Variable-speed Air Conditioners Research Articles

Unlocking energy savings and emissions reduction: A comparative study of fixed-speed and variable-speed room air conditioners in high ambient temperature environments

Developing countries, particularly those with high ambient temperatures (HAT), are experiencing a surge in air conditioner (AC) installations. Fixed-speed ACs, which rely on on–off control, are the most used. However, fixed-speed ACs lack humidity control and experience compressor cycling, leading to poor thermal comfort and increased energy consumption. Variable-speed compressor technology eliminates compressor cycling, which increases the effective coefficient of performance, especially at part-load conditions. This study compares the transient performance of variable-speed and fixed-speed AC units in Cairo, Egypt, as an example of a HAT environment. During a 2-month experimental investigation, the variable-speed unit provided 41% electrical energy savings while maintaining a comfortable environment. Analytical modeling using a machine learning model trained by the experimental measurements predicted annual energy savings of 473 kWh/year and an overall electrical energy savings percentage of 30.5%. The study also explored different scenarios for implementing variable-speed ACs in Egypt, a developing HAT country. With a 60% market penetration for variable-speed AC as the most probable scenario, the electrical energy savings up to the year 2032 add to 1.33 TWh, leading to 79.3 million USD in cost savings and 2.64 MMT of CO2 emissions reduction.

Stochastic modelling of flexible load characteristics of split-type air conditioners using grey-box modelling and random forest method

Split-type air conditioners (ACs) are the major contributors to the total electricity use and peak power demand in residential buildings due to their high penetration. Accurate prediction of their energy consumption plays a significant role in demand side management (DSM), because it can help exploit the demand response (DR) potential of these ACs fully. However, the existing studies on the load characteristics modelling of split-type ACs are still not comprehensive, especially in the consideration of occupant behavior and appliance characteristics. To solve this problem, this study has developed a novel flexible load characteristics model by combining the stochastic method, grey-box modelling (i.e., equivalent thermal parameter (ETP) model) and random forest method. The stochastic method can help capture the dynamic occupants’ energy-related behaviors considering various family structures. Random forest can address the difficulties in simulating the power characteristics of variable-speed ACs under various operating conditions. With the prediction error of 2.8%, the proposed model can effectively characterize the energy performance of split-type ACs at both individual and aggregate levels. To better show the load flexibility of ACs, an investigation on DR potential of split-type ACs was also carried out by resetting temperature setpoints. The result showed that the maximum DR potentials at the scope of 1000 aggregated households are 394.54 kWh and 323.82 kWh on weekdays and weekends, respectively. The developed flexible load characteristics model of ACs can be used by utility companies for DR potential assessment and model-based DR control for a single household or building clusters.

A modeling study on developing the condensing-frosting performance maps for a variable speed air source heat pump

For a variable speed (VS) space heating air source heat pump (ASHP) unit, to comprehensive study its frosting suppression and heating performances, a condensing-frosting performance map has been proposed. An experimental study using an experimental VS ASHP unit to obtain condensing-frosting performance maps was previously reported. However, obtaining such performance maps experimentally was time consuming and costly, and it was therefore considered highly necessary to develop a mathematical model to obtain performance maps through modeling study. In this paper, therefore, a mathematical model for the experimental VS ASHP unit was firstly developed by referring to previously published mathematical models for VS air conditioners. The developed model was experimentally validated using reported experimental data. The average relative errors between the measured and predicted total output heating capacity and COP were at 3.7% and 3.6%, respectively, and the average error between the measured and predicted outdoor coil surface temperature was at 0.2 °C. A follow-up modeling study was then carried out using the validated model to obtain condensing-frosting performance maps for the experimental VS ASHP unit having different outdoor coil surface areas and at different outdoor operating conditions. The modeling study results suggested that by increasing outdoor coil surface area of the experimental VS ASHP unit from 50% to 150%, its surface temperature on average was increased by more than 1.37 °C, which was inducive to a better frost suppression performance, and the total output heating capacity by more than 11.07%, but at a higher initial manufacturing cost. The modeling study results also indicated that the developed model can be a useful tool in studying the characteristics of VS ASHPs during both frosting and frost-free operations, which was important for guiding the design and control of ASHPs for their efficient and reliable operations.

Identification of simplified energy performance models of variable-speed air conditioners using likelihood ratio test method

Variable-speed air conditioners (ACs) are gradually replacing single-speed ACs in residential buildings in densely populated cities like Hong Kong due to better control accuracy and higher energy efficiency at part-load conditions. Simplified energy performance models of variable-speed ACs are needed for different purposes, including building energy analysis, model-based fault detection and diagnosis, and model-based optimal control. However, how to identify the most suitable model from a series of candidate models with various complexities is rarely discussed. This study presents a model selection approach based on the likelihood ratio test (LRT) method to identify the most suitable energy performance model of variable-speed ACs. A full model and a range of reduced models/submodels for variable-speed ACs are first formulated for model selection procedure. The maximum likelihood estimation method is applied to estimate the parameters in each candidate model. Performances of the candidate models in each step of the selection process are compared using LRTs. Test results demonstrate that the model selection approach can effectively select the cooling capacity and coefficient of performance (COP) models for a typical variable-speed AC with reasonable complexity and satisfactory accuracy. The root mean square errors of the selected models of cooling capacity factor and COP factor are 0.0188 and 0.0463, respectively.

