With urbanization, the public is increasingly surrounded by skyscrapers, which contribute to global warming. One of the main energy consumers in any building is the Heating, Ventilation, and Air Conditioning (HVAC) system. The HVAC system accounts for more than 40% energy consumption alone of any building. It is almost 17% of total electricity consumption worldwide, and 8% of worldwide greenhouse emissions. The system may deplete non-renewable resources, such as fossil fuels used for the generation of electricity or thermal energy. This contributes to environmental pollution in the form of discharge of contaminated water and air, lubricating oils, refrigerants, heat transfer fluids, particulate matter, and microbiological organisms.
By correctly insulating pipes, installing accurately sized units, and considering various types of HVAC devices, it is possible to save significant amounts of money while practicing sustainable business. However, one should be mindful that size affects pricing, too. A unit that is too small will not be able to keep up with demand. The results may be a shorter life span, uncomfortable temperatures, and greater energy use. A system that is too large costs more to purchase, will cycle more frequently, and will result in higher energy cost and wear. In either case, an improperly sized unit will result in economic loss. The best purchasing and operational cost estimates may be obtained from manufacturers.
The energy-efficient HVAC technologies for buildings have the potential to provide economic and environmental benefits. With proper planning and optimizing energy-efficient HVAC technologies, the potential in energy-saving can be achieved by up to 40%.
Today, HVAC systems are designed as per energy standards codes, such as American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) standards, to achieve higher levels of green building Leadership in Energy and Environmental Design (LEED) ratings. There are current HVAC technologies that are considered energy-efficient, improve environmental performance, and reduce total system costs. These technologies are described below:
- Underfloor air-supply systems/underfloor air distribution (UFAD)
This is an alternate method of conventional ceiling airflow duct. UFAD is a cost and energy-efficient method. All the external ventilation occurs near the occupants. Typical applications are large, high spaces like convention centers and airport terminals. This method is known as displacement ventilation. Another approach utilizes cabling systems for delivering conditioned air. It is flexible with the potential to deliver thermal comfort, ventilation quality, and savings. However, issues of discomfort due to dust and draft need to be investigated.
- Desiccant-based cooling systems/DeVAP (Desiccant Enhanced Evaporative) HVAC
These systems deliver cooling/heating with evaporation/desiccation in conjunction with thermal energy sources. Commercially available desiccants are silica gel, activated alumina, and titanium silicate. These systems use less electricity than a typical HVAC system with no harmful refrigerant (like R-32). Desiccant-based systems are more economical than refrigeration systems at lower temperatures and moisture levels. Typically, a desiccant dehumidification system is utilized for applications below 45% RH down to 1% RH. The difference in the costs of electrical power and thermal energy (i.e., natural gas or steam) will determine the ideal mix of desiccant to refrigeration-based dehumidification in each application. If thermal energy is cheap and power costs are high, a desiccant-based system will be most economical to remove the bulk of the moisture from the air.
- Variable flow volume (VFV) systems
VFV systems are ductless systems that are highly flexible in capacity and design. These systems use multiple compressors and provide part-load performance and zoned temperature control, saving energy while ensuring occupant comfort.
- Demand-controlled ventilation
Demand-controlled ventilation systems regulate ventilation and cooling, according to feedback provided by sensors and controls. Adjusting ventilation, based on occupancy can result in cost savings. Furthermore, using CO2 sensors can reduce over-ventilation. The biggest gain from this strategy is realized in low occupancy buildings. However, their use might be resisted by local regulatory bodies.
- Solar cooling and refrigeration
Various systems using solar power to provide cooling and ventilation exist. The availability of solar energy coincides with demand for cooling and therefore, provides a supply-demand match. Furthermore, these systems are environmentally friendly and reduce dependency on fossil fuels.
- Thermal energy storage
Thermal energy storage provides cooling capacity by extracting heat from storage material, such as ice or chilled water. It shifts the energy usage of HVAC systems from on-peak hours to off-peak hours when rates are lower, thus reducing energy consumption and capital costs.
- Energy recovery ventilation (ERV)
In ERV, energy is recovered in the exhaust air stream and uses a precondition (temperature and humidity) to supply air in the building. This process captures both heating and cooling output from the wastage outdoor stream. During summer ERV can pre-cool and dehumidify exhaust air, and during winter it preheats the air supply. ERV technologies save energy by reducing heating and cooling loads.
Performing regular maintenance on existing systems can optimize performance and reduce costs. This includes checking for leaks on the boiler, running a combustion-efficiency test on the HVAC system, running a periodical test for carbon monoxide (CO), removing corrosion regularly, and ordering general inspections to find out if this requires a basic repair or total replacement.
There are a number of simple, low-cost or no-cost methods of reducing the utility bill. These methods include giving special attention to the ductwork, considering zone heating, considering a programmable thermostat with a program that makes sense, testing economizers twice per year, and, if needed, replacing the economizer altogether.
When it comes to HVAC, there are many options to consider. If properly studied, it is possible to save a significant amount of money by selecting the best option and carrying out proper system maintenance. Ideally, these factors should be considered during the planning of a building’s construction. When this is done, the quality of human life improves substantially.
Here, this disclaimer informs readers that the views, thoughts, and opinions expressed in the article belong solely to the authors, and not necessarily to the author’s employer or organization.
Master in Environmental Engineering and Management from IIT Kanpur, has experience in academics and in corporate sector as a consultant. She has co-authored a book on disaster management and pursuing Ph.D. in Civil Engineering.
Department of Civil Engineering,
University of Toledo, Toledo, Ohio.