Air Conditioning Process Research Articles

00/00504 Optimal control of time-scheduled heating, ventilating and air conditioning processes in buildings

00/00504 Optimal control of time-scheduled heating, ventilating and air conditioning processes in buildings

Optimal control of time-scheduled heating, ventilating and air conditioning processes in buildings

The problem of computing optimal control strategies for time-scheduled operation of heating, ventilating and air conditioning systems is explored. A two-zone variable air volume heating system consisting of a 4 ton heat pump, a storage tank, water and air flow networks and two environmental zones is considered. The optimization problem that takes into consideration the building operation schedules consisting of night-setback, start-up, occupied modes and energy price discounts is formulated and solved for a given predicted weather profile. Results showing the optimal mass flow rates to the zones, air and water supply temperatures, energy input to the heat pump and the resulting zone temperatures are given.

Physical properties and thermorheological behaviour of a dispersion having cold latent heat-storage material

A dispersion of n-alkanes in water has been elaborated for thermal energy storage and transport. Quantitative results regarding the thermophysical properties of the material are presented and compared with results obtained from correlations based on combination of the properties of the suspending phase and the dispersed phase. Thermorheological investigations of the material at various temperatures have shown a shear-thinning behaviour. The temperature dependence of the viscosity exhibits a slight jump near 9.5°C, corresponding to the phase change temperature. This deviation is interpreted in terms of a change in the particle state near the phase change temperature. This thermorheological behaviour obeys a power law model in which the parameters are temperature dependent. Its range of viscosity and its high heat capacity render the material particularly attractive in cooling and air conditioning processes.

96/06499 Energy saving through central air conditioning equipment with bypasses

A study was carried out to investigate the effect of heat-pipe air-handling coil on energy consumption in a central air-conditioning system with return air. Taking an office building as an example, the study shows that compared with conventional central air-conditioning system with return air, the heat-pipe air-conditioning system can save cooling and reheating energy. In the usual range of 22–26 °C indoor design temperature and 50% relative humidity, the RES (rate of energy saving) in this office building investigated is 23.5–25.7% for cooling load and 38.1–40.9% for total energy consumption. The RES of the heat-pipe air-conditioning system increases with the increase of indoor design temperature and the decrease of indoor relative humidity. The influence of indoor relative humidity on RES is much greater than the influence of the indoor design temperature. The study indicates that a central air-conditioning system can significantly reduce its energy consumption and improve both the indoor thermal comfort and air quality when a heat-pipe air-handling coil is employed in the air-conditioning process.

NHR-200 nuclear energy system and its possible applications

The 200MWt Nuclear Heating Reactor (NHR-200) is designed with a number of advanced and innovative features to achieve its economic viability and safety goal, including integrated arrangement, natural circulation, self-pressurized performance, hydraulic control rod drives and passive safety systems. As a new promising energy system for resolving the energy supply and environmental problems caused by massive coal burning in China, the NHR-200 can serve for district heating, air conditioning, sea-water desalination and other industrial processes. The paper describes the significance of nuclear heat application in China as well as the development status, main design features, safety concepts and possible applications of the NHR-200.

Desiccant solar air conditioning in tropical climates: I—Dynamic experimental and numerical studies of silicagel and activated alumina

This paper presents a dynamic study of moist air dehumidification in view of its use in an air conditioning process by evaporative cooling in tropical climates. A special device has been built to study dehumidification of tropical-like inlet air, through a fixed compact bed of silicagel and activated alumina. The compact desiccant storage is composed of two parallel beds to reduce the pressure drop. A good agreement is obtained for our experiment, and the computed amount of cycled water from the numerical model in the adiabatic process. This analytical model is used to simulate a complete air conditioning open cycle operating with hot and humid air.

Integrated operation planning: Intelligent system approach for HVAC processes

This paper describes the construction of an Intelligent System for Operation Planning (ISOP) in heating, ventilating, and air conditioning (HVAC) processes. The system contains important expertise, qualitative reasoning, and quantitative computation. It is used to assist or train operators to achieve better operation in HVAC systems. Expertise about operation planning is expressed as air enthalpy, and moisture conditions and air supply are considered as dynamic parameters. Therefore, it provides a real-time integrated operation planning method in HVAC processes. It offers better energy conservation, comfort and indoor air quality than other methods being currently used. ISOP consists of two levels of frames. The first level classifies HVAC systems by qualitatively reasoning the system structure information, and activates the subframe. In the second level, 16 frames that correspond to the HVAC system structure, accomplish indoor comfort setting, supply air parameter estimations, air enthalpy, and misture evaluation, and then recommend optimal operation conditions. An integrated distributed intelligent system framework is introduced to integrate qualitative reasoning and quantitative computation.

