D. Pahud, Central solar heating plants with seasonal duct storage and short-term water storage: Design guidelines obtained by dynamic system simulations, SOLAR ENERG, 69(6), 2000, pp. 495-509
A central solar heating plant with seasonal ground storage is analysed by d
ynamic system simulations. A reference system, involving a collector area,
water buffer storage and ground duct storage, is defined for typical Swiss
conditions and simulated for several types of heat load. A methodology is e
stablished for the optimisation of the main system parameters. The thermal
behaviour of such a system is highlighted. The short-term heat requirements
are covered by the buffer unit, whereas the seasonal heat requirements are
covered by the ground duct storage. As a consequence, a system such as thi
s is intended to supply a large solar fraction ( > 50%). Optimal ratios bet
ween the main system parameters are sought for an annual solar fraction of
70%. An optimal buffer volume of 110 to 130 l per m(2) of collector area is
obtained. The optimal duct storage volume and collector area vary respecti
vely from 4 to 13 m(3) per m(2) of collector area and from 2 to 4 m(2) per
MWh (3.6 GJ) of annual heal demand. They depend mainly on the specific heat
losses from the duct storage unit. A large annual heat demand ( > 3600 GJ
or 1000 MWh) and/or low temperatures in the heat distribution are essential
for satisfactory system thermal performance. The spacing of the boreholes
which form the ground heat exchanger of the duct store is fairly constant a
nd is found to be about 2.5 m for a ground thermal conductivity of 2.5 Wm(-
1) K-1. Some improvements of the system control are also investigated to as
sess the influence on the overall thermal performances of the system. They
indicate that the system thermal performances are only slightly improved in
contrast to the improvement brought by a simple but optimised system contr
ol. (C) 2000 Elsevier Science Ltd. All rights reserved.