Energy-efficient air conditioners – New Technologies

LG Multi V Outdoor Air Conditioners

LG Electronics showcased its latest HVAC and energy solutions air conditioners at ACREX India 2014, one of the largest international expositions in India exclusively for the air-conditioning, refrigeration, heating and allied industries. Mahendra Agarwal speaks on the novel ways to reduce energy consumption in buildings without compromising on comfort.

Mahendra Agarwal

Mahendra Agarwal

Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning, comprising cooling and dehumidification, has become a necessity in commercial and residential buildings and industrial processes. It accounts for a major share of the energy consumption of a building or facility. In tropical climates, the energy consumed by heating, ventilation and air-conditioning (HVAC) can exceed 40per cent to 50per cent of the total energy consumption of a building. This significant figure is primarily due to the heavy duty placed on cooling technologies to remove both sensible and latent heat loads. Therefore, there is tremendous potential to improve the overall efficiency of the air-conditioning systems in buildings.

Decreasing the energy consumption of heating, ventilation and air conditioning (HVAC) systems is becoming increasingly important due to rising cost of fossil fuels and environmental concerns. Therefore, finding novel ways to reduce energy consumption in buildings without compromising comfort and indoor air quality is an ongoing research challenge.

 

Variable Refrigerant Flow Systems: “An Emerging Trend”

Variable refrigerant flow (VRF) systems, which technology originated from Asia more than 20 years ago, have become popular in many countries. The technology has gradually expanded its market presence and steadily gaining market share throughout the world. In India, VRF systems are gaining its market shares both on medium – sized commercial buildings and premium segmented dwellings.

Variable refrigerant flow (VRF) systems, technology is quite innovative and fullfills the requirement for green building certification.

The term “variable refrigerant flow” refers to the ability of the system to control the amount of refrigerant flowing to each of the evaporators, enabling the use of many evaporators of differing capacities and configurations, individualized comfort control in different zones, and heat recovery from one zone to another. Most VRF condensing units have inverter based variable speed compressors to control the flow of refrigerant to the evaporators. Refrigerant flow control lies at the heart of VRF systems and is the major technical challenge as well as the source of many of the system’s advantages.
The energy efficiency of the VRF systems derives from several factors. The VRF essentially eliminates duct losses, which are often estimated to be between 10 to 20 per cent of total air flow in a ducted system. The VRF systems typically include minimum two or three compressors, all of which is variable speed or one is variable speed, in each condensing units, enabling wide capacity modulation. The system having all inverter compressors have better efficiency than the systems having one inverter compressors and others fixed speed ones. All inverter systems yields high part – load efficiency, which translates into high energy efficiency ratios, because HVAC system typically spend most of their operating hours in the range of 30per cent to 70per cent of maximum capacity. The variable refrigerant technology provides the best of features on the diversity between the indoor and the outdoor unit capacities. The diversity on the indoor can go as high as upto 130 per cent of its outdoor unit capacity and on special applications with detailed engineering the diversity can cross even 150per cent.
VRF outdoor condensing units are available with some of the manufactures are on both air cooled and water cooled units. The water cooled VRF outdoor units has an excellent EER as compared with its counterpart. The water cooled VRF condensing units may be an alternative to traditional water cooled HVAC equipments for medium size commercial buildings.
Manufacturer’s data and few case studies indicate that VRF systems are cost effective, but results, again, depend on specific application features. Typically, energy savings are achieved, ranging from 10per cent to 60per cent, depending on climate and the type of system displaced, among other factors.
Some of the power saving features of variable refrigerant system is as follows:
• Good part load performance due to multiple compressor and variable speed compressor systems permitting capacity modulation to serve 15per cent to 130per cent of the cooling or heating load. Many hours of HVAC system operation are spent between 30 per cent and 70 per cent of maximum capacity where the VRF system efficiency is high.
• Good zone control, saving by not conditioning unoccupied zones and by providing capability to condition single zones off hours at a reasonable cost.
• VRF air conditioners are controlled precisely with the sophisticated micro computer based controllers, to maintain the precise indoor climatic conditions.
• VRF systems are operated mainly with eco friendly non ozone depleting refrigerant and the equipments meets all the criteria’s of Green Building.
VRF systems can provide zone control, including heating and cooling. Refrigerant is used directly as both the working fluid and the heat transfer fluid tending to make the VRF system more efficient than systems that use air or water as a secondary heat transfer fluid for delivering heating or cooling.
Currently on the advancement of VRF technology manufactures like LG Electronics etc have developed a new product range of 4th generation VRF systems on the segment, where a VRF condensing unit either of their air cooled or water cooled can be connected with air handling units as indoor units to meet the requirement of higher static, air quantity etc for factory, medical, hospital applications, auditoriums etc.
VRF systems are suitable for all types of commercial building applications of medium – sized and all types of residential building applications. For larger sized commercial building applications VRF can be one more tool for engineers to consider.

(The author is presently working with LG electronics as Business Head of ‘System air conditioner division’. Prior to joining LG he has worked with M/S Voltas Limited as General Manager in its Electro Mechanical & refrigeration business group. He is a B.TECH (mechanical engineering) with over 30 years of experience in HVAC field. He has been very active in professional bodies like ISHRAE and ASHRAE. He has been the National president of ISHRAE in 2009-10 and also the president of ASHRAE – Mumbai chapter in 2010-11.)

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