Mechanical systems — heating, ventilation,
air-conditioning, and the associated component such as fans,
pumps, etc. for space conditioning — are the second largest user
of energy in most buildings, exceeded in most cases only by
lighting energy consumption.
Effective HVAC maintenance provides a number of
practices that can help reduce overall HVAC energy consumption.
• Focus on keeping people comfortable instead of
keeping buildings in “comfort zones.” Where possible, provide
temperature for spaces according to their function to reduce
HVAC loads (e.g., hallways can be cooler in the winter and
warmer in the summer than office areas). Allow occupants to
self-regulate temperature within a predetermined range through
better access to vents and thermostats;
• Install blinds, window shades, and other
devices to control HVAC loads in areas with load factors not
considered in the HVAC control loop (e.g., leaky windows, heat
gain in east and south facing offices, poorly insulated walls);
• Look for low-cost or no-cost
system modifications, such as changing operation procedures or
automating system settings, and
• Stay current on routine
maintenance practices.
Field studies and
computer-based simulations of commercial HVAC equipment revealed
that “common” problems with equipment and controls can increase
a building’s energy consumption about 15 to 30 percent. Often,
these problems can be eliminated by better maintenance and
inspection practices.
Locating and sealing leaky
ducts in older buildings is another area where system efficiency
can be improved. Leaky ducts can account for 25 to 30 percent of
the energy losses in HVAC systems.
Therefore, you may want to
consider implementing a systematic and regular inspection and
maintenance program to locate and fix leaky ducts throughout the
buildings and systems. Similarly, insulation on ducts, hot water
lines, and chilled water pipes and fittings should be repaired
or added where missing.
While a program such as this
may requires a higher effort, it can pay for itself. Note that
the typical duct leakage in light commercial buildings has been
found to average about 26 percent of the fan flow, which is
nearly 50 percent higher than the average leakage of 17 percent
found for residential duct systems.
HVAC systems can suffer from
infrequent inspection and maintenance without a comprehensive
schedule by the maintenance staff — overworked staff sometimes
inspect the system only if problems are reported.
One of the most simple and
effective methods of increasing an HVAC system’s airflow and
efficiency is to inspect and replace system air filters on a
regular basis. Clean air filters increase airflow through the
system, resulting in improved system efficiency, indoor
air-quality, and better occupant satisfaction.
Filters work by capturing dust
particles through a variety of common methods: centrifugal,
gravity, screening, impingement, and adsorption. For filter
material, there are two separate metrics to determine their
performance:
Filter Efficiency refers to
how well the filter material works to remove dust particles from
the air stream.
Pressure Drop measures how
much fan energy is needed to move air through the filter
material. Maintaining a proper pressure drop across filter
materials is an extremely important maintenance task, as dirty,
too thick (or the wrong thickness), and poorly designed and
maintained filters can create a system pressure.
A higher pressure drop forces
the fan or fans in the system to work harder, thereby consuming
additional energy. The higher pressure needed also increases fan
noise and vibration, can result in duct leakage, and generally
increases the wear and tear on the entire mechanical system,
resulting in increased maintenance needs and costs.
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