• The Red line and zone is the heating requirement of the house, based on heating degree days, as recorded by the weather station at East Midlands Airport.
• The Blue line and zone is the demand of the GSHP in kWhs.
The two lines are of different units but they are scalar, they are directly proportional. During the long summer of 2011, the GSHP has required no heating at all as the incidental gains were enough to warm the house on the few days that heat was needed.
The first Sunboxes were installed in March 2010. So GSHP consumption for the period 1 Oct 2009-2010 was mostly without the help of the Sunboxes until the last month of spring. The consumption was 4,025 kWh. During the matching period 1 Oct 2010 - 1 Oct 2011, the GSHP consumption with the help of the Sunboxes was 3,265 kWh. Towards the end of this period, the boxes were taken off and replaced with the new model (although this makes no difference to the graph above, as no house heating was required.)