Tankless Water Heater Research Articles

Measurement and quantification of methane emissions from residential gas stoves and tankless water heaters in China

Methane is a short-lived and potent greenhouse gas with a rapid warming effect. Gas stoves and water heaters, which are the most widely used domestic gas appliances (over 250 million in China), emit methane because of incomplete combustion and leakage. This study quantified the methane emissions of these two gas appliances at different ages through field measurements and laboratory tests to assess their impact on the climate. Their methane concentrations typically spiked quickly and decayed rapidly during ignition and extinguishment, but were low and stable during the steady-on state. Tankless water heaters emitted 1.69‰ (95% confidence interval: 1.44‰, 2.01‰) of the natural gas consumed, primarily during the on-pulse phase. More than four-fifths of the methane emissions from gas stoves occurred in the steady-on state, and the emission rates were positively correlated with the age of the gas stoves (r2 = 0.79, p < 0.001). Therefore, approximately 28.1 (27.5, 28.6) Gg of methane emissions annually can be attributed to Chinese residential gas appliances, corresponding to a 0.8 Mt. carbon dioxide equivalent over a 100-y scale.

In Situ Performance Analysis of Hybrid Fuel Heating System in a Net-Zero Ready House

The global population’s growth and increased energy consumption have driven greenhouse gas (GHG) emissions. In Canada, the residential sector accounts for 17% of secondary energy use and 13% of GHG emissions. To mitigate GHG emissions, promoting renewable energy and efficient heating systems is crucial, especially in cold climates like Canada, where there is a heavy dependency on fossil fuels for space heating applications. A viable solution is hybrid fuel heating systems that combine electric-driven air-source heat pumps (ASHPs) with natural gas tankless water heaters (TWHs). This system can alternate its operation between the ASHP and TWH based on efficiency and real-time energy costs, reducing grid peak demand and enhancing resilience during power outages. Although lab experiments have shown its benefits, in situ performance lacks evaluation. This study analyzes the in situ energy performance of a net-zero ready house and its hybrid fuel heating system, assessing energy consumption, hourly space heating output, and system heating performance. HOT2000 is a robust simulation software designed for assessing energy consumption, space heating, cooling, and domestic hot water systems in residential buildings. An artificial neural network model was developed to predict the energy performance of the hybrid fuel system, which was used as a substitute for monitored data for evaluating the HOT2000’s simulation results under the same weather conditions. Therefore, this study proposes a comprehensive framework for the in situ performance analysis of hybrid fuel heating systems. This study then, using HOT2000 energy consumption results, evaluates the life cycle costs of the hybrid fuel system against conventional heating systems. Furthermore, this study proposes an economical control strategy using in situ data or manufacturer specifications.

Evaluación Tecno-económica de alternativas para calentamiento doméstico de agua para la ciudad ecuatoriana de Cuenca

INTRODUCTION. Homes in the Andean region of Ecuador, due to the relatively cold ambient temperature, require energy services such as hot water in a daily basis along the year. In that context, the preferred technologies used for such purpose run on LPG, mainly, due to its low cost as it is highly subsidized. This situation poses certain challenges for the energy policy of the country. OBJECTIVE. This case study aims to discuss more sustainable alternatives to obtain hot water for household use in the context of the Andean city of Cuenca. METHOD. Firstly, solar and meteorological data has been processed to characterize local conditions. Then, different technologies able to provide hot water have been simulated. Further, an economic analysis was performed to determine costs per unit of energy required. RESULTS. The use of subsidized LPG reduces the real cost of water heating between 47% and 72% depending on the daily levels of consumption. In the event of a subsidy removal, electric tankless water heaters, along with reduced electricity tariffs, become competitive for levels of consumption up to 120 liters per day. For higher levels of consumption solar thermal systems or heat pumps may become viable only when providing rebates DISCUSSION AND CONCLUSIONS. The presence of benefits of scale among levels of consumption need to be regarded when designing incentives for energy services such as domestic hot water.

Anaerobic Digestion of Dairy Effluent in New Zealand, Time to Revisit the Idea?

