Domestic Hot Water Systems Research Articles

Building hvac retrofitting using a pv assisted dc heat pump coupled with a pcm heat battery and optimal control algorithm

In the last years, the EU and scientific community put a lot of effort in trying to increase the sustainability in renovated buildings by introducing novel concepts and technologies. This paper presents the outcomes of a retrofit case study carried out within the Heat4Cool H2020 project concerning space heating (SH) and domestic hot water (DHW) systems. The case study is a multi-family residential building located in Chorzow, Poland, where the SH and DHW are provided by natural gas boilers present in each apartment. The proposed approach is to combine the existing gas boilers with phase change material storages (PCM) and a direct current air source heat pump (DC-EHP) assisted by a photovoltaic system (PV) connected to the grid. TRNSYS was used for the dynamic simulations, and to support the introduction of the retrofit layout. New custom TRNSYS’ types were developed for each technology and tested against experimental data provided by industrial partners. Furthermore, a state-of-the-art rule-based controller was developed combining TRNSYS with a MATLAB’s script and tested against an interior point optimal control algorithm. In the best-case scenario the yearly primary energy savings are more than 30% accounting for the PV energy sold to the grid and around 11% considering only self-consumption, while the pay-back time is around 10 years considering EU28 economic conditions and 20% overall discount for the renovation project.

Analysis of a heat pump assisted solar water heating system using TRNSYS program

Traditional solar hot water system (SDHW) is an important system for the use of renewable energy sources. In this system, while water is heated by sun in summer or hot days, it is heated by electric heaters in winter, or cold days. So efficiency of this system is low in winter because of very high electric consumption. This problem can be solved using heat pump instead of electric heaters. In this study, a heat pump assisted solar domestic hot water system (HP_SDHW) was designed to increase efficiency. Both systems were modelled and simulated depending on time using (TRNSYS) program. An analysis was performed through the year for both systems at SARAJEVO/Bosnia and Herzegovina conditions. As a result of the annual analysis, it was found that the HP_SDHW system consumes approximately 40% less electricity than the traditional SDHW system. The solar fraction of the HP_SDHW (%67) was found higher than the SDHW system (%46).

Experimental determination of cold water temperature at the inlet to solar water storage tanks

In the present work, results of experimental research on the mains water temperature supplying the Solar Domestic Hot Water system in the period from 2016 to 2018 are shown. The test object is located in the Hotel for Research Assistants on Bialystok University of Technology campus in Poland. One of the elements that will guarantee the correct energy balance of a hot tap-water system is the exact determination of the cold water temperature. The aim of this study is estimation of the temperature of the mains water flowing into the district heating substation and the water feeding directly the heat storage tanks. The research results showed that the average value of the cold water was 14.09°C during the 3 years of measurements. Moreover, it was shown that this temperature increased by about 0.4°C as a result of heat exchange with the air inside the substation. In the article, the author proposed modifications of coefficients in a commonly used model developed by National Renewable Energy Laboratory for determining the temperature of mains water in energy simulations. The proposed changes allow for accurate modelling of the cold water temperature under the climate conditions of north-eastern Poland.

An analysis of low flow for solar thermal system for water heating

The mass flow rate in the collector loop of a solar domestic hot water system (SDHW) affects its thermal performance. The initial investment and the operation cost are also affected by the selection of the primary flow. Common design rules state a standard specific flow rate of 50 l/hm2 for most collector models. However, the emergence of electronically commuted motors recommends reviewing the interest of the low flow alternative (7–14 l/hm2) for solar thermal systems.In this paper, the thermal performance of a typical serpentine collector has been measured for different mass flow rates. The resulting performance curves and associated measurement uncertainty bands show only a moderate improvement in performance as the flow rate increases. Once the collector thermal behaviour has been characterized, the whole system is modelled, and the initial investment and operating cost are calculated for two design options: high flow (80 l/hm2) and low flow (20 l/hm2). As expected, the solar fraction is slightly higher for the high flow system (4.6% higher) and the number of hours of operation is lower for this system (4.4% less hours of operation).Considering the lower investment cost of the low flow system, the best thermal behaviour of the high flow system requires near 18 years to amortize the largest investment. If other considerations like embodied energy are accounted for, the common practice in designing SDHW systems should promote low flow.

