Domestic Hot Water Demand Research Articles

A comprehensive feasibility study of applying solar energy to design a zero energy building for a typical home in Tehran

In this paper, a comprehensive feasibility study of solar zero energy building for a typical detached house in Tehran is investigated. This house is designed with respect to a moderately warm climate and a family of four members. Using meteorological data, house loads are calculated. Substantial part of total heating and cooling load is provided by applying Trombe-wall, roller shading and thermal mass as main passive strategies. A solar absorption heat pump is utilized to supply both heating and cooling demands. An optimization is done to determine the appropriate combination of flat-plate and evacuated collectors. Domestic hot water demand is also supplied through the common tank. Fiber optics provides the lighting by transmitting natural sunlight to the inner spaces of the house. DIALux 4.1 is used to model the lighting system. Photovoltaic panels are chosen to generate electricity that is stored in batteries. Remaining energy is sent to the grid. Regarding environmental features, rate of reduction of released CO2 to the atmosphere is calculated per house. Finally, by exploiting present worth method, rate of return is discussed with respect to present energy cost. Sensitivity analysis shows that only with actual prices of energy and low interest rate, the investment is justified.

Analysis of Net Zero-energy Building in Spain. Integration of PV, Solar Domestic Hot Water and Air-conditioning Systems

In this work, global energy balances for grid-connected Spanish buildings have been carried out to evaluate the potential of self- consumption applying European Directives. Using the software TRNBuild, five three-story buildings have been created and run in TRNSYS Simulation Studio. Four end-user categories (hospitals, offices, shopping center, schools) and five Spanish provinces with different weather conditions have been selected to calculate total thermal, electrical and domestic hot water (DHW) consumptions. It was assumed thermal (heating and cooling) and DHW demands could be supplied without direct consumption of fossil fuels, using air-to-air heat pumps and solar collectors with electric auxiliary resistances. Hence, for each case, a global electrical balance (discounting solar thermal contribution) between demands and the PV array production has been performed. Finally, parametric and economic analyses have been carried out, demonstrating the feasibility of these systems.

Minimization of the Residual Energy Demand of Multi-storey Passive Houses – Energetic and Economic Analysis of Solar Thermal and PV in Combination with a Heat Pump

The optimum share of PV and Solar thermal in combination with air sourced heat pumps or ground water heat pumps is determined for multi-family passive houses depending on the demand for heating and domestic hot water. Starting with an actual project, Innsbruck Vögelebichl the optimum configuration is determined by means of simulation. More general results are derived by virtually changing the number of storeys. Results are investigated with respect to energetic and economical aspects.

A Simplified Procedure for Sizing Solar Thermal Systems; Based on National Assessment Methods in the UK and Ireland

Solar heating systems have the potential to be an efficient renewable energy technology, provided they are sized correctly. Sizing a solar thermal system for domestic applications does not warrant the cost of a simulation. As a result simplified sizing procedures are required. The size of a system depends on a number of variables including the efficiency of the collector itself, the hot water demand and the solar radiation at a given location. Domestic Hot Water (DHW) demand varies with time and is assessed using a multi-parameter detailed model. Secondly, the national energy evaluation methodologies are evaluated from the perspective of solar thermal system sizing. Based on the assessment of the standards, limitations in the evaluation method for solar thermal systems are outlined and an adapted method, specific to the sizing of solar thermal systems, is proposed. The methodology is presented for two common dwelling scenarios. Results from this showed that it is difficult to achieve a high solar fraction given practical sizes of system infrastructure (storage tanks) for standard domestic properties. However, solar thermal systems can significantly offset energy loads due associated DHW consumption, particularly when sized appropriately. The presented methodology is valuable for simple solar system design and also for the quick comparison of salient criteria.

Integrated Solar Thermal System for Water and Space Heating, Dehumidification and Cooling

This paper describes the design, construction and initial experimental performance testing of a novel integrated solar thermal system prototype for the provision of space cooling and dehumidification, space heating and domestic water heating. The integrated system aims to replace and duplicate the performance of conventional vapour compression air conditioning and domestic water heaters, and is designed to operate effectively in hot and humid environments, using a liquid desiccant dehumidifier and indirect /direct evaporative cooling components. The liquid desiccant is regenerated using a custom designed heat exchanger that is driven by a solar generated hot water, which is also used to meet domestic hot water and space heating demands. Initial regenerator and cooling results are shown, the latter of which are compared with TRNSYS based simulations.

