Air velocity and airflow

The evaluation of energy conservation opportunities often neglects previously established requirements

mcreasing temperature

Figure 10.12 Sensible heat and latent heat.

mcreasing temperature

Figure 10.12 Sensible heat and latent heat.

for air velocity and airflow. As discussed above, the volume of air supplied and its velocity have a profound influence on human thermal comfort. ECOs which reduce airflow can inadvertently decrease thermal comfort. Even more important, airflow cannot be reduced below the volume of outdoor air required by codes for ventilation.

The design of an all-air or air-water HVAC system is much more complex that just providing a supply air duct and thermostat for each space. The completed system must be balanced to assure adequate airflow to each space, not only to offset the thermal loads, but also to provide the appropriate pressurization of the space.

It is a common practice for supply air to exceed return air in selected spaces to create positive pres-surization, which minimizes infiltration and prevents the intrusion of odors and other contaminants from adjacent spaces. Similarly, negative pressurization can be achieved by designing exhaust or return airflow to exceed supply air requirements in order to maintain a sterile field or to force contaminants to be exhausted. Any alterations in air supply or return requirements upset the relationship between supply and return airflows requiring that the system be rebalanced.

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