Domestic Hot Water Consumption Research Articles

Dynamic simulation of the energy consumption and carbon emissions for domestic hot water production in a touristic region

At a buildings’ level, domestic hot water consumption is amongst the most relevant examples of the water-energy nexus. As such, understanding its drivers and forecasting domestic hot water and associated energy consumption are of paramount importance for decision making from the individual household level to a national, or even international, sustainability policy level. However, detailed end-use measurements of either energy or water are seldom available and large scale (city, region or country) estimates are often done based on annual average values. The present research effort aims at large scale estimation of the energy use and carbon emissions due to domestic hot water consumption in two, predominantly residential, locations in a touristic region in Portugal. A novel dynamic modelling approach is proposed and used, which accounts for the variability of: i) the cold water temperature based on measured data; ii) the total amount of water consumed based on measured data; and iii) the fraction of the water consumed as domestic hot water corrected by the air temperature. The results are compared with alternative modelling approaches of the same degree of complexity, revealing differences ranging between −18% and +11% in both net energy required to produce the domestic hot water and the corresponding carbon emissions. Differences in the results are found to exist not only due to the modelling approach, but also between the locations, highlighting the importance of both the simulation approach and the particularities of the context being captured.

Dynamic simulation of hydrogen-based off-grid zero energy buildings with hydrogen storage considering Fanger model thermal comfort

In this study, some locations with different climates, off-grid zero energy buildings with hydrogen energy storage systems are designed, and transient analysis is conducted. These considered buildings supply their electricity consumption without using the electrical grid and PV panels or wind turbines. Also, they supply thermal comfort to occupants by using a vapor compression chiller and humidifier. Domestic hot water of occupants is supplied using solar collectors. For analyzing building's performance and objectives achievement, TRNSYS software is used. Also, for evaluating occupant thermal comfort, the Fanger model is used. The considered building is a one-story building with a 150 m2 area. Four occupants are considered. Both of them are seated at rest, and another is seated with light working such as typing. Using the Fanger model equation and MATLAB software, the thermal comfort of occupants is determined. For domestic hot water consumption, verified profiles that vary during 24 h of the day are considered. Achieved results show that for humid and cold cities, PV panels with an area of 73 and 76 m2 can be supplied the required electricity of considered building with four occupants and battery state of charge is higher than 50% and 10%, respectively. Moreover, with a suitable air conditioner system, the predicted percentage of dissatisfied (PPD) can be lower than 12% and 8% for humid and cold cities. Therefore, the building can be converted to a zero-energy building using its rooftop area.

Thermal behavior of a combi-storage in a solar-ground source heat pump system for a single-family house

Experimental investigations on thermal behavior of a combined solar and ground source heat pump (SGHP) system for a single-family house are presented. The SGHP system was installed at the Lyngby campus of Technical University of Denmark. Detailed experiments were carried out on the system in 2019 under real weather conditions covering domestic hot water (DHW) consumption and space heating (SH) demand. Depending on the contributions of the energy inputs to the combi-storage, five typical daily operation modes are classified. The focus of the investigations is on the dynamic thermal behaviors of the heat storage under different operating conditions. When the combi-storage was primarily heated by solar energy, the inlet stratifier in the storage performed well, ensuring thermal stratification and a good utilization of solar energy. Water temperature in the storage reached up to about 68℃ at the end of the solar heating process. When the combi-storage was primarily heated by the ground heat, the water temperature near the outlet for SH was kept at a temperature range from 26℃ to 31℃ in the heating process to ensure the outlet temperature level of SH, and the water temperature near the outlet for DHW was in the temperature range 47℃∼51℃ in DHW volume. When there was no heat input to the combi-storage, the pre-stored heat can meet the daily heating demand, and the number of days on this mode was up to 9.4% of the total experimental days. The paper gives valuable inputs for researchers and engineers who plan to integrate the combi-storage in a renewable heating system with solar collectors and ground source heat pumps.

