Heating, ventilation, and air conditioning (HVAC) systems play a pivotal role in maintaining the comfort and health of occupants in commercial buildings. However, HVAC systems are also a significant source of energy consumption. It is estimated that approximately 10-20% of all energy produced in the United States is used for comfort conditioning of indoor occupied spaces. While there is a variety of cutting-edge HVAC technologies aiming to utilize more sustainable sources of energy and improve major system efficiencies, there are also sources of energy loss associated with HVAC systems that can be improved upon with much simpler means and without completely renovating existing HVAC systems.
Duct Distribution Leakage
Almost all modern HVAC systems involve conditioned air routed through distribution utilizing sheet metal ductwork. These ductwork distribution systems typically carry air that has been conditioned utilizing centralized HVAC equipment and pushed through the ductwork distribution with centralized fans within. Energy is spent in both the conditioning of this air, as well as at the fan to push or pull the air through the distribution. Losses associated with air leaking out of imperfections in the ductwork throughout the building can amount to considerable energy wasted. Typical HVAC ductwork distribution systems built in the last three decades can expect as much as 10% of the total system airflow and 30% of the total energy spent, to be wasted via duct leakage. By sealing and properly insulating ducts, energy losses can be reduced significantly.
HVAC Distribution Insulation
Another key way to improve the efficiency of commercial HVAC distribution systems is to ensure the entire system has high-performance insulation coverage. Improving duct insulation performance helps to prevent the loss of heated or cooled air as it travels through the building’s ductwork and minimizes heat transfer to unconditioned air in cases where ductwork is routed through unoccupied spaces such as attics or ceiling plenums. In addition, energy loss associated with poorly insulated hydronic heating and cooling piping systems, and steam systems, can attribute to as much as 15% of the total energy spent back at the boiler and chiller plants.
Building Management System (BMS) Control Schemes
A variety of modern control schemes can be implemented into existing systems to realize further energy conservation as well. Additional sensors and programming can be provided with all existing equipment in order to take advantage of some of these more modern control techniques. Demand control ventilation takes advantage of occupancy or air quality sensing in spaces with greater variability in occupancy such as conference rooms or auditoriums, and minimizes the energy spent associated with ventilating them by only introducing high rates of ventilation when the spaces are fully occupied. Night setback schedules utilize a building time clock, or occupancy sensors to scale comfort settings back and save additional energy in spaces that are typically empty at certain times.
Temperature reset schemes can be used both in air and hydronic heating and cooling systems as well. These reset schemes can work in a variety of ways. Still, the most basic concept is for the building control system to compare supply and demand of a given system and incrementally adjust the supply temperature of that system accordingly. For example, a hydronic boiler heating system may compare how many pieces of equipment connected to the hot water distribution are using heat, and scale how hot the water it makes accordingly, or the same system may compare the outdoor air temperature and anticipate demand based on ambient conditions and control how hot to make the water that way. Either way, reset schemes take advantage of the diversity seen in buildings, and only spend peak energy when contextual clues dictate it to be relevant. Much like the distribution improvements discussed above, all of these control schemes can be implemented on fully existing systems for building owners to realize energy savings without replacing major systems or equipment.
Conclusion
While there are many new ways to save energy and more sustainable solutions for buildings utilizing new HVAC technologies, implementing them can mean complete system renovations and major capital investments for the building owner. Ensuring distribution systems are optimized with minimal leakage and high-performance insulation, and by implementing modernized control schemes with existing equipment, building owners and managers can realize significant benefits from these relatively small investments.
Stay tuned for the full guide, coming in May 2023!
Written by:
Derek Day
Mechanical Project Engineer