Tap Water Heating Research Articles

Monitoring of fresh water consumption and energy needs for hot tap water heating in residential buildings

The study addresses discrepancies between design and measured values in building energy systems, focusing on water heating inside buildings in Central and Eastern Europe. Using data measured by the authors from 2010 to 2019 in Czech cities, a novel empirical calculation relationship for water flow estimation in apartment buildings is introduced, which is different from the outdated 1940 equation. The proposed calculation is refined and validated based on the measured values, allowing for accurate specification of daily and hourly water demands. The innovative approach is expected to result in tangible savings and a 10–20 % reduction in energy consumption for hot water heating, emphasising its significance for sustainable energy supply to buildings.

Screening of thermal characteristics and assessment of comparative energy efficiency potential in a residential district

ABSTRACT By identifying buildings with poor thermal performance and prioritizing these in terms of energy efficiency potential, a sustainable transformation of the building stock may be accelerated. However, there is currently a lack of thermal characteristics (TCs) differentiating total energy use from hot water circulation (HWC), hot tap water (HTW) and space heating in large building portfolios. This research demonstrates a methodology based on a change-point model for identifying and prioritizing TCs, which also enables prediction of the Comparative Energy Efficiency Potential (CEEP). The change-point model allows for the differentiation of various processes, i.e. space heating, HWC and HTW, using only heating supply data and outdoor temperature. The studied district consists of 70 multi-family buildings in the Vasastaden district in Linköping, Sweden. The findings demonstrate that the proposed methodology allows for identifying and prioritizing TCs connected to HWC, HTW and space heating. The highest CEEP is in space heating, corresponding to a maximum of 2,016 MWh (16% of the district’s energy use), followed by HWC, 699 MWh (6% of the district’s energy use) and HTW, 520 MWh (4% of the district’s energy use). Consequently, a total decrease of 3,235 MWh (26%) is made possible according to the studied energy efficiency targets. HIGHLIGHTS A methodology for the prediction of the Comparative Energy Efficiency Potential (CEEP) in a building portfolio based on the identification and prioritization of TCs is proposed The study is enabled by the use of a unique change-point model (DTPC) for differentiating TCs solely from digital heating supply data and outdoor temperature 70 multi-family buildings (total heated area of 121,692 m2) in the Vasastaden district in Linköping, Sweden, are investigated The methodology is successful in identifying and prioritizing TCs related to HWC, HTW and space heating The highest CEEP is in space heating calculated at a maximum of 2016 MWh, which corresponds to 16% of the district’s total energy use

Case studies of four installed wastewater heat recovery systems in Sweden

The energy demand for tap water heating is significant in the developed world and significant to buildings energy performance. However, little attention is given to this untapped potential of heat recovery from wastewater. The purpose of this investigation is to investigate performance of different wastewater heat recovery systems to obtain more knowledge on how these systems perform in reality. Four systems were investigated showing that the annual heat recovery ratios between 17 and 43% and annual heat recovery per heat transfer areas between 1586 and 13 108 kWh/m2.The paper also proposes a design equation with a validated accuracy of ±15% for sizing horizontal wastewater heat exchangers in wastewater heat recovery systems.

Experimental validation of new approach for waste heat recovery from combustion engine for cooling and heating demands from combustion engine for maritime applications

Abstract Waste heat recovery is one of the crucial and fundamental issue of energy management related with energy efficiency improvement, fuel savings, and reduction of greenhouse gases emissions. The paper provides with the experimentation of the prototype heat recovery system dedicated to the small and mid-sized maritime combustion engines of the nominal load of 100–250 kW. The waste heat recovery system is covering the innovative low-pressure steam indirect heat transfer subsystem. The recovered heat is consumed by a heating system and a prototype heat driven ejector refrigeration cycle operating with environmentally safe refrigerant. It was demonstrated that the refrigeration system produces up to 30 kW of cold by consuming 75 kW of heat gathered from flue gases. This is the first prototype of the compact heat driven refrigeration system for marine applications. The waste heat recovery system additionally provides with approximately 60 kW heat recovered from water jacked cooling of the engine block which is used for heating capacity dedicated for tap water and space heating purposes. This covers almost all small and mid-sized vessels needs for thermal energy. The prototype design has been approved by two independent maritime classification societies.