Numerical and experimental study on the thermal performance of the concrete accumulator for solar heating systems

The article presents the concept of the solar facility operating in the domestic hot water and space heating system, equipped with thermal energy storage based on a water tank and an auxiliary storage module made of concrete elements. A mathematical model of transient heat transfer in the concrete structure using the Control Volume Finite Element Method (CVFEM) has been proposed. The method allows modelling the transient heat conduction based on a rare mesh of nodes in a relatively short time, with accuracy comparable to traditional Finite Element Method (FEM) results including CFD modelling. A laboratory stand has been made for the verification of the model, and a set of comparative measurements has been carried out.

Energy efficiency measures implemented in the Dutch non-profit housing sector

The existing housing stock plays a major role in meeting the energy efficiency targets set in EU member states such as the Netherlands. The non-profit housing sector in this country dominates the housing market as it represents 31% of the total housing stock. The focus of this paper is to examine the energy efficiency measures that are currently applied in this sector and their effects on the energy performance. The information necessary for the research is drawn from a monitoring system that contains data about the physical state and the energy performance of more than 1.5 million dwellings in the sector. The method followed is based on the statistical modeling and data analysis of physical properties regarding energy efficiency, general dwellings’ characteristics and energy performance of 757,614 households. The outcomes of this research provide insight in the energy efficiency measures applied to the existing residential stock. Most of the changes regard the heating and domestic hot water (DHW) systems, and the glazing. The rest of the building envelope elements are not improved at the same frequency. The results show that the goals for this sector will be hard to achieve if the same strategy for renovation is followed.

Energy efficiency state of non-profit housing stock in the Netherlands

Improving energy efficiency of buildings is widely considered as the one of the most promising, fast and cost-effective ways to mitigate climate change and achieve the 2020 and 2050 goals set for the built environment (European Commission 2011; Aedes 2017). Energy efficiency of the building stock is hard to achieve if we only focus on the design of new dwellings. In this chapter, we will analyse the energy efficiency state of the existing Dutch non-profit housing stock using data from 2015. We examine the energy efficiency state of the stock using data from the SHAERE monitoring system. The data from SHAERE include the age, type, useful floor area, thermal resistance (Rc-value) of the envelope (roof, facades and floor), thermal transmittance (U-value) of the windows, heating and domestic hot water (DHW) systems, ventilation system, the predicted heating energy consumption and energy production systems, if present. We also use actual heating energy consumption data from Statistics Netherlands to calculate the mean actual energy consumption of the stock. The chapter aims at setting the current energy performance state of the Dutch non-profit housing stock. A complete and detailed assessment of the current efficiency state of the non-profit housing stock in the Netherlands is necessary in order to examine the energy renovation pace and energy saving measures realised. The following sections present the results and conclusions drawn from this chapter. Section 2.2 presents the development of energy efficiency policies in the built environment. The SHAERE monitoring system is presented in 2.3. Section 2.4 sums up the methods used. Section 2.5 brings attention to the results of the research study. Section 2.6 presents the conclusions of this chapter.

Comparison of two dynamic approaches to modelling solar thermal systems for domestic hot water

In developing countries, the increase in the electricity access and therefore in the energy consumption through distributed energy solutions, leads to searching energy saving strategies. Solar Thermal Systems (STS) have been widely used to increase energy efficiency in residential sector in many countries, and several models are being developed to improve their performance and deployment. However many of existing software tools somehow fail to provide more sensitivity analysis to different parameters of STS performance, given their wide applicability.In this paper, two dynamic approaches to model STS are discussed: a developed hourly model based on energy balance of the STS components, and the simulation tool Polysun. A sensitivity analysis is made to different domestic hot water demand profiles and tank sizes, using as case study, a typical 5-person family house in Maputo, Mozambique.The results show that the developed hourly model can be used to evaluate and size solar thermal systems, having similar results to Polysun. However, regarding the auxiliary heating, Polysun approach leads to a higher or lower electrical auxiliary heating, depending on the control layer, resulting in over-sizing or under-sizing of the system, given that it considers the temperatures stratification while the developed model considers the energy balance in the tank as a whole.

Design of a New Solar Thermal Collector with Ceramic Materials Integrated into the Building Facades

The work presented here aims to demonstrate the technical, architectural, and energy viability of solar thermal collectors made with ceramic materials and their suitability for domestic hot water (DHW) and building heating systems in the Mediterranean climate. The proposal is for the design of a ceramic shell, formed by collector and non-collecting panels, which forms part of the building system itself, and is capable of responding to the basic requirements of a building envelope and harnessing solar energy. Ceramics considerably reduce the final cost of the collector system and offer the new system a variety of compositional and chromatic finishes, occupying the entire building surface and achieving a high degree of architectural integration, although less energy-efficient compared to a conventional metallic collector.

