Domestic Air Conditioning Research Articles

Performance assessment of an off-the-shelf R744 heat pump equipped with an ejector

This paper presents the experimental analysis of a prototype R744 water/water heat pump (5 kW heating power at 0 °C evaporation temperature, 100 bar gas cooler pressure, 35 °C gas cooler outlet temperature) which was equipped with a two-phase ejector. According to the traditional lay-out, the energy that was recovered from the expansion process inside the ejector improved the circulation of refrigerant through the evaporator. The same heat pump was also provided with a back-pressure valve as the expansion device, i.e. a direct comparison of the performance was possible between the heat pump systems, either equipped with the ejector or the expansion valve.Tests were performed to evaluate the performance when the heat pump produced hot tap water, i.e. heating water from the main waterworks temperature to storage temperature (∼60 °C). Additionally, an investigation took place to understand how the system performed when space heating was required, i.e. providing hot water with a limited temperature lift, however at relatively high inlet temperatures.Experiments demonstrated that the ejector is helpful to improve the heat pump performance, thus promoting the diffusion of R744 units also for domestic space heating and air conditioning. Technological issues related to lubricant recovery were faced.

Numerical Simulations of a Aluminium Microchannel Condenser for Household Air Conditioner

In recent years, microchannel heat exchangers are intensively used in refrigeration and air conditioning systems as they are super efficient. This paper introduces a microchannel condenser for domestic air conditioners with a simulated model to evaluate its performance using MATLAB results. The model was used to obtain the optimal geometrical, operating and performance parameters for different number of microchannels with various no of passes with different number of tubes per pass for one ton of refrigeration system using R134a as the refrigerant. In this paper simulated results of two phase heat transfer coefficient and two phase pressure drop using the selected correlations are plotted against mass flux, dryness fraction, number of microchannels, number of passes in the condenser, saturation temperature and overall conclusions are made.

Branding and product evaluation across Chinese regions

PurposeThis paper aims to explore two fundamental aspects of branding in emerging markets. First, are there significant differences in product evaluation behaviour between regions within a large emerging market such as China? Second, how important is branding relative to other product cues in the product evaluation among consumers in emerging markets?Design/methodology/approachData were collected from a sample of respondents in three Chinese cities (Hong Kong, Shanghai, and Chongqing). Respondents were asked to evaluate combinations of a hypothetical product (domestic air conditioning) varying in brands, prices and country of origin (COO). ANOVA, t‐tests and regression were conducted to test for significant differences in ratings brand, price and COO, perceived product quality and purchase intention.FindingsThe results show significant differences between the three regions in product evaluation processes and outcomes. In addition, the study identifies a general preference across regions for global brands over local brand competitors.Research limitations/implicationsWhile the findings may be due to the particular Chinese locations and/or the product chosen, nevertheless, the differences identified in the product evaluation processes and outcomes point to the importance of considering the potential differences between regions in diverse emerging countries like China. In addition, the general preference for international brands suggests important implications for foreign and local manufacturers.Practical implicationsManagers will develop an improved awareness of the importance of brands in emerging markets and of the regional differences in diverse markets such as China.Originality/valueBy focussing on regional differences within diverse emerging markets (rather than treating such markets as homogeneous), this study extends understanding of the complexities facing international and domestic marketers.

Housing, heat stress and health in a changing climate: promoting the adaptive capacity of vulnerable households, a suggested way forward

