Thermal mass - has anybody toyed with this

[RUFUS HOUND]

hi all,

 

Ive been having a smoke and pondering about the effects of thermal mass in a grow enclosure (as you do!)

 

wondering if anybody used thermal mass in their design set up, what did you use and did it help with your temps? 

 

I was thinking of covering the floor of my tent (its only a tiddler 60x60) in block pavers on a slab of insulation - theory being, this would absorb the heat when lights on and slowly release this stored heat at lights off. 

[NezA]

If you were to do this I'd highly recommend painting the slabs with an ultra black paint such as Black 3.0 it would maximise the heat absorption from your stone. No idea if the difference would be noticeable in a grow room but I've applied the same theory to the firebox of an offset smoker I built and I can confirm thermal mass makes a noticeable difference there but obviously the source of heat is much more intense and the time frames are much shorter.

 

But the theory is sound.

[Smokey90]

A small fuck knows what there called my mind has gone blank reptile??? Heater is it. Would help sorry just done 4 pipes of grade I'm meshed I just use a old oeccy blanket for my small tent  u nder carpet and just for a bit of heat 

[RUFUS HOUND]

@NezA good idea the black paint 

@Smokey90 I was thinking about that as well as the lights as I have a 20w heat mat

[Larry Badgeley]

@RUFUS HOUND

 

What I have done is put my heat mat on the floor, drip tray on top and I had 4 tiles left over from the bathroom floor. These sit on top of the tray. It keeps the roots lovely and warm as well as the tent. Doing this stops the heat mat cooking the roots and allowing the pots to not dry out too quickly. I also grow in a 60 x 60.

 

Here is the floor of the tent: You can see the tiles on the floor of the tent

 

[MindSoup]

It wasn't actually intentional, but now I have a big old bed full of soil In my tent I'm finding the temperature drop at lights off is a bit less dramatic. I think you're onto something with this idea. I'm thinking thick ceramic pots, painted black could be a good way to keep the heat directly around the roots. 

 

[Dodgee]

Sand + heated cable.

[BilgePump]

Water is great for holding heat when used as thermal ballast , if you can find a solid plastic tub the same footprint as yer space that's not too tall so as not to sacrifice headroom I'd black 3.0 that and fill it up with water 

 

Or sand and cables , that's a great idea.

 

[Mr mcgregor]

Black buckets of salty water .....

Edited March 31, 2022 by Mr mcgregor

[RUFUS HOUND]

The sand bed idea is not an idea Ive heard of but makes me curious, would a heat mat buried in it work? as on a hot day only the surface of the sand gets red hot, if you scrape away the top inch or two of sand, its cool underneath !

 

Water is a great as well but why the salt , does it improve heat retention, dissipation ???

 

[MindSoup]

I think it would take a fair while to warm it up, but once it was it would stay warm. I think you're supposed to keep it slightly damp iirf.  Its quite common to see in greenhouses you can buy specific sand bed heat cord from garden centres and such but I imagine a heat matt would work as long as its waterproof. 

Edited April 2, 2022 by MindSoup

[Dodgee]

Just now, RUFUS HOUND said:

on a hot day only the surface of the sand gets red hot, if you scrape away the top inch or two of sand, its cool underneath

Sand has a very high thermal capacity. Able to store large amounts of heat. 

But it has low thermal transfer capacity.  It's an insulator in a way. 

 

This is why the top later gets hot hot, and underneath remains cool.  

 

In the case of beach's it also the fact that only an inch or two beneath the surface the sand is wet, the water above has evaporated. 

 

If you feel the sand in a child's sand pit or even in the dunes it's warmer down to a greater depth than coastal deposits. 

 

When you use a heater cable buried in the sand the heat is able to disperse throughout the mass more efficiently because of the fact heat rises going in your favour of you follow... 

 

There are a few projects ongoing for grid level energy storage using sand as the storage medium. 

 

Atb

 

[ratdog]

On 31/03/2022 at 1:08 AM, NezA said:

I'd highly recommend painting the slabs with an ultra black paint such as Black 3.0 it would maximise the heat absorption from your stone.

 

 

i would agree with this using led's but if using hps it could cook the roots. i've had pots on big black trays, and they heated up to well over 30 degrees and the plants were not happy, slabs may not get to that temp, but it's worth keeping in mind

[BilgePump]

I know a couple of lads who grow in outbuildings that actually wrap soil warming cables around their pots , iirc they use 22L fab pots in easyfeeds sat on kingspan 

 

[RUFUS HOUND]

Perhaps if the thermal mass was isolated from the pots (insulation on top), this would heat the enclosure rather than heating the pots directly.

 

I going to give this a try over the weekend, the plants are small enough to move easily and I have all the bits - I do like an experiment.

 

Im off the bring the blocks inside, need to get them up to room temp before putting them into the tent.