The simulation of a commercial-scale, hybrid solar and heat pump water heating system

Abstract

Due to the rotation of the earth and climatic conditions, the available solar radiation varies, not only in the 24-hour period but also daily. The latter poses a significant challenge to the designer of solar water heating systems. In order to ensure the constant availability of sufficiently hot water, large commercial scale or industrial installations use heat pumps. The combination of solar and heat pump technology has been introduced in various configurations to the commercial market to curb electricity usage. Several factors influence the performance of such systems: The size and performance of the solar collectors, the capacity of the storage vessels, the hot water demand profile, the size and performance of the heat pump, control systems and climatic conditions. The design and optimisation of such systems are, therefore, not straightforward. Simulation programs are often used for the design and optimisation of such systems. Researchers and designers use simulations to design the system for maximum efficiency, user comfort or even a combination thereof. The problem, however, with most component-based simulations is that they often require specialist knowledge not only for the use and input requirements but also for the realistic calibration of the program. There exists a need to implement a simulation that uses readily available manufacturer performance curves and matrices of the various sub-components that make up the system. Parametric studies and optimisation methods can often take long periods of time on simulation packages. Optimisation in a limited number of independent parameters becomes near impossible when a single simulation can take days to complete. This problem becomes even more evident when extended periods are simulated. For optimisation of such systems, a quick and accurate solver is required that can manage continually evolving boundary conditions. The conducting of parametric studies design simulations and stochastic optimisation studies on SWH/ASHP (SolarWater Heater and Air Source Heat Pump) systems, therefore, mandates the use of simulations programs with swift simulation times.