Domestic Hot Water Preparation Research Articles

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.

Environmental and cost life cycle analysis of the impact of using solar systems in energy renovation of Southern European single-family buildings

Nowadays, in the European Union (EU) the construction rate of new buildings is very low and therefore achieving the EU targets regarding the energy efficiency of the building sector is only possible through the reduction of the energy needs of the existing building stock. A building design based on passive measures is a priority to reduce operational energy consumption but it is not enough to achieve the nearly Zero Energy Building (nZEB) level. Consequently, the design must also consider active systems with high efficiency and the use of renewable energy sources to partially/totally replace the use of non-renewable energy. At this level, solar thermal and photovoltaic panels play an important role, mainly in countries with high levels of solar radiation, as in the Southern European countries. Nevertheless, there are still some barriers to overcome for the broader dissemination of the implementation of these systems. One of the most important is that building owners are not fully aware of the life cycle benefits that these systems have at environmental and economic levels. The best way to raise awareness to these benefits is through the analysis of case studies, highlighting the short or mid-term benefits resulting from the integration of these active solutions. Thus, this paper is aimed at analysing the environmental and life cycle costs of different energy renovation scenarios, assessing the contribution of the solar systems to achieve three levels of energy performance. The study is focused on the energy renovation of a detached single-family house considering the climatic conditions of Porto, Portugal. From the results, it is possible to conclude that, on an annual basis, and for the Portuguese climate, it is possible to overcome, many of the energy needs for acclimatization and preparation of domestic hot water with the integration of these systems. The study also shows attractive economic and carbon payback times resulting from their use.

Analysis and comparison of methods for the preparation of domestic hot water from district heating system, selected renewable and non-renewable sources in low-energy buildings

The article presents an economic analysis and comparison of selected (district heating, natural gas, heat pump with renewable energy sources) methods for the preparation of domestic hot water in a building with low energy demand. In buildings of this type increased demand of energy for domestic hot water preparation in relation to the total energy demand can be observed. As a result, the proposed solutions allow to further lower energy demand by using the renewable energy sources. This article presents the results of numerical analysis and calculations performed mainly in MATLAB software, based on typical meteorological years. The results showed that system with heat pump and renewable energy sources Is comparable with district heating system.

Evaluation of long-term operation of combined system for heating the building and preparation of domestic hot water

The paper presents, the results of research on the operation and energy efficiency of a 186 kW gas-fired condensing boiler operating in a hybrid heat source system. The boiler co-operates with an 81.1 kW (electric) brine-to-water compressor heat pump, a 27.4 kW air-to-water heat pump and 6 flat solar collectors. A local, built-in, hybrid heat source is located in a public building and is intended to satisfy the building needs. The study was conducted over a period of 1 year - from 1 September 2014 to 31 August 2015. The gas-fired boiler operates in the heating buffer system all year round. The boiler performance is characterized both in the winter and in the summer season, in terms of the amount of heat produced and the heating power. The calculations results of the heat generation efficiency obtained in the measuring period are also presented

Evaluation of energy effects of the heat distribution network modernization

The work concerns the estimation of energy effects of modernization of a part of an existing heat distribution main, which is part of a system that supplies heat for heating and domestic hot water preparation. The energy effect was defined as the difference between heat losses in the installation previously operated, developed in the technology of traditionally insulated pipes placed in dedicated underground channels and newly built installations made of pre-insulated pipes located directly in the ground. In the paper, in a synthetic way, the method of calculation is presented, as well as the accompanying assumptions. Two basic approaches to determine the heat losses are discussed. The first one was based on detailed calculations based on real operational data, whereas the second one used the indicative method recommended by the National Fund for Environmental Protection and Water Management (NFOŚiGW). The results obtained on this basis show that the modernization of the installation returns measurable energy effects in the form of reduced heat losses, which translates into the efficiency of its operation and operation of the source. At the same time, they show that the size of obtained energy effect depends on the applied methodology of calculations.

Energy performance for residential building – comparison between theoretical method and real measurements

This paper presents an energy performance of residential building (two – family building) located in Poznan. Both apartments were analysed separately. By using a method of energy performance calculations valid in Poland, a theoretical energy performance had been prepared. The calculations were conducted assuming real changeability of climatic data in years: 2010–2017. The real energy performance was prepared based on actual gas consumption for the purpose of heating and domestic hot water preparation (DHW) within the years of measurements taken, being a subject of analysis. The findings from this study revealed that a theoretical energy performance significantly deviates from the results obtained by means of energy consumption measurements, which resulted from variability of basic climatic data over time and also from theoretical usage profile of the apartments.

