So I had half given up on doing better than last year.... :)
Au contraire mes amis! I did a ground test on Sun 5th Dec and it was 10.8º. What!? Sunday has been a good day for sunshine, with 11 kWh banked by the Surya Sunboxes during the day at an average of over 2 kW per hour of running. The weather forecast is suggesting several more days like this, a foggy start finishing with good sunshine.
We have had no good sun since end of November, but I had a hint of this performance benefit on a sunny Sunday morning of 5th December, when observing the system at work. Just before I had to go out at 11am, the GSHP was busy heating the house:
- External temp: 0.4º.
- Sunbox air temp: 24.5º.
- House air temp 20.0º.
- The GSHP was pushing glycol up to the boxes at 2.0º, and
- it was coming down at 4.9º - disappearing into the ground....
- and returning to the GSHP at 5.7º.
- So the GSHP is getting a very favourable delta-T with little depletion of the ground heat, and working above zero degrees.
Seems to be working!
Next year? I am fully prepared for it to go under 10.0º, or even below 9.0º for much of January and February. The graph of the ground temperature for 2010 has looked like a soft mound shape, part of a Sin wave... but I wonder what shape it will take as the spring sunshine takes effect?
6 Dec '10 Postscript: Monday was even sunnier than the day before, and the sunboxes banked 13kWh during the day despite the ambient air temperature falling to the lowest of the year. The daily consumption of the GSHP managed to stay under 30kWh and the temp of outgoing glycol to the ground loop remained above Zero.
Looking at the diagram above, it seems amazing that we all thought of Spring 2010 as a 'severe winter'. It now seems a mild period compared with the present month of December 2010.
12 Dec '10 Postscript: Deep ground temperature was 10.4º , after a week of continuing cold but thawing temperatures. We have had a good run of sunny mornings, banking 48 kWh of Sunbox heat during the week. Exactly a year ago the deep temperature was 7.2º .... when exactly will the dividend from this greater reservoir cut in, I ask? I don't know! Let's hope it is after the New Year celebrations. At face value, it doesn't look so good, as our GSHP consumption for the last 52 weeks has been 4,235 kWh and when computed in 1 Oct, it was 3,996 kWh. This is entirely explicable by the earlier starting and extra-cold autumn-winter. The current 52 week block includes two unusually cold winter semesters, whereas back in October, it only included one.
One dividend I notice is that the GSHP consumption is more closely related to fluctuations in air temperature, whereas it was more erratic a year ago. Put it another way, the consumption reduces if the air temperature rises, proportionately and promptly - I hope that is because it finds the heat below more easily. So as the weather warms, I hope to see that annual figure sinking back to and below 3,996 kWh!
19 Dec '10 Postscript: The ground temperature is on 10.3º, despite this long cold season! There was some sun at the weekend. One year ago it was 7.1º
26 Dec '10 Postscript: The ground temperature is on 10.0º, despite this continuing cold weather! Just holding in there, in double figures, and I hope for some sunny days as the days draw out into Spring, and we get a bit of recharging from winter sun. One year ago it was 7.5º.