Domestic hot water consumption prediction models suited for dwellings in central-southern parts of Chile

Domestic hot water (DHW) consumption in dwellings can play a key role in the development of policies that are focused on energy poverty, and in improving energy efficiency, among other aspects. There is an important variability observed with DHW among different countries due to technical, sociological, climatic, and economic factors. Most studies that deal with DHW predictions are based on stochastic models, and only a few apply time series or statistical methods. In the case of Chile, the country is undergoing a policy development process, and there is little information about DHW consumption. As a result, it is fundamental to have DHW consumption prediction models that are focused on dwelling. For this reason, the study analysed the possibility of using time series models to make future estimations about monthly domestic hot water (DHW) consumption. To this end, consumption data obtained from 98 apartments between 2015 and 2021 were used, and 3 approaches were applied namely, exponential smoothing, basic structural model (BSM), and state-space model (SSM). The results showed that exponential smoothing and state-space methods allowed to obtain satisfactory results with regard to percentage error and confidence levels. Therefore, these models could be used to make future estimations of domestic hot water (DHW) consumption.

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m2 PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m2 evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between −0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.

Model and simulation of multi-functional variable refrigerant flow systems in EnergyPlus

The multi-functional variable refrigerant flow (MFVRF) system is a promising solution to meet the UE objective that all new buildings shall be nearly zero-energy buildings (NZEBs). In particular, it is a high-efficiency system able to supply space cooling, space heating and domestic hot water (DHW) production simultaneously in different zones allowing also for waste heat recovery. The aim of this work is to implement a novel dynamic model of the MFVRF in EnergyPlus 9.4 in order to assess its final energy consumption and to account for the heat recovered when working in cooling mode to be used for DHW production. The developed model is employed to compare the performance of a MFVRF system in a multifamily residential building of 858 m2 with that of a conventional solution. The simulations are performed for two different climate conditions in Spain and two different DHW consumption temperatures. The results show significant energy savings achieved with the MFVRF system and DHW being consumed at 60 ºC for both Madrid (63.82%) and Seville (51.8%). Additionally, energy savings were even further enhanced for DHW being consumed at 45 ºC for Madrid (73.69%) and for Seville (70.71%). It is concluded that part of the annual DHW energy demand is covered by heat recovery for Madrid (4.96%) and Seville (5.69%) at a DHW consumption temperature of 60 ºC and for Madrid (6.42%) and Seville (8.96%) at a DHW consumption temperature of 45 ºC.

Residential domestic hot water consumption analysis for multifamily buildings supplied by district heating

The exact knowledge of DHW and heat consumption is necessary in the process of heat cost allocation and planning. In Hungary, heat cost allocation is based on summer months? heat demand. This method doesn?t lead to an accurate result due to the fact that the DHW demand varies throughout the year. There are several studies dealing with consumption data analisys, but only some of them have exact estimations on DHW usage patterns the Central-Eastern European countries. In this paper the DHW consumption was analysed in 115 ?commi block? buildings, which are common in Central-Eastern Europe and Russia and are usually connected to the district heating network. The examined buildings are located in Budapest, Hungary. The installation of the monitoring system has started in December 2012. The consumption data is collected since March 2014. The DHW usage was calculated in different cases for every month: per heated area, per heated volume and per flat. Average daily and annual data was also determined, the share of yearly DHW consumption over the months was calculated. The average daily and annual DHW consumption are 126 l/flat and 892 l/m2, respectively. The average net heat consumption is 28.2 kWhm-2a-1. Different DHW demand influencing factors were examined: the outdoor temperature and the residents? travelling habit is clearly influencing the DHW usage but no connection was found between the DHW consumption and economic indicators. The DHW consumption is approximately 30% higher in the winter than in the summer.

Hourly and daily domestic hot water consumption in social housing dwellings: An analysis in apartment buildings in Southern Brazil

Solar water-heating systems have been widely implemented in Brazilian social housing buildings. Although these systems have been extensively explored regarding energy consumption, little is known about the water consumption. This article analyzes hot water consumption data from 154 social housing apartments in Southern Brazil. Hourly and daily consumption were analyzed regarding volume, profile and seasonal variations. The current system design was analyzed and compared to optimum configurations. The water-heating system only provides hot water for the shower, and the measurements presented refer to untempered hot water – before mixing with cold water to reach end-use temperature. Three peaks were found to occur during the day: in the morning, during lunch time and in the evening, which was the highest. In addition, seasonal ambient temperature and solar radiation showed significantly correlated to daily hot water consumption. Summer average per capita hot water consumption was lower than other seasons’, while the average consumption during fall was the highest. If the collectors were installed facing North and with a 26° inclination, the solar hot water system would provide more adequate temperatures.

