Bricks as heat source

[Jimmy]

I was wondering, my GH gets quite warm in the day.
I was thinking of a pile of say 6 bricks on my bench and standing a seed tray/propagator on it.
Do you think it might protect against frost through the night.
Thanks
Jimmy

[nickdub]

anything with enough mass can act as a heat sink to warm up during the day etc - give or take the more mass something has, the more heat it can store and a litre of water has a mass of almost exactly one kilogram

Generally I'd say a large tank of water is easiest for most people as obviously it is also useful for a water source for your plants and if you want to move it for some reason like cleaning, its relatively easy to empty and move. (It gathers heat a bit better as well, due to convection)

[DannyK]

I wouldn't chance it. Failed physics A level 54 years ago so no idea on scientific workings.

I use 6pt milk containers full of water around base of greenhouse but also have heaters.

If you get direct sunlight painting whatever you use as a heat sink black will make a difference.

[Jungle Jane]

You could put a candle under a clay pot,then a larger clay pot over that as a mini heater under the seeds on top of the bricks if that’s possible with shelving,the bricks can take the candle pot warmth? Some candles last longer than others

[fishpond]

I use a 45 gall water butt.
Many advantages, 1 of which is warmish water for watering

[Nicos]

On a vidé geprenier (car boot sale) last week I saw a 1 ft x 6" Slab of clay and asked what it was.
"It was used in the past to hang in the fireplace to heat up and then used to heat the bed"
Good grief! I thought it was a door stop!
So... lateral thinking n'all that...maybe putting some stones/bricks on top of a radiator might heat them up enough to put in a greenhouse overnight????
But.....isn't' that the principle of Night storage heaters????

[Chestnut]

You could go all Victorian and build a hot bed in your greenhouse- if you can find a biggish supply of fresh manure
Theres a you tube video of Charles Dowding doing the same thing here;
https://m.youtube.com/watch?v=NhPh4sYCW5Q

[Jimmy]

OK thanks for the replies.
Once this big blow is over I will do an experiment.
I havd a logging thermometer with 2 sensors.
I will set up 2 trays and monitor for a few nights as a base line.
Then add bricks to one and monitor for some more nights.
Will post results.
Jimmy

[bikermike]

Any mass heats up when in the sun. The problem with the ground is that it is quite big, so heats up very slowly. It also cools down very slowly which is why soil is warmer in summer.

A pot on it's own is very small - heats up and cools down very quickly.

On the warm weekend, it was interesting that the air above waist height in my greenhouse was warm, but the air lower than that was really noticeably cold, so even in small spaces, you can get temperature gradients very easily.

If you put a bunch of bricks together they should act as a mass that heats up and cools down somewhere in between. I *think* you'd be best off with them raised off the ground at this time of year (and possibly better on the ground at the end of summer), but I would suggest checking this experimentally.

Heat transfer is either by convection or conduction (I will be vaguely worried if you get you get your bricks hot enough to make material amounts of infra-red radiation). Hence the *think* above. It may be that a layer of air underneath simply convects (ie rises up when hot and is replace by cold air) all the heat away.

Ideally, you probably want your bricks to be surrounded by a layer of air-trapping insulation, but with all sides that get sunlight to be exposed during the period of solar gain. possibly a blow-away or a propagator top over the top of bricks and plants overnight if you put the whole thing in the greenhouse.

Painting your bricks non-gloss black will help too.

You may be better of spending the time making all necessary bribes to gain control of the windowsills instead...

[bikermike]

my father's phd was in "heat transfer in buildings", so I can supply a lot of algebra on the above if you really want... (not that I will understand it, mind...)

[Aberdeenplotter]

On a vidé geprenier (car boot sale) last week I saw a 1 ft x 6" Slab of clay and asked what it was.
"It was used in the past to hang in the fireplace to heat up and then used to heat the bed"
Good grief! I thought it was a door stop!
So... lateral thinking n'all that...maybe putting some stones/bricks on top of a radiator might heat them up enough to put in a greenhouse overnight????
But.....isn't' that the principle of Night storage heaters????

As a youngster we heated fire bricks in the oven and wrapped them in towels and then used them as bed warmers. They stayed warm all night too. Also when we suffered from mumps, my dad made small pillows filled with salt and these were also heated in the oven. Also needed a towel as the salt got really hot but the salt was easier to mould to the shape of a small swollen face than a fire brick

[MarkPelican]

OK thanks for the replies.
Once this big blow is over I will do an experiment.
I havd a logging thermometer with 2 sensors.
I will set up 2 trays and monitor for a few nights as a base line.
Then add bricks to one and monitor for some more nights.
Will post results.
Jimmy

A couple of years ago, I set up a temperature measuring system with a sensor in a waterbutt full of water, one above it, one at the other end of the polytunnel and one outside.

The result was "don't think it made a difference". The waterbutt got warmer and colder (by a few degrees), the two temperatures in the polytunnel were the same as each other (more or less) and the outside temperature was (in general) colder at night than the temperature in the polytunnel (but not by much).

The problem days/nights were when there wasn't much sun. The waterbutt didn't have enough solar gain to output anything overnight so I concluded that I wouldn't bother again.

[Jimmy]

The temperature graphs for two identical seed trays, i.e. no bricks was identical through the night.
With one seed tray on 6 bricks through the night the brick one was 0.5 to 1.0 deg C warmer.
So not much of a gain really.
Jimmy

[bikermike]

1C could be a big difference round 0C I would think