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[EnergyPlus_Support] Re: Btu Of Basement Concrete?

James V. Dirkes II

Thank you for helping me.  I thought  0.156 Btu / F would dramatically alter my view.  Though my original view of it was from the R factor and Btu/hour/degree F vantage for the Btu loss rate through concrete to around 55F geo thermal.  0.156 Btu / F sufficed to demonstrate to me that it takes a large magnitude of thermal energy to raise the concrete mass temperature by 1 degree F.  Which in my example of just computing the floor slab was 12.7 kW/h @ 1F change.  ~ In joules per second terms.  

I realize now why I was not thinking of specific heat.  My text book details the subject in calories / grams / Celsius instead of Btu.  So I was not making the association with the Btu. And now I have some thoughts in this regards about solar heated thermal mass and Trombe Walls to explore later on.

In calculating that it would take 12.7 kW to change my concrete slab floor temperature in my model basement 1 degree F.  Will help me to demonstrate to others.  That the concrete mass would always remain cold.  And act like a heat sponge.  Via the 2cd Law Or Thermodynamics.  Hence we would never place enough heat into a large uninsulated portion of a basement capable of changing the concrete mass temperature to notice it by touch.  So I see allot of potential for a heat removal scheme.  Yet since the concrete is also a part of the geo thermal mass of the earth that surrounds it.  The above Btu energy input of 12.7 kW (in watt terms) for the slab floor would never heat the mass by 1F.  Since some of that energy would go to the ground.  (At a rate of which the R factor demonstrates.)  And I believe most people would agree that attempting to calculate and illustrate the temperature changes in the geo thermal mass of the earth surrounding the basement concrete.  Would be meaningless to attempt.  So the mass will always be thermally cold mass.  And a constant (sustainable) source for renewable energy of the thermally cold kind.

~ The limiting factor still remains.  To occur when the temperature of the two volumes of air being exchanged through the heat recovery ventilator.  Reach the same temperature.  And so, the math for examining that.  Details looking at the two volumes of air in terms of 0.018 Btu per degree F per cubic foot of air.  And the heat ventilator fan speed in CFM compared to the cubic volume of air moved.  As well as the rated efficiency of the heat ventilator.  And whether or not we want to remove heat from the entire building or a single area such as the kitchen.  My concern is the heat gain of such things as refrigerators and freezers.  And so, the kitchen volume of air is smaller than the volume of air in the crawl space (concept) for a basement.  And hence, we can keep the kitchen cool because of the larger volume of cool air in the crawl space.  We are exchanging the heat to.  My model has a 6:1 volume of crawl space air volume to kitchen air volume.

Looking merely at the Btu/hour/degree F losses through the concrete to the geo thermal temperature of the earth.  I can see that we can easily remove a few kilo watts per hour of heat from the kitchen.  And reduce the heat gain load upon the central air conditioner.  We however could not rely upon this as a soul air conditioning system for an entire building.  Naturally we need allot more Btu's.  And we have the humidity of the interior air to remove.  To deal with the Latent Heat problem.  Hence the central air conditioner remains.  Yet we are using a low powered electrical energy means to move air, to have renewable geo thermal energy to remove the heat from the air.  To reduce the load upon the air conditioner.  And stop paying twice for the energy we use to power our refrigerator and freezers.  And I believe we can help keep the kitchen cooler when we are cooking.  

Well I suppose this remains to be seen.  If it can be modeled in software.




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