Effect of cycle-induced crack formation on the hydration behaviour of K2CO3 particles: Experiments and modelling

Thermochemical energy storage using salt hydrates is a promising concept to bridge the gap between supply and demand for solar thermal energy in residential buildings. Using a suitable thermochemical material such as a salt hydrate, a thermal energy storage device, also known as a heat battery, can be created to supply low-temperature thermal energy during colder periods. To generate adequate power from a heat battery for the production of domestic hot tap water or space heating, the hydration rate of the salt hydrate needs to be sufficiently fast. It is hypothesized that the hydration rate of the material increases over multiple charge and discharge cycles due to crack formation and volume increase of the salt hydrate particles. This hypothesis is tested by performing two kinds of experiments: optical microscopy experiments using a micro-climate chamber to evaluate the particle size, and Thermo Gravimetric Analysis (TGA) experiments to determine the hydration rate of the particles. The hydration rate and particle size are input for a nucleation and growth model that takes into account crack formation and particle growth. Optical microscopy experiments show a particle expansion of approximately 30 % over 12 cycles. Typical hydration rates are increased by a factor 15 comparing the first and the 12th TGA cycle. It is shown that particle growth and crack formation significantly contribute to the improvement of the hydration rate. Finally, taking into account crack formation and particle growth in the numerical model results in a good agreement between model and experiments. Such a numerical model can be used for heat battery design.

Optimization study of heat pumps using refrigerant blends – Ejector versus expansion valve systems

This article investigates tap water heating systems to highlight an ongoing debate. Some report that CO2-based transcritical heat pumps with an ejector have the best coefficient of performance (COP), while others report that blend-based refrigerant systems (without an ejector) are better. In the literature, however, these systems are only compared with conventional heat pump designs, and not against each other, making it difficult to conclude which design is the best. In addition, the outcome of combining the two modifications has not been explored extensively. This article investigates the performance of heat pumps using mixtures of CO2 and propane, with and without an ejector or a suction gas heat exchanger. It presents a novel method for modeling blend-based heat pumps with an ejector using an optimization approach and a minimum allowed temperature pinch in heat exchangers. A sensitivity study explores how the heat pump performance depends on operating conditions, ejector efficiency and the refrigerant blend. The sensitivity studies allow for the comparison of the heat pump designs. For example, the results show that it is inefficient to use CO2 and propane blends in systems with an ejector. A blend-based system with a suction gas heat exchanger was found to outperform a CO2-based system with an ejector if either the tap water is above 25 °C, the ejector efficiency is below 0.17, or the temperature of the heat source is reduced with more than 10 K when flowing through the evaporator.

The thermomodernization of a single family house located in the Świętokrzyskie Mountains - a case study

The paper presents the energy performance of a single-family house located in Domaszowice, the Kielce poviat. The analyzed object has been put into use in 2010 year. Due to the devices using non-renewable energy sources, installed in the building for the needs of hot tap water and central heating, for servicing, which human presence is necessary, two thermomodernizations were performed. The purpose of the calculations was to indicate the financial benefi ts, i.e. to reduce the costs of maintaining the home and to provide its residents with proper comfort of use of the building, bearing in mind also the health aspect. Changes have been proposed to reduce the demand for non-renewable primary energy of EP using renewable energy sources. As a result, the energy-efficient building that meets WT 2017 was obtained. The Certo 2015 program was used in the analysis.

Households as infrastructure junctions in urban sustainability transitions: The case of hot water metering

The integration of infrastructure domains and resource flows such as electricity, heat, water and waste increasingly gains currency in strategies to achieve more resource-efficient, smart and resilient cities. While widely discussed concepts of a nexus of resource systems, such as energy–water–food, aim at a more optimised and integrative management of resource flows, this article investigates how infrastructure integration is accomplished through the establishment of new interfaces and junctions between formerly separated systems. In particular, it focuses on households as an arena where different urban infrastructures intersect and different kinds of sometimes contradicting demands are imposed to co-manage these infrastructures, such as in the case of own electricity generation from photovoltaics along with the charging of electric cars and the management of household energy consumption. The installation of meters and the constant monitoring of resource use and consumption feedback to household members is regarded as a crucial element in such a transition towards more sustainable urban infrastructures. Empirically, the article studies the introduction of hot tap water meters in urban households in Sweden and the resistance and reactions of these households to such a metering regime. Our study shows how meters as new junctions between energy suppliers and users but also between separate infrastructures of electricity, hot tap water and room heating become contested political terrains which are linked to broader socio-political questions of urban change. In contrast to system management perspectives, such an ‘inside-out’ approach rather lends itself to context-sensitive and navigational governance approaches of infrastructure integration.

