Specifications

18
CONTROLLING PUMPS AND VALVES
The unit logic should control the pumps
and/or heat medium bypass valve rather
than any remote system such as BMS.
Field-supplied voltage is provided to terminal
CM1 in the junction box. This voltage is then
controlled through dry-contact relays by the
unit logic. See Figure 3 – Controls Wiring
Diagram for further details.
1. Chilled Water Pump Control: The unit
logic will output the voltage provided to
terminal CM1 to terminal P when the
chilled/hot water pump is demanded.
2. Cooling Water Pump Control: The unit
logic will output the voltage provided to
terminal CM1 to terminal CP when the
cooling water pump is demanded.
3. Heat Medium Pump Control: To control
the heat medium pump, use the dry contact
terminals S3 and S4 in the right section of
the junction box. A jumper may be placed
between CM1 and S3 if necessary to
provide voltage for the dry contacts. Unit
logic will close the factory-supplied dry
contacts between terminals S3 and S4
when the heat medium pump is demanded.
4. Heat Medium Bypass Valve Control: To
control the heat medium bypass valve, the
unit logic will output the voltage provided to
CM1 to terminal P3A when the unit logic
wants heat medium flow through the
chiller/chiller-heater. Similarly, the unit
logic will output the voltage provided to
CM1 to terminal P3B when the unit logic
wants the heat medium flow to bypass the
chiller/chiller-heater.
While it is preferable to have both a Heat
Medium Bypass Valve and control of the
Heat Medium Pump (P3), there are times
where this simply cannot be accomplished.
In such cases, by using modified wiring, just
having one of these two devices is enough to
control heat medium flow through the unit.
If the unit has a Heat Medium Bypass
Valve (HMV), but does not have control of the
P3 pump, then wire the valve as shown in
Figure 17. This configuration will allow any
alarms or control signals that would normally
be directed to the P3 pump to act on the
HMV instead. If only one device is possible,
the HMV is the preferred device as it will
provide positive shut off during the off cycle,
preventing any possible thermal siphoning.
Figure 17 – No Control of Heat Medium Pump
If the unit has control of the P3 but not of
the HMV, or there is no HMV at all, then wire
the P3 pump as shown in Figure 18. This
will allow any alarms or control signals that
would normally act on the HMV to act on the
P3 instead. Be cautious. Without the HMV,
there is no positive shut off in the off cycle,
and thermal siphoning could occur easily.
Anti-thermal siphoning steps will be crucial.
Figure 18 – No Heat Medium Bypass Valve
COOLING TOWER FAN CONTROL
The unit logic can control the cooling
tower fan if necessary. It is a simple On-Off
control scheme, but it is better than nothing
at all, provided the cooling tower fan in use
can handle being cycled in that fashion.
This control scheme should not be
considered superior to other methods of
cooling water temperature control such as
VFD fans, etc. and should not be used in
conjunction with any other method of cooling
water temperature control.