Air Conditioning Applications Research Articles

Performance testing of a counter-cross-flow run-around membrane energy exchanger (RAMEE) system for HVAC applications

A novel run-around membrane energy exchanger (RAMEE) system is designed, built, and tested for heating, ventilating, and air-conditioning applications. The RAMEE system consists of two counter-cross-flow liquid-to-air membrane energy exchangers, one located in the supply and the other in the exhaust air streams of a building. Inside each exchanger, a micro-porous membrane separates the air and desiccant solution streams. This membrane allows heat and water vapor exchange between the two streams. The RAMEE system thus exchanges sensible and latent energy between the supply and exhaust air streams by using a desiccant solution as the energy carrier that is pumped in a loop between the two exchangers. The RAMEE performance is evaluated by testing the system with various air and desiccant solution flow rates during standard summer and winter operating conditions. During summer test conditions, the total system effectiveness increases with increasing desiccant flow rate, but decreases as the air flow rate increases. Under winter test conditions, the total effectiveness changes little with changes in the air and desiccant flow rates. For some test conditions, the maximum total effectiveness of the system is between 50 and 55%. The effectiveness data are compared to available correlations and reasons for discrepancies are discussed.

Novel ammonia sorbents “porous matrix modified by active salt” for adsorptive heat transformation: 3. Testing of “BaCl2/vermiculite” composite in a lab-scale adsorption chiller

A composite adsorbent composed of BaCl2 impregnated into expanded vermiculite has been synthesized and tested in a laboratory scale adsorption chiller. Previous work has established the promising theoretical performance of this adsorbent with ammonia as a refrigerant, in terms of equilibrium uptake, suitable equilibrium temperatures for use in air conditioning applications and good reaction dynamics. Analysis of the adsorption phase revealed a simple exponential approach to equilibrium uptake which was not previously observed in larger scale experiments. It was demonstrated that this material can provide effective operation of the chiller using a low potential heat source (80–90 °C) giving COP as high as 0.54 ± 0.01 and SCP ranging from 300 to 680 W/kg. The specific cooling power depends strongly on the driving temperature difference and the cycle duration.

Research on ground-coupled heat exchangers

Ground source heat pump (GSHP) has been considered as one of the most promising low-carbon technologies for building heating, ventilation and air conditioning (HVAC) applications at present. Since a GSHP relies heavily on the performance of ground-coupled heat exchangers (GCHEs), this paper was focused on GCHEs key technical issues and presented results of experimental investigation and computer simulation. A test rig was built to carry out the thermal response test, and test results for a double-U tube GCHE were analyzed. Software Fluent was used to simulate the GCHEs and simulation models were created for single-U-type and double-U-type GCHEs for the depths of 50, 60 and 70 m. Based on dissipation simulation it was found that using a double-U-type GCHE to replace a single-U-type GCHE can gain an increase in the total heat dissipation capacity by over 50%, with a drawback of 20% reduction of circulating water temperature difference. The borehole depth of a GCHE can be increased to meet the requirement of a larger heat dissipation capacity. The specific heat dissipation rate will drop about 6% for every 10 m increase in borehole depth. This study is useful for design GCHEs and the ground-coupled heat pump technology. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

Heating, Ventilating and Air Conditioning Systems Control Based in the Predicted Mean Vote Index

Abstract In this work a numerical model, which simulates the buildings thermal response and evaluates the indoor environment comfort, in transient conditions, is used in the application of Heating, Ventilating and Air Conditioning (HVAC) systems control, based in the Predicted Mean Vote (PMV) index, in the energy and thermal comfort performance in a kindergarten school building, in the South of Portugal, in Winter conditions. In the control the PMV index, based in the mean air temperature, the mean air velocity, the mean air relative humidity, the mean radiant temperature, the clothing level and the activity level, are used. In the numerical simulation of the kindergarten, the 25 compartments, the 498 building main bodies and the 42 windows glasses, as well as two schools and three residential surrounding main buildings, are considered.

Application of energy and exergy analyses for efficient energy utilisation in the Nigerian residential sector

This paper presents energy and exergy analyses as a useful concept in analysing true efficient energy utilisation of the Nigerian residential sector by considering energy and exergy flows in this sector for a period of 15 years from 1991 to 2005. The energy and exergy flows considered include the commercial and the 'non-commercial' energy sources. The most efficiently utilised energy source appears to be the Liquefied Petroleum Gas and the least efficient, kerosene. Electricity utilisation exergy efficiency has been adversely affected by the vapour-compression air-conditioning application apart from low potential thermal energy applications. The overall utilisation energy and exergy efficiencies have been found to be 19.89% and 4.38%, respectively.

