Requirements for Indoor Environment

8.2.2.1 Air Conditioning Demands for Human Occupancy

Requirements for indoor environment quality must be discussed and de­cided before the air conditioning design is performed. Criteria for acceptable indoor air quality and thermal comfort must be set.

Health hazard due to exposure to contaminants by inhalation is the most important issue. International or national health and building regulations or codes and recommendations are used as basis for the discussion of what re­quirements should be used for design. In regulations, worker exposure limits for airborne gases are normally expressed as

Time-weighted average concentration, TWA, based on a 40-hour work week,

Short-term exposure limit, STEL, which can be exceeded for periods of up to 15 minutes, and

Threshold limit value, TLV, a concentration level not to be exceeded any time.

Combinations of different substances in the air might be more harmful than the added effect of the two substances.

Most industrial companies would like to set air quality requirements re­garding health hazard at a lower concentration level compared to values found in regulations. For example, when a TWA concentration is given as x kg per m3 of air for a certain contaminant, the required concentration level for design of general ventilation in an industrial enclosure could be chosen as one — third of that value. This value can be considered the target value for the first design.

Target values must be rough for early design and must be refined for later stages in the design process. The main reasons for this are that details often are scarce and that calculation methods are rough at early design. One exam­ple of selection of target values is shown in Table 8.1. Some target values are not possible to consider at early design but should nevertheless be satisfied when production has commenced. General advice should be used during the design procedure to avoid such exposure problems at the future work condi­tion.

The company must decide the air quality target values for breathing zones in the work environment after discussion with industrial hygienists and venti­lation engineers.

Design criteria with respect to health-hazardous gases could alternatively be given as an accepted daily exposure of contaminant (for each hazardous substance, or a combination of substances).

Hazards from explosions, spills, and extreme working conditions should be considered according to national regulations.

Target values for thermal conditions at different design stages must also be considered. One example, for a scenario similar to regular office work, is shown in Table 8.2. The activity level and clothing insulation of the workers must always be taken into consideration when target values are chosen. Dif­ferent target values other than the ones used in this table could be required, for example, for very cold and very hot and humid environments.

Air quality for breathing zone

First design

Main design

Evaluation

Odor from production processes, materi­als, and humans1

Humans

Use at least Q = 0.7 17(sp)N + 1.0 L/(sm2^), where N is the number of persons and A/ is the floor

COz level < 650 ppm over outdoor level

Processes and materials

Avoid release of unpleasant Use local extract odor from processes and materials

Tracer gas experiment with mathematical or physical model to check efficiency

Humidity

Avoid condensation on surfaces

20% < RH < 60%

Particles

Avoid release of particles

Use local extract

< 20 Hg/m5 for PM7 ?-

< 40 Ug/m’ (d < 0.05 |im)

< 90 Hg/m’ (all diameters)

Health-hazardous

Radon

Check ground

On construction site

< 200 Bq/m’

TVOC

Avoid moisture and release of fuels and similar contaminants

< 400 ug/m’1

Other substances

Use environment-friendly substances Use one-third of regulation TWA

Concentration in breathing zones lower than chosen target value

Regulation concentration limits given by local authority

‘European Committee for Standardization. CEN/TC 156/WG6 Ventilation for Buildings: Design Criteria for Indoor Environment. Draft, European Prestandard prENV 1752, June 1996.

2PM2 s is the concentration of the fraction of particles where at least 50% (by weight) have an aerodynamic diameter less than 2.5 nm.

The definition of the breathing zone and of the zone of occupancy must be revised at each stage in the design process to make the climatization design ef­fective and efficient.

Accepted acoustical conditions should be considered according to na­tional regulations.

8.2.2.2 Conditioning Demands Other Than for Human Occupants

Industrial processes often require environmental conditions within certain limits.

Air quality requirements may be set as content of particles and as con­tent of chemical substances. Other requirements for temperature, humid­ity, and air speed could be set. One example is the spray painting process, which is very dependent on a minimum relative humidity (RH) level to

TABLE 8.2 Example of Target Values of Thermal Conditions at Different Stages of Design

Thermal conditions for zone of occupancy

First design

Main design

Evaluation

Genera’ comfort

Relative air humidity RH < 70%

RH < 70%

Winter

(1.1 m above floor)

Air temperature 21 °C

Operative temperature 22.0-2.0 °C Air speed <0.16 m/s

PPD’ < 10%

(-0.5 < PMV < 0.5i

Summer

(1.1 m above floor)

Air temperature 25 °C

Operative temperature 24.5 ± 1.5 °C Air speed < 0.22 m/s

PPD < 10%

Local discomfort

Draft

Winter (ankles 0.1 m)

Air speed < 0.16 m/s

PPD < 20%

Summer (neck 1.8 m)

Air speed < 0.20 m/s

PPD < 20%

Vertical temperature gradient

<3°C (0.1—1.1 m above floor)

PPD < 5%

Radiant asymmetry

<10 DC for cold wall

< 23 °C for warm wall

< 14 °C for cold ceiling

< 5 °C for warm ceiling

PPD < 5 % with respect to cold wall, warm wall, cold ceiling, and

Warm ceiling

Hot or cold floors

19-26 0 C at surface

PPD < 10%

‘PPD—percentage of people dissatisfied.

Obtain a high-quality result. Refer to Chapter 2 and Chapter 6 for further information.

Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK


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