Comprehensive Energy Diagnostics Carried Out In a Residential Building – A Case Study

Abstract The article presents the case study of the comprehensive diagnosis of an existing residential building with natural ventilation. The results of quick diagnostics of thermal insulation of the building, the heating system, ventilation, domestic hot water preparation and the quality of the environment in the rooms were presented. Based on the data obtained by measurements, the energy performance of the building was prepared using the building certification calculation method. The energy performance of the building was also prepared using the developed method of determining energy performance based on measurements.

Energy efficient heat pipe heat exchanger for waste heat recovery in buildings

This study presents a Computational Fluid Dynamics (CFD) Heat Transfer Analysis for an originally designed Energy Efficient Heat Pipe Heat Exchanger for Waste Heat Recovery in Buildings. The research is focused on developing a heat pipe heat exchanger for domestic hot water and thermal agent preparation, preheating / heating the air from ventilation systems in buildings, using as a primary agent the return of the existing heating system. The proposed device has a lot of advantages as high efficiency for heat recovery, low cost of manufacturing, exploitation and maintenance and it is very easy to install and use.

An assessment of the financial efficiency of a heat recovery system from graywater in a hotel

The purpose of the article is to determine the profitability of investing in a graywater heat recovery system in a hotel facility located in south-eastern Poland whichis dependent on three heat sources for the domestic hot water preparation system, i.e. gas boiler, biomass boiler and electric heater. There were also various options for accommodation use: 25%, 50%, 75% and 100% occupancy of the hotel. The research was focused on the most frequently used methods for the absolute assessment of the effectiveness of investment projects enabling the creation of an objective criterion. Thus, both the simple method - Simple Pay Back Period SPBP and dynamic methods based on the discount account were used in calculations: Net Present Value NPV, Internal Rate of Return IRR, Profitability Index PI, Discounted Pay Back Period DPBP. The analysis also includes the annual increase in the purchase price of energy carriers. The conducted research has shown that in most cases the installation of the DWHR (Drain Water Heat Recovery) system is beneficial and profitable to the investor.

Development for CO2 emissions reduction by the use of solar thermal collectors in the process of urban planning

Using RES is one of the most important characteristics of the sustainable and resilient development. Nowadays, need to minimize CO2 emissions is obligatory, especially in the sector of urban and architectural planning, since in Serbia approximately 50% of produced energy is spent in buildings. The CO2 emission, in urban structures, can and must be reduced at the different levels: building level, block, and city level. For the city of Kragujevac, based on urban parameters defined in General Urban Plan, typical urban block was chosen and typical building structure developed. Calculation were made, based on recommendations developed by the Ministry of mining and energy and Serbian regulations, for the energy needed for domestic hot water preparation. In this paper, the influences of architectural and urban parameters on the use of solar thermal collectors at the typical building and urban block level is investigated. Recommendations are prepared for principles of urban and architectural design in order to enable the use of collectors for domestic hot water preparation and in that way CO2 emission reduction. Developed methodology for the city of Kragujevac can be applied in defining design principles in whole the country and Balkans region, not only for the use of solar thermal collectors but also for the use of other RES.

Status Quo of the Air-Conditioning Market in Europe: Assessment of the Building Stock

This study fills in knowledge gaps for the European air-conditioning (AC) market, which is fundamentally important to raising awareness about primary energy utilization. In contrast to space heating (SH) and domestic hot water (DHW) preparation, the European Union (EU) AC market is barely explored in scientific literature. While the focus of previous research has been on the residential sector, a shortfall of data for the services (wholesale and retail, offices, education, health, hotels and bars) exists. In this paper, data describing the actual space cooling (SC) market in Europe (quantity of SC units, equivalent full-load hours, installed capacities, seasonal energy efficiency values as well as cooled floor area per AC type and/or sector) is collected and explored using a bottom-up approach. Results indicate that SC is responsible for a significant portion of EU electricity consumption in households (nearly 5%) and even more in the service sector (~13%). Energy consumption for SC in the EU28 appears to be more than 140 TWh/y. The quantification of the European AC consumption shows a significant difference between the service and residential sectors: about 115 versus 25 TWh/y respectively. The SC market in Europe is characterized by a high potential for growth, especially in households.

