Unoccupied Economizer Free Cooling Outside Lockout Temperature (FC.LO) — This configuration option allows the user to select an
Unoccupied Economizer Free Cooling Logic — The follow- ing qualifications that must be true for unoccupied free cooling to operate:
•Unit configured for an economizer
•Space temperature sensor enabled and sensor reading within limits
•Unit is in the unoccupied mode
•FC.CF set to 1 or FC.CF set to 2 and control is within FC.TM minutes of the next occupied period
•Not in the Temperature Compensated Start Mode
•Not in a cooling mode
•Not in a heating mode
•Not in a tempering mode
•
•Economizer would be allowed to cool if the fan were requested and in a cool mode
•OAT > FC.LO (1.0° F hysteresis applied)
•Unit not in a fire smoke mode
•No fan failure when configured to for unit to shut down on a fan failure
If all of the above conditions are satisfied:
Unoccupied Economizer Free Cooling will start when both of the following conditions are true:
{SPT > (OCSP + 2)} AND {SPT > (OAT + 8)}
The Unoccupied Economizer Free Cooling Mode will stop when either of the following conditions are true:
{SPT < OCSP} OR {SPT < (OAT + 3)} where SPT = Space Temperature and OCSP = Occupied Cooling Set Point.
When the Unoccupied Economizer Free Cooling mode is active, the supply fan is turned on and the economizer damper modulated to control to the supply air set point (Setpoints→ SASP) plus any supply air reset that may be applied (Inputs→ RSET→SA.S.R).
ECONOMIZER OPERATION CONFIGURATION — The configuration items in the E.CFG menu group affect how the economizer modulates when attempting to follow an economizer cooling set point. Typically, they will not need adjustment. In fact, it is strongly advised not to adjust these configuration items from their default settings without first consulting a service engineering representative.
In addition, the economizer cooling algorithm is designed to automatically slow down the economizer actuator’s rate of travel as outside air temperature decreases.
ECONOMIZER DIAGNOSTIC HELP — Because there are so many conditions which might disable the economizer from being able to provide free cooling, the control has a display table to identify these potentially disabling sources. The user can check ACTV, the “Economizer Active” flag. If this flag is set to Yes there is no reason to check DISA (Economizer Disabling Conditions). If the flag is set to No, this means that at least one or more of the flags under the group DISA are set to Yes and the user can discover what is preventing the econo- mizer from performing free cooling by checking the table.
The economizer’s reported and commanded positions are also viewable, as well as outside air temperature, relative humidity, enthalpy and dew point temperature.
The following information can be found under the Local Display Mode Run Status→ECON. See Table 80. Economizer Control Point Determination Logic — Once the economizer is allowed to provide free cooling, the economizer must determine exactly what set point it should try to maintain. The set point the economizer attempts to maintain when “free
cooling” is located at Run Status→VIEW→EC.C.P. This is the economizer control point.
The control selects set points differently, based on the control type of the unit. This control type can be found at Configuration→UNIT→C.TYP. There are 6 types of control.
C.TYP = 1 | |
C.TYP = 2 | |
C.TYP = 3 | TSTAT |
C.TYP = 4 | TSTAT 2 Stage |
C.TYP = 5 | SPT |
C.TYP = 6 | SPT 2 Stage |
If the economizer is not allowed to do free cooling, then EC.C.P = 0.
If the economizer is allowed to do free cooling and the Unoccupied Free Cooling Mode is ON, then EC.C.P = Setpoints→SASP + Inputs→RSET→SA.S.R.
If the economizer is allowed to do free cooling and the Dehumidification mode is ON, then EC.C.P = the Cooling Control Point (Run Status→VIEW→CL.C.P).
If the C.TYP is either 4 or 6, and the unit is in a cool mode, then
If Stage = 0 EC.C.P = the Cooling Control Point (Run Status→VIEW→CL.C.P)
If Stage = 1 53.0 + economizer suction pressure reset (see below)
If Stage = 2 48.0 + economizer suction pressure reset (see below)
NOTE: To check the current cooling stage go to Run Status →Cool→CUR.S.
If the C.TYP is either 1,2,3 or 5, and the unit is in a cool mode, then EC.C.P = the Cooling Control Point (Run Status→ VIEW→CL.C.P).
Economizer Suction Pressure Reset for
mostat or
If either circuit’s suction pressure drops to within 5 psig of the low suction pressure trip point, the control will start adding reset to the economizer control point if it is active. It will be possible to reset the control point upwards, 10 degrees (2 degrees per psig), between the low suction pressure trip point of 52 psig for 48/50AJ,AK,AW,AY units or 93 psig for 48/50A2,A3,A4,A5 units. If this does not work, and if the suc- tion pressure drops below the trip point, then the control will further reset the control point 1 degree every 15 seconds up to a maximum of 10 degrees. The resulting effect will be to warm up the mixed air entering the evaporator, thereby raising the suction pressure.
Building Pressure Control — The building pressure control sequence provides control of the pressure in the build- ing through the modulating flow rate function of the modulat- ing power exhaust option. This function also provides control of the constant volume
BUILDING PRESSURE CONFIGURATION — The build- ing pressure configurations are found at the local display under Configuration→BP. See Table 81.
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