Wednesday, June 16, 2010

Summer! - 17p Resistor tunes GSHP efficiency!

June 16 2010: I have been too busy to do anything on the earth charging project in the last week due to the end of term shenanigans at the university, a non stop round of marking, re-marking, filling in feedback and spreadsheets, attending examiners meetings etc.

But, hey! it's summer, and the system is working well, energy is being captured by the roof, energy is being pumped deep into the earth, and the whole process is being metered, all along awhile.
   The datalogger is still working fine, but there's not a lot to report. The GSHP remains in sleep for such long periods. So we may unplug it (label the cables for reconnection next autumn) and put the datalogger on other projects at the Uni. So there's not a lot to say right now.

   One small thing remains - the external air temperature is a primary way to control the actions of the GSHP and the Underfloor heating system. The external air temp GT2 drops below 15º in the night time so the Underfloor heating pump wants to run all night, checking the temperature. But as it always gets a 'warm' response, the GSHP does not do any heating. ergo, 2-3 kWhr is wasted everynight with pumping around the floor for no result. (We wouldn't want the heating on at night even in winter).
   In a cold house this would be necessary. In a very well insulated house, this is unnecessary, even in the depths of winter - the temperature holds good most of the night, losing one degree at most even with a bedroom window open.
  Now I have followed David Atkins' advice and rigged up 17 pence worth of resistor, all 4.7 kilOhm of it, inside a domestic 2-way light switch. When this is switched to the external thermistor, GT2 displays the correct temperature. When switched the other way, the GT2 temperature climbs to 25.0 ºC, and then sits there - tricking the GSHP into thinking it's summer - all night long! We can now leave the GSHP on 24 hours to avoid HW pasteurisation, but have no heating required until late September perhaps. Having underfloor circulating pump turned off, and using the GSHP's own timeclock to prevent water or heating during the night,  we hope to use even less electricity in the 24 hour cycle.

July Postscript: This Resistor has improved efficiency, along with my mastering the inner timeclock of the GSHP, and the warming effect of the sunboxes. During June, the GSHP should have used 110 kWh in the month for water heating. The actual consumption was 71 kWh, nearly 40 kWh less than expected.

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