Feasibility Study on Variable-Speed Air Conditioner under Hot Climate based on Real-Scale Experiment and Energy Simulation

It is well known that inverter-driven variable-speed compressor (or inverter) air conditioners are more efficient than constant-speed compressor air conditioners. Therefore, most countries have employed part-load assessment test standards such as ISO 16358, EN 14825 and ASHRAE 116 in addition to the conventional ISO 5151 full-load test standard to appropriately evaluate the part-load efficiencies of variable-speed air conditioners. However, many countries in the Middle East and South America still use the ISO 5151 standard owing to policy or high- temperature environmental considerations. In this study, we experimentally verify the energy saving effect of the inverter air conditioner with respect to the constant-speed air conditioner under the Korean climate with distinct temperature changes of four seasons and under the hot climate of Saudi Arabia throughout the year. ISO 5151 defines test conditions for a single temperature, whereas ISO 16358, EN 14825 and ASHRAE 116 simulate seasonal efficiencies using interpolation of several climate test results. Herein, we directly employ the environmental changes during a day or season in a qualified test room with specific dimension. Using extensive regional and seasonal climate data for Saudi Arabia and South Korea, the changes in temperature conditions are applied directly to the outdoor side and appropriate building cooling load conditions are applied to the indoor side of the air-enthalpy-type test room. The energy savings of the inverter air conditioner were analyzed experimentally according to the spatial and temporal temperature changes. The energy reduction effects of the inverter air conditioner largely depended on the temperature and cooling load changes for a day or season. Furthermore, a feasibility study based on an energy simulation showed that the variable-speed air conditioner could be economical even in hot climates.

Analysis of a variable speed air conditioner considering the R-290/POE ISO 22 mixture effect

Air-conditioning applications using propane (R-290) have several environmental and thermodynamic advantages over more commonly used refrigerants, such as R-410A and R-22. This paper presents the development of a mathematical model for variable capacity air conditioning systems that use R-290/POE ISO 22 as refrigerant/lubricant. The thermodynamic performance of the refrigeration system is evaluated in terms of the SEER (Seasonal Energy Efficiency Ratio). The thermodynamic properties of the refrigerant/lubricant mixture were obtained from a departure-function approach using the Peng-Robinson equation of state. The effect of the oil on the condenser and evaporator heat transfer coefficients and pressure drops was also taken into account. Sub-models were developed for each component of the air conditioning system, including the connecting lines and the scroll compressor. Furthermore, an air conditioner experimental calorimeter was constructed and tested in order to validate the proposed model.

An experimental investigation of energy saving potentials for room type variable-speed air conditioners in public offices: A case study from Istanbul

This study includes the comparison of constant speed air conditioners (non-inverter AC) and variable speed air conditioners (inverter AC) in two identical public office rooms in terms of the energy consumption by reflecting user comfort conditions as a field test. The period of this field test was totally 64 days from 31st of July to 2nd October 2012 and ACs were operated for 43 days intermittently. After collecting real data, total and operational energy consumptions, weighted average power and energy consumptions of the selected typical days were conducted. As can be derived from the conducted analyses, the energy saving ratio of inverter AC to non-inverter AC varies between 11% and 38%. The second important observation is that the lower cooling loads than minimum rated power results in shifting inverter AC to on/off mode. The last but not the least, usually energy efficiency ratio (EER) is used as an indicator for evaluating cooling efficiencies of ACs and in this field test although both inverter and non-inverter ACs have the similar EER values, their energy consumptions differ from each other. This results in the requirement of a new indicator for better comparison of energy efficiencies of ACs.

Different Arrangements for Dual-Rotor Dual-Output Radial-Flux Motors

This paper describes different arrangements for a dual-rotor, radial-flux, and permanent-magnet brushless dc motor for application to variable-speed air conditioners. In conventional air conditioners, two motors of appropriate ratings are usually used to drive the condenser and evaporator separately. Alternatively, a motor with two output shafts may be employed, and this is studied here. The motor has inner and outer rotors with a stator in between which is toroidally wound or axially wound with inner and outer slotted stator surfaces. The power sharing on the two rotors is designed to meet the requirement of the condenser and evaporator. Finite element analysis (FEA) is employed to verify the designs. A prototype is made and tested to evaluate the performance. Alternative windings are investigated to assess the possibilities of decoupling the rotors so that they run independently. In the final section, a new and novel arrangement is proposed, where one three-phase winding set and one two-phase winding set (both toroidal) are wound on the same stator to control two rotors of different pole numbers. The two winding sets can be bifilar or share the same set of phase windings. This design simplifies the winding (because it is toroidal) and reduces the copper loss or amount of copper required. The design is tested using FEA solutions, and the initial results indicate that this machine could operate successfully.

