Gas-fired Water Research Articles

Natural ventilation of a room with an atmospheric-vent water heater in both on- and off-states

Instantaneous or tankless gas-fired water heaters are widely used in residential buildings to heat water for domestic use. For the combustion can process properly, a minimum amount of air is required, which can be obtained directly from outdoors or from inside the room. This latter case corresponds to the operation mode of the atmospheric-vent water heater, which is one of the most frequently encountered appliances to heat domestic water. As the room where the water heater operates is generally a living area, the installation design should account for the health and comfort requirements. Increasing the room airflow rates reduces the risk of harmful products from incomplete combustion but, as counterpart, important impacts on the thermal and energy performance of the room can occur. In this paper the natural ventilation conditions of a room with an atmospheric-vent water heater are investigated. Moreover, the effects on energy demand for thermal comfort are assessed. The study was conducted through the EnergyPlus simulation program, whose applicability to the problem was first tested. The results obtained are consistent with the expectations, allowing for a better insight into the level of compliance of the combustion air requirements and respective impacts on energy performance.

In Situ PLIF and Particle Image Velocimetry Measurements of the Primary Entrainment Fuel Jet in a Naturally Aspirated Water Heater

The time-averaged characteristics of a fuel jet have been measured via acetone planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) in the primary mixing region of an operating gas-fired water heater. These measurements allow for experimental characterization of the cross-sectional scalar and velocity fields as well as the estimation of the mass entrainment as the flow enters the burner in a practical system. In these experiments, reasonable results were obtained when only the fuel jet was seeded with acetone or PIV particles rather than the entire flow, thus demonstrating the potential for simplified experimental configurations in some applications where controlling or seeding the entire flow may be difficult. The entrainment characteristics of the fuel jet are compared with benchmarks from literature. The commercial device exhibits a larger mass entrainment rate than is found in typical free jets that have been studied in the literature. This may be a result of the jet's low Reynolds number (9,600) in comparison with other literature studies, and a result of initial conditions.

Effects of Incorporated Heat Exchangers on the Thermo Economic Analysis of a Water/LiBr Absorption Refrigeration System Part I: Formulations

This paper is the first part of a study on the effects of the incorporation of additional heat exchangers on the performances of a Water/LiBr absorption refrigeration system (ARS). A thermo-economic approach is used to evaluate this effect. This first part presents the formulations developed for such a comprehensive analysis while the second paper deals with the application of the developed formulation to three configurations of an air cooled gas-fired water bromide ARS. In this paper mass, energy, and exergy balances are illustrated and applied to components system. Also, a thermoeconomic methodology is established to evaluate the economic costs of all internal flows and a product of system by formulating thermoeconomic cost balances and variables. The thermoeconomic cost balances and variables formulated here have significant importance to carry out the effects of including of heat exchangers on thermoeconomic analysis of the ARS and to determinate the optimal performances of system accounting economic constraints

Gas-fired instantaneous water heaters with combustion chamber sealed with respect to the room in multi-storey residential buildings—Results of pilot plants tests

In recent years, the literature on HVAC has been predominantly devoted to the problems of increasing the efficiency of buildings, reduction of CO2 emission or ensuring user-friendly indoor air quality. However, in many countries, including Poland, ensuring safety for the users of gas appliances is a key issue. That particularly concerns the gas-fired water heaters with open combustion chamber (Type B). The problem can be solved by replacing the traditional heaters with combustion chamber sealed with respect to the room (Type C) equipped with air supply and combustion product ducts systems. Two pilot plants were built, corresponding with the conditions of a typical Polish multi-storey residential building. During the designing process, the CFD Fluent software was used, making it possible to optimally select the dimensions and configuration of the tested plants. The tests were conducted for different operation variants, during which the appropriate functioning of the appliances was evaluated as well as the energy efficiency of hot water production. Moreover, selected ways of enhancing the operation of such appliances as well as the impact of wind on their work were examined. The experimental results presented in the paper should make it easier to implement gas-fired instantaneous water heaters Type C, particularly in the already-existing multi-storey residential buildings.

