Well, Jewsons are handy, but their prices for compression fittings almost made me choke and I didn't even bother to ask what their copper tube prices were! By all accounts, B&Q are actually cheaper, plus I now have Tradepoint so I get their products at a significant discount. I'll pick up what I need tomorrow and finish the plumbing on Sunday. Instead of working on the plumbing side of things, I had a session on the panel itself.
I needed to glaze the panel. This keeps in solar heat that would otherwise radiate straight back off the collector - rather like a greenhouse, the solar energy gets in but has a hard time getting back out again. Eco had a couple of old sealed double glazing units behind a shed. He asked me a while ago if we had any use for them and I'd mentioned using them to glaze a solar collector.
Sometimes in life you get just a bit lucky. Ideally, I needed a piece of glass 60" by 25" and there was one unit that caught my eye in particular. When I ran a ruler over it, it turned out to be 52" x 25". Not perfect - a spot on 60" would have made me very happy, but I figured 52" would do to be going on with.
First job was to take a Stanley knife to the sealed unit and remove the aluminium foil from around the edge of the unit and cut through the mastic to try and separate the two panes of glass. Double-glazing sounds like a good idea for a solar collector - if one pane of glass keeps the heat in, surely two is better? Not so, apparently. It seems that two sheets of glass with an air-gap in between not only reduces the heat energy impinging on the collector but doesn't work as effectively as a greenhouse.
The missing 8" of glass cover has been overcome with two strips of wood 4" wide, one at each end. The collector's effective area has been slightly reduced, but I gain the advantage that the glass can be sealed to the frame in a permanent manner, but the ends of the radiator can still be accessed just in case I need to get to the compression fittings for maintenance purposes. All things considered, I think that works a little better.
On the return side of the panel, I have fitted a tee and an appliance valve. This will allow me to drain down the system if necessary, for maintenance or if extremely cold weather is expected in winter. The system will be protected by antifreeze, but you can't be too careful in a Welsh winter. Rather than take the return pipe through the wall of the van at this end, it folds back under the panel so both the flow and return enter inside the 'plant room'. This means the main internal wall of the body is free of pipework.
On the flow side, or outlet, I have fitted a Y strainer. Whereas this is possibly not essential, it does include an isolating valve. I'm not sure how bad the inside of the radiator is, but I have to assume there will be some scale, rust and debris in there. The strainer will allow me to sieve out any grollies before the pump while I am commissioning the system. I expect the first couple of hours of testing will entail several draindowns and refills to get the worst of the detritus out of the system. The pump itself will tolerate some degree of contamination, but I also have a very tight bend in the immersion primary in the calorifier so I want to try not to let that get blocked.
The total capacity of the system's primary circuit is about 5 litres, so I have used an 18 litre plastic lidded box as my feed and expansion tank. This doesn't have a water supply so filling and topping up will be done manually as part of my daily checks. I now need to find another box...the one I had immediately to hand was my tea-boat! Just in case of overenthusiastic filling, it does sport an overflow, but this is hopefully just for testing and will be removed and blanked off once up and running. The hole in the back of the wall letting the sun in is the hole where the return pipe will leave the van. You can just make out a foot of pipe missing between the tee piece and the pump inlet. The arm of the tee is the vertical feed pipe from the F&E tank. I may need a vent pipe in there too, like a standard vented CH system. Experimentation will determine if this is needed not.
Here you can see my modified OSO undersink water heater I am using as my calorifier/heat exchanger. The immersion has been replaced with a couple of loops of microbore pipe, one for solar and one for an alternate heat source. In the old Tool Shed, this loop was fed from my incinerator loop. The pump is my Topsflo Solar circulator, again repurposed from the old shed. Just behind this on the wall is my pump controller. It is simply a temperature sensor on a flying lead which generates a small voltage on one input of a comparator chip. This is compared againt a 'set point' which can be adjusted, therefore acting as a simple DC thermostat driving the pump relay. In the past, as soon as enough heat was generated in the incinerator, the flow pipe got hot and the sensor picked up this heat and turned the pump on. When the water started to flow, the pipe cooled down enough to switch off the pump and then the heat would build up again and the system would cycle.
I have the option to modify the system to work as a differential controller and use two sensors. One will monitor the panel output and the other will monitor the calorifier. If there is more heat in the panel than in my water tank, the pump will run. As soon as equilibrium is achieved, the pump will stop. This ensures that the system will only pump when there is a net energy gain to be had. Whether I need to go to a differential system, I shall find out once the system is tested.
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