Honeywell W7750A Manual

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EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER

74-2958—160

STAGED COOLING CONTROL

The Excel 10 W7750 Controller supports up to four sta

g

es of

D/X coolin

g

. As space temperature rises above the current

Coolin

g

Setpoint, the controllers mode of operation is

switched to the COOL mode. When in the COOL mode, all

heatin

g

outputs are driven closed or off

(

with the exception

that occurs durin

g

IAQ Override Operation, see above

)

, and

the sta

g

ed coolin

g

outputs are enabled for use. When in the

COOL mode, the PID coolin

g

control al

g

orithm compares the

current space temperature to the EffectiveCoolSetPt, and

calculates a PID error si

g

nal. This error si

g

nal causes the

coolin

g

sta

g

e outputs to be c

y

cled as re

q

uired to drive the

space temperature back to the setpoint. Fi

g

. 50 illustrates the

relationship between PID error and sta

g

ed output activit

y

. As

the error si

g

nal increases and the space temperature is

g

ettin

g

farther awa

y

from setpoint, or is remainin

g

above

setpoint as time elapses, additional sta

g

es of coolin

g

are

ener

g

ized until, if PID error reaches 100 percent, all

confi

g

ured sta

g

es are on.

Fig. 50. Staged output control versus PID Error.

If economizer dampers are confi

g

ured, and the outdoor air is

suitable for free coolin

g

, the economizer operates as the first

sta

g

e of coolin

g

. For example, if a controller was confi

g

ured

with two sta

g

es of mechanical coolin

g

and an economizer, the

application should be viewed in Fi

g

. 50 as a

three

-sta

g

e

s

y

stem.

Setpoints for the PID

g

ains allow for unit-b

y

-unit ad

j

ustment of

the control loop, if re

q

uired; however, an

y

chan

g

e from the

default values should be minimal.

The PID control al

g

orithm used to control sta

g

ed coolin

g

is

anticipator-driven, and is similar to the al

g

orithm used in the

T7300 commercial thermostat. All sta

g

in

g

events are sub

j

ect

to a minimum intersta

g

e time dela

y

, which is based on the

c

y

cles per hour user settin

g

(

CoolC

y

cHr

)

. The minimum

intersta

g

e time dela

y

ran

g

es from 90 seconds

(

at 12 c

y

cles

per hour

)

to 8.5 minutes

(

at two c

y

cles per hour

)

, see Table

17. The user has the option to disable the minimum run timer

(

DisMinClTimer for coolin

g)

. If the minimum run timer is

disabled, the intersta

g

e time dela

y

is fixed at 20 seconds. The

c

y

clin

g

rate is separatel

y

selectable for heatin

g

and coolin

g

between 2 and 12 c

y

cles per hour

(

cph

)

.

Table 17. Interstage Minimum Times

STAGED HEATING CONTROL

The Excel 10 W7750B,C Controller supports up to four sta

g

es

of heatin

g

. As space temperature falls below the current

Coolin

g

Setpoint, the controller mode of operation is switched

to the HEAT mode. When in the HEAT mode, all coolin

g

outputs are driven closed or off, and the sta

g

ed heatin

g

outputs are enabled for use. When in the HEAT mode, the PID

NO. STAGES

CONFIGURED

PID

ERROR

ONE STAGE

TWO STAGES

THREE STAGES

FOUR STAGES

0% 25% 33% 50% 66% 75% 100% > 100%

CYCLING

STAGE 1

CYCLING

STAGE 1 LOCKED ON

STAGE 2 CYCLING

STAGE 1

CYCLING

STAGE 1 LOCKED ON

STAGE 2 CYCLING

STAGE 1,2 LOCKED ON

STAGE 3 CYCLING

ALL STAGES

LOCKED ON

ALL STAGES

LOCKED ON

ALL STAGES

LOCKED ON

ALL STAGES

LOCKED ON

STAGE 1

CYCLING

STAGE 1

LOCKED ON

STAGE 2

CYCLING

STAGE 1,2

LOCKED ON

STAGE 3

CYCLING

STAGE 1,2,3

LOCKED ON

STAGE 4

CYCLING

M10112

Cycles/Hour Selection Minimum On/Off time (Min.)

28.5

35.5

44.0

53.5

63.0

72.5

82.0

92.0

10 2.0

11 1.5

12 1.5