Energy efficiency improvement and fuel savings in water heaters using baffles

Thermal efficiency improvement of a water heater was investigated numerically and experimentally in response to presence of a baffle, particularly designed for modifying the flow field within the water reservoir and enhancing heat transfer extracted into the water tank. A residential natural gas-fired water heater was selected for modifying its water tank through introducing a baffle for lowering natural gas consumption by 5% as a target. Based on the geometric features of the selected water heater, three-dimensional models of the water heater subsections were developed. Upon detailed studies of flow and heat transfer in each subsection, various sub-models were integrated to a complete model of the water heater. Thermal performance of the selected water heater was investigated numerically using computational fluid dynamics analysis. Prior to baffle design process and in order to verify the developed model of the water heater, time-dependent numerically-predicted temperatures were compared to the experimentally-measured temperatures under the same conditions at six (6) different locations inside the water tank and good agreement was observed. Upon verifying the numerical model, the fluid flow and heat transfer patterns were characterized for the selected water heater. The overall design of the baffle and its location and orientation were finalized based on the numerical results and a set of parametric studies. Finally, two baffle designs were proposed, with the second design being an optimized version of the first design. The verified three-dimensional model of the water heater was modified to include the baffle designs and same thermal performance analysis was simulated confirming potential improvements in thermal efficiency. Thereafter, designed baffles were prototyped and assembled in identical water heater units and experiments were conducted according to standard water heater test procedures. Finally, numerical and experimental results verified thermal efficiency improvement in the water heater after introducing the baffles. As a result, baffle’s second design is capable of lowering the natural gas consumption of the water heater by 4.95% under steady-state thermal efficiency test condition which meets the target of this research. However, the gas savings under actual usage patterns might be less than this value.

Computational fluid dynamic simulation of oxyfuel combustion in gas-fired water tube boilers

Carbon capture is essential to enable the use of fossil fuels while reducing the emissions of CO 2 into the atmosphere. Among the methods of CO 2 capture and storage, oxyfuel technology provides a promising option for power and steam generation systems. In this technology, the fuel is burned in pure oxygen instead of air, and the flue gas consists primarily of CO 2 and H 2O that can be easily separated via condensation. In order to moderate the furnace temperature in the absence of N 2, a fraction of the flue gas is recycled in the combustion chamber. In this work, the characteristics of oxyfuel combustion are compared to those of air–fuel combustion in a typical natural gas fired package boiler and the results can be applied to large boilers such as industrial and utility boilers. The percentages of recycled CO 2 considered in this study are 83.8% and 77% by mass. The first corresponds to 21% O 2 and the second corresponds to 29% O 2 by volume. Validations for both oxyfuel combustion and air–fuel combustion are conducted through comparison with the available experimental data. Results indicate that the temperature levels are reduced in oxyfuel combustion. As the percentage of recirculated CO 2 is increased, the temperature levels are greatly reduced. We found that the fuel and oxygen consumption rates are slower in oxyfuel combustion relative to air–fuel combustion. Heat transfer from the burnt gases to the water jacket along the different surfaces of the furnace is calculated. It is shown that the energy absorbed is much higher in the case of air–fuel combustion along all surfaces except for the end part of the furnace close to the furnace rear wall. The heat transfer in the return chamber (tube bank) was also calculated and the results indicated higher heat transfer in the oxyfuel case in comparison with the air fuel case as a result of ignition delay in the vicinity of the furnace entrance region.

An aquifer thermal storage system in a Belgian hospital: Long-term experimental evaluation of energy and cost savings

Over a three years period, an aquifer thermal energy storage system was monitored in combination with a heat pump for heating and cooling of the ventilation air in a Belgian hospital. The installation was one of the first and largest ground source heat pump systems in Belgium. Groundwater flows and temperatures were monitored as well as the energy flows of the heat pumps and the energy demand of the building. The resulting energy balance of the building showed that the primary energy consumption of the heat pump system is 71% lower in comparison with a reference installation based on common gas-fired boilers and water cooling machines. This corresponds to a CO 2-reduction of 1280 ton over the whole measuring period. The overall seasonal performance factor (SPF) for heating was 5.9 while the ATES system delivered cooling at an efficiency factor of 26.1. Furthermore, the economic analysis showed an annual cost reduction of k€ 54 as compared to the reference installation, resulting in a simple payback time of 8.4 years, excluding subsidies.

