Air Conditioning Plant Research Articles

An ice thermal storage computer model

In hot humid countries such as Thailand, air conditioning plant is installed in most commercial and industrial buildings. A conventional air conditioning system, which is normally operated when cooling is required, is the most favored option. Ice thermal storage on a large scale, used to provide a cool reservoir for use in peak periods, is however an attractive financial option for large buildings to supply coolness. There are two means of operating ice thermal storage systems, namely full storage and partial storage. In this paper, a computer model has been developed in order to compare energy use in conventional air cooling systems and ice thermal storage systems. Under Thailand electricity tariff rates, the results from the simulations show that the full ice thermal storage can save up to 55% of the electricity cost required for cooling per month when compared with the conventional system. It is also found that using full storage option can reduce the total energy consumption by 5% for the selected building.

Windows for buildings in hot arid countries

Too often, in the last 50 years, the energy-thrift lessons of vernacular architecture have been forgotten or ignored. In the Middle East, many recently-designed commercial buildings, with large areas of glazing, incur excessively high electricity-demands to provide energy for the required air-conditioning plant. One way of reducing the magnitude of this demand is through better window design. For this purpose, a new form of triple-glazed window is proposed to facilitate achieving improved thermal comfort within buildings, while simultaneously reducing the expenditures on purchased energy.

Impact of energy-conservation measures on cooling load and air-conditioning plant capacity

Energy conservation measures have been in practice in Kuwait since 1983, through a well defined code of practice enforced by the Ministry of Electricity and Water (MEW). Additional energy-efficient products and techniques developed thereafter, however, have not been introduced as the electricity is highly subsidized and the code has not been modified. Application of some of the cost-effective energy-conservation measures and use of cool storage for peak-power shaving have been carried out as a demonstration project in a two-storeyed building housing the Center for Speech and Audio Therapy (CSAT). As a first step, the cooling load of the building was reestimated using an energy simulation computer program and proper design specifications. It was found to be 31.4% lower than the original estimated load of 161.3 tons of refrigeration (RT, 1 RT=3.517 kW of heat absorption), which is equal to 567.3 kW. Use of energy-efficient windows and cooling recovery units were found to be cost-effective and resulted in a final building load of 64.5 RT. Finally, ice storage was incorporated to meet 50% of the peak cooling-load.

Development of solar heat gain factors database using meteorological data

In tropical and subtropical regions, solar heat gain via fenestration, particularly on vertical surfaces, plays an important role in determining the thermal performance of a building. For sizing air-conditioning equipment, maximum solar heat gain factors (SHGFs) are used for estimating the design peak load. Recently, the SHGF data representing the prevailing weather conditions have become essential and more practical for part load performance designs and daylighting schemes evaluation. In the absence of measured solar radiation data for the determination of SHGFs, meteorological radiation models may be used. This paper presents the validation of SHGFs prediction models based on sunshine hours and horizontal solar data. Statistical assessments for the models have shown that using sunshine hours to predict the hourly SHGFs may not be appropriate for dynamic building simulation studies. For the average SHGFs computation, all models present acceptable results. In determining the SHGFs for horizontal and vertical surfaces at the peak and other significant levels, all prediction models perform better than the ASHRAE clear sky approach, particularly at high significant levels. This finding also provides information for the estimation of total air-conditioning plant capacity at both the peak load operation and the multiple equipment sizing under part load condition.

00/02919 Sizing of air-conditioning plant for commercial buildings in Hong Kong

00/02919 Sizing of air-conditioning plant for commercial buildings in Hong Kong

A dynamic mathematical model of a direct expansion (DX) water-cooled air-conditioning plant

A dynamic mathematical model for a direct expansion water-cooled air-conditioning plant typical to many actual installations in buildings has been developed. The system components modelled are a compressor, a thermostatic expansion valve, a water cooled condenser and a direct expansion evaporator which is also the cooling and dehumidifying coil in the air side. The evaporator (cooling coil) model consists of a novel set of equations which can distinguish between two-phase superheated and refrigerant region in the refrigerant side, and between dry and wet cooling of an air handling process in the air side. The model has been validated using the experimental data collected from the plant, and was separately reported.

