Combination of Target Levels and Design Methodology

The combination of target levels and design methodology is of vital impor­tance. One of the main items in the INVENT program in Finland over the years 1991-1996 was the development and utilization of these concepts in the ventilation of industrial premises.1 Together, these two concepts form the basis for industrial ventilation systems.

The target level concept was introduced and developed by the Association of Finnish Manufacturers of Air Handling Equipment (AFMAHE) in 1985.2’3 In­door climate target levels have been utilized in the ventilation of public buildings, apartments, and offices for years.4-6 The Finnish Institute of Occupational Health began to develop the concept for industrial ventilation in 1991.7,8 The target level procedure for industrial air quality is described in more detail in Section 6.4.

In the design methodology, the whole life cycle of the process must be considered. The life cycle of the process can be divided into four parts: design, construction, operation, and end of the process. Each consists of different tasks. The design methodology process can be described as follows:

Given Data

• Collect and identify data that do not change during the design process, such as outdoor conditions.

• Understand the industrial process and identify subprocesses.

• Identify possible emission sources, occupational areas, effects of environmental parameters on production, needs for enclosure, and ventilation equipment.

• Divide the process in parts such that their inputs and outputs to the environment can be defined.

Building Layout and Structures

• Collect data on building layout, openings, and their properties as basic values for load calculations.

• Complete zoning of the building based on division of the process and building layout.

• Make space reservations and add structures needed for ventilation equipment.

Target Level Assessment

• Define target levels for indoor zones and outdoor conditions.

• Specify design conditions for which the target levels are to be met.

• Define target levels for ventilation system, such as reliability, energy consumption, investment, and life cycle costs, etc.

Source Description

• Determine characteristics of the sources and methods for calculation of local loads.

Calculation of Local Loads

• Calculate loads from individual sources to the environment.

Calculation of Total Building Loads

• Calculate total loads (heat, humidity, contaminants) from different subprocesses and the environment to ventilated enclosures.

• Take into account the fact that loads are usually time dependent.

Selection of System

• Select an applicable system on the basis of the target levels.

• Compare acceptable systems to choose the most desirable one.

Detailed Design

• Provide detailed layout and dimensioning.

• Design adjustment and control system.

• Consider special issues, such as thermal insulation, condensation risk, fire protection, and sound and vibration damping.

These are the main steps of design methodology. In some cases all the steps are not needed, but in most cases it is important to take all of them into consideration. In addition to the construction and the use of the system,

Attention should also be paid to its demolition. It is worth noting that the feedback is always a typical feature of the design methodology.

Using the procedure described above, the target levels can be deter­mined. Relevant calculation methods and expertise are needed in all the phases. Although the calculation of target levels takes place in different ways for particular cases, the basic procedure remains the same. The target level calculation also varies for different outside temperatures and different pro­cess parameters.

6. 1.4,1 Example from Paper Industry

Industrial ventilation in a paper mill is always combined with the process itself. Process ventilation together with machine hall ventilation has an impact on the energy efficiency of the whole process. Contractors assign target levels to environmental conditions in a machine hall for parameters such as air qual­ity, air temperature, air humidity, and draftiness. Another target level parame­ter may be the number of stops over a certain period of time. Table 6.1 gives the target levels for thermal factors combined with the design methodology of one paper mill ventilation case.

The setting of indoor air quality targets is much more complicated and in­dividualized. This is due to the fact that the chemical process in paper making differs from paper type to paper type. Also, the amount of particles is highly dependent on the speed of the machine, the percentage of recycled mass, and the percentage of “stone” in the paper.

The target level for particles in the air of a paper printing machine hall is 0.5 mg/m3, but in some cases the level can be as low as one-tenth of this num­ber. Tissue paper mills are very complicated in this respect. Depending on the process and other factors, the particle level can be as high as 10 mg/m3, bur levels as low as 1 mg/m3 can be found. The targets are selected between those figures depending on the type of paper mill.

The target level assessment process for paper machine halls is the result of long historical development. The performances of installed paper machine hall ventilation systems are measured very often and the results are compared with input data used as the basis for design. As a result of these comparisons cor­rections are made to the design process as necessary.

ЯВІ TABLE 6.1 Example of Target Values for a Paper Machine Hall Ventilation

Location

Air temperature

Air velocity

Machine room

•Winter

+ 20 °С

<0.5 m/s

•Summer

< outside temp + 5 °С

0.5 m/s

Basement

< +15 °С

•Winter

•Summer

< outside temp + 10 °С

’No visible condensation on the ceiling or absolute wafer content < outdoor water content f 20 g/kg,

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