First things first: What do developers look for in an HVAC system? Air-conditioning accounts for the biggest portion of energy consumed by a building – 55-65 per cent, reckons Bishnu Swaroop, President - Technical, Ambuja Neotia. Thus, he identifies energy-efficiency or lifetime cost as the most important criterion when choosing a system, followed by ease of maintenance, capex (as this defines the payback period), ease of installation, cooling capacity and interior design needs. “Our HVAC system designs depend on the end utilisation of the building (whether residential or commercial), expected load, available earthing arrangement, need for air-conditioning in individual residences, the type of electrical supply the building requires (such as single-phase for normal split unit and three-phase for variable refrigerant flow, or VRF), and ease of maintenance,” shares Devaraja TH, Executive Vice President & HOD, M&E - Electrical & HVAC, Sobha. “Further, we consider the climatic conditions that may adversely affect the electrical installation and thus increase the operational and maintenance cost. Finally, the HVAC design considers the reliability of power supply and redundancy of sources and distribution paths to cater to the need for emergency and standby power for continued operation of systems, as well as the integration of alternate sources of energy, such as diesel generation, solar energy, wind power, etc.” “We choose a type of air-conditioning for various segments of residential properties depending on various factors contributing to the heat load of those dwellings,” explains V Gopal, Executive Director, Projects & Planning, Prestige Constructions. “Typically, the heat load is impacted not just by the active occupancy but also by passive contributions from building materials, predominantly those that radiate heat.” So, regardless of the segment of property, Gopal points out that a complete concrete/masonry structure could still make do with high wall splits, whereas a similar-sized unit in glass may entail a more effective centralised air-conditioning solution, that is, variable refrigerant volume(VRV) or chillers. That said, the HVAC preferences for different classes of real estate are fairly well defined. Chilled water units In the commercial segment, until about a decade ago, the only option was chiller packages with ductable, fan coil unit (FCU), air-handling unit (AHU) indoor units, says Chandrasekar Narayanan Srikantan, National President, ISHRAE, and Consultant & Certified Energy Auditor, Genex Consultants. “With the advent of VRF outdoor units, which work in combination with different types of indoor units, the options have increased.” Larger commercial properties opt for chilled water units, preferably water-cooled type systems offering better energy-efficiency despite being a little more expensive to maintain and needing more manpower, explains Chandrasekar. From the perspective of energy efficiency, water, having the best latent heat capacity, is the best medium for the transfer of heat from inside to outside (for cooling) and hence underlies the most efficient system, opines Swaroop of Ambuja Neotia. “Accordingly, for large commercial spaces suchas retail malls (in Kolkata, Patna, Raipur, etc) and office spaces (Ecospace, Ecocentre, etc), we have opted for water-cooled large chillers of varying tonnage from 100 tr to 1,500 tr.” “In the Sobha Corporate Office, we have installed a conventional chiller system HVAC,” shares Devaraja. “Our commercial, retail and hospitality developments like Prestige Minsk Square, Forum Mall (Kanakapura Road), Conrad (Bengaluru) and Sheraton (Bengaluru) are mostly fitted with centralised air-conditioning with chillers and in a few cases with VRVs,” shares Gopal. “Within chilled water systems, the preference is for scroll compressors for up to 60 tr capacity, screw chillers from 100 tr to 500 tr and centrifugal chillers beyond this capacity,” continues Chandrasekar. “In all these systems, variable speed compressors are preferred, although installations with multiple chillers prefer a combination of constant speed and variable speed compressors to save costs. Currently, controls and monitoring systems exist to get the benefit of energy conservation as well as in pumping systems.” Disadvantages associated with water-cooled cooling machines are their copious water consumption and intricate network of chilled water piping, pumps, cooling towers, etc, which makes such systems a bit complicated to design, install and maintain, points out Swaroop. So, for small offices/residences/hospitality requirements and in locations where the availability of water is an issue, even in case of large cooling capacity requirement, Ambuja Neotia opts for air-cooled chillers or compressors. Where water quality or availability is an issue, air-cooled chillers are preferred,” agrees Chandrasekar. Commercial VRF applications Commercial applications of less than 10,000 sq m of air-conditioned area generally use VRF air-conditioners, according to Chandrasekar. Standalone multiplexes use large-capacity packaged units or VRF systems, opines Ashutosh Joshi, Sr Consultant, Vision Electro Mechanical Consultants. A VRF system has been installed in Ambuja Neotia’s restaurants