Ingersoll-Rand ReliaTel, Manual, Page: 131 / 176

RT-SVD03L-EN 131
Figure 80. Comparative enthalpy enable
Economizer Enabled
Economizer Disabled
OA Enthalpy - RA Enthalp y
Compar ativ e Enthalp y Hysteresis
Reference Enthalpy Method
OA Enthalpy is compared with a reference enthalpy
point.
• The economizer is enabled when OA Enthalpy <
[reference enthalpy point - 0.5 BTU/lb.].
• The economizer is disabled when OA Enthalpy >
[reference enthalpy point + 0.5 BTU/lb.].
• While [reference enthalpy point - 0.5 BTU/lb.] < OA
Enthalpy < [reference enthalpy point + 0.5 BTU/lb.],
the economizer enable/disable status is not
changed.
Figure 81. Reference enthalpy enable
Economizer Enabled
Reference Enthalpy H ysteresis
OA Enthalpy - R ef Enthalp y (BTU/lb.)
Economizer Disabled
Reference Dry Bulb Method
OA temperature is compared with a reference dry bulb
point.
• The economizer is enabled when OA Temp ≤
reference dry bulb point.
• The economizer is disabled when OA Temp ≥
(reference dry bulb point + 5.0)°F.
• While reference dry bulb point < OA Temp <
(reference dry bulb point + 5.0ºF), the economizer
enable/disable status is not changed.
Figure 82. Dry bulb enthalpy enable
Dry Bulb Hysteresis
Economizer Enabled
O AT - reference point (°F)
Economizer Disabled
N No otte e:: If on a unit with comparative enthalpy control
the OA or RA temp is greater than 120°F or
less than 32°F, the economizer control will
revert to reference enthalpy control if the OA
temp is within 32°F and 120°F. If the unit is
configured with comparative or reference
enthalpy control, if the OA temp. is not within
this range, the economizer control will revert
to dry bulb control. Once this occurs, the "out
of range" temperature(s) must fall to 118°F or
rise to 34°F to again enable comparative or
reference enthalpy control. If either OA or RA
humidity is measured to be greater than 90%
or less than 10%, the value of humidity which
is reported by the RTEM and used for
enthalpy calculation will be 90% or 10%
respectively.
Internal Calculations
Air enthalpy is a value calculated from the air
temperature and relative humidity using the
relationship:
E En ntth ha allp py y= = 0 0..2 24 4 x x O O..A A..T Te em mp p((d de eg g.. F F)) + + h h((R R..H H..,,O OA AT T))
Air enthalpy is calculated (Btu/Lb. dry air) using:
H = 0.24 * T + W * Hv
Where
T= dry bulb temperature, deg. F
W= humidity ration, lb. water/lb. dry air
W = 0.622 * P/ (14.696 - P)
Hv= enthalpy of water at T, Btu/lb.
Hv= 1062.1 + 0.43 * T
Also,
P= partial pressure of water at T, psia
P= (0.421 - 0.01503 * T + 0.000202 * T**2) * RH
ReliaTel ™ ™ Economizer Operation &
Inputs
ReliaTel ™ ™ Economizer Inputs
Terminals to read voltage:
Mixed Air Sensor ECA Module MAT
Return Air Sensor ECA Module RAT
E Ecco on no om miizze err