Solar Domestic Hot Water Heating Research Articles

Ground source heat pump control methods for solar photovoltaic-assisted domestic hot water heating

Domestic hot water (DHW) heating is one of the most energy-consuming activities in a typical household. Photovoltaics (PV) connected with a ground source heat pump (GSHP) offers a low-emission method for DHW heating. This paper studies four different control methods for DHW heating in a building with a GSHP and a PV system. The main control method aims to minimize DHW heating costs by utilizing Nord Pool Spot market information together with a PV production output forecast. The results of this control method, implemented with a perfect PV output forecast and assessed over three years of hourly data, indicate that annual cost savings over other methods are achievable. Results with the real-world actual PV output forecast, evaluated between June–September 2020, demonstrate DHW heating cost savings up to 36–53%, even though forecasting errors are present. The heating costs are 9–11% higher compared against the perfect forecast case. The suggested control method thereby effectively reduces the costs when compared with all other methods, and its performance is not significantly affected even when an actual imperfect forecast is implemented. The results also indicate that minimizing energy consumption does not offer the lowest cost.

Determination of Heat Losses from the Pipeline in SDHW System during the Continuous Change of the Supply Temperature

In this article, the research object is the solar domestic hot water (SDHW) heating system that has been in operation since 2015 and is located on the campus of the Bialystok University of Technology (Poland). The thermal performance of solar collectors are thoroughly investigated so far. Therefore, special attention was paid to the issue of the heat loss from pipes. The measurements showed that the heat transfer in circulation pipes is quite complex due to continuous fluctuations in water temperature at the supply of this loop. As it turned out, the application of the classical method of energy balancing and the readings from heat meters gave inaccurate results in this case. The main aim of this study was to develop a different approach to solving the problem of determination of heat losses. The method presented in this article is based on computational fluid dynamics (CFD) and measurement results as the input data. The practical result of this study was the development of two relationships for calculating the heat loss from pipes. A separate issue, that is discussed in this paper, concerns the impact of the time intervals used in numerical simulations on the accuracy of calculation results.

Net energy analysis of a solar combi system with Seasonal Thermal Energy Store

EU targets require nearly zero energy buildings (NZEB) by 2020. However few monitored examples exist of how NZEB has been achieved in practise in individual residential buildings. This paper provides an example of how a low-energy building (built in 2006), has achieved nearly zero energy heating through the addition of a solar domestic hot water and space heating system (“combi system”) with a Seasonal Thermal Energy Store (STES). The paper also presents a cumulative life cycle energy and cumulative life cycle carbon analysis for the installation based on the recorded DHW and space heating demand in addition to energy payback periods and net energy ratios. In addition, the carbon and energy analysis is carried out for four other heating system scenarios including hybrid solar thermal/PV systems in order to obtain the optimal system from a carbon efficiency perspective.

An investigation of the technoeconomic feasibility of solar domestic hot water heating for the Canadian housing stock

This study evaluates the impact on energy consumption and GHG emissions as well as the technoeconomic feasibility of retrofitting solar domestic hot water (DHW) heating systems to all houses in the Canadian housing stock (CHS). The study was conducted using the Canadian Hybrid Residential End-Use Energy and GHG Emissions Model (CHREM). It was assumed that all houses that have a DHW system with a tank, and a roof facing south, south–west or south–east could be retrofitted with a solar DHW system. As to be expected, the energy and GHG emissions impact of retrofitting SDHW systems into the CHS is substantial. If all eligible existing DHW systems (30% of those existing in the CHS) were to be retrofitted with SDHW systems, the energy consumption and GHG emissions of the Canadian residential sector would be reduced by about 2%. This is equivalent to 22.7 PJ of end-use energy savings and 1 Mt of GHG emissions reduction, or 11.8% and 11.9%, respectively, of the current amounts associated with domestic hot water heating. The energy savings potential with SDHW systems in all provinces are similar, while the GHG emission reductions vary significantly due to the substantially different fuel mix used in different provinces. The economic feasibility results demonstrate the impact of installation and fuel costs, as well as interest and energy price escalation rates on payback period.