Domestic hot water consumption pattern: Relation with total water consumption and air temperature

From a sustainable development perspective, reducing hot water consumption poses the opportunity for increasing water and energy efficiency simultaneously. Comparing with the research on total water and water end-use distribution, quantitative data on domestic hot water consumption and understanding/modeling the drivers underlying its use is scarcer. More importantly, since total water consumption is frequently measured at a household level, estimating the portion that is used as domestic hot water would allow a simpler modeling approach than accounting for all the factors affecting water consumption in general, and domestic hot water consumption in particular.The present research effort aims at providing insights on domestic hot water consumption in households by using 3 years of cold and hot water monthly records from around 10 300 apartments divided by 500 buildings spread over 3 regions of Belgium. In addition to the expected seasonal variation, the proportion of the water consumption used as hot water was found to vary between 28% and 36%, on average. Also, domestic hot water consumption variation was found to be strongly correlated with the outside air temperature. The results presented provide a simple tool to estimate the order of magnitude of domestic hot water consumption knowing the total water consumption.

Domestic Hot Water Consumption Profiles Applied to a Flat Tubular Collector for Solar Water Heating in Bogotá

The use of Flat Solar Collectors for the generation of Domestic Hot Water (DHW), facilitates access to this resource in an efficient, economical and sustainable way. The Sustainable Development Goals proposed by the UN, referring specifically to sustainable water management and access to renewable energy, are the main motivation for this work, since the former is an essential vital resource and its access reduces the inequality index, in developing countries such as Colombia, while the use of solar thermal energy reduces the environmental impact of the water heating process, thus reducing the consumption of electrical energy in the residential sector. Therefore, this work proposes to estimate DHW profiles through a spreadsheet that models the DHW flow thermodynamically for a whole year, making it possible to evaluate the energy performance of a Solar Collector available in the Colombian market and that is used in four types of dwellings located in the city of Bogotá. The simulation results present the DHW consumption profiles in kg/h per year, with DHW temperatures of up to 21°C, for a total transmitted irradiance of the order of 1100 W/m^2, which produces thermal energy close to 1kW. This comparative analysis allows us to review the technical and economic feasibility of solar collectors installed in single-family homes and with a DHW consumption profile close to the Colombian socio-economic reality.

Domestic hot water system in residential buildings: production, distribution and consumption energy loss. Monitoring campaign in two Danish detached houses

The share of the energy use for domestic hot water (DHW) in the total energy consumption of buildings is becoming more and more prominent. Depending on the building typology it varies between 20% to 50% of the total energy usage for old and new built single family house, respectively. The aim of this paper is to determine the energy losses in the DHW installation with division between: a) loss at the production point, b) loss in the distribution, and c) loss at the draw-off points using the results of the measurements of DHW consumption in two single family houses connected to district heating grid. The total Eloss for the two houses vary between 17% and 26%. For House 1, the production loss accounts for 8%, the pipe loss for 15% and loss at the draw off points for 3%. Moreover, the results shown that the layout of the house, in particular the placement of the bathrooms with showers or bath tubs has significant impact on the size of the distribution losses.

Performance and dynamics of active greywater heat recovery in buildings

In the effort to de-carbonize the building stock, heat pumps are increasingly utilized in Switzerland, with 70% of the fast-growing heat pump market using ambient air as heat source. Inexpensive and easy to implement, these heat pumps are, however, less efficient than their ground- or water-source counterparts. In this modeling study, we aim at increasing the efficiency of air-source heat pumps using domestic greywater-contained heat. We assess the performance improvement relative to standard heat pump configurations across various climates, seasons, building envelopes, and domestic hot water consumption patterns. The results show that the annually-averaged coefficient of performance improves by 4.1% on average – ranging from 0.6% to 7.5%. This efficiency gain translates on average to 1.8 kWh/week of compressor electricity savings. Although attractive due to its simplicity, the proposed open-loop configuration – preheating of an external heat source – only leads to moderate performance improvement of air-source heat pumps. Based on these results, we extensively discuss and compare alternative system configurations and identify several fundamental differences in the heat recovery dynamics of each configuration. We show that closed-loop systems – using greywater as direct heat source – show the largest performance improvement potential, although being more expensive and complex to implement.

