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The Direction of the Wind

HVAC industry in India is growing in terms of the technology, product offering and awareness about energy efficiency. Air-conditioning is no longer considered a luxury product in residential segment and is more of a necessity in commercial and industry sectors. In the past few years, to address the latent issue of high power consumption and environmental impact, HVAC industry developed many new installation, operation and energy saving technologies. The coming year too has many new technologies on anvil.

The concept of Green buildings has brought with it new strategies for higher energy performance such as Variable Refrigerant Volume (VRV) for large sized buildings. The system use refrigerant as the cooling and heating medium, offers large outdoor capacities, greater energy savings and easier installation. Another effective means of reducing energy cost and heating and cooling loads is Energy recovery ventilation (ERV) that also allows for the scaling down of equipment. It is the energy recovery process of exchanging the energy contained in a building and using it to treat (precondition) the incoming outdoor air. M. Selvarasu, Director-LEAD Consultancy & Engineering services (India) explained, “The HVAC system selection should be as per building type, loads and climatic conditions. Measures like variable frequency drives, heat recovery wheels, separate air distribution system for solar exposed zones, higher IPLV of chillers, underflow air distribution system, etc., enhance energy performance for long term sustainability. These technologies can be determined with the help of energy modeling software and payback analysis.” In terms of cooling refrigerants, R-22 refrigerant is being phased out which contains ozone-depleting chlorine. It is being replaced by chlorine free R-410A refrigerant and considered ozone-friendly. Kanwal Jeet Jawa, Managing Director, Daikin India adds, “Daikin Super Multi Hot Water air-conditioning solution utilizes disposed energy to heat water. In addition, our Room Precise Temperature Control, the electronic expansion valve continuously adjusts the refrigerant volume in response to load variations in indoor units, maintaining comfortable room temperature at a virtually constant level without temperature variations typical of conventional on/off control systems.”

Some of the major advances in HVAC we have already seen are, passive dehumidification that works by using a system of evaporator coils & heat recovery system, sophisticated zoning system which includes placing several zoning units with dampers and a thermostat in the ducts and vents that open and close the dampers as necessary, and the highly developed home automation systems that control the “Energy Triangle,” which is the HVAC system, artificial and natural lighting and other systems.

Increasingly being used as an alternative to conventional ceiling-based air distribution systems is the underfloor air distribution (UFAD) because of its significant energy savings, improved thermal comfort & indoor air quality. The open space between the structural concrete slab and the raised access floor system delivers conditioned air directly into the occupied zone and is returned from the room at ceiling level. This produces an overall floor-to-ceiling air flow pattern that efficiently removes heat loads and contaminants from the space, particularly for cooling applications. A chilled beam is another air distribution device with pipes of water passed through a “beam” (a heat exchanger) either integrated into standard suspended ceiling systems or suspended a short distance from the ceiling of a room. As the beam chills the air around, it is replaced by warmer air moving up from below, causing a constant flow of convection and cooling the room. Active chilled beams have ductwork while passive chilled beam is one that is not ducted. “Classrooms, private and public office buildings, meeting facilities, health care facilities, other environments that may have moderate to high sensible heat ratios, and building retrofits where space for new mechanical equipment may be limited are all good applications for active chilled beams. Passive chilled beams are a good solution to provide sensible cooling in labs or other spaces where processes and people generate high heat loads.” elaborated architect R.M. Srivastava.

Globally, institutions are also employing mechanical heating and cooling systems like solar power, geothermal power or other sources of green energy. Advanced energy programs are another way of optimizing HVAC energy efficiency. “Today energy analysis tools are becoming common and are being applied much earlier in the design process. Energy programs are primarily designed to predict the annual energy consumed by a structure in terms of BTUs or pollution avoidance. Whereas, Sizing programs are primarily designed to calculate peak hourly loads during the heating and cooling seasons. Almost all buildings of any complexity have a sizing analysis of some kind run by an architect, engineer, or mechanical contractor.” says Richard Paradis, P.E., Director, Whole Building Design Guide at National Institute of Building Sciences, Washington D.C., USA.

HVAC Developments

Radical and more innovative air-conditioning technologies being developed and tested are:

Desiccant enhanced evaporative air conditioning (DEVAP): National Renewable Energy Laboratory’s (NREL) Eric Kozubal co-invented an air-conditioning system that’s energy efficient while incredibly effective at both cooling a building and managing its humidity levels. The technology abandons the compressor-driven refrigeration process but combines evaporative cooling and liquid desiccants. It uses micro-porous membrane to maintain the necessary liquid and air separation in the heat and mass exchanger to cut electrical demand by up to 90% and works well in both high humidity and dry heat conditions.

Ice-powered air-conditioners: Ice Energy, California has developed a system that converts water to ice, which is then used to run an air-conditioning unit. At night, the unit freezes 450 gallons (1,703.81 liters) of water by circulating refrigerant through a system of copper coils. The water that surrounds the coils turns to ice, which is then stored. As temperatures rise the next day, the existing AC unit stands down, and the ice, rather than the AC unit’s compressor, cools the hot refrigerant, which keeps the building temperature nice and comfortable and cuts overall energy consumption by about 30%.

Salt-driven air-conditioner: Massachusetts based company7AC Technologies is beta testing an airconditioner which uses plastic plates and a high-tech membrane to draw water from the air and cut energy use by 50% or more. The air-conditioner is designed around a series of flat, multilayered plastic plates covered with a proprietary membrane licensed from the NREL. With water flowing inside each plate, a solution of salt water is sprayed over the surface of the plate that rolls down attracting water vapor from humid air. The salt water is then collected and passed through another set of plates which heat the solution and exhaust hot, moist air. This salt solution, minus some water, is recirculated back toward the dehumidification plates. One of the advantages of the system is that it can operate using relatively low heat that could come from natural gas, solar panels, or even waste heat from a commercial building.

New materials to regulate temperature: Dr. Aaswath Raman of Stanford University has invented a way to encourage buildings to dump their heat without the need for pumps and compressors. Instead, they simply radiate it into outer space. According to the proposed theory, outer space is very cold (about 3°C above absolute zero) and very big, so it is the perfect heat sink. To encourage an individual building to cool down, all you need do in principle is reflect the sunlight which falls on it back into space, while also encouraging as much radiative cooling from it as possible. Dr. Raman has made a material which reflects 97% of sunlight while itself radiating at a wavelength of between eight and 13 microns (or millionths of a metre. It consists of four layers of silicon dioxide interspersed with three of hafnium dioxide. Each of these seven layers is of a different, precisely defined thickness, ranging from 13 to 688 nanometres. It is backed by a layer of silver 200 nanometres thick, to act as a mirror. The result, a sheet with a total thickness of less than two microns, is the photonic equivalent of a semiconductor: it does to light what a semiconductor does to electricity, namely manipulates its energy levels.

 

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