Large Solar Assisted Heat Pump Systems in Collective Housing: In-situ Monitoring Results for Summer Season

This article presents the behavior of an existing system combining solar collectors and heat pumps at large scale (10’000 living m2, more than 1’000 m2 solar collectors) for space heating and domestic hot water production, focusing on summer period. Ongoing detailed monitoring enables to measure its energy performance. The monitoring results for 2012 show a system SPF of 2.9 (2.6 in winter and 4.4 in summer). The direct solar fraction in summer is lower than 50%, which is low considering the oversizing of the solar collector area for domestic hot water production. The high domestic hot water demand (∼50 kWh/m2/yr whereas the usual value is around 20) can partly explain this low value, but other factors should also be considered. The results presented in this article are part of a research project aiming to assess the relevance of the concept of coupling solar thermal and heat pumps in various types of building (especially existing buildings with low efficient thermal envelope).

Life Cycle Assessment of Central Solar Heating Plants with Seasonal Storage

Renewable energies can play a very important role in the development of a new energy model contributing effectively towards a more sustainable development in the mid and long term. In this context Central Solar Heating Plants with Seasonal Storage (CSHPSS) are able to provide space heating and Domestic Hot Water (DHW) to residential buildings with high solar fractions (>50%). These systems are already being used in Central and Northern Europe, as well as in Canada, where there is an important experience in district heating systems. Life Cycle Assessment (LCA) is an objective methodology that evaluates the environmental loads associated with a product, process, or activity, identifying and quantifying the use of mass and energy as well as environmental emissions over its life cycle. It provides a comprehensive view of the environmental aspects of a product or process and a more accurate picture of the true environmental trade-offs in product and process selection. In this paper is presented a LCA of a CSHPSS, which should cover the space heating and DHW demand of 500 dwellings of 100 m2, located in Zaragoza, Spain. Environmental burdens through the life cycle of the system are estimated based on relevant emissions to the atmosphere, e.g. greenhouse gases, NOx, SOx, and comprehensive environmental indicators as, for instance, the IMPACT 2002+ and CED (Cumulative Energy Demand). These indicators allow to evaluate the reduction of the environmental load achieved by the CSHPSS analyzed with respect to conventional space heating and DHW systems, as well as to identify the most critical aspects since an environmental perspective.

Sizing of thermal energy storage devices for micro-cogeneration systems for the supply of domestic hot water

Cogeneration technologies are increasingly being utilised in the construction sector. Micro-cogeneration technologies only become economically feasible after they have been in operation over a lengthy period of time and this makes necessary the sizing of appropriate storage systems. The integration of cogeneration within overall heating and cooling loads requires the use of complicated simulation codes. However the need for this integration can be removed with the design of a cogeneration system which only covers the thermal demand required for the provision of domestic hot water, this demand being relatively easy to forecast. Based on a given domestic hot water demand, a calculation procedure for sizing the storage system is presented. This procedure is experimentally validated with only minor differences between expected and actual results, this being attributable to the limitations of the experimental set-up. It achieves more than acceptable results when compared with other model designed for heating applications in the building sector.

Solar Assisted Ground Source Heat Pump Performance in Nearly Zero Energy Building in Baltic Countries

Abstract In near zero energy buildings (NZEB) built in Baltic countries, heat production systems meet the challenge of large share domestic hot water demand and high required heating capacity. Due to passive solar design, cooling demand in residential buildings also needs an assessment and solution. Heat pump systems are a widespread solution to reduce energy use. A combination of heat pump and solar thermal collectors helps to meet standard requirements and increases the share of renewable energy use in total energy balance of country. The presented paper describes a simulation study of solar assisted heat pump systems carried out in TRNSYS. The purpose of this simulation was to investigate how the performance of a solar assisted heat pump combination varies in near zero energy building. Results of three systems were compared to autonomous (independent) systems simulated performance. Different solar assisted heat pump design solutions with serial and parallel solar thermal collector connections to the heat pump loop were modelled and a passive cooling possibility was assessed. Simulations were performed for three Baltic countries: Lithuania, Latvia and Estonia.