Intelligent control strategies for HVAC processes in buildings

Intelligent control strategies for heating, ventilating and air conditioning (HVAC) processes are studied by considering a single-zone air-handling unit (AHU) and a two-zone space-heating system (TZSHS). Temperature responses of the AHU with single and multiple input controls are given. Application of decentralized control to the TZSHS, with and without preview action, is described. The implementation of intelligent strategies such as variable cold-deck temperature and night setback are illustrated with examples.

Knowledge-based automation for energy conservation and indoor air quality control in HVAC processes

Heating, ventilating, and air conditioning (HVAC) processes provide a comfortable environment, but consume a great deal of energy. Many efforts have been put into building energy conservation since the energy crisis of 1973. On the other hand, the energy conservation efforts have led to tight building envelopes and low ventilation rates, which cause poor indoor air quality (IAQ), the so called “Sick Building Syndrome”. A conflict exists between energy saving and indoor air quality improvement. In this paper, a knowledge-based automation approach is proposed to support HVAC operations, aimed at improving energy conservation and IAQ control. The construction of an Intelligent Operation Support System (IOSS) for HVAC processes is described. It consists of expert systems for operation planning, comfort setting, conflict reasoning and some other functions. The expert system for operation planning provides recommendations of energy saving operation modes for HVAC processes. The comfort indoor setting system sets indoor temperature by a comfort strategy with the advantages of energy saving, thermal comfort and better indoor air quality, instead of thermostats. The conflict reasoning system obtains a conflict resolution for energy saving and IAQ control. An integrated distributed intelligent system framework is introduced to integrate these systems. IOSS provides a real-time integrated operation planning method and can be used to assist or train operators to achieve better operation in HVAC systems.

Automatic Control Systems of Marine Conditioners and Refrigerating Plants

During navigation the heat-and-moisture conditions of the environment are changing. The parameters modification of external air causes heat and mass transfer processes in ship’s space. A ship conditioner has to provide air feed of predetermined parameters at minimum necessary power expenditure to ship’s space. However, traditionally, the composition and capacity of a ship conditioner is determined by means of heat and cold plant capacity necessary for supporting predetermined air parameters in space at the extreme heat-and-moisture duty. Consequently, automatic control systems realized on the base of standard regulators are used for conditioner equipment. Real operation conditions of the ship air conditioning devices are characterized by instability with respect to external meteorological factors. As a result, air conditioning is carried out in conditions differing from designed ones, under high power expenditure. The objective of the investigations consists of the definition and development of methods for maintenance of required air parameters for conditioning under low power expenditure. The analysis of stationary operation regimes has determined seven "winter" and "two" summer operation regimes of conditioner which depend upon the state of external air parameters. By using theoretical considerations of the methods based on the process analysis in I-d diagram, the optimal process organization methods of heat-and-moisture air treatment in conditioner have been determined. For the present conditions of external air the optimum method of air conditioning process organization is the method under which power expenditure is minimum and the realization of which requires the least number of conditioning technologic equipment taking part in collaboration. Problem solving of optimum methods realization of process organization of conditioner technologic equipment required to rise the automation level is considered. Analysis of the conditioner as an automatic control object has been carried out and its mathematical model describing static and dynamic properties as well as disturbing effects has been developed. According to investigations, a two-level automatic control system is proposed, which is designed in order to obtain efficiency rise of ship conditioner in different interval regimes.

Air-conditioning processes

Air conditioning is one of the essential techniques employed to provide human comfort, as well as to generate favourable conditions for industrial, agricultural and biological processes. In this paper, the means for simulating the principal air-conditioning processes are discussed. Interactive computer routines (in Basic language) have been composed for (i) estimating the relevant properties of atmospheric air (i.e. the psychrometric properties), and (ii) predicting the behaviour of air when undergoing constant-pressure mixing, heating, cooling, humidification and dehumidification processes. The developed programs are listed. Samples of the predictions are also presented. The computer programs should help in obtaining the necessary data when designing the hardware, and selecting the appropriate control equipment, for an air-conditioning system in an envisaged application.

Exercise-induced asthma: a difference in opinion regarding the stimulus.

