Dear Jean,
This is my “practical vs. theoretical” side:
How much impact do you suppose 3W / m2 will have on overall results? for the limited number of days when it’s really cold or warm in the garage?
Every now and then, I find myself doing something in EnergyPlus or other endeavors, “just because I can”. In other words, I’m proud of my capability and enjoy demonstrating it to myself (because none of my friends have a clue about it J)
On more rare moments, I ask myself if it really benefits my client or the world in general by getting that extra imagined accuracy. There are so many variables that we estimate or make assumptions about in a typical energy model, and so many more that will get built differently than the “perfect” scenario shown on the plans, that the overall accuracy is ….. not very good.
That said, you clearly and regularly demonstrate on this forum a desire to provide outstanding simulations to your clients, and the world needs more of that! Just try to maintain a reasonable balance between accuracy and making enough money to keep food on the table.
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jean marais
Sent: Wednesday, December 14, 2011 5:39 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Easy question - Very thick massive external floor
Just a follow up post. I have made some (simplified) sums. Turns out the conductivity of this very thick slab is (obviously) dependant on the Temperature at my radiant floor internal source (32 deg C) and the outside external floor surface area (ceiling of underground parking open to outdoor air, somewhere between -12 and 18 deg C).
At the -12 deg C scenario, results in steady state conduction of about 9 W/m2.
At the more likely 18 deg C scenario, results in steady state conduction of about 3 W/m².
My conclusion is that heat transfer is not adiabatic enough to use this solution (applicable better when the dT is almost zero).
I'm running a simulation ATM (with the conversion errors) and reporting the inside temp after the main insulation layers to see if a pattern for the Temp here emmerges that i can use for the otherside coeff solution path.
Will report back when I find some time.
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