Comparison of System Concepts
To compare the solar fractions that are reached with and without a conventional storage tank, the ranges of solar fractions from both nomograms are shown in a single diagram in Figure 7.
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Because of the limited storage capacities of the concrete slab, significantly larger collector areas are necessary to reach the same high solar fractions as with a conventional storage tank. Therefore, the cost-to-benefit optimum for systems using the concrete slab as a heat store has been limited to a solar fraction of 30%. Please note that this is only an approximate value and depends strongly on the boundary conditions of each project.
Solar thermal energy is a good solution for space heating of industrial buildings if there is no or not enough waste heat available. When considering solar thermal energy for space heating of a factory building, the first steps should be to reduce the heat demand of the building by insulating the building and reducing infiltration losses (e. g. loading docks instead of open doors). The nomograms were developed to provide a means for rough dimensioning typical system configurations. A system concept with a water storage tank and a system concept using the concrete floor slab as storage medium were analyzed and described in detail. If the utilization ratio is high, the solar fractions that can be reached are similar for both system concepts. Solar fractions reached with systems without storage tank can even be higher compared to systems with storage tanks. High utilization ratio means that either one or both the collector area or the heat requirement is low. In these cases, the cheaper system concept without a storage tank makes a lot of sense. However, if the heat requirement is relatively large or if very high solar fractions should be reached, the system concept with a storage tank has an advantage. It should be noted that the option of having no storage tank and reaching a 100% solar fraction is feasible if an air temperature in the building that sometimes falls below the desired set value can be tolerated.
The presented work was performed as part of IEA-Solar Heating and Cooling and Solar Paces Task 33/IV “Solar heat for industrial processes”. The Austrian participation was financed by the Austrian Federal Ministry of Transport, Innovation and Technology.
[1] Klein, S. A. et al. (2005). TRNSYS, A Transient System Simulation Program - University of Wisconsin - Madison, Solar Energy Laboratory, Version 16.
