Home | Business News | Browse by Publication | A | ASHRAE Transactions

A comparative study between a constant-speed air-conditioner and a variable-speed air-conditioner.

Article Excerpt
INTRODUCTION

Air conditioners are the necessities of life at home as well in public areas due to the large demands for comfort in the thermal environment of living space in modern society. For better and stable control of the air-conditioning system, recently, small and medium-sized buildings have employed an inverter driven air-conditioning system. The major benefits of the inverter air conditioning system over a conventional air conditioning system include excellent thermal comfort, noiseless, and precise controllability. In addition, an inverter-driven conditioner provides not only precise capacity modulation, but also energy conservation and possibility of application into an intelligent building system (Zubair and Bahe 1989; Qureshi and Tassou 1996). The inverter-driven air conditioner varies cooling capacity by controlling compressor speed with respect to cooling loads. The constant-speed air conditioner, the dominant type in the air conditioner market in the past, is now gradually replaced by the inverter air conditioner. There are some studies concerning the performance of constant-speed and variable-speed compressors and system (Fischer et al. 1998; Domanski and Didion 1984; Liaw et al. 2002; Vargas and Parise 1995; Koury et al. 2000; Park et al. 2001; 42: Shao S, Shi et al. 2004). However, the relevant experimental data are comparatively rare.

Performance of air-conditioners is normally evaluated by the Energy Efficiency Ratio (EER) which is the net cooling capacity to the total rate of electric input in watts under designated operating conditions. However, it is insufficient to evaluate the actual air-conditioner (AC) performance with just only EER rating. This is because the outdoor temperature, sun radiation, the humidity and the indoor temperature setting are varied during AC operation. Therefore, EER can not truly represent the AC performance in the whole cooling season. In that regard, ASHRAE (1995) and JIS (1999) had utilized a calculation method which depends on outlining system capacity and power profiles over different temperature bins using laboratory test results. The seasonal energy-efficiency ratio, SEER, is then calculated by the following equation:

SEER = [8.summation over (j = 1)] q ([t.sub.j])/[8.summation over (j = 1)] E([t.sub.j]) (1)

The terms of the AC cooling capacity q([t.sub.j]) and the consumed electric input E([t.sub.j]), summed over temperature bins, are evaluated at each temperature bin according to the bin hours in the season (ASHRAE 1995), where the subscript j is the number of temperature bins.

Currently, except for Japanese market, most of the air-conditioners being used are constant-speed. However, 85% of the air-conditioners produced from Japan industry are variable-speed. Also, R-410A is selected to replace R-22 as the working refrigerant in the new air-conditioners for saving the useful ozone layer in the stratosphere that protects the earth from the sun's harmful ultraviolet rays (Jeng et al. 2001). The conventional constant-speed air conditioner (C-SAC) is operated via typical on-and-off control when load varies. Since a large electrical power is required to start the compressor, the electrical energy consumed is expected to be much higher via this on and off mode. The inverter-driven variable-speed air conditioner (V-SAC) can modulate the speed of the compressor for maintaining the indoor temperature irrespective of changes in outdoor condition or heat load requirement. The utilization of V-SAC can greatly improve the system performance and energy efficiency. Although an AC maker claimed that V-SAC can save more than 30% of the consumed energy as compared to the C-SAC at the same cooling capacity. Unfortunately, field test comparisons between these two air-conditioners are...

View this article FREE - Now for a Limited Time, try Goliath Business News
Free for 3 Days!