Basic Documentation
Table Of Contents
- Ventilation System Characteristics
- Constant Air Volume (CAV) 1-Position
- Constant Air Volume (CAV) 2-Position
- Low Air Flow (LAF) 1 & 2-Position
- Variable Air Volume (VAV)
- Ventilation System Functions
- 1. Small Testing and Analysis Facility
- 2. Small College
- 3. Large College or University
- 4. University Research Laboratories
- 5. Government Agencies
- 6. Government Research
- 7. Small/Mid-Sized Commercial and Industrial Firms
- 8. Large Commercial and Industrial Firms
- Life Cycle Cost Analysis
- Life Cycle Energy Cost
- Life Cycle Cost
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Siemens Industry, Inc. Printed in the USA
Building Technologies Division Document No. 149-980
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Life Cycle Cost
The annual energy cost along with the respective
ventilation system's initial cost, maintenance costs,
training costs, and other operating factors are then
used in determining the life cycle cost for the
ventilation systems being compared.
Normally a life cycle cost should cover at least 10
years and oftentimes a few years longer. A constant
air volume (CAV) system will usually provide the
optimum expenditure based upon a 2 to 4-year life
cycle. A VAV system will likely have the lowest life-
cycle cost based upon 5 or more years.
Note that ventilation system operating factors can
have a substantial effect on annual energy usage.
For instance, maintaining unnecessarily narrow
operating ranges for relative humidity results in
consuming large amount of energy due to extra
cooling and reheating. If only certain rooms require
tight operational parameters, they should be on a
separate HVAC system.
When feasible, use the exhaust airflow from offices
as part of the supply airflow for the laboratories. Be
sure to right-size equipment and not oversize central
heating and cooling equipment. Studies and
practical experience have shown that in large
laboratories with many fume hoods, about 30% to
70% of the hoods are either closed or only partially
used at any time. This yields an overall VAV
diversity factor of approximately 50%. Therefore,
select equipment with part-load operation and
variable conditions in mind. Rather than having one
or two large chillers, they should be sized in
incremental modules that will activate singly or in
tandem to meet variable loads while operating at
maximum efficiencies. Two chillers of unequal size
can provide more flexibility in matching variable
loads than one large one or two equal sized units.
Air duct sizing is important in that ducts should be
designed for low-pressure drops. Consider
designing the ventilation system with slightly
oversized ducts that can reduce pressure drops as
well as efficiently handle future needs.