Air-cooled Air-conditioning Systems Research Articles

First of its kind in Hong Kong - innovative reuse of treated effluent and enhanced energy efficiency for air-conditioning systems

In Hong Kong, air-conditioning (A/C) systems are major consumers of electricity. Although water-cooled air-conditioning systems (WACSs) are more energy efficient, the need for water towers, water treatment and other operation and maintenance (O&M) demands restrain their application in most buildings. This paper reviews a pilot application of treated effluent from sewage treatment works as a cooling medium for the Direct Expansion type of A/C system within the treatment Plant. The Drainage Services Department (DSD) installed a WACS with a self-assembled effluent-cooled condenser to study the energy efficiency, cooling performance and actual O&M requirements of the new system over a one-year pilot. It revealed that an energy saving of up to 27.6% per year could be achieved when compared with a conventional air-cooled air-conditioning system (AACS). This innovative effluent cooling A/C system achieves innovative reuse of treated effluent as well as reduction in carbon footprint as a result of higher energy efficiency for sustainable development.

Selection of HVAC technology for buildings in the tropical climate case study

In this paper, the integral performance indicator for selecting HVAC systems (ACPI) is applied to select the Air Conditioning (AC) system with better results in their life cycle for a typical building in Barranquilla, Colombia. The AC systems under study were: direct expansion system (Split and VRF), air-cooled system (VAC and VAV), and water-cooled system (Chiller). Of the six selection criteria of ACPI, the energy consumption index (EC) and thermal comfort (TC) were calculated through energy simulation of buildings, the regulations were used for IAQ and carbon emissions (CE), and were estimated the investment costs (IC) and operating and maintenance costs (OMC). The best-performance AC system for the building was the air-cooled AC system got the best ACPI values between 25 % and 22.4 %, followed by the water-cooled system with 22.3 %, and finally the direct expansion systems between 16.8 % and 13.5 %, influencing in this level of priority the IAQ and IC criteria. This study contributes to introducing in Colombia a multifactorial analysis to select the more proper AC system technology according to the building and location conditions.

Performance maps for an air-cooled air conditioning system as a preliminary instrument for the diagnosis of evaporator fouling

During the past few decades, there has been increased interest in the development of automated approaches for detecting and diagnosing faults in air conditioning systems. Among them, thermoeconomic diagnosis is a technique which involves the use of exergy analysis. As a first step towards improving its performance, this work is focused on the thermodynamic and exergy analysis of a direct expansion air conditioning system used in small commercial building applications. The analysis was carried out by means of experimental activities on a 17.5 kW rooftop unit installed at the Herrick Laboratories, Purdue University, Indiana (USA). The system under investigation was equipped with a variable-speed compressor and variable-speed fans, thus allowing the unit to meet different loads. A detailed mapping of the performance of this system was carried out by considering the effect of the outdoor temperature and the cooling load. In addition, the effect of evaporator fouling was investigated. Results showed that poor exergy performance were achieved due to the exergy destruction occurring in the evaporator. Also, when testing evaporator fouling, results showed that this fault contributed to increase the consumption of the mechanical exergy of the air, thus allowing for an easy detection of this fault.

Thermoeconomic diagnosis of an air-cooled air conditioning system

Diagnosis of a 120-kW air-cooled air conditioning system under faulty conditions was performed using modified productive structure analysis. Unit cost of cooling capacity for the system and lost cost flow rate for components were calculated based on data obtained by using a simulator for the cases of pre-fixed faulty and normal operating conditions. The relative malfunction (RMF) and the relative difference in the lost cost flow rate between real and normal operations (RDLC) were found to be effective indicators to identify the malfunction components. Results revealed that malfunction due to fouling at the condenser and evaporator, compressor valve leakage, the superheating in the suction line and refrigerant undercharge, whose fault levels by the percent degradation induced in the cooling capacity are 3.4%, 10.5%, 15.1%, 3.5% and 4.1%, respectively, can be identified. Unit cost of the cooling capacity of the system increases when malfunction occurs at any component in the air conditioning system.

