In India, HVAC needs for residential buildings are generally measured by the climatic conditions rather than the internal loads. Window-mounted units, typically located outside are by far the most common product used in homes. These are unitary systems that operate on the refrigeration cycle and function well in most climates.Another popular product, the split air-conditioner comprises the compressor and condenser as part of the external unit and the evaporative coil as an indoor AHU (Air Handling Unit). While, split and window ACs can be equally efficient, what matters in both the cases is the amount of cooling it can provide per watt of electricity it consumes.
For a multi-room application, Multi-Split systems that connect up to four indoor units to a single outdoor unit can provide a space and electricity saving option. Suitable for both new building and renovation projects they offer energy efficiency levels up to SEER 19.5 (Seasonal Energy Efficiency Ratio). The system is available in both wall mounted and slim duct built-in units. Similar but more advanced to Multi-split system is the VRF (variable refrigerant flow) system that offers individual control over the multiple indoor units. By communicating with the indoor units through microprocessor, the outdoor unit controls the flow of refrigerant to each one of them as per their cooling or heating loads. This enables independent operation for each of the indoor units providing optimum energy-saving operation.
Central air-conditioning units are the latest trend in residential buildings today. The new central HVAC systems apart from heating and cooling include components that not only improve comfort and indoor air quality but reduce energy costs as well. These air-conditioning units include an air distribution system (ductwork, dampers, grilles and registers), the temperature control and schedule control system. Each of these components contributes towards increasing the performance and efficiency of the system as a whole.
Ducting: A correct installation and properly sized ductwork sealed with mastic minimizes air leakage and balances the airflow throughout the house.
Air Filtration Systems: The advanced filtration systems help keep indoor air free from allergens and dust and can even rid the air of certain types of bacteria and airborne viruses.
Moisture Control Systems: Overly dry air creates health problems and excessively moist air can contribute to the growth of unhealthy mold and mildew. Moisture control system regulates the amount of moisture in the air. Some advanced HVAC systems also include ultraviolet light within the system to help prevent mold growth.
Variable Speed Motors: Variable speed motors allow for more precise control of airflow throughout the home. By regulating the air through the system, a variable speed motor aids air filtration and moisture control systems.
Programmable Thermostats: Smart thermostats deliver the right temperature at the right time delivering consistent temperatures. By switching the system into high-efficiency mode during low occupancy or in low activity areas, the programmable thermostat helps reduce energy wastage.
Within any HVAC unit, compressor is the main component that uses the most energy. So, to improve the overall efficiency of a HVAC unit- unitary, split or central system, one needs to improve the efficiency of the compressor. Ideal for home HVAC systems, scroll compressors operate with far fewer parts than reciprocating compressors and deliver maximum energy efficiency. The scroll compressorsare compact in size, offer noiseless performance and provide the same cooling capacity as a standard model but use much less power.
In addition, for the split HVAC unit, the latest Inverter technology is now being used which is integrated in the outdoor unit of the system. The technology automatically adjusts unit’s capacity based on the requirement of the room it is cooling or heating. As a result, air-conditioner unit may run continuously but will draw only that much power that is required to keep the temperature stable at the level desired. This function helps save almost 30-50% of electricity (units consumed) compared to a regular split air-conditioner.
Energy & Environment Conservation
An oft neglected aspect in the residential HVAC application is the selection of right size of air-conditioner (available from 1.0 Tonne – 5.0 Tonne) which can have a major impact on power consumption. With an undersized air-conditioner, thermostat temperature at 18oC-20oC is required to get the ambient temperature which otherwise can be easily achieved at a higher setting of 25oC with a right sized air conditioner. Conversely, an oversized air-conditioner cools the room quickly with shorter run cycles. But as air-conditioners are designed for optimum run cycles, a shorter cycle means reduced energy efficiency.
Maintenance of filters, condenser and refrigerant are another important element of energy saving. Recycling or changing the refrigerant and cleaning the condenser periodically make the air-conditioning more effective. In addition, air-conditioning units using materials with superior heat transfer qualities allow for higher efficiency as heat gets transferred to the outdoors effortlessly. Also, load reduction allows HVAC equipment to be smaller and more energy optimization. External heat gains can be avoided with architectural form, light-coloured surfaces and high performance glazing. Internal heat gains can be reduced by using energy efficient lights, kitchen appliances, computers and other equipment. Some other easy steps towards energy saving include maintaining right insulation of the room for effective cooling and keeping the HVAC unit at ideal temperature of 24-25oC for right amount of cooling.
Furthermore, in response to growing environmental and indoor air quality concerns, systems using R-22 refrigerant are being replaced by R-410A refrigerant cooling system which is chlorine-free and considered ozone-friendly. To maintain indoor air quality ASHRAE recommends a minimum of 15 cubic feet of outdoor make-up air per minute (CFM) per person for living areas of residential buildings and higher for kitchens and bathrooms. As the fresh make-up air dilutes indoor contaminants and helps exhaust them from the home, regular cleaning of air filters is necessary for adequate air flow, volume and distribution into the air-conditioner. This also ensures lessor consumption of power by the unit to draw air.