Passive cooling, simulations and experiences from realized projects in Sweden.

The use of computers for simulating building thermal behavior started early at the Royal Institute of Technology in Stockholm, Sweden. The first example of such use dates from a 1957 study of an exterior wall exposed to solar radiation. The simulation program, later named BRIS, has gradually evolved with regard to the users and growing computer capacity. It has been used since the early sixties for research projects, design work and development of new systems, among others the ventilated hollow-core slab (Thermodeck) system. In 1990 the originators of BRIS recieved Swedish Great Energy Award for "distinguised contributions in the field of energy conservation". The jury stated that the knowlege we got from the simulations has lead to an annual saving of energy worth 100 millions Swedish Crowns. BRIS contains different installation- and control components representing generic models rather than specific implementations. The components can be combined freely to correspond to the principal operation of any HVAC system. The control strategy is based on a sequence of restrictions on the possible sources for heating, cooling or heat recovery. The restrictions are relaxed successively within each time step in the building model until a solution is found. The order in which the restrictions are to be relaxed may be varied, the capacity intervals can be open ended on one side, etc. By combining loads and systems minimum energy strategies can be defined and found by the program. When limiting the installed capacities the building dynamics will be more active in the control process which has shown to give a surprisingly high potential to reduce peak power problems and energy use. We now have experience from over 300 buildings using the Thermodeck system for passive cooling. Some of these experiences are reported and commented in this paper.