Monday, June 24, 2013

Dump the Tubes!

22 June 2013: Many of my problems with the system comes from the small circuit that goes to the evacuated tubes. Before they were fitted, the solar recharging system was very stable for 2 years. The leaks and bursting airlock removers etc happened after that. the tubes circuit has never recovered more then 7 kWh on the very best of days, and mostly less than one per day, even on good days.
       The lesson is that if you have one element that can make over-high temperature, it must be on its own closed high-pressure circuit. It cannot be on the same loop as the heat pump or the low temperature fittings. This was the idea behind fitting the heat exchanger, but I have had endless problems with the heat exchanger, possibly due to airlocks.

  As of this week, they are isolated with valves closed and the electricity to the controller turned off, but I might make the big decision to isolate them entirely, i.e drain the coolant, and disconnect altogether, and put stop-ends on the pipes.

Expansion Tanks
One thing I must do is make sure the existing expansion vessels are more effective. This is the primary method for preventing leaks. I read up on them recently and found the opposite of what I expected. They all have the bicycle valve (Schraeder) on top and for some reason, I thought that letting them off a bit would provide more expansion. If this occurs, more liquid flows in, and there is less air space for expansion. They are intended to be pumped up to about 30psi (about 2kg/cm2). 

Wednesday, June 19, 2013

Twin boreholes in the same hole: Calgary solar

18 June 2013: Robert from Norfolk sent me a link to a paper published in 2007 for the 2nd Canadian Solar Buildings Conference, Calgary, June 10 - 14, 2007. It is authored by Bernier and Shirazi. The link is:
http://sbrn.solarbuildings.ca/c/sbn/file_db/Doc_File_e/Solar%20heat%20injection%20into%20boreholes.pdf

Very interesting. I note that the abstract claims that their purpose is to find a way of reducing the depth of the borehole, which seems a small cost saving to aim for. It seems to be based entirely on mathematical modelling, I cannot find a mention of a real building being used as a case study. There are some very useful and deeply mathematical methods of calculating the borehole size.

That part of Canada has a 'continental' climate, and there's a very short summer, and a long long winter. See the above Degree Day graph to compare Calgary [blue] with Nottingham [red]. This degree day curve symbolises the amount of heat required for comfort. It's so cold in Winter that you would keep the heating on overnight, whereas a well insulated house like ours in Nottingham, England needs no heating at night. Even in winter, it is off from 9pm to 8am.
    Solar heat is 'interesting' in a climate like that, but with such short summers and long winters, its a tough call for it to be significantly useful - but one of the most famous examples in the world is Drakes Landing, about 30km south of Calgary.
Diagram by Bernier and Shirazi
It's useful to have that article with the formulae. It is also interesting that they propose to use an entirely separate but along-side set of pipes for the solar ground loop and GSHP ground loop. That is a good idea, if you are going to drill the hole:- make it big enough to drop two sets of pipes in, not one. This would avoid cross contamination, pressure variations, etc. The GSHP loop can continue on cheerfully, even if the Solar loop is discontinued or faulty.

Monday, June 10, 2013

Repairs to the Tee piece, done!

10 June 2013: The repair is done, and the system ran for many hours without any sign of a leak (the jubilee clipped hose joints have never ever leaked.)
I now have to close up the sun boxes and we are in business again. I forgot to photograph the finished tee close up, sorry! I don't see how the tee piece can fail now, but if there is excess pressure, it's a bit worrying that a fail could happen elsewhere. That's why there are 4 expansion vessels on this system!

The tee piece is in place and I have restored the centre panel cover, and the insulated ducting to the inflow pipe. Here is a view of the repaired tee piece, looking upwards!
The left hand outer ETFE panel goes on. I needed a helper, but managed somehow. The main problem was the risk of puncturing the ETFE by letting the panel fall against the sunbox sharp corners. Now the right hand panel goes on. 
I have another week of the scaffolding, so I will hope for some sunny days and monitor the performance of the system. After just one day of working, I noticed that the ground temperature has risen from 12.7º on Saturday to 13.1º on Sunday evening.
I have some numberplate lettering so I can have
S U R Y A
on the panel


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