Green buildings are the need of the hour due to depletion of natural resources across the globe. They are designed or constructed with the aim of sustainable development and help to reduce the harmful impact on natural resources. They are designed to consume the optimal amount of energy so green buildings by their definition have low impact on the environment and consume minimal energy and water as well as minimise waste. Based on the building design, the building envelope and the varying climate of the location of the building, it is quite possible to operate such a building without air conditioning by adopting natural cooling or forced ventilation.
Heating, Ventilating, and Air-Conditioning (HVAC) Systems play a key role in green buildings since many of the green building factors are directly or indirectly affected by the performance of the HVAC systems. HVAC accounts for nearly 50-60 per cent of the energy used in commercial buildings in India.
“However, the density of the occupancy, the building’s internal loads as well as the climate may necessitate air conditioning to be installed and operated. In such a case the designer of the green building must achieve very low use of air conditioning system energy per unit area of the occupied space. Air conditioning may be driven partly by alternate energy sources too,” states Vikram Murthy, National President of ISHRAE (Indian Society of Heating, Refrigerating and Air Conditioning Engineers).
Since HVAC energy costs account for more than 40 – 50 per cent of the building’s energy expense, it is critical that the HVAC system operates as efficiently as possible. Elaborating on this, Abhijit Pisal, Business Head, Godrej Green Building Consultancy Services, states that the HVAC system for green building shall be designed to reduce energy consumption while maintaining the interior conditions at a comfortable level to keep occupant’s health and productivity. HVAC system design should not only meet the standard on energy front but beat the standard codes like Energy Conservation Building Codes (ECBC), Indian and American Society of Heating, and Refrigerating and Air Conditioning Engineers (ASHRAE) standards to achieve higher level of green building rating.
Any commercial building has the potential to realise significant savings by improving its control of HVAC operations and improving the efficiency of the system it uses, he further adds.
“In industrial applications, the share of energy consumption of HVAC systems can be even more. Hence, it is important to design and install the most energy efficient HVAC system to reduce the total energy consumption. The lower energy consumption will reduce the carbon footprint of the building and make the building green,” informs Senthil Thangam, Senior General Manager, Commercial Air Conditioning Division, Blue Star Limited.
Eco-friendly HVAC system in green buildings
HVAC systems have major carbon footprint on the environment by use of energy that results in depletion of non-renewable energy resources and impact the performance of a building.
An eco–friendly air conditioning system focuses on a low carbon footprint design that may be an outcome of passive measures in building design and building materials to reduce heat load, the use of natural ventilation and cooling by natural cooling systems for non-critical areas and non-conventional cooling systems such as radiant cooling.
Depending on a combination of the above strategies, the first or installed cost of an eco-friendly HVAC system for a green building may cost just between 5 to 10 per cent higher than a conventional system, and the savings in operating cost will pay back the higher investment, opines Murthy.
Pisal emphasises on improving control of HVAC operations in any commercial building in order to realise significant savings and thus, improving the efficiency of the system. An integrated and holistic design process beginning at a project’s inception is required to optimise the HVAC design, HVAC commissioning and operation for green buildings.
Senthil from Blue Star gives prominence to use of eco-friendly refrigerants that are responsible for reduction in energy consumption of HVAC system in green buildings. He further adds that the choice of the refrigerant will have a direct impact on depletion of ozone and also on global warming. Hence, it is imperative to use eco-friendly refrigerants such as R-134a which has zero ozone depletion potential and lower global warming potential. Every customer must opt for higher energy efficient products even if the initial cost is higher by approximately 25 per cent as the additional cost of investment can be recovered in less than 24 months and after that the customer will save month after month.
