Page 403 - Industrial Ventilation Design Guidebook

358 CHAPTER 6 TARGET LEVELS

by measurements. Different kinds of target levels can be set—for example,
for indoor air quality, temperature, energy usage, and various efficiencies. In
specific areas of process ventilation, the determination of target levels has
been a common procedure for a long time. For example, in paper machine
hall ventilation, the contractor guarantees the use of energy per produced ki-
logram of paper or fresh steam used (see the example at the end of this sec-
tion).
The use of target levels is spreading to other branches of industrial venti-
lation, and one big problem associated with the verification of system perfor-
mance has occurred. In the absence of clearly defined target values,
administrative regulations have been used as targets. However, administrative
regulations, such as occupational exposure limits, are seldom rigorous. In
most cases the fulfillment of these figures guarantees only satisfactory perfor-
mance of the system. On the other hand, the use of administrative regulations
as targets has obviously led to the prominence of equipment-based thinking
because of the lack of other, exact figures. Typically, in equipment-based
thinking the focus is placed on such parameters as fan power, performance of
filters, and efficiency of heat exchangers instead of the target value for the en-
tire system.
Exposure to air contaminants in work rooms is regulated by the occupa-
tional exposure limits (OELs) (see Sections 5.2 and 6.2). From the point of
view of design and construction, these limits cannot be regarded as proper ge-
neric targets for various reasons. In addition to physiological and toxicologi-
cat factors, the process of setting occupational exposure limits involves expert
judgments nearly always resulting in compromises in numerical values. Fur-
thermore, the national occupational exposure limits may differ from country
to country due to differences in national priorities, technological development,
and revising periods. Full harmonization among all industrial countries can-
not be expected in the near future. In addition, the legal status of the OELs
may vary from binding regulations for some substances to simple recommen-
dations for others.
In the ideal case the target level procedure for industrial ventilation
can be compared with materials selection. Somebody who wants steel AISI
316, for instance, just selects and buys it by specifying this standard. The
person will obtain steel with the desired properties, because the steel is
made according to the producer's quality requirements and the producer
guarantees its quality.
A similar procedure must be followed in industrial ventilation in the fu-
ture. If the end user wants target class 1, the manufacturer must produce it. If
the producer fails to deliver target class 1, the end user can ask the producer to
make changes in the system such that the target can be achieved. In the worst
case the producer will have to change the whole system. Specifying the differ-
ent targets is just like selecting materials. The end user selects the IAQ, ther-
mal conditions, energy efficiencies, and other efficiencies. Fulfilling all
requirements in industrial ventilation is, of course, more difficult than in ma-
terials production, because industrial ventilation is affected by many different
items that may be outside the hands of the contractor. In any case, all relevant
items should be attached to the contract.