Monday, March 14, 2011

Annual consumption figures go below target - good!

14 Mar '11: Weekly Summary of annual figures
I recompute the annual figures every week - for consumption and power/heat generation.
  • The house annual consumption is now safely below 5,600 kWh and 
  • The GHSP annual consumption is below 3,600 kWh

Let us hope that the weather is 'average' enough not to bring a last cold snap of the winter, so we can stay below these figures all summer! I fixed a cylinder thermostat a while back to reduce overheating of the DHW, so with some luck, the summer GSHP consumption will be lowered. 

With our recent run of grey days in February, our PV annual is below expectation -  3,240 kWh - we hope to catch up - March is not half done yet, and it has already overtaken the total for February. March of the previous year was extremely sunny, and if this month is not as good, the annual figure may remain stuck at 3,250.

Comparison of GSHP consumption and
Degree days, done at weekly intervals
If our final PV harvest is as good as last year (3,325 kWh best figure), it would be great if the GSHP gets closer to this... but I think that with all my best efforts, that 300 kWh gap between 3,300 and 3,600 is not bridgeable. The PV annual is more likely to be 3,250 or less in the future, our score for the first year was unusually high!
    The effect of the sunboxes is not to put heat into the house, but to improve the GSHP efficiency by 15-18% - not enough to close that gap! Now that we have passed the one-year anniversary of the Sunboxes, their effect on cutting annual consumption is going to be less dramatic. 


What else can be done? The fitting of window mirrors is designed to increase our incidental solar gain on the south elevation (thus reducing equinoctial heating requirements), and I am minded to fit a heat recovery unit for the kitchen dining space. A whole house MVHR unit is not totally out of the question, but the fitting of air ducts is problematic. Perhaps keeping them within the house (and not using the loft space) might be an answer.

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