[TRNSYS-users] TRNBuild Internal Gains

David BRADLEY d.bradley at tess-inc.com
Fri Mar 14 07:29:43 PDT 2014

   Make sure that the gains are specified in kJ/h and that there is not 
any kind of multiplication or addition factor on them if you are 
entering them as inputs (instead of as constant or scheduled values).

   There are a few more things to check as well. First, make sure that 
you have a reasonable value of the thermal capacitance of the zone. By 
default, TRNBuild sets the capacitance to the thermal capacitance of the 
air in the zone. In reality, the capacitance ought to be about 5 times 
the default value. This will cause your zone to heat up and cool down 
more slowly. Second, make sure that you have not neglected infiltration 
in your model; outside air always enters a building no matter how well 
it is sealed. The infiltration rate should probably be somewhere between 
0.3 and 0.7 airchanges per hour. In residences, the infiltration rate 
can be quite a lot higher.

   As a check, you can pretty easily compute what the temperature gain 
of the volume of air in your zone would be since you know what the total 
equipment and lighting gains are and you know the volume of air.
Kind regards,

On 3/12/2014 12:11, em09008 wrote:
> Good afternoon,
> I'm having a problem defining the internal gains of a residential 
> house, because as soon as I add them the temperature in each zone 
> increases about 10ºC, which is in my opinion too much...
> I believe I have not used exaggerated schedules or equipment power, so 
> I really don't know what could be wrong.
> Does anyone know what could possibly be the problem here?
> Thank you very much for all your attention.
> Best regards,
> João Mata
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Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

d.bradley at tess-inc.com


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