[Paul Corfield]

Quote

Chris Lloyd - 16/7/2011 19:24 Well, I have managed to make a second panel now - this time using a radiator that I have painted black. I have enclosed it in a box again, underneath which there is aluminium foil and a layer of 20cm loft insulation. I put my glass on yesterday with high temperature sealant and filled it with water. Placed it in the partial sun this afternoon and drained some out. It was a very nice 62 degrees celcius. So I would imagine in the midday sun on a clear day it will work pretty well. I have to say, even though there is a larger quantity of water in the rad than in the 10mm copper pipe - once the system heats up I think he transfer of heat energy will be better as the water is inside rather than me bracing the copper pipe down onto the collector as I did before. Just waiting for some help to get it up on the flat roof. Just have to plumb it in series with the other and away I go.

I make similar things to this but they heat the air instead of water and I use them to pump warm air into my art studio. Some people heat their homes with them too. Look up solar air heaters on youtube.

Paul.

[Paul Corfield]

I've seen figures from users in America where they use the solar air heaters in winter and at -15°c outside the heater will put out 30°c heat at the fan. Generally you get about a 40°c to 50°c increase in heat but you can get double that amount in the summer. The fan is usually thermostatically controlled and only pumps in heat when it reaches a certain temperature inside the solar panel.

Paul.

[Paul Corfield]

Hmmmm, I'd tend to disagree that winter sun is too cool to sufficiently warm a large black panel in an insulated box. Scandinavia is somehwere close to us where they are used extensively to heat homes and their sun is at a much lower angle than ours in winter. A panel can be angled to face the sun direct or even track the sun to maximize the gain. I'll do some tests this winter with mine and see what sort of heat can be generated on a cold day at our latitude.

Paul.

[Paul Corfield]

Are you heating the water to over 65 degrees each day? This is to kill Legionella bacteria.

Paul.

[Paul Corfield]

The main way to get it is as you said, it gets into the lungs through breathing or choking, although I read it can also be contracted from just drinking water, but only in susceptible people. I supose the main thing is that the risk is there for it to multiply. I read it multiplies in temperatures from 20-45°c with 37 degrees being optimal. 55-65°c they will die in a few hours. Above 65 degrees it can't survive.

 

Some info from legionella.org in relation to water tanks.

What is the natural habitat of Legionella bacteria?

        Legionella organisms are readily found in natural aquatic bodies and some species have been recovered from soil. The organisms can survive in a wide range of conditions, including temperatures of 0 to 63o C, pH of 5.0 to 8.5, and dissolved oxygen concentrations of 0.2 to 15 ppm in water. Temperature is a critical determinant for Legionella proliferation. Colonization of hot water tanks is more likely if tank temperatures are between 40 and 50°C (104 to 122° F). Legionella and other microorganisms become attached to surfaces in an aquatic environment forming a biofilm. Legionella has been shown to attach to and colonize various materials found in water systems including plastics, rubber, and wood.

Paul.

 

[scrapemedic]

Chris are you solar heating water that then goes on to heat mains water that comes out of your tap? If so then mains water should contain enough chlorine to kill off any bacterial growth and is never around too long to have substantial growths in it, as long as the two systems are seperate; that is there is a break in the system that feeds the solar panels, such as a header tank with a ball valve in it.

A Thermal store should heat up to about 60 °C for a viable system supplying hot water for baths and washing; its high enough to keep most growths at bay but may need premixing with a little cold before going to the taps. (To avoid a scalding risk).

[ldavidcooke]

scrapemedic, on 07 March 2012 - 12:58, said:

Chris are you solar heating water that then goes on to heat mains water that comes out of your tap? If so then mains water should contain enough chlorine to kill off any bacterial growth and is never around too long to have substantial growths in it, as long as the two systems are seperate; that is there is a break in the system that feeds the solar panels, such as a header tank with a ball valve in it.

A Thermal store should heat up to about 60 °C for a viable system supplying hot water for baths and washing; its high enough to keep most growths at bay but may need premixing with a little cold before going to the taps. (To avoid a scalding risk).

Hey Liz,

You are correct of course, unless he is on a well pump. Though in that case we are talking about his routing the water through copper, (so other then the lead/tin solder the health worries are minimal).

Most cases of bacterial invasion of hvac systems are two fold. One, in the case of an open air heat exchanger-evaporator is the surfaces are not anti-microbial such as are gold, silver, tin and copper. Secondly, if the water in the system is in contact with wood, aluminum, galvanized steel, and subject to optical stimulation of algae growth it will be more likely to be hazardous or can become hazardous.

Chris΄s, designs are inline with standard solar system practices..., well except for the use of a car radiator which has a high level of solder binding the top and bottom tanks. As long as he wicked the solder away and ground the joints to bear copper and then used silver solder and a torch with acid flux to reattach the tanks he is fine. There were several articles about this in "Mother Earth News" and "Backpacker" over the years. The main points are, use anti-bological or inhibitor metals in your system, do not expose consumables to open air or in-direct light (UV in direct sunlight will act similar to chlorine, the problem is clouds...), finally insure your system does not contain hazardous materials or materials that are soluable, (IE: Nylon, acetate or polyester tubing/materials versus polyethylene).

[ldavidcooke]

Hey Chris,

I remembered that your system was a two stage/heat exchanger. The main reason I posted was to clarify the potential hazards if others were not aware. As to the precautions I mentioned, if you were to have a failure, these measures would minimize potential exposures, unlike several nuclear plant cooling designs we have seen fail, I prefer incorporating failsafes.

If your solar systems first stage were truly a closed loop, I would recommend changing the working fluid to a highly saline liquid as the sodium would improve heating and conductivity. As to the plastic tubing, generally most black tubing today is non-hygroscopic polyethylene, if you also employ high temperature stable, schedule 40-80, CPVC you generally can use a copper tubing preheating single stage panel interconnected via plastic pipes, with a thermally triggered bypass valve, (to insure sufficient temperature to minimize non-solar water heating, especially if you incorporate a single stage system with recycling).

(The problem is sometimes it is unclear if the hot water holding tank is actually a separate or two stage system versus a recycling one stage system. I have found it is always a good idea to test the division in the systems by adding a strong heat impervious dye to the first stage of the solar heat exchanger...)

[grahamread]

You make your own risk assessment of course, but personally I wouldn't consider a solar system any greater risk than large parts of the rest of a HW system. It's regular use of the HW pipe network that I would imagine matter more to flush the system of any nasties.

After all, irrespective of any solar system, there are large parts of most domestic systems sitting at 20C or so:
- the bottom third of the HW tank after any draw-off
- the cold water tank in the loft in the summer months
- all the warm water pipe runs inside the house - particularly those to showers and baths.

Our's is a direct (open loop) Evacuated Tube system (10mm copper pipe). This time of year the panels can get the tank up to about 45 from about 25 degree start. The boiler does the rest if required (for 6 months of the year it's off most days). A decent day from April on, the panels would push the tank to 60C, and June-Aug they'd boil the tank if I let them - which we don't of course.

Here's an example from October last year:
(Black line - panel, blue - tank bottom, red - tank top, green - ambient. Boiler heater tank at 18:30)

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This post has been edited by grahamread: 09 March 2012 - 22:36

[grahamread]

...here's an example of Solar heating to higher temps in the late summer (15/09/11) and one day (02/09/11) when, due to the fact I'd set the thermostat wrong so it didn't stop heating and the tank was already hot from the day before, we had a "slight problem" with the tank at 87C ( oops) - it did eventually dump the hot water (15:00). It's a vented tank so no pressure issue. I've since changed the settings.

(I would point put we have mixer valves on the bath/showers)

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This post has been edited by grahamread: 09 March 2012 - 22:34