Reduction of return temperatures in urban district heating systems by the implementation of energy-cascades

High return temperatures in district heating networks are a significant barrier for the transformation into 4th generation systems. In order to transport high amount of heat in winter times, there is the need of increased supply temperatures (>120 °C) or mass flow rates due to high return temperatures. This leads to an inefficient operation of the system. High heat losses, decreased efficiency of heat production units, reduced potential of alternative heat sources and increased pumping costs are the consequences. Further is the connection of new customers often linked with high investment costs due to limited transport capacities in an existing system.The aim of this paper is to analyse potentials and to develop concepts to reduce return temperatures by implementing thermal energy cascades between different building types in order to improve the performance of the system. This is related to the use of the return flow of high-temperature consumers (e.g. buildings with high-temperature heating systems) for supplying low-temperature consumers (e.g. buildings with floor heating and direct domestic hot water preparation). Based on available data from existing buildings, energy suppliers and network structures, potentials for energy-cascades for representative case studies have been evaluated. To enable energy cascaded interconnections, the temperature and heat load profiles of the investigated buildings in characteristic districts were analysed and different connection scenarios were developed and evaluated. Special attention was given to the hygienic preparation of domestic hot water in the low-temperature consumers and the security of the heat supply.As a result, the temperature level of the local return line could be reduced (up to >10 K) and transport capacities in the districts were increased (up to 16 %). By implementing this approach in several districts of an urban network, the overall system efficiency can be increased.

Achieving low return temperature for domestic hot water preparation by ultra-low-temperature district heating

District heating (DH) is a cost-effective method of heat supply, especially to area with high heat density. Ultra-low-temperature district heating (ULTDH) is defined with supply temperature at 35-45 °C. It aims at making utmost use of the available low-temperature energy sources. In order to achieve high efficiency of the ULTDH system, the return temperature should be as low as possible. For the energy-efficient buildings in the future, it is feasible to use ULTDH to cover the space heating demand. However, considering the comfort and hygiene requirements of domestic hot water (DHW) preparation, supplementary heating devices should be combined, which can affect the return temperature in different extents. This study analysed the return temperatures of different types of substations for DHW preparation with ULTDH, and developed improvements in the substation for better energy efficiency. Both the instantaneous and storage-type electric heating methods were Long-term measured as supplementary heating for ULTDH in the case substations in Denmark. We analysed the seasonal impacts of the return temperature from the DHW loop on the overall return temperature of district heating. To achieve lower return temperature and higher efficiency for DHW supply, an innovative substation was devised, which replaced the bypass with an instantaneous heat exchanger and a micro electric storage tank. The energy performance of the proposed substation and the resulting benefits for the DH system by the lower return temperature were investigated

Model predictive control for demand response of domestic hot water preparation in ultra-low temperature district heating systems

In ultra-low temperature district heating the supply temperature is less than required to heat the domestic hot water and a heat pump is therefore often proposed to raise the temperature. This paper investigates how this heat pump can be utilized for price based demand response to induce peak reductions and energy cost savings. A model predictive control strategy is proposed and evaluated through co-simulations where a model predictive controller is formulated in MATLAB and connected to an EnergyPlus hot water storage tank. It is demonstrated that the system is capable of reducing the district heating morning peak and the electric grid evening peak as well as providing energy cost savings for the end-user without compromising hygiene and comfort.

Comprehensive On Site Thermal Diagnostics Of Buildings – Polish Practical Experience

Abstract The Polish National Centre for Research and Development has been coordinating the implementation of a strategic research project “Integrated System for Reducing Energy Consumption in the Maintenance of Buildings”. The main goal of the project is to support Poland’s efforts to reduce energy consumption in buildings, which is a strategic goal of the European Union. Within the scope of the aforementioned project, Task 4, “Development of thermal diagnostics of buildings”, was realized. Silesian University of Technology in Gliwice was a leader of the scientific-industrial consortium implementing the task. The main objectives of Task 4 and achieved relevant results are presented in the paper. A new method for the rapid on-site thermal diagnosis of a building envelope and systems of heating, ventilation, air conditioning and domestic hot water preparation and the diagnosis of indoor environment quality, as well as a method for drawing up energy performance certificates based on the measurements were developed.

ENERGY EFFICIENT PIPE HEAT EXCHANGER FOR WASTE HEAT RECOVERY FROM EXHAUST FLUE GASES

This study presents an original method for waste heat recovery from exhaust flue gases using a heat pipe heat exchanger. For the proposed paper we analyzed using Autodesk Simulation CFD Software the operation of the originally designed heat pipe heat exchanger system in different hypothesis. For the complete analysis we realized a study case for a pizza restaurant building located in Iasi, Romania to prove the energy efficiency of the heat pipe heat exchanger unit. By applying our system, we achieved a percent of energy savings of 30.9% for the total heat requirement for heating and domestic hot water preparation. In the end we realized a financial study using the RETScreen 4 Software to demonstrate the feasibility of using the heat pipe heat exchanger for waste heat recovery from exhaust flue gasses.

