Building Design and Construction Handbook - Merritt - Ventech!

HEATING, VENTILATION, AND AIR CONDITIONING 13.17
13.3.1 Significance of Design Criteria
Achievement of the desired performance of any HVAC system, whether designed
for human comfort or industrial production or industrial process requirements, is
significantly related to the development of appropriate and accurate design criteria.
Some of the more common items that are generally considered are as follows:
1. Outside design temperatures:
Winter and summer
Dry bulb (DB), wet bulb (WB)
2. Inside design temperatures:
Winter: heating �F DB and relative humidity
Summer: cooling �F DB and relative humidity
3. Filtration efficiency of supply air
4. Ventilation requirements
5. Exhaust requirements
6. Humidification
7. Dehumidification
8. Air-change rates
9. Positive-pressure areas
10. Negative-pressure areas
11. Balanced-pressure areas
12. Contaminated exhausts
13. Chemical exhausts and fume hoods
14. Energy conservation devices
15. Economizer system
16. Enthalpy control system
17. Infiltration
18. Exfiltration
19. Controls
13.3.2 Design Criteria Accuracy
Some engineers apply much effort to determination of design conditions with great
accuracy. This is usually not necessary, because of the great number of variables
involved in the design process. Strict design criteria will increase the cost of the
necessary machinery for such optimum conditions and may be unnecessary. It is
generally recognized that it is impossible to provide a specific indoor condition that
will satisfy every occupant at all times. Hence, HVAC engineers tend to be practical
in their designs and accept the fact that the occupants will adapt to minor variations
from ideal conditions. Engineers also know that human comfort depends on the
type and quantity of clothing worn by the occupants, the types of activities performed,
environmental conditions, duration of occupancy, ventilation air, and closeness
of and number of people within the conditioned space and recognize that these
conditions are usually unpredictable.