Page 562 - Mechanical Engineers' Handbook (Volume 4)

7 Equipment for Environmental Control 551

Figure 11 CFD result for CO 2 distribution in an office with displacement ventilation (blue, fresh air
with CO 2 around 350 ppm; red, room air with CO 2 over 1000 ppm).

tages, so coupling of simulation tools is the way to mitigate respective weaknesses and create
a new generation of building environment simulation programs. The coupling of energy
simulation and CFD programs is not a new idea. Chen (1988) was probably first to show
how coupled energy simulations and CFD can provide more accurate predictions of cooling
loads for different cooling and heating systems. Furthermore, recent coupling of multizone
and CFD models (Yuan and Srebric, 2002) has shown how CFD models can help increase
the accuracy of multizone models while the multizone model eliminates the requirement of
applying CFD to the entire building. Future generations of building simulation software will
integrate all the components: energy, CFD, and multizonal modeling. Such a sophisticated
tool will allow building HVAC designers to accurately calculate the heating/cooling load,
thermal comfort, indoor air quality, and contaminant concentrations while exploring different
innovative HVAC solutions.

7 EQUIPMENT FOR ENVIRONMENTAL CONTROL
The capacity of the HVAC equipment based on indoor and outdoor design conditions and
U factors for envelope assemblies or load simulation programs gives the HVAC equipment
capable of handling the peak design conditions. It is important to notice that besides the
performance requirements (removal of contaminants) and capacity requirements (building
loads), an HVAC system also needs to satisfy spatial, initial cost, operating cost, reliability,
flexibility, maintainability, and other special requirements. HVAC systems are typically cou-
pled with heating/cooling production systems such as boilers for production of hot water or
steam and chillers for production of cold refrigerant. Based on the fluid used to condition
building spaces, an HVAC system can be all-air, air–water, or all-water systems. In the United
States, all-air systems are the most widely used for environmental control. These systems
include air-handling, air-distribution, and control systems.

7.1 Air Handling and Distribution Systems
Air handling and distribution systems have a capacity calculated based on the design thermal
loads. Heaters, coolers, and humidifiers are sized for the air-handling system, while supply/