Flexibility Estimation of Residential Heat Pumps under Heat Demand Uncertainty

With the increasing penetration of intermittent renewable energy generation, there is a growing demand to use the inherent flexibility within buildings to absorb renewable related disruptions. Heat pumps play a particularly important role, as they account for a high share of electricity consumption in residential units. The most common way of quantifying the flexibility is by considering the response of the building or the household appliances to external penalty signals. However, this approach neither accounts for the use cases of flexibility trading nor considers its impact on the prosumer comfort, when the heat pump should cover the stochastic domestic hot water (DHW) consumption. Therefore, in this paper, a new approach to quantifying the flexibility potential of residential heat pumps is proposed. This methodology enables the prosumers themselves to generate and submit the operating plan of the heat pump to the system operator and trade the alternative operating plans of the heat pump on the flexibility market. In addition, the impact of the flexibility provision on the prosumer comfort is investigated by calculating the warm water temperature drops in the thermal energy storage given heat demand forecast errors. The results show that the approach with constant capacity reservation in the thermal energy storage provides the best solution, with an average of 2.5 min unsatisfactory time per day and a maximum temperature drop of 2.3 °C.

Stochastic energy optimization of residential heat pumps in uncertain electricity markets

The penetration of renewable energy sources is increasing in power systems all over the world. Due to the intermittency and volatility of renewable energies, demand-side management is a practical solution to overcome the problem. This paper proposes a stochastic model predictive control for heat pumps to supply space heating and domestic hot water consumption of residential buildings. Continuous-Time Stochastic Model is coded in R language to address the model identification approach. The approach uses the sensor data of households to extract the thermal dynamics of the building. The controller participates in three floors of power markets with high renewable power penetration. The three-stage stochastic programming is suggested to unlock power-to-heat flexibility in the day-ahead, intraday, and balancing markets on long, mid, and short advance notices, respectively. Regarding the close correlation between renewable power availability and electricity price, the price data is modeled as probabilistic scenarios through Auto-Regressive Integrated Moving Average. The ambient temperature, as well as the domestic hot water consumption, are addressed as envelope-bounds with upper and lower thresholds. Finally, the operational strategies of the controller are examined on a 150 m2 test house under uncertain electricity prices, weather variables, and occupancy patterns.

Real Domestic Hot Water Consumption in Residential Buildings and Its Impact on Buildings’ Energy Performance—Case Study in Poland

A building’s energy consumption is assessed considering the energy required for heating, cooling, lighting, and domestic hot water (DHW). Methodologies used to calculate energy certificates in European Union countries consider hot water consumption rates per person or per heated (floor) area, giving wide-ranging values (35–88 dm3/person/day). Using extreme parameters, it is possible to obtain a primary energy index that meets the legal requirements, although unrealistically large proportions of domestic hot water use relative to the total energy balance of the building may marginalize the influence of other components, such as fluctuations in heating, ventilation, or lighting. In the current work, the DHW consumption of three residential buildings was measured to verify the energy consumption for hot water preparation. Investigations were conducted based on the consumption of natural gas for DHW preparation. Experimentally obtained water consumption rates were determined per m2 of a dwelling and per person living in the building. The calculated indicators (0.85 ± 0.005 dm3/m2/day and 27.4 ± 1.4 dm3/person/day) were lower than those used for energy certifications of buildings. The experimentally obtained indicators were used in further theoretical energy assessments of six residential buildings. By adopting the designated indicators, the analyzed buildings met the legally required primary energy value (<70 kWh/m2/year) when using natural gas as a heat source. Applying more realistic DHW consumption values resulted in more accurate energy certifications.