Many studies have proved that use of high efficiency, low IKW chillers in HVAC can give better energy savings as against the standard chillers in the market. The reduction in energy costs for chiller operations can vary between 10 – 25 per cent, depending on the usage and design of the system. Payback periods for retrofits can range from three to five years. “With the current state of the environment and the impact of climate change so strongly visible, the question is not of the economics of eco-friendly chillers as we have crossed the tipping point. The time is now to put in the best possible chiller available irrespective of cost so that the environmental impact of chiller operations can be minimal,” informs Aneesh Kadyan, Aneesh Kadyan, Executive Director, CBRE
Variable speed drives can help to reduce fan and pump capacities and speed and thus, lead to reductions in both peak and off-peak energy. “They pay off better if the systems they are applied to operate at part load for relatively long hours. Variable speed pumping can dramatically increase energy savings, particularly, when it is combined with demand-based pressure controls,” states Pisal from Godrej Green Building Consultancy Services.
Achieving efficiency in HVAC
It is important to select the right HVAC products and systems while designing green buildings. For example, by installing and operating a more energy efficient product the customer can achieve lower energy demand even if the product has a slightly higher initial investment.
Optimising the operations and maintenance of an HVAC system in a green building is a key to achieving efficiency. According to Murthy from ISHRAE, a good facility management system can achieve it in following multiple ways:
- Re-commission an HVAC system regularly to operate as per original design or an upgraded design.
- Monitor minute operations of pressure, temperature and current extensively with multiple individual sensors to detect likely failure or higher energy consumption and take action to prevent it or reduce it.
- Improve efficiencies of subsystems, one or two at a time by retrofitting complete system components – such as Air Handling Units (AHUs), pumps and chillers.
- Routine maintenance, predictive maintenance to change parts based on its running time.
- Plan on operating systems at part load based on varying demand using variable speed drives connected to occupancy or temperature sensors.
If the plant and associated systems are maintained regularly and correctly, then the system will run to its design parameters and the energy consumption will be optimised. “Another key factor is to run the plant and systems as per the OEM recommendations, especially, the loading of the system. Design changes in the work space require changes to the HVAC system but in the most cases, this is not undertaken resulting in improper loading of the system,” states Kadyan.
Thangam observed in many applications that installation of Variable Frequecy Drive (VFD) driven HVAC equipment result in maximising the overall efficiency of HVAC systems. “Additional incorporation of heat recovery system for fresh air applications can also enhance the efficiency,” he suggests.
Another key factor that is driving the demand of sustainable HVAC systems is the cost of running plants and operating buildings. There is pressure from the occupants to reduce operating expenses and since the HVAC system is a major contributor to the energy cost, building owners are looking at bringing down costs by use of more efficient chillers.
Now a days, consumers prefer HVAC systems with lesser energy consumption. There is also greater emphasis by the government on promoting more energy-efficient equipment. The recent Chiller labelling program and India Cooling Action Plan are some of the important initiatives by Government of India to encourage the use of energy efficient of HVAC equipment in India.
Green buildings require selection of the most energy efficient equipment including HVAC. “These energy efficient systems offer the least life cycle cost even though they may have higher initial purchase cost. Generally, energy efficient HVAC products used for green buildings would have a return on investment of less than two years. The average of life of these are around 10-15 years thereby, resulting in significant savings on the operating cost every year,” states Thangam from Blue Star.
Echoing the opinion of Thangam, Murthy adds that customer or occupant delight can be enhanced due to enhanced system reliability and efficiency; improved indoor environment quality and low HVAC systems failure. Reduced energy costs can be used to amortise retrofit costs.
Although HVAC systems offer many opportunities for recovery and re-use of thermal energy, the preferred solution is to use less energy in the first place. This is achievable by more energy efficient buildings, systems and equipment and through improved operating and maintenance procedures. “More attention should be paid to the thermal characteristics of building and strategies for minimising internal loads, examining in detail the opportunities for natural ventilation and daylighting, and exploring ways to reduce the energy requirements of HVAC,” suggests Pisal from Godrej Green Building Consultancy Services.
By Supriya A Oundhakar, Associate Editor