Carrier 50EJQ Información técnica descargar pdf (Pagina 10)

The following qualifying conditions must be met for the

Cooling Control Submaster Loop to be active:

• the indoor fan has been ON for 30 seconds

• Heat mode is not active

• Occupied, Temperature Compensated Start, or Cool mode

is active

• SAT reading is available

• if number of stages is equal to 0: the economizer position

is 100% open or economizer is not usable

• if number of stages is equal to 0 and VAV unit, Tempera-

ture compensated start, Morning warm-up, or Occupied

heat mode enabled (occupied heating set point [OHSP] avail-

able) and RAT reading is available: RAT ≥ OHSP + 1.0.

When any of the above conditions are not met, the num-

ber of Stages is set to 0, SUM = 0, Z = 10. Once all of the

qualifying conditions are met, the control will wait 60 sec-

onds before starting the calculations. For the following con-

ditions: if number of stages is equal to 0 and the economizer

position is 100% open or economizer is not usable; and if

number of stages is equal to 0 and VAV unit, Temperature

compensated start, Morning warm-up or Occupied heat mode

enabled and RAT reading is available and RAT ≥ OHSP +

1.0, the delay will be extended to 2.5 minutes.

Cooling Control Submaster Loop Calculation — The con-

trol tries to maintain SAT at the CCSR value by cycling the

compressors and unloader(s). Both SAT and RAT (SPT for

CV units) sensors are used to adjust the cycling deadband to

match the actual load. The logic for determining when to

add or subtract a stage is a time-based integration of the de-

viation from set point plus the rate of change of the supply-

air temperature. The following equations are used to accom-

plish this:

SUM = SUM + DT + (3 x DTR) (PID control factor)

Z = 10 + (4 x SD) (Adjustable Integration Limit)

where

DT = SAT − CCSR (Deviation from Submaster Reference)

SD = (temp − SAT)/no. Stages ON (Drop per stage)

where temp is RAT for VAV, and SPT for C V.

DTR = Rate of change of SAT Deviation in Degrees F/ minute

and are subject to the following limits:

−10 ≤ DT ≤ 50

0 ≤ SD ≤ 10

−5 ≤ DTR ≤ 5

Each of the above equations are updated every

30 seconds.

If SAT is above the set point and DTR is positive, then

SUM will increase. If the next capacity stage is a compres-

sor, when SUM becomes greater than Z, a stage of capacity

is added and SUM is set to zero. If the next step of capacity

is an unloader, when SUM becomes greater than .6 x Z, a

stage is added and SUM is set to zero.

If SAT is below the set point and DTR is less than or equal

to zero, then SUM will decrease. If the next capacity stage

is a compressor, when SUM becomes less than −Z, a stage

of capacity is removed and SUM is set to zero. If the next

step of capacity is an unloader, when SUM becomes less

than −.6xZastage is removed and SUM is set to zero.

Cooling Control Submaster Loop Overrides — The algo-

rithm also provides for the following overrides in the order

of decreasing priority.

Economizer Interlock — Stage is held at zero whenever

the economizer is active and at less than 100% open. Once

the commanded position reaches 100%, the loop is delayed

by 2.5 minutes in an attempt to satisfy the load with the

economizer.

Low Temperature Override — Ensures against rapid load de-

creases by removing a stage every 30 seconds whenever

DT <−875 x SD and DTR >−5.

High Temperature Override — Protects against rapid load

increases by adding a stage once a minute whenever

DT > .875 x SD and DTR > 0.5.

Time Delay — Sets SUM to zero for 90 seconds since the

last capacity change. This prevents stages being added or

removed faster than every 90 seconds.

Slow Change Override — Prevents the addition or subtrac-

tion of another stage when SAT is close to the set point and

gradually moving towards the set point. If the absolute value

of DTR is less than 0.3° F and the absolute value of DT is

less than Y (where Y = .4375 x SD) then SUM will be set

to zero if either DTR > 0 and DT < Y, or DTR < 0 and

DT > −Y is true.

First Stage Override — If the current stage is zero, the in-

tegration deadband Z is multiplied by 1.2 to reduce cycling

on the ﬁrst stage of capacity.

Outdoor Fan Control — The Outdoor Fan Submaster

Loop inputs and outputs are shown in Tables 7 and 8.

Table 7 — Outdoor Fan Submaster Loop Inputs

INPUTS TYPE

OAT (Outdoor-Air Temperature) Analog Input

Compressor 1 Status Internal Parameter

Compressor 2 Status Internal Parameter

Table 8 — Outdoor Fan Submaster Loop Outputs

OUTPUTS TYPE

Outdoor Fan 1 (OFC1) Discrete Output

Outdoor Fan 2 (OFC2) Discrete Output

The control will be active when one or more stages of DX

cooling are on. It will turn OFC1 on whenever DX cooling

is on, and cycle OFC2 based on outdoor-air temperature.

Examples:

Compressor 1 or 2 is ON

and OAT >65 OFC1 = ON, OFC2 = ON

Compressor 1 or 2 is ON

and OAT <55 OFC1 = ON, OFC2 = OFF

Compressor 1 or 2 is ON

and OAT reading not available OFC1 = ON, OFC2 = ON

Compressor 1 and 2

are OFF OFC1 = OFF, OFC2 = OFF

In heat pump units during a Heat mode with compressors

on, both outdoor fans shall be energized regardless of OAT.

In heat pump units during defrost, both outdoor fans will be

turned off.

Time Guards — The control will maintain the follow-

ing time guards for compressor cycling:

• compressor minimum OFF time of 5 minutes

• compressor minimum ON time of 10 seconds

• minimum delay before turning on second compressor

10 seconds

• compressor OFF time after safety trip is 15 minutes

• three safety trips in 90 minutes results in compressor

lockout (manual reset required)

• an additional random 1to63seconds to sequentially start

multiple units after a power failure

On power-up, a random 1 to 63 seconds plus a 5-minute

time guard is loaded into the compressor time. Whenever a

compressor time guard (5 minutes) has more than 30 sec-

onds left, it can be forced to 30 seconds by switching DIP

switch no. 6 from the OFF to the ON position. Moving DIP

switch no. 6 from the OFF position to the ON position ini-

tiates the Time Guard Override once, at that moment only.

DIP switch no. 6 must be toggled from the OFF to the ON

position every time Time Guard Override is desired.

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