Trane TRG-TRC014-EN Variable Air Volume to the Space, warm, cool, Components of a VAV System

period two

Components of a VAV System

notes

Variable Air Volume to the Space

100%		heating		tempering	maximum
					primary
					airflow
to space		warm
airflow		primary air			minimum
					primary
%
			cool	primary air	airflow
0%	design				design
			space load
heating load					cooling load

Figure 35

As before, this graph indicates how the air supplied to the space by the terminal unit varies as the space loads change. The vertical axis indicates the total airflow (cool primary air plus warm primary air) supplied to the space. The horizontal axis indicates the space load.

To deliver a variable volume of supply air to the space in a two-fan, dual-duct system in the cooling mode, the dual-duct unit is controlled in the same manner as the cooling-only unit. The cool primary airflow is reduced as the cooling load in the space decreases. When the space cooling load drops below the minimum cool primary airflow setting for the unit, overcooling the space, the second modulating device begins to open. This allows the warm primary air to mix with the cool primary air and provide warmer supply air to the space.

As the cooling load decreases further and the space requires heating, more warm primary air is mixed with the minimum amount of cool primary air.

TRG-TRC014-EN 23