CENTRIFUGAL CHILLERS SINGLE COMPRESSOR
PART 3 EXECUTION 3.1 INSTALLATION
2.4 CHILLER COMPONENTS A. Compressors
1. Unit shall have two single-stage hermetic centrifugal compressors. Casing design shall ensure major wearing parts, main bearings and thrust bearings are accessible for maintenance and replacement. Lubrication system shall protect machine during coast down resulting from a loss of power.
2. Impeller shall be statically and dynamically balanced. The compressor shall be vibration tested and not exceed 0.14 IPS.
3. Movable inlet guide vanes actuated by an internal oil pressure driven piston shall accomplish unloading. Compressors using an unloading system that requires penetrations of the compressor housing for linkages that must be lubricated and adjusted are acceptable provided the manufacturer provides a five-year inspection agreement consisting of semi-annual inspection, lubrication, and annual changeout
ASME stamp indicating compliance with the code and indicating a test pressure of 1.3 times the working pressure but not less than 100 psig. Provide intermediate tube supports at a maximum of 24 inch spacing.
2. Tubes shall be enhanced for maximum heat transfer, rolled into steel tube sheets and sealed with Locktite or equal sealer. The tubes shall be individually replaceable and secured to the intermediate supports without rolling.
3. Provide sufficient isolation valves and condenser volume to hold full refrigerant charge in the condenser during servicing or provide a separate pumpout system and storage tank sufficient to hold the charge of the largest unit being furnished.
4. The water sides shall be designed for a minimum of 150 psig or as specified elsewhere. Vents and drains shall be provided.
5. Chilled water minimum refrigerant temperature shall be 33qF.
6. A self-metering and adjustable thermal expansion valve shall control refrigerant flow to the evaporator. Fixed orifice devices or float controls with hot gas bypass are not acceptable because of inefficient control at low load conditions. The liquid line shall have a moisture indicating sight glass.
7. The evaporator and condenser shall be separate shells. A single shell containing both vessel functions is not acceptable because of the possibility of internal leaks.
8. Reseating type spring loaded pressure relief valves according to ASHRAE-15 safety code shall be furnished. The evaporator shall be provided with single or multiple valves. The condenser shall be provided with dual relief valves equipped with a transfer valve so one valve can be removed for testing or replacement without loss of refrigerant or removal of refrigerant from the vessel. Rupture disks are not acceptable.
9. The evaporator, suction line, and any other component or part of a component subject to condensing moisture shall be insulated with UL recognized 3/4 inch closed cell insulation. All joints and seams shall be carefully sealed to form a vapor barrier.
10. Provide water pressure differential switches on each vessel to prevent unit operation with no flow, furnished, installed and wired by the contractor.
D. Prime Mover: Squirrel cage induction motor of the hermetic type of sufficient size to efficiently fulfill compressor horsepower requirements. Motor shall be liquid refrigerant cooled with internal thermal overload protection devices embedded in the winding of each phase. Motor shall be compatible with the starting method specified hereinafter. If the Contractor chooses to provided an open drive motor or compressor, verify in the submittal that the scheduled chiller room ventilation system will accommodate the additional heat and maintain the equipment room at design indoor temperature based on 95qF outdoor ambient ventilation air available.
If additional cooling is required, manufacturer shall be responsible for the installation, wiring and controls of a cooling system. Chiller selection shall compensate for tons and efficiency loss to make certain the owner is not penalized.
E. Motor Starters:
1. The main motor starters are to be factory mounted and fully wired to the chiller components and factory tested during the run test of the unit.
leakage of oil and refrigerant to the outside of the refrigerating unit for a period of 5 years from the initial start-up including parts and labor to replace a defective seal and any refrigerant required to trim the charge original specifications.
4. The starters must comply with Section 1.2 as required.
5. All controllers are to be continuous duty AC magnetic type constructed according to NEMA standards for Industrial Controls and Systems (ICS) and capable of carrying the specified current on a continuous basis. The starters shall be:
Autotransformer - The autotransformer starters shall be of the closed transition type and equipped with multiple taps for 80%, 65%, 50%, and set up for the 65% tap. A clearly marked timer shall be adjustable from 0 to 30 seconds.
-- Or --
Wye-Delta Closed Transition - The wye contactor shall be capable of handling 33% of the delta locked rotor current and be equipped with properly sized resistors to provide a smooth transition. The resistors shall be protected with a transition resistor protector, tripping in a maximum of two seconds, locking out the starter, and shall be manually reset. A clearly marked transition timer shall be adjustable from 0 to 30 seconds.
-- Or --
Solid-State Reduced Voltage - Starter shall be furnished with silicon controlled rectifiers (SCR) connected for starting and include a bypass contactor. When operating speed is reached, the bypass contactor shall be energized removing the SCRs from the circuit during normal running. The starter shall be capable of across-the-line starting in an emergency.
6. Starters shall be coordinated with the chiller package(s) making certain all terminals are properly marked according to the chiller manufacturer’s wiring diagrams.
7. The starters shall be equipped with redundant motor control relays (MCR) with coils in parallel. The relays interconnect the starters with the unit control panels and directly operate the main motor contactors. The MCRs shall constitute the only means of energizing the motor contacts.
8. The main contactors shall have a normally open and a normally closed auxiliary contact rated at 125VA pilot duty at 115 VAC. An additional set of normally open contacts shall be provided for each MCR.