The impact of scheduling appliances and rate structure on bill savings for net-zero energy communities: Application to West Village

This paper investigates the financial incentives of load shifting under a time-of-use rate and Net Energy Metering pertaining to the solar net-zero energy apartment community, West Village in Davis, California. By “smart-scheduling” the electricity and domestic hot water demand of the dishwasher, clothes washer, dryer, sinks and showers solely to off-peak periods, the peak demand is reduced by 18%, the part-peak demand by 32% and the off-peak demand increased by 12%. With this shifted schedule customers accrue twice as many credits as they would receive under a non-shifted schedule with the same time-of-use rate, totaling to $2975 of “free” electricity per year for one 12unit building. But, under current rates smart-scheduling is found to be worthwhile only during the months from May through October, when 96% of the credits are accumulated. If the rate schedule is altered to include peak-periods during the winter months, the credit savings will double again in value. These comparisons are prepared using two photovoltaic simulation programs (PolySun by Vela Solaris and System Advisory Model by the National Renewable Energy Laboratory) and for apartments using an electric heater and a heat pump for domestic hot water. By quantifying these savings, PV generating customers are informed that a time-of-use rate can benefit them significantly, especially if the surplus generation is maximized and sold to the grid during peak day time hours. With this information, housing developers can create effective incentives for residents, and utility companies, policy makers and designers of smart-scheduling household appliances can encourage a more reliable, clean and economical national grid.

Hellenic renewable energy policies and energy performance of residential buildings using solar collectors for domestic hot water production in Greece

Total final energy consumption in Hellenic buildings reached 6.5 × 106 tons of oil equivalent (Mtoe) or 34.2% of the total (2010), of which 4.6 Mtoe in residential buildings. National implementation of the European Directive on the energy performance of buildings (EPBD) in Greece since 2010 is the first coordinated attempt to improve the energy performance of Hellenic buildings. In this framework, as of 2011, new buildings have an annual solar fraction of 60% for sanitary hot water production from solar thermal systems. Efforts are currently underway to comply with the EPBD recast so that by the end of the decade, all new buildings are nearly zero-energy buildings and that the very low amount of energy required should be covered to a very significant extent by energy from renewable energy sources (RESs). At the same time, the unprecedented financial crisis and escalating energy costs in Greece have reemphasized the need to explore the opportunities of renewables and energy conservation measures (ECMs). This paper reviews the relevant RES policies and status, with an emphasis to the Hellenic buildings. Using Hellenic typical residential buildings, the national requirements, and methodologies, this work quantifies the benefits of using solar thermal collectors to cover 100% of the domestic hot water demand. The results illustrate that, even as a single action, this popular ECM can improve the energy class of existing residential buildings and in some cases even reach an energy class-B, which is the minimum requirement for new buildings. Combining with other cost effective ECMs and exploiting RES for space heating and cooling can help building owners to not simply comply with new regulations but most important reduce the operational cost of buildings while maintaining a comfortable indoor thermal environment.

Sizing the prime mover of a residential micro-combined cooling heating and power (CCHP) system by multi-criteria sizing method for different climates

In the present study, a multi-criteria sizing function (MCSF) is proposed for designing the optimum size and operating strategy of the prime mover of a residential micro-combined cooling heating and power (CCHP) system. The CCHP prepares the electrical, thermal, cooling, and domestic hot water demands of the same building in five different climates in Iran. The MCSF integrates fuel energy saving ratio (FESR) and exergy efficiency as the thermodynamical parameters, net present value, internal rate of return and payback period for the economical criteria, and CO2, CO and NOx reduction for the environmental evaluations. Analytical hierarchy process is used to weigh each criterion with respect to others. The engine proposed by MCSF results in considerable fuel saving and pollution reduction and a payback period of about 6 years for the 5 climates. In addition, the best strategy according to the engine size is determined for every climate.

