REDUCE LOADS, MAINTAIN COMFORT, SAVE MONEY

Your building’s heating, ventilating and air conditioning (HVAC) system includes the equipment and distribution duct network required to move heated and cooled air throughout your building.  HVAC systems are large consumers of energy and significantly affect the health, comfort and productivity of building occupants.  The operation of cooling systems, in particular, often coincides with utility peak demand pricing periods.  Prior to upgrading your HVAC system, you should attempt to reduce your required heating and cooling loads by exploring opportunities to tighten your building shell and to improve the efficiency of your lighting system and other building equipment.  Upgrades to your HVAC system can require significant investments in time and resources. You will likely want to consult an HVAC system professional and have a formal energy audit of your facility conducted.  The answers to the questions below will help you identify some simple steps you can take to improve your existing HVAC system’s performance and will also give you some initial guidance regarding issues to consider in retrofitting your system.

HVAC FAQ

1. What should I do prior to upgrading my HVAC system to reduce my building’s heating and cooling loads?
2. What are some basic tips that I should consider when upgrading my building’s HVAC system?
3. What types of control systems can be used to reduce my HVAC system’s energy use?
4. What basic maintenance procedures can be used to help the HVAC system operate more efficiently?
5. What basic information should I know about air handling systems?
6. What are some of the best opportunities for reducing energy consumption with air handling system upgrades?
7. What basic information should I know about heating and cooling systems?
8. What are some alternative strategies for meeting heating and cooling loads?
9. What incentives and rebates are available to help reduce the cost of my HVAC system upgrades?

1. What should I do prior to upgrading my HVAC system to reduce my building’s heating and cooling loads?

• Tighten your building shell by adding insulation and sealing leaks.
• Install energy-efficient windows or retrofit existing windows with appropriate films.
• Upgrade lighting systems to reduce heat emitted to conditioned spaces by inefficient lighting technologies.
• Take steps to reduce solar gains in the cooling season and to increase solar gains in the heating season.
• Select efficient office equipment to reduce heat output.
• Control ventilation to improve occupant comfort and to save energy.
• Use fans to increase occupant comfort at higher temperatures and humidity levels.

2. What are some basic tips that I should consider when upgrading my building’s HVAC system?

• Implement efforts to reduce heating and cooling loads by tightening your building’s shell and upgrading your lighting system before sizing your system.
• Avoid oversizing equipment.  Oversizing increases both initial capital and long-term operating costs.  Have an HVAC professional perform a Commercial Load Calculation according to the Air Conditioning Contractors of America guidelines to properly size your system.
• If you are purchasing room air conditioners or light commercial heating and cooling units, select ENERGY STAR® qualified equipment.
• Install programmable thermostats and establish automatic settings to reduce energy consumption.
• If purchasing condensers or evaporator fans, consider specifying variable speed drives.
• Specify National Electrical Manufacturers Association premium motors on HVAC equipment.
• In dry climates, consider using evaporative coolers to save energy for cooling compared to compressor air conditioners.
• If your facility includes processes that generate significant amounts of heat (such as cooking), consider installing heat recovery systems that can be used to pre-heat incoming air.
• Radiant heating systems that warm objects, such as the floor instead of the air, can be very effective in large volume interior spaces such as warehouses and garages and for outdoor areas like patios.

3. What types of control systems can be used to reduce my HVAC system’s energy use?

• ENERGY STAR® qualified programmable thermostats can be installed for relatively low costs and can be easily set to adjust temperatures to decrease heating and cooling loads at times when your building is not in use.
• Multiple zones can be used to allow building occupants in different areas to separately adjust temperatures and are particularly useful if your facility has both interior rooms and rooms with windows with south and western exposures.  Multiple zones help eliminate discomfort and wasted energy associated with measuring temperatures from one central sensor point.
• Demand (CO2) sensors allow your HVAC system to regulate the amount of ventilation air drawn into a space by the actual occupancy in a space instead of relying on assumed occupancy levels yielding energy savings and better air quality.

