Domestic Hot Water Consumption Research Articles

Domestic hot water consumption in multi-apartment buildings

The article presents the analysis of the hot water consumption in apartment buildings. This study was conducted basing on the data gathered from 626 apartments during two following years. By statistical analysis of the collected data, the correlation between the DHW consumption and both the size of the apartments and the number of occupants in the dwellings was evaluated. The dependencies between the hot water consumption and these two parameters were calculated. The results were compared to the data available in the literature. The article lists the areas of the greatest inaccuracies in the calculations basing on the available indicators and proposes an alternative method that corrects them. The results were used to develop a calculation model for daily hot water usage in multi-apartment buildings.

A new test procedure to evaluate the performance of substations for collective heating systems

The overall heat demand of a single dwelling, existing out of space heating and domestic hot water production, decreases due to higher insulation rates. Because of this, investing in efficient and renewable heat generation becomes less interesting. Therefore, to incorporate renewables or residual heat on a larger scale, district heating or collective heating systems grow in importance. Within this set-up, the substation is responsible for the interaction between local demand for comfort and overall energy performance of the collective heating system. Many different configurations of substations exist, which influence both local comfort and central system performance. Next to that, also hybrids exist with additional local energy input. To evaluate performance of such substations, a new experimental-based test procedure is developed in order to evaluate these different aspects, characterized by the two roles a substation has, namely as heat generator and as heat consumer. The advantage of this approach is that an objective comparison between individual and central systems regarding performance on delivering local comfort can be executed experimentally. The lab set-up consists out of three different subsystems, namely the central system, the domestic hot water consumption and the local space heating. The central system can work with different temperature regimes and control strategies, as these aspects have proven to have the largest influence on actual performance. The domestic hot water system is able to generate similar tap profiles according to eco-design regulation for domestic hot water generation. The space heating system is able to demand a modular heat load.

Impact of the circulation system on domestic hot water consumption

The article presents the results of researches for domestic hot water in two, the same buildings – students dormitories. There was not working circulation system in one of the objects. Characteristics of hot water intake and the size of the design flows were determined. The influence of circulation loop existence on the size of hot water consumption and characteristic values which are describing the size of hot water abstraction in analyzed buildings was pointed out.

Retrofitted Solar Domestic Hot Water Systems for Swedish Single-Family Houses—Evaluation of a Prototype and Life-Cycle Cost Analysis

According to recent technology road maps, system cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. Previous studies have investigated such retrofitting, using theoretical simulations and laboratory tests, but no actual installations were made and tested in practice. This article describes the installation, measured performance and cost effectiveness of a retrofitting solution that converts existing domestic hot water heaters to a solar domestic hot water system. The measured performance is characterised by the monthly and annual solar fractions. The cost effectiveness is evaluated by a life-cycle cost analysis, comparing the retrofitted system to a conventional solar domestic hot water system and the case without any solar heating system. Measurements showed that approximately 50% of the 5000 kWh/year of domestic hot water consumption was saved by the retrofitted system in south Sweden. Such savings are in agreement with previous estimations and are comparable to the energy savings when using a conventional solar domestic hot water system. The life-cycle cost analysis showed that, according to the assumptions and given climate, the return on investment of the retrofitted system is approximately 17 years, while a conventional system does not reach profitability during its lifetime of 25 years.

Hourly consumption profiles of domestic hot water for different occupant groups in dwellings

Hourly consumption data of domestic hot water (DHW) is essential to compute the energy demand, and for system sizing. Few on-site measured data and simulation based studies are available to forecast DHW consumption focusing on a daily average, hourly average, appliance consumption, and occupant number. This study derived the hourly DHW profiles for 5 different groups of 1 person, 3 people, 10 people, 31 people and more than 50 people as a function of the number of occupants. Weekday (WD), Weekend (WE) and Total day (TD) consumption variation were analyzed. The study accomplished with on-site hourly DHW consumption measurement from 86 apartments with 191 occupants during one year and findings was also validated against a larger sample from previous study. A specific selection procedure was developed to find out the most representative DHW profile among measured candidates of each group fulfilling the selection criteria. Selected profiles had similar daily consumption (L/per./day) to an average of all profiles and also followed similar consumption pattern during a day. Two sharp peaks with large consumption variance were found in each day and smaller groups had higher consumption during peak hours. Result also found higher evening peak compared to the morning peak and the average consumption of peak hours was 2–4 times higher than non-peaks hours. Morning peaks of WE shifted 2–3h later from WD’s and kept similar position during the evening. Profiles of 5 groups were necessary to normalize with scaling factor to maintain the daily average value. Derived hourly values could be used with monthly factors to deliver hourly profiles of all months and the format of hourly and monthly factors used allows to define DHW consumption in relevant simulation and sizing software.

