Domestic Hot Water Preparation Research Articles

Systematic investigation of building energy efficiency standard and hot water preparation systems’ influence on the heat load profile of districts

Heat load profiles of new residential developments in rural, sub-urban, and urban context were generated by means of a generic model and dynamic simulations. The combined effect of district building density, building energy efficiency standard, and hot water preparation system on the heat load is discussed in detail. Hundred residential districts representing medium sized developments were defined by varying the distribution of building types. Therefore, a simplified building typology of 13 fictitious buildings was developed. The presented methodology allows to quickly estimate the total heat demand of new residential developments based on the plot ratio and buildings’ energy efficiency standard only.The investigations reveal that the building density as well as the hot water preparation system have a significant impact on the yearly district heating return temperatures. Instantaneous domestic hot water preparation results in up to 14 K lower annual average district heating return temperatures. However, the building density also has a significant influence on the return temperature, resulting in important differences between urban and rural districts.

Solar energy as a tool of renovating soviet-type multi apartment buildings

The paper analyses the energy and technical possibilities of installing systems that use renewable energy sources (solar energy) to renovate soviet type apartment buildings. The aim of the analysis is to study the possibilities of using solar energy systems to renovate apartment buildings (five-storey, nine-storey and sixteen-storey), which are built in Lithuania, provide detailed conclusions about the energy and engineering aspects of such systems. The authors also intend to determine the optimal technological combinations and solutions that would allow achieving maximum energy benefits (solar collectors for domestic hot water preparation and photovoltaic panels for electricity use). For the research computer simulation tools EnergyPRO and PV*SOL Premium were selected. Actual collected heat and electricity consumption data is also used for the analysis.

A Standard-Based Method to Simulate the Behavior of Thermal Solar Systems with a Stratified Storage Tank

Thermal solar systems are interesting solutions to reduce CO 2 emissions and gradually promote the use of renewable sources. However, sizing such systems and analysing their behavior are still challenging issues, especially for the trade-off between useful solar energy maximization and stagnation risk minimization. The new EPB (Energy Performance of Buildings) standard EN 15316-4-3:2017 offers several methods to evaluate the performance of a forced circulation solar system. One of them is a dynamic hourly method that must be used together with EN 15316-5:2017 for the simulation of the stratified storage tank connected with the solar loop. In this work, such dynamic hourly method is extended to provide more realistic predictions. In particular, modeling of the pump operation due to solar fluid temperature exceeding a set threshold, or due to low temperature differential between solar field and storage tank, is introduced as an on–off control. The implemented code is applied to a case study of solar system for the preparation of domestic hot water and the impact of different design parameters is evaluated. The model predicts a higher risk of overtemperature lock-out or stagnation when the solar field surface is increased, the storage volume is reduced and water consumption is set to zero to simulate summer vacation periods. Finally, a simple modulating control with a time step of a few seconds to a few minutes is introduced, quantitatively showing the resulting benefits in terms of useful solar energy increase, back-up operation savings and reduced auxiliary energy use.

Experimental validation of a model-based method for separating the space heating and domestic hot water components from smart-meter consumption data

Smart meters are currently being rolled out in European district heating (DH) systems at a large scale to enable time-varying district heating tariffs and improve consumer awareness about their own consumption. Smart-meter data can also be used in more advanced applications, e.g. for establishing model-based control schemes for demand response purposes and data-driven building energy performance labeling schemes. Many of these applications require separate measurements of the consumption for space heating (SH) and preparation of domestic hot water (DHW); however, smart meters often only provide the total DH energy consumption (SH+DHW) in truncated units (e.g. whole kWh on an hourly basis). Typical approaches for separating these two components of DH consumption require measurements with a high temporal and numerical resolution and are therefore not applicable to smart-meter data. New methods suitable for disaggregating the combined DH demand are therefore needed. This paper presents a validation of a model-based method for disaggregating DH consumption using ground truth data from 44 residential buildings.

Performance analysis of glazed PVT collectors for multifamily building

The paper deals with performance analysis of potential application of glazed photovoltaic-thermal collector for domestic hot water preparation for multifamily building in European climatic conditions. Two different solutions are studied, glazed photovoltaic-thermal collectors integrated in the building envelope and glazed photovoltaic-thermal collectors fixed on the roof of the building. Moreover, the paper presents a comparison with conventional side by side installation of solar thermal collectors and photovoltaic panels to show the benefit of photovoltaic-thermal collectors. Simulation analysis has been done in TRNSYS with use of developed and validated mathematical model of glazed photovoltaic-thermal collector.

