Retrofitting Domestic Hot Water Heaters for Solar Water Heating Systems in Single-Family Houses in a Cold Climate: A Theoretical Analysis

Abstract

Abstract:One of the biggest obstacles to economic profitability of solar water heating systems is the investment cost. Retrofitting existing domestic hot water heaters when a new solar hot water system is installed can reduce both the installation and material costs. In this study, retrofitting existing water heaters for solar water heating systems in Swedish single-family houses was theoretically investigated using the TRNSYS software. Four simulation models using forced circulation flow with different system configurations and control strategies were simulated and analysed in the study. A comparison with a standard solar thermal system was also presented based on the annual solar fraction. The simulation results indicate that the retrofitting configuration achieving the highest annual performance consists of a system where the existing tank is used as storage for the solar heat and a smaller tank with a heater is added in series to make sure that the required outlet temperature can be met. An external heat exchanger is used between the collector circuit and the existing tank. For this retrofitted system an annual solar fraction of 50.5% was achieved. A conventional solar thermal system using a standard solar tank achieves a comparable performance for the same total storage volume, collector area and reference conditions.

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

“…Retrofitting existing domestic hot water (DHW) boilers using plug-and-play docking units has the potential to meet these goals. The investment cost can be significantly reduced both in material and installation costs [1,4,5]. The largest part of the solar thermal market involves retrofitting situations where the investment cost is the main bottleneck [6].…”

“…A theoretical analysis, based on TRNSYS simulations, was performed earlier on several retrofitting system possibilities using forced circulation flow [4]. The results showed that, when designed according to a load, a system where an additional storage is connected in series with the retrofitted tank achieves the highest performance.…”

“…When a standard hot water boiler is retrofitted for solar thermal use, the two connections that were previously used only for hot water discharge to the user should now also be used for charge the storage with solar energy. In the theoretical analysis [4], since a technical solution for the flow reversion was not yet achieved, it was assumed that charge and discharge could occur simultaneously and independently. Even if this was a simplification of reality it was valid for a comparison of different retrofitting configurations in relative terms.…”

A New System to Estimate and Reduce Electrical Energy Consumption of Domestic Hot Water in Spain

“…In the second option, users need to spend money to obtain energy savings, drawing on the research by Washlstrom [43]. In this research 65 flats in Gothenburg (Sweden) were measured where electrical energy consumption of DHW [44] is very similar to many Spanish cities. Results shows that 26% cold water and 28% DHW could be saved when modern taps were installed, thermostatic mixers in the bath/shower and single-lever mixer in the basin and kitchen.…”

Dissemination of Solar Water Heaters in Taiwan: The Case of Remote Islands

“…Therefore, significant efforts have been devoted during the past three decades toward the development and dissemination of biomass energy, geothermal energy, ocean energy, photovoltaic energy, solar thermal energy and wind power generation [2], despite the intermittent OPEN ACCESS nature of those renewable energy resources. For solar thermal energy, it is known to be the most widely used in many countries [3][4][5][6][7]. In Taiwan, the climatic conditions are predominantly very sunny, with daily average solar radiation of 3.25 kWh/m 2 in the north and 4.64 kWh/m 2 in the south.…”