The calibration and validation of a model for predicting the performance of gas-fired tankless water heaters in domestic hot water applications

Gas-fired tankless water heaters are gaining popularity as a means of producing domestic hot water for residential applications. As they become more widespread, these devices are increasingly becoming important to researchers who are seeking models of these devices that can be used to make reasonable predictions of their energy consumption. This is especially true for the case of condensing tankless water heaters as they have been shown to be the most efficient method of producing domestic hot water. Current models of these devices do exist, however, the uncertainties of their predictions are unclear and require data collected from onerous field-trials for calibration.This article makes a contribution by introducing a new model of a condensing tankless water heater whose uncertainties are well described that can be calibrated by a less-onerous experimental program in a laboratory. The model was calibrated with data spanning a range of conditions: inlet temperatures between 10 and 23°C, water flow rates between 0.08 and 0.27Ls−1 and outlet temperatures between 36 and 48°C.The model predictions were validated against data emanating from a previous field-trial. Above domestic hot water consumption values of 15MJday−1, the coefficient of determination (r2 value) was 0.98. The average error (difference between the average model predictions and the measured values) was 3.0% (in relative terms) while the root mean square error was 4.2%. The maximum error for a single point was 8.7% at a domestic hot water consumption of approximately 30.2MJday−1.

A stochastic bottom-up model for space heating and domestic hot water load profiles for German households

In 2013 83% of energy in the German residential sector is used for the preparation of domestic hot water (13%) and space heating (70%). Thermal demand profiles are essential to correctly determine operation and sizing of heating technologies. In this work, the stochastic bottom-up approach for electric loads is extended to cover domestic hot water (DHW) and space heating demands. The approach is presented for individual buildings and residential areas, validated and compared to currently used approaches. A behavioural model is used to determine DHW tappings, electric appliance use and temperature settings of the building. Building heat load is calculated using a simplified physical model, to allow for realistic energy demand profiles, efficient model parametrisation and fast computation. A randomisation approach for building heat load based on a clustered building typology, a variation of building parameters and heating settings is presented which allows the simulation of larger quantities of similar buildings. Validation against measured data for German single family houses shows a correlation of the typical daily load profile for DHW consumption of 0.92 and a mean relative error of 3% and for space heating 0.89 and 9% respectively.

Utilising Time of Use Surveys to Predict Domestic Hot Water Consumption and Heat Demand Profiles of Residential Building Stocks

Utilising Time of Use Surveys to Predict Domestic Hot Water Consumption and Heat Demand Profiles of Residential Building Stocks

High-resolution stochastic integrated thermal–electrical domestic demand model

This paper describes the extension of CREST’s existing electrical domestic demand model into an integrated thermal–electrical demand model. The principle novelty of the model is its integrated structure such that the timing of thermal and electrical output variables are appropriately correlated. The model has been developed primarily for low-voltage network analysis and the model’s ability to account for demand diversity is of critical importance for this application. The model, however, can also serve as a basis for modelling domestic energy demands within the broader field of urban energy systems analysis. The new model includes the previously published components associated with electrical demand and generation (appliances, lighting, and photovoltaics) and integrates these with an updated occupancy model, a solar thermal collector model, and new thermal models including a low-order building thermal model, domestic hot water consumption, thermostat and timer controls and gas boilers. The paper reviews the state-of-the-art in high-resolution domestic demand modelling, describes the model, and compares its output with three independent validation datasets. The integrated model remains an open-source development in Excel VBA and is freely available to download for users to configure and extend, or to incorporate into other models.

Dynamic Simulation of Solar Thermal Collectors for Domestic Hot Water Production

In this paper a system for the Domestic Hot Water (DHW) production based on solar collectors is analyzed by means of a dynamic approach based on a Simulink model and by using the F-chart method, able to evaluate system performances on a monthly basis. Following the dynamic approach, it is possible to evaluate hour by hour the energy collected by the solar panels and the temperature of the hot water produced by the system, by taking into account the impact of different daily DHW consumption profiles on the percentage of thermal energy produced by the solar collector (Solar Coverage Factor, SCF). The comparison between the prediction made both by using the Simulink model and the F-Chart method in terms of SCF is shown by taking into account the effect on SCF of the typology of solar collector (unglazed, glazed and evacuated collectors), of the storage tank volume connected to the solar panels and of the hourly DHW consumption profile. The results point out that SCF is strongly dependent on the daily DHW consumption profile, which cannot be taken into account in a quasi-static approach like the F-chart method.