Performance of heat pump system for water heating in European climate

A performance of air-to-water and brine-to-water heat pump for domestic hot water preparation was analyzed in different climates of Europe. Air-source heat pumps are widely used energy source for domestic applications with low operation costs. Their system SPF was found at level of 3.0 for domestic hot water preparation for medium latitudes in Europe. Investigations on the ground-source heat pump performance show their average SPF are close to air-source technology.

Multi-mode control method for the existing domestic hot water storage tanks with district heating supply

The hot water tank is widely used for domestic hot water (DHW) preparation. When supplied by district heating (DH), the operation of DHW tanks directly influences the DH return temperature, thereby affecting the DH system efficiency, supply capacity and the realization of the low temperature district heating. However, the conventional charging method often results in high DH return temperature. This study develops a new charging method aiming at reducing the DH return temperature without violating the comfort or hygiene requirements. The concept uses the multi-mode charging method considering the periodical characteristics of the load pattern. Multi scenarios are simulated by dynamic models using the practical DHW load profiles from a case study. Moreover, the impacts of the tank configuration, the location of the temperature sensor, and the distribution heat loss are investigated. The results show that the new control method can reduce the primary return temperature by 5–8 °C compared to the conventional control method. The distribution heat loss imposes great impact on the DH return temperature. In addition, the tank with the external heat exchanger performs better than the tank with the internal heating coil if the circulation heat loss is less than 50% of the DHW demand.

Geo-Solar District Heating – Lessons Learnt from a not Realised Project

For the new housing area with approx. 130 low energy residential houses, located in Kassel, Germany, various supply concepts are investigated. Main objective of the project is the development of an innovative and optimised heat supply concept based on renewable energies and a low temperature district heating for later realisation.During the course of the project several heat supply concepts have been investigated and compared to give an input to the decision and realisation process. A promising heat supply concept is based on a central ground source heat pump in combination with a low temperature district heating (40°C supply temperature) for space heating and decentralised solar thermal systems for domestic hot water preparation. The advantages of this supply variant are comparable low annual heating costs and about 60% lower CO2-emissions in comparison to the reference system (decentralized air / water heat pump with solar thermal system).Due to time constrains it was decided not to realise the above mentioned energy concept. However, the research project took up the task to investigate the transferability of the concept in technological and economical perspectives to other locations and boundary conditions. From the results of the study the importance of a very high connection rate can be highlighted. Also the question of the particular business models for such capital demanding projects (high investment costs for the heating grid vs. low energy demand/sales) has been regarded.

Passive Cooling in the System of a Heat Pump with a Vertical Ground Collector

Heat pumps from more than ten years are known as an alternative source of thermal energy. They are primarily used for central heating and domestic hot water preparation. Next to the solar collectors, they are the cheapest and easiest way to save energy. But heat pump can also be used for cooling. Heat can spontaneously flow from a colder to a hotter body. Flows from a body with a higher temperature to a body with a lower temperature are commonly known as the second law of thermodynamics. The heat pump pulled out of cooler ambient heat which may be used for central heating or for domestic hot water. There are many types of cooling pumps. This depends mainly on the type of pump, and actually kind of heat source that can be used in two ways: as a heat receiving surface - or as a source of cooling for utilization. Knowing the general principle of operation of the pump, we can introduce innovative technologies that allow more devices to reduce the operating costs. In this solution, the heat pump installation, initially designed only for heating or, ultimately, also for cooling purposes, enables the use of a system that will be based on the part of the installation associated with the lower heat source, but not as a source of heat but as a source of coolness. This system is often referred to as “natural cooling” or as a passive cooling system. In such a system, during the production of chilled water, a significant reduction in production costs is obtained due to the lack of energy consumption for the drive of refrigeration compressors, and only the use of circulation pumps for the lower and upper circulation of the heat source. The disadvantage of this solution is the limitation resulting from the situation of close connections between ground temperature and chilled water temperature in the supply, which causes the limitation of its use for the period beyond the maximum peak demand for cold in the cooling season, i.e. most often at the highest outside temperatures. Thanks to the economical use of electricity, we can contribute to protect the environment.

Simulation study on the efficiency of thermochromic absorber coatings for solar thermal flat-plate collectors

We present a comparative simulative study to evaluate the efficiency and stagnation behavior of commercially available absorber coatings for solar thermal flat-plate collectors. A market survey has revealed different absorber coatings, which exhibit solar absorptances of α > 90% and thermal emittances ε of 5–90%. All these coatings can be classified as wet-chemically electroplated coatings on the basis of black chrome, highly selective sputtered PVD coatings, solar paints and novel thermochromic coatings. We calculated the annual solar collector energy output by means of collector simulations with the tool ScenoCalc and compared the collector efficiency of several absorber coatings. We have carried out TRNSYS simulations both with systems for solar domestic hot water preparation and solar-assisted space heating. In a solar domestic hot water system with a daily tapping volume of 100 L we report an increase in the auxiliary energy demand of up to 6% with black chrome, 7% with thermochromic and 21% with solar paint coatings compared to sputtered PVD coatings. In a solar combisystem the increase in the auxiliary energy demand does not exceed 1.4% for thermochromic and black chrome coatings and 6.1% for solar paints. The stagnation period can be reduced from 178 h per year (PVD coatings) to 118 h, 62 h and 11 h for black chrome, thermochromic and solar paint coatings, respectively. The maximum absorber temperatures decrease from 175 °C (PVD coatings) to 165 °C for black chrome, 145 °C for thermochromic and 135 °C for solar paint coatings.

