In this episode of throwback Friday, we?ll revisit the subject of water vapor?s damping effect on radiant temperatures!

To my knowledge, only IES, the CSE as described by Chip, and possibly ESP-r model this effect within the zone model. E+ version 9 certainly doesn?t.

I recently revisited some IES simulations with the Riyad weather file with and without the effect enabled. It had up to 1.5 Celsius effect on MRT for a large space with direct adiabatic spray cooling in the AHU.

Comfort was still pretty bad (that?s why the contractor went for chillers and fan coils instead ?). However, it might not be such an insignificant effect that it can be ignored especially in locations such as atria and warehousing.

Also, interestingly, this is essentially a greenhouse effect ? water vapor being a greenhouse gas.

For those wishing to know more, the write-up in IES apache methods succinctly describes the effect. https://help.iesve.com/ve2021/long_wave_radiation_heat_transfer.htm

Chris