Uncertainty quantification and sensitivity analysis of the domestic hot water usage in hotels

The water heating system is a major contributor to building energy consumption and carbon emissions in the United States, especially for the Hotel/Motel sector. Various factors in the design and operation stages are found to have great influences on the hot water usage and associated energy usage. There has been an increased number of studies on optimizing the design and sizing of the water heating system in commercial buildings in recent years. However, most of these studies focused on the collection and analysis of the actual data of hot water usage with rare acknowledgments of uncertainties from a variety of influential parameters such as occupant behaviors and operational schedules. The current understanding of the sensitivity of the hot water usage related to these influential factors is still limited.This paper aims to conduct an uncertainty and sensitivity analysis (UA & SA) to investigate the behavior of the domestic hot water (DHW) usage in hotels and its key influencing factors. An EnergyPlus Monte Carlo simulation is performed by using the large hotel building prototype model developed by the U.S. DOE as the baseline model. 161 input parameters ranging from equipment parameters (e.g., size, efficiency, operation schedules, etc.) to occupant behaviors are perturbed using Monte Carlo and Karhunen-Loève expansion sampling methods. Eight outputs associated with the hot water usage (i.e., the peak/annual whole building water consumptions, DHW system water consumption, DHW system gas consumptions, and DHW system electricity consumptions) are specified as the outputs of interest. Five locations, which are Burlington, VT; Chicago, IL; San Francisco, CA; Houston, TX; and Miami, FL are selected to investigate the influence of the climate condition. 3000 sample EnergyPlus files are created for each location. Two indicators (i.e., the PEAR index, and the variance-based Sobol index) are computed for the sensitivity analysis. It suggests that the SA results from the PEAR index and the Sobol index are very similar in this case study.

Test method for evaluating and predicting thermal performance of thermosyphon solar domestic hot water system

A test method for evaluating and predicting the thermal performance of thermosyphon Solar Domestic Hot Water (SDHW) system was proposed. The evaluating mathematical model of SDHW system was developed based on the two-node theory – a SDHW system was divided into the solid part and the fluid part. By combining the dynamic energy conservation equations of the solid part and the fluid part, the evaluating mathematical model of SDHW system was derived. The model parameters have clear physical meaning which can be used to evaluate the SDHW systems. The evaluating mathematical model was further processed by using the Laplace transformation technique and the predicting mathematical model was then derived. The predicting model can be used to predict the thermal performance of SDHW system for short and long term period with flexible draw off load conditions. The experimental method was designed and experiments were carried out to validate the test method. The measured mean fluid temperature in the storage tank was compared to the predicted mean fluid temperature. The annual thermal performance prediction of the system with two draw off load conditions at different daily hot water consumptions was also carried out.

Fluid Flow Control in Domestic Hot Water Systems During Days with Different Radiative Stability Levels

Abstract This paper presents models/strategies for optimum performance of solar collector in closed loop systems. These models aim to maximize the obtained energy by thermal conversion of solar energy. The mass flow rate of the fluid from the primary circuit of the system is the control parameter. The semi empirical models and optimal control methods are in brief presented. The volume of the storage tank is important and the ratio Vs/Ac between this volume and area of the collectors is a key factor in appropriate sizing of the DHW system. Therefore, the paper establishes a relationship between this ratio and the mass flow rate of the fluid in the collector This paper also analyses the variation of the energetic performance (useful heat flux transferred to the storage tank, heat flux transferred to the water, water temperature in the storage tank) with the volume of the storage tank. Analysis was performed on an extensive set of meteorological data from Timisoara, Romania, with instantaneous data (measured at 15 seconds) for summer days, from July 2009, with different relative sunshine values, σ. Important differences have been observed between days with different stability levels - days more or less stable.

