Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 133

setpoint is exceeded, a supply air temperature cascade takes place. First the supply air
humidifier is switched on, then the exhaust air humidifier together with the rotating
heat exchanger and finally the sorption wheel. The minimum supply air tempera-
ture is limited to 17 ◦ C. The regeneration air stream is preheated by waste heat from
the factory machines. A flap to the air collectors opens if the temperature difference
between the absorber and entry temperature exceeds 6 K with a maximum volume
flow through the 100m 2 collector field of 6000m 3 h − 1 . The total regeneration air flow
can be heated by an additional auxiliary heater with a maximum allowed regeneration
temperature of 72 ◦ C, as a cellulose rotor with LiCl solution is used. Again the room
exhaust humidity is limited, here to a maximum value of 11.7 g kg − 1 .

5.2.3 Monitoring Results in Matar o

The monitoring results obtained during the commissioning period in 2002 confirm the
correct functioning of the whole desiccant cooling unit: during full desiccant cooling
operation the cooling power reaches 55 kW (enthalpy difference between room air and
exterior air) or 35 kWwhen referred to the enthalpy difference between room exhaust
and exterior air. When the machine starts up for afternoon operation, the heating power
is initially very high as the solar collector field is at standstill temperature. The COP
is correspondingly low and then stabilizes around 0.6 (see Figure 5.16). The main
factor limiting the COP is the rather low heat recovery efficiency of the rotating heat
exchanger. On average the measured heat recovery efficiency is 68% for volume flow
rates of 12 000m 3 h − 1 . Both fresh and exhaust air humidifiers worked satisfactorily at
85% humidification efficiency.
The 12 000m 3 h − 1 of fresh supply air volume flow is cooled down from31 ◦ Coutside
air temperature to 17 ◦ C supply air at regeneration temperatures of about 70 ◦ C (see
Figure 5.17). The regeneration air flow measured is 8000m 3 h − 1 .
Higher COPs close to 1.0 were obtained at lower regeneration temperatures around
50 ◦ C at similar regeneration volume flows of 8000m 3 h − 1 (see Figures 5.18 and 5.19).

0.7

140

COP

0.6

120

0.5

heating power regeneration

100

0.4

80

cooling power (exterior inlet)

0.3

60

0.2

40

20 0.1

cooling power (room exhaust inlet)

0 0

13:00 13:30 14:00 14:30 15:00 15:30 16:00

Time on 17 June

Figure 5.16 Heating and cooling power measured during plant commissioning in Mataro. The COP
relates the ambient air cooling power to the heating power