29
FORM CIM 0203
content of the air.
When these conditions meet the setting selected on
the enthalpy sensing unit, a SPDT switch is ener-
gized and a call for cooling from the first stage of
the room thermostat is then directed to the damper
controller, which is usually mounted in the condi-
tioned space near the regular thermostat.
The damper controller has its own temperature sen-
sor, which causes the unit to send a signal of vari-
able strength to the damper motor(s), depending on
the difference between the sensed temperature and
the selected setting on the controller.
This signal controls the ratio of how far open the
outside and re-circulated air dampers are to each
other, resulting in just the right amount of outside
air that must be introduced into the room to main-
tain the selected temperature that has been set on
the damper controller.
Some accommodation must be made to exhaust ex-
cess air, brought into the conditioned spaces from
outside. In the case of a full economizer installa-
tion, this can be as much as the total volume of air
circulated in normal cooling operation.
When outside conditions are no longer suitable for
cooling the conditioned space, the outdoor air en-
thalpy sensor will return control of room tempera-
ture to the regular room thermostat , which will then
cycle the compressors on and off as required to
maintain the set space temperature.
Refer to the system electrical control circuit dia-
gram for proper wiring to integrate the enthalpy
sensor and damper controller into the remainder of
the system control circuitry.
ECONOMIZER OPERATION –
(WATERSIDE)
The waterside economizer is also referred to as a
“free cooling coil”.
The free cooling coil is installed after the DX cool-
ing coil in the cabinet.
is to be mounted in the outlet line of the coil.
COMPRESSOR
The standard compressor is reciprocating. Scroll com-
pressors are available in certain sizes and voltages.
THREE-WAY WATER REGULATING
VALVE
Three-way water regulating valves modulate the
water flow through the heat exchanger to main-
tain the head pressure.
HIGH PRESSURE WATER REGULAT-
ING VALVE
Water regulating valves with a pressure rating of
350 PSIG are available.
ECONOMIZER OPERATION
(AIRSIDE)
The optional economizer operation utilizes outside
air as much as possible for temperature and humid-
ity control in the conditioned spaces.
To ensure that outside conditions are suitable for
this, an enthalpy sensor, mounted in a position
where it is continuously exposed to the ambient,
decides whether a call for cooling is best answered
by mechanical cooling or by a mixture of outside
and re-circulated air. If the system brings in a con-
tinuous supply of some fresh air, the sensing unit
can be mounted on the duct with the sensor in the
air stream.
The enthalpy sensor and its associated signal con-
ditioner measures both humidity and temperature.
The combination of both determines the total heat
FIGURE 26:
3-Way Single Circuit
0025CA
Condensing
Coil
3-Way
Valve
Water
In
Water
Out
Tee
Содержание 4CA1901
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