Carrier 48MA User Manual
Page 5
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GRAINS OF MOISTURE/
LBS OF DRY AIR
% removed
99 - 68
100
=
88.5%
99 - 64
The 1000 cfm of outdoor air at 68 grains is mixed
with 8000 cfm of return air at 75 F/50% room
conditions (64 grains). This mixture then enters
the zone modules and is cooled and dehumidified
by the zone coil.
Heating (General)
— The 48MA/50ME modular
multizone units offer a wide range of factory-
installed heating options.
In all cases, the modular design provides a
number of small heating steps to maintain very
close discharge temperature control without wide
variation. Conventional multizones cycle a few
large increments to maintain the necessary hot
deck temperatures and, thus, cannot control dis
charge temperature as well as the modular units.
Another feature of the modular design is the
reduced impact of heater malfunction. Any unit
can have a malfunction — such as an open coil in a
relay or contactor or gas valve failure in a gas-fired
unit. The Carrier 48MA/50ME units, with 8, 10 or
12 independent heating sections, would experience
heat failure in one module only and all others
would operate normally. Conventional multizones
could lose a large percentage of heating capacity or
the entire heat source in the hot deck could
become inactive.
The Carrier modular multizone units are de
signed to provide reliability, serviceability, oper
ating economy and comfort control — features
difficult to match with conventional hot deck/cold
deck reheat multizone units.
GAS HEATING SYSTEM (48MA) Each module
has a 2-stage burner, with one pilot per pair of
modules. The first-stage gas valve (115-v) controls
gas flow to the main orifice and to the second-stage
valve. A 24-v solenoid valve provides gas to the
second stage when open (see Eig. 3). Both heating
stages are contained in one valve body.
The gas heating section has standing pilots and
continuous forced draft combustion. The pilots
have automatic spark relight for dependable
ignition.
The 48MA modular multizone has individual 18
ga Chromized steel heat exchangers and stainless
steel main burners in each module.
Safety features on the heating system include:
1. A.G.A. certification of the entire unit design as '
well as the furnace section.
2. Airflow switch for indoor fan motor.
3. Airflow switch for forced draft fan motors.
4. Door switch for combustion compartment.
5. Pilot switch to ensure a pilot flame