Heat Consumption Assessment of the Domestic Hot Water Systems in the Apartment Buildings

This study presents the analysis of energy consumption for domestic hot water in apartment buildings in Riga, Latvia. The aggregate data contains information about 39 apartment buildings, including heat energy consumption and domestic hot water (DHW) consumption. The analysis is focused on the heat energy consumption and seasonal characteristics in the DHW system. The analysis characterizes the DHW consumption, energy consumption for DHW and energy losses in the DHW systems in apartment buildings. The energy consumption of DHW needs of households and some other building sectors constitutes a significant part of the building's energy balance. The building energy efficiency improvement measures reduce the heating energy required proportion and logically increase the share of energy consumption for DHW needs. It is likely that the production and distribution of DHW in buildings will constitute a dominant share of both the present, and in particular, the future energy design requirements of buildings. (1) Previously studies carried out in various European countries (2), (3), (4), China (5), (6), Japan (7), (8), (9), USA (10), (11), Canada (12) points the many differences in DHW consumption as well as the tendency to change over time due to a global increase of energy prices, changes in technologies, introducing of individual metering, as well as wide variety of other factors that may appear on local or regional level. Measurements in Denmark documented not only a relatively high energy consumption for DHW in apartment buildings, but also recorded surprisingly large heat losses from the DHW circulation lines (13), (14). Recent investigation of 24 buildings in Danmark shows that most of the energy demand for DHW is lost in the circulation system. The efficiency was 0.30-0.77 (heat loss 23-70%) in apartment buildings and efficiency 0.11- 0.46 (heat loss 54-89%) in office buildings. (1) The Energy Performance of Buildings Directive (EPBD) (15) in the version of 2010, the so-called recast EPBD, demands in annex I 'Common general framework for the calculation of energy performance of buildings (referred to in Article 3)' that '(1) the energy performance of a building shall be determined on the basis of the calculated or actual annual energy that is consumed in order to meet the different needs associated with its typical use and shall reflect the heating energy needs and cooling energy needs (energy needed to avoid overheating) to

Energy Saving and GHG Emission Reduction in a Micro-CCHP System by Use of Solar Energy

Abstract In this work, the reduction of greenhouse gas emission, and the energy saving by integrating solar collectors and photovoltaic panels in a Stirling engine based microcombined cooling, heating and power (mCCHP) system are studied. The mCCHP system consists of a natural gas Stirling CHP and an adsorber chiller. When the thermal outputs of the Stirling CHP and solar collectors are not sufficient to cover the heat demand for domestic hot water (DHW), heating/cooling, an auxiliary heating boiler starts to operate. The energy saving by using solar energy varies from 13.35% in December to 59.62% in April, in the case of solar collectors usage and from 7.47% in December to 28.27% in July, in the case of photovoltaic panels usage. By using solar energy the annual GHG emission decreases by 31.98% and the fuel cost reduction varies from 12.73% in December to 49.78% in June.

Energy and exergy analysis of low temperature district heating network

Low temperature district heating with reduced network supply and return temperature provides better match of the low quality building heating demand and the low quality heating supply from waste heat or renewable energy. In this paper, a hypothetical low temperature district heating network is designed to supply heating for 30 low energy detached residential houses. The network operational supply/return temperature is set as 55 °C/25 °C, which is in line with a pilot project carried out in Denmark. Two types of in-house substations are analyzed to supply the consumer domestic hot water demand. The space heating demand is supplied through floor heating in the bathroom and low temperature radiators in the rest of rooms. The network thermal and hydraulic conditions are simulated under steady state. A district heating network design and simulation code is developed to incorporate the network optimization procedure and the network simultaneous factor. Through the simulation, the overall system energy and exergy efficiencies are calculated and the exergy losses for the major district heating system components are identified. Based on the results, suggestions are given to further reduce the system energy/exergy losses and increase the quality match between the consumer heating demand and the district heating supply.

