Simulation and Evaluation of Stratfied Discharging and Charging Devices in Combined Solar Thermal Systems
Abstract
Combined solar thermal systems for domestic hot water preparation and space heating are usually equipped with water storage tanks. The stratification behavior of the tank including its external connections is significant for the collector yield and the saving of conventional backup energy. The charging and discharging units take a decisive role for the development of the stratification. While many studies analyzed the stratified charging process in detail, investigations about stratified discharging units are rare. Stratified discharging means, that the fluid is leaving the tank from at least two different heights, which are nearest to the demand temperature, using a mixing device, in order to consume the smallest possible amount of the hottest water. It could more clearly be called “layer related discharging”. This simulation study analyzes the effects of different discharging and charging strategies on the performance of a combined solar thermal system in a single-family house. Based on the system according to Task 32 of the Solar heating and Cooling Program of the International Energy Agency (IEA SHC) the system layout and in specific the storage connections are modified to investigate different stratified charging and discharging concepts realized by external valves or devices within the storage tank.