The system under consideration is designed to air-condition a group of offices on the top floor of the Energy Research Center building at the Technion — Israel Institute of Technology (Haifa, Israel). The conditioned space consists of three offices, with one north­facing exterior wall each (including a window). The total floor area of the conditioned space is 35 m2. The walls and roof are made of 8” (20 cm) prefabricated low-weight concrete, not insulated, with cement plaster. Each office serves two people and their computers; hence total occupancy is 6 persons.

The city of Haifa is an ideal site to test such a system. Located on the Mediterranean coast at 33 degrees north latitude, it has the typical climate of Mediterranean cities. Outside summer conditions (typical for design) are 30oC and 70% relative humidity. Room design conditions have been selected at 24oC and 50% relative humidity.

A load calculation for the three typically staffed and equipped offices shows about 4.2 kW with a room sensible heat factor (RSHF) of 0.92. At 30 cfm (51 m3/hr) of fresh air per occupant (ASHRAE air quality recommendations), the additional fresh air-associated load is about 3.0 kW, most of which (2.4 kW) is latent. Thus, the total cooling capacity required is 7.2 kW, with a grand sensible heat factor (GSHF) of 0.62. The total supply air circulation needed (based on 12 air changes per hour) is 0.4 kg/sec (720 cfm). The desired conditions of the supply air are 14.7oC and 86% relative humidity.

The desiccant solution is regenerated by solar heat, supplied by flat-plate solar collectors of conventional design, of the type widely employed in Israel for domestic water heating, but with better than average quality to enable higher efficiency at high temperatures. The solar collectors and remaining parts of the system are located on the roof immediately above the top floor. Solar-heated water serves as the heat carrier. The option of heating the regenerated solution directly, by exposing it to the sun and to ambient air simultaneously, had been explored but found to be somewhat problematic. The advantages of the current option are simpler construction technology, simpler storage capability, dirt control and simpler ability for using an air-to-air heat exchanger for heat recovery. With the total latent heat load of 2.75 kW, the solar energy demand was calculated to be 4.77 kW. Assuming ten hours of continuous operation daily, and taking a small safety factor, the solar collector area was selected at 20 m2. Solution storage in the amount of 120 liters of LiCl solution at 43% concentration and a 1000 liter hot water tank added to the system make it possible to operate for a total of four hours with no insolation — a typical situation in the summer during the morning hours.