4. What basic maintenance procedures can be used to help the HVAC system operate more efficiently?

• Contract with a qualified HVAC maintenance firm to give your HVAC system a tune-up prior to both the heating and cooling seasons.
  • The North American Technician Excellence (NATE) is the nationwide, industry-endorsed certification program for residential and light commercial heating, ventilation, air conditioning and refrigeration (HVACR) technicians.  Ask your technician if they are NATE certified.
  • Heavy commercial, institutional and industrial customers should look for MSCA STAR® qualified firms that have been recognized for their excellence by the Mechanical Service Contractors of America (MSCA).  MSCA GREEN STAR qualified contractors have been further recognized for promoting sustainability in their organizations and for using sustainable mechanical services practices and green HVAC equipment.
• Air filters are inexpensive.  Clean or replace them regularly (based on manufacturer’s recommendations) to prevent the accumulation of dirt and dust that reduce both the efficiency of your system and the air quality of your facility.

5. What basic information should I know about air-handling systems?

• The Air Distributions Systems chapter of the ENERGY STAR® Building Manual contains an excellent detailed discussion of building air distribution systems and their components such as fans, filters, dampers and ducts. Some of the highlights include:
  • The air distribution system itself should be upgraded (including potentially insultating ducts) prior to selecting new heating and cooling equipment.
  • Fans that move conditioned air (i.e., cooled or heated) can account for up to 7% of an office building’s total energy consumption.  Typically, more than 50% of building fan systems are oversized by at least 10%.
  • The two types of air handling systems are constant volume (CV) systems that move the same amount of air whenever they are on and variable air volume (VAV) systems that change the air flow based on cooling and heating loads.  VAV systems offer substantial energy savings over CV systems, but CV systems are installed in a large percentage of existing commercial buildings.
  • CV systems can have reheat systems or constant-volume, variable-temperature systems to control different cooling or heating requirements for multiple zones.
  • If your building was built during the 1960s or 1970s, it may have a dual-duct CV system that maintains separate warm and cool ducting system and then uses local mixing areas to feed the proper temperature air into each zone.  Dual-duct systems tend to be inefficient, as a greater volume of air than is actually required to heat or cool a space is moved around the building.
  • Multi-zone CV systems use similar principles as the dual-duct system, but the air is mixed near the fans with dampers and then the conditioned air is fed to each zone at a different temperature based on its needs.  The multi-zone design allows for less duct work, is quieter and is easier to maintain, but energy is still wasted by the requirement for simulataneous heating and cooling.
  • Modern VAV systems can adjust to changing heating and cooling load requirements efficiently by varying the amount of heated or cooled air circulated to the conditioned spaces.  Dampers can be used to control air flow to spaces and variable-speed drive motors can be used to significantly reduce fan energy consumption.
  • Converting existing CV systems to VAV systems is a popular upgrade for building owners.

6. What are some of the best opportunities for reducing energy consumption with air handling system upgrades?

• Consider an approach that first examines the conditioned space and then works back through the system to the air handling unit to maximize efficiency gains.  Fixing downstream systems first may reveal opportunities for making adjustments to upstream equipment.  For more details on all of these opportunities, review the Air Distributions Systems chapter of the ENERGY STAR® Building Manual.
  • Optimize zone-level performance by recalibrating thermostats, inspecting dampers, disabling reheat systems in summer months, examining your system to prevent overcooling and regulating static pressure.
  • Convert constant volume (CV) systems to variable air volume (VAV) systems.  These conversions are among the most common HVAC system retrofits as they can reduce typical airflow requirements by up to 40%.  The conversion requires significant expertise and you will likely need to hire an engineering firm with HVAC experience to perform the work.  Simple paybacks (time required for the savings from your energy bills to equal the capital outlay for the building improvements without considering interest) can be as short as three years or up to more than 10 years depending on implementation costs and annual energy cost savings with implementation costs being the most variable.  Factors that can impact the implementation costs include:
    • Ease of access for the contractor to the zone dampers
    • Presence of asbestos-containing materials in the building
    • The age and condition of existing zone dampers and actuators
    • The presence of two actuators on your current system to independently control hot and cold air dampers.
  • Size fans properly.  Replacing oversized fans with properly sized fans that have premium-efficiency motors, energy-efficient belts and variable speed drives can be an excellent way to save money.
  • Install variable-speed drives on existing VAV systems to allow the speed of the motor to better adjust to changing air exchange demands.  Reducing a fan’s speed by 20% can reduce energy consumption by up to 50%.
  • Modify controls to optimize system scheduling based on seasonal demands, to reset supply-air temperature settings to prevent the wasteful reheating of overcooled air, to utilize economizers to cool the building with outside air when appropriate, and to implement demand-controlled ventilation systems to reduce the need to condition outside air when occupancy levels are low.
  • Select efficient motors that perform to National Electrical Manufacturers Association’s premium efficiency standards when replacing system equipment.
  • Consider replacing standard V-belts with cogged V-belts that grip better and slip less than standard V-belts to gain a 2-5% efficiency bonus.
  • Inspect ducts and piping for leakage or damaged insulation and use duct sealer, tape or insulation to repair as needed.
  • Repair old valves and steam traps to prevent significant wasted energy.
  • Use larger duct sizes to decrease fan speed requirements by reducing pressure drops.

