHW tank to the acceptable temperature even if the panels are always fed with very low temperature water - just rig the controller to cycle the pump on only when the temperature at the panel reaches the target.

This isn't as efficient though, as the panels obviously work best when raising a large volume of water at a low temperature to a very slightly higher temperature :)

DF thanks- The heatpump - when on heats the preheat cylinder and that water goes to the dishwasher and washing machine working ok. This has reduced our electric bill as we are rural not on gas. It also reduces ( via cop)the paid for energy for the dhw.
Going to wait and see how the solar works as the thermosyphon should act as a control on overheating the preheat cylinder.
Just bought another 2 panels making just under 20 sq metres of flat plates.
Depending on how it performs I am considering the possibility of a single panel dedicated to the dhw cylinder.- have to see what temps the preheat cylinder gets to first tho.