JOHNSON CONTROLS
98
FORM100.50-EG12 (918)
Guide Specifications (Cont'd)
Burner(s) and Ignition Control:
The burner(s) shall include a direct-driven induced-
draft combustion fan with energy efficient intermittent pilot spark ignition, redundant
main gas valves with pressure regulator.
Combustion Air Fan(s):
The inducer fan(s) shall maintain a positive flow of air
through each tube, to expel the flue gas and to maintain a negative pressure within
the heat exchanger relative to the conditioned space.
Safety Devices:
A high limit controller with automatic reset to prevent the heat ex-
changer from operating at an excessive temperature shall be included. A centrifugal
switch on the induced draft fan motor shaft shall prevent ignition until sufficient air-
flow is established through the heat exchanger. A rollout switch shall provide second-
ary airflow safety protection. The rollout switch shall discontinue furnace operation if
the flue becomes restricted.
Flue:
The furnace flue shall be shipped loose to protect it from damage during tran-
sit. The flue shall be field-mounted by the installing contractor. The flue outlet shall be
located above the unit to help prevent recycling of combustion gases back through
the heat exchanger.
Agency Certification:
Gas heating sections are ETL listed to both US and Canadian
safety standards.
4.
Electric Heat:
An electric slip-in heater is installed within the single package unit
discharge plenum to provide the heating requirements per the schedule shown on
the plans. The electric heater is wired in such a manner as to provide a minimum of
two steps of capacity.
Heat Exchanger:
The furnace is an industrial grade design using an open coil made
of the highest-grade resistance wire containing 80% nickel and 20% chromium. The
resistance coils are adequately supported in the air stream using ceramic bushings
in the supporting framework. Terminals of the coil are stainless steel with high tem-
perature ceramic bushings.
Safety Devices:
The primary high temperature protection is a manual reset type
thermal cut out. Secondary protection is a manual reset type thermal cut out. Sec-
ondary protection is a replaceable thermal link.
Agency Certification:
The operation of the electric heater is an integral part of the
single package units control system. Power connection to the heater is through the
power panel for the unit. Electric heat is ETL certified to both US and Canadian safety
standards.
5.
Hot Water Heating Coil:
A hot water coil shall be installed in the single package
unit discharge plenum.
Construction:
The hot water coil shall have 8 [10, 12, 14] fins per inch, 2 tubes per
circuit, and an 2-inch inlet and outlet connection. Primary surface shall be 1/2
-inch
OD copper tube, staggered in direction of airflow. Connections have 1/4-inch FPT
drain plug on each connection. A structural galvanized steel casing shall protect the
coil. An intermediate coil support shall be provided. The coil shall be circuited to
provide free draining and venting, through one vent and drain. Freezestat shall be
provided to prevent coil freeze-up.
Testing:
Completed coil, including headers, connections and return bends shall be
tested with 325 pounds compressed air under water. Coils shall be designed for op-
eration at 250 psig design working pressure.