Pros & cons of a large heat bank

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Pros & cons of a large heat bank

Postby Chaff_Cutter » Tue Sep 23, 2014 10:36 pm

Hi,
I was wondering if I could pick the minds of anyone that reads this post and ask for constructive criticism.

I’m thinking of a heat bank and how I can utilise it to the fullest.

A large tank, underground and insulated, about the size of a 20’ – 40’ sea container, filled with large clean gravel (maybe railway ballast) and the voids between the gravel filled with water. You may be thinking that ‘earthworks are expensive’, let’s discount that because I am the proud owner of an excavator.

I’m thinking that the preferred insulation would be 3 or 4 inch Styrofoam placed between the earth and the ‘bessa’ brick walls. No real need for insulation on the floor because heat rises and I can’t imagine that Styrofoam would cope with the weight. The lid could be Styrofoam again along with some sheets of compressed cement sheet, a layer of plastic then about 2 or 3 feet of earth.

Anyway, connect a SHW system (maybe closed loop with heat exchanger), and a low wattage pump, so that hot water enters at the top at one end, heating the rocks on the way thru to the cooler lower (other) end of the bank. This would allow the bank to heat from the top down until the whole thing is at a temperature of around the low to mid (and maybe high) 50’s. Any more than that and I think the longevity of the
waterproofing membranes, insulation, (etc.) would decrease.

The idea is that I want to create the heat bank so I can draw off that heat to supplement the heating needs of anything I can think of. With this potential setup being used in Tassie, I’m thinking that they’ll be more than a few heating needs. There are a few things I’m thinking of that could use this heat…in-slab heating for a residence, underground heating of a greenhouse (roots like to be warm), anything else that fellow forumites could suggest would be seriously considered.

I am also thinking that is could be reversed, or a duplicate made, for the summer months. So that it’s a heat bank in winter and a cool bank in summer, or just reverse the setup so that the bank can be cooled for use thru the summer months.

So, fire away, throw some thoughts and ideas around and I’ll see if I can make this happen.

Cheers,
Scotty
If it all gets too hard, just remember we are talking monkeys floating through the universe on a spaceship called Earth!
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Re: Pros & cons of a large heat bank

Postby Gordon-Loomberah » Tue Sep 23, 2014 11:09 pm

Forget the rocks! Water has twice the specific heat capacity of most rock, it's the best substance to use for storing heat.
More insulation is better, work out how much you think you'll need, then add some more. It will bleed a lot of heat into the ground, especially when wet, if you don't have good insulation, so I'd suggest using something like Hebel AAC blocks underneath, and maybe sides and top in addition to the polystyrene foam
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Re: Pros & cons of a large heat bank

Postby Cherokee Solar » Wed Oct 01, 2014 9:18 am

Hi Chaff Cutter,

The system will lose most of its energy to the ground in short order. Mind you, being in Tassie will produce a good cooling result with such a system over summer. Tassie has a few caves, which may be worth checking out if you are seriously going to chuck money at this idea. ;) The ones in the middle and to the south of the island both have temperatures around the average ground temperature which happens to be about 9'C to 12'C.

As you head further north on the mainland, the caves get progressively warmer until by the time you are in the top end just south of Darwin, they're in the high 20'C to low 30'C.

Oh yeah, the soil pressure and ground water pressure exerted on the sides of the sunken tanks would be massive.

It is simply not a cost effective idea. Why not build a house that has a ton of insulation in it in the first place and while you're at it put the place on stumps so that any heat in the house doesn't leach into the ground. Slabs in the south of the continent lose internal heat to the ground at a huge rate.
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Re: Pros & cons of a large heat bank

Postby Chaff_Cutter » Fri Oct 03, 2014 11:04 pm

Hi,

I love working in the remote pilbara, even with all the comms problems... :oops: grrrr
No matter.

Anyway, it seems that so far the idea of storing heat produced through the summer for use in winter is a good one, just that the practicality of it is a non event.

Maybe I should just forget the 'tank' and just use solar heated water to warm the house slab directly.
Even with the insulation to prevent heat loss, a warm floor is something I have experienced first hand.
It's great to not only have a warm house but a warm floor as well.
Seeing as heat rises, I figured it'd be better to heat from the floor up.

I've done some extra reading of the experience of others and it seems the tank idea is dead and buried!

Thanks for the input :D

Scotty
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