Solar heat gain factors and the implications to building designs in subtropical regions

In subtropical Hong Kong, solar heat through fenestration, particularly on vertical surfaces, plays a major role in determining the thermal performance of a building. For sizing air-conditioning equipment, maximum solar heat gain factors (SHGFs) are used for estimating the design peak load. Recently, the SHGF data representing the prevailing weather conditions have become important and more practical for evaluating daylighting designs and the determination overall thermal transfer value (OTTV). This paper describes a procedure for calculating hourly SHGFs for horizontal and vertical surfaces based on the 8-year (1991 to 1998) horizontal global and diffuse radiation and the 3-year (1996 to 1998) vertical global solar radiation data measured at the City University of Hong Kong. A simple approach for estimation of solar heat gain is developed. Average and peak SHGFs and sky factors for OTTV are computed and compared. An analysis of the SHGF data has shown that except for the north-facing surface, the ASHRAE clear sky approach tends to overestimate the solar heat gains, particularly at large significant levels. The findings provide information for the determination of the total air-conditioning plant capacity at peak load operation and multiple equipment sizing under part load condition.

Sizing of air-conditioning plant for commercial buildings in Hong Kong

Results of a survey indicate that 89% of the respondents use PC-based software packages to size their air-conditioning plant; 67% of them care about the building energy use; 83% adopt either ASHRAE standards or CIBSE guides in their design work; 67% intentionally oversize; and 87% use central air-conditioning plant with primary air fan-coil (PAF) systems in their recently completed commercial building projects.

Shading effects due to nearby buildings and energy implications

This paper investigates the shading effects due to neighbouring buildings in seven main business districts in Hong Kong. A total of 120 commercial buildings have been selected in the survey. It has been found that the degree of shading at the local peak design condition (i.e. 15:00 July) ranges from 25 to 31%. The older and more established districts tend to have slightly higher degrees of shading. Computer simulation techniques using the DOE-2.1E building energy program and a generic office building have been employed to analyse the amounts of heating, ventilation and air conditioning (HVAC) plant oversizing (as a result of solar heat overestimation) and to assess the likely energy penalty. It has been found that the total building cooling load is overestimated by about 2%. The corresponding plant oversizing seems to be marginal, and the impacts on the total building energy budget are not significant. Implications for energy efficiency in the design of commercial buildings are discussed and further research and development work is suggested.

99/03942 Experimental analysis of a condenser heat recovery in an air conditioning plant: Schibuola, L. Energy 1999, 24, (4), 273–283

99/03942 Experimental analysis of a condenser heat recovery in an air conditioning plant: Schibuola, L. Energy 1999, 24, (4), 273–283

Energy audit case studies II—air conditioning (cooling) systems

This paper discusses a novel methodology for determination of the efficiencies of each segment in a centralized air conditioning (A/C) plant. The methodology is useful analytical tool in energy audit where it can be used for decision support for evolution of energy conservation measures and techno-economic evaluation of the various options. The procedure is applied to three A/C plants of capacity range from 50 to 500 TR. Losses in chilled air ducts and cycling losses in the refrigerant circuit are identified to be the major causes for decrease in the efficiency and capacity under rating of the systems. Effective controls and insulation of air ducts: have been shown to be the most cost effective solutions to improve the energy efficiency of the A/C plants. The generalized experimental data on overall performance of sixteen A/C plants is also provided.

New transfer function coefficients to calculate building load

In the actual phase of extension of the European Standard concerning energy saving in buildings to air conditioning plants, a simplified procedure based on empirical correlations has been proposed for the calculation of transfer function coefficients to evaluate room thermal load in the dynamic state. The possibilities and limits of this technique are discussed here and verified by comparison with comprehensive computer programs such as DOE and BLAST.

