Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 129

based on the Navier-Stokes equations (Maclaine-Cross, 1988; Gao et al ., 2005). This
allows the evaluation of the influence of flow channel geometry, sorption material
thickness, heat capacity, rotational speed, fluid velocity, etc. They are mostly too time
consuming to be used in full system simulations including solar thermal collectors,
where mostly simpler models are available, based either on empirical fits to measured
data (Beccali et al ., 2003) or on models of dehumidification efficiency.
Different control strategies have been compared by Ginestet et al ., (2003) to study
the influence of air volume flow and regeneration temperature. As the increase in
regeneration temperature does not linearly lower the supply air temperature, the study
concluded that increased air flow rates are preferable to increased thermal input, if the
cooling demand is high. Mean calculated COPs for the climatic conditions of Nice,
France, were between 0.3 and 0.4. Henning and others also remarked that increasing
the air flow is useful in desiccant cooling mode, but that the minimum acceptable flow
rate should be used in adiabatic cooling or free ventilation mode to reduce electricity
consumption (Henning et al, 1999). When thermal collectors with liquid heat carriers
are used in combination with a buffer storage, Bourdoukan and others suggested
operation of the cooling system only in adiabatic cooling mode during the morning
and then allowing desiccant operation in the afternoon, using heat from the buffer
storage (Bourdoukan et al ., 2007). However, in many applications, dehumidification
is already required during the morning hours. Also, if cheaper air collectors are used,
heat storage is not possible.
InEurope there are only a few implemented demonstration plantswhich are powered
by solar energy, so operational experience from such plants is very scarce. To introduce
the technology onto the market, information about the energetic performance (effi-
ciency, heat and electricity consumption), water consumption and maintenance issues
needs to be provided. In the following, experimental results from two large European
installations are presented together with laboratory measurements on desiccant rotor
systems. Special emphasis is placed on the performance analysis of each individual
component as well as the optimization of the overall control strategy.
5.2.1 Desiccant Cooling System in the Matar o Public Library
Adesiccant cooling plant with a process air volume flowof 12 000m 3 h − 1 was installed
in the public library building inMataro (Spain) with a 3500m 2 cooled surface area. The
buildingwas equippedwith four conventional air-conditioning units, where the cooling
energy was provided by heat exchangers from a central electrical compressor chiller.
One of the air-conditioning units for the children's reading and multimedia room
with a 510m 2 surface area was replaced by a desiccant cooling plant and provides
cool fresh air via 15 ceiling air outlets. The building has a ventilated photovoltaic
fa¸ade of 244m 2 and 330m 2 of shed roofs with a total electrical power of 55 kW p .
The heat produced by the photovoltaic modules is transferred into on air gap 14 cm
wide, which is exhausted by the desiccant cooling regeneration fan. Two additional