Consumer choice on ecologically efficient water heaters: Marketing strategy and policy implications in Japan

This study examines how consumers select ecologically efficient water heaters in Japan. Energy conservation in household water heating is increasingly important for reducing an amount of CO 2 emission, because the share of water heating in household energy consumption is approximately 30%. Recently, Japanese households have widely used ecologically efficient electric heat pump water heaters (Eco Cute) or gas-fired water heaters (Eco Jozu). The total number of such efficient water heaters sold in Japan was more than 2.5 million at the end of 2008. This study investigates various factors and impacts of marketing strategy for promoting the appliances in Japan. We apply mixed and nested logit models to a disaggregated choice data on water heaters from 2004 to 2008. This study considers retail energy prices, a government financial support and marketing activities as important factors for appliance selection. In addition, we consider consumers' housing attributes such as floor space and age of building. This empirical study finds two business implications. One of the two implications is that an increase in an energy price may enhance a choice probability of Eco Cute and Eco Jozu because a price increase invites consumer's consciousness on energy conservation so that a cost reduction on energy consumption becomes essential in a use of the efficient appliances. The other implication is that marketing activities, especially by recommendations from sales representatives and/or housing suppliers, are important for consumer behaviors. The other important findings are discussed in this study. This business experience in Japan is useful to the other countries where ecologically efficient water heaters are not popular at the current moment.

Energy and exergy analysis of multi-functional solar-assisted heat pump system

This paper reports the exergetic modeling and performance evaluation of a novel multi-functional solar-assisted heat pump (SAHP) system based on an experimental study. Comparisons between the multi-functional SAHP system and conventional hot water heating systems, i.e. electric water heater, gas-fired water heater and air source heat pump, are made with respect to energy and exergy efficiencies. The results show that the multi-functional SAHP system has the highest energy performance, average 2.98. In addition, the multi-functional SAHP system offers the highest exergy efficiency among the four kinds of hot water heating systems. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

Hybrid Gas Water Heater Combined with Adsorption Heat Pump Cycle for Commercial Use

To improve the heat efficiency of gas water heaters, we studied a hybrid type water heater that combines a conventional gas-fired water heater and an adsorption heat pump cycle. With a target heat efficiency of approximately 120%—a dramatic increase over the 85% efficiency of a conventional gas water heater—this hybrid gas water heater (HGWH) is expected to be an energy-saving replacement for commercial users. The HGWH combines a boiler and a heat pump cycle that uses city gas as its heat source, which are operated either simultaneously or independently depending on the outside temperature, making year-round high heat efficiency operation. Considerations regarding the heat pump cycle have taken into account the adsorption cycle, the absorption cycle, and the vapor compression cycle, but our study focused on the adsorption cycle from the standpoint of overall priorities. There are two possible adsorption cycles: a dual single-stage heating cycle, which heats the water supply in two stages, and a single-stage cycle, which heats the water in one stage. We evaluated the feasibility of both systems using prototypes. We found that a compact system can be achieved by combining a single-stage adsorption cycle and a gas water heater, and the heat efficiency of this HGWH achieves 110% to 120%, which is greater than a dual single-stage heating cycle.

Design of School Building HVAC Retrofit with Hybrid Geothermal Heat-Pump System

This paper describes a proposed energy-efficient retrofit of a heating, ventilating, and air-conditioning system for a school building in southeastern Wyoming. The existing system consists of six conventional constant air volume heating and ventilating units with heat provided by a gas-fired hot water boiler. The proposed replacement is a novel system application that consists of a geothermal heat pump (GHP) system with a supplemental solar thermal collector array. Ventilation air heat recovery and variable-speed pumping are also included. Innovative design of both the ground loop and the interior building loop are accomplished using a whole system approach. System simulation analyses show a simple payback period of less than 10 years. An extra benefit of the GHP system not accounted for in the economic analysis is added cooling capability.

Response to “Effectiveness of Gas Fired Water Heater Elevation in the Reduction of Ignition of Vapors from Flammable Liquid Spills”

Response to “Effectiveness of Gas Fired Water Heater Elevation in the Reduction of Ignition of Vapors from Flammable Liquid Spills”

Effectiveness of Gas Fired Water Heater Elevation in the Reduction of Ignition of Vapors from Flammable Liquid Spills

Elevating ignition sources to protect against the ignition of vapors from flammable liquid spills has a long history in the national standards and codes. Accident data from the Consumer Product Safety Commission and the National Fire Protection Association identify gas fired water heaters as the major ignition source of flammable liquid vapor accidents in the home. During the past ten years, numerous different laboratories have conducted tests to evaluate the effectiveness of elevating gas fired water heaters to prevent the ignition of flammable liquid vapors. Analysis of the results of 48 tests from three laboratories demonstrate the effectiveness of elevating gas fired water heaters in reducing the ignition of flammable liquid vapors in the home.

