Dave
2022-06-27 09:55:33 UTC
Here one I would buy, if available in the market, and cost like GBP 10 -
a subsidised price for planet saving, just like I got 4 rolls of good
loft insulation for GBP 10.00 a few years ago.
Design is portable using the advection concept. i.e. you take it
outside in the sun, and move it about your garden until warm enough as
necessary. Then before the sun goes in you bring it inside where the
heat is needed.
Picture: a square about 0.5 along the horizontal sides, about 0.1m high,
weighing about 12kg,
4 main layers,
1- glass or acrylic top,
2- matt black aluminium sheet, on the back of this are parallel fins
about 25mm high. the full width or height.
3- the accumulator substance, e.g. wet sand, or even a phase change
material like sodium sulphate. This fills the void.
4- an insulation layer behind the accumulator
5- handle
No stand necessary, but possible, as is a flat top hinged mirror to
reflect a low sun a bit more.
The important thing is that there is wet/phase change substance against
matt black metal which gets hot. Also maximising the area.
In GB, with variable pricing on windy days, want a 200W heater with a
thermostat so you can accumulate heat when the electricity is at a low
price.
Sums for wet sand - why sand - with water need to pay a lot more to make
sure the thing doesn't leak. i.e. all in one mould or heat bonded joints.
Assume quite wet i.e. 2000 J/kg K. Assume density of 2000Kg/m^3 - a lot
depends on the mix
Volume is 0.45m x 0.45m x 0.025m = 0.00506 m^3
Mass is 0.005 x 2000 = 10kg
Assume spring at an imperfect angle with 500W/m^2 - convert kWh to J
multiply by 3600000
In 4 hours get to 0.5 x 0.45 x 0.45 x 4 x3600000 = 1.458 MJ: half a kwh,
value 10 cents, seems about right.
For 10kg of this sand this gets up to
temperature, gets to : temp = 1 458 000 / (2000 x 10) = 72.9 Celsius
i.e. nice and toasty.
Maintenance- keep the glass clean, and the sand moist. Mix in some
sodium sulphate (a phase change salt) for a boost? Don't want paraffin
wax due to flammable vapours.
With say 12m^2 covered, this is
Say 4m x 3m covered i.e 8x6 heater units needed i.e. 48 units giving 24kWh.
What's the snag? Laziness, not cleaning the glass, forgetting to fill a
new unit with sand and wet. (Obviously you want sand shipped more
locally.) Might need to fasten into a frame for stormy days. Initial
cost, hence subsidy needed.
24kWh is a sensible amount of energy for space heating.
a subsidised price for planet saving, just like I got 4 rolls of good
loft insulation for GBP 10.00 a few years ago.
Design is portable using the advection concept. i.e. you take it
outside in the sun, and move it about your garden until warm enough as
necessary. Then before the sun goes in you bring it inside where the
heat is needed.
Picture: a square about 0.5 along the horizontal sides, about 0.1m high,
weighing about 12kg,
4 main layers,
1- glass or acrylic top,
2- matt black aluminium sheet, on the back of this are parallel fins
about 25mm high. the full width or height.
3- the accumulator substance, e.g. wet sand, or even a phase change
material like sodium sulphate. This fills the void.
4- an insulation layer behind the accumulator
5- handle
No stand necessary, but possible, as is a flat top hinged mirror to
reflect a low sun a bit more.
The important thing is that there is wet/phase change substance against
matt black metal which gets hot. Also maximising the area.
In GB, with variable pricing on windy days, want a 200W heater with a
thermostat so you can accumulate heat when the electricity is at a low
price.
Sums for wet sand - why sand - with water need to pay a lot more to make
sure the thing doesn't leak. i.e. all in one mould or heat bonded joints.
Assume quite wet i.e. 2000 J/kg K. Assume density of 2000Kg/m^3 - a lot
depends on the mix
Volume is 0.45m x 0.45m x 0.025m = 0.00506 m^3
Mass is 0.005 x 2000 = 10kg
Assume spring at an imperfect angle with 500W/m^2 - convert kWh to J
multiply by 3600000
In 4 hours get to 0.5 x 0.45 x 0.45 x 4 x3600000 = 1.458 MJ: half a kwh,
value 10 cents, seems about right.
For 10kg of this sand this gets up to
temperature, gets to : temp = 1 458 000 / (2000 x 10) = 72.9 Celsius
i.e. nice and toasty.
Maintenance- keep the glass clean, and the sand moist. Mix in some
sodium sulphate (a phase change salt) for a boost? Don't want paraffin
wax due to flammable vapours.
With say 12m^2 covered, this is
Say 4m x 3m covered i.e 8x6 heater units needed i.e. 48 units giving 24kWh.
What's the snag? Laziness, not cleaning the glass, forgetting to fill a
new unit with sand and wet. (Obviously you want sand shipped more
locally.) Might need to fasten into a frame for stormy days. Initial
cost, hence subsidy needed.
24kWh is a sensible amount of energy for space heating.