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Old 10-31-11, 08:57 PM   #1
AlanE
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Default Radiant tubes under newly constructed root cellar

I'm desiring a root cellar for a new construction home and, at this stage of the planning process, I'm interested in doing some brainstorming before any concrete is poured and before the house plans are finalized.

Here are my concerns and possible trade-offs:

1.) The house will incorporate seasonal heat storage under the basement slab.
2.) Hot water will use solar thermal system.
3.) Home heating from radiant heating system embedded in floor.
4.) GSHP in conjunction with vertical, closed-loop wells.
5.) I'm open to the idea of adding homemade solar thermal charging plates near the well-field so as to add additional heat capacity to the field as the field will be used to primarily extract heat and send it to the home, that is, the house won't be sending waste heat back into the field during the summer.

Now for the root cellar.

The vision at this point is to have the root cellar outside of the basement envelope, built of concrete and with a series of barrel vaults on the roof, with a door way, or even a small tunnel, leading into the basement, and then burying and surrounding the root cellar with earth.

Here's a graphic of the layout at this stage:


The plan is to run the radiant tubing underneath the freezer section to collect all of the cold migrating into the foundation and ground, and pipe the coldness to the adjacent sections - more tubing in the two cellars adjoining the freezer (because they are to be kept at a temperature just above freezing) and then the tubing continues into cellars #3 and #4 so as to lower the temperature in those rooms below the ambient below-ground temperature but not so low as cellars #1 and #2 and then finally the tubes run into the larger common room in front, cellar #5, to aid in keeping the temperature at a little below ambient.

The heat generated by the freezer unit would be piped out of the cellar and dumped into the home's hot water heating system.

My concern in how to marry the idea of seasonal heat storage in the below basement ground while mitigating the flow of cold/heat between the house and the cellar. My idea, at this point, is to have the cellar placed a few feet beyond the basement wall and construct a small passage way between the basement and the cellar. With the exterior of the cellar insulated and dry earth filling the space between the basement wall and the cellar wall I'm hoping it's possible to have two dissimilar temperature building envelopes being in such close proximity.

Of course the easy solution is to place the cellar far away from the home but if we do this then we lose the convenience of having this cellar within the home and we have to trudge outside to get anything from the cellar and this decreases the convenience.

Any feedback would be appreciated. I've searched the intertubes and I haven't really come across any reference to such a cellar design. There is discussion about running glycol underneath freezer units/buildings in order to prevent frost heaving but no one has written about taking that migrating cold temperature and distributing it over a larger area in order to make refrigerated compartments with cooling done passively.

I've read the radiant heating thread and the DIY heat pump thread and I was impressed by the referencing of engineering details in those threads and was hoping that perhaps some of you had come across work that deals with the cooling/freezing side of things. Condensation isn't a problem in this case because I'm aiming for high humidity in most every small room in that cellar. Cellars #1 and #2 will he having dirt floors in order to aid in the boosting of the humidity levels. The roof will be a barrel vault in order to prevent condensation from forming on angular objects and dripping down onto the food.

I'm hoping to make this a DIY project - the construction of the concrete structure will pose the least problems for me in terms of experience and knowledge. The environmental controls and radiant systems are new territory for me, so I'm reaching out to the collective knowledge base here for ideas and feedback.

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Old 11-01-11, 12:38 AM   #2
Ryland
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If I was building something like this I would keep the freezer out of the root celler because the freezer is a source of heat, sure you can collect that heat and shuffle it around but the best option is just to put it closer to where you want the heat and where you want to use the freezer.
As for partition walls, is there an issue with using pressure treated wood with foam insulation? mineral wool insulation is ok below grade as well, not everyone is ok with the chemicals but once the walls are sealed up it shouldn't be an issue and pressure treated wood is still sometimes used to make wood foundations on houses, not my first choice but it works.
As for the cooling of the root ceiler rooms, it sounds like you have some complex ideas and I have to wonder if just using a window A/C unit might be the best rout to go, having it pump heat in to the warmer side of the basement, with a good thermostat you more or less end up with a walk in cooler built in to the house.
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Old 11-01-11, 02:46 AM   #3
AlanE
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I'm under the impression that putting a walk-in freezer where it is surrounded by a heated building envelope (the freezing temperature will migrate into the surrounding home + the warmer living environment will increase the costs of maintaining the freezer temperature) is less efficient than what I'm proposing, that's why I'm interested in isolating the cold food storage area away from the warm living area.