High resolution measured domestic hot water consumption of Canadian homes

The modeling and simulation of domestic hot water systems, including solar thermal and co-generation technologies, relies on accurate, high time-step resolution water consumption profiles. Due to the expensive nature of field studies, previous profiles have been limited in number of participants, or have been generated synthetically using probabilistic modelling techniques. The Solar City program in Halifax has measured hot water flow rate and temperature data in 119 homes at a time-step of 1min; and includes a survey of occupancy rates and other relevant meta-data. In this paper, we discuss the data acquisition and processing (with a focus on flow rate data), and conduct analysis to reveal consumption trends and produce a new set of time-step profiles for modeling and simulation. Average hot water consumption per household is 172L/day with a strong dependency on number of occupants. The hourly profile peaks twice daily, and shifts by several hours on Sunday. The average draw temperature was found to be 51.8°C, which is lower than the default value of 55°C applied by many building modeling/simulation packages. The average cold water supply temperature was found to be roughly sinusoidal about 12.4°C with approximately one-month lag compared to ambient air temperature.

Dimensioning of Solar Thermal Systems for Multi-Family Buildings in Lithuania: an Optimisation Study

Small-scale solar thermal domestic hot water (DHW) systems in Lithuania can produce up to 523 kWh per year per one square meter of solar collector area. It is therefore one of the most common solar thermal applications in the country with the expected payback period of approximately 10 years. However, the number of solar water heating systems (SWH) installed in the renovated multi-family buildings is quite limited. On the other hand, the potential of integrating solar thermal systems in these buildings is much higher as DHW usage during the day is more uniform in multi-family buildings compared to the single-family houses. This aspect brings out a higher solar energy share without adding additional volume to the hot water storage tank. Simplified optimization tools for solar collector area selection, volume selection for the accumulation tank, installation costs and payback period estimation are required for promoting SWH systems for DHW production in multi-family buildings. This paper deals with DHW consumption analysis in multi-family buildings in Lithuania as well as modelling of solar thermal systems to produce a tool for decision makers for preliminary analysis of SWH systems integration in renovated multi-family buildings. The main target group for the tool developed are multi-family buildings connected to district heating network. Simulation software “T*SOL 5.0 Pro” was used for SWH systems performance evaluation as well as financial analysis of SWH system alternatives.DOI: http://dx.doi.org/10.5755/j01.sace.11.2.12459

Regulatory energy calculations versus real energy use in high-performance houses

How accurately can official energy performance calculations assess the real energy use in high-performance houses? This question was investigated by analysing 537 dwellings. Data on building characteristics and calculated performance from the Flemish Energy Performance of Buildings (EPB) database were complemented with data from energy utilities and surveys of inhabitants, their socio-demographic characteristics and user behaviours. While the real and theoretical energy uses were strongly correlated, the official calculation method overestimated the heating energy use of most houses while neglecting important electricity end uses. The prediction error varied strongly between individual cases. Two options within the calculation procedure had a significant impact on these prediction errors: the use of default values for the air tightness of the building envelope and the reported return temperature of the space heating system. The simplified calculation of net domestic hot water consumption and the real heating of the master bedrooms also affected prediction accuracy. However, extrapolations are hazardous due to the risk of selection and non-response biases implied by the approach and the need for further research into the causalities. Nonetheless, the findings stress the importance of accurate input data and realistic default values for calculation models used for high-performance buildings.

Statistical Modeling for Real Domestic Hot Water Consumption Forecasting

Abstract In this paper, we study the real domestic hot water (DHW) consumptions from single family houses equipped with solar hot water tank. We model it to understand and forecast the daily needs of inhabitants. Thus, the forecasts can be integrated in a control strategy to optimize the energy cost by heating only the necessary DHW volume. At first, we realize a data analysis from real uses of several dwellings to lay assumptions of the statistical model. This study highlights a weekly periodicity, random fluctuations and the different profiles of consumption following the residence, the season, and the day of the week. Otherwise, having no prior information like the location or the number of residents, we propose an adaptive time series model which does not require strong a priori and computational time. Then, we develop an ARMA model to forecast the daily DHW volume and we apply it on each individual installation. This model allows to take into account the periodicity of one week, the consumption of the previous days and random fluctuations. The results obtained on real data show that this approach is very promising.

Large solar driven heat pump system for a multifamily building: Long term in-situ monitoring

This article presents the monitoring results of an existing large scale system that combines heat pumps with unglazed solar collectors (used for heat production or as heat source for the heat pumps). The system provides space heating and domestic hot water to a new housing complex (∼10,000heatedm2) in Geneva, Switzerland. Detailed monitoring of one of the blocks (∼1000heatedm2, 32 inhabitants) enables to characterise the behaviour of the system (building demand, control strategy, temperature levels) and to determine the energy flows as well as the performance of the system. The results show a very low space heating demand for Switzerland (∼20kWh/m2/yr), and an unusually high domestic hot water consumption (∼50kWh/m2/yr). The measured seasonal performance factor of the system, including backup electric heating and heat source circulation pump, is 2.9 for 2012 (average of 2.5 in winter and 4.4 in summer). This result can partly be explained by the high domestic hot water consumption, which implies a heat production at high temperature. This project is part of IEA SHC Task 44 “Solar and Heat Pump Systems”.

