Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 130

Figure 5.13 System concept of the desiccant cooling plant in Mataro with ventilated photovoltaics
and series-connected solar air collectors

air collector fields in the fa¸ade (50m 2 ) and roof (105m 2 at 34 ◦ tilt angle) increase the
temperature level to the required regeneration air temperature (see Figure 5.13). The
common regeneration ventilator is volume flow controlled to provide a regeneration
temperature between 50 and 70 ◦ C. With a yearly irradiance of 1020 kWhm − 2 a − 1 on
the vertical south fa¸ade and 1570 kWhm − 2 a − 1 on the shed roofs the combined solar
thermal energy system is calculated to produce nearly 70 000 kWh of useful thermal
energy from April to October, covering 93% of the cooling demand of 44 000 kWh.
Exterior air can be added to the regeneration air just before the sorption wheel, so
that temperature peaks from the solar collectors after stagnation can be avoided. The
sorption wheel is a silica gel rotor with a nominal rotation speed of 15 h − 1 . Auxiliary
cooling energy is supplied from the existing compression chiller via a heat exchanger
after the fresh air humidifier.
The thermal efficiency of the ventilated photovoltaic system is rather lowat 12-15%,
because flow velocities in the many parallel large air gaps reach only 0.3m s − 1 . The
maximum air temperature level increase is between 10-15 K. The complete volume
flow through the ventilated PV system is between 3000 and 9000m 3 h − 1 and is fed
into three parallel air collector fields. Flow velocities in the 9.5 cm air channels are
between 3 and 9m s − 1 and efficiencies are in the range of 50%.
An important result from the design study was that only 9% of the total cooling
energy is provided with a full volume flow of 12 000m 3 h − 1 in desiccant cooling