Use of Target Levels

It is the responsibility of the end user and the contractor to determine tar­get levels. It is essential that the target levels be specified in such a way that they can be unambiguously measured. It is also important that the respon­sibilities of each stakeholder be clearly defined, particularly in case some­thing goes wrong. This includes financial responsibilities. In addition to the designer and end user, other stakeholders are involved in the construc­tion of a plant or building. In the simplest case, the overall contractor takes care of the design and construction of the plant or system, and then the end user buys it. In this case only two stakeholders are involved. In more complicated cases, the number of stakeholders may total 10. For in­stance, the supplier side may be represented by the consulting engineer, manufacturer, ventilation contractor, and building contractor, and the end user side by the real estate company, plant owner, plant engineers, and other occupants.

The use of clearly defined target levels has become more and more im­portant in industrial ventilation. The targets must be realistic and verifiable

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 ki­logram of paper or fresh steam used (see the example at the end of this sec­tion).

The use of target levels is spreading to other branches of industrial venti­lation, and one big problem associated with the verification of system perfor­mance 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 en­tire 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 ge­neric targets for various reasons. In addition to physiological and toxicologi — cal factors, the process of setting occupational exposure limits involves expert judgments nearly always resulting in compromises in numerical values. Fur­thermore, 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 can­not 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 fu­ture. 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 differ­ent targets is just like selecting materials. The end user selects the IAQ, ther­mal conditions, energy efficiencies, and other efficiencies. Fulfilling all requirements in industrial ventilation is, of course, more difficult than in ma­terials 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.

In most cases the main steps in defining target levels relating to industrial ventilation are as follows.

Step!: Musts

Ascertain the requirements of laws, regulations, and standards related to legislation, processes, and equipment, and compare them with customer needs. Of course, before this step, needs of the end user—for example, eco­nomical boundary conditions—are identified. At this stage the tentative target levels have also been selected.

Step 2: Needs

Ascertain nonbinding standards, human comfort standards, guidelines, codes of practice, and custom needs.

Step 3: Target Levels

Define the target levels based on musts and needs.

Step 4: Design Conditions

Suggest and confirm with customer the outdoor or process conditions within which the target levels must be met (e. g., absolute maximum tempera­ture versus 95 percentile temperature).

Step 5: Reliability

Find out the customer reliability requirements of the process. Define and obtain the customer’s acceptance of the needs for ventilation system reliability (e. g., what is the allowed break-off time).

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