The HVAC Factor: Thinking “Inside The Box”
By Bob Gray
Originally published in the January/February 2013 issue of Today’s Facility Manager
Today’s facility managers (fms) must continually look for ways to lower total cost of operations, and this includes reducing energy consumption and extending the life of heating, ventilation, air conditioning and refrigeration (HVAC/R) equipment to avoid capital expenditures. And, of course, fms are looking to achieve these goals with little or no out-of-pocket (capital) expense.
It is no longer enough to just properly maintain HVAC/R mechanical systems. Though maintenance is very important, with the cost of energy on the rise it’s almost impossible to decrease energy costs even if HVAC/R equipment is maintained and running as if it were brand new.
In the U.S., up to 40% of an electric bill is attributable to the costs for delivering that electricity, and that cost has been rising quickly. The increase can be explained by the ways utility companies are building transmission lines, repairing and revamping old power plants, and passing those costs to consumers through higher rates. Gas is cheaper, and much of the electricity used today is generated by gas; however, these savings are offset by the increase in delivery charges. In order for fms to decrease costs, they need to decrease consumption.
So, what can fms do if they are operating their facilities with reasonably well maintained HVAC/R systems, scheduled equipment “off times” through thermostats, and/or building automation systems, but still see utility costs increasing? What additional steps can be taken to decrease consumption, keeping in mind a comfortable, safe, and productive environment must be maintained?
One possible alternative to replacing mechanical systems is to upgrade or retrofit HVAC/R equipment with new and innovative machine controllers and components. This approach delivers substantial reductions in electrical consumption and does not require total equipment replacement. Thinking “inside the box” of existing HVAC/R equipment, here are 10 ways fms can make the most of energy consumption.
1.) Replace the control panel for an existing air-cooled chiller with one that provides innovative control algorithms and advanced function blocks to perform floating high-pressure and superheat control. This retrofit alone can yield up to a 30% reduction in energy consumption, extend the life of equipment, and typically provide less than a three year return on investment.
2.) Convert an air-cooled chiller’s constant speed compressors into variable speed compressor operation. For an air-cooled chiller, this means adding a variable speed drive to the existing compressor motor(s), a slight piping modification, and a new controller capable of applying the proper innovative application function blocks and control algorithms. This conversion reduces energy consumption and extends the life of the equipment. A typical return on investment for this retrofit would be less than three years.
3.) For centrifugal chillers, adding a variable frequency drive (VFD) to the compressor motor will yield significant reductions in electrical consumption. Substantial savings can be achieved during partial load conditions—which is nearly 95% of the time. For optimal machine control, fms should include a new controller containing the application function blocks and control algorithms for efficient and safe operation of the machine. Coupling the VFD with variable condenser water temperature control can result in even greater reductions in energy consumption by reducing the “lift” on the compressor. For most applications, this retrofit is a two to three year payback.
4.) Install a VFD on the supply and return fans for constant speed air handling units. Monitoring carbon dioxide and space temperature can ensure compliance with building codes and standards. Affinity laws indicate that with only about a 20% reduction in fan speed, operators will yield about 50% reduction in consumption.
5.) Employ heat recovery retrofits for 100% outside air intake air handling units. These energy recovery ventilation (ERV) add-ons typically pay back in three years or less.
6.) A retrofit of cooling tower fans with an intelligent VFD and controller yield, in many cases, up to a 50% reduction in energy consumption. The application of a VFD and proper controls for the cooling tower keeps the fan from cycling, which reduces kW and kWh while maintaining a constant temperature in the tower water basin.
7.) Apply VFDs to pumps to reduce energy consumption substantially. In many pumping systems, operators can apply a 20% reduction in motor speed and achieve similar reduced energy consumption results as in fan applications. Flow rate is a major consideration. Fms want to make sure to achieve at least the minimum flow rates required throughout their systems, or they may end up sacrificing comfort conditions or even damaging chillers and boilers.
Also key is incorporating some feedback (such as gallons per minute or space temperature and humidity) to help gauge just how much operators can reduce the speed of the pumps and still provide adequate heating and cooling for the facility. All pumps in a facility are candidates for variable speed drives.
8.) Upgrade combustion controller for boiler(s) in order to yield significant energy reduction. Recent advances in boiler control algorithms improve efficiency and reduce gas consumption. For larger boiler systems with multiple boilers and pumps, a central boiler plant optimization control panel is most effective.
9.) Add outdoor air economizers for ventilation and air handling units to bring in free cooling during those times when the outside air is within 55°F to 65°F. By coupling this action with better control of the facility’s ventilation system fms can yield huge reductions in energy consumption.
10.) Automate the entire central plant to optimize operation of all HVAC/R systems (chillers, boilers, pumps, cooling towers, AHUs) and assure they are all working together as one mechanical system instead of segregated individual components.
In most cases, implementing these types of changes requires working with a vendor partner to help determine which retrofits are best. Deeper internal control of HVAC/R equipment is a significant option for fms looking for new ways to reduce energy consumption.
Gray is HVAC/R OEM segment manager, Industry Business for Schneider Electric. With over 25 years of experience in the HVAC/R industry, his expertise range from commercial and industrial automated controls to large mechanical HVAC/R systems. He holds a Bachelors degree in Mechanical Engineering and Marketing.
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