The influence of different water efficiency ratings of taps and mixers on energy and water consumption in buildings

This paper analyses two different models (methods) used for determination of water consumption in residential buildings. For this purpose, some basic sanitation facilities were implemented in the models as typical household equipment. As there is a big variety of sanitary solutions available, in order to achieve a significant reduction in water consumption, a novel classification of faucets (taps and mixers) is proposed. This classification also allows for the assessment of energy efficiency ratings of sanitary appliances. On the basis of this classification, water savings resulting from the use of faucets with different water efficiency ratios were determined. Depending on the type of faucet, it is possible to achieve more than 50% water savings, as well as a significant reduction in energy demand for heating and pumping water to customers. The paper also discusses the equations used to determine the energy demand for domestic hot-water preparation and its pumping to consumers. The results of the energy consumption calculations for the above-mentioned purposes were determined per person.

Performance Modelling of Dual Air/Water Collector in Solar Water and Space Heating Application

In the present work, the detailed mathematical model of a dual air/water solar collector (DAWC) has been developed and experimentally verified. To demonstrate the application of the DAWC, three buildings with different energy performance levels and three building locations were chosen in analyzed case studies. Four solar collector systems were compared with one another. The solar yield of the described systems was determined by simulation using the detailed theoretical model of DAWC. The results indicate that in the case of combining a domestic hot water preparation system and recirculating-air heating system based on DAWC, it is possible to achieve up to 30% higher solar energy yield compared to a conventional solar domestic hot water preparation system dependent on climate and building performance.

Performance of a demonstration solar PVT assisted heat pump system with cold buffer storage and domestic hot water storage tanks

The design and demonstration of a solar PVT assisted - heat pump system with a cold buffer storage tank on the source side of the heat pump and a hot storage tank for domestic hot water preparation is presented. The system was subject to real weather conditions and hot water draw offs. Measurements over nine months are presented and analyzed. The focus was on the thermal dynamic of the system and the interplay between the heat pump, the storage tanks and the thermal absorber of the uninsulated PVT panel. The hot water demand was almost completely covered by the thermal part of the PVT collector in sunny summer periods. In less sunny periods, the brine-water heat pump recharged the hot water tank after draw offs and discharged the buffer storage tank. The uninsulated PVT collector worked as an energy absorber and was able to extract heat form the ambient air and recharge the buffer storage tank to the ambient air temperature when no solar irradiance was available. In the less sunny and colder periods, the PVT added a significant amount of energy to the cold storage tank.

Experimental Measurements of Hot Water Stratification in a Heat Storage Tank

The contribution focuses on the experimental measurement of the method of accumulation of hot water with its temperature layer in storage heaters using elementary cone elements. The basic principle of these elements is the automatic temperature distribution of water temperatures according to the temperature and flow rate for a specified storage time of heat energy from different heat sources in the heating system and hot water preparation. The thermal stratification in the stratified storage tank ensures maximum energy savings of up to 60% compared to standard storage tanks. The values of measurement were processed in a simulation fashion and compared to the real measured values. The aim of the experiments was to prove maximum energy savings and to determine the actual efficiency of elementary elements in stratification storage heaters with different heat sources. Storage of heat energy and its use is an important way of energy saving systems under Directive 2010/31 / EU of the European Parliament and of the Council on the energy performance of buildings. Stratification storage systems are used for different types of heating and also for domestic hot water preparation in all types of buildings. Their importance is evident when there is a need for efficient use of thermal energy in low-energy buildings and buildings with zero energy consumption, where they can be used for common use of hot water (50 - 60 °C) with different temperatures for heating (e.g. floor heating, convective heating, etc. ranging from 25 to 60 °C). The most efficient way is to combine stratified heat storage tanks with solar heating systems, heat pumps, or boilers. Every building must be assessed individually in terms of requirements for heating and the method of domestic hot water preparation and distribution. Furthermore, when engineering a heating system for any building, the use of a renewable energy source has to be taken into consideration too.

