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

[Bjoern Nienborg]

Hello together,

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.

Problem No. 1 is that I use a hysteresis controller which has my 
building cooled from 26°C to 24°C. If I calculate the cooling load for 
26°C I may get values greater 1 for the solar fraction since the 
building is cooled down to 24°C. If  I take 24°C for calculating the 
cooling load I make it bigger than it acutally is. Does anyone have an 
idea how to solve this problem?

Problem No. 2: I have a 3-zone building. One zone is cooled by a chilled 
ceiling, the remaining two by providing the active layer in the floor 
(floor heating) with cold water. Even in july/august, when all 3 rooms 
are above set-temperature a great part of the time, I get solar 
fractions of min. 43% (for 24°C-cooling load) and min. 62% (for 26°C 
cooling load). To me this seems too much. Is it possible that I mustn't 
compare cold from active layers directly to the cold load  (Qcool-demand 
output of the building)??

I use the operative temperature for controlling my system. To obtain the 
cooling load I calculate the required set temperature input for every 
zone from the mean surface temperature in a seperate equation.

I hope i explained myself. Thanks for any help!

Björn

-- 
Björn Nienborg
Thermal Systems and Buildings
Fraunhofer Institut für Solare Energiesysteme ISE
Heidenhofstr. 2, 79110 Freiburg, Germany
Tel.: +49 (0)761 4588-5303 FAX: +49 (0)761 4588-9333
http://www.ise.fraunhofer.de