Modine MDB Série Manuel D'installation Et De Maintenance page 14

control descriPtions
maXitrol system 44
space temperature control
System 44 is an electronic modulating room temperature
control system, which utilizes a Selectra-Stat modulating room
thermostat to control the main burner firing rate based on the
room air temperature set point. The stat monitors the room
space temperature and sends a signal back to the control
amplifier to modulate the gas control valve to maintain proper
space set-point temperature. The temperature set point range
for this system is 55-90 degrees F.
This control system also includes a field mounted and
wired discharge air sensor, which is used as a high and low
temperature limit control. The discharge air sensor will prevent
make-up air from being delivered to the space at temperatures
below the low setpoint, even if the room thermostat is satisfied.
It will also prevent the room thermostat from over firing the
burner when mild outdoor temperatures exist and the maximum
firing capacity of the burner is not required to achieve an
appropriate discharge air temperature.
When specifying this control system, the accessory System
44 Remote Panel must be used. The System 44 Remote
Panel includes an electronic Modulating Room Thermostat, a
Summer/Off/Winter selector switch, a Main Valve On light and a
Flame Failure Alarm light (see Figure 14.1).
For return air units, model MRB, depending on design
conditions, this control may be acceptable, but requiring
additional control devices with the system. Also included are
a factory installed/set return air stat and a factory installed/
set outside air stat. If the temperature sensed falls below the
setpoint for either stat, the unit will go to 100% outside air mode
until both stats are satisfied. Please refer to the Gas Control
Selection Table 14.1 for additional guidance.
The Selectra-Stat is used in conjunction with a discharge air
sensor and air mixing tube. The discharge air sensor serves to
limit the minimum and maximum discharge air temperature from
the unit.
Figure 14.1 - room stat for maxitrol 44
14
ddc compatible controls
Building management control (4-20ma or 0-10vdc)
The DDC compatible control system is an electronic
modulating control system, which utilizes a 4-20mA or
0-10VDC input signal (by others) to control the discharge air
temperature. This system is available on MDB units only.
This system requires a field supplied air temperature sensor
that is compatible with the building management system. This
sensor is wired to the building management system and based
on the temperature reading from that thermostat, the building
management system will increase or decrease the signal to the
makeup air unit gas controls. An increase or decrease in the
input signal modulates the main burner gas flow to maintain the
desired discharge air temperature.
Provided with this system is a discharge air sensor which is
used as a high temperature limit control. The discharge air
sensor will prevent make-up air being delivered to the space
that is above the maximum operating limit of 105°F. The
sensor is factory mounted for single blower units (unit sizes
110-130) and field installed for twin blower units (unit sizes
220-230).
For return air units, model MRB, depending on design
conditions, this control may be acceptable, but requiring
additional control devices with the system. Also included are
a factory installed/set return air stat and a factory installed/
set outside air stat. If the temperature sensed falls below the
setpoint for either stat, the unit will go to 100% outside air
mode until both stats are satisfied. Please refer to the gas
Control Selection Table 14.1 for additional guidance.
Gas control selection for model mrB units
Table 14.1 is to be used for Model MRB units only to determine
applicability of the various available gas control systems to
meet requirements of ETL certification and ANSI Z83.18. For
additional information on these control systems, please see
Gas Control Descriptions above.
table 14.1 - Gas control system selection for model
mrB units
Gas
ra/oa
control
ratio
system
75/25
Maxitrol 70/30
14
70/30
75/25
Maxitrol
44
or
SC11 70/30
j Minimum return air temperature is 55˚F. For return air temperatures below 55˚F,
please contact the factory.
k Room override accessory can override discharge air setting by 15˚F to a
maximum discharge air temperature of 105˚F.
7-500.10
minimum outside maximum
air temperature discharge
(per ashrae) j air temp
-30˚F and Above
90˚F
-30˚F to Lower than
10˚F
10˚F and Above 90˚F k
-30˚F to Lower than
90˚F
-10˚F
-10˚F to Lower than
95˚F
0˚F
0˚F and Above 100˚F
-30˚F to Lower than
95˚F
-20˚F
-20˚F to Lower than 100˚F
-10˚F
-10˚F and Above 105˚F
room
override
Not
Available
Accessory
Not
Applicable