Figure 6 - Head Pressure Control System - York YVWA Installation Operation & Maintenance

SECTION 2 - PRODUCT DESCRIPTION
Head Pressure Control
(Applicable to software version Y.WCS.31.05 or
Y.WCS.41.05, and later.)
Head Pressure is the pressure difference between con-
denser and evaporator. It is of a crucial requirement to
maintain sufficient head pressure for normal oil circu-
laiton in lubrication system.
YVWA Chillers are capable of operation with-
in a wide range of condenser water tempera-
tures. If condenser water temperatures meet the
guidelines documented in the Engineering Guide
(FORM 201.30-EG1), then head pressure regulation is
not necessary. However, chiller operational issues may
occur if the condenser water temperature is colder than
usual. A customer facility control may be provided to
ensure adequate head pressure exists.
Compressor
Motor

FIGURE 6 - HEAD PRESSURE CONTROL SYSTEM

22
Tower
Condenser
Hot
TXV
Gas
Evaporator
The preferred means is cooling tower bypass circuit,
since this would maintain adequate tube velocity in the
condenser, by regulating the return cooling water to the
chiller. Additionally, a two-way condenser water throt-
tling valve, a variable speed cooling tower pump, or
tower fan control circuit might be employed.
The Head Pressure Control function provides an output
control signal that will respond to a programmed mini-
mum chiller differential pressure.
DIFFERENTIAL PRESSURE =
DISCHARGE PRESSURE - EVAPORATOR PRESSURE
The output to the above equation will be a direct im-
pact. An increasing head pressure differential provides
more water flow to the cooling tower or less tower by-
pass.
Tower
Cooling Tower
Bypass
Valve
TBV
CWP
ChWP
Cooling Load
FORM 201.30-ICOM1 (318)
ISSUE DATE: 3/29/2018
LD26904
JOHNSON CONTROLS