The anaerobic digestion of New Zealand low-input dairy farms has previously been evaluated for energy production, but farming systems have recently become more intensive with increased feed supplementation and feed replacement; therefore, we are studying how these changes affect the overall energy production for water heating. A combination of literature review, surveys, chemical analyses, biomethane potential analysis, and modeling were used for this study. On a case study farm with a solid separator, it was found that 558 MJ/day and 176–861 MJ/day could be produced with the solid and liquid portions of effluent, respectively. There is enough biogas to satisfy the dairy farm’s water heating requirements with a tankless water heater.

A field study of combo heating systems in Canadian single-family buildings

This study presents a field study of the performance of three multi-zone gas-fired comboheating systems that provide space heating and domestic hot water in three new single-family houses in the Greater Toronto Area in the Province of Ontario, Canada. Two systems are composed of a gas-fired condensing tankless water heater integrated with a smart air handling unit, while the third system is composed of a gas-fired condensing combi boiler integrated with a smart air handling unit. The performance of the three combo heating systems was monitored, analyzed and evaluated over one heating season. The gas consumption of the three systems were compared with traditional gas-fired heating systems (composed of forced-air gas furnace and gas storage tank water heater). Results showed that combo heating systems tested in this study are reliable, met the peak space heating load, improved the indoor thermal comfort by providing two independently controlled temperature zones and achieved significant gas savings compared to traditional natural gas heating systems. The annual gas consumption and greenhouse gas emissions of the combo heating systems tested in this study are less than the traditional gas-fired heating system (forced-air gas furnace and gas storage tank water heater) by up to 29%.

Experimental design and numerical validation of a low-cost water heater by electromagnetic induction

This study shows a new approach to heat water in a residential environment. An electromagnetic heating method is proposed. A steel bar inside a pipeline filled with water is heated by five arrangements of a copper coil which incites the steel bar by electromagnetic induction. Consequently, numerical simulation and experimental evaluation are compared. The outcomes evaluated two different scenarios: steady water and a water flow of 0.16 kg/s. Three rods demonstrated that current induction of 20 A at the surface of the steel bar heats at 157°C. Also, the maximum value reached is 58°C. Heating the water upon for those conditions, the proposed tankless instantaneous water heater (TIWH) reaches a temperature of 41.01°C with one rod but only reaches 37.92°C with three rods in a series configuration, in a parallel configuration, the maximum temperature reached was 28.73°C.

An innovative control system of a hybrid tankless water heaters using LabVIEW

This paper presents an innovative control system of a hybrid tankless water heater that provides a rapid response to deliver hot water within a desired temperature range at lower energy consumption. The proposed tankless water heater provides a hybrid heating process that composes of a gas fired heater as primary heater and an electric heating system as secondary heater. LabVIEW designing software was used in designing the control system. A controller was designed using a PID controller which response with respect to given input parameter such as changes in water flow and the inlet temperature. Through alteration of heat source, this efficiently reduces the power consumption of the tankless water heater during low water demand, and eliminate overshoots. Simulation results demonstrated that the proposed system has performed efficiently in a range of water flow and temperature demand while reducing power consumption for about 30%.

Quantifying Methane Emissions from Natural Gas Water Heaters.

Methane emissions from natural gas appliances remain the least characterized portion of the fossil-fuel supply chain. Here we examine water heaters from 64 northern California homes to (1) quantify methane emissions from natural gas leaks and incomplete combustion while off, turning on or off, and in steady-state operation from 35 homes; and (2) characterize daily usage patterns over ∼1-2 months per water heater to estimate activity factors from 46 homes. Individual tankless water heaters emitted 2390 [95% CI: 2250, 2540] g CH4 yr-1 on average, 0.93% [0.87%, 0.99%] of their natural gas consumed, primarily from on/off pulses. Storage water heaters emitted 1400 [1240, 1560] g CH4 yr-1 on average, 0.39% [0.34%, 0.43%] of their natural gas consumption. Despite higher methane emissions, tankless water heaters generate 29% less CO2e20 than storage water heaters because they use less energy to heat a unit of water. Scaling our measured emissions by the number of storage and tankless water heaters in the United States (56.8 and 1.2 million, respectively), water heaters overall emitted an estimated 82.3 [73.2, 91.5] Gg CH4 yr-1, 0.40% [0.35%, 0.44%] of all natural gas consumed by these appliances, comparable in percentage to the EPA's estimate of methane emissions from upstream natural gas production.

