AAON M1-011 - Manual (Page 20)

20
If the control wires are to run inside the same conduit,
use 600-volt wire or as required by applicable codes.
The units must be electrically grounded in accordance
with the National Electric Code, ANSI / UL 1995 when
installed if an external source is utilized; in Canada
use current C.S.A. Standard C22.2, No. 236,
Canadian Electric Code Part 1.
Power wiring is to the unit terminal block. The
manufacturer has done all wiring beyond this point.
Power can be applied to the unit after the control
wiring is connected, and start up checks are complete.
Thermostat
The low voltage room thermostat should be located on
an inside wall 4 to 5 feet a above the floor where it will
not be subjected to drafts, sun exposure or heat from
electrical fixtures or appliances. Control wire size
must be large enough to prevent excess voltage drop
that may cause improper operation of the equipment.
Follow manufacturer’s instructions enclosed with
thermostat for general installation procedure.
Filters
Open filter access door and slide correct filter in with
arrow pointing towards the blower in the direction of
airflow.
THIS SECTION IS FOR INFORMATION ONLY, AND
IS NOT INTENDED TO PROVIDE ALL THE
INFORMATION REQUIRED BY THE DESIGNER OR
INSTALLER OF THE REFRIGERANT PIPING
BETWEEN THE CONDENSING UNITS AND THE
LOW SIDE COMPONENTS. AAON, INC. IS NOT
RESPONSIBLE FOR INTERCONNECTING
REFRIGERANT PIPING. THE APPROPRIATE
SECTIONS OF THE ASHRAE GUIDE AND THE
ASME STANDARDS SHOULD BE USED FOR FINAL
INFORMATION.
The piping between the condenser and low side must
assure:
1. Minimum pressure drop, and
2. Continuous oil return, and
3. Prevention of liquid refrigerant slugging,
or carryover
Acceptable system design and installation will include
consideration as follows.
General
Use only clean type L copper tubing (type K for
underground) that has been joined with high
temperature brazing alloy.
The pipe sizes must be selected to meet the actual
installation conditions, and not simply based on
the connection sizes at the evaporator and/or
condensing unit.
When sizing refrigerant lines, cost considerations favor
keeping line sizes as small as possible. However,
excessive suction or discharge line pressure drops
cause loss of compressor capacity and increased
power usage, resulting in reduced system efficiency.
Furthermore, excessive liquid line pressure drops can
cause the liquid refrigerant to flash resulting in faulty
expansion valve operation.
Correct sizing must be based on minimizing cost and
maximizing efficiency. Pressure drop calculations are
referenced as normal pressure loss associated with a
change in saturation temperature of the refrigerant.
Typically, the refrigeration system will be sized for
pressure losses of 2°F or less for each segment of the
discharge, suction, and liquid lines.
Liquid Line Piping
Systems are normally designed so that the pressure
drop in the liquid line (due to friction) is not greater
than that corresponding to an approximate 1 to 2°F
change in saturation temperature. Liquid sub cooling
is the only method of overcoming the liquid line
pressure loss to guarantee presence of liquid at the
expansion device in the evaporator.
If the sub cooling is insufficient, flashing will occur
within the liquid line and the system efficiency will
suffer. Accessories such as solenoid valves, filter
driers, and hand valves, as well as the actual pipe,
fittings between the receiver, or condenser outlet, and
the metering device cause friction pressure drops in
the liquid line. Liquid line risers are also a source of
pressure loss, and add to the total loss of the liquid
line. The loss due to risers is approximately 0.5 PSI
per foot of liquid lift. The total loss is the sum of all
friction losses plus the pressure loss from liquid risers.
If the refrigeration system has no liquid risers, and the
evaporator is below the condenser/receiver, then it
benefits from a gain in pressure due to liquid weight,
and can tolerate larger friction losses without flashing.
When flashing takes place, regardless of the routing of
5. Refrigerant Piping &
Line Sizing Information