Technical, economic and environmental investigation of using district heating to prepare domestic hot water in Chinese multi-storey buildings

The development of DH (District Heating) is an environmentally friendly and energy-efficient strategy in China. Currently, the vast majority of DH systems are SH (Space Heating) only and do not provide DHW (Domestic Hot Water). DHW is mainly produced by individual water heaters due to the cost-effective issues of the centralized DHW systems. From the perspective of long-term development, DHW produced via DH systems would be more sustainable because DH is an important precondition for an environmental safe use of domestic waste fuels. This paper presents an approach that uses flat stations meanwhile utilizes the industrial waste heat to prepare DHW via the DH network. A building model of a multi-storey building in Beijing was developed to investigate the technical feasibility. An economic evaluation was made using net present value to compare the annualized cost for individual water heaters and flat stations. The environment impact in terms of CO2 emission when fossil fuels are used to produce DHW was quantified. The results show that flat stations are technically feasible if a few renovations are implemented, and that the use of flat stations is a more sustainable, economic and environmentally friendly approach than the existing DHW preparation technologies.

Large-scale solar water heating in South Africa: Status, barriers and recommendations

This work evaluates large-scale solar thermal systems in South Africa. A database of 89 systems has been generated and analysed with regards to cost, applications and beneficiary industries. Since 2007 the average total annual commissioned collector area was only 1544 m2. Most systems are used for domestic hot water preparation. The average system cost is currently 603 EUR/m2, which is higher than the costs achieved in other countries. A brewery solar process heat case study compares 10 proposals for a tender. Proposed system installation costs varied by a factor of 2.5, suggesting low maturity in this market. The winning proposal has a 120.7 m2 gross collector area, LCOH = 7.9 EURc/kWh, IRR = 16.7% and payback = 9.3 years. A key barrier is the low cost of coal of 2 Eurocent/kWh, which is the dominating fuel. Current systems can already well compete with heat sources like paraffin, diesel, petrol and gas, which is shown by a detailed financial analysis. Besides the low coal price, other key barriers for increased market diffusion are long payback times, the technical complexity of the technology, as well as the lack of awareness and trust in the technology.

Flat Plate Collectors with Thermochromic Absorber Coatings to Reduce Loads During Stagnation

Thermochromic absorber coatings, which switch their emissivity for thermal radiation depending on temperature, are developed to reduce the stagnation temperature of solar thermal collectors: In the operating range of the collector, the surface exhibits a low emissivity (ɛ = 10%). At higher temperatures, the emissivity is increased by a multiple (ɛ = 35%). Thus, the collector heat losses raise and the stagnation temperature is reduced. Efficiency measurements on a prototype collector employing this thermochromic absorber show, that below the switching temperature the efficiency is nearly identical to that of a conventional collector with a highly selective absorber plate. Due to the increased emissivity in the switched state of the coating, the stagnation temperature is lowered by more than 30 K. System simulations exhibit, that the performance of the system is not significantly affected: in a combined system for space heating and domestic hot water preparation the conventional energy demand of the gas boiler is increased by 1.5% to 4.5% using the thermochromic collector instead of a standard collector. In contrast, the duration when formation of vapour in the collector circuit occurs, is reduced by 70% to 75%. By further optimizing thermochromic collectors, the formation of vapour in the solar circuit could be completely prevented during stagnation. This would allow the use of lower cost materials in the solar circuit and reduce the cost of installation and maintenance of the solar circuit significantly.

Laboratory Testing of Solar Combi System with Compact Long Term PCM Heat Storage

To enable the transition from fossil fuels as a primary heat source for domestic hot water preparation and space heating solar thermal energy has great potential. The heat from the sun has the disadvantage that it is not always available when there is a demand. To solve this mismatch a thermal seasonal storage can be used to store excess heat from the summer to the winter when the demand is higher than the supply. Installing a long term thermal storage in a one family house it needs to be compact and sensible heat storages are not suitable. A latent heat storage with a phase change material (PCM) can provide a more compact way of storing heat. Sodium acetate trihydrate (SAT) is a good candidate material as it has a relatively high heat of fusion and in addition it has the ability to supercool to room temperature without solidifying. In this paper results from the test of a solar combi system with a latent heat storage with SAT is presented. The SAT heat storage modules were heated to 80°C by the solar collectors 53 times in the test period from June to November 2015 and this enabled the modules to supercool. Supercooling was achieved for 39 days for a SAT module after which 11 kWh of heat were discharged.