9. There shall be electronic overloads in each phase set at 107% of the rated load amps of each motor. Overloads shall be manual reset and shall de-energize the main contactors when the overcurrent occurs. The overloads shall be adjustable and selected for mid-range. Overloads shall be adjusted for a locked rotor trip time of 8 seconds at full voltage and must trip in 60 seconds or less at reduced voltage (33%
2. A digital regulator shall provide V/Hz control.
3. The VFD shall have 110% continuous overload of continuous amp rating with no time limit, PWM (pulse width modulated) output, IGBT (insulated gate bipolar transistors) power technology, full power rating at 2kHz, DC bus inductor (choke), and wireless construction.
4. Units 240 amps and below shall be air-cooled, units above 241 amps shall be water- cooled. All heat producing devices shall be contained in a single heatsink with single inlet and out connections for the connection of chilled water. When factory mounted on the chiller package, the water connections shall be piped and leak tested at the factory.
F. CONTROL PANELS
A microprocessor based control panel shall be furnished for each compressor and shall be fully wired and factory-mounted on the chiller. The control panels shall be independent allowing one compressor to operate with the other panel removed. The control panels shall also be interconnected to provide lead and lag control as well as load balancing when two compressors are running. The compressor with fewest starts will start first and the unit with the most hours will shut off first. Each panel shall have the following features:
1. The display shall have a minimum of 160-character liquid crystal display and be backlit with a light emitting diode. Messages shall be in plain English. Coded two or three character displays are not acceptable.
2. The following information shall be available on the display with simple entry on the keypad:
a) Entering and leaving chilled and condenser water temperatures b) Evaporator, suction, discharge, condenser, and liquid temperatures c) Suction and discharge superheat
d) Liquid subcooling, evaporator and condenser approach temperatures e) Evaporator, condenser, and lift pressures
f) Oil feed and sump temperatures
g) Oil pump discharge and oil differential pressure h) Motor amps and amps as a percent of rated load amps
i) Hours of operation and number of starts, time of last start and stop j) Chilled water setpoint and reset temperature setpoint
k) Amp limit for manual and remote
l) History of last 8 failures with date and time plus critical sensor values m) Unit status; start-up and shutdown sequence, operational status
3. The microprocessor shall either unload or shut down one or both compressors during an abnormal condition. At a minimum the following safeties shall be incorporated in the control system:
a) High and low discharge pressure b) Low evaporator pressure c) High discharge temperature
d) Chilled or condenser water pump failure e) No evaporator or condenser water flow
6. The controller shall be able to reset chilled water temperature by controlling return chilled water temperature or from a remote 4-20 mA DC signal.
7. Soft loading shall be provided to prevent the unit from operating at full load during pulldown if desired.
8. A time clock shall be incorporated to allow daily timed starts and stops and to allow for holiday and weekend schedule changes.
9. The control system shall have automatic restart after a power failure and not require a battery backup for memory continuity. A battery shall be provided for the time clock only.
10. The controller shall be capable of starting and stopping chilled water and condenser water pumps. It shall also be capable of four-step control of cooling tower fans and analog control of a tower bypass valve.
11. The microprocessor shall be capable of communicating to other units or a PC using a twisted pair communication interface of RS-232 (100 feet) or RS-422/485 (5000 feet) or with a 9600 baud modem.
2.5. MISCELLANEOUS ITEMS
A. Pumpout System: The unit shall be equipped with a pumpout system complete with a transfer pump, condensing unit, and storage vessel constructed according to ASME Code for Unfired Pressure Vessels and shall bear the National Boards stamp. If the design of the unit allows the charge to be transferred to and isolated in the main condenser, then a pumpout system is not required. Transfer of refrigerant charge shall be accomplished by either main compressor operation, migration, or gravity flow. Isolation shall be accomplished with valves located at the inlet and exit of the condenser. The main condenser shall be sized to contain the refrigerant charge at 90qF according to ANSI-ASHRAE 15.
B. Purge System (HCFC-123 Chillers Only):
1. The chiller manufacturer shall provide a separate high efficiency purge system that operates independently of the unit and can be operated while the unit is off. The system shall consist of an air-cooled condensing unit, purge condensing tank, pumpout compressor and control system.
2. A dedicated condensing unit shall be provided with the purge system to provide a cooling source whether or not the chiller is running. The condensing unit shall provide a low purge coil temperature to result in a maximum loss of 0.1 pounds of refrigerant per pound of purged air.
3. The purge tank shall consist of a cooling coil, filter-drier, water separation tube, sight glass, drain, and air discharge port. Air and water are separated from the refrigerant vapor and accumulated in the purge tank.
4. The pumpout system shall consist of a small compressor and a restriction device located at the pumpout compressor suction connection.
5. The purge unit shall be connected to a 100% reclaim device.
C. Vacuum Prevention System (HCFC-123 Chillers Only): Chiller manufacturer shall supply
PART 3 — EXECUTION 3.1 INSTALLATION
A. Install per manufacturer’s requirements, shop drawings, and Contract Documents.
B. Adjust chiller alignment on foundations, or subbases as called for on drawings.
C. Arrange piping to allow for dismantling to permit head removal and tube cleaning.
D. Furnish and install necessary auxiliary water piping for oil cooler.
E. Coordinate electrical installation with electrical contractor.
F. Coordinate controls with control contractor.
G. Provide all materiel required to ensure a fully operational and functional chiller.
3.2 START-UP
A. Units shall be factory charged with the proper refrigerant and oil.
B. Factory Start-Up Services: Provide for as long a time as is necessary to ensure proper operation of the unit, but in no case for less than two full working days. During the period of start-up.The Start-up Technician shall instruct the Owner’s representative in proper care and operation of the unit.