A Heating, Ventilation and Air Conditioning System (HVAC) is designed to maintain and control air temperature, humidity and purity. It is needed in most buildings to provide comfort for the occupants and ensure equipment works properly. It is important to maintain a whole-system approach to your HVAC as this will result in a much more energy-efficient system than considering components separately. The key to saving energy lies in sizing, installing, maintaining, and using the HVAC system correctly. It is important to choose the correct technology and type of system for your organisation's application. Since heating and cooling are major contributors to peak demand for energy, they contribute disproportionately to energy bills, which increasingly includes extra charges for high energy demand. This means great savings can be made by increasing HVAC efficiency. Other benefits include better working conditions and health for occupants. Improving your existing system Look at minimum air levels Outside air is used in most air-conditioning systems to control air quality (e.g. to remove odours and CO2). However, it is important to ensure that excess outside air is not used as this can increase the amount of heating or cooling required. This means outside air flow rates should match what is actually required, based on floor area and occupancy level. Modern control systems allow the ventilation rate to be varied with building occupancy. The minimum outdoor air supply is often set at 1 Litre/second/ square metre. This can be reduced where there is low occupancy or highly filtered air. Expert advice should be sought in this regard. Outside air economy cycles (also known as "free cooling") When the outdoor air temperature is at or below that required indoors, an economy cycle draws in outside air to cool the indoor space. This lowers the air conditioning requirements. Outside air economy cycles can also be used to control air quality by removing odours and CO2. For example, in the morning, when outdoor air is cooler, the economy cycle can operate until the temperature rises above what is required, then the air conditioning system can start up. Ensure the dampers used to control economy cycles are well maintained. Poor maintenance can mean the dampers jam partly open, allowing a constant volume of air into the system regardless of outside air temperature, therefore increasing energy costs. Optimal Start (flushing or night purge) Buildings can trap heat overnight, so on cool mornings it may be more economical to 'flush' the building with outside air before starting the air conditioning system. In mild weather, turn chillers on later and off earlier. Check the performance of your HVAC system Performance of HVAC equipment often deteriorates over time. Therefore, thorough maintenance programs can bring substantial, cost-effective savings (a sample of nine office buildings in Sydney that implemented such maintenance programs, achieved median energy savings of 23%). The ongoing annual cost of the maintenance program was typically around 15 per cent of the ongoing annual energy savings.

Save between 20% and 70% of HVAC operating costs by using and maintaining your system effectively. Ensure thermostats are not located near heat sources such as photocopiers, natural sunlight or space heaters. Regularly clean or replace filters. Control on/off times to avoid HVAC running unnecessarily. Check economy cycles to make sure energy is not being wasted by cooling and heating of excess outside air. Alter thermostat set points up and down by one degree in summer and winter respectively. Install glazing/tinting or blinds on windows to minimise heat gain from the sun. Use a night purge to flush out excess heat from the building in the early hours of the morning.

• Clean coils, fins and filters and replace filters in air-conditioners regularly. A dirty filter will mean more energy is needed to pump air across the coils. If the coils or heat exchanger become dirty, their efficiency will decrease and the building will not be able to maintain its temperature settings.
• Check for air leaks. Ensure no air is leaking from air ducts. Recent studies indicate that 10-30% of the conditioned air in an average central air conditioning system escapes from the ducts. Test for air leaks in ducts by listening, visually inspecting damage, or by brushing soapy water across joints and watching for bubbles.
• Seal air leaks around doors and windows.
• Insulate air ducts and pipes to reduce excess heated or cooled air being lost.

Check for a rise or drop in temperature in ducts and pipes by measuring the temperature at both the beginning and end of pipe runs. If there is a significant temperature change, upgrade insulation, especially if pipes are exposed to the outdoors or enclosed in a roof space that gets hot.

• Check thermostat calibration. Check sensors and controllers are operating correctly.
• An operational check on chillers and boilers, which can be done for a small cost, will indicate how efficiently the equipment is operating and what areas need attention. The staging of chillers and boilers is also important to ensure the correct equipment operates efficiently for the load of the day. Attention to chillers and boilers can reduce energy use by up to 30%.

2.Install controls

Control systems monitor the heating and cooling requirements of the building and vary the operation of the HVAC system to maintain comfort. They can also be part of a Building Management System (BMS).

• Systems in most commercial buildings automatically start and stop each day using a time switch or a BMS. Ensure the time switch is set to the correct time and does not start the plant on public holidays (saving 10 days out of 250 working days each year - a 4% saving).

Temperature controls

• Increase your thermostat set point by 1 to 2°C in warm weather, and decrease it in cool weather.
  For a minimal temperature change, large energy savings are possible whilst maintaining comfort.
• Chilled water or evaporator temperature controls can be increased in cooler weather, reducing energy costs due to the improvement in refrigeration efficiency.

Zone controls

• Different sections of a building may have different air conditioning requirements, depending on the direction of the sun and occupancy patterns. Depending on your existing system, it might be possible to divide the air conditioning distribution system into zones. This will save energy as only the sections that need air-conditioning will be cooled. It also means excessive reheat is eliminated. For example, in the morning, the east side of the building will need more cooling than the west side and zone controls can allow this to occur. If there was no zoning, the entire building would be initially cooled, and areas that become too cold (those not exposed to the sun) would have to be reheated.

CO₂ sensors

• These sensors monitor CO₂ levels in the air from people exhaling. Therefore they can modify air conditioning levels to match outside air volume to occupancy levels.

Variable Speed Drives

• Install variable speed drives on your pumps and cooling tower fans. This can generate large savings as a 20% reduction of flow = 50% of energy saved. See Motor Systems and Pumps and Fans sections for more information.

Calculate your savings

1. Download Free Software QuikChill. Users can assess potential chiller plant upgrades with economic and energy analyses. http://www.energystar.gov/index.cfmfic=business.bus_quikchill

QuikChill looks at a simple relationship between outdoor air temperature and the cooling load chillers must meet and calculates savings from each scenario. It also provides graphs of energy consumption before and after the upgrades.

As U.S. units are used, refer to the Units and Conversions section in this Manual to convert to the Metric system.

3.Installing a new system

• By replacing air conditioners that are more than 10 years old, you can save 20% to 40% of your heating and cooling energy costs. One way of doing this is to replace an old system with a newer, more efficient model such as a screw chiller with electronic expansion valves. See the Technology Table for more information.
• HVAC equipment varies in scale and complexity from a simple wall-mounted air-conditioner, through standard packaged units, to large and complex central systems with boilers to provide heat, and chillers and cooling towers to provide cooling.

When buying a new system, look for the Coefficient of Performance (COP) of the system. The higher the COP, the more energy efficient the system is. For room and split-system air conditioners, look for the star rating. The more stars, the more energy efficient the system is.

Size

It is important to purchase the correct size air-conditioner because buying an oversized air-conditioner can penalise you in a number of ways:

• It costs more, both in capital costs and energy costs, to buy a larger system than you need.
• The larger-than-necessary system cycles on and off more frequently, reducing its efficiency. This makes indoor temperatures fluctuate more, results in a less comfortable environment and wears out the compressor and electrical parts more rapidly.
• For most of the year, air-conditioners operate at partial load. Therefore, the size and number of chillers and boilers should be selected to operate efficiently at part load and should allow for future changes in load.
• It is important to choose equipment that will fit into the plant room and to allow sufficient space for it to be serviced and maintained.

More Information
– Australian Institute of Refrigeration, Air conditioning, and Heating (AIRAH) Great starting point for anyone interested in finding out more about HVAC systems. http://www.airah.org.au