Thermoeconomic diagnosis of an air-cooled air conditioning system

Thermoeconomic diagnosis of an air-cooled air conditioning system

Investigation of energy-efficient strategy for direct expansion air-cooled air conditioning systems

This paper addresses the energy saving significance of air-cooled direct expansion (DX) air conditioning systems using liquid pressure amplification (LPA) technology along with proposed theoretical–empirical models for the system components. This method utilizes a refrigerant pump in the liquid line to allow the system operation at lower condensing pressure. An actual DX rooftop package is used for data collection. The performance of the proposed method is simulated using transient simulation software. Simulation tool was validated by comparing predicted and measured power consumption of the rooftop package. Results show that up to 42% power savings can be obtained using this approach.

Innovative thermoeconomic diagnosis of multiple faults in air conditioning units: Methodological improvements and increased reliability of results

Thermoeconomic faults diagnosis of air conditioning units is a pioneeristic approach to detect single or multiple faults and quantify their impact in terms of additional energy consumption. The poor reliability of conventional thermoeconomic approaches has been limiting the interest for practical applications of this technique. In this paper an improved thermoeconomic diagnosis is proposed and applied to a reference 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions. Four faults are individually or simultaneously imposed: fouling at condenser and evaporator, refrigerant undercharge and compressor valve leakage. For setting up the diagnostic tool only a few numerical or experimental tests are required; the results testify the procedure to be sufficiently reliable both when heavy or light faults are considered. Also, the performance of the diagnostic procedure slightly improves when the effects of “system level” faults like refrigerant undercharge are preliminarily filtered.

Study on Energy Materials with the Impact of Using Chilled Water Storage Systems on the Performance of Air Cooled Chillers

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. It is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Proposal of an eco-friendly high-performance air-conditioning system. Part 1. Possibility of improving existing air-conditioning system by an evapo-transpiration condenser

Air-conditioning (AC) system consumes high energy and releases waste-heat. In the present study, we propose a method to improve its performance and minimize waste-heat by replacing existing air-cooled condenser by an evaporation and transpiration, evapo-transpiration, condenser. The improvement is confirmed by performing experiment for a conventional air-cooled AC system and a water-cooled AC system. Condenser temperature in the air-cooled system is higher than outdoor-temperature by 5–10 °C, while it is −5 to 5 °C in case of the testing system. From simulation results, saving energy consumption is expected to reach up to 30% in summer with the testing system. Based on these results, an evapo-transpiration heat-exchanger was developed as a new condenser. Heat-transfer coefficient of the testing heat-exchanger is at least 4 times higher than that of air-cooled condenser. Even hot fluid is used inside copper-tubing, its outlet-air temperature is as nearly as outdoor temperature.

Critical analysis of conventional thermoeconomic approaches to the diagnosis of multiple faults in air conditioning units: Capabilities, drawbacks and improvement directions. A case study for an air-cooled system with 120 kW capacity

Faults diagnosis in air conditioning systems is a crucial activity, since malfunctions may induce heavy degradation of performance. Among the available techniques, thermoeconomic diagnosis has played a marginal role due to the difficulties encountered when applying the methodology to refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis is proposed. The reference plant is a 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions, setting up “virtual experiments” to simulate each fault. Five malfunctions are imposed, either individually or simultaneously: fouling at condenser and evaporator, refrigerant undercharge, compressor valve leakage and extra-superheating along suction line. From a qualitative viewpoint, the examined approach resulted efficient in identifying some faults, although false fault signals eventually emerged. Methodological improvements were suggested, to make thermoeconomic diagnosis capable of quantifying the additional energy consumption provoked by any specific fault.