Energy code compliant house design for lowest lifecycle cost based on market-available technologies

Investigating code-compliant and market-available options for building envelope, domestic systems, and solar photovoltaic systems accounting for construction and operational cost, the near-lowest lifecycle cost (LCC) design compliant with building energy codes is identifiable following the methodology proposed in this study. A case study of a house design in Edmonton, Canada, is conducted to demonstrate the methodology; the 30-year LCC of options for code-compliance are calculated for three energy cost scenarios. The results indicate that the most cost-effective design may have a 16% to 30% lower LCC than other investigated designs. In terms of achieving a similar level of energy performance, a house that uses a heat recovery ventilator, forced-air gas-fired space heating system, tankless water heater, and features a less-insulated building envelope offers the lowest LCC. The results of this study suggest that LCC should be considered in the development of building energy regulations to include economic aspects while proposing energy standards.

Unburned Methane Emissions from Residential Natural Gas Appliances.

Methane, the primary component of natural gas (NG), is a potent greenhouse gas. NG is a common fuel for residential appliances because of low cost, high energy density, and relatively clean combustion. NG exhaust contains some unburned methane due to inevitable incomplete combustion. A field campaign measuring methane concentrations in exhaust from residential NG appliances was conducted in Boston and Indianapolis to determine their contribution to overall emissions. NG space heating, water heating, and cooking appliances were measured in 100 homes. Appliance exhaust typically exhibits a brief methane concentration spike during ignition and extinguishment and relatively low concentrations during steady-state operation. Exceptions to this pattern include ovens, suboptimal stove burners, and tankless water heaters, which either have a different operating pattern or nontrivial steady-state concentrations. Findings were combined with appliance usage and prevalence assumptions to estimate total emissions. Annually, ∼30 [97.5% CI: 19-160] Gg of methane emissions can be attributed to U.S. residential NG appliances, corresponding to ∼830 [530-4500] Gg carbon dioxide equivalent (CO2e100). This accounts for ∼0.1% [0.08-0.7%] of U.S. anthropogenic methane emissions (which account for ∼10% of total U.S. greenhouse gas emissions) and corresponds to an emission factor of 0.38 g/kg of NG consumed (0.038% [0.024%-0.21%]).

A review of water heating technologies: An application to the South African context

Abstract The process of water heating consumes enormous amounts of energy. South African households may see up to 40% of their total energy be allotted to the heating of water. The implementation of energy efficient or renewable energy source technologies, for the main purpose of heating water, may assist in reducing the magnitude of the energy crisis that South Africans are facing daily. This will, in turn, reduce energy consumption and costs, so that the energy price hikes do not affect the consumers as severely as it would otherwise. The purpose of this paper is to provide a survey of the most frequently used domestic water heating technologies. The paper aims to critically analyse and summarize recent advancements made in renewable and non-renewable water heating technologies, particularly in the South African case. These technologies include the electric storage tank water heater, solar water heaters (passive and active circulation), heat pump water heater, geothermal water heating, photovoltaic-thermal water heater, gas-fired tankless water heater, biomass water heater and oil-fired water heater. Substantial research works and other academic studies focusing on efficiency improvement, optimal design and control, were consulted and categorized in terms of contributions, focus and respective technologies. The key findings of the review conducted on the various water heating technologies are discussed and organized, based on the advantages, drawbacks, approximate initial investment, average life expectancy and payback period. The results of this survey identify gaps in existing research. The aim is to propose a new perspective on the importance of energy efficient hybrid water heating systems and the cost savings they might offer.

An Estimate of Natural Gas Methane Emissions from California Homes.

