IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, Date: November 2010
5 Experiences / Lessons Learned
The average electrical COP 2010 of about 3.4 is still too low and should be improved. Main
focus should be the part load conditions.
• Main components focus: recooling pump, cooling tower
• Control strategy
o Lower flow rate (constant or variable) for driving pump
o Including the actual load to speed control of main components
• Reactivation of free cooling mode with better control strategy
6 Conclusions
Analysis of the operation stability of the system shows reliable running conditions over the
whole summer with only a few days where the absorption chiller did not work due to
electrical problems.
The daily operation performance indicates that the radiant ceiling is dimensioned to small for
the system or vice versa. If the radiant ceiling is under-dimensioned for the cooling plant, as
it is the case at the Solid plant, the whole cooling system is running in part load.
Matching the temperatures between two systems is important. The solar cooling system was
designed for running on a 9°C/17°C nominal flow/ret urn temperature, but the cold
distribution (radiant ceiling) requires only 16°C/1 9°C. Consequently this leads to high mixing
losses in the radiant ceiling inlet temperature regulating valve. This affects mainly the
absorption chiller, because it leads to lower thermal COPs but also to higher system losses
and therefore to lower electrical COPs.
The free cooling mode (2009) delivers one third of the total cooling load to the building. The
electrical COPs of the free cooling mode are not satisfying. Due to the low heat storage
capability of the building the cooling effect is very limited. Maybe there are other reasons that
make a further running on the free cooling mode feasible. If the free cooling mode is
continued a new time control has to be implemented in the control strategy in order to run
the mode only in times when the office is occupied. Free cooling of an empty office with low
heat storage capability just raises electricity costs.
Measurement results show that the heat rejection system including the cooling tower and the
recooling pump plays a key role in reducing the electrical consumption of the plant.
Replacing the existing cooling tower to a smaller and more efficient one could be one
solution. With a more efficient cooling tower and more efficient pumps the electrical COP
could easily be doubled. Therefore a pure wet cooling tower is preferable.
Expected improvements of these suggestions are higher thermal and electrical COPs as well
as improved conditions in the office. In order to simulate other changes of the system in the
course of the Solar Cool Monitoring Project simulations will be carried out.
SOLID: “…Sophisticated solar cooling systems need 1 to 3 years of surveillance and
optimization after start-up. This ensures optimal operation according to the customer’s needs
high efficiency and long life time of the system…”
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