Monday, February 1, 2010

Reflections on the work

Feb 1: Until the Glycol goes in, I am still not in a position to know if this will work overall, but with the number of holes drilled in my south wall, it's going to be a sad and messy thing if it does not work! Even if we only put heat down in the summer, it is worth trying.

Climatically, I have noticed that being 5-6 weeks after the Solstice, there are significant amounts of sunshine daily (even if the air temperature is cold). So we would get sunshine directly, and the air temperature inside the boxes would also contribute to the harvest of the panel.

Sunspace effect: I make the suggestion that the idea of building glassy boxes could be linked either to an airbased heatpump (drawing heat from air in the trombe wall effect behind the polycarbonate), or indeed using MVHR (mechanically ventilated Heat Reclaim) with the first air being drawn through a larger space behind a glass wall - a shallow sunspace in effect - in fact, MVHR would be tooooo hot, you need a heatpump to adjust the temperature up or down as required.

Polycarbonate: I know know that for serious buildings, you could not build with Polycarbonate as it is far too easy to drill and cut and no building would be secure against someone with a hand held power drill or cutter (unless it is so high that it is out of reach). Without stiffening, it could have a tendency to behave like a Rolf Harris's wobble-board. However, for domestic use, I know that I could not have done this if I had pre-ordered some sheets of real glass - because of the weight, because of the drilling and curved cutting, and because it is structural, i.e. cantilevering and prone to flex in the wind, etc. For a serious commercial building there is little doubt that the boxes would have to be better designed in Glass with all holes pre-located, making the whole thing a lot more expensive.

Insulation: My biggest worry now is the amount of Insulation required for the indoor piping. This may not be such a problem in the loft, where the surrounding air is colder and drier, although of course it will still be insulated. The insulation I am using is 19mm, and it's difficult to fit around the pipes at any junctions or turns. I shall need lots of self adhesive Insulating Bandage at all junctions and at joints with objects, eg Valves, Air releases, Flowmeter or Pump.

Condensation:  My bigger worry here is Condensation where the pipes pass through the house, close to timber joists etc., where there is plenty of warm damp air. With Hotwater systems, insulation matters merely to retain efficiency (avoid heat loss). But the hot water in the heating pipes cannot set the house on fire, or cause harm. Some installers dont even bother to insulate on the grounds that heatloss from narrow pipes is small and is escaping to where it is wanted, i.e. it becomes an 'internal gain' in the house. By comparison, Cold (below room temperature) plumbing turns out to be a real headache, as the insulation needs to be 100%, including bandage and duct tape everywhere - a small gap somewhere could precipitate damp patches, or worse, the watery equivalent of fire, i.e. dry rot. Small amounts of warm air getting access to the cold pipe can set off a trickle, perhaps making a joist permanently damp, with damp spreading into the ceiling.
     The whole system will have to be checked carefully, with the circuit pump on and the heatpump turned off, so that I can check all joints for leaks (so I don't see condensation and think that it is a leak). Then, when the heatpump takes over (as it must, during winter) any liquid which forms will be condensation, not leaks. As there is no going back on this I have to make it work, so am prepared to put drip trays in the loft underneath parts of the piping, either a wide rainwater gutter or planting trough drip trays.

Replicatability: This is a prototype, and one of the benefits of a blog is to record the problems that occured along the way. I have a CAD model of the panels and boxes, and a real one to measure off, so a future one could be manufactured with accurate dimensions, 1/4 of the effort, and an even smaller fraction of the risk. I also know if things are too over-engineered and stiff, or too flimsy and flexible. Even the choices of screw and bolt sizes has evolved.
  I somehow think that this experiment will have to have a significant benefit for the coefficient of performance of the Heatpump for them to think that this is a system worth offering commercially.
   Meanwhile, the heatpump is using more and more of the Immersion heater function (as the ground gets colder), there are plenty of sunny days up top, so I really want to get this working, even if only to benefit our house. If others can use it later, that will be great!

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