In many places extreme heat causes more deaths than floods, cyclones and bushfires. However, efforts to manage the health implications of heat and increase the adaptive capacity of vulnerable populations are in their infancy, requiring urgent attention from research and policy. This paper presents a case for research exploring the influence of social and contextual factors on vulnerable populations' capacity to adapt to heat in the context of climate change. We argue such research is imperative given current prioritization of short-sighted policy solutions such as installation and use of greenhouse-intensive domestic air-conditioners as moderators of heat stress. Globally, vulnerability to heat stress is most often assessed by epidemiological analysis of past morbidity and mortality data; yet a range of other factors need to be accounted for in interpreting and understanding these patterns of ill-health and loss of life, and further in determining how vulnerability is created, exacerbated and alleviated by broader societal conditions. Such factors include: the cooling technologies and infrastructures available to householders, practical knowledge about how to moderate heat stress, and social and cultural understandings of comfort and vulnerability. To investigate these factors, new methodologies are required. Social practice theory, which conceptualizes the dynamic interactions between individuals and wider systems of power, infrastructure, technologies, society and culture as components of practices such as household cooling, is presented as a way forward. The development of a practice-based methodology and conceptual framework to understand adaptation to heat will provide a multidimensional, systems-oriented understanding of how vulnerability can potentially be reduced.

Study on Electricity Consumption for Domestic Refrigerators, Air Conditioners, and Water Dispenser in Guangzhou (China) urban area based on Questionnaire Data

In China, since the 1990's, as household incomes have increased, many kinds of appliances have been purchased, causing the electricity demand to grow from year to year. Widely-used air conditioners and recently penetrated water dispensers, in particular, contribute mainly to increased electricity consumption in the household sector. In this context, we conducted a study to provide descriptive information on the effects of this recent electricity consumption of installed air conditioners, refrigerators, water dispensers, and the standby power of electric devices of urban households in Guangzhou based on the result of our survey in 2004. The result of this study suggests that in terms of water dispensers extending operation time is a serious factor affecting increased electricity consumption. Moreover, replaced air conditioners for power saving may not be enough to reduce the growing electricity consumption.

427 PROPOSAL OF A SMALL EXHAUST HEAT AIR CONDITIONING SYSTEM

In order to make lower environmental effect of domestic air conditioning system, we propose a new air conditioning system using cooling tower principle for outdoor unit. By performing experiment with a testing system, which is modified by replacing the air-cooled condenser by a water-cooled condenser, we confirmed a possibility to make lower condenser temperature. Moreover, the proposed system's performance is simulated using vapor compression cycle theory at a condition of the common cooling load for existing system. We compared the amount of power consumption with the conventional case. Saving power consumption is possible as outdoor temperature increases and it reaches up to 30% in the summer at temperatures of outdoor between 27 and 37 ℃. Amount of external exergy loss of the air-cooled condenser due to high temperature exhaust heat can reach to about 300 W at outdoor temperature of 37 ℃ and exhaust heat of 1.1 kW, while it is assumed to be nearly zero in case of the new system due to no temperature difference between condenser and the environment. Last but not least, a prototype of new heat exchanger is proposed and tested in summer weather. The results shows that heat-transfer coefficients are at least 4 times higher than the compact-heat-exchanger which is popularly used in air-cooled condenser of conventional air conditioning system.

Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait

The summer season in the state of Kuwait is long with a mean daily maximum temperature of 45 °C. Domestic air conditioning is generally deployed from the beginning of April to the end of October. This accounts for around 75% of Kuwaiti electrical power consumption. In terms of energy conservation, increasing the thermostat temperature by 1 °C could save about 10% of space cooling energy [1,2]. However, knowledge of indoor domestic temperatures and thermal comfort sensations is important to aid future advice formulation and policy-making related to domestic energy consumption. A field study was therefore conducted during the summers of 2006 and 2007 to investigate the indoor climate and occupants' thermal comfort in 25 air-conditioned domestic buildings in Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait domestic residences, together with an analysis of domestic-occupant thermal comfort sensations. With respect to the latter, a total of 111 participants provided 111 sets of physical measurements together with subjective information via questionnaires that were used to collect the data. By using linear regression analysis of responses on the ASHRAE-seven-point thermal sensation scale, the neutral operative temperatures based on Actual Mean Vote (AMV) and Predicted Mean Vote (PMV) were found to be 25.2 °C and 23.3 °C, respectively, in the summer season. Findings from this study provide information about the indoor domestic thermal environment in Kuwait, together with occupant thermal comfort sensations. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.