Optimizing production efficiencies of hot water units using building energy simulations - Trade-off between Legionella pneumophila contamination risk and energy efficiency

The energy needed for domestic hot water represents an important share in the total energy use of well-insulated and airtight buildings. One of the main reasons for this high energy demand is that hot water is produced at temperatures above 60°C to mitigate the risk of contaminating the hot water system with Legionella pneumophila. However, this elevated temperature is not necessary for most domestic hot water applications, and has a negative effect on the efficiency of hot water production units. A simulation model has been developed which proposes an alternative to this constant 60°C by predicting the Legionella pneumophila concentration dynamically throughout the hot water system. Based on this knowledge, a hot water controller is added to the simulation model that sets a lower hot water comfort temperature in combination with heat shocks. In this paper, the simulation model is used to estimate the energy saving potential in a case study building, at the level of the heat production system by reaching higher production efficiencies. Three different production units, namely an electric boiler, heat pump and solar collector have been investigated. The controller is expected to become an alternative for the current, energy intensive, high temperature tap water heating systems.

Small ammonia heat pumps for space and hot tap water heating

In this study a small ammonia ground source heat pump with a capacity of 8,4 kW has been designed to provide space heating and hot water preparation with estimated max heat load of 7,5 kW for space heating and 2 kW for hot tap water preparation. The main components and materials have been chosen to avoid corrosion and to be compatible for work with ammonia. Calculations with engineering equation solver (EES) have been done to estimate heat pump performance and evaluate the necessary size of the water tank for the heating system. Heat transfer from the heat pump to the storage tank has been calculated considering seven different working regimes with variable heating demand from 1 to 7 kW. Usually the storage tank for heat pumps is designed to prevent very frequent on/off operation of the compressor due to variations in the heating load. In this case the optimal volume of the tank was found in order to cover heating demand during the peak hours of high electricity price according to the Nordic power market. Calculated COP = 4 (Tevap = -3°C, Tcond = 40°C) provides energy savings of up to 75% in comparison with the electrical heaters. In case of the variable price of the electricity it is possible to achieve more savings with the installation of the storage tank. Optimal volume of the tank is 1000 litres to cover 2-3 hour peaks of the high electricity price.

Energy efficiency evaluation of integrated CO2 trans-critical system in supermarkets: A field measurements and modelling analysis

This paper investigates energy efficiency of an integrated CO2 trans-critical booster system installed in a supermarket in Sweden. The supermarket has applied several features to improve energy efficiency including space and tap water heating, air conditioning (AC), and parallel compression.Using field measurement data, the system performance is evaluated in a warm and a cold month. Furthermore, this integrated energy system concept is modelled and compared with stand-alone HFC-based energy systems.The results show that the system provides the entire AC demands and recovers a great share of the available heat, both with high COP values. The comparative analysis shows that integrated CO2 system uses about 11% less electricity than stand-alone HFC solutions for refrigeration (i.e. indirect HFC), heating and AC in North of Europe.Energy efficiency analysis of the integrated CO2 system proves that this system is an environmentally friendly all-in-one energy efficient solution suitable for cold climate supermarkets.

Thermodynamic analysis of vapor compression heat pump cycle for tap water heating and development of CO2 heat pump water heater for residential use

The ideal vapor compression cycle for tap water heating and its coefficient of performance (COP) have been studied theoretically at first. The ideal cycle is defined as the cycle whose high temperature heat source varies temperature with constant specific heat and other processes are same as the reverse Carnot cycle. The COP upper limit of single stage compression heat pump cycle for tap water heating with various refrigerants such as fluorocarbons and natural refrigerants was calculated. The refrigerant which achieves the highest COP for supplying hot water is CO2. Next, the prototype of CO2 heat pump water heater for residential use has been developed. Its outline and experimental results are described. Finally its further possibility of COP improvement has been studied. The COP considered a limit from a technical point of view was estimated about 6.0 at the Japanese shoulder season (spring and autumn) test condition of heating water from 17°C to 65°C at 16°C heat source air temperature (dry bulb)/12°C (wet bulb).

