Very high CIBSE Solar Gains

RE: Very high CIBSE Solar Gains

Duncan Brown — Fri, 19 Aug 2016 10:28:30 GMT

Gary - The software runs a 24 hour admittance calculation, rather than an instance solar gain calculation. Sun position, absorption and re-radiation are taken into account, along with immediate gains. I strongly recommend consulting the manual to examine the process we use, as it is laid out in some detail.

regards,
Duncan

RE: Very high CIBSE Solar Gains

Gary Jackson — Fri, 19 Aug 2016 10:15:03 GMT

Duncan, thanks for the help. I have managed to get the environment and shading coefficient data from Pilkington spectrum which also have a heavacomp values section to make life easier. using these values have reduced the solar gains to 7.6kW which is closer although still 1.4kW above the figures I got using CIBSE guides. Could this be because I am put the value for the g-factor for SHGC?

RE: Very high CIBSE Solar Gains

Duncan Brown — Fri, 19 Aug 2016 09:38:39 GMT

Gary - the first document I linked to you contained a link to the calculation methods. You can go directly to it here. Information on the method used for calculating solar gains can be found in the software manual, which is usually available by pushing F1 or clicking on the ? icons that are scattered through the software.

Regards,
Duncan

RE: Very high CIBSE Solar Gains

Gary Jackson — Fri, 19 Aug 2016 09:33:01 GMT

Duncan,

I will look into the shading coefficient. Reference the environmental figures, I used the default figures from Heavacomp as I do not have any manufacturers data covering these parameters. I had assumed that the CIBSER method used the Solar Gains data set published in the guides and simply multiplied them by the g-factor and area but it looks like this is not the case. is there anything in the wiki about calculating the environmental figures?

Gary

RE: Very high CIBSE Solar Gains

Duncan Brown — Fri, 19 Aug 2016 09:11:48 GMT

Gary - A couple of things stand out - the SHGC is unlikely to be the same as the Shading Coefficient - this (3rd party) document provides information on this. And my other concern is where did you get the Environmental figures from? These are paramount to the CIBSE Gain calculation.

Regards,
Duncan

RE: Very high CIBSE Solar Gains

Gary Jackson — Fri, 19 Aug 2016 08:56:49 GMT

Duncan, Thank you for the swift response. For reading the linked document, I believe I entered the correct data. I have attached the screenshot of the Glazing Data Page and the Manufacturer's datasheet I am using (I am using the top glazing product in the list). As you can see the calculated data is very close to the manufacturers data and I also enter the figures into the Glazing Properties Fields.

communities.bentley.com/.../Pilkington_5F00_energiKare_5F00_Triple_5F00_and_5F00_Pilkington_5F00_Insulight_5F00_Triple_5F00_Low_5F00_Window_5F00_U_2D00_values.pdf

RE: Very high CIBSE Solar Gains

Duncan Brown — Fri, 19 Aug 2016 08:38:18 GMT

Gary - It would appear that you have defined your glazing incorrectly. The steady state calculations (CIBSE Gains, Carrier Gains etc) use the information from the Glazing Properties box in the top right corner of the glazing program.

Please consult this document for more information. Note that all the information in the Glazing Properties section should be populated. Simply changing the U value is not sufficient. SHGC (Solar Heating Gain Coefficient) is analogous with the Carrier F Factor.

regards,
Duncan