Investigation of prototype thermoelectric domestic-ventilator

Applications of thermoelectrics had been enlarged from conventional single refrigeration or generation to waste heat recovery with tough energy consumption of the world. With improvement of living standard more and more domestic air-conditioners are used in Chinese families now. Percentage of power consumption of domestic air-conditioner caused by heat load of fresh air supply increased after SARS, which could be prevented efficiently with sufficient fresh air supply, broke out in China in 2003. A novel prototype thermoelectric domestic-ventilator with heat recovery of exhaust of air-conditioned room had been made in Hunan University thermoelectric lab. A thermoelectric heat exchanger and a flat-fin cross flow heat exchanger were integrated in this ventilator. This ventilator was investigated and its cooling (and heating) performance were evaluated in terms of the coefficient of performance, cooling and heating powers, and being handled temperature difference of fresh air. The coefficient of performance of this ventilator was found to be over 2.5 in the whole experiment. The optimal working parameters of this ventilator were studied in this paper. The potential improvements in performances and market prospects were also discussed in this work.

Performance of mixture refrigerant R152a/R125/R32 in domestic air-conditioner

This work reports a ternary blend R152a/R125/R32 with a mass ratio of 48/18/34 as a potential alternative to R22. A computer code has been developed with NIST REFPROP 7.0 for the comparative analysis of thermophysical properties and refrigerant performance of this new mixture and of R22. A drop-in test of this new mixture was performed in a domestic air-conditioner originally designed for R22. Both the calculation and experimental results showed that this new mixture could be regarded as a most likely drop-in substitute for R22 in many applications. The flammability of this ternary blend was also studied with an explosion apparatus to prove that it could be used safely. Besides, simulation of the refrigerant cycle leakage showed that the variation of composition due to leakage was so little that there is no much performance degradation.

Influence of air conditioners utilization on urban thermal environment

The urban heat island effect is essentially a kind of thermal pollution caused by artificial activity. Air conditioning units used in buildings release a great deal of heat into outdoors while they improve the indoor thermal environment. Therefore, it will cause a rise in the outdoor air temperature and worsen the urban thermal environment. A “box” model is presented in this paper; it is used to quantitatively determine the rise in outdoor air temperature caused by using domestic air conditioners in Wuhan. The results demonstrate the rise degree is 2.56 °C under inversion conditions and 0.2 °C under normal conditions, which indicates that thermal pollution is serious at stable atmosphere. To a certain extent, the rise of atmospheric temperature can be verified by the rise of lowest atmospheric temperature in Wuhan over recent years.

Flow Characteristics of Refrigerants Flowing Inside an Adiabatic Spiral Capillary Tube

An analytical model has been developed to predict the length of adiabatic capillary tubes used in domestic refrigerators and low-capacity residential air conditioners. The model predicts the length of two types of tubes—straight and spiral adiabatic capillary tubes. The proposed model is based on the homogenous two-phase flow model, which predicts the length of the adiabatic capillary tubes as a function of refrigerant mass flow rate, capillary tube diameter, degree of subcooling at capillary inlet, internal surface roughness, and the pitch of the Archimedean spiral. The existence of subcooled liquid at the entry of the capillary tube requires the computation of single-phase and then two-phase lengths of the tube. The McAdams et al. (1942) viscosity correlation has been used to evaluate the two-phase viscosity of the expanding refrigerant in the latter part of the capillary tube. All the thermophysical and transport properties of the refrigerants are evaluated by the REFPROP Version 7 database, which is based on the Carnahan-Starling-DeSantis equation of state. The simulation results are validated with the experimental findings of previous researchers. The performance of the above two geometries of adiabatic capillary tube is compared, and it is established that for the same state of refrigerants at the inlet and exit of the adiabatic capillary, spiral capillary is found to have a shorter length. Parametric study of the adiabatic capillary tubes is also carried out. Further, the effect of geometric and physical parameters has been presented in detail. A much smaller capillary tube is required when the eco-friendly refrigerants R-134a and R-152a are used in place of refrigerant R-12 for similar conditions across the adiabatic spiral capillary tube.