Combining Heat Pumps with Solar Energy for Domestic Hot Water Production

In a simulation study two combinations of air-to-water heat pumps with either solar thermal collectors or photovoltaics have been scrutinized. Other heating systems have been included in the comparison. All system components applied are field proven and available on the market. Although all heat generators were sized to cover space heating and domestic hot water demand, the focus lays on domestic hot water preparation. As required by local regulations, all systems cover 50% of the final energy demand from solar insolation. The results show that both air- to-water heat pump combinations are nearly equivalent regarding economic feasibility and environmental impact.

The Influence of Energy Conservation on the Performance of Solar Thermal Systems – A Cold Country Case Study

The European Union has set a goal that the energy use in the built environment shall be reduced by 41% to the year 2050 compared to 2005-2006. This could introduce new opportunities for solar thermal systems in cold countries. In such countries, like Sweden and Canada, the economy in solar thermal collector installation projects is often spoiled by the fact that most of heating energy demand of the building occurs during periods when the available solar energy is low.The present paper investigates the performance of solar thermal systems subjected to different quota between space heating and domestic hot water demand (DHW). This study investigates the performance of a solar thermal system integrated to four different buildings with varying heating loads in two different locations, Sweden and Canada. Models of single family houses are created which are able to simulate the total heating demand with different heating demand profiles but the same DHW demand. Simulations are performed in TRNSYS, an advanced tool used to simulate transient systems. Results indicate that solar combisystems tend to generate more useful energy and therefore be more cost effective when installed in buildings with higher heating demands.

Solar Systems for Heating and Cooling of Buildings

Recently, the concept of net zero energy buildings has become a major topic in the R&D work on future buildings. In order to achieve a zero energy balance on annual level energy saving and energy efficiency measures have to be fully exploited. However, a demand for active heating and/or cooling will remain in most buildings and under most climatic conditions. Solar energy is the main on-site renewable energy source which can be used to achieve a high fraction of renewable energies to cover the remaining energy demand in buildings. Main energy needs in buildings are due to heating and/or cooling, depending on local climatic conditions and type of building. In this paper principle ways of covering part of the demand for heating, cooling and domestic hot water by using solar technologies are discussed and a design study of a solar thermally driven heating and cooling system for a virtual hotel is presented. A model of the same hotel has been investigated under various climatic conditions in order to study the impact of sizing of key components on the overall performance. In addition an analysis of economic performance is presented for the example of the location Malta in Mediterranean Sea.

SOFC Management in Distributed Energy Systems

Among the distributed generation emerging technologies, solid oxide fuel cells (SOFCs) seem to be the most promising for small and medium power (up to 1 MW) as they feature extremely high efficiency and low pollutant emissions, and the high-grade waste heat can be utilized for space heating, process steam, and/or domestic hot water demands. As their main drawbacks are high cost and relatively short lifetime, much research is devoted to solve technological problems and to develop less expensive materials and mass production processes. However, even if SOFCs are close to commercialization and several demonstration units are already running, only few researches have been performed on their integration in power plants for distributed power generation, which are complex systems made up of different components that have to satisfy energy requirements (heat, electricity, and cooling). In this paper, we investigate the behavior of SOFCs in distributed energy systems and how their operation in terms of load and fuel utilization factor could optimize fuel consumption and/or minimize energy costs. The potential advantages of SOFCs related to their excellent part-load operation and their ability to meet and follow the highly noncoincident electric and thermal loads in either grid-connected or stand-alone configurations are discussed.

Thermodynamic and Economic Analysis for Simple Cogeneration Systems

ABSTRACT Many countries in Europe promote cogeneration as a way to meet energy needs in residential and commercial buildings. They do this to save primary energy and reduce CO2 emissions. This article presents an energy and economic analysis approach for cogeneration plants hosted by such buildings. The plants use gas-fired internal combustion engines as prime movers. Technical criteria to characterize annual operation for cogeneration systems with seasonally and daily variable heat demand are defined. The focus is on determining the total engine size or output by considering different operational strategies. The methodology is illustrated by applying it to a cogeneration plant that meets domestic hot water and heating demand in a residential complex in Spain. The resulting graphical analysis allows one to compare various operational strategies.