7. What basic information should I know about heating and cooling systems?

• The Heating and Cooling chapter of the ENERGY STAR® Building Manual contains an excellent detailed discussion of building heating and cooling systems and their components.  Some of the highlights include:
  • Evaporator and condenser coils need to be cleaned regularly to enable proper heat transfer for efficient operation.
  • Heating and cooling systems are classified as either central systems or unitary systems.
  • Approximately 40% of all U.S. buildings larger than 100,000 sf utilize centralized chilled water systems with compressors.  Chiller plant efficiency can be improved with the use of controls to ensure proper sequencing, the resetting of chilled-water and condenser-water temperature with changing outdoor conditions, and the regular cleaning of tubes and cooling towers.  Other options for efficiency gains include replacing standard valves with low-friction units to reduce flow resistance, insulating chilled water pipes, replacing standard-efficiency or oversized pumps with premium efficiency, properly sized units, upgrading the chiller compressor and controlling chilled-water pumps with variable-speed drives (VSD).
  • Central heating systems are comprised of either boilers or furnaces with boilers and furnaces each accounting for approximately 30% of the heating of commercial building floor space in the U.S.
  • Boiler system savings can be achieved by replacing existing boilers with new properly sized energy-efficient units that can increase combustion efficiency by as much as 15%.  Staging multiple small boilers is generally more efficient than relying on a single large boiler if retrofitting the system.  To improve the performance of the existing system, consider insulating hot-water distribution lines, installing VSD controls on pump motors, installing a combustion monitoring and control system, and installing temperature and pressure reset controls and set backs, and installing a stack economizer.
  • Furnace system efficiency can be improved by replacing existing systems with new, more energy-efficient models, by using programmable controls to set back supply temperatures during unoccupied building hours, and by installing two-stage setback controls for electric furnaces.
  • Unitary systems are comprised of either a heat pump (for heating and cooling) or an air conditioner in a single or split package that are assembled at the factory.  Unitary systems cool 70% of commercial buildings in the U.S. and have median service lifetimes of 15 years.  Types of unitary systems include packaged rooftop units, split-system packaged units, air-source heat pumps, and ground-source, closed-loop heat pumps.
  • The Department of Energy’s Energy Cost Calculator for Commercial Unitary Air Conditioners can help you calculate projected energy costs for selecting different types of unitary systems and the potential life cycle energy cost savings for installing higher efficiency units.

8. What are some strategies for efficiently meeting heating and cooling loads?

• Air-side economizers can be used to assist in the cooling of a conditioned space by delivering outdoor air to the conditioned space when outdoor air temperature and humidity levels are appropriate.
• Heat recovery systems can be used to transfer the energy from the exhaust air of your HVAC system to incoming outdoor air in order to pre-condition the incoming air.
• Night precooling can be used in the summer when night temperatures are cool by setting the air handling system and economizer to flush the building with night air to reduce the temperature of the building mass, allowing it to act as a heat sink the next day.  An office building in Denver could save up to 18% on cooling costs from the appropriate use of night precooling.
• Evaporative cooling uses 75% less energy than compression air-conditioning systems and works by using the heat in the air to evaporate moisture from a surface, thereby cooling the temperature of the air.  These systems are most effective in dry climates.

9. What incentives and rebates are available to help reduce the cost of my HVAC system upgrades?

Incentives and rebates may be available to help your business with its HVAC system upgrade efforts.  Use the Energy Action Planner to identify opportunities that match your needs.