FEASIBILITY OF A BRAYTON CYCLE AUTOMOTIVE AIR CONDITIONING SYSTEM

The goal of this work is to develop a preliminary analysis on the feasibility of using an alternative automotive air conditioning system based on the Brayton cycle, to be assembled using a turbocompression-intercooling system configuration available in the market. The first step of the analysis was a thermodynamic study to define the system capacity and parameters for selecting the system components. The next step was to select from turbocompressor maps a suitable model for the application, and to determine pressures/temperatures throughout the system in order to evaluate intercooler capacity and select a suitable model available in the market. The impact of the turbocompression system was also analyzed in engine performance. The proposed turbocompression system requires 1,7 kW from the engine, which is very similar to a conventional air conditioning system requirement. In terms of weight, this preliminary analysis indicated that the proposed system is about 1,0 kg heavier than the conventional system. The analysis indicated that the alternative system is about 56% more expensive than the conventional one, but on the other hand presents a 24% lower maintenance cost . Considering the results of the preliminary analysis, the proposed system is technically feasible for application in automotive air conditioning, but requires a design optimization process in order to reduce its weight and initial costs, which might allow lower maintenance costs to payback the alternative system.

Energy conservative building air conditioning system controlled and optimized using fuzzy-genetic algorithm

In this work, the combined effect of the energy conservative variable refrigerant volume (VRV) system and the variable air volume (VAV) system was experimentally investigated using genetic fuzzy optimization method that yielded better thermal comfort, indoor air quality (IAQ) requirements without compromising on the energy savings potential. The proposed system was tested using the demand controlled ventilation (DCV) combined with the economizer cycle ventilation (ECV) techniques and examined for a year-round building air conditioning (A/C) application. The supply air temperature (SAT) set points were varied under three distinct strategies and the optimal solutions obtained for the fuzzy systems designed resulted in an enhanced energy conservative potential. The test results of the proposed system were compared with the conventional fan coil A/C system. Based on the three strategies of the supply air temperature, the proposed system yielded an improved per day energy savings potential of 54% in summer and 61% in winter design conditions. Furthermore, for the strategies considered the proposed system achieved an annual energy conservative potential of 36% and exhibited more possible ways to achieve thermal comfort, IAQ and energy conservation.

An experimental study of a novel dew point evaporative cooling system

A novel dew point evaporative cooling system for sensible cooling of the ventilation air for air conditioning application was constructed and experiments were carried out to investigate the outlet air conditions and the system effectiveness at different inlet air conditions (temperature, humidity and velocity) covering dry, temperate and humid climates. The results showed that wet bulb effectiveness ranged between 92 and 114% and the dew point effectiveness between 58 and 84%. A continuous operation of the system during a typical day of summer season in a hot and humid climate showed that wet bulb and dew point effectiveness were almost constant at about 102 and 76%, respectively. The experiment results were compared with some recent studies in literature.

Energy efficient fuzzy based combined variable refrigerant volume and variable air volume air conditioning system for buildings

Energy conservative building design has triggered greater interests in developing flexible and sophisticated air conditioning systems capable of achieving enhanced energy-savings potential without sacrificing the desired thermal comfort and indoor air quality (IAQ). This research work greatly aimed at achieving enhanced energy conservation, good thermal comfort and better IAQ for space conditioning with the application of combined variable refrigerant volume (VRV) and variable air volume (VAV) air conditioning (A/C) systems. Experimental investigation on the proposed combined air conditioning system with the application of intelligent fuzzy logic controller was performed for summer and winter climatic conditions to substantiate the energy-savings capability. The proposed system experimentally analyzed under fixed ventilation, demand controlled ventilation (DCV) and combined DCV and economizer cycle (EC) ventilation techniques effectively conserved 44% and 63% of per day average energy-savings in summer and winter design conditions respectively, while compared to the conventional constant air volume (CAV) A/C system. The results of the present investigation have proved that the proposed combined air conditioning system operated under the different ventilation strategies and controlled by the intelligent fuzzy logic controller (FLC) can be considered as an efficient technology to achieve good thermal comfort, IAQ and energy conservation in the modern heating, ventilation and air conditioning (HVAC) applications.