MEASUREMENT OF THE EFFICIENCY OF EVACUATED TUBE SOLAR COLLECTORS UNDER VARIOUS OPERATING CONDITIONS

The operating efficiency of evacuated tubes themselves under varying environmental conditions and installation scenarios, independent of water and space heating auxiliary equipment, are not readily available values. Further, Manitoba specific data has not been established. The purpose of this research program was to measure the efficiency of evacuated tube solar collectors under various operating conditions including: the angle of inclination towards the incident solar radiation, heat transfer fluid flow rate, glazing installation, and number of evacuated tubes. The operating conditions and configurations were chosen to represent realistic or probable installation scenarios and environmental conditions. Furthermore, the research aimed to identify the suitability of evacuated tube solar collectors to each of the scenarios. These design values are of use for appropriate sizing of water or space heating systems, system configuration and optimization, and calculation of return on investment. The scope of the research project was limited to the efficiency of various configurations of a 32-tube panel, not the entire solar domestic hot water or space heating system. Thus, factors such as heat loss in the tubing, solar storage tank, and heat exchanger efficiency were not investigated. The findings indicated that efficiency varied by approximately 5% between the different collector configurations, as observed from the overlay graph of results. When the efficiency of a collector is considered within a system it is proposed that effectiveness may be a better measure of overall performance.

Energy savings for solar heating systems

In this paper the realistic behaviour and efficiency of heating systems were analysed, based on long term monitoring projects. Based on the measurements a boiler model used to calculate the boiler efficiency on a monthly basis was evaluated. Comparisons of measured and calculated fuel consumptions showed a good degree of similarity. With the boiler model, various simulations of solar domestic hot water heating systems were done for different hot water demands and collector sizes. The result shows that the potential of fuel reduction can be much higher than the solar gain of the solar thermal system. For some conditions the fuel reduction can be up to the double of the solar gain due to a strong increase of the system efficiency. As the monitored boilers were not older than 3 years, it can be assumed that the saving potential with older boilers could be even higher than calculated in this paper.

Simulation Study on Solar House with Floor and Hot Water Heating System

In this study, a two storied single family house with solar floor and domestic hot water heating system is simulated to examine the usefulness of the simulation for predicting the indoor thermal environment and energy consumption to evaluate the system performance throughout a year. The effects of the solar floor and hot water heating system were evaluated with comparison of the simulated results for the cases with and without solar heating system. The results showed that the solar house provided comfortable environment with an average annual total purchased electric power of 40.4 GJ/year, which was lower than that of the house without solar heating system by 17 %. In addition, the effect of tilt angle of solar collector on the total energy performance of this house was examined to discuss the suitable angle in considering roof design of the house. It was found that the effect of collector tilt angle on the solar energy contribution was much smaller than the difference in solar radiation on the tilt angle. This implies the flexibility in designing the roof shape of solar houses.

00/00478 Computer simulation of a two phase thermosyphon solar domestic hot water heating system

00/00478 Computer simulation of a two phase thermosyphon solar domestic hot water heating system

Computer simulation of a two phase thermosyphon solar domestic hot water heating system

The present work deals with a theoretical analysis by computer simulation of a two phase thermosyphon solar domestic hot water system using R-11 as a working fluid. The performance was studied by the aid of a simulation procedure for a typical day period divided into equal time intervals of 15 min. Instantaneous values of solar radiation intensity and ambient temperature were applied at the beginning of each time step. The insolation was calculated according to the procedure suggested by ASHRAE. The variation of ambient temperature during the day was approximated by a sine function. The variation of working fluid properties with temperature was also taken into account. The computer program and calculation procedure were first validated by comparing the results with established results of single phase systems. Then, calculations were performed for the two phase thermosyphon system to evaluate mass flow rate, saturation pressure and temperature in the collector and condenser, together with tank temperature, and collector and condenser thermal efficiencies. These calculated values were obtained for three cases, namely, the no loading case of no water withdrawal from the tank, continuous loading and intermittent loading. The results obtained showed that, in the two phase system, the saturation pressure and temperature increase continuously during the day and follow the tank temperature pattern. This makes the system pressure dependent on the tank loading. The collector efficiency did not reveal a serious change with the loading condition. This behavior differs from that which occurs in the single phase system, where the collector efficiency increases considerably with loading. Comparison of the two phase system with a single phase system of the same collector area and tank volume showed a significant increase in collector efficiency and tank temperature for the case of the two phase system.

Analysis of a Load-Side Heat Exchanger for a Solar Domestic Hot Water Heating System

Testing is done of an unpressurized drainback system with a load-side heat exchanger. Analytical calculations for the heat exchanger effectiveness and three models for convective heat transfer coefficients from correlations are compared against the experimental data. TRNSYS simulations were performed using the average effectiveness of 0.78 (the calculated effectiveness varies from 0.68 to 0.95); the results compare favorably with experimental results, indicating that a constant effectiveness is an adequate model for the system.

