[TRNSYS-users] solar fraction of solar chilled ceiling system

[Jeff Thornton]

> for my simulation of a solar cooled building I want to determine the
> solar fraction. The system works without backup (so, if solar power is
> to low, room temperature rises above set temperature). This I  calculate
> the cooling load in a separate simulation, then I divide the produced
> cooling power (which I suppose is entirely transmitted to the building)
> by the cooling load. So far so well.

By definition, your solar fraction is identically one.  There is no system
providing back-up - you said the temperature of the building rises - so
therefore all cooling that is done is done by solar.  You can't just
calculate the building cooling load in another simulation without the
solar and then divide the cooling load met in one system by the cooling
load met in another simulation - with differing temperatures the loads
will not be the same - they may be close but they will not be the same. 
Why don't you add a secondary cooling system to meet the loads during peak
periods and then calculate the solar fraction as 1 - (load met by
auxiliary / total load met).

As to your second question, instantaneous solar fractions are worthless
and shoudn't be used in systems that have any sort of capacitance.  They
can range from -Infinity to Infinity.  Only integrated solar fractions are
worth calculating and reporting.

Jeff

Jeff Thornton
President - TESS, LLC

2916 Marketplace Drive - Suite 104
Madison WI 53719 USA

Phone: 608-274-2577
Fax: 608-278-1475
E-mail: thornton at tess-inc.com
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