Semitheoretical Model of an Evaporator to Reduce Design Cycle Time

Original equipment manufacturers are looking for ways to reduce the product development cycle. A tool to reduce this time in the design of air conditioning systems is introduced in this paper. This is done by using a semitheoretical model of each of the components of a system. The semitheoretical model has the advantage of reducing the number of geometrical inputs that need to be specified when compared with a “theoretical” model. This paper focuses on the most complex of the components—the evaporator. A tube and fin evaporator was successfully modeled and validated. The model was tuned using supplier component data (Luvata, 2005, Heatcraft Evaporator—Version 3.07.05.122 B-DHLEX.EVP) for the evaporator. The tuned accuracy of heat transfer rate and pressure drop, both air- and refrigerant-side, was within 5% over the range of conditions representative of air conditioning applications.

Thermal-economic analysis of a heat pipe heat exchanger for energy recovery in air conditioning applications

The computer simulation and working fluid selection of a heat pipe heat exchanger (HPHE) system appropriate for both heating and cooling modes in air conditioning applications are performed in this article. The studied heat pipes had a screened mesh wick and methanol as the working fluid. Various numbers of heat pipes and different values of return to the total outlet air mass flowrate ratio were considered. The heat transfer rate in HPHE was computed by the ε—NTU method by considering appropriate heat pipe thermal resistance. Because of its higher evaporation enthalpy and appropriate working limits, methanol was selected as the working fluid. Checking the heat transfer limits showed that the minimum heat transfer rate was well above the required heat transfer rate. Furthermore, the economic analysis of the HPHE was performed considering initial (investment) and operational costs as well as annual savings due to energy recovery for different numbers of heat pipes and various values of return air ratio. The results showed that there was a design point at which the savings of energy recovery was the maximum. The characteristics of this point at various values of return air ratio were determined and reported for the most economical HPHE design and for manufacturing purposes.

Study on adsorption of methanol onto carbon based adsorbents

This paper presents the isothermal characteristics of methanol onto two specimens of activated carbons namely Maxsorb III and Tsurumi activated charcoal. Dubinin Raduskevich (D-R) equation is used to correlate the adsorption isotherms and to form the pressure–temperature–concentration diagram for both of the assorted pairs. Experimental results show that the maximum adsorption capacity of Maxsorb III/methanol pair is 1.76 times that of activated charcoal/methanol pair. Employing a time-independent mathematical model, the performance of adsorption cooling cycle using Maxsorb III/methanol and activated charcoal/methanol pairs has been studied and compared with that of three other types of carbon based adsorbent/methanol pairs. Theoretical calculations show the superiority of Maxsorb III/methanol pair for both of air-conditioning and ice-making applications.

Experimental assessment of heat storage properties and heat transfer characteristics of a phase change material slurry for air conditioning applications

A new microencapsulated phase change material slurry based on microencapsulated Rubitherm RT6 at high concentration (45% w/w) was tested. Some heat storage properties and heat transfer characteristics have been experimentally investigated in order to assess its suitability for the integration into a low temperature heat storage system for solar air conditioning applications. DSC tests were conducted to evaluate the cold storage capacity and phase change temperature range. A phase change interval of approximately 3 °C and a hysteresis behaviour of the enthalpy were identified. An experimental set-up was built in order to quantify the natural convection heat transfer occurring from a vertical helically coiled tube immersed in the phase change material slurry. First, tests were carried out using water in order to obtain natural convection heat transfer correlations. Then a comparison was conducted with the results obtained for the phase change material slurry. It was found that the values of the heat transfer coefficient for the phase change material slurry were higher than for water, under identical temperature conditions inside the phase change interval.

Carbon dioxide as a secondary fluid in natural circulation loops

In recent years there is growing interest in the use of carbon dioxide as a secondary fluid in various cooling and heating applications. In the present work a comparative study is made between carbon dioxide and conventional secondary fluids that can be used in natural circulation loops for various refrigeration and air conditioning applications. For the same heat input and total loop length, the results are presented in terms of the ratios of pipe diameter required when a conventional fluid is used to the required pipe diameter with carbon dioxide as the secondary fluid. Results are presented for both laminar and turbulent flow conditions. It is observed that due to its excellent thermo-physical and transport properties and near critical point operation, carbon dioxide gives rise to very compact systems when compared to most of the conventional secondary fluids. The difference in size is much greater for laminar flow conditions compared to turbulent flow conditions. Also, for a given system size, the temperature rise/drop across the heat exchangers is much smaller in case of carbon dioxide in comparison to other fluids.