Afraa and AltAir, in small office spaces like Ecostation, Ecospace Business Towers, etc, and in 60-100-room hotels and resorts such as Taj Chia Kutir, Taj GurasKutir, Ecopark Banquet, RaajKutir IHCL Seleqtions and the premium residency Utalika. The VRF system’s added advantage of distribution of functionality, a single outdoor machine (holding the compressor) serving multiple indoor units (ceiling-suspended cassette, wall-hung units or FCUs concealed above the false ceiling) placed inconspicuously as per the architectural need has served Ambuja Neotia well. Such VRF systems have been installed in hotel and resort projects with dwelling units distributed in a large complex. Hospitality establishments and hospitals have similar needs as commercial properties with additional filtration and other inclusions for indoor air quality to maintain the IEQ levels, points out Chandrasekar. “Like commercial spaces, hospitality spaces choose an air-conditioning system depending on the scale of operations and areas to be covered, with some opting for centralised air-conditioning systems or VRF systems depending on their location and availability of water,” adds Joshi. Residential preferences In the residential segment, air-conditioning principally involves ensuring independent controls for every zone/room, says Chandrasekar. To achieve this, he points out that the preference in mid-segment residences, where mostly only the bedrooms are air-conditioned, is for split air-conditioners (hi-wall type or cassette type). In contrast, in the West and Middle East, the preference is for rooftop packaged units. “Most residences use single-phase normal split units,” agrees Devaraja. “We have provided a single-phase normal split unit HVAC system in Sobha HRC Pristine, and are in the process of installing single-phase normal split units in SobhaCity Gurugram.” “For mass housing, we have window units where the compressor and indoor machine with a recirculating fan are built in one single unit and installed in the windows, says Swaroop “For lower-end mid-segment projects like Udvita and Uddipa-The Condoville, our choice is DX machines with wall-hung indoor units with traditional scroll or rotary compressors to achieve the energy efficiency of 5*.” “For our standard (Prestige Kew Gardens) and premium (Prestige Misty Waters) developments, we have been making provisions for occupants to install hi-wall splits in the building architecture,” shares Gopal. It’s vital to buy the right kind of window or split air-conditioner. “Window air-conditioners and split air-conditioners generally used in small residences are star-rated for energy efficiency by BEE [Bureau of Energy Efficiency] India and the split AC models with both fixed speed and inverter-based compressors are also star-rated by BEE,” points out Joshi. Among the upper middle-income group, VRF with hi-wall or cassette indoor units are gaining popularity for saving on energy bills, needing the least possible space for outdoor units, better reliability and lesser failures, notes Chandrasekar. “Fully air-conditioned high-income residences typically prefer VRF with hi-wall, FCUs, cassette or AHUs.” “VRF systems used in larger high-end residences have power and space-saving outdoor units with an inverter-based variable speed compressor,” says Joshi. “While cost majorly impacts these buying decisions, the choice takes into consideration energy-efficiency, environment friendliness and maintenance costs too.” “For medium-range projects such as Urvisha-The Condoville, we have installed inverter machines with rotary compressors that are fairly energy-efficient and also offer limited (defined distance) indoor unit options,” shares Swaroop. “Typically, for upscale developments we have been providing VRV-based air-conditioning solutions (Prestige Golfshire and Kingfisher Towers),” says Gopal. Evolving products HVAC is an evolving market.“Refrigerant use policies, eco-friendly norms, safety measures, technology advancements and product efficiencies are driving product development,” observes Joshi. “For instance, inverter technology air-conditioners with variable speed compressor motors were developed in Japan but now most manufacturers in India have incorporated this technology in their products.” Recent innovations for energy-saving include the use of timer-based temperature control, or scheduling, to cater to peak client presence as well as very low occupancy periods, adds Chandrasekar. “Many Ratnadeep, Vijeta and Ushodaya Supermarkets have incorporated these controls. In dense occupancy areas the best way to maintain IEQ levels is to have fully fresh air systems and avoid recirculating the same air by introducing three-stage cooling (indirect and direct cooling systems followed by a chilled water cooling coil). A recent such installation was at the Yadagirigutta Temple complex.” Heat pump type ACs can be used for both cooling and heating, and are useful in Northern states like Haryana, Punjab, Delhiand Uttar Pradesh, according to Joshi. “Also, in view of the deteriorating air quality in cities, most manufacturers are now using anti-bacterial/anti-allergy filters in air-conditioners to improve performance.” Growing HVAC options indeed bode well for the realty industry.