Flow characteristics of HFC407C/HC600a/HC290 refrigerant mixture in adiabatic capillary tubes

HCFC22, the commonly used refrigerant in window air-conditioner is to be phased out completely due to Montreal Protocol regulations. Hence the search for drop in substitutes to retrofit window air-conditioner is of current interest. Capillary tube is commonly used in domestic refrigeration and air conditioning systems as expansion devices. This paper presents an experimental study on the flow characteristics of HFC407C/HC600a/HC290 a new refrigerant mixture in adiabatic capillary tubes. The experimental work investigates the effect of capillary length, capillary diameter, condensing pressure, and refrigerant subcooling on the mass flow rate through the capillaries. Based on the experimental data for HCFC22 and HFC407C/HC600a/HC290 refrigerant mixture, a new correlation has been developed to predict the mass flow rate through the adiabatic capillary tubes for different operating conditions, capillary tube geometry and refrigerant properties. The non-dimensional correlation predicts closely the mass flow rates which are in good agreement with the experimental data for HCFC22 and HFC407C/HC600a/HC290 with average deviations of 0.618% and −0.11% and mean deviations of 5.536% and 4.448%, respectively. The mass flow rates predicted using the developed correlation are found to be in good agreement with the results in published literature also.

A new core

This article discusses motors for compressors in domestic air conditioners, an area in which there is a strong demand for high efficiency and also reports the results of the efficiency improvement and productivity of a new core structure. An innovative core structure and manufacturing method boosts efficiency of permanent-magnet motors. This article presents the close relationship between the motor characteristics and the manufacturing method and indicates a way to improve both motor characteristics and the productivity. To pursue further improvement in motor performance by improving the coil space factor further using the joint-lapped core and manufacturing cores with smaller magnetic resistance.

The optimal design for a ground cooling tube in a hot, arid climate

In many hot, arid climates there is a high level of use of domestic air conditioning which can make heavy demands on local electricity generation. A passive strategy which could mitigate this demand is the deployment of ground cooling tubes in which external air is drawn into the building/plant via a tube buried below ground. Whilst this principle has been known of for a considerable time, and many example installations described, there has been no systematic investigation of the influence of the design parameters on the viability of the system. The paper describes a method for carrying out a systematic parametric optimization for a ground cooling tube by coupling a validated numerical model of the system with a constrained optimization method using an evolutionary strategy. Optimizations were based on a thermo-dynamic objective function (minimizing external energy consumption of the whole system) and an economic function (payback time for the tube). Whilst the results are specific to the hot, arid climate of the state of Kuwait, the methodology has universal applicability and illustrates the functional power of combining a performance model with an optimization method in producing optimized designs of energy systems. Practical application: Building and plant simulation programs are becoming increasingly accepted as a design tool: for confirming the performance of a proposed design or for carrying out ‘what if?’ studies to evaluate the effects of varying design parameters or equipment selection. This paper illustrates that, provided the design problem can be modelled in all relevant aspects, linking the simulation program to a constrained optimization can provide significantly more decision support to the designer.

Performance of multi-functional domestic heat-pump system

The working principles and the basic features of a multi-functional domestic heat-pump (MDHP) system are introduced in this paper. Comparatively, the system can provide much better energy performance and higher equipment utilization throughout a year, causes less thermal pollution than the heat-pump water heater and the domestic air-conditioner. A prototype model of the MDHP system was assembled and its operation performance was tested. The results indicated that the new system can save energy through multi-duties, and can work stably under prolonged operation in regions having mild-winter temperatures. A numerical model of the system was also developed, and calibrated by the experimental data. The numerical model was found robust and accurate in predicting the equipment operation, and therefore can be applied to evaluate the system's performance under a spectrum of working environment and alternative equipment designs.

