Lennox International Inc. 505 - Manual (Page 10)

Page 10
EDA 01/06
EDA Unit Operation
The EDA coil is added to an HVAC system downstream of
the indoor coil. In dehumidification mode, the coil becomes
an extension of the condenser coil and injects heat into the
indoor air stream.
This dehumidification mode allows significantly improved
control of the humidity in the conditioned space without
overcooling the space. The assembly includes a set of
3−way diverting valves which will either route refrigerant
through the EDA coil, or cause the refrigerant to bypass
the EDA coil, depending on the mode of operation.
Operation Notes
1. IMPORTANT REMINDER! Dehumidification will not
occur when the outside temperature is at or above
95ºF.
2. When operating in cooling (or heat pump heating)
mode, all temperatures and pressures will be as in a
normal system.
3. When the thermostat is in HUMIDITROL mode, and
after a cooling demand has been satisfied but a dehu-
midification demand persists and the room tempera-
ture is not more than 2°F below the setpoint, the air
handlers will operate at reduced airflow with the com-
pressor at high speed.
4. When the unit is in the dehumidification
mode, the display will show a raindrop"
icon with an imbedded negative sign and
the current relative humidity to its right.
Cooling Mode (Dehumidification ON)
If the room thermostat’s cooling demand has been satis-
fied but the dehumidification setting has not been satisfied,
the unit continues to run in dehumidification mode. The
room thermostat sends a signal to the EDA unit’s 3−way di-
verting valve assembly to begin operating in the dehumidi-
fication mode.
Figure 9 shows refrigerant flowing from the outdoor unit,
entering the EDA, passing through the first 3−way diverting
valve, then entering the EDA coil. There, heat from the
warm refrigerant is transferred into the indoor air stream.
The refrigerant exits the coil through the second 3−way di-
verting valve and into the indoor coil expansion valve.
During dehumidification, the indoor air blower (and outdoor
fan, if an outdoor relay is used) operates at a lower air vo-
lume. The cool, dehumidified air leaving the indoor coil is
warmed as it passes over the EDA coil. Air temperature
rise across the EDA coil can be from 10° to 25°F, depend-
ing on the operating ambient and air-conditioned space
conditions.
The warm vapor−liquid−refrigerant mixture entering the
EDA unit from the outdoor unit will be subcooled in the EDA
unit and enter the expansion valve at a lower-than-normal
temperature. Liquid temperatures can be in the 65° to 70°F
range, with a 10° to 40°F temperature change across the
EDA.
INDOOR
UNIT
INDOOR
COIL
air flow
INDOOR
BLOWER
VAPOR
LINE VALVE
CHECK/
EXPANSION
VALVE
See note 1 See note 1
NOTE 1. With EDA Coil Active, expect a 10 to 25ºF air temperature rise across EDA coils.
NOTE 2. With EDA Coil Active, expect a 10 to 40ºF liquid line temperature change across EDA coils.
NOTE 3. Charge compensator and 1/4" line not required on all systems. See Engineering Handbook.
See note 2 See note 2
CHECK/FLOW
RESTRICTOR
(flow permitted)
7/8 x 7/8 x
3/8 TEE CHARGE COMPENSATOR
(holding some refrigerant)
See note 3.
LIQUID
LINE
VALVE
Cooling Cycle with EDA Coil Active (Model EDA−036C shown)
Figure 9
OUTDOOR UNIT
3−WAY
DIVERTING
VALVE