Uncertainties in Non-Domestic Energy Performance Certificate Generating in the UK

In light of the recent launch of the Minimum Energy Efficiency Standard targeting the energy performance of commercial buildings, this study compares the energy performance certificates of three UK hotels generated by two different software, EDSL TAS and SBEM, both accredited by the UK government for the purpose. Upon finding the results discrepant, the study finds that the two software’s different assumptions for the air permeability rate contribute to the discrepancy. While modifying this value makes the results from the two software more aligned, further issues regarding the validation process arise. The study continues to find that the underlying issue can be found within the National Calculation Methodology’s assumption about domestic hot water consumption in hotels. These assumptions are compulsory to follow when generating a non-domestic energy performance certificate in the UK, therefore, any uncertainties within them can affect all the buildings seeking an energy performance certificate within that sector. Finally, the study discusses that, for meeting the carbon dioxide mitigation goals, it is necessary to make changes to the current procedure of energy performance certificate generating in the UK to increase its reliability.

Comparison of the performance of a domestic solar water heater in different climates in Algeria

A simulation with TRNSYS of an individual solar water heater for the hot water needs of an average family in Algeria was made; three cities of different climates were chosen to the north on the coast, in the highlands and in a desert region, the solar water heater consists of a flat panel of 4m² and a storage tank of 300 liters, a back-up electrical energy is activated when solar radiations are insufficient or during the night, the consumption of domestic hot water leaving the tank at 60 °C follows a typical profile, the results show significant performance in the south and similar data in the north and in the highlands.

Global-Local Heat Demand Development for the Energy Transition Time Frame Up to 2050

Globally, the heat sector has a major share in energy consumption and carbon emission footprint. To provide reliable mitigation options for space heating, domestic hot water, industrial process heat and biomass for cooking for the energy transition time frame up to the year 2050, energy system modeling relies on a comprehensive and detailed heat demand database in high spatial resolution, which is not available. This study overcomes this hurdle and provides a global heat demand database for the mentioned heat demand types and in a resolution of 145 mesoscale regions up to the year 2050 based on the current heat demand and detailed elaboration of parameters influencing the future heat demand. Additionally, heat demand profiles for 145 mesoscale regions are provided. This research finds the total global heat demand will increase from about 45,400 TWhth in 2012 up to about 56,600 TWhth in 2050. The efficiency measures in buildings lead to a peak of space heating demand in around 2035, strong growth in standards of living leads to a steady rise of domestic hot water consumption, and a positive trend for the worldwide economic development induces a growing demand for industrial process heat, counterbalanced by the efficiency gain in already industrialised countries. For the case of biomass for cooking, a phase-out path until 2050 is presented. Literature research revealed a lack of consensus on future heat demand. This research intends to facilitate a more differentiated discussion on heat demand projections.

New Deterministic Mathematical Model for Estimating the Useful Energy Output of a Medium-Sized Solar Domestic Hot Water System

According to the authors of this paper, the mathematical point of view allows us to see what sometimes cannot be seen from the designer’s point of view. The aim of this study was to estimate the influence of the most important parameters (volume of heat storage tanks, daily consumption of domestic hot water, optical efficiency, heat loss coefficient, and total area of a solar collector) on the thermal power output of solar domestic hot water (SDHW) system in European climatic conditions. Three deterministic mathematical models of these relationships for Madrid, Budapest, and Helsinki were created. The database for the development of these models was carried out using computer simulations made in the TRNSYS software environment. The SDHW system located at the Bialystok University of Technology (Poland) was the source of the measurement results used to validate the simulation model. The mathematical optimization procedure showed that the maximum annual useful energy output that can be obtained from 1 m2 of gross collector area is 1303 kWh in the case of Madrid, 918.5 kWh for Budapest, and 768 kWh for Helsinki weather conditions.

Predictability analysis of domestic hot water consumption with neural networks: From single units to large residential buildings

Domestic hot water is a major energy load in current residential buildings. Improving the energy management and efficiency of water heating systems with smart predictive control requires forecasting the domestic hot water consumption. However, accurate prediction models have proven to be difficult to obtain, which is a major barrier to the applicability of predictive control strategies and their ability to reduce the energy consumption. This work optimizes the input parameters and architecture of neural networks to produce prediction models of the future domestic hot water demand. The methodology is tested on domestic water heating systems of various sizes by using data measured in a 40-unit multifamily residential building. The prediction model provides a good performance for the domestic hot water consumption of the entire building (R2 of 0.88). However, for smaller system sizes, the prediction performance is quite variable. This work proposes graphical tools to evaluate the expected predictability of DHW consumption profiles for systems of different sizes and reveals the close relation between the predictability of a given profile and its coefficient of variation.