Experimental analysis of a condenser heat recovery in an air conditioning plant

A total heat recovery system performances are analysed by monitoring building–plant system long term behaviour. Some of the installed chillers offer in fact the possibility of a total recovery of the heat rejected by condenser. The results are very satisfactory both in energy and economic–financial terms. The experimental test takes advantage of the supervisor just existing in the building. Therefore it is an example of how these control systems can be used not only for safety and management needs, but also for a detailed performance analysis able to permit an easy simulation of the effects of different design and control options.

Evaluation of Swirl-Flo™ Clarifier and UV/H2O2 Process for Domestic Wastewater Treatment

Pilot scale investigations were conducted to evaluate the efficacy of a novel process comprising of Swirl-Flo™ Clarifier (SFC) and Ultraviolet light/Hydrogen Peroxide (UV/H2O2) reactor for treatment of domestic wastewater. Overall Total Suspended Solids (TSS) and Chemical Oxygen Demand (COD) removal of over 82 % and 90 %, respectively was achieved in the plant. TSS removal in SFC was influenced by feed flow rate. TSS removal efficiency of about 45–50 % was achieved in SFC at flow rate of about 5.5–6.0 m3 hr−1 equivalent to overflow rate of 3.1–3.4 m3 m−2 hr−1. This compared favorably against an overflow rate of up to 1.0 m3 m−2 hr−1 obtainable in gravity settling units. COD removal in SFC was about 37–42 %, while that in UV Reactor was 18–23 % at H2O2 dosing of 800–900 ppm. Further polishing of the treated effluent by sand filter and activated carbon adsorption column yielded the effluent quality satisfactory for use as make up water in cooling towers for central air-conditioning plants. The treated effluent quality was consistent and showed little variation compared to the variation in influent wastewater characteristics.

Evaluation of Swirl-Flo™ Clarifier and UV/H2O2 Process for Domestic Wastewater Treatment

Pilot scale investigations were conducted to evaluate the efficacy of a novel process comprising of Swirl-Flo™ Clarifier (SFC) and Ultraviolet light/Hydrogen Peroxide (UV/H2O2) reactor for treatment of domestic wastewater. Overall Total Suspended Solids (TSS) and Chemical Oxygen Demand (COD) removal of over 82 % and 90 %, respectively was achieved in the plant. TSS removal in SFC was influenced by feed flow rate. TSS removal efficiency of about 45–50 % was achieved in SFC at flow rate of about 5.5–6.0 m3 hr−1 equivalent to overflow rate of 3.1–3.4 m3 m−2 hr−1. This compared favorably against an overflow rate of up to 1.0 m3 m−2 hr−1 obtainable in gravity settling units. COD removal in SFC was about 37–42 %, while that in UV Reactor was 18–23 % at H2O2 dosing of 800–900 ppm. Further polishing of the treated effluent by sand filter and activated carbon adsorption column yielded the effluent quality satisfactory for use as make up water in cooling towers for central air-conditioning plants. The treated effluent quality was consistent and showed little variation compared to the variation in influent wastewater characteristics.

A design day for building load and energy estimation

We describe how a design day for building energy performance simulation can be selected from a typical meteorological year of a location. The advantages of the design day weather file are its simplicity and flexibility in use with simulation programs. The design day is selected using a weather parameter comprising the daily average dry bulb temperature and total solar insolation. The selection criterion addresses the balance between the need to minimise the part-load performance of the air-conditioning systems and plants and the number of hours of load not met. To validate the versatility of the design day weather file, we compare simulation results of the peak load and load profile of a building obtained from the DOE-2.1E code and a specially developed load estimation program, PEAKLOAD. PEAKLOAD is developed using the transfer function method and ASHRAE databases. Comparative results are in good agreement, indicating that a design day thus selected can be used when quick answers are required and simulations using a TMY file cannot be easily done or justified.

