period two
Chilled-Water System Design
notes
Three-Way Valve Control
airflow | | | |
three-way | | | | bypass |
| | |
modulating | | | pipe |
valve | | | |
Figure 34
A three-way control valve is one method used to regulate the flow of chilled water through a cooling coil. As the space cooling load decreases, the modulating valve directs less water through the coil, decreasing its capacity. The excess water bypasses the coil and mixes downstream with the water that flows through the coil. As a result, the temperature of the water returning from the system decreases as the space cooling load decreases.
Systems that use three-way valves have the following characteristics:
nThe temperature of the water returning from the system varies as the cooling load varies.
nThe water flow through each load terminal (water through the coil plus water bypassing the coil) is relatively constant at all load conditions.
nThe pump energy is constant at all loads because the use of three-way valves results in constant water flow throughout the system.
nWater-flow balance is very critical to proper operation because the flow is constant.