Modeling and Prediction of Distribution System Voltage Distortion Caused by Nonlinear Residential Loads

Electric utilities have expressed concern over increased nonlinear loading of residential power distribution systems. The number and variety of power electronic products found in the typical home continues to grow rapidly, imposing a burden on local power companies to supply reliable, distortion-free service. In order to adequately prepare for the future, utilities must be able to predict the harmonic impact of new power electronic equipment and evaluate the ability of existing power systems to accommodate these nonlinear loads. This paper describes a modeling methodology that uses SPICE simulation software to predict the voltage distortion caused by nonlinear residential loads. Results of applying the methodology to a specific distribution system containing either of two different types of harmonic-rich loads, i.e., variable speed air conditioners or electric vehicle battery chargers, are presented as well.

Modeling and prediction of distribution system voltage distortion caused by nonlinear residential loads

Electric utilities have expressed concern over increased nonlinear loading of residential power distribution systems. The number and variety of power electronic products found in the typical home continues to grow rapidly, imposing a burden on local power companies to supply reliable, distortion-free service. In order to adequately prepare for the future, utilities must be able to predict the harmonic impact of new power electronic equipment and evaluate the ability of existing power systems to accommodate these nonlinear loads. This paper describes a modeling methodology that uses SPICE simulation software to predict the voltage distortion caused by nonlinear residential loads. Results of applying the methodology to a specific distribution system containing either of two different types of harmonic-rich loads, i.e., variable speed air conditioners or electric vehicle battery chargers, are presented as well.

Statistical summation of the harmonic currents produced by a large number of single phase variable speed air conditioners: a study of three specific designs

The variable speed air conditioner (VSAC) is a large domestic distorting load. We investigate the impact of a large number of VSAC's on domestic harmonic levels. We present a general method to build a harmonic numerical model of a passive filtered rectifier supplied by a distorted voltage; a statistical method to assess the total harmonic currents produced by a large number of units running at various power levels and supplied by various distorted voltages. These two methods are applied to a rectifier used by many VSACS. We also present results for two other rectifiers.

96/03888 Decision steps for implementing a BACnet TM interface project

In this paper, several capacity-control schemes for conventional air-conditioning systems are discussed. An inverter-driven, variable-speed air-conditioner (VSAC), which allows continuous adjustment of system capacity, is investigated from an energy-conservation standpoint. Energy savings are estimated for a 100-m2 residence in Dhahran equipped with a 17.6-kW, fixed-speed air-conditioner (FSAC). The simulated VSAC is driven by three different power sources. The use of a sine-wave motor-generator set, which produces the highest motor efficiency as a function of motor speed, will save 29% of the 20,000 kWh consumed by the FSAC, which agrees within 5% of the annual measured. Pulse-width-modulated (PWM) and six-step inverter systems will provide energy savings of 19 and 23%, respectively. Simulation results indicate that VSACs will operate for 5500 h, while the fixed-speed system will run for 3200 h annually.

Applying power electronics to residential HVAC-the issues

Several of the market and application issues bearing on the economics of residential variable speed air conditioners and heat pumps are outlined. Technical details of capacity modulated systems are avoided, along with design issues involving power semiconductors, motor torque and speed control strategies, and integration in silicon for these applications. The author intends to provoke the development of creative improvements in the economics and application of variable speed electronics technology. He identifies the more important issues to aid the development of marketing strategies that will exploit the potential of air conditioning products containing power electronics, enabling them to penetrate the heating, ventilation, and air conditioning (HVAC) market and compete successfully against conventional systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of an inverter-driven air-conditioning system and its application in a hot and humid area

In this study, the energy saving effect and dehumidification enhancement of the variable speed air conditioner (VSAC) have been analysed theoretically and experimentally. The results indicated that the VSAC in subtropical areas could provide annual energy savings of 20%. Even more important, the 3 RT-unit VSAC successfully lowered its apparatus sensible heat ratio (ASHR) from 0.80 to 0.60, which made it superb for applications in hot and humid areas. The VSAC has a vast application potential in these climates.

Capacity control of air-conditioning systems by power inverters

In this paper, several capacity-control schemes for conventional air-conditioning systems are discussed. An inverter-driven, variable-speed air-conditioner (VSAC), which allows continuous adjustment of system capacity, is investigated from an energy-conservation standpoint. Energy savings are estimated for a 100-m 2 residence in Dhahran equipped with a 17.6-kW, fixed-speed air-conditioner (FSAC). The simulated VSAC is driven by three different power sources. The use of a sine-wave motor-generator set, which produces the highest motor efficiency as a function of motor speed, will save 29% of the 20,000 kWh consumed by the FSAC, which agrees within 5% of the annual measured. Pulse-width-modulated (PWM) and six-step inverter systems will provide energy savings of 19 and 23%, respectively. Simulation results indicate that VSACs will operate for 5500 h, while the fixed-speed system will run for 3200 h annually.