A comparison of the energy consumption in two passive houses, one with a solar heating system and one with an air–water heat pump

Detailed measurements of the auxiliary energy consumption for space heating and domestic hot water preparation in two detached passive houses south of Oslo are reported for the full year 2013. The study compares two equal, new built houses heated with different technologies, one by solar thermal heating and the other with an air-to-water heat pump. The houses are built by central actors from the building industry with high potential of being representative for a sizable, new-built housing stock rather than with focus on system optimisation. The results show that the need for additional energy, corrected for differences in domestic hot water consumption and indoor temperature, is 15–20% higher in the heat pump heated house than in the solar heated house. However the general energy consumption exceeds significantly the dimensioned figures for passive houses in Norway. The measurements demonstrate that solar thermal heating is competitive with heat pump technology even at high latitudes under Norwegian climate even in the case of a non-optimised system. With the available data potential heating system design improvements were pointed out.

A New System to Estimate and Reduce Electrical Energy Consumption of Domestic Hot Water in Spain

Energy consumption rose about 28% over the 2001 to 2011 period in the Spanish residential sector. In this environment, domestic hot water (DHW) represents the second highest energy demand. There are several methodologies to estimate DHW consumption, but each methodology uses different inputs and some of them are based on obsolete data. DHW energy consumption estimation is a key tool to plan modifications that could enhance this consumption and we decided to update the methodologies. We studied DHW consumption with data from 10 apartments in the same building during 18 months. As a result of the study, we updated one chosen methodology, adapting it to the current situation. One of the challenges to improve efficiency of DHW use is that most of people are not aware of how it is consumed in their homes. To help this information to reach consumers, we developed a website to allow users to estimate the final electrical energy needed for DHW. The site uses three estimation methodologies and chooses the best fit based on information given by the users. Finally, the application provides users with recommendations and tips to reduce their DHW consumption while still maintaining the desired comfort level.

Forecasting household consumer electricity load profiles with a combined physical and behavioral approach

In this paper, a simulation model that forecasts electricity load profiles for a population of Swedish households living in detached houses is presented. The model is constructed of three separate modules, namely appliance usage, Domestic Hot Water (DHW) consumption and space heating. The appliance and DHW modules are based on non-homogenous Markov chains, where household members move between different states with certain probabilities over the days. The behavior of individuals is linked to various energy demanding activities at home. The space heating module is built on thermodynamical aspects of the buildings, weather dynamics, and the heat loss output from the aforementioned modules. Subsequently, a use case for a neighborhood of detached houses in Sweden is simulated using a Monte Carlo approach. For the use case, a number of justified assumptions and parameter estimations are made. The simulations results for the Swedish use case show that the model can produce realistic power demand profiles. The simulated profile coincides especially well with the measured consumption during the summer time, which confirms that the appliance and DHW modules are reliable. The deviations increase for some periods in the winter period due to, e.g. unforeseen end-user behavior during occasions of extreme electricity prices.

Water Label to Improve Water Billing in Spanish Households

A significant decrease in water consumption has been achieved in recent years thanks to different campaigns run by different institutions in Spain. However, most citizens do not have a very clear idea about whether or not they are efficiently using water. To solve this situation, this paper aims is to develop two water labels in order to improve the current water billing. These water labels evaluate the total water consumption and the domestic hot water consumption. To make the tags, several research studies were tackled for establishing consumer trends and behavior patterns. Furthermore, a survey and data collection were conducted to obtain updated values to validate information obtained from previous studies. The result are two water labels that establish six different levels to graphically show the efficiency, and they also include a comparison with the average consumption by customers of the same province. To ensure that the benefits of this evaluation are available to citizens, its inclusion on the water bill is proposed.

Implementation and Control of a Residential Electrothermal Microgrid Based on Renewable Energies, a Hybrid Storage System and Demand Side Management

This paper proposes an energy management strategy for a residential electrothermal microgrid, based on renewable energy sources. While grid connected, it makes use of a hybrid electrothermal storage system, formed by a battery and a hot water tank along with an electrical water heater as a controllable load, which make possible the energy management within the microgrid. The microgrid emulates the operation of a single family home with domestic hot water (DHW) consumption, a heating, ventilation and air conditioning (HVAC) system as well as the typical electric loads. An energy management strategy has been designed which optimizes the power exchanged with the grid profile in terms of peaks and fluctuations, in applications with high penetration levels of renewables. The proposed energy management strategy has been evaluated and validated experimentally in a full scale residential microgrid built in our Renewable Energy Laboratory, by means of continuous operation under real conditions. The results show that the combination of electric and thermal storage systems with controllable loads is a promising technology that could maximize the penetration level of renewable energies in the electric system.