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.