Gas-fired Water Research Articles

Management of domestic hot water system based on the example of a gas-fired instantaneous water heater

Purpose: The aim of the study was to present the actual efficiency of a gas-fired instantaneous water heater for the production of domestic hot water. Design/methodology/approach: The object of the study was a gas-fired instantaneous domestic hot water heater located in a flat in Krakow. Measurements with a suitable device were carried out for three basic variants of hot water preparation, defined as showering, washing hands and washing dishes. Findings: The tests and analyses carried out have revealed that the current efficiency (average efficiency based on 3 measurements – 77.61%) differs radically from that indicated on the water heater data sheet. Such a drop in efficiency may be caused e.g. by fouling of the surface of the heat exchanger on the flue gas side and scaling of the exchanger on the heated side. Research limitations/implications: The tests proved that the heater did not reach its nominal efficiency during the tests, but on the other hand, simulations of different intensities and durations of water consumption did not drastically change the efficiency of hot water preparation. Practical implications: Regular cleaning of the exchanger would probably reduce the difference between the efficiency declared by the manufacturer and the one achieved during the tests. A clean heater will also ensure a sufficiently low level of carbon monoxide in the flue gas, which has a real impact on the safety of the appliance. Social implications: The values obtained from the measurements for each operating mode can help occupants understand how to prepare water most efficiently with this particular appliance, which will have a real impact on the bills they pay. The user will be provided with information on what percentage of energy they use from the volume of gas burned. Originality/value: Gas-fired instantaneous water heaters provide an efficient and energy-saving solution, especially in situations where the demand for hot water is low, and immediate access to it is crucial. Keywords: hot water, hot water management, gas-fired instantaneous water heater. Category of the paper: Research paper.

Simulating Combustion-Induced Noise from a Gas-Fired Water Heater

Residential and commercial gas water heaters are designed for optimal performance for different operating conditions. These differences could arise from regional changes in fuel, local regulations for emissions, and the temperature preferences of the customer. From an engineering perspective apart from performance, other issues such as fire safety, longevity (thermo-mechanical durability) and though rarely, noise and vibration (N & V) need to be addressed. Unlike other appliances, there are almost no moving mechanical parts in an atmospheric gas water heater. This makes the N & V problem an interesting engineering challenge to diagnose and fix. In this paper, the authors consider different hypotheses for understanding the origins of combustion-induced noise. They propose a hybrid simulation methodology to predict noise and finally present the sound pressure level comparison with the physical test.

Analysis of the Causes of the Emergency Shutdown of Natural Gas-Fired Water Peak Boilers at the Large Municipal Combined Heat and Power Plant

The paper presents a cause-and-effect analysis of the failure of a 130 MWt gas-fired water boiler. The fault was a rupture of the helically finned tubes in the first rows of the second-stage water heater (ECO2). The high frequency of failures forced the boiler user to investigate their causes. The rapid drop in water flow in the ECO2 and the tightly finned pipes suggested that the permissible operating temperature of the steel used was exceeded. The only possible way to assess the working conditions was through a CFD simulation of the operation of the ECO2. Validated with the data acquisition system, the results show that the main reason for the failure was the overheating of the first rows of finned water heater pipes, regardless of the boiler load. The high heat flux value, exceeding 500,000 W/m2, and the increased flue gas temperature in front of the ECO2, almost reaching 900 °C, affected the appearance of the boiling film, limiting the cooling of the tube wall. Heat radiation and eddies behind the tubes significantly impacted the non-uniform temperature distribution, resulting in high pipe wall stress. By analyzing the service life of the first row of pipes based on the Larson–Miller parameter, it was concluded that the pipes would fail after only a few tens of hours.

Multi-objective optimization of three different fins of the heat exchangers used in the domestic gas-fired water heaters: a hydrothermal performance and entropy generation analysis

Multi-objective optimization of three different fins of the heat exchangers used in the domestic gas-fired water heaters: a hydrothermal performance and entropy generation analysis

Numerical assessment of a gas-fired condensing boiler model for residential buildings application

According to the official statistical reports, gas-fired boiler units still remain to be one of the main equipment types for meeting the space heating and daily hot water demand of the residential dwellings across the European Union. Due to the prevalence of the natural gas grid and performance stability, gas-fired boilers are considered to remain as one of the standard energy sources. On the other hand, even though gas-fired water heating technology is a well-known concept, existing numerical models found in the literature are often case-specific with poor reusability mostly reflected in fitted efficiencies. Algorithms behind these models usually require the input of large amount of hardly attainable design characteristics of the units. In this paper, a modelling method for acquiring the performance of a heating gas-fired condensing boiler unit will be shown. The model is based on the limited input data available in the official characteristics of the units issued by the relevant manufacturers. The simulations are programmed by using the programming language Modelica and the software tool Dymola. The model is based on the fixed natural gas intake which combusts into a stable mixture of the combustion gases that further heat the circulating water. During the heat transfer process inside the condensing boilers there is a possibility for condensate formation out of the water vapour of the combustion gases which increases the efficiency of the unit. The formation of condensate, however, is depending on the return water temperature of the unit which has to be lower than the dew point temperature of the combustion gasses. The goal of this research is to determine how accurate can performance indicators of gas-fired boilers be attained with the use of a limited amount of available input data together with clearly defined assumptions that follow the modelling methodology.

Escenarios de exposición a monóxido de carbono que orientan la sospecha clínica de intoxicación aguda

Carbon monoxide accumulates in closed environments when there is unnoticed combustion. Signs of poisoning are non-specific, and thus circumstances around poisoning may constitute a diagnostic guide.Objective: to strengthen the clinical capacities to suspect and confirm carbon monoxide poisoning.Method: descriptive, transversal study of suspicious cases (patients with neurological or digestive symptoms for which an indoor combustion source is identified) who consulted at the Poisoning Center in 2017.Results: 111 cases were included in the study, 52 of which occurred in 22 episodes of collective exposure. 37 patients were under 15 years old and the percentage of children identified in collective poisoning (23/37) was significantly greater than the one representing adults. 67 cases occurred in winter, minimum average temperature being 9.3°C. The combustion equipment most frequently involved in poisoning events were gas-fired water heaters in the first place, followed by gas stoves. The most frequent initial symptom was headache. Average COHb was 14.7%. Severe cases (45/111) were significantly corelated to carbon monoxide exposure from gas-fired water heaters.Conclusions: the poisoning rate is low when compared to countries in a similar latitude, what suggests the possibility of under-diagnosis. Minimum environment temperature under 10°C, staying in spaces with combustion-based heating and the use of gas-fired water heaters were the typical poisoning scenarios. Headache is a key symptom to search for exposure. The diagnostic suspicion may be lower when it involves individual cases, mainly in children.

Typical Case Analysis of the Building-type CCHP System

Introduction The paper aims to obtain optimal configuration and operation strategy of the distributed energy system which is based on the calculation of the annual typical daily cooling， heating and electric load demand of various buildings. Method The energy station was equipped with a variety of energy-saving and cost saving equipments， such as internal combustion engine， flue gas and hot water lithium bromide unit， centrifugal electric refrigeration （heat pump） unit， ground source heat pump， gas-fired hot water boiler and water storage （heat） tank， which realized the gradient utilization of energy and better match the load demand of the client. Result The results show that it is feasible in technology and economy. Conclusion Reasonable allocation of units in the energy station can save investment， protect environment and save energy. Make use of the difference between peak and valley electricity prices which can reduce operating costs and improve system efficiency.

Assessment of the risk of poisoning by combustion products from domestic gas-fired appliance using CFD modeling

Gas-fired appliances, including water heaters, are widely used in households and may have a significant impact on their gas atmosphere, i.e. reduction of oxygen concentration and appearance of toxic oxides (especially CO). Therefore, the paper deals with the assessment of the risks of poisoning by combustion products from a gas appliance using CFD modeling. A three-dimensional numerical CFD (Computational Fluid Dynamics) model of a real apartment was developed, in which the gas-fired instantaneous water heater with a standard power of 20 kW works in the bathroom. The model enabled the performance of transient simulation calculations for various air inflows (ventilation) to the abovementioned apartment (30 - 120 m3/h) as well as for various concentrations of carbon monoxide in combustion gases (0.1 - 1%). It was assumed that combustion gases inflow entirely into the room for 10 minutes. Based on the calculations performed, it was shown that the main threat occurs in the room where gas-fired water heater is located, i.e. in the bathroom. Moreover, changes in concentration of carbon monoxide and oxygen over time, and depending on the room height, were analysed. In addition, an analysis of the impact of combustion gases inflow on the temperature in the bathroom and the whole apartment was made.

Life cycle assessment of a domestic gas-fired water heater: Influence of fuel used and its origin

The objective of this study is to apply a cradle-to-grave life cycle assessment to a gas-fired instantaneous water heater for domestic uses in order to identify the stages and processes with the largest impacts, as well as to evaluate the influence of different fuels (natural gas and liquefied petroleum gas) and country of use when natural gas is used as fuel. Primary data supplied by a Portuguese manufacturer contributed for achieving accurate life cycle inventory data that were then modelled in SimaPro 8.5.0 complemented with data from Ecoinvent database 3.4. The assessment was performed using the Recipe 2016 Midpoint V1.01 at the Hierarchist perspective. The results of the study show that the use stage (mainly owing to water consumption and fuel pre-combustion and combustion) is by far the largest contributor to the environmental burdens, followed by the raw materials production stage. The comparison between the two fuels considered demonstrates that liquefied petroleum gas leads to higher impacts than natural gas, mainly as a result of emissions from its own life cycle. The environmental damage varies noticeably in some impact categories depending on the country where this water heater is used, due to different natural gas origins. Practical implications of this work will enable the manufacturer to identify where to focus on the new water heaters that will be developed to achieve better levels of environment-friendliness.

Simulation of the performance of a gas-fired hot water system with compression-enhanced ejector heat pump using R152a

Natural gas is widely used for space heating because of its low pollutant emissions and high combustion efficiency. Nevertheless, the primary energy efficiency of a gas-fired boiler cannot exceed 100% based on high calorific value. In order to improve the efficiency of natural gas for heating, a gas-fired hot water system with a compression-enhanced ejector heat pump is proposed. The simulation results show that the compressor can sustain the ejector’s high efficiency range while in operation. When the ambient temperature is 0 °C, the primary energy efficiency is substantially higher than that of the conventional ejector heat pump system and gas-fired boiler by 40 and 36%, respectively. When the supply water temperature does not exceed 46 °C, the coefficient of performance and primary energy efficiency of the novel gas-fired hot water system can reach 1.65 and 1.22, respectively.

Fireside Corrosion on Heat Exchanger Surfaces and Its Effect on the Performance of Gas-Fired Instantaneous Water Heaters

The heat exchanger in a gas instantaneous water heater is a thermal device used for heat transfer from the high-temperature flue gas to the low-temperature water. The fireside corrosion, due to the reaction of acidic condensate formed on the heat exchanger surfaces and its metallic material, is one of the major hazards for gas instantaneous water heaters. This paper focuses on identifying and quantifying the fireside corrosion on the surface of heat exchangers in gas-fired instantaneous water heaters. Durability tests lasting for 2000 cycles were undertaken for five gas-fired instantaneous water heaters, which were different in terms of the heat input and coating of heat exchangers. The corrosion deposits on the surface of the heat exchangers were surveyed by several methods. The results show that the corrosion deposit grew as the test duration increased. The fins of the heat exchanger with a lead coating had been corroded and copper was exposed. Cu4(OH)6SO4 was the main corrosion product of heat exchangers without a lead coating, whereas PbSO4 was the main corrosion product of heat exchangers with a lead coating. The experiments demonstrate that the corrosion rate decreased with the increase of the heat input. The experiments also show that the thermal efficiency of gas instantaneous water heaters decreased by 2.4% to 6% at the end of the test duration.

Assessment of development scenarios of district heating systems

In this study sustainability of the different district heating (DH) system development scenarios were evaluated and quantified. For this purpose, developed district heating planning tool (DHPT) was used. DHPT development was based on a diversified approach considering the expected reduction in heat consumption. This paper describes the DHPT development methodology and proposed criteria for the assessment of DH systems efficiency. Five development scenarios for specific DH system (heat source: two water heating boilers 2 × 2.6 MW, cogeneration unit 0.6 MWth, DH network total length of 1890 m, 23 consumers with a total heated area of 51,069 m2) were assessed using DHPT and the optimal scenario was justified. Three building renovation scenarios with different supply water temperatures were evaluated using energy dynamic simulation tool IDA ICE, with the purpose to assess the potential of existing non-renovated buildings to switch to a fourth-generation district heating (4GDH) system.In optimal DH development scenario the heat losses in the distribution network are only 3.8% and the share of renewable sources has reached 47%, but natural gas-fired water boiler is used only for coverage of peak loads. Results from IDA ICE simulations have shown that in non-renovated buildings indoor temperature drop below 18 °C lasted 32 h during the whole heating season.

Investigation of the combined efficiency of a solar/gas hybrid water heating system

In climate regions with large seasonal variations in solar radiation, such as the Pacific Northwest of the United States, a solar thermal energy collector might not economically satisfy year-round domestic water heating demands, requiring an auxiliary unit, such as a natural gas-fired water heater. Previous studies have shown that the burner efficiency of a gas-fired water heater varies depending on the log-mean temperature difference between the cold fluid (water) and the hot fluid (combustion gases). In a solar/gas hybrid water heating system, where solar collectors are used in conjunction with a gas-fired heater, the partial heating of water provided by solar input reduces the log-mean temperature difference value for the gas heater, reducing the efficiency of the gas burner. Since this efficiency reduction varies depending on the amount of pre-heating provided by solar energy input, it is difficult to accurately predict the actual cost and energy savings offered by solar/gas hybrid water heaters in different climates and operation scenarios. Hence, to predict the actual energy and cost savings under various design conditions, the performance of solar/gas hybrid systems must be better understood.The objective of this work is to experimentally determine the thermal performance of a solar/gas water hybrid water heating system with a 6.44 m2 flat plate solar collector array and a 22.3 kW natural gas burner in Corvallis, Oregon, USA. Under different temperature lifts and solar insolation values, the system was operated at three different modes of heating: solar, gas, and combined solar/gas mode. The overall system thermal efficiency value for each mode is calculated. The efficiency of the solar collector heating system was found to be 41.97%, 39.82%, and 35.05% at initial water temperature of 20, 30, and 51.5 °C, respectively. For initial water temperatures of 20, 30, and 51.5 °C, the efficiency of the gas burner was found to be 69.2%, 66.4%, and 65.5% at the HHV, and 76.7%, 73.6%, and 72.6% at the LHV of natural gas, respectively. In the combined solar/gas heating mode, the efficiency of the gas burner decreased with increasing solar fraction. For solar fractions of 4.93%, 9.40%, 11.39%, and 14.27%, the efficiency of the gas burner in terms of the HHV of natural gas was found to be of 69.08%, 66.80%, 66.17%, and 65.18%, respectively. Based on the experimental results, a configuration that would provide higher overall system efficiency for combined solar/gas heating is suggested.

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 energy and cost comparison of residential water heating technologies

Water heating is a significant user of energy. Several studies have investigated the development of more efficient systems. The present study compares several commercially available options for water heating and compares them with the performance of a recently developed of a gas-fired heat pump water heating system. Comparisons of each technology are conducted using annual energy use and operating cost metrics. Payback period predictions for the gas and electric heat pumps are performed with the electric and non-condensing gas storage units as a base case. Electric and gas heat pumps, at total initial costs of $2,400, are estimated to require 3.6 and 3.1 year payback periods when compared to an electric storage unit, respectively, while a gas heat pump with a total initial cost of $2000 is estimated to require 2.3 years. For this study a gas heat pump cost of $2400 was assumed. Daily total draw cases for a gas heat pump of 243, 303 and 379 L compared to a non-condensing gas storage unit as the base case show payback periods of 4, 3.2 and 2.5 years, respectively. This analysis shows that electric and gas heat pump technologies offer significant energy use and operational cost savings compared to baseline water heating technologies with reasonable payback periods.

An Analysis of Allocation Plan for Urban Complex Air Conditioning Cold and Heat Sources in Severe Cold Regions Area

According to the climate characteristics of severe cold area, the buildings function and the status quo of the architecture energy resources, this paper have researched a scheme of a certain urban complex air conditioning cold and heat sources relatively in Changchun. It analyzed dynamic load of annual building air conditioning, and calculate the energy consumption for two types of configurations in air-condition cold and heat sources schemes.It also synthetically analyzed the factors such as initial investment, operating cost, comfort and stability. The result shows that electrical refrigeration combined with gas-fired hot water boiler system is superior to direct-fired combined with gas-fired hot water boiler system when the architectural scale is larger and when it needs providing air conditioning and hot water. With the rapid development of China's economy, urban complex with high efficiency and multi-function is springing and thriving. In the large commercial complex, air conditioning cold and heat source is the core of the whole air conditioning system. It’s significant to optimize the energy in air conditioning cold and heat sources system for reducing building energy consumption in commercial complex. At present, HVAC technology is developing rapidly, the performance of cold and heat source unit is continuously improving, and unit configuration is gradually perfected. In the construction engineering design of the urban complex, it is an extreme problem of how to choose reasonable the scheme of the air conditioning cold and heat sources according to the architectural features for the engineering designers. There has been a lot of researches about the scheme of air conditioning cold and heat sources [1][2][3], in this paper, we will optimize the scheme of commercial complex of air conditioning cold and heat source in a typical city—Changchun City, which is located in the cold area. This paper analysed two different designs of cold and heat source system based on the annual dynamic of buildings, and makes an analysis and comparison on the initial investment, operation cost etc., we aimed to find the scheme of the air-conditioning cool and heat sources most suitable for the region of the type of which is most suitable for the region and the type of building.

Primary energy savings in desiccant and evaporative cooling-assisted 100% outdoor air system combined with a fuel cell

The main purpose of this study involved investigating the primary energy saving potential of a liquid desiccant and evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) integrated with a proton exchange membrane fuel cell (PEMFC). During the cooling season, the heat produced by the PEMFC was used to regenerate a weak desiccant solution, and the electricity generated was used to operate the LD-IDECOAS. A pilot LD-IDECOAS powered by a PEMFC was installed and operated in an office space to experimentally verify the annual operating energy savings of the proposed system. The findings indicated that the heat reclaimed from the PEMFC saved 42% of the desiccant solution regenerating energy when compared to that in the case of a conventional gas-fired water heater. The results also suggested that the LD-IDECOAS combined with a PEMFC consumed 21% less primary energy when compared with that of a system powered by grid electricity and a conventional gas-fired water heater.

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.

二次計画法を用いた業務用エネルギー供給システムにおける部分負荷特性のエネルギー消費特性への影響分析

The main objective of this study is to clarify the impacts of partial load characteristics in industrial energy supply system on optimal operating planning and capacity of storage tanks through a numerical experiment. In order to analyze effects of non-linearity of partial load characteristics of the equipment, we calculate operational planning problems with various demand pattern adopting optimal approach based on Mixed Integer Quadratic Programming. In this paper, the industrial energy system consists of combined heat and power generator, absorption heat pump, gas-fired water heater, vapor compression refrigerator, storage tanks of hot and cold water, photovoltaic power generator and circulation pumps. As a result, it is found that equipment with strong non-linear partial load characteristic is operated at part-load operating point rather than rated point. Additionally, primary energy consumption can be reduced by 1.19% compared to regardless of non-linearity of partial load characteristic. Furthermore, method for regression of partial load characteristics affects optimal capacity of storage tanks. Each capacity corresponded to about 10 % of the cumulative daily load of peak day.

The Energy Efficiency of Hot Water Production by Gas Water Heaters with a Combustion Chamber Sealed with Respect to the Room

This paper presents investigative results of the energy efficiency of hot water production for sanitary uses by means of gas-fired water heaters with the combustion chamber sealed with respect to the room in single-family houses and multi-story buildings. Additionally, calculations were made of the influence of pre-heating the air for combustion in the chimney and air supply system on the energy efficiency of hot water production. CFD (Computational Fluid Dynamics) software was used for calculation of the heat exchange in this kind of system. The studies and calculations have shown that the use of gas water heaters with a combustion chamber sealed with respect to the room significantly increases the efficiency of hot water production when compared to traditional heaters. It has also been proven that the pre-heating of combustion air in concentric chimney and air supply ducts essentially improves the energy efficiency of gas appliances for hot water production.