Check the rain flags in the weather data. Energyplus intentionally sets the exterior heat transfer coefficient to 1000 W/m2-K whenever it is raining (and then uses the ambient wetbulb instead of drybulb in the delta T). The idea is if the surface is wet from rain its temperature will be close to the surrounding wetbulb temperature. If that is not acceptable, then you can modify the weather data so the rain flag is always set to no rain.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Monday, September 1, 2014 1:07 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] External convection coefficient [3 Attachments]
Dear all,
During a research to understand the heat balance in the roof of a computer simulation model using EnergyPlus, some incoherent results were found.
After several simulations where parameters of the model were changed, it was noticed that the incoherent results are due probably to some error in the weather data file adopted. We noticed that the problem may be caused by the weather file as the errors do not occur when we simulate the same model with another weather file.
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The errors found are related to the convection heat gain. Initially, a convection heat gain peak was observed on the outside surface of the roof (Figure 01 - attached). However, this peak are not observed by taking into account another weather file from the same city (Figure 02 - attached).
Then, it was noticed that during the heat convection peaks, the external convection coefficient reached unacceptable values: up to 1000 W/m²K (Table 1 - attached). However, looking into the weather file parameters it was not possible to understand what was causing such incoherent results.
I attached both weather files and figures/table.
Could you please help us to understand this problem?
Thanks for all.
Regards,
Ana Paula Melo.
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Posted by: "Brent Griffith" <Brent.Griffith@xxxxxxxxxxxxxxxxxx>
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