Experimental Study of the Air Heat Pump for Domestic Hot Water

The article contains the results of the experimental research of the air heat pump for the preparation of domestic hot water (DHW). An installation consisting of a modular heat pump for hot water connected to two storage tanks with a capacity of 130 dm3 each was the object of the research. The article presents the results of investigations on the influence of the supply air temperature in the evaporator cycle and the variable heat load of the condenser on the heating capacity of the heat pump and the coefficient of performance (COP). The tests were carried out for water heating cycles in the storage tank from room temperature to 50 °C. The research shows that heating water in a 130 dm3 storage tank with ventilation or external air at a temperature above 15 °C takes an average of 2 h, and the heat pump consumes approx. 2.2 kWh of energy per heating cycle. Pump operation in winter is possible with the use of ventilation air, but with the discharge of air cooled outside the building. In order to ensure conditions for effective compressor operation, it is advisable to gradate heat load of the heat pump. The optimal solution is to use a circulating pump with smooth regulation of performance. The air source heat pump for DHW heating is an ideal solution for heating systems equipped with solid fuel boilers. It is a maintenance-free and economical system for producing domestic hot water outside the heating season.

100% 에너지자립 제로에너지주택을 위한 비용효과적 신재생 설비시스템 최적구성에 관한 연구

Purpose: The domestic thermal insulation standard value has significantly increased to realize the Zero Energy House and many passive houses or zero energy houses are being built recently. Passive technology, which is represented by high thermal insulation and high density, shows relatively stable implementation by development of building materials and accumulated construction experience. On the other hand, there are not matured technologies for heating and cooling, hot water supply and ventilation including new and renewable energy. This study investigated the possibility of constructing optimal renewable energy and facilities system in terms of cost and effectiveness for zero energy houses that can achieve 100% of energy independence rate at current level. Method: The target building is a single story house with a floor area of 100 ㎡ located in Gyeonggi-do. Outer wall and roof floor are composed of 200mm SIP (Structural Insulation Panel) structure and window is vacuum window with U = 0.5 w/㎡℃. As a building equipment, this study considered following systems: ground source heat pump (GSHP), air source heat pump (ASHP), electric heating boiler (EHB), electric cable heating (ECH), electric air conditioner (EAC), solar domestic hot water system (DHWS), and solar PV. Finally, this study selected four combinations of systems (GSHP, ASHP+EAC, EHB+EAC, ECH+EAC) for the investigation. Result: This study assumed that all the loads in the building are covered by electric energy, and the calculation of the annual energy cost was based on the current electric charge system. Therefore, all loads are supplied by domestic electricity except GSHP. In addition, this study assumed that all renewable energy facilities for 100% energy self-reliance are supplied by solar power and then calculated the capacity to cover all household electricity with PV to derive the range of required PV capacity. Finally, this study calculated the initial investment cost range for each system configuration and the investment payback period, and determined the cost effective system configuration.

Techno-economical analysis of building envelope and renewable energy technology retrofits to single family homes

In recent years, the popularity of single family homes, which have higher energy intensity than multi-family homes, has increased steadily in Turkey. This trend can be contributed to the interest of middle and high-income families towards living in larger homes, which also offer more privacy. Since multi-family homes are prevalent in Turkey, various studies are conducted to investigate the application of energy efficiency measures to these type of homes. Due to the increase in the number of single family homes and lack of research conducted to reduce the energy consumption for these type of dwellings, determining the feasibility of energy efficiency measures for the Turkish single family housing stock is an important concern. In this study, the techno-economic feasibility of applying a wide range of energy efficiency measures and renewable energy technologies to existing single family homes is investigated using monitored energy consumption data and building energy simulation program. The findings are extrapolated to the existing single family housing stock in three major cities of Turkey, namely Ankara, Istanbul, and Izmir, to estimate the potential for energy and emission reductions in Turkey. The results indicate that applying window glazing, roof, and a combination of window, wall, and roof improvements reduce heating energy demand by 21%, 34%, and 50%, respectively, with favorable payback periods. Among the renewable energy technologies analyzed, solar domestic hot water system results in the highest energy savings with the shortest payback period. Applying the combination of wall, window, and roof improvements and the retrofit of solar domestic water heating systems to existing single family homes in Ankara, Istanbul, and Izmir result in reductions of about 14 million, 8 million, and 15 million m3/year natural gas consumption in Ankara, Istanbul, and Izmir, respectively. These results can be used to develop policies for building insulation and equipment standards towards achieving low energy and emission national housing stock.

