Johnson Controls York YCRL0064, Installation Operation & Maintenance

Page: 38 / 162

JOHNSON CONTROLS
38
FORM 150.27-NM1
ISSUE DATE: 09/30/2015
SECTION 4 – INSTALLATION
REMOTE CONDENSER PIPING
Improper design and sizing of refrigerant piping may
result in loss of system efficiency and/or eventual fail-
ure of the system. Factors that must be considered in a
piping design are the inter-relationships between ve-
locity, pressure, friction, as well as, economics. Eco-
nomics favor the use of the smallest possible line sizes.
However, high suction and discharge line pressure
drops will cause loss in capacity and increased power
consumption. Another important design criterion is oil
return to the compressor. The refrigerant line velocities
have to be sufficiently high to carry oil up suction or
hot gas risers at all operating capacities.
Johnson Controls assumes no warranty
responsibility for system operation or
failures due to improper piping of piping
design.
REFRIGERANT LINE LOSSES
The pressure drops (line losses) are typically presented
as a given change in the corresponding saturation tem-
perature. The effect of line losses on the capacity and
energy consumption (kW/ton) is illustrated in
Figure
12 on page 38 . Line sizing is a balance between
pressure drop (reflected in system performance) and
oil return (for system reliability).
PRESSURE DROP CONSIDERATIONS
Pressure drop calculations are determined as pressure
changes associated with a change in saturation temper-
ature of the refrigerant. Systems are typically sized for
pressure losses of 2°F or less for the discharge, suction
and liquid lines. This is the conventional method for
sizing and is accepted practice throughout the industry
(ASHRAE).
Table 2 on page 40 and Table 3 on page 41 show
capacities HFC-410A at specified pressure drops for
the various refrigerant lines.
LD13974
FIGURE 12 - EXAMPLE OF TYPICAL EFFECT OF
SUCTION AND DISCHARGE LINE PRESSURE
DROP ON CAPACITY AND POWER (ASHRAE)
DISCHARGE LINE
System operating at 100°F saturated condensing and
40°F saturated evaporating temperature. Energy per-
centage is rated at kW/ton.)
REFRIGERANT LINE SIZING
Refrigerant piping systems must be designed to pro-
vide practical line sizes without excessive pressure
drops, prevent compressor oil from being “trapped” in
the refrigerant piping, and ensure proper flow of liquid
refrigerant to the thermal expansion valve. Be sure to
review DX Piping Guide (Form 050.40-ES2) . Consid-
erations should be given to:
1. Discharge line pressure drop due to refrigerant
flow.
2. Discharge line refrigerant velocity for oil return.
3.
Liquid line pressure drop due to refrigerant flow.
4. Liquid line pressure drop (or gain) due to vertical
rise of the liquid line.