Secondly, I want to work with passive physical processes as much as possible - circulating glycol (needed to prevent the ground under the freezer from freezing solid) dissipates the cold temperature over a larger area - moving very cold glycol from underneath the freezer (20 sf footprint) across a larger area (200-250 sf) and cooling that area to below the ambient underground temperature. An air conditioner with a Coolbot controller involves more energy input and more machinery than a simple pump to circulate the glycol. This approach now requires a process of cooling the root cellar with an air conditioner, dissipating the heat and now there is the added problem of having the freezer sitting smack dab in the middle of the living environment and dealing with the waste heat generated by the freezing machinery.

Walk-in freezers with underfloor systems have to dump that coldness somewhere, I just want to use it by diluting it and chilling a larger area for free.

The heat generated by the freezer's machinery can be isolated from the root cellar by walling off the above-freezer machinery and piping the heat out.

Or so I think. I'm not really up to speed on my laws of thermodynamics - it may very well be that shedding the heat from the freezer unit (a couple of sq ft footprint isolated behind a well insulated box above the freezer) in a room temperature (root cellar) of 34 -55 F is less energy efficient than dealing with a freezer operating at 5 - 10 F sitting smack dab in the middle of a heated 70 F kitchen. What we absolutely want to avoid is having any cold spots from that freezer in the kitchen because we will spend a lot of time in that room and this implies that the insulation on the freezer has to be pretty impressive to isolate a 10 F environment sitting in the middle of a 70 F environment. Secondly, I'd like to minimize the cooling cycles on the unit in order to increase longevity.
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Old 11-01-11, 08:45 AM   #4
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Nearly every chest freezer that I've looked at, and I assume that is what you are talking about using for a freezer, has the coils right under the outside skin of the freezer, so the outside of it is warm, I have mine sitting in the corner of my living room right now and it helps keep the living room warm because of the slight heat it gives off, same reason the kitchen is always 2 degrees warmer then the rest of the house from the fridge running and I've put the kill-a-watt meter on both appliances and they are both pretty efficient.

To thermally isolate the root ceiler from the rest of the house you just want a good R-value in the wall that is separating the two, insulation is going to work better then dirt or cement, if you are worried about cold creeping from one slab to the other slab then insulate it, insulate it just like you would under the slab and outside of your poured concrete walls.
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Old 11-01-11, 01:01 PM   #5
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Quote:
Originally Posted by AlanE View Post
I'm open to the idea of adding homemade solar thermal charging plates near the well-field so as to add additional heat capacity to the field as the field will be used to primarily extract heat and send it to the home, that is, the house won't be sending waste heat back into the field during the summer.
Curious what you mean by "charging plates"?

Also, why have you decided to not send the house's waste heat back to the field during the summer?

-AC_Hacker
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Old 11-01-11, 02:58 PM   #6
AlanE
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Quote:
Originally Posted by Ryland View Post
Nearly every chest freezer that I've looked at, and I assume that is what you are talking about using for a freezer
My mistake, I meant to specify that I was talking about a walk-in freezer of 5' x 4' x 6' dimensions. I looked back at my OP and noticed that I didn't specify that.


Quote:
Originally Posted by AC_Hacker View Post
Curious what you mean by "charging plates"?

Also, why have you decided to not send the house's waste heat back to the field during the summer?

-AC_Hacker
By charging plates I meant the solar collector surface.

I live in a climate where we might have call for air conditioning of the home only 5-10 days per year, so over the course of a year, there would not be a balance between extracting heat from the GSHP vertical field during the winter and replenishing that heat during the summer.

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