Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 131

mode; 24% of the time the volume flow is between 6000 and 12000m 3 h − 1 and 27%
at 6000m 3 h − 1 . The rest of the cooling energy comes from free cooling operation.
Variable volume flow is thus extremely important for reducing the rather high electrical
energy consumption of the ventilators. The calculated COPs are 0.52 on average over
the whole operation period, with higher values of 0.65-0.73 in July and August and
decreasing values of 0.2-0.53 in April and October (Mei and Infield, 2002).
If the regeneration air flow is kept at a constant value of 9000m 3 h − 1 the solar
fraction to the total cooling demand is 84%. The monthly distribution of total cooling
energy, desiccant cooling contribution and auxiliary compression cooling as calculated
with the simulation system INSEL is shown in Figure 5.14.

Control Strategy

If the room air exceeds the setpoint temperature, a supply temperature cascade is
executed by the control system. Process and room exhaust air are set to 50% of the
maximum volume flow, that is to 6000m 3 h − 1 . The exhaust air humidifier is then
switched on together with the rotating heat exchanger. In the following, the supply air
humidifier is switched on with each of the three stages of the contact matrix evaporator.
Finally the sorption rotor is started and regeneration takes place. If the cooling load
can still not be met, the volume flows are gradually increased up to 12 000m 3 h − 1 .
The regeneration air volume flow is reduced from the maximum value of 9000 m 3 h − 1
until the air collector exit temperature reaches 70 ◦ C. The room exhaust air humidity
is limited to a maximum allowed value and the controller switches off the supply air
humidifier as soon as the maximum admissible humidity is reached.

10 000

cooling energy demand produced energy sorption system

9 000

8 000

7 000

auxiliary energy

6 000

5 000

4 000

3 000

2 000

1 000

0

123456789 0 1 2
Month

Figure 5.14 Monthly cooling energy demand of the public library rooms and the contributions of the
sorption system and the auxiliary cooling source