Daikin WSC, Инструкция по установке, эксплуатации и обслуживанию

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IOM 1274-3 • CENTRIFUGAL WATER CHILLERS 12 www.DaikinApplied.com
Installation
provides several options to assist the chiller plant designer in
providing the optimum control of condenser water temperature.
Cooling Tower Control
Control of the cooling tower is required to maintain stability and
avoid operational issues. This can be achieved through a BAS
or by using the MicroTech ® II controller. For systems utilizing a
common condenser water loop for multiple purposes, the BAS
contractor must provide the control but use of the MicroTech®
output signal is still recommended.
The preferred cooling tower control utilizes a variable speed
fan. MicroTech
®
II will provide a control signal to determine the
proper fan speed. It can also control up to three stages of fan
cycling. Note that fan cycling can cause cooling tower water
temperature to fluctuate as fans stage on/off, potentially adding
instability to the system.
Special consideration must be given to starting the chiller when
cold condenser water is present, such as with inverted starts
or changeover from free (tower) cooling to mechanical cooling.
Daikin Applied chillers will start with entering condenser water
temperature as low as 55°F (42.8° C) providing the chilled
water temperature is below the condenser water temperature.
The minimum entering condenser water temperature while
operating is a function of the leaving chilled water temperature
and load. It is required that some method be used to control
the condenser water to maintain proper head pressure as
indicated by the MicroTech
®
II controller. Refer to “Tower
Control Settings” on page 51 for details in the HMI.
Each of the following acceptable methods can be controlled by
the MicroTech® II or through a BAS utilizing the MicroTech®
output signals:
1. Three-Way Bypass Valve Operation
A traditional method for building condenser pressure at
startup with colder condenser water is with the use of
a three-way bypass valve. The device blends warmer
water leaving the condenser with cooler water from the
cooling tower at the condenser inlet. The bypass valve
position will change until full flow from the tower to the
condenser is obtained. The MicroTech
®
II provides only
the valve position control signal. Main power to drive
the valve actuator must be provided by the installer. The
three-way valve should be located close to the chiller
within the equipment room to minimize the water volume.
2. Two-Way Valve Operation
Another condenser control method is to use a modulating
two-way control valve located on the outlet connection of
the condenser. The valve will be nearly closed at startup
to restrict water flow, which keeps generated heat in
the condenser until an acceptable minimum condenser
pressure is reached. As heat builds, the valve will open
slowly until a full flow condition from the cooling tower
is established. A separate power source is required to
provide power to the valve actuator.
NOTE: To ensure proper operation, caution should be
used when utilizing the two-way valve option.
3. VFD Operating with a Condenser Water Pump
A third method of condenser control for startup is
utilizing a variable frequency drive with the condenser
water pump. The speed will change as directed by the
MicroTech
®
II output signal until design flow is reached.
Speed adjustments may be required during the initial
chiller startup as determined by the service technician.
NOTE: Not using the MicroTech
®
II logic to control valves
and variable frequency drives may result in system
instability, capacity reduction, and issues starting the
chiller with cold condenser water temperature.
Condenser Pump Sequencing
It is recommended to utilize the logic built into the MicroTech
®
II controller to start the condenser pump. MicroTech
®
II has the
capability to operate a primary pump and a secondary standby
pump. The condenser water flow should be stopped when
the chiller shuts off. This will conserve energy and prevent
refrigerant from migrating to the condenser. Moisture in the
air can condenser on the cooler surfaces of the un-insulated
condenser barrel if flow is present when the chiller is idle.
Water Side Economizer Cycle Operation
Water side economizers are commonly used for ASHRAE 90.1
compliance and energy savings. This system utilizes a heat
exchanger external to the chiller when cold cooling tower water
is available to provide cooling. The most common system uses
a heat exchanger in conjunction with the chiller’s evaporator.
The BAS contractor will need to provide controls for the heat
exchanger including isolation valves and temperature control.
The BAS contractor will also need to control the isolation
valves for the chiller. It is important to use slow-acting type
valves to prevent rapid changes in system flows. Changeover
from economizer cooling to mechanical cooling requires one
of the methods previously mentioned to maintain suitable
condenser head pressure. Contact your local Daikin Applied
representative for more information on this application.
Heat Recovery Chillers
HSC heat recovery chillers control based upon the chilled
water leaving temperature. The cooling load determines
compressor loading and unloading, the same as in a
conventional chiller. A heat recovery control algorithm is
identical to a conventional cooling-only chiller. The amount
of heat recovered from the condenser shall depend on the
cooling load. If cooling load on the chiller drops, the hot water
temperature supplied by the heat recovery condenser would
also drop.
Alternately, the 3-way cooling tower bypass valve, controlled
by heating water inlet temperature to the recovery bundle of
the condenser, can be used to manipulate the cooling tower
water loop. Based on the signal the 3-way valve gets from
the hot inlet water temperature sensor, it will bypass sufficient
water around the tower to increase the condenser water loop
temperature at the inlet. The supply water temperature to the
heating load will “float” depending on actual chiller load. This
3-way valve along with the necessary controls and wiring are