Monday, September 7, 2009

A way to reduce Stasis in Solar Thermal tanks?


7 Sept '09: We seem to be far down the road with this idea of hanging the black pipe-grid on the south wall. I did get slightly talked into this, as Ice Energy are keen to see if these will work. So I got talked out of a flat plate panel on the roof, and into using the uninsulated black plastic 'kompakt-kollektor' on the south wall. And the idea is much cheaper to carry out.

I do actually have a planning permission to hang a solar collector on the south wall that cost me £170 to apply for 2 yrs ago! So I am not worried about planning.

The whole purpose of this is to be experimental, but I am disappointed that one thing we are not doing at all is preheating the water - one of our earliest ideas was to do this, and only to throw heat down below as an incidental; we moved sideways, and found a new focus. With the idea of charging the earth, it would now confuse data collection to add water preheating to the mixture.

We all know that one the biggest problems with Solar water heating is that if you don't use a lot of the hot water, the tank and the panel reach a stasis, where no further heat goes into the tank. It just sits there being hot. And we do not use much hot water, and I don't want an incentive to use more hot water. So, what to do with all that heat? Can the heat of the stasis be the heat we pump into the depths?

I am weighing the much earlier idea to preheat water using an industry standard flat plate solar panel. As we use very little hot water, the tank would spend a lot of time in a hot condition. Most tanks are available with two coils, so the lower one is for the solar panel, the upper one is spare. The idea could be to have a glycol loop in that upper coil linked to our ground loop. Whenever the sun shines some heat goes first and only to the tank. When the temperature in the tank is above a defined temperature, say 30º it will trigger the pump to send surplus heat down to the borehole, till another defined figure, such as 25º. In summer, solar preheater tanks get to over 40º so there would never be a chance of wasteful stasis. The water would be delivered to the GSHP at something between 25 and 30, reducing the energy required to heat water up to 51º.
    Although we could not easily isolate the data for the solar charging, we would monitor the overall increase in efficiency, by monitoring as many temperatures and flow rates as is possible - it should be possible to derive some figures for the solar charging. The final arbiter is the annual electricity consumption, which is a measure of the carbon emission. A significant drawback is the embodied energy of a large insulated copper water tank, and then there is the question of how to get it up into the loft.

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