Retrofitting Conventional Electric Domestic Hot Water Heaters to Solar Water Heating Systems in Single-Family Houses—Model Validation and Optimization

Abstract

System cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. In this study, the TRNSYS simulation models of the retrofitting solar thermal system were validated against measurements. Results show that the validated models are in good agreement with measurements. On an annual basis a deviation of 2.5% out of 1099 kWh was obtained between the auxiliary energy from results and from the simulation model for a complete system. Using the validated model a system optimization was carried out with respect to control strategies for auxiliary heating, heat losses and volume of auxiliary storage. A sensitivity analysis was carried out regarding different volumes of retrofitted hot water boiler, DHW profiles and climates. It was estimated that, with adequate improvements, extended annual solar fractions of 60%, 78% and 81% can be achieved for Lund (Sweden), Lisbon (Portugal) and Lusaka (Zambia), respectively. The correspondent collector area was 6, 4 and 3 m 2 , respectively. The studied retrofitted system achieves a comparable performance with conventional solar thermal systems with the potential to reduce the investment cost.

Retrofitted Solar Domestic Hot Water Systems for Swedish Single-Family Houses—Evaluation of a Prototype and Life-Cycle Cost Analysis

“…It is important to note that the measured load of 5000 kWh/year corresponds to gross consumption, i.e., including circulation losses. The measured annual solar fraction of nearly 50% is in line with previous theoretical estimations [24] and laboratory measurements [25], and the energy savings would be somewhat higher if energy production in January and February had been included. The collectors were placed on the same slope as a roof tilted 20 • from horizontal facing south-east.…”

“…This was expected from previous calculations for such a large family size in comparison with the size of the auxiliary heater (35 litres) [25]. Nevertheless, this was one of the aspects that were to be tested.…”

“…Nevertheless, this was one of the aspects that were to be tested. The main ways to solve this problem are to either increase the volume of the auxiliary storage or to use the existing hot water storage for preheating in the winter [25]. In climates where solar radiation is more evenly distributed throughout the year, this challenge should be easier to overcome [25].…”

Investigation of the Dynamic Melting Process in a Thermal Energy Storage Unit Using a Helical Coil Heat Exchanger

“…Over the last decade, a variety of solar energy utilization systems have been extensively used in actual applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. These systems are deemed to be an attractive approach for solving global energy shortage problems due to its renewable and sustainable nature.…”

Thermal Behavior of a Storage Tank of Solar Water Heater in Cases of Charge and Discharge

“…Among the physical phenomena occurring in the tank and that may affect the performance of such an installation the stratification continues to raise the interest of many researchers [4]. It is in this sense that this work was conducted to better understand the thermal behavior of a storage tank.…”