The Air-Side Thermal-Hydraulic Performance of Flat-Tube Heat Exchangers With Louvered, Wavy, and Plain Fins Under Dry and Wet Conditions

The air-side thermal-hydraulic performance of flat-tube aluminum heat exchangers is studied experimentally for conditions typical to air-conditioning applications, for heat exchangers constructed with serpentine louvered, wavy, and plain fins. Using a closed-loop calorimetric wind tunnel, heat transfer and pressure drop are measured at air face velocities from 0.5 m/s to 2.8 m/s for dry- and wet-surface conditions. Parametric effects related to geometry and operating conditions on heat transfer and friction performance of the heat exchangers are explored. Significant differences in the effect of geometrical parameters are found for dry and wet conditions. For the louver-fin geometry, using a combined database from the present and the previous studies, empirical curve-fits for the Colburn j- and f-factors are developed in terms of a wet-surface multiplier. The wet-surface multiplier correlations fit the present database with rms relative residuals of 21.1% and 24.4% for j and f multipliers, respectively. Alternatively, stand-alone Colburn j and f correlations give rms relative residuals of 22.7% and 29.1%, respectively.

Two-stage heat pump system with vapor-injected scroll compressor using R410A as a refrigerant

Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both flash tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.

Solar-powered cooling systems: Technical and economic analysis on industrial refrigeration and air-conditioning applications

In the last years, the growing demand for air conditioning has caused a significant increase in demand for primary energy resources. Solar-powered cooling is one of the technologies which allows to obtain, by using the renewable solar source, an important energy saving compared to traditional air conditioning plants. The paper describes different technical installations for solar cooling, their way of operation, advantages and limits. The objective of the present study has been to analyze the technical and economic feasibility of solar absorption cooling systems, designed for two different application fields: industrial refrigeration and air conditioning. The possibility to replace or integrate the existing plants is studied, by considering the refrigeration requirements of a company, which works in meat manufacturing, and the heating and cooling demands of a hotel located in a tourist town in Italy. In the first case, the system comprises an absorption chiller coupled to solar flat plate collectors, whereas the second application is about a hybrid trigeneration plant, known as thermo-solar trigeneration; this option allows having greater operational flexibility at sites with demand for energy in the form of heating as well as cooling, for example in a hotel. In this way the authors could compare different results obtained by a technical and economic experimental analysis based on existing users and evaluate the advantages and disadvantages in order to suggest the best solution for the two studied cases.

Effect of Coolant Temperature on the Condensation Heat Transfer in Air-Conditioning and Refrigeration Applications

This article directly investigates the effect of a cooling medium's coolant temperature on the condensation of the refrigerant R-134a. The study presents an experimental investigation into condensation heat transfer, vapor quality, and pressure drop of R-134a flowing through a commercial annular helicoidal pipe under the severe climatic conditions of a Kuwait summer. The quality of the refrigerant is calculated using the temperature and pressure obtained from the experiment. Measurements were performed for refrigerant mass fluxes ranging from 50 to 650 kg/m2s, with a cooling water flow Reynolds number range of 950 to 15,000 at a fixed gas saturation temperature of 42°C and cooling wall temperatures of 5°C, 10°C, and 20°C. The data shows that with an increase of refrigerant mass flux, the overall condensation heat transfer coefficients of R-134a increased, and the pressure drops also increased. However, with the increase of mass flux of cooling water, the refrigerant-side heat transfer coefficients decreased. Using low mass flux in a helicoidal tube improves the heat transfer coefficient. Furthermore, selecting low wall temperature for the cooling medium gives a higher refrigerant-side heat transfer coefficient.

Comparison of adsorption systems using natural gas fired fuel cell as heat source, for residential air conditioning

This article aims to evaluate the performances of an adsorption system driven thanks to the heat rejected by the post-combustion exhaust gases of a reformer/fuel cell system for residential air-conditioning application. Three adsorption pairs were compared: activated carbon/methanol, silica gel/water and zeolite/water. Taking into account both cooling power and sensitivity to performances of the heat rejection and recovery exchangers, it appears that zeolite 13X/water is the adsorption pair giving the best performance for this application. Nevertheless, a more detailed model would be of interest to better quantify the heat transfer impact on performance.

Theoretical study of a novel refrigeration compressor – Part I: Design of the revolving vane (RV) compressor and its frictional losses

This paper presents a new rotary type compressor, named ‘Revolving Vane (RV) compressor’, in which frictional losses are effectively reduced through the radical use of a rotating cylinder. The friction at various contact regions are formulated and analyzed, after which a parametric study is conducted to reveal configurations of the compressor that achieves high mechanical efficiencies. Inadvertently, the rotating cylinder is also found to enhance the smoothness of the compressor's operation by reducing its torque fluctuations. Besides good mechanical performance, the RV compressor is also found to possess a high volumetric efficiency, as shown in Part III of this paper series ( Teh and Ooi, in press). In further consideration of the small number of parts and simple geometries of its components, it is believed that the RV compressor is well suited and can be readily adopted for refrigeration and air-conditioning applications.