The ITW solar heating system: An oldtimer fully in action

Public awareness of energy in the early 1970s stimulated a number of projec ts on alternative ways of heating. The 'Institut fur Thermodynamik und Warm etechnik' (ITW) of the University of Stuttgart has been operating a solar h eating system since 1985. Ever since, this system has been minutely monitor ed. In particular, the storage was painstakingly considered as it was inten ded to serve as a pilot facility for the much discussed problem of seasonal storage. This storage unit should be simple and cheap but heavily instrume nted in order to obtain many and accurate data and it should be versatile i n order to gain knowledge for operation. The solar heating is provided by c ollectors that are unglazed, so a heat pump is required for appropriate hea ting temperatures. However, the heat pump allowed for a combination of hear ing and cooling in our system and this proved to be very advantageous, as c ooling energy is more expensive and more in demand in our building than hea ting energy. The system was used in various seasonal cycles with changing conditions. It has now been operating for almost 15 years. During this period. neither st orage nor collectors caused any trouble. Some difficulties were experienced with the heat pump. The first one had to be replaced; we made suggestions for improvement of the second one. This provided good COPs but there has be en an occasional defect. The experience with our solar heating system was s o satisfactory that, based on the knowledge gained from it, large housing p rojects in Friedrichshafen and Hamburg and an office building project in Ch emnitz were conceived and built and are now being monitored. (C) 2000 Elsev ier Science Ltd. All rights reserved.