Honeywell THM5421C1008 Benutzerhandbuch

68-0287—1

32

NOTE: It takes about a week for the thermostat to adjust to 

local weather, the schedule, the construction of the 

home and the heating and/or cooling system. Each 

day it adjusts the next day’s recovery start time 

accordingly.

The thermostat microprocessor-based control requires that the 

user understands temperature control and thermostat 

performance. A conventional mechanical or electronic 

thermostat does not control temperature precisely at setpoint. 

Typically there is an offset (droop) in the control point as the 

system load changes. This is a phenomenon that most people 

in the industry know and accept. Many factors contribute to 

offset including switch differential, thermal lag, overshoot, cycle 

rates and system load.

The thermostat microprocessor simultaneously gathers, 

compares and computes data. Using this data, it controls a 

wide variety of functions. The special proprietary algorithm 

(program) in the thermostat eliminates the factors causing 

offset. This makes temperature control more accurate than the 

conventional mechanical or electronic thermostats. The 

temperature control algorithm is called proportional plus 

integral (P+I) control.

The thermostat sensor, located on the thermostat or remote, 

senses the current space temperature. The proportional error 

is calculated by comparing the sensed temperature to the 

programmed setpoint. The deviation from the setpoint is the 

proportional error.

The thermostat also determines integral error, which is a 

deviation based on the length of error time. The sum of the two 

errors is the (P+I) error. The cycle rate used to reach and 

maintain the setpoint temperature is computed using the P+I. 

The addition of the integral error is what differentiates the 

thermostat from many other electronic and mechanical 

thermostats. See Fig. 33.

The Thermostat has built-in compressor protection (minimum-

off timer) that prevents the compressor from restarting too 

early after a shutdown. The minimum-off timer is activated after 

the compressor turns off.

If there is a call during the minimum-off timer, the thermostat 

shows “Wait” in the display.

When the minimum-off timer expires, “Cool On” or “Heat On”

a

 

appears in the display and the compressor and fan turn on.

_________

a

Heat Pumps only.

The humidity level in the home is shown in the lower right 

corner of the Home Screen.

NOTE: If an outdoor temperature sensor is present, the out-

door temperature will be displayed in this location 

rather than the indoor humidity. To see indoor humid-

ity, display the humidity settings menu.

If thermostat is set to Auto Changeover System mode, press 

the More key until the humidity level is shown on the screen.

HEATING

COOLING

PERCENT LOAD

TEMPERATURE

THERMOSTAT

HEAT SETPOINT

P+I CONTROL

POINT

PROPORTIONAL COOL 

CONTROL POINT

THERMOSTAT 

COOL SETPOINT

P+I CONTROL POINT

PROPORTIONAL HEAT 

CONTROL POINT

M4414

100

50

0

50

100

M23513 

SCHED HOLD CLOCK SCREEN 

MORE 

WED 

 

AUTO 

HEAT

 

COOL

 

SCHED HOLD CLOCK 

SCREEN MORE 

TUE 

 

AUTO 

 

COOL 

M23678