[EnergyPlus_Support] Skylight / Radiant Cooling Strange Behavior

["Ian Doebber" <ian.doebber@xxxxxxxx>]

I'm modeling a single retail space with 100 sky lights and a radiant cooled slab.  I modeled the skylights as prismatic glass (Diffusing=Yes) with SHGC~.40.  

 

When I modeled the space using purchased air to validate the loads etc, the sky light transmitted solar was ~10% less than the total sky light heat gain which makes sense.

 

Yet, when I model the space using radiant cooling, the sky light transmitted solar remains the same as expected but the total sky light heat gain is 10x what it should be which is impossible.  For example, at peak summer noon, with 1000 W/m2 of incident solar radiant, 360 W/m2 is transmitted which is correct but the total heat gain is 3400 W/m2 which doesn't make any sense.

I've side stepped the problem by having only 10 sky lights so the gain is roughly correct but this adds too much convective heat gain to the space increasing my internal temperature with minimal solar radiation component reducing the effectiveness of the radiant floor, the very reason I'm doing the analysis.

I've tried many combinations of changing the diffusing option to No, changing the reflectance calculation under the Building heading, changing the internal emmissivity of the glazing all to no avail.  I would imagine there is something quirky with the radiative heat exchange between the skylights and the floor that is throwing everything off.

Any assistance would be greatly appreciated.

 

Thanks

Ian

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