Simulation study of a combined solar and heat pump system for heating and domestic hot water in a medium rise residential building at Concepción in Chile

Combined solar and heat pump (SHP) systems have not yet been introduced massively in Chile. On the other hand, large-scale residential buildings offer an interesting emplacement for applying these kinds of systems, but the methodologies for predicting accurately its performance are not so obvious. Thus, this paper presents the modelling of a SHP system designed for a five floor residential building, developed in TRNSYS 17. First, a detailed model of a residential building is done to understand their thermal behaviour. In this analysis, it is determined that the heat load of each building apartment depends strongly on its location. Notably, the first floor is the most demanding one, reaching the highest load for an apartment: 7.52 (kW). The total heat load of the buildings is 348.35 (kW) and the total space heating energy demand in winter season is 932,295 (kWh). On the other hand, two parallel SHP systems with air-to-water heat pumps are simulated: one for the domestic hot water demand; the other one for the heating demand. For evaluating the latter, a reduced simulation model is considered by coupling the system to 18 different air nodes, selected in function of their location in the building. The results show that the SPF for a same system in different apartments depends primarily on its heating demand. Thus, the individual components performance remains practically invariant. This allows to estimate the overall performance of a centralized heating system for the whole building, whose predicted SPFheat is 4.64 using Flat Plate Collectors (FPC) and 4.88 using Evacuated Tube Collectors (ETC). On the other hand, the performance figure of the DHW system is lower, reaching SPFDHW of 3.93 and 4.27 using FPC and ETC respectively ETC in a system that provides around 378,353 (kWh) useful energy a year.

Optimization of Photovoltaic Self-consumption using Domestic Hot Water Systems

Optimization of Photovoltaic Self-consumption using Domestic Hot Water Systems

Analysis of Numerical Error in One-Dimensional Storage Tank Models for Solar Energy System Simulations

This study investigates the temperature profiles predicted by trnsys one-dimensional (1D) thermal storage tank models for typical charging conditions. Simulation parameters, such as grid spacing and time-step size, were varied to observe the changes in the numerical error when compared with an exact analytical solution. A Taylor series expansion was also performed on the discretized, 1D, advection–diffusion equation to obtain an expression for this numerical error. A numerical diffusion term was found which could be used to improve the prediction of the temperature profile in a storage tank simulation. Finally, the influence of this error on predictions of the annual solar fraction for a domestic hot water system was explored.

Investigation of PCM charging for the energy saving of domestic hot water system

In this paper an investigation on the charging process of a phase change material (PCM) integrated in a domestic hot water system is presented. In order to increase the amount of the stored energy in a limited portion of time during maximum solar radiation it is preferred to reduce the melting time of the PCM used in the heat exchanger. Therefore the effect of mass distribution of a PCM in a multi-tube heat exchanger is studied. Paraffin RT50, is used as the PCM and water as the heat transfer fluid (HTF) carries the energy gained in solar flat plate collector. Enthalpy porosity method is applied for modeling the phase change process and an experimental result is used to validate the model. There are six different cases in order to examine the effect of mass distribution on the melting time to reach the minimum value. Temperature and heat flux versus time as well as liquid fraction contours and behavior of the charging process are described. The results show that by distributing the PCM mass in a specific arrangement in which 40% of PCM mass is in inner tube, 52% reduction in melting time is achieved hence solar energy can be used more efficiently in the time of maximum solar radiation.

Numerical and empirical evaluation of a novel building integrated collector storage solar water heater

Abstract Integrated collector storage is a long established simple low cost solar water heater configuration combining the solar collector with a storage tank into a single unit. Previous studies have shown the potential of integrated collector storage solar water heaters to significantly reduce domestic energy requirements for water heating, however challenges still remain to integrate them in roof/facades and ensure appropriate domestic hot water demand. In this article, a novel integrated collector storage solar water heaters is being investigated. The configuration and geometry proposed incorporates an embedded heating element to provide a self-contained domestic hot water system and consider roof integration restriction allowing the unit to be embedded within a structural insulated roofing panel system. The proposed system also utilizes an inlet diffuser designed to reduce the disruption to the stratification within the storage during and following draw-off. This article presents a Computational Fluid Dynamic analysis of internal flows and heat transfer regimes within this new collector configuration and compares its performance against previous developed prototypes using empirical testing. The increased aspect ratio of the new design was shown to significantly alter the heating and cooling characteristics of the collector, both gaining and loosing heat at a greater rate than the original prototype. The computational analysis showed that the collector charges effectively with some stratification. Higher draw-off rates however resulted in higher bulk water outlet temperatures, providing better energy delivery efficiency. The inlet diffuser was also shown to improve the thermal efficiency of the unit overall. The empirical testing shows the improvement in performance of this novel integrated collector storage solar water heaters against previous developed prototypes. The study highlights the need to review the effect of draw-off regime upon the performance of such systems in order to identify optimal regime and control strategy.