Lifecycle carbon implications of conventional and low-energy multi-storey timber building systems

A consequential-based lifecycle approach is used here to explore the carbon implications of conventional and low-energy versions of three timber multi-storey building systems. The building systems are made of massive wood using cross laminated timber (CLT) elements; beam-and-column using glulam and laminated veneer lumber (LVL) elements; and prefabricated modules using light-frame volume elements. The analysis encompasses the entire resource chains during the lifecycle of the buildings, and tracks the flows of carbon from fossil energy, industrial process reactions, changes in carbon stocks in materials, and potential avoided fossil emissions from substitution of fossil energy by woody residues. The results show that the low-energy version of the CLT building gives the lowest lifecycle carbon emission while the conventional version of the beam-and-column building gives the highest lifecycle emission. Compared to the conventional designs, the low-energy designs reduce the total carbon emissions (excluding from tap water heating and household and facility electricity) by 9%, 8% and 9% for the CLT, beam-and-column and modular systems, respectively, for a 50-year lifespan located in Växjö. The relative significance of the construction materials to the fossil carbon emission varies for the different energy-efficiency levels of the buildings, with insulation dominating for the low-energy houses and plasterboard dominating for the conventional houses.

Rapeseed pellet - a byproduct of biodiesel production - as an excellent renewable energy source / Wytłoki rzepakowe - produkt uboczny w produkcji biodiesla - jako doskonałe źródło energii odnawialnej

Abstract Vegetable oils are renewable feedstock currently being used for production of biofuels from sustainable biomass resources. The existing technology for producing diesel fuel from plant oils, such as rapeseed, soybean, canola and palm oil are largely centered on transesterification of oils with methanol to produce fatty acid methyl esters (FAME) or biodiesel. Rapeseed pellet - crushed seed residue from oil extraction is a byproduct of biodiesel production process. As other types of biomass, it can either be burned directly in furnaces or processed to increase its energetic value. The interest to use different types of biomass as fuels has grown rapidly during the last years as a mean to reduce the CO2 emissions of energy production. Biomass is renewable, abundant and has domestic usage, the sources of biomass can help the world reduce its dependence on petroleum products and natural gas. Energetically effective utilization of rapeseed pellet could substantially improve the economic balance of an individual household in which biodiesel for fulfilling the producer’s own energetic demand is obtained. In this article the experimental results of analyzing the emissions levels of different pollutants in exhaust fumes during different stages of biomass boiler operation were presented. It has been proved that that the pellet, a byproduct of biodiesel production, is an excellent renewable and environmentally-friendly energy source, especially viable for use in household tap water heating installations.

Utilization of rapeseed pellet from fatty acid methyl esters production as an energy source

Rapeseed pellet – crushed seed residue from oil extraction is a by-product of fatty acid methyl esters production process. As other types of biomass, it can either be burned directly in furnaces or processed to increase its energetic value. Biomass is renewable, abundant and has domestic usage; the sources of biomass can help the world reduce its dependence on petroleum products, fossil coal and natural gas. Energetically effective utilization of rapeseed pellet could substantially improve the economic balance of an individual household in which biodiesel for fulfilling the producer's own energetic demand is obtained. In this article, the experimental results of combusting rapeseed pellet in a calorimeter, combustion in a boiler heater and the analysis of the emissions level of different pollutants in exhaust fumes during different stages of biomass boiler operation are presented. It has been proved that the pellet, a by-product of biodiesel production, is not only a valuable substitute of animal fodder, but also an excellent renewable and environmentally friendly energy source, viable for use in household tap water heating installations.