An improved fuzzy logic controller using genetic algorithmic techniques for building management systems

Abstract This paper presents the design and control performance of a fuzzy logic controller (FLC) based on the system’s output errors for a building management system (BMS). The system comprises a heating, ventilating and air conditioning (HVAC) plant which regulates the air temperature and relative humidity in a full-scale office room. The plant has 3 control inputs, namely the heater, cooler and humidifier. It has been shown that good set point regulation can be achieved by employing 5 fuzzy input set membership functions for each output error and 3 fuzzy output set membership functions for each incremental control input as well as having good relational rules to determine the control strategy. It is also shown that the performance can be further improved by employing genetic algorithms to search for the 9 optimal fuzzy set output membership functions while maintaining the 10 fuzzy input sets constant.

Intelligence in buildings: the potential of advanced modelling

“Intelligence” in buildings usually implies facilities management via building automation systems (BAS). However, present-day commercial BAS adopt a rudimentary approach to data handling, control and fault detection, and there is much scope for improvement. This paper describes a model-based technique for raising the level of sophistication at which BAS currently operate. Using stochastic multivariable identification, models are derived which describe the behaviour of air temperature and relative humidity in a full-scale office zone equipped with a dedicated heating, ventilating and air-conditioning (HVAC) plant. The models are of good quality, giving prediction accuracies of ±0.25 °C in 19.2 °C and of ±0.6% rh in 53% rh when forecasting up to 15 minutes ahead. For forecasts up to 3 days ahead, accuracies are ±0.65 °C and ±1.25% rh, respectively. The utility of the models for facilities management is investigated. The “temperature model” was employed within a predictive on/off control strategy for the office zone, and was shown to substantially improve temperature regulation and to reduce energy consumption in comparison with conventional on/off control. Comparison of prediction accuracies for two different situations, that is, the office with and without furniture plus carpet, showed that some level of furnishing is essential during the commissioning phase if model-based control of relative humidity is contemplated. The prospects are assessed for wide-scale replication of the model-based technique, and it is shown that deterministic simulation has potential to be used as a means of initialising a model structure and hence of selecting the sensors for a BAS for any building at the design stage. It is concluded that advanced model-based methods offer significant promise for improving BAS performance, and that proving trials in full-scale everyday situations are now needed prior to commercial development and installation.

Model-based fault diagnosis using fuzzy matching

A new fuzzy-model-based approach to fault detection and diagnosis is proposed. The scheme uses a set of fuzzy reference models which describe faulty and fault-free operation, and a classifier based on fuzzy matching for fault diagnosis. The reference models are obtained off-line from simulation data. A fuzzy model which describes the actual behavior of the plant is identified online from normal operating data and compared to each of the reference models. A degree of similarity is evaluated every time the online fuzzy model is identified. Dempster's rule of combination is used to combine new evidence with that already collected. The method of diagnosis accounts for any ambiguity (which may result from fault-free and faulty operation, or different faults, having similar symptoms at a given operating point) by comparing the fuzzy reference models with each other. Results are presented which demonstrate the effectiveness of the scheme when it is used to detect and identify faults in the cooling coil subsystem of the air-handling unit of both simulated and experimental air-conditioning plant.

A generalized methodology for determining the total heat gain through building envelopes

We present a generalized methodology for determining the annual total heat gain through external walls and proofs of large air-conditioned buildings. The methodology is based on the concept of the overall thermal transfer value (OTTV). Respective OTTV equations for building envelopes and roofs are developed through parametric simulations using the DOE-2 computer code. The equations are valid for buildings having different aspect ratios and wall masses. Appropriate coefficients for heat conduction through fenestrations and opaque walls and solar correction factors for wall facades of different orientations are computed from local weather data. The equations allow building designers to make accurate estimates of the total heat gain for the purpose of evaluating energy-efficient building envelope components and air-conditioning systems and plant options. The methodology is validated using DOE-2 computed heat gain results and can be applied to different classes of buildings, construction types and locations.