Comparative investigation of thermoelectric air-conditioners versus vapour compression and absorption air-conditioners

This paper compares the performance of three types of domestic air-conditioners, namely the vapour compression air-conditioner (VCAC), the absorption air-conditioner (AAC) and the thermoelectric air-conditioner (TEAC). The basic cycles of the three types of air-conditioning systems are described and methods to calculate their coefficients of performance are presented. General specification data for each type of air-conditioner are given, and performance characteristics are presented. The comparison shows that although VCACs have the advantages of high COP and low purchase price, use of these systems will be phased out due to their contribution to the greenhouse effect and depletion of the ozone layer. AACs are generally bulky, complex and expensive but operate on thermal energy, so their operational consumption is low. TEACs are environmental friendly, simple and reliable but still very expensive at present. Their low COP is an additional factor limiting their application for domestic cooling. TEACs however, have a large potential market as air-conditioners for small enclosures, such as cars and submarine cabins, where the power consumption would be low, or safety and reliability would be important.

Investigation into the effectiveness of heat pump assisted clothes dryer for humid tropics

The paper discusses the finding of the investigation conducted to determine the feasibility of drying clothes using waste heat of a condenser of a typical split type domestic air conditioner used in high rise urban apartments. Tests were conducted in a drying chamber housing the condensing unit, wherein the waste heat rejected by the condenser was used for drying clothes. Drying of a batch of spin dried clothes took about 2 h compared to 2.5 h in a commercial dryer and more than 6 h for natural drying indoors. The drying rate for the test configuration was 0.424 kg/h compared to 0.319 kg/h for a commercial clothes dryer and 0.139 kg/h for indoor natural drying. The energy consumption was nil against 1.909 kW h/kg of moisture removal by the commercial dryer. Experimental results indicate the viability of developing an integrated air conditioner cum dryer suitable for humid tropical climates.

On noise indices for domestic air conditioners

A survey was carried out in the present study to determine the noise indices which are capable of describing the nuisance caused by exposure to air-conditioner noise inside residential apartments. This survey consisted of a questionnaire, which asked the respondents to rate their feelings of annoyance and loudness on the air-conditioner noise and to give their preference of a change in the noise levels. Physical noise measurements were also carried out. A total of 57 noise spectra and 399 respondents were involved in the survey. Results show that the Zwicker's loudness level and the percentile level of 90% exceedence are the two major indices for air-conditioner noise assessment. Tonality appears not to be a good indicator for such a purpose.

Domestic air-conditioner and integrated water heater for subtropical climate

The technology of using a heat pump for space conditioning and domestic hot water heating in residences has been developed for half a century. The earlier air-to-water heat pumps and water-heating heat pumps suffered from drawbacks like high costs, unreliable operation, and inflexible applications. They were not well positioned in the market to attract customers. This paper introduces a novel air-conditioning product that can achieve the multi-functions with improved energy performance. The basic design principles and the laboratory test results are presented. The results showed that by incorporating a water heater in the outdoor unit of a split-type air-conditioner so that space cooling and water heating can take place simultaneously, the energy performance can be raised considerably.

Transient characteristics and performance of a novel desalination system based on heat storage and spray flashing

A hybrid latent heat storage and spray flash evaporation system has been devised in an attempt to develop an energy saving desalination system that stores intermittent thermal energy such as waste heat, solar heat or heat from the surplus steam of a power station at night and utilizes the stored energy not only for the generation of process steam from seawater for industries and domestic air conditioning but also for the production of fresh water from the generated steam for industrial and domestic uses on demand. Experimental results of the transient discharge characteristics of the heat storage column packed with the phase change material and the transient spray flash evaporation characteristics are reported. It is also shown that by using the numerical results of the discharge characteristics and the empirical equation of the efficiency of spray flash evaporation, the amount of generated steam and produced water can be predicted with sufficient accuracy. The utilization of more than 95% of the amount of stored energy for the generation of process steam and the production of fresh water, substantiated experimentally, confirms the high efficiency of the hybrid system.