York YK Manual page 103

FORM 160.75-EG1 (519)
Guide Specifications (Cont'd)
refrigerant side of each shell is designed, tested and stamped in accordance with ASME
Boiler and Pressure Vessel Code, Section VIII – Division I, or other pressure vessel code
as appropriate.
Heat exchanger tubes shall be high efficiency, externally and internally enhanced type.
Tubes shall utilize the "skip-fin" design, providing a smooth internal and external surface
at each intermediate tube support. This provides extra wall thickness and non work-hard-
ened copper at the support location, extending the life of the heat exchangers. If skip-fin
tubes are not used, minimum tube wall thickness shall be 0.035" (~1 mm). Each tube shall
be roller expanded into the tube sheets providing a leak-proof seal, and be individually
replaceable. Water velocity through the tubes shall not exceed 12 ft. /sec. (3.7 m/sec.).
A liquid level sight glass shall be provided on the side of the shell to aid in determining
proper refrigerant charge and to check condition of the refrigerant charge.
The condenser shall have dual refrigerant relief devices; each sized to meet the require-
ments of the ASHRAE 15 Safety Code for Mechanical Refrigeration. Arrangement shall
allow either valve to be isolated and replaced without removing the unit refrigerant charge.
(Option) The condenser shall be provided with positive shutoff valves in the compressor
discharge line to the condenser and in the liquid line leaving the condenser. This will allow
pumpdown and storage of the refrigerant charge in the condenser. Due to the possibility
of not seating properly, check valves are not acceptable for isolation purposes. If a check
valve is used, a positive shutoff valve must be provided in series with the check valve.
Waterboxes shall be removable to permit tube cleaning and replacement. Stubout water
connections having ANSI/AWWA C-606 grooves shall be provided. Waterboxes shall be
designed for 150 psig (10.3 barg) design working pressure and be tested at 225 psig (15.5
barg). Vent and drain connections with plugs shall be provided on each waterbox.
REFRIGERANT FLOW CONTROL
Refrigerant flow to the evaporator shall be controlled by a variable orifice. The variable ori-
fice control shall automatically adjust to maintain proper refrigerant level in the condenser
and evaporator. This shall be controlled by monitoring the refrigerant liquid level in the
condenser, assuring optimal subcooler performance.
OPTIVIEW™ CONTROL CENTER
General – The chiller shall be controlled by a stand-alone, microprocessor based control
center. The chiller control panel shall provide control of chiller operation and monitoring of
chiller sensors, actuators, relays and switches.
Control Panel – The control panel shall include a 10.4-in. (264 mm) diagonal color liquid
crystal display (LCD) surrounded by "soft" keys which are redefined based on the screen
displayed at that time. This shall be mounted in the middle of a keypad interface and in-
stalled in a locked enclosure. The screen shall detail all operations and parameters, using
a graphical representation of the chiller and its major components. The panel verbiage is
available in eight languages as standard and can be changed on the fly without having to
turn off the chiller. Data shall be displayed in either English or Metric units. Smart Freeze
Point Protection shall run the chiller at 36°F (2°C) leaving chilled water temperature, and
not have nuisance trips on low water temperature. The sophisticated program and sensor
shall monitor the chiller water temperature to prevent freeze-up. When needed, Hot Gas
Bypass is available as an option.
JOHNSON CONTROLS 103