Discrepancies between result table and graph

Gary Jackson — Wed, 24 Aug 2016 13:37:33 GMT

Using CIBSE Heat Gain to show solar gains and fabric loss I have noticed that the graph does not match the results table for one of my rooms. Instead the results in the Graph of the are roughly double the values in the table.

Any ideas as to why this is?

Very high CIBSE Solar Gains

Gary Jackson — Fri, 19 Aug 2016 07:31:26 GMT

I modelled a simple 5mx5m glass box with no heat transfer across the floor or ceiling and I created a custom glass to replicate a Pilkington glass (U-Value of 0.6 and g-factor of 0.55). When I checked the solar gains using CIBSE Gains they were 10.8kW. However when I calculate the gains manually using the CIBSE guide I calculate the solar gains to be 6.2kW.

Furthermore the CIBSE Gain results on Heavacomp gives the average solar gain as 410W/m2 where as in the CIBSE guide, 410W/m2 is the solar gain for a southern aspect only (E&W are 189W/m2 and north is 117W/m2). Therefore this is leading to conclude that Heavacomp has not adjusted the solar gains for each wall aspect but rather used the max solar gains for all four walls. If I do the same in my hand calcs, I get a total solar gain of 11.3kW so pretty close.

Also I have noticed that the CIBSE Solar Gains are double the Carrier and ASHRAE Solar Gains.

Can you think of an explanation for the large discrepancy for the two values?

Gary

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Discrepancies between result table and graph

Very high CIBSE Solar Gains