By Grainger Editorial Staff 9/15/23
Many commercial facilities serve a variety of purposes. Different areas of the building are created for different functions, including machine shops, office and meeting spaces, storage areas, dining rooms and data centers. Each of these areas has different recommendations for optimal temperature, humidity and ventilation levels to ensure occupant comfort, safety and productivity. With so many competing uses, how can building engineers ensure one HVAC system can deliver the appropriate settings for each area? One solution is a zoned HVAC system.
A zoned HVAC system divides your facility into zones that can be heated, ventilated, and cooled at different rates. Instead of keeping the entire building at one temperature, a zoned system lets occupants in different areas set their part of the building to a temperature that is comfortable for them.
Trying to keep a large building at a single temperature setting is a recipe for inefficiency. Not only will unoccupied spaces be heated and cooled, but some workers will likely end up uncomfortable. For example, a typical commercial facility might have an office area, a machine shop, and some warehouse space. The office workers will likely prefer a room temperature working environment, while machinery operators may want to turn the thermostat down a few degrees.
Compromising on a single temperature would leave everyone too hot or too cold. You might even see wasteful behavior, like cracking open the shop’s windows in wintertime, or space heaters running beneath office workers’ desks in the summer.
Equipment can also be impacted by the temperature. Some work areas might need to be kept cooler for the operation of machinery or computer servers.
HVAC zones let occupants set their working environment to a temperature that suits them. The system can also allow the temperature in unoccupied spaces like storage areas to fluctuate with the weather, saving on heating and cooling costs.
When linked to building automation controls, zoned HVAC can also switch off heating and cooling at different times throughout the building. For example, if your facility’s office empties out at 5 p.m. but the machine shop operates a second shift, a zoned HVAC system can idle the office area while continuing to cool the workshop. Within the office space, intermittently used areas like conference rooms can be operated as their own zone, with heating and cooling automatically switched on by occupancy sensors.
The U.S. Energy Information Administration estimates that heating and cooling accounts for more than 40% of energy consumption in commercial buildings, so investments in efficiency can pay big dividends. The potential savings from installing a zoned HVAC system will depend on your climate and the equipment being upgraded or replaced.
A study by the Pacific Northwest National Laboratory found that the changes made possible by zoned HVAC, such as minimizing airflow volume and turning off heating and cooling in unoccupied spaces, can reduce a building's total energy consumption by about 13%.
When installing zoned HVAC means upgrading to more efficient equipment, the savings can be greater. A Department of Energy study found HVAC energy savings could exceed 60% for an office building that replaces a single-zone gas heating system with a zoned system powered by a high-efficiency heat pump. And a Pennsylvania State University study found that retrofitting an office building with zoned HVAC controlled by occupancy sensors resulted in total energy savings between 36 and 43% during the cooling season.
The cost of converting a building to zoned HVAC varies widely, depending on which components will need to be upgraded. Some buildings may require extensive ductwork and entirely new air handlers. Other buildings may be able to retrofit much of their existing infrastructure.
Energy Star found the cost of upgrading a ducted commercial HVAC system could range from $0.67 to $7.10 per square foot, and a study by the American Council for an Energy-Efficient Economy found that upgrading a ductless HVAC system cost between $0.60 to $6 per square foot. These studies found a similarly varied payback period on the investment, ranging from a matter of months to over seven years.
For the building’s occupants, operating a zoned HVAC system can be as simple as adjusting the nearest thermostat. But behind the scenes, zoned HVAC relies on sophisticated building management software and versatile air handling machinery.
To keep zones at different temperatures, the building’s HVAC system needs to be able to selectively deliver heating and cooling to different areas. This can be achieved in two ways.
Variable Air Volume (VAV): A VAV system controls the indoor temperature by circulating air through ductwork. Inside the ducts, a network of automatic dampers open and close to direct heating, cooling, and ventilation to each zone as needed.
In a VAV system, the hot or cold air is typically supplied by a single large air handler, often located on the building’s rooftop. The air handler must have a variable speed blower fan to deliver only as much air as the system requires. This system has the advantage of only requiring a single rooftop compressor, but it requires installing and wiring a number of dampers in the building’s air ducts.
Variable Refrigerant Flow (VRF): Another method of creating HVAC zones is to selectively circulate refrigerant—rather than air—through the building. Instead of forcing air through ductwork, a VRF system has a variable-speed compressor that pumps refrigerant through copper piping to serve fan coil units throughout the building. As the refrigerant flows through the fan coil, it evaporates and absorbs heat from the air, and a fan blows the chilled air out into the room. In the winter, the refrigerant’s flow is reversed, and the system operates as a heat pump.
Instead of using dampers to adjust airflow inside ducts, a VRF system uses valves to control the flow of coolant to each zone’s fan coils. A thermostat also controls the fans that circulate air across the coils. The VRF system’s compressor, located outside the building, must have a variable speed pump to send only as much refrigerant through the building as demanded.
In addition to being highly efficient, a VRF system has the advantage of using relatively narrow copper pipes, rather than bulky air ducts. This can make installation considerably easier in a building that lacks a drop ceiling or crawlspace.
A VRF system can also be set up for high-efficiency heat recovery, using refrigerant to move excess heat from one area of the building to provide heating elsewhere. Heat recovery can be especially valuable for facilities with a persistently warm zone. For example, a network server room may generate so much heat that it requires air conditioning year-round. A VRF system can capture the server room’s heat in the winter and circulate it to other areas of the building, using it to heat other zones.
The primary disadvantage of a VRF system is that it does not provide ventilation, since refrigerant is circulated through the building instead of air. This means a VRF system will often be paired with a separate ventilation system that introduces fresh air to the room through ductwork.
A multi-split HVAC system is similar to VRF, circulating refrigerant from an outside condenser to indoor fan coils. Split systems are typically found in smaller buildings, since only a handful of fan coils can be served by a single condenser.
Regardless of which type of HVAC your building uses, a zoned system will rely on building automation software. A zoned system requires coordination to match the air handler or compressor’s output to the building’s demand. Building automation software can also enable energy-saving technologies like occupancy sensors, timed thermostat adjustments, and even lowering the blinds on sunny afternoons.
Upgrading your facility to zoned HVAC may bring big improvements in comfort and efficiency. Get more information about managing building operations here.
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The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.