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We believe this provides the opportunity for the control strategies to be further optimized to minimize cooling and reheat loads in the building.”Most organisations recommend a series of generic ‘tips’ for the operation of a HVAC system, that encourage best practice and good maintenance before significant funds are spent on upgrades. UK business Efficient Air says something as basic as assessing existing air change rates against minimum fresh air supply rates may provide an opportunity to significantly reduce supply and extract fan motor input power, and potentially heating and cooling load costs when installed in an Air Handling Unit. “Payback would be within 6 to 24 months,” the company says.It also recommends good practice benchmarks: “Measuring your existing systems performance and comparing with published best practice guides to identify worst offending systems for improvement as a monitoring and targeting exercise,” the company says.UK-based utility company National Grid has advice for its US customers on general monitoring of a building’s energy consumption: “Install paddle fans, stratotherm fans, or other re-circulating systems to create air movement,” the company says. “Ceiling temperatures can often be 30° to 40°C higher than floor temperatures, and air movement from fans can enhance the cooling ability of air conditioning systems.“Install time clocks, set-back thermostats, and microprocessor thermostats to monitor HVAC systems when buildings are unoccupied.”ASHRAE lists fifteen tips for operating a HVAC system efficiently:• Adjust workplace schedules to reduce energy use during the hours when there is most demand for electricity. If employees start work earlier or have lunch during the hottest hour of the day, a company can save on air conditioning, lighting and other electricity use during the hours of peak electricity demand.• Prevent solar entry and air-conditioning loss during the summer. Use shades and blinds to keep the sun out. Close doors to the outside to keep in cooler air. Perform regular maintenance to keep HVAC systems running more efficiently. Maintenance activities can save up to 30% of fan energy and up to 10% of space conditioning energy use.• Occupancy sensors can be used to turn off lighting and change zone temperature setpoints when spaces are unoccupied.• Reduce air conditioning and heating hours by installing a time clock to turn off the system when the building is unoccupied.• Perform regular maintenance on cooling equipment. Regularly clean condenser coils, change belts and filters and fix duct leaks. Also check for proper economizer operation and adequate refrigerant levels. Maintenance activities can save up to 30% of fan energy and up to 10% of space conditioning energy use.• Add controls to the exhaust fan. Ask an air conditioning contractor to install timers and switches to shut them off when they are not needed, such as when the building is unoccupied.• Perform regular maintenance on heating equipment. Inspect and patch leaky heating ducts. Fix steam leaks. Clean blower coils and heat exchanger surfaces.
Adjust belt drives, dampers, valves and linkages.• For US businesses, install an Energy Star programmable thermostat to automate the HVAC system. An “old-fashioned” thermostat turns the HVAC on and off based on temperature, not whether the building is occupied, or whether users benefit from the cooling/heating. A programmable thermostat can optimize HVAC operation 24/7. For example, instead of heating or cooling all night, so users can enter a comfortable building in the morning, this “smart thermostat” can turn on the HVAC one hour before users arrive, based on their daily/hourly needs. • Install a high efficiency HVAC system. • Install an energy management system (EMS), and save 30 – 40% on annual investment. An EMS is especially useful when the air conditioning system is too complex to control with time clocks or programmable thermostats. An EMS lets users choose different cooling temperatures for different zones, optimum equipment start and stop times and control strategies that keep building occupants comfortable while minimizing energy use.• Consider installing variable frequency drives (VFDs), and save 30 – 40% on annual investment. Air conditioning system has fans that move air throughout the building. It is possible to reduce the cost of operating these fans by installing VFDs, which can change the speed of the fan motors to match the amount of air that is needed.• When fan and pump motors need repair, consider replacing them with premium efficiency models, and save 35 to 45% on annual investment.• Pressurize and test all ducts for leakage.• Install utility meters to track HVAC energy consumptionBe holisticAlthough it is important to assess the equipment efficiency within the HVAC system itself, it is clear that the system cannot be viewed in isolation from other – perhaps design-oriented elements – of a building’s energy efficiency and consumption rate. It is not always possible to address the issue of energy efficiency at the schematic design stage in a building’s life, but as can be seen from the award winning example at California State University, taking a holistic approach to a system in need of an upgrade can work. As the US DOE puts it: “The best HVAC design considers all the interrelated building systems while addressing indoor air quality, energy consumption, and environmental benefit.”•