On the possibilities to increase energy efficiency of domestic hot water preparation systems in existing buildings – Long term field research

Energy consumption for domestic hot water (DHW) preparation is one of the main components of the energy balance of the existing and newly designed buildings. However, based on the number of existing buildings and the related opportunities to improve energy efficiency, an important issue is to propose effective and low cost methods that allow to reduce the heat consumption in existing domestic hot water systems and are fast in the implementation.This article presents the results of an experimental research conducted in 12 objects (9 multifamily buildings and 3 thermal substations) assigned to three groups (A, B and C), depending on the analyzed feature of the domestic hot water system. The objects in the group A were analyzed in detail (each 1 h during one full heating season) in order to clearly show the amount of the heat used for circulation of hot water. The group B of objects characterized by the installation of temperature control valves (TCVs) under the risers of circulation installation. The third group consisted of the objects in which the temperature of hot water was decreased during the night hours. The objects from group B and C were analyzed over 8 years.The share of heat losses associated with the circulation of hot water in the total heat consumption supplied for its preparation was in the range from 56.7% to 70.5% for the Group A objects.On the other hand, the energy savings were calculated using different methodologies and for the recommended one they ranged from 8.5% to 49.5% for group B objects and from 6.0% to 14.4% for group C objects.

Environmental and social effects of the change of heat sources on the example of a selected quarter of tenement houses in Wroclaw

The energy consumption for space heating and domestic hot water preparation are significant burdens of a polish household budget, especially in old tenement houses. Simultaneously, lowering the emission of pollutants is under the great importance and one of main goals to achieve in big cities. This policy results in the need of elimination of systems based on solid fuels. The article analyses the environmental and social consequences of the exchange of heat sources in such buildings in one of the quarters in Wroclaw. It presents how this change will affect the levels of low emission and costs of energy supply to tenement buildings.

A multipurpose test rig for district heating substations: domestic hot water preparation and keep-warm function comparison

A well performing District Heating Substation (DHS) is crucial for the efficiency of the District Heating (DH), especially with the shift towards low temperature 4th generation DH systems. For this reason, testing and characterization of commercially available DHSs becomes important to estimate their effect on the DH network. Within the thermo-technical laboratory of EnergyVille, a multipurpose test rig has been built for testing DHSs. In this setup, different DH conditions and heat demand profiles for space heating and for Domestic Hot Water (DHW) can be emulated. Independent tests have been performed on 4 DHSs from three different manufacturers, focused on the DHW preparation for low DH supply temperature and on the stand-by/keep-warm operation of the substations. The latter maintains a certain temperature within the heat exchanger to avoid delays in the delivery of DHW. The results showed that improvements are needed on DHW production for lower DH supply temperatures. Also, enhancements are needed to reduce losses from the keep-warm function. Given that DH systems can have thousands of substations, this will reduce the overall losses and improve the performance of the DH network.

Analysis and simulation of the circulation pump operation

The operation of the circulation installation has a significant impact on the energy efficiency of the building and it contributes to its reduction. The article refers to the actual measurement data obtained from the measurements of the domestic hot water (DHW) preparation system in a multi-family residential building in Wroclaw. On their basis, various possibilities of controlling the operation of the circulation installation without reducing the comfort of DHW operation system were presented and simulated. The results are illustrated in the form of measurable savings in energy consumption and related costs.

Performance assessment between a ground coupled and air source heat pump used for domestic hot water preparation

A ground-coupled heat pump system (GCHP) and an air source heat pump (ASHP) driven by photovoltaic panels are used to provide domestic hot preparation for a NZEB house. The experimental measurements are used to test both the heat pump models in the same conditions of water temperature and volume of domestic hot water. A comparative analysis of the two heat pumps for domestic hot water preparation is performed. In addition, using the software TRNSYS (Transient Systems Simulation), two numerical simulation models of thermal and electrical energy consumption in DHW mode are developed. Finally, the simulations obtained using TRNSYS software are analysed and compared to the experimental data.

Air source heat pump for domestic hot water supply: Performance comparison between individual and building scale installations

Air source heat pump (ASHP) for domestic hot water (DHW) preparation under cold climatic conditions is studied by TRNSYS simulation. Emphases are focused on comparing different strategies of installation using energy efficiency performance criteria. Studied strategies include individual (apartment-scale) and collective (building-scale, centralized) installations. Different daily hot water consumption profiles are considered in the annual simulation program. Simulation results show higher annual system efficiency from individual installations than centralized system. In the latter case, pump consumption during hot water recirculation makes the overall system less efficient. Due to lower over-sizing factor, the centralized installation is more favourable to the ASHP performance than individual ones. In both the two cases, GHG emissions can be significantly reduced by 7 thanks to ASHP. This paper provides decision-making information regarding energy efficiency incentive policies of heat pumps for a more sustainable energy supply.