Energy Reduction: Space Heating & Cooling
Commercial
and industrial buildings use a variety of air handling systems to
provide heating, cooling and ventilation. These systems are usually the
largest energy consumers in a building (unless there are a significant
number of electric motors in the facility).
In
addition to the primary functions of heating and cooling, a significant
part of this energy consumption is caused by ancillary functions such
as air delivery and reheat. Much of this non-core energy use can be
reduced or eliminated at relatively modest cost, with rapid payback.
Air Handling Systems: Air-handling systems typically have 3 elements:
- Intake, recirculation and exhaust
- Distribution & temperature control
- Exhaust fans
Intake, Recirculation and Exhaust:
This part of the system controls the intake of outside air,
re-circulates air between spaces and exhausts air back to the outside.
This determines the pressure in each space and therefore air flows
between spaces.
Distribution and Temperature Control:
These components of the system connect the cooling coils and supply
fans to the spaces. They move air between spaces and regulate space
temperature by heating, coling and controlling humidity of the air.
Exhaust Fans:
These fans, which exhaust air from spaces such as kitchens, toilets,
paint booths, welding shops etc,. are typically not connected with the
supply-side air system.
Where Energy can be Saved:
Experience has taught us that air-handling systems connected to
centralized chillers waste air in ways that smaller, ‘rooftop’ type
systems serving smaller spaces do not.
The main areas of waste are:
- Outside Air Intake Conditioning:
Outside air is significantly more expensive than inside air because its
temperate and humidity may differ substantially from that inside the
building. Many systems lack the capability of controlling outside air
makeup accurately.
- Fan Power:
Air handing systems connected to central chillers typically require
long duct systems to reach all the spaces. The cost of duct work,
frequently of smaller diameter to fit into tight ceiling spaces,
requires more powerful fan motors.
- Reheat:
Central air may need to be reheated in some spaces but not in others
(e.g. where there are windows or not). Both temperature and humidity in
the spaces are controlled in this way.
- Inconsistent Air Distribution:
Many air handling systems combine the functions of heating, cooling and
ventilation (i.e. the introduction of a controlled amount of outside
air). Systems typically cannot deliver adequate ventilation to all
spaces if they don’t all require the same amount of ventilation.
- Variable Air Volume Handlers:
Though some systems have individual damper controls, many don’t, and
therefore can’t control heating, cooling or ventilation to individual
spaces.
Variable air volume air-handlers, which
were designed to solve most of these problems are ubiquitous, but they
have not been entirely successful in doing so and many comfort and
efficiency problems remain. This may be due, in part, to system
designers trying to accomplish too many things with a single system.
One school of thought is to separate the functions of outside air
ventilation from those of heating and cooling , allowing purpose
designed systems to handle each in an optimal fashion.