95/03803 Technology for sustainable development: A case study of solar domestic hot water heating in Ontarlo

95/03803 Technology for sustainable development: A case study of solar domestic hot water heating in Ontarlo

Technology for sustainable development: A case study of solar domestic hot water heating in Ontario

In Ontario, potential contributions of solar domestic hot-water (SDHW) heating to air-emission mitigation have been identified. The provincial utility Ontario Hydro does not include solar heating in its current demand-side management plans because of the capital cost barrier. We present results of life-cycle cost analyses for installing a typical solar system in single-family dwellings in Toronto. For high hot-water load, the generated societal benefits make solar domestic hot-water heating an economically viable option.

Comparison of Experimental and Simulated Thermal Ratings of Drain-Back Solar Water Heaters

Short-term experimental tests of drain-back solar water heaters are compared to ratings obtained using TRNSYS to determine if computer simulations can effectively replace laboratory thermal ratings of solar domestic hot water heating systems. The effectiveness of TRNSYS in predicting changes in rating due to limited changes in collector area, collector flow rate, recirculation flow rate, storage tank volume, and storage tank design is validated to within ±10 percent. Storage tank design is varied by using a stratification manifold in place of the standard drop tube. Variations in other component sizes and operating factors are based on current industry standards.

Water conservation in solar domestic hot water systems

The effect of using solar domestic hot water heating systems on water consumption is investigated for different system configurations. Random samples of actual data for water consumption, obtained from the water authority, together with data from solar heating collector manufacturers for systems installed, have been analyzed. It was found that the water consumption varies with the following parameters: length of the piping system and design of the domestic heating system network. In general, an average increase of 36.6% in water consumption has been found. Techniques and suggestions have been proposed for reducing the water consumption.

System design optimization for large building integrated solar heating systems for domestic hot water

Performance and economy for building integrated solar domestic hot water (DHW) heating systems have been calculated as a function of installed solar collector area per housing unit, and benefits from having a high summer solar fraction are calculated and discussed. A presentation of new Danish solar heating DHW demonstration projects, where a high solar fraction is combined with heat loss savings in the summer, is also given.

Plume entrainment effects in solar domestic hot water systems employing variable-flow-rate control strategies

Solar domestic hot water heating systems perform more efficiently if their storage tanks are perfectly thermally stratified. In real tanks, which do not perfectly stratify, the most important mechanism destroying stratification is plume entrainment. Plume entrainment occurs when cooler water is inserted into the tank top which contains hotter water. The resultant falling plume of cool water causes mixing. This paper uses computer simulation to evaluate and compare two strategies by which plume entrainment is minimized by controlling the collector flow rate. One strategy (calleá “SCOT”) maintains a constant collector outlet temperature, and the other (called “FCTR”) strategy maintains a constant temperature rise Δ T set from inlet to outlet of the collector. The results of the study show that the SCOT strategy always produces a system that performs more poorly than the corresponding system with a fixed flow rate. The FCTR strategy, on the other hand, consistently out-performs the fixed flow strategy, but only by a few percent. When the FCTR strategy is used, the optimum Δ T set to use is 20°C for the SDHW system simulated.

Measured and Simulated Performance of a Solar Domestic Hot Water System

A commercially available solar domestic hot water heating system installed in a private residence in Vancouver. Canada has has been intensively monitored over a four month period. Simulation of the system was performed using a modified version of the WATSUN-3 Domestic Hot Water (DHWA) model. Model predictions are compared against actual system measurements on an hourly and daily basis. Reults show that the model is able to consistently track thermal conditions within the system and is capable of predicting system performance to within 5 percent.

Comparison of actual and predicted performance of five domestic hot water systems

SYNOPSIS Performance data has been obtained on five solar domestic hot water heating (DHW) systems for a period of approximately three years In Rhode Island. Actual physical performance has been analysed using computer techniques and compared to F-CHART predictions [1] using actual loads and state-wide insolation rates for the period under study. Brief descriptions of the systems, a sample data set, the results of the analyses, and a comparison of actual performance with calculated predictions for each system are presented While F-CHART predictions are generally higher than actual performance estimates for four of the five systems under study, the results are consistent with experimental and computational uncertainties and known systematic effects in the theoretical analysis.

Optimal sizing of solar collectors by the method of relative areas

A method is presented for calculating directly, without iteration, the approximate collector area which minimizes the total life-cycle cost of an active solar space and/or domestic hot water heating system. The method is based on an empirical relationship between annual solar load fraction and relative collector area. This relationship was determined by correlating data that were generated by the Klein, Beckman and Duffie F-Chart program, which in turn is based on a correlation of digital computer simulation results. The calculations may be performed in a few minutes using a hand-held calculator. Required data are tabulated for 170 locations, and a solved example is included. Compared to results from the F-chart program, deviations of total life-cycle costs from the minima are typically less than 3 per cent. Uncertainty of future energy prices is regarded as the limiting factor in the accuracy of the optimization calculations. A detailed economic analysis is included.