Heating and cooling systems consume nearly 25 percent of the energy used in commercial buildings in the United States. Only lighting systems rank higher in energy use. Before beginning a heating and cooling system upgrade other less costly upgrades should have been installed. These upgrades, in order of importance, are retro-commissioning, lighting upgrades, supplemental load reductions and air distribution systems.
By installing energy efficient upgrades in other areas it is possible to reduce the size of the HVAC system. Besides saving energy, proper sizing will reduce noise, lower equipment costs, optimize equipment operation, reduce future maintenance costs, and extend the life of the equipment.
Once your system is installed implement an annual maintenance program to keep the system running efficiently. Clean or replace filters regularly, verify proper refrigerant levels and air flows, and inspect equipment for malfunctions such as stuck dampers.
Central Cooling Systems
Chilled water systems (Chillers) consist of central chillers and air handlers connected by a network of pipes and pumps; and are most commonly used for large commercial, industrial, and institutional projects. Before starting a retrofit project consider using a building energy performance simulation program to evaluate how your building uses energy. This computerized program will allow the designer to see how modifications to any of the building’s systems will affect the building’s annual energy consumption.
Evaporative cooling typically uses less than one-fourth the energy of vapor-compression air-conditioning systems. Air is blown over a wet surface; heat in the air evaporates moisture from the surface and in turn lowers the temperature of the air. Types of evaporative cooling systems include direct, indirect and indirect-direct. Direct coolers are also known as swamp coolers and evaporate moisture directly into the air stream which increases the humidity. Indirect units cool the building supply air through a heat exchanger with a separate air stream cooled by a direct evaporative cooler. Indirect-direct coolers first cool the supply air indirectly and then directly.
Central Heating Systems
Boilers produce hot water or steam which is then distributed throughout a building to heat the floor space. Since boiler systems are typically more complicated than furnaces there may be a greater opportunity to improve efficiency. Replacement of an existing boiler with a new energy-efficient unit, sized to reflect reduced loads from other building upgrades should be a consideration. However, if replacement is not an option there are a number of retrofit options that will improve the efficiency of an existing boiler system, including insulation of hot-water distribution lines; combustion monitoring/control system; temperature/pressure reset controls; controls to set back temperatures during unoccupied hours; baffle inserts, stack economizer, automatic blowdown control system; etc. Whether replacing or keeping the old unit, a maintenance plan can provide significant energy savings.
Furnaces heat air instead of water and distribute to occupied spaces. If it is not feasible to replace the existing furnace with a new energy efficient model you can still install controls to set back the temperature during unoccupied hours. Two-stage set-back controls can be installed on electric furnaces.
Unitary Systems include packaged rooftop units, split-system packaged units, air-source heat pumps and ground-source closed-loop heat pumps. Unitary equipment cools about 70 percent of air-conditioned commercial buildings in the U.S. and is available as single-package or split-system units. Unitary system equipment includes an evaporator, blower, compressor, and condenser; but may also include an electric resistance or gas heater section, providing both heating and cooling. Regular tune-ups, correcting refrigerant charge, cleaning & adjusting and verifying economizer operation present opportunities for energy savings. Typically, due to expense and installation considerations, unitary systems are not replaced until the end of their useful life.
If replacement of a system is not economically feasible there are a number of low-cost improvements that can increase efficiency:
- Seal the duct system – replace damaged ductwork and seal joints with mastic.
- Install tight-fitting insulated dampers between the exhaust dampers and outside air.
- Insulate any portion of the duct system that is exposed to unconditioned air.
- Adjust the ventilation to match the occupancy of the building
- Reduce the temperature of the building during unoccupied times in winter months. Increase the temperature during unoccupied times in summer months.
- Program the air handler to cycle off during unoccupied periods.
- Balance the air handling systems to ensure that each zone receives the design air flow
Regardless of the age of the system routine maintenance should be performed at least annually1.
1EnergyStar