We estimate postmeter methane (CH4) emissions from California's residential natural gas (NG) system using measurements and analysis from a sample of homes and appliances. Quiescent whole-house emissions (i.e., pipe leaks and pilot lights) were measured using a mass balance method in 75 California homes, while CH4 to CO2 emission ratios were measured for steady operation of individual combustion appliances and, separately, for transient operation of three tankless water heaters. Measured quiescent whole-house emissions are typically <1 g CH4/day, though they exhibit long-tailed gamma distributions containing values >10 g CH4/day. Most operating appliances yield undetectable CH4 to CO2 enhancements in steady operation (<0.01% of gas consumed), though storage water heaters and stovetops exhibit long-tailed gamma distributions containing high values (∼1-3% of gas consumed), and transients are observed for the tankless heaters. Extrapolating results to the state-level using Bayesian Markov chain Monte Carlo sampling combined with California housing statistics and gas use information suggests quiescent house leakage of 23.4 (13.7-45.6, at 95% confidence) Gg CH4, with pilot lights contributing ∼30%. Emissions from steady operation of appliances and their pilots are 13.3 (6.6-37.1) Gg CH4/yr, an order of magnitude larger than current inventory estimates, with transients likely increasing appliance emissions further. Together, emissions from residential NG are 35.7 (21.7-64.0) Gg CH4/yr, equivalent to ∼15% of California's NG CH4 emissions, suggesting leak repair, improvement of combustion appliances, and adoption of nonfossil energy heating sources can help California meet its 2050 climate goals.

Hot water tanks from the point of view of temperature and energy confrontation

The main cause of outbreaks of Legionnaires' disease is from contaminated water sources. About 3 in 10 cases of Legionnaires' disease are due to poorly maintained water storage in buildings. A Tankless water heater can reduce your water-heating bill by five percent to fifty percent or more. A Tankless water heater is a continuous flow of hot water because it instantly heats the water as it goes through the heater. The question is if the Tankless water heater is more efficient than the tank water heater? In our experiment, using Water Quality Management methods, the water heater tank was verified as a source of ubiquitous bacteria’s that can cause health problems to users. Are the solar hot water systems also dangerous? The use of solar energy is very prospective and in the future it will be used in various sectors. The subject of the paper is a simulation of the operational modes of hot water preparation focused on its temperature and energy impact.

Analysis of the performance of a tankless water heating combo system: Space heating only mode

Advancements in water heating and control technology have improved the performance of tankless water heaters in recent years. A tankless water heater coupled with a hydronic air-handling unit functions as a novel system known as a combination system that is used for residential space heating. To quantify the effect of the outlet water temperature from the water heater on the time-averaged thermal efficiency of a tankless water heater-hydronic heater combo system, an experimental method was developed. With the experimental assembly, it was found that the thermal efficiency of the tankless water heater during space heating varied monotonically between 39% and 95% for outlet water temperatures settings respectively between 38°C and 60°C. Energy losses from the flue gases represented 3%–47% of the total energy that was supplied to the system for the same respective outlet water temperature settings. An exergy analysis of the air handling unit was performed and results are presented. The results suggest tankless water heater-hydronic air heater combo systems can be an efficient configuration for space heating at tankless heater outlet water temperature settings of 60°C. Water temperature settings below 60°C produced transient variations, including cycling, in the system that became important and system performance deteriorated.

Analysis of the performance of a tankless water heating combo system: Simultaneous space heating and domestic hot water operation

In Canada, the overall energy usage in residences for space and water heating has increased year over year despite the introduction of higher efficiency furnaces and water heaters, creating an opportunity for alternative space and water heating systems. A tankless water heater, coupled with a hydronic air handling unit, functions as a novel system known as a combination system that provides water and space heating as a unified system. Previous studies have quantified combo system performance for space heating only; but currently, no studies have quantified simultaneous space and water heating operation. An experimental method was developed in order to quantify the effect of the outlet water temperature from a tankless water heater and domestic hot water draw rate on the performance of a combo system. With the experimental assembly, it was found for outlet water temperature settings between 38°C and 60°C, the thermal efficiency was between 88% and 94% for water draw of 7.6L/min and between 74% and 94% for water draw of 15.1L/min. An exergy analysis of the air heater unit was performed and the results are presented. The results suggest that a tankless water heater combination system can be an efficient configuration for residential space and water heating though there are challenges in managing the large dynamic range such combo systems face.

Micro-cogeneration versus conventional technologies: Considering model uncertainties in assessing the energy benefits

Fuel cells with nominal outputs of approximately 1kWAC are emerging as a prime-mover of a micro-cogeneration system potentially well-suited to compete, on an energy basis, with conventional methods for satisfying occupant electrical and thermal demands in a residential application. As the energy benefits of these systems can be incremental when compared to efficient conventional methods, it is especially important to consider the uncertainties of the models on which simulation results are based. However, researchers have yet to take this aspect into account.This article makes a contribution by demonstrating how these model uncertainties may be propagated to the simulation results of a micro-cogeneration system for comparison to a reference scenario using a case study. This case study compares the energy performance of a fuel-cell based micro-cogeneration system serving only domestic hot water demands to an efficient reference scenario where the conventional methods for providing electrical and thermal demands are considered to be a central gas-fired combined-cycle plant and a condensing tankless water heater respectively. The simulation results demonstrated that if model uncertainties were ignored, it would have been possible to demonstrate that the considered micro-cogeneration system was more efficient than the reference scenario for average consumption levels of domestic hot water. However, when model uncertainties were considered, the efficiency of the considered micro-cogeneration system could not reliably exceed that of the reference scenario by serving the domestic hot water needs of a single-family home.

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.

Simulation and Optimization of Solar Thermal Cooling System in Manufacturing Research Center Building to Reduce Operational Cost Using Software EnergyPlus and GenOpt

Solar Thermal Cooling System with its absorption cycle is expected to replace the conventional air conditioning system with vapor compression cycle because it is more efficient in terms of cost and energy. However, due to the heat of the sun is not always stable, the system needs to be equipped with a backup energy source, one of which is CNG. In the Manufacturing Research Center building, the lack of facilities that support availability of CNG causes large operational cost. Therefore, optimization efforts with the aim to reduce operational cost are needed. Simulation and optimization performed with EnergyPlus and GenOpt. The conclusion is that the installation of 187.5 kW electric tankless water heater is able to reduce total operational cost by 34.65% compared to system that uses combination of solar thermal and CNG and 49.69% compared with system that uses only CNG.

Performance of gas tankless (instantaneous) water heaters under various international standards

This paper presents a novel review and laboratory test results of four standard test methods for determining the energy consumption of microprocessor controlled gas tankless water heaters. The test standards examined are from Australia, Europe, Japan and North America. The European test standard is found to be technically the most comprehensive in measuring all aspects of energy consumption for these types of appliances. Four water heaters, both conventional and condensing type, ranging in capacity from 28 to 55kW are tested to each of the test standards. The European and North American tests deliver similar results. Those to the Australian standard yield higher energy use while the Japanese method produces the lowest consumption. The relative difference in energy use between water heater models tested to any single standard is consistent, with the exception that the Australian test appears to favour the smaller water heater. Therefore, while consumers cannot use standard test results to calculate their actual running costs, in general, any of the standards will reasonably predict relative running cost differences between models if used as part of the product selection process. While the correlation between the standards varies according to the capacity of the water heater, a simple approximation is developed to convert from the efficiency measured by one standard to another.

Performance Comparison of Control Methods for Tankless Water Heaters

Tankless water heaters (TWH) have several advantages and disadvantages when compared with storage water heaters. One disadvantage is that the outlet temperature of the water is difficult to control. To address this problem, the authors apply seven different control approaches and conduct experiments to test the effectiveness of each approach. The experiments are carried out on a commercially available electric TWH, using a test method and apparatus developed by the authors. The seven approaches include various configurations of feedback or feed-forward control, or both. One fairly simple approach devised in this project combines feedback and feed-forward control. This combined approach gives excellent performance, even when compared to a very sophisticated and complex approach (model predictive control). Furthermore, the approach does not impose a manufacturing cost premium for the subject TWH. The improvements in control that are possible with the approaches described in this paper are considerable when compared with approaches being used in electric TWH that are currently available to consumers.