Overall energy performance of semi-transparent single-glazed photovoltaic (PV) window for a typical office in Hong Kong

Abstract This paper develops an overall methodology for investigating the thermal and power behaviors of semi-transparent single-glazed photovoltaic window for office buildings in Hong Kong. In order to estimate its overall energy performance, this study is conducted in terms of total heat gain, output power and daylight illuminance. Three simulation models are established, including one-dimensional transient heat transfer model, power generation model and indoor daylight illuminance model. A typical office room reference is chosen as case study, and the weather data from 2003 to 2007 from the Hong Kong Observatory are used as the simulation inputs. By incorporating the simulation results, the overall energy performance can be evaluated in terms of electricity benefits corresponding to five orientations of the studied typical office. The priority of office orientation considering overall energy performance is: south-east, south, east, south-west and west. The findings show that thermal performance is the primary consideration of energy saving in the entire system whereas electricity consumption of artificial lighting is the secondary one. The overall annual electricity benefits are about 900 kWh and 1300 kWh for water-cooled and air-cooled air-conditioning systems respectively. The application of semi-transparent PV glazed window can not only produce clean energy, but also reduce building energy use by reducing the cooling load and electrical lighting requirements, which definitely benefits our environmental and economic aspects.

Code compliance of fully glazed tall office buildings in hot climate

In this research, the effect of glazing type and other energy conservation measures on the peak power demand of air-conditioning (AC) systems is investigated for tall and fully glazed government and private office buildings. The EnergyPlus building simulation program is used in the analysis assuming climate conditions similar to that experienced in hot countries of the Arabian Gulf, such as Kuwait. The main objective of the investigation is to meet the limits stipulated in the mandatory Kuwaiti code of practice for energy conservation, with respect to peak AC demand, for both air-cooled and water-cooled AC systems. It is found that for government office buildings with air-cooled AC system, the code limit of 70 W/m 2 for the AC peak power is met when tint low-e glazing is used with either heat recovery units or with AC systems with higher coefficient of performance (COP); whereas for private office buildings, the limit can be met when using a number of conservation measures. Overall, the water-cooled AC system showed better performance even though the code limit is 50 W/m 2 which is mainly due to the higher COP values achievable with such AC systems.

Critical Factors in Adopting Cooling Media for Central Air-Conditioning Systems in Hong Kong

There has been a dilemma about whether to adopt water-cooled or air-cooled air-conditioning systems at various times for different developments in Hong Kong, strongly influenced by the local government. Fresh water has been a scarce resource as a cooling medium; however, in recent years, the local government has advocated water-cooled air-conditioning systems, using fresh water or sea water as a cooling medium in the condenser units. Although such water-cooled air-conditioning systems use less energy than air-cooled systems, they can be potentially harmful to the environment and end users if not adequately designed and maintained. There are obvious pros and cons to both systems. Moreover, sea water as a cooling medium has its limitations if one expects to achieve more sustainability, inevitably at a higher initial cost compared with other systems. In this research, detailed studies are carried out on water-cooled and air-cooled air-conditioning systems in buildings in Hong Kong, aiming to achieve more sustainable design while comparing the cost implications of adopting an appropriate system or converting an existing system. In addition, the government's water supply policy, operation theory of water-cooled and air-cooled condenser units, environmental implications, difficulties in conversion and professionals' opinion are explored. Major stakeholders such as developers, facilities managers, engineers, surveyors and architects could benefit from this research into air-conditioning systems with respect to fulfilling further sustainability criteria and providing environmental protection at optimal costs. This research will be useful in sustainable green building design and also in reducing energy consumption and adverse environmental impacts such as global warming, air pollution and climate change.

The impact of using chilled water storage systems on the performance of air cooled chillers in Kuwait

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations in Kuwait has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. Since the chiller in an air cooled AC system represent more than 75% of the total electrical power consumed by an AC system during the peak demand period, the impact of using CWS systems with alternative operating strategies including partial (load levelling), partial (demand limiting) and full load has been investigated. In our conclusions we estimate that approximately 45% of the total annual exported electrical energy is consumed solely by AC systems as a result of the very high ambient temperatures occurring between March and October. Furthermore, it is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending upon the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

