IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, Date: November 2010
Storage management
As shown in Figure 2 the entire system has three 1500 liter hot water storages. To use this
volume for storing the solar energy effectively, it is important to have a straight forward
storage control strategy as it can be seen in Figure 4.
Depending on the temperature T5 the storages 1 to 3 can be charged from the solar
collectors. This is especially useful in winter time and transition periods where solar energy
should be stored as much as possible. In summer time, when the solar cooling plant is in
operation, only the hottest storage (storage 3) is in use. The main reason for not using the
entire storage size is the driving temperature of the absorption chiller. Following the
manufacturing information of the chiller, a constant driving temperature of 75°C to 80°C is
recommended. Nevertheless the machine is running down to 65°C driving temperature, but
with poor thermal COPs. To reach those heating temperatures for the chiller it would take too
long for the solar plant to charge all three storages. A time offset of cooling demand and
cooling distribution would occur. Using only storage 3 brings down the required temperature
difference done by the solar panels and raises the volume flow through the collectors. This
reduces the time in the morning until the chiller can be started.
4 Monitoring Equipment
4.1 Installed Equipment
Figure 5 shows the symbolic scheme of the system indicating all monitored energy fluxes.
The heat flow from the district heating Q2 is partly used direct and partly heating the hot
water storage. This fraction cannot be calculated and therefore Q2 is handled as input to the
storage. The heat back up is used for space heating, domestic hot water as well as an
unmeant heat back up for the chiller. The heat source from the local district heat is
additionally monitored from the district heat supplier. The small hydraulic switch linked to the
central distribution station is not taken into account. Cold losses due to the switch are
expected quite low.
Figure 5: Monitoring scheme of the plant including electricity and heat measurement points
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