Commercial / Industrial HVAC
January 25, 1999
Overview: Propane gas can be used as a cost-saving, high-performance energy source in a wide range of commercial/industrial HVAC applications. The use of propane in heating and cooling has increased for several reasons, including the low cost of propane compared with electricity, improved heat transfer designs, greater venting options, improved combustion technologies and other advancements.
Heating: The four main commercial/industrial heating applications for propane gas are boilers, infrared heaters, make-up air systems and unit heaters.
Boilers: Boiler systems today have been improved through more effective burners, more efficient heat transfer material and design, electronic control circuits and modular systems. Traditionally, boilers often were oversized to meet or exceed peak demand. (Actual system load usually was much lower than design load.) Now, however, propane can be used to fuel modular boiler systems — a series of boilers connected by piping. These systems achieve higher operating efficiencies (up to 88 percent) and are flexible enough to meet the varying load requirements that occur in space heating in large buildings.
Infrared Heaters: Commercial infrared heaters emit radiant heat that is absorbed by the objects it strikes, including floors, machinery, vehicles and people. These systems are ideal for transit boarding areas, drive-through banks and restaurants, garage bays with high ceilings, airplane hangars, outdoor patios, shopping center walkways, loading docks, golf driving ranges and other areas that need to be heated. Infrared heaters often are less expensive to use than air heating systems and operate at efficiencies of 84 to 90 percent. Since propane gas is clean burning and economical and does not require extensive piping, it is a preferred fuel for infrared heating devices and systems.
Make-up Air Systems: These systems bring outside air in though a heat exchanger, where the air picks up heat from the exhaust of a central heating device. For example, outside air at 10ç F is directed through a heat exchanger with 80 degrees F exhaust heat. The resulting warm air is circulated to areas that need heat. These devices are 100 percent efficient and can complement central heating systems in large buildings.
Unit Heaters: Unit heaters, which economically heat large volumes of air, are well suited for stores, showrooms, factories, warehouses, garages and greenhouses. Propane-fueled versions of these units are popular because of their ease of installation and low initial and operating costs. A unit heater consists of a motor, blower and heating element. Warm air is directed to areas as needed with adjustable controls. Unit heaters operate at 70 to 80 percent efficiency and can also be used to prevent condensation on cold walls, ceilings or other cold surfaces in buildings where moisture is prevalent.
Cooling: New improvements in gas space cooling systems can provide cost-effective alternatives to electricity in many commercial/industrial settings. Because of technology advances, more HVAC engineers are specifying propane gas for desiccant cooling, absorption cooling and chilling/heating systems that maintain high efficiencies over a wide range of load levels. Additionally, most propane-fueled cooling systems have few moving parts, resulting in quiet operation and minimal vibration.
Desiccant Cooling Systems: Desiccant or dehumidification cooling systems remove moisture from air before chilling it to cool spaces more effectively and efficiently. Before chilling, air passes through a desiccant wheel or other device that is filled with water-absorbing desiccant materials. An energy benefit is gained because desiccant dehumidified air requires far less energy and chilling system capacity to be effectively cooled.
Eventually, desiccant material becomes saturated and needs to be dried or 'regenerated.' This can be accomplished with heat from propane-fueled burners. Furthermore, when a propane gas-fueled refrigeration system is used with desiccant dehumidification, its waste heat can be 'bottom cycled' to regenerate the desiccant dehumidifier to further decrease overall energy consumption.
Absorption Cooling: Propane gas can be used to fuel burners in efficient, environment-friendly absorption cooling systems that use no CFCs or HCFCs. In absorption cooling systems, pressure in an evaporation unit is lowered until water, which is sprayed into the unit, boils at 39 degrees F. As the water evaporates, it absorbs heat. In turn, this process is used to chill contained, circulated system water to roughly 41 degrees F.
Absorption cooling systems have high coefficients of performance (COPs) that reach 1.4 when they operate at full capacity and 2.0 when they run at loads up to 60 percent. When the high efficiency is combined with the affordable price of propane, propane-powered absorption systems can be operated for one-fourth to one-third the cost of electric cooling systems.
Chiller/Heaters: Propane also can be used to power units that chill water for cooling systems. At the same time, propane can be used to produce thermal energy for space or water heating. By combining cooling and heating capabilities in one unit, chiller/heaters use less floor space than do separate space heaters and air conditioners.