Does anybody know the best validated method for dynamically calculating the CHTC for a concrete ceiling inside a building? I know that great variations are reported (below are two good sources), but just wondered if anybody has a source that gives the best results for a naturally-induced scenario.
1- Review of external convective heat transfer coefficient models in building energy simulation programs: Implementation and uncertainty
2- Variability and impact of internal surfaces convective heat transfer coefficients in the thermal evaluation of office buildings
If you are doing experiments, you could use Thin Film Heat Flux Sensors at various locations to monitor variation in CHTC both in space and time. If you want this information in simulations, local temperature gradient at the roof surface will help you in calculating local CHTC.
Thanks Sreenvas
We are not seeking to deploy any equipment, we have some simulation results (in EnergyPlus) and we wish to compare that with a manually calculated set of results. I have the concrete ceiling surface temperature and the air temperature close to it. I am ultimately interested in convective heat transfer, and the only missing parameter in the formula (q = hc A dT) is CHTC for concrete. Any respected source for dynamic or static figures for CHTC of concrete?
CHTC, h = -Ka (TS-T1)/(ZS-Z1) ( 1 / (Tm-TS) )
Where, TS and T1 are temperatures of concrete surface and first point in air in a given location respectively ; (ZS-Z1) is grid spacing near the concrete surface; Ka is the thermal conductivity of the air; Tm is the reference/mean temperature of the room, based on which you wish to define your CHTC, h.
Did you try with the estimation of convective heat transfer based on Raleigh number for free convection as it is described in literature like "fundamentals of heat Transfer". It will cause some time to model but my experience with These empirical Solutions was always very good. And very important, if you have heat exchange between surfaces do not forget the radiation. In systems with free convection and radiation the heat transfer via radiation usually is higher than the transfer via convection.
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