There has been some controversy regarding the mechanism whereby exercise can provoke an attack of asthma. It is generally agreed that heat and water are lost from the respiratory tract in bringing the air inspired to body conditions. During strenuous exercise, there is a marked increase in ventilation rate and some of the burden to heat and humidify the inspired air is transferred to the intrathoracic airways. The net effect of the air conditioning process is to cool and dehydrate these airways. There have been two hypotheses put forward to account for the mechanism whereby these events lead to exercise-induced asthma (EIA). One hypothesis proposes that cooling of the airways followed by rapid rewarming, at the end of exercise, leads to a reactive hyperemia and edema of the bronchial vascular bed "which if sufficiently severe results in the airway obstruction of EIA." The other hypothesis proposes that the rate of loss of water from the periciliary fluid during exercise exceeds the rate of return and, as a result, there is an increase in ion concentration and subsequent hyperosmolarity of the periciliary fluid. Thus the events related to drying rather than cooling are the stimulus to EIA. This paper presents the case against rapid rewarming of the bronchial vasculature as the stimulus to EIA and puts forward an argument and data in support of the case for airway drying and an increase in osmolarity being the critical event which determines the presence and severity of EIA.

The influence of climatic conditions on the reliability of electronic components in telephone exchanges

AbstractThis paper shows the significant influence of climatic conditions on the reliability of components in telephone exchanges. The great number of observations made enabled numerous data to be collected. Sophisticated data processing was used using data analysis methods, in particular factor analysis. Prominence was thus given to the various parameters affecting the reliability of components (temperature, hygrometry, location of the board, air conditioning process…). A physical analysis of the failure of components complemented the statistical study. It resulted in taking practical measures to improve the field reliability of French telecommunication equipment.

Adaptive control of thermal processes in buildings

Application of a self-tuning controller to heating, ventilating, and air-conditioning (HVAC) processes is reported. Adaptive control techniques are attractive in HVAC applications because process characteristics change widely due to variations in weather and building occupancy. Successful implementation of adaptive control techniques is limited by current practices in building instrumentation. Control actuators exhibit significant nonlinearities, while sensing is inadequate to compensate for load disturbances. A self-tuning control system consisting of an autotuner, recursive least-squares estimator, and a performance monitor is flexible and easily configured.

A theoretical model of localized heat and water vapor transport in the human respiratory tract.

A steady-state, one-dimensional theoretical model of human respiratory heat and water vapor transport is developed. Local mass transfer coefficients measured in a cast replica of the upper respiratory tract are incorporated into the model along with heat transfer coefficients determined from the Chilton-Colburn analogy and from data in the literature. The model agrees well with reported experimental measurements and predicts that the two most important parameters of the human air-conditioning process are: the blood temperature distribution along the airway walls, and the total cross-sectional area and perimeter of the nasal cavity. The model also shows that the larynx and pharynx can actually gain water over a respiratory cycle and are the regions of the respiratory tract most subject to drying. With slight modification, the model can be used to investigate respiratory heat and water vapor transport in high stress environments, pollutant gas uptake in the respiratory tract, and the connection between respiratory air-conditioning and the function of the mucociliary escalator.

A stationary evacuated collector with integrated concentrator

A comprehensive set of experimental tests and detailed optical and thermal models are presented for a newly developed solar thermal collector. The new collector has an optical efficiency of 65 per cent and achieves thermal efficiencies of better than 50 per cent at fluid temperatures of 200°C without tracking the sun. The simultaneous features of high temperature operation and a fully stationary mount are made possible by combining vacuum insulation, spectrally selective coatings, and nonimaging concentration in a novel way. These 3 design elements are “integrated” together in a self contained unit by shaping the outer glass envelope of a conventional evacuated tube into the profile of a nonimaging CRC-type concentrator. This permits the use of a first surface mirror and eliminates the need for a second cover glazing. The new collector has been given the name “Integrated Stationary Evacuated Concentrator”, or ISEC collector. Not only is the peak thermal efficiency of the ISEC comparable to that of commercial tracking parabolic troughs, but projections of the average yearly energy delivery also show competitive performance with a net gain for temperatures below 200°C. In addition, the ISEC is less subject to exposure induced degradation and could be mass produced with assembly methods similar to those used with fluorescent lamps. Since no tracking or tilt adjustments are ever required and because its sensitive optical surfaces are protected from the environment, the ISEC collector provides a simple, easily maintained solar thermal collector for the range 100–300°C which is suitable for most climates and atmospheric conditions. Potential applications include space heating, air conditioning, and industrial process heat.