Gas Water Heater Research Articles

Failure Analysis of Corrosion Pit on Outer Wall of Membrane Wall Pipe

Abstract Flue gas pipework is a critical component of a flue gas treatment system, mainly transporting the flue gases produced by a combustion plant from the source to the vent. Flue gas pipework is vital in all applications, such as thermal storage gas stoves, heaters, and gas water heaters. However, due to negligent management during the use of piping. Corrosion pits were created in several places on the outer wall of a membrane wall pipe located on the flue gas side of the membrane wall pipe. The external circulation medium of the membrane wall pipe is mainly high-temperature flue gas, and the internal circulation medium is water. This paper determines the causes of the corrosion pits by macroscopic observation, metallographic microstructure analysis, scanning electron microscopy, and energy dispersive spectroscopy (EDS). It was found that the outer wall of the flue gas sidewall pipe of the failed part was covered with reddish-brown rust, wide and shallow corrosion pits were observed, and the detection area of the inner surface of the pits had a high ‘S’ content. To reiterate, it was concluded that the cause of the corrosion pits was the flue gas dew-point corrosion.

Optimal Disturbance Control for Energy Feedback of Gas Water Heaters

Optimal Disturbance Control for Energy Feedback of Gas Water Heaters

Comparative analysis of energy efficiency for three heating and cooling supply schemes in a region with hot summers and cold winters in a chemical industrial park

Building energy consumption in China accounts for 45% of the total national energy consumption, with air conditioning energy consumption representing approximately two-thirds of that. Therefore, energy efficiency in buildings is of utmost importance. This study focuses on a chemical industrial park located along the Fujiang River and compares three heating and cooling supply schemes: the river water source heat pump system, which utilizes river water as the heat source and heat sink; the water cooling unit and boiler system, which uses water-cooled electric compression chillers for cooling and an oil-fired boiler system for heating; and the split air conditioning and gas water heater scheme, which relies on refrigerants such as fluorine-containing compounds for cooling and a gas water heater for heating. By calculating the energy consumption of the above three schemes and conducting a comparative analysis, it is found that the river water source heat pump system exhibits significantly higher energy efficiency throughout the year compared to the water cooling unit and boiler system and the split air conditioning and gas water heater scheme. This highlights the notable energy efficiency advantage of the river water source heat pump system.

Numerical investigation of the performance improvement of instantaneous gas water heater by introducing new geometries for the heat exchanger

Tankless gas water heaters are known for their efficient energy consumption, as they only heat water on demand, resulting in reduced energy usage compared to traditional storage tank water heaters. A typical water heater uses a U-shaped heat exchanger. To enhance the performance of instantaneous gas water heaters, as well as reduce energy consumption and save energy in residential buildings, a numerical study on heat transfer in the heat exchanger of these water heaters is presented in this paper. The main purpose of this study is to achieve a better performance for gas water heaters by examining the geometry change of the heat exchanger using Computational Fluid Dynamics (CFD). Four different geometries, namely U-shaped, W-shaped, spiral, and sinusoidal tubes, were investigated. The results demonstrate that spiral geometries increase the Nusselt number significantly by creating secondary flows with a much lower pressure drop. SP-L-1.5L, SP-1.5X2, and SP-0.75X3 geometries exhibited the best thermal performance under all conditions, with maximum thermal performance factor of 13 %, 11 %, and 8 %, respectively.

Characterization of Water-Based Anti-Corrosion and Anti-Fouling Coating in the Heat Exchanger Tube of Gas Water Heater

Due to the fouling and corrosion issues with gas water heater heat exchangers during use, a water-based coating is created using the sol-gel method and applied to the inner surface of the copper tube of the heat exchangers. The water-based coating can reduce the surface energy of copper that is oxygen-free by 82.40 % and has outstanding hydrophobicity. The coating's adhesion strength was 8.46 MPa, and its wet adhesion reduction rate was only 0.0375 MPa·d-1 when submerged in a bath of water at a constant temperature. Its water contact angle remained above 110° even after being abraded by sandpaper, demonstrating its excellent wear resistance. At a constant temperature of 45 °C, the corrosion experiment was carried out in salt, acid, and alkali solutions. The maximum corrosion rate of the coating was 3.24 × 10-2mg∙(cm2∙h)-1, which was only 20.85 % of that of the oxygen-free copper substrate. The dynamic fouling experiment shows that the coating can effectively inhibit fouling growth, prolong the fouling induction period and reduce the average fouling rate. By factoring in the fouling thermal resistance and the coating thermal resistance, the overall heat transfer coefficient of the copper tube was computed. The results demonstrate that after applying this water-based coating, the copper tube can continue to have a high heat transfer coefficient for an extended period, ensuring the continuous and effective operation of the heat exchanger and having practical application value.

Analysis of combustion and heat transfer performance in a slit-type fully premixed burner

Since most gas water heaters on the market still use diffusion or partially premixed combustion. Fully premixed combustion, with its advantages of complete combustion and low CO and NOx emissions, offers a promising alternative. In response to this, a slit-type fully premixed gas water heater with a rated power of 20kW was designed. The combustion and heat transfer performance, as well as the combustion temperature and burnout characteristics, were analyzed under ten different load conditions ranging from 100% to 8% using theoretical modeling. The study identified the variations in physical parameters and used numerical simulations to partially validate the theoretical results. Subsequently, by individually modifying structural variables, the optimal structure under single-variable conditions was determined. This optimal structure was then combined in various configurations to form a multi-variable structural design. Further theoretical analysis was conducted to assess whether the changes in the multi-variable structure, as well as the original design, met economic efficiency requirements. The results showed that the slit-type fully premixed burner achieved optimal performance when the number of burner plates was 120, with a length of 99 mm and a height of 10 mm.

Carbon Monoxide Poisoning in People: Recognition and Prevention

Background: Carbon monoxide (CO) is a toxic gas that lacks discernible color or scent. Individuals may experience the impact of carbon monoxide (CO) emissions originating from a range of sources, such as gas stoves, water heaters, fireplaces, and motor vehicles. Objective: The objective of this study is to evaluate the perception and knowledge pertaining to symptoms, risk factors, causes, and preventative strategies of carbon monoxide (CO) poisoning among the general population in the Kingdom of Saudi Arabia (KSA). Subjects and methods: The present investigation constitutes a cross-sectional study conducted on the overall population of the Kingdom of Saudi Arabia (KSA). The research focused on those who are not involved in the healthcare profession, utilizing an electronic survey as the primary data collection method. The questionnaire primarily comprises three sections: socio-demographic information, knowledge evaluation, and habitual factors and behaviours pertaining to carbon monoxide poisoning. Results: Out of 568 participants, (52.8%) were aged between 18 to 25 years with (64.1%) being females. A significant proportion of the participants exhibited little knowledge (67.6%), unfavorable attitudes (72.4%), but shown commendable adherence to preventive measures (64.4%). Conclusion: There was a lack of knowledge and a weakness in attitude. Nevertheless, preventive practices are highly motivating. Individuals who possess awareness of carbon monoxide (CO) poisoning tend to demonstrate superior levels of knowledge and adherence to safety precautions when compared to those who lack such awareness.

Investigation on the Combustion Characteristics and Environmental Effects of Hydrogen-doped Natural Gas for Domestic Water Heaters.

The addition of hydrogen to natural gas is an effective approach to broaden the range of applications for hydrogen and address the issue of global warming. However, the inclusion of hydrogen alters the combustion properties of natural gas. The paper established a simplified mechanism consisting of 19 components and a 67-step reaction for hydrogen-doped natural gas combustion. With this simplified mechanism, the effects of hydrogen doping and the utilization of porous media combustion techniques on the combustion characteristics of natural gas were investigated numerically. The results suggested that the utilization of porous media combustion technology is beneficial for achieving the complete combustion of hydrogen-doped natural gas and reducing pollutant emissions. Additionally, the total gas cost and environmental impact of domestic gas water heaters with hydrogen-doping natural gas were estimated. The findings show that the use of 20% hydrogen-doped natural gas contributes to a decrement in fuel costs and reduced emissions of CO by 25.4%, NOX by 53.9%, and CO2 by 6.78%.

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.

Code generation for embedded predictive control of gas water heaters

Conventional control strategies usually employed in tankless gas water heaters present difficulty in controlling the hot water temperature when subjected to sudden changes in water flow rate. Inadequate control leads to temperature overshoots and undershoots with long settling times that severely affect the user comfort, increasing water and energy wastage and associated gas emissions. A strategy based on model predictive control is presented to reduce the impact of changes in hot water demand. A semi-empirical model, parameterized with experimental data and compatible with real-time simulation, is used for the heat cell. A tailored state observer is proposed, considering time-varying delays characterizing this thermal process. An automatic code generation software tool was developed for the embedded implementation of gas water heater predictive controllers. Numerical simulations and hardware-in-the-loop experiments were established to evaluate conventional and predictive control strategies. It was demonstrated that embedded model predictive control could be successfully implemented on computationally limited microcontrollers, even for thermal systems with extensive varying time delays. Predictive control has shown significant performance improvements, with decreased temperature fluctuations, a gain in comfort index from 36% to 75% and a reduction of up to 32 s in the settling time.

Embedded Model Predictive Control of Tankless Gas Water Heaters to Enhance Users’ Comfort

Water heating is a significant part of households’ energy consumption, and tankless gas water heaters (TGWHs) are commonly used. One of the limitations of these devices is the difficulty of keeping hot water temperature setpoints when changes in water flow occur. As these changes are usually unexpected, the controllers typically used in these devices cannot anticipate them, strongly affecting the users’ comfort. Moreover, considerable water and energy waste are associated with the long-time response to cold starts. This work proposes the development of a model predictive control (MPC) to be deployed in low-cost hardware, such that the users’ thermal comfort and water savings can be improved. Matlab/Simulink were used to develop, validate and automatically generate C code for implementing the controller in microcontroller-based systems. Hardware-in-the-loop simulations were performed to evaluate the performance of the MPC algorithm in 8-bit and 32-bit microcontrollers. A 6.8% higher comfort index was obtained using the implementation on the 32-bit microcontroller compared to the current deployments; concerning the 8-bit microcontroller, a 4.2% higher comfort index was achieved. These applications in low-cost hardware highlight that users’ thermal comfort can be successfully enhanced while ensuring operation safety. Additionally, the environmental impact can be significantly reduced by decreasing water and energy consumption in cold starts of TGWHs.

Determinants of the adoption of energy efficient water heaters in the residential sector: Evidence from a survey in Japan

The purpose of this paper is to explore the determinants that promote the replacement of water heaters with more energy efficient models (e.g., gas or electricity-based energy efficient water heaters). By using survey data on Japanese households' water heater choice collected from an online questionnaire, this paper examines the effect of peers, choice context, and households’ perception of energy sources. The following results are obtained: First, households tend to choose gas or electricity-based energy efficient water heaters which, at the point when the households start to consider replacement, are known to have been used by peers (peer effect). Second, households are more likely to choose a gas or electricity-based energy efficient water heater in the context where they simultaneously replace their water heater and other home facilities (context effect). Finally, as for electricity-based energy efficient water heaters, households with a positive (negative) perception of electricity are more (less) likely to choose an electricity-based energy efficient water heater (perception of energy sources). These results imply the importance of considering these factors when designing policy instruments to promote the adoption of energy efficient water heaters in the residential sector.

Study on reproducibility of exhaust diffusion properties of gas water heaters in apartment complexes

Gas water heaters in Japan are generally in shared corridors. However, there are restrictions on the installation location and the shape of the corridor to avoid the stagnation of exhaust gas in the corridor and its flow into the rooms through the external air supply opening. These installation standards limit building planning and require further mitigation. Although experiments using full-scale models have been conducted, it is still difficult to consider all possibilities as the shared corridors can be of many shapes. The relaxation of standards should be studied through simulations using computational fluid dynamics (CFD). First, the target data for reproducing the exhaust properties in the CFD analysis are collected via actual measurement. Subsequently, the exhaust diffusion properties of gas water heaters are reproduced by simulation using CFD analysis based on the measured data. Reproducibility is improved by changing the location of the outlet boundary condition in gas water heaters. Finally, the reproducibility of the exhaust diffusion properties is examined for the gas water heater installed in the shared corridor. Comparing the experimental and simulation results, confirms the reproducibility of the concentrations at the exhaust trajectories and air supply outlets.

Fatal Carbon Monoxide Poisoning

Liquefied petroleum gas on combustion with deficient oxygen produces toxic carbon monoxide. It is used as a fuel to heat water in gas geysers. Here, we report a fatal case of carbon monoxide poisoning resulting from the usage of gas water heater. A 24-year-old female had gone to take bath in a bathroom where a gas geyser was installed to heat the water. As she did not come out of the bathroom even after more than an hour, the door was broken down by the relatives and she was found dead. Cherry red postmortem hypostasis, congested and edematous pinkish lungs, and cerebral edema were salient autopsy findings. Carboxyhemoglobin was quantified in blood to 76.55%. The cause of death was attributed to carbon monoxide poisoning; accidental in manner. This case highlights the hazards of using a gas geyser in an ill-ventilated bathroom.

Variant analysis of financial and energy efficiency of the heat recovery system and domestic hot water preparation for a single-family building: The case of Poland

Significant amounts of waste heat are deposited in wastewater, which can be used e.g. for heating domestic water. The aim of the paper was to analyze the efficiency of energy recovery from gray water using a new horizontal heat exchanger in the form of a linear drainage equipped with a wavy middle wall. The experimental research consisted of the analysis of efficiency of the device prototype, and then the calculation of energy savings for the preparation of domestic hot water for 81 test cases. Installations cooperating with an electric and gas water heater were analyzed. A Life Cycle Cost analysis was carried out for the financial effectiveness of a conventional installation and an installation equipped with a heat exchanger for a family of 3. Research have shown that the new heat exchanger reduces energy consumption for hot water preparation by an average of 22–31%. It was established that when using an electric water heater, the investment costs pay back in the period of 4–9 years, and in the case of a gas heater, at least 12 years. The sensitivity analysis showed that an increase in energy prices can significantly shorten the payback period, to 6 years for a gas heater and 2 years for an electric heater. Research has shown that the new heat exchanger can significantly reduce the amount of energy needed to prepare domestic hot water. The research results can be useful for researchers, designers and potential users of heat recovery systems.

Thermo-economical performance analysis of a direct-expansion solar heat-pump water heater driven by a photovoltaic array and the electrical grid in Medellín Colombia

Sustainable water heating technologies with competitive costs can contribute to meet carbon reduction goals. In this study. the dynamic performance of a proposed configuration for a photovoltaic direct-expansion solar heat-pump water heater (PV-DX-SHPWH) with 110L capacity is assessed by means of a validated numerical dynamic model at typical meteorological conditions in Medellín, Colombia. Refrigerant R1234yf is selected as the working fluid due to its low global warming potential and its zero ozone depletion potential. A photovoltaic panel system is included as the main power source for a DC variable speed compressor in order to harness a renewable source of energy, while energy backup is provided by the electric grid. After validating the numerical approach by comparison to experimental data from the literature, the behavior of the PV-DX-SHPWH is simulated for values of installed photovoltaic peak power between 200 and 1000 W during a complete typical meteorological year to estimate the average thermal performance. From these simulation results, thermal performance for three representative days is analyzed in detail in terms of water temperature and coefficient of performance (COP) evolution. Also, an economic analysis is performed for the yearlong simulations results in terms of the levelized cost of heat (LCOH), and the results for the PV-DX-SHPWH are compared with other traditional water heating systems. According to the thermo-economic analysis, the COP of the system is higher at low installed photovoltaic powers, and a photovoltaic power range is found (200 W–800 W) whereby high performance of the system (COP greater than 3.5) is achieved at a low LCOH. Also in this range, the proposed system is more competitive than traditional alternatives such as electric and natural gas water heaters.

Investigating the effects of salt spray corrosion on mechanical properties of steel sheets of HVAC heat pumps coated with zinc and polymeric substances

Steel sheets are extensively used in various industrial applications because of their high mechanical properties, costs, and availability. However, in some applications such as gas, oil, and solar water heaters and heating, ventilation, and air conditioning (HVAC) systems, corrosion properties need to be further improved through new surface coatings for enhanced protection against corrosion, degradation, and abrasion. In many cases, a duplex coating system is used to provide extra protection against corrosion and degradation. In this study, steel sheet samples with varying levels of protective zinc coating thicknesses were individually tested as well as in conjunction with polymeric-based paint coatings through equal exposure times in a salt spray chamber for several days. Corrosion and mechanical testing of varying zinc coatings, especially in duplex systems are hardly available in the literature reviews, and this study reports new findings in the HVAC field. The prepared samples were kept in a salt spray chamber for different time frames (250 -- 1000 hours), and the effects of corrosion damages over time were investigated. Before and after the evaluations, all the sheet samples were subjected to tensile testing to study the changes in mechanical properties. It was discovered that duplex coating systems that involve a zinc coating with an organic polymer-based powder coat or pre-painted finishes on metal sheets (G30, G60, and G90) showed little or no sign of corrosion degradation over time, and therefore experience substantially fewer property changes. However, the surfaces of the uncoated or one-layer coated samples were severely damaged in the salt spray chamber, reducing the lifetime of the HVAC system. It is concluded that the duplex system provided better corrosion and chemical resistance against environmental degradations.

Experimental study on flow and heat transfer performance of condensing gas-fired boiler

In the process of energy utilization, a large amount of heat transfer needs to be realized through the heat exchange process. Therefore, the development of efficient enhanced heat exchange technology has important theoretical and application value for realizing the efficient utilization of energy and reducing pollutant emissions. Condensing heat exchanger is the core component of condensing water heater. Firstly, this paper analyses the development trend of condensing heat exchanger at home and abroad, and studies the heat exchange, pollutant emission and structural optimization design of condensing heat exchanger by using the gas water heater test-bed. Using the field synergy theory, the flow channel and fin structure of the heat exchanger are optimized. The series flow channel on the water side of the heat exchanger is optimized as the structure of first parallel and then series flow, so that the heat transfer capacity of the water side of the heat exchanger can be increased by 5.6% at the maximum, the reduction of NOx emission concentration is relatively less than 6.7%.

Effect of hydrogen-blended natural gas on combustion stability and emission of water heater burner

To study the effect of hydrogen-blended natural gas on the combustion stability and emission of domestic gas water heater, a test system is built in this paper, taking a unit of the partial premixed burner commonly used in water heaters as the object. Under the heat load of 0.7–2.3 kW, the changes of flame shape, burner temperature and pollutant emission of natural gas with hydrogen volume ratio of 0–40% are studied with independent control of primary air supply and mixing. The results show that: with the increase of hydrogen blending ratio, the inner flame height increases firstly and then reduces, while the change of burner temperature is opposite. The maximum inner flame height and the minimum temperature of the burner both appear at the hydrogen blending ratio of 10–20%. It can be seen that the limit of hydrogen blending ratio which can maintain the burner operate safely and stably under rated heat load is 40% through the maximum temperature distribution on the burner surface. The CO emission in the flue gas gradually decreases with the increase of hydrogen blending ratio, while the NO x emission fluctuates slightly when the hydrogen blending ratio is less than 20%, but then decreases gradually.

A comprehensive review and analysis on CO2 heat pump water heaters

• Existing CO 2 HPWHs in industrial and residential sectors are reviewed. • Performance restricted by the pinch point effect is analyzed. • Limitations in CO 2 compressors and lubrication are revealed for the first time. • Current enhancements to overcome the limitations are summarized. In the context of the Montreal Protocol, CO 2 is considered as an appropriate natural refrigerant with an Ozone Depletion Potential (ODP) of zero and a Global Warming Potential (GWP) of one. A CO 2 heat pump water heater (HPWH) can provide hot water with a relatively high COP and consume significantly less energy than all electric or gas water heaters. This study reviews and analyses the existing CO 2 HPWHs both in industrial and residential sectors, where the low-temperature and high-temperature systems are classified by the heat delivery temperature of below and above 80 °C, respectively. The significance and features of existing CO 2 HPWHs are also summarised in this study. Moreover, the performance limitations of current CO 2 HPWHs are discussed considering the temperature gliding matching, and the technical constraints in both CO 2 compressors and heat exchangers. Due to the drastic variation of CO 2 heat capacity with temperature and pressure, the heat exchange process between sCO 2 and water is affected by the pinch point. The temperature gliding matching can be enhanced by optimising the parameters in both the CO 2 and water sides, using zeotropic refrigerant mixtures, or adding new devices or cycles to the existing CO 2 system. Another way to improve the system performance is increasing the discharge pressure or discharge temperature, while current CO 2 reciprocating compressors have an upper-temperature limit of 140 °C and upper-pressure limit of 140 bar, as well as some constraints in the heat exchangers. Due to the decomposition risk of lubricant in the compressor, two types of oil-free compressors (turbo and scroll) have been described. But it is found that the turbo-compressor is hard to provide a competitive efficiency when the pressure is high, and there is a significant leakage flow in a scroll compressor.