‘Flash pasteurization’ of contaminated streams using a direct contact gas-fired water heater

A commercial direct contact gas-fired water heater was modified for in-lab evaluation of microbial reduction and temperature consistency at various water flow rates. The water heater was modified so that a contaminated input stream could be treated using 50-gal (189.3-l) bulk feed tanks. A final reservoir tank was bypassed using six sampling ports placed in pairs along three locations in the vertical heating column with which to test the efficacy of a single pass at different positions in the heating zone. Temperature probes were utilized to follow water temperature at 8, 10, and 12 gal min −1 (30.3, 37.9, and 45.4 l min −1). When using inoculated water streams, we obtained 4–7 log 10 cycle reductions of various micro-organisms tested suggesting that this may have potential use in situations where water recycling is of interest in food processing environments.

A TURBULENCE INTEGRAL MODEL FOR THE EVALUATION OF THE THERMAL EFFECTIVENESS OF A STATIC DAMPER IN GAS-FIRED WATER HEATERS

A semi-analytic mixed convection model is developed for the solution of forced and free convection heat transfer in the center flue of gas-fired water heaters. The model can be used to examine the feasibility of a new static damper concept in the flue design. The static damper provides a trouble-free and economical alternative to conventional electric vent dampers. An integral model with profile assumptions characterizes the turbulent flow during the main burner operation and a laminar free convection analysis characterizes the standby mode conditions. The numerical and experimental results indicate the damper provides an effective mechanism for a 20% reduction of standby heat losses together with a high relative dynamic pressure drop while introducing only a low pressure difference during the combustion mode of operation. These results indicate an improvement of standby efficiency in comparison to a conventional internal baffle flow obstruction which leads to low dynamic pressure drops during the standby mode of the water heater operation. Applications of the static damper concept to other appliances such as boilers may also be beneficial.

Hot water service using high-efficiency gas-fired appliances†

Smnmary Research on boilers used for heating systems has been extensive but less attention has been paid in the past to hot water appliances. Improved boiler performance, higher insulation of buildings and increased adventitious gains have meant that energy use for the supply of hot water has become more significant. Field and laboratory studies have therefore been carried out to investigate the performance of recently available high-efficiency gas-fired water heaters. A field study of a plate heat exchanger used in conjunction with a high-efficiency boiler was also undertaken to gain some knowledge of an alternative method of supplying hot water. The results obtained show that changes to the existing system at the field trial site reduced running costs considerably and improved control of the delivered water temperature. Gas-fired appliances with heat transfer efficiencies of up to 94% are now available for the supply of hot water to commercial premises.

Chimney Venting Performance Study

Abstract An investigation was undertaken to determine the levels of house depressurization against which naturally vented gas-fired furnaces and domestic water heaters can establish and maintain safe venting of combustion products. Also investigated were the maximum depressurizations of buildings which could be achieved by the installed fans and fireplaces. A test procedure was developed whereby venting failure can be artificially induced by depressurizing the house with a large fan. Results show that it is highly improbable that the maximum depressurizations found in houses by operating all the fans and the fireplaces at the same time will cause the chimney to vent improperly even in conditions under which venting failure would be most likely to occur (cool temperatures, low wind, cold chimney, large number of exhaust fans, weak venting furnace/chimney combination, relatively tight house).

4658803 Gas-fired water heaters : Geoffrey Ball, Robi Galliver, Martin White, Epsom, United Kingdom assigned to British Gas Corporation

4658803 Gas-fired water heaters : Geoffrey Ball, Robi Galliver, Martin White, Epsom, United Kingdom assigned to British Gas Corporation

Design and Performance of a High-Efficiency Commercial

A gas-fired commercial water heater has been developed which achieves a steady-state efficiency of over 95 percent and can obtain overall service efficiencies above 90 percent in many applications. These high levels of efficiency are obtained by operating in the condensing mode over a substantial portion of the duty cycle. The use of a power burner and a coil-type heat exchanger results in a compact configuration which produces both high efficiency and low emissions. The design, operating principles, and performance characteristics of the water heater are described.

Energy conservation options for residential water heaters

Current designs of gas-fired and electric water heaters present a substantial opportunity for energy conservation through reductions in jacket losses, pilot losses and flue-gas losses. A systematic analysis and comparison of alternative energy-conserving designs has been carried out. Promising options for gas-fired water heaters include increased insulation, thermostat setback, forced-draft burners with intermittent ignition and flue closure, and instantaneous (low storage) designs. High efficiency electric water heaters incorporate increased insulation, thermostat setback, solar preheat, and heat pump operation. The evolution and market penetration of these alternative designs, some of which are commercially available at this writing, can reduce the energy usage for residential water heating in the U.S. by approx. 0.3 quads in the near-term, and up to 1.0 quads in the long-term as advanced designs achieve widespread saturation.