Combined heat and power plant integrated with mobilized thermal energy storage (M-TES) system

Energy consumption for space and tap water heating in residential and service sectors accounts for one third of the total energy utilization in Sweden. District heating (DH) is used to supply heat to areas with high energy demand. However, there are still detached houses and sparse areas that are not connected to a DH network. In such areas, electrical heating or oil/pellet boilers are used to meet the heat demand. Extending the existing DH network to those spare areas is not economically feasible because of the small heat demand and the large investment required for the expansion. The mobilized thermal energy storage (M-TES) system is an alternative source of heat for detached buildings or sparse areas using industrial heat. In this paper, the integration of a combined heat and power (CHP) plant and an M-TES system is analyzed. Furthermore, the impacts of four options of the integrated system are discussed, including the power and heat output in the CHP plant. The performance of the M-TES system is likewise discussed.

Life cycle primary energy implication of retrofitting a wood-framed apartment building to passive house standard

Here we analyze the life cycle primary energy implication of retrofitting a four-storey wood-frame apartment building to the energy use of a passive house. The initial building has an annual final energy use of 110 kWh/m 2 for space and tap water heating. We model improved thermal envelope insulation, ventilation heat recovery, and efficient hot water taps. We follow the building life cycle to analyze the primary energy reduction achieved by the retrofitting, considering different energy supply systems. Significantly greater life cycle primary energy reduction is achieved when an electric resistance heated building is retrofitted than when a district heated building is retrofitted. The primary energy use for material production increases when the operating energy is reduced but this increase is more than offset by greater primary energy reduction during the operation phase of the building, resulting in significant life cycle primary energy savings. Still, the type of heat supply system has greater impact on primary energy use than the final heat reduction measures.

Derivation of Ideal Heat Pump Cycle for Hot Water Supply and Its COP and Evaluation of Hopeful Refrigerant

The reverse Carnot cycle, the high and low heat source of which are constant temperatures, decides the theoretical limit of COP of conventional heat pumps used as air conditioners etc. But the cycle which decides the theoretical limit of COP of a heat pump used as tap water heater is defined as the cycle whose high heat source varies temperature with constant specific heat, because the specific heat of tap water is constant and tap water heating with high temperature rise is needed. In this paper, the COP of this ideal cycle is clarified. And upper limit of COP of heat pump cycle with various refrigerants for tap water heating is studied and finally the refrigerant which achieves the highest COP for supplying hot water is clarified.

ETransport: Investment planning in energy supply systems with multiple energy carriers

Abstract The need for local energy planning is not reduced after liberalization. Both integrated energy companies and local governments have to consider alternative solutions across traditional supply and demand sectors and make plans for the total integrated energy infrastructure. This situation has created a need for new improved methodologies and tools for system planning and operation that include multiple energy carriers and sufficient topological details. In this paper, a novel optimisation model ‘eTransport’ is presented that takes into account both the topology of multiple energy infrastructures and the technical and economic properties of different investment alternatives. The model minimises total energy system cost (investments, operation and emissions) of meeting predefined energy demands of electricity, gas, space heating and tap water heating within a geographical area over a given planning horizon, including alternative supply infrastructures for multiple energy carriers. The model employs a nested optimisation, calculating both the optimal diurnal operation of the energy system and the optimal expansion plan typically 20–30 years into the future. The model is tested on a number of real case studies, and a full graphical user interface has been implemented. A sample case study is included to demonstrate the use of the model.

Modeling the thermal absorption factor of photovoltaic/thermal combi-panels

In a photovoltaic/thermal combi-panel solar cells generate electricity while residual heat is extracted to be used for tap water heating or room heating. In such a panel the entire solar spectrum can be used in principle. Unfortunately long wavelength solar irradiance is poorly absorbed by the semiconductor material in standard solar cells. A computer model was developed to determine the thermal absorption factor of crystalline silicon solar cells. It was found that for a standard untextured solar cell with a silver back contact a relatively large amount of long wavelength irradiance is lost by reflection resulting in an absorption factor of only 74%. The model was then used to investigate ways to increase this absorption factor. One way is absorbing long wavelength irradiance in a second absorber behind a semi-transparent solar cell. According to the model this will increase the total absorption factor to 87%. The second way is to absorb irradiance in the back contact of the solar cell by using rough interfaces in combination with a non-standard metal as back contact. Theoretically the absorption factor can then be increased to 85%.