Systems that employ water chillers are commonly called chilled- water systems. As its name suggest, this system makes use of water as its secondary refrigerant. Chiller is used to remove heat from the water which is then circulated through other components to absorb heat from the space.

Chilled water air conditioning systems are commonly used in applications that need large cooling capacity such as hypermarket, industrial process, commercial air conditioning such as offices and factories. More and more homes are using this system to air conditioned their entire house because of its cost-effectiveness and no hazard of having refrigerant piped all over the house.

In a chilled-water system, the entire air conditioner is installed on the roof or behind the building. A Water chiller cools water to between 40 and 45 degrees Fahrenheit (4.4 and 7.2 degrees Celsius). The chilled water is then piped throughout the building and connected to air handlers. This can be a versatile system where the water pipes work like the evaporator coils in a standard air conditioner. If it’s well-insulated, there’s no practical distance limitation to the length of a chilled-water pipe.

• The evaporator cools water to about 45 .That chilled water is pumped to cooling coils in the areas being cooled, and a fan draws the air in those areas through the chilled water coils, cooling the air.
• In comparison, with standard air conditioning, the evaporator coil directly cools the air. The refrigerant flows all the way to the air handlers in the areas being cooled, and a fan draws the air in those areas through the evaporator coils, cooling the air.
• With chilled water air conditioning, the compressor is usually mounted on a rack or frame, within a few feet of the evaporator that cools the chilled water. If the condenser is water cooled, it’s usually mounted on the same rack. If the condenser is air cooled, it will be installed outside the building.
• One advantage of chilled water air conditioning is that if the chilled water piping leaks somewhere in the building, only water is lost, and repairs only require plumbing work.
• In comparison, with standard air conditioning, a leak in a refrigerant line inside the building will probably require brazing, leak testing with nitrogen, evacuation of the system, and recharging with a refrigerant that is a lot more expensive than water.
• Another advantage of chilled water air conditioning is that if air stops flowing through the cooling coil, the chilled water will simply return to the chiller. Since the water will not have picked up any heat, it will still be cold, and the chiller will respond by unloading and turning off.
• With standard air conditioning, if air stops flowing through the cooling coil, there is a possibility that liquid refrigerant will return to the compressor and damage it.

1.1- Lay-out and Installation requirements

• Air-cooled chillers with helicoids fans such as Ecologic or NEOSYS are designed for outdoor installation. Please consult Lennox prior to implementing other types of installation.
• Locate the chiller where it is least affected by wind (install windbreaks where wind speeds > 2.2 m/s).
• The ground beneath the unit must be flat, level and of sufficient strength to support the weight of the unit with its full liquid charge, and the occasional presence of the usual service equipment. In locations exposed to frost, the supporting surface, if the unit is installed on the ground, must be built on concrete stakes extending downwards beyond the normal depth of frost. It is always advisable to build a supporting surface detached from the general building structure to avoid transmission of vibrations.
• On normal applications, unit rigidity and point load positions enable installation to minimise vibrations. Vibration isolators may be used by contractors on installations requiring particularly low vibration levels.
• It is essential that the units be installed with sufficient free space around them to enable proper circulation of air ejected by the condensers and to provide easy access to all unit components for servicing and maintenance. If the air rejected by the condenser encounters any obstacles.
• To prevent air flow to be reversed due to prevailing winds, units cannot be completely shrouded with a higher, uninterrupted wind shield. If such a configuration cannot be avoided, an air ejection duct must be installed at the same height as the surrounding shield.

1.2 WATER CONNECTIONS

•  The water circulating pump will be preferably installed upstream so that the evaporator/condenser will be subjected to positive pressure. Entering and leaving water connections are indicated on the certified drawing sent with the unit.
• The water must be analyzed; the water circuit installed must include all items necessary for treatment of the water: filters, additives, intermediate exchangers, bleed valves, vents, isolating valves etc… depending on the results of the water analysis.
•  The glycol/water solution must be sufficiently concentrated to ensure proper protection and prevent formation of ice at the lowest outdoor air temperatures expected on an installation. Take precautions when using non passivated MEG antifreeze solutions (Mono Ethylene Glycol or MPG Mono Propylene Glycol).
•  To enable drainage of the circuit, make sure that drain cocks are installed at all the low points of the circuit.
•  To drain the circuit, the drain cocks must be opened and an air inlet ensured.
•  The minimum volume of the chilled water circuit must be calculated with the formulas here under. If necessary, install a buffer tank. Proper operation of regulating and safety devices can only be ensured if the volume of water is sufficient.
•  A flow switch must be installed on the evaporator water inlet or outlet, so as to enable detection of water flow through the heat exchanger before the unit is started up. This will protect the compressors against any eventual liquid slugging during the starting phase and prevent accidental ice formation in the evaporator, if the flow of water is interrupted.

1.3 ELECTRICAL CONNECTIONS

• First of all, make sure that power supplies from the building to the place where the unit is installed are properly established and that wire gauges are in keeping with the start up and running currents.
• Check tightness of all electrical connections. You MUST make absolutely certain that the power supplies applied to the power and control circuits are those for which the electrical panel was manufactured.
• A main isolator switch must be inserted between the end of the power supply cable and the unit to enable total isolation of the latter when necessary. Chillers are supplied as standard without a main isolator switch. This is available as an option.

1.4 SOUND LEVELS

• Liquid chillers are a significant source of noise in refrigeration and air conditioning systems. Account is taken of technical constraints, both in design and manufacturing, sound levels cannot be improved much further than specified.
• Sound levels must therefore be accepted for what they are, and the area surrounding the chillers should be treated as necessary. The quality of installation can either improve or decrease initial sound characteristics: it may be necessary to provide further treatment such as sound-proofing or installation of screens around units installed externally. The choice of the location for the installation can be of great importance: reflection, absorption, transmission of vibrations.
• The type of unit support is also very important: inertia of the room and the structure of the walling, interfere with the installation and its behavior. Determine what level of sound proofing is necessary on the equipment, the installation (silencer, vibration isolators, and screens) and on the building (reinforcement of flooring, false ceilings, and wall coverings).

Procedure to follow when starting a unit:

1-a) Press the power “ON-OFF” switch. The compressor will only start if the evaporating pressure is greater than the cut-in set point of the low pressure switch. Check immediately the good rotation of the compressor.

Evaporating pressure drops steadily, the evaporator empties itself of the liquid refrigerant accumulated in it during storage. After a few seconds, the solