Will this heater idea work

The amount of heat needed depends on room size, how well insulated it is, and how warm the occupant wants it to be. In a typical UK home, between 1500 and 8000 BTU. A heating engineer typically puts the biggest radiator in the living room (a large room we like to be cosy in), and a small one in cool places like hallways and workshops.

If Andrew's room has a 10 foot ceiling, he's looking to heat a space of 1500 cubic feet. With poor insulation, this will take about 8000BTU. 8000 BTU is equivalent to about 2.3kW, so a 300W solar panel or several tea-lights won't touch the sides. Frost protection rather than comfy.

Difficult to beat gas central heating on cost if the goal is to save money. That suggests the answer is to run the central heating system with most radiators switched off. Insulation makes a big difference, as does facing south. Avoid serious leaks like chimneys and patio doors.

Health permitting it may be possible to reduce temperatures in the home significantly. In winter I run my heating for only 6 hours a day at up to 18°C in the hottest room. I dress warmly. Got used to it and now I find buildings warmer that 18°C downright uncomfortable!

An electric radiant heater might be the answer. They throw heat at people rather than warm the whole room up, and then people don't notice it's cold until they move. Arguably a better way to use a small amount of heat. Foot warmers work in the same way - heat where it makes the body happy.

Dave

We have a high efficiency gas fire (balanced flue) in the room we use most. It claims 90% efficiency. Central heating goes on for a short time each day in really cold weather just to take the arctic chill off the rest of the house. I agree with SOD, if you put a jumper on 18C is plenty warm enough. I also wear my woolly hat, but then I'm bald on top so lacking insulation.

Unmarked kerosine is sold at the full rate of duty.

Robert.

Most of the adverts for '200w solar panels' on ebay won't even produce 10W if you work out the area of them. I don't know how they are allowed to get away with such lying. In theory you can get about 200W/m2 at midday, but probably not.

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Haven’t found a video, but here’s a reasonably detailed write-up explaining the principle:

**LINK**

http://www.reuk.co.uk/print.php?article=Solar-Greenhouse-Heat-Sink.htm

MichaelG.

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Which reminds me … there’s a handy but of ‘schoolboy physics’ here:

**LINK**

http://www.reuk.co.uk/wordpress/solar/measuring-the-power-of-a-solar-panel/

MichaelG.

Just been doing a bit of thinking about solar panels. My weather station records incident solar radiation. Here, in the south of France during the winter solstice the maximum I recorded was 335 W/square metre at 12:49 pm on a sunny day. The average over 24 hours was about 50 W/m2. Now the conversion efficiency of solar panels is about 15 to 20 % so I would be getting, at best 10Wh of electricity. Depending on your lattitude in the UK you would be getting about half that (on a sunny day).

How big is your 300W panel?

Russell

I’ll keep out of this thread, except to say that one solar panel will be about as useful as a chocolate teapot in the winter period. Better posted on s renewable energy forum.

Too much twaddle about how good chinese diesel heaters are and kerosene purchases. Also some misunderstandings re solar panels? Natural gas is as cheap, or cheaper than oil at the present time, btw.

Sand or crushed glass?

Chemically they are the same so theoretically each kg of either would store the same heat for the same input.

However the problem may be that of heating enough of the substance to be effective. It is a poor conductor of heat and the coarser the particles I would expect the less conduction through the mass due to the intervening air, also a poor conductor.

Might a more effective approach be a solar water-heater that transfers its heat to the sand or glass via a matrix of tubes, rather like a boiler "inside out"? Or use storage-heater bricks?

Certainly no harm experimenting as you don't run into problems with dodgy fuels, fire safety, badly-made oil-heaters, etc.

My brother has installed a very effective solar-panel water heater on his home's flat roof, using two commercially-made panels plus one he built from an ordinary central-heating radiator painted matt black, inside a suitable glass-fronted enclosure. I can vouch for it having used the shower heated indirectly by the installation. (They also have an instant-heat shower for when there is not quite enough of Old Sol, in Southern Scotland.)

For my workshop (concrete-block single-skin walls with internal insulation, wriggly asbestos-cement roof with an insulated ceiling, crude "double-glazing", I use a small electric radiant heater when really necessary, but warm clothes and an hour of machining seems enough for bearable conditions.

Water has a far higher heat capacity than glass, by a factor of ~5 so just use a big tank of water. The only advantage of adding glass to the equation is it's heavier, so takes up less volume, but only by about factor 2.5 even for solid, less for crushed, so I think you'd be better of with just water. The potential advantage of electrical solar panel is you can get a higher temperature, so need less mass, like a storage heater.

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I think the ‘Strawbridge’ design used crushed glass for two reasons:

1. He was making a clever TV series, to get people inspired
2. The glass, being crushed bottles normally destined for re-processing was much coarser than your average sand

The design used a small fan to draw air through the ‘heat-reservoir’, thus making better use of the mass.

Surface area to volume ratio would be enormous compared with a pit full of sand … and therefore it should work [at least sufficiently well for demonstration purposes] in a greenhouse.

It’s all fairly well documented in the link I provided 22/09/2023 21:54:50 but I don’t think enough emphasis was ever put on the fact that the ‘packing density’ of the glass product is very significant.

MichaelG.

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This is worth a look:

https://gaskellswaste.co.uk/recycling/glass-reprocessor/#:~:text=Glass%20recycling%2C%20or%20glass%20reprocessing,quality%20to%20the%20end%20product.

Edited By Michael Gilligan on 25/09/2023 06:55:36

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Sorry … I expressed that rather badly

What’s important is that the useable surface area to volume ratio is enormous

Drawing air through the mass, using a small fan requires the porosity to be optimised.

[ The sand has the higher surface area, but would require much more energy to draw air through it. ]

MichaelG.

Edited By Michael Gilligan on 25/09/2023 08:10:07

Thank you for that explanation, Michael.

In which case I wonder if moderately fine gravel would work just as well and may be easier to obtain. Flint gravel is the same material as sand and glass - silica- but the type of stone might not matter very much.

Having seen the difference bringing a solar panel off the sun by even a few degrees makes, any figures as to output would need taking with a generous portion of salt  Since the OP has welding gear why not make a small wood burner ? The fuel will be free and if built to be almost air tight will be both economical and controlable. OR plan B make a larger one and only have to fuel it once every 24Hrs. All shut down mine was known to go 36Hrs on a fill. Pallet wood is free on most industrial estates ( and other places ) and a small circular saw will convert it into fuel. A walk in the country will keep you warm and a few bits of wood picked up will keep you warm when you get home ! Noel.

Edited By noel shelley on 25/09/2023 10:00:35

A sound engineering explanation for why heating and cooling systems often contain water!

Not the whole story though. Water being liquid adds an extra problem, which is the need for leak-proof containment. That bumps up the initial cost and adds a maintenance problem. In contrast glass doesn't require a well-made container, the system is low maintenance, and sand on the carpet is trivial compared with hot dirty water. However, for a little more dosh, cast-iron or fire-brick store more heat than glass, which might be important.

Solid heat storage systems create a new problem: how is the heat to be transferred to where it's needed? Hot water can be piped through radiators. Solid usually means fan-blown air, requiring trunking etc. Despite needing a fan, the system is much more reliable than gas central heating, which might be more important.

Which brings us to the cost of fuel : gas is cheap (at the moment), electricity expensive (at the moment). Coal is messy hard work and has to be delivered into a bunker. Oil is cleaner, fairly cheap (at the moment), and has to be pumped into a large storage tank. Wood is hard work, needs dry cover, and the cost depends on where you live.

My view is all heating systems have pros and cons, making it unwise to generalise. Engineers have to understand the full requirement and come up with a matching answer. Considering the full requirement often changes the answer, for example, Vehicle Diesel Heaters come with a long list of disadvantages making them inappropriate for heating homes. In the same way, the clean convenience of electricity often outweighs the advantage of cheap fuel, and costly but reliable local fuel is a better bet than unreliable cheap imports. There are many possibilities, and few shortcuts!

Dave

Phase change heat storage is the way to go though probably beyond the scope of home construction.

https://sunamp.com/plentigrade/

**LINK**

My response was in answer to Nigel's suggestion which used solar water heaters. If you're starting with electricity, I wouldn't mess with water

Not sure about the beyond scope comment, there are various companies experimenting with encapsulating waxes for mixing with plaster etc to construct rooms that ‘hang’ at a certain temperature. The idea is that during the day when the solar gain from windows is high the room temperature rises to the point where the encapsulated wax changes phase from solid to liquid. So the room absorbs energy but doesn’t get any hotter. In the evening when the outside temperature drops the reverse happens and the beads give out heat as they solidify and hold the room at a comfortable temperature. The result is less burden on the air con or the heating system and it’s totally passive to boot.

regards Martin

The disadvantage of water as a thermal store is that the maximum temperature must be less than 100C (unless the store is constructed like a steam boiler with all that entails). If it were a good choice, electrical storage heaters would use it. Instead, the material they use stores much more heat by exploiting a large temperature range, even though the specific heat capacity is less than water.

The Sunamp idea is good as a hot water store because water taken from storage is delivered at a constant temperature until the capacity is exhaused. The inverse, "wax coolers" using latent heat have been used for decades for rocket and missile electronics, since there is no air for cooling once out of the atmosphere.

Not straying too far off-topic, I hope

Does anyone have experience of these: **LINK** https://sahp.info

Solar Assisted Heat Pumps for domestic hot water

… I am tempted by the SAHP 130

MichaelG.