Monday, August 17, 2009

What are we planning to do?

We are planning to have 4sqm of Solar Thermal panels to deliver heat deep into the ground - Charging the Earth!

1. Our original idea had been just to top up the hotwater by preheating it before it went to the Heatpump (GSHP). Delivering water at 40degs instead of the 10-12 that the mains supply comes up from the ground at. This would reduce the running cost of the heatpump.

2. We then found that the proportion of workload of the heatpump is 27% HW and 73% space heating. So saving only on hot water will not save as much as intended. We also found (from the log on the GSHP) that although it had used the immersion heater function for 440 hours since commissioning, only 13% of this had been on DHW, and the 87% balance on house heating. So.... house heating is the problem that most needs solving.

3. The idea migrated to one or two tanks in the loft, one that would be for preheating water for the domestic HW system, and the other one for space heating. This would be easier to get data from, but way too expensive for householders to copy our example, and difficult to get all this in the loft. So we reduced it to the idea of ONE large tank, big enough to store heat and for the ground loop to borrow heat from that, and for some incidental gains to be transferred do the 48m deep boreholes. The loft is big enough to take any weight and size of tank as long as it fits through the loft hatch.

4. The benefit would only happen in equinox and winter when the pump is pushing glycol round, so is very hit and miss. In summer, the tank would get very hot, and the heat pump would not transfer heat down to the ground.

5. After talking to the Heatpump supplier, Ice Energy, we realised through discussion, that the glycol could be routed directly to the Solar Thermal panels, using a simple thermostatically activated diverter valve and pump that would work even when the pump is turned off or hibernating - during the summer months.

6. This means that throughout the summer, every small amount of energy is stored underground, for our heat pump to retrieve in the winter. The ground below, approx 8,000 tons of dense clay, could absorb a delivery of heat during the summer, diffusing out to the clay around the boreholes.

If it works, but needs more panels, we can add a extra. If it doesnt work, then? ... well, we know it will work to some extent, even if its only benefit is to maintain stability in the ground temperature and thus ensure the optimum coefficient of performance of the Heatpump.

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