Bypass Valve Control - Daikin MicroTech III Operation Manuals

Bypass Valve Control

This section describes the operation of an analog output used
to control a valve that allows water to bypass a waterside
economizer and flow directly into a condenser.
When the bypass valve is closed, all water flows through the
waterside economizer before it flows through the condenser.
Figure 15: Bypass Control Diagram
Slave Control
The bypass valve is linked electrically to the economizer valve
so that the bypass valve closes as the economizer opens .
This provides a nearly constant flow of water through the unit
regardless of the requirements of the economizer . When there
is no cooling required, the bypass valve will be open and the
waterside economizer valve is closed allowing water to flow
through the condenser . This valve control option can be used
in either a variable or constant pumping system .
Bypass Control
The bypass valve and waterside economizer valve are
independently controlled . The bypass valve to the condenser
is closed in all states except the Fan only, Mechanical cooling,
and Economizer . The bypass valve is open when mechanical
cooling is required and the water is not flowing through the
waterside economizer . When the unit is OFF: Unoccupied,
both the bypass valve and the waterside economizer valve are
closed. No water is allowed to flow through the unit. This valve
control option is typically used in variable pumping system or a
constant pumping system with a bypass loop
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When the Bypass Valve is open, all water that flows into the
self-contained unit flows directly to the condenser without any
water going through the waterside economizer . There are two
different methods for controlling this valve; Slave Control and
Bypass Control .
Water Regulating Valve Control
In the Cooling state, the Water Regulating Valve stays at its last
commanded position when the last compressor is turned OFF .
When all compressors are OFF and a compressor needs to be
turned ON, the Water Regulating Valve must be driven open
long enough to prevent the compressor from being locked
out due to high pressure, but not so long that it is locked out
due to low pressure . The WRV Start Sequence described
below is used to make sure this is the case . This is required
when transitioning to the Cooling state from the Fan Only or
Economizer state .
In the Fan Only state, the Water Regulating Valve is normally
closed . The WRV Start Sequence described below is initiated
in the Fan Only state whenever all of the following are true:
• Cooling Status=Enabled or Off Ambient
• Airside Economizer operation is disabled or not installed
• Either of the following are true:
– Both of the following are true:
— Control Temperature Source is something other
than None
— Control Temperature > Occupied Cooling Setpoint
+ ½ the cooling dead band
– Both of the following are true:
— Control Temperature Source is set to None
— DAT > DAT Cooling Setpoint + ½ the cooling dead
band
107 OM 920-6 • MICROTECH UNIT CONTROLLER
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