Wednesday, November 25, 2009

Big Decision about the Battery

25 Nov : Also, after much agonising, and much time spent on design I have had to make a decision about the battery with the phase change spheres. I have at least two, perhaps three students dependent on me for a dissertation now, and I am aware that the battery brings two undesirables to the table: a big Delay, and excess Complexity - both of which are bad for them, and bad for me too.

To prove my basic hypothesis that the ground can be warmed to counteract its heatloss, the best route is PLAN ONE, which is to take the solar and air heat directly to the boreholes.

The other reasoning behind this decision is that the Delta-T between the Solar-Air panels and the Ground is perfect. For the battery idea to work perfectly, I would really need a high temperature flat-plate solar panel, as I would have if using a large tank of water. If I did that, I might as well go the whole hog and have my original idea (of a large water tank), which would also have reduced the cost of warming the domestic hot water. With the PCM balls in the battery sticking at around 23º, the panels would not often be hot enough to send warmth to the tank - whereas when comparing with the ground temperature of 8-13ºC, the Delta-T is favourable for most of the year, even at night.

Since a part of my idea is to see if the low-cost low-temperature air panels will do the job of warming the ground, then the use of a battery or tank introduces a level of complexity that is just too confusing. I will retain the balls and consider making the battery in a year or two. (The balls can be stored in the loft until then, and it will be easy enough to plumb in the battery in two summer's time.)

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