A Performance Prediction Methodology for Integral Collection-Storage Solar Domestic Hot Water Systems

A performance prediction methodology is developed which is applicable to most commercially available integral collection-storage passive solar domestic hot water systems. A computer model of a general ICS component was created to be compatible with the transient simulation program TRNSYS [3] , and was used to develop and verify the simpler monthly performance prediction method. The method uses the system parameters from available test methods, monthly average climatic data, and load size to predict long term performance of ICS systems. I Introduction Integral collection-storage (ICS) units are passive solar water preheaters which combine solar collection with thermal storage. They are usually roof or ground mounted in series with a conventional domestic water heater and supplied by mains water. An ICS unit is basically a black tank in an enclosure with an optical cover system. Today, many units are commercially available with variations on this design. Some units have several tanks plumbed in' series within the box. Others have internal reflector systems, non-flat covers or finned tanks. Often these variations are combined and other design innovations are included. ICS solar domestic hot water (SDHW) systems usually cost less than active systems and are inherently simple to install and maintain. They often operate without heat exchangers, pumps or controllers. A number of studies have proposed methods for predicting ICS monthly or annual performance. Huggins and Block The California Energy Commission [5] has adopted an interim annual performance prediction method for ICS and thermosyphon SDHW systems. Experimental data have not been compared to these annual predictions. Cummings and Clark Lindsay and Thomas [11] have developed a detailed transient model of a system with an internal optical system. Simulations using the model were successful in predicting tank temperatures under no-draw conditions. Because of its complexity, the model is not easily adaptable to other internal geometries. This paper suggests the use of existing test procedures to obtain performance parameters useful for predicting long term performance. A transient model of an ICS system is developed for use with TRNSYS [3] program. Simulations using this model are compared with experimental data for validation. An analytical procedure is then presented based on results obtained with the simulation model, which uses the experimentally determined parameters to obtain an estimate of ICS system monthly performance. II Test Methods Currently ICS systems can be tested for overall performance by the ASHRAE 95-1981 test procedure. This is