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Thu, 12 Dec 2019 00:39:00 GMT

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Fresh Air To The Back of FCU's - Which Fresh Air Load Option Is Best?

Simon Radcliffe — Thu, 12 Dec 2019 11:34:56 GMT

I am working on an office fitout project trying to establish the cooling loads using CIBSE Gain. The space is cooled by FCU's and we have primary fresh air delivered into the space at 18deg C close to the back of the FCU in the ceiling void. The ceiling void is being used as a return plenum. I have selected the 'conditioned primary fresh air' option and specified the temperature at 18deg C. Is this the best option to use for this scenario? In the manual this option appears to be the best suited rather than the other three options. Has anyone else experienced this?

Fresh Air Having Large Effect on CIBSE Gain Results

Simon Radcliffe — Thu, 12 Dec 2019 15:54:42 GMT

Hi, I am carrying out cooling calculations for an open plan office with FCU's. When using CIBSE Gain to calculate the room cooling loads I am selecting 'conditioned primary fresh air' as I have air at 18deg C from a central AHU with no humidification.

When I compare the results for one of the internal zones to my manual calculations the loads are significantly lower.

I have checked the model and all input parameters are as expected, the CIBSE Gain result is just lower than expected.

I would like to know how HevaComp treats fresh air introduced with this option.

The CIBSE Gain results for the perimeter zones with solar gain are close to the manual calcs

Any assistance would be much appreciated.