Analysis of a novel absorption refrigeration cycle using centrifugal separation

Water-cooled air-conditioning systems (WACS) are, in general, more energy efficient than air-cooled air-conditioning systems (AACS). The Laws of Hong Kong prohibit the use of fresh water from town mains for comfort air-conditioning, which rules out the use of cooling towers to most air-conditioned buildings. In the absence of lakes or major rivers in Hong Kong, only those buildings that are situated near the harbor can adopt WACS. As a measure to cut down greenhouse gases emissions, the Hong Kong Government is currently exploring the feasibility and viability of widening the use of WACS by the provision of centralized, district-wide water supply systems, which include seawater supply systems for once-through condenser cooling or for making up of water losses at cooling towers, and district cooling systems. Evaluation of the likely energy, economic and environmental benefits of such capital-intensive infrastructure developments requires estimation of the simultaneous cooling demand of a large group of buildings on a district scale, and the energy use for air-conditioning such buildings. This paper describes the method used in these estimations. Comparisons of the results estimated by this method with results obtained by detailed simulation, and with building energy use data obtained from surveys and audits are presented.

A study on the energy performance of three schemes for widening application of water-cooled air-conditioning systems in Hong Kong

The Hong Kong Government intends to reduce greenhouse gases emissions from power stations through widening application of the more energy efficient water-cooled air-conditioning systems (WACS) in buildings. Consideration is being given to the development of centralized, district wide systems for supplying seawater for once-through condenser cooling (the CPSSCC scheme), or for make-up of water losses at cooling towers (the CPSSCT scheme) such that buildings that are restricted to using air-cooled air-conditioning systems (AACS) may adopt or convert to WACS. Development of district cooling systems (DCS) for supplying chilled water to buildings is another feasible option. This paper describes a study into the energy benefits of implementing these schemes in Hong Kong. Application of the analysis method to a territory-wide study for Hong Kong showed that these schemes were all technically feasible and economically viable. It was estimated that compared with all buildings using AACS, the economic saving that could be realized through implementing these schemes in large scale are around 6% for the CPSSCC scheme, 2–3% for the CPSSCT scheme and 20–23% for the DCS scheme.

Predicting air-conditioning energy consumption of a group of buildings using different heat rejection methods

Water-cooled air-conditioning systems (WACS) are, in general, more energy efficient than air-cooled air-conditioning systems (AACS). The Laws of Hong Kong prohibit the use of fresh water from town mains for comfort air-conditioning, which rules out the use of cooling towers to most air-conditioned buildings. In the absence of lakes or major rivers in Hong Kong, only those buildings that are situated near the harbor can adopt WACS. As a measure to cut down greenhouse gases emissions, the Hong Kong Government is currently exploring the feasibility and viability of widening the use of WACS by the provision of centralized, district-wide water supply systems, which include seawater supply systems for once-through condenser cooling or for making up of water losses at cooling towers, and district cooling systems. Evaluation of the likely energy, economic and environmental benefits of such capital-intensive infrastructure developments requires estimation of the simultaneous cooling demand of a large group of buildings on a district scale, and the energy use for air-conditioning such buildings. This paper describes the method used in these estimations. Comparisons of the results estimated by this method with results obtained by detailed simulation, and with building energy use data obtained from surveys and audits are presented.

Water-cooled air-conditioning systems for energy and power saving

The paper presents the results of an experimental investigation to compare the performance of water-cooled and air-cooled air-conditioning systems. Two identical chilled water air-conditioning syst...

Solid-State Controller for Air Conditioning Units

It is essential to maintain the condensing temperature of air-cooled air conditioning systems at certain minimum levels when operating during cold weather. Recent advances in solid-state technology have opened up new approaches to controlling condensing temperatures at any desired minimum level. The solid-state control system described uses an SCR with a unijunction transistor firing circuit to control directly the power to the specially designed fan motors. In designing such a control system, consideration has to be given to matching properly the solid-state control, fan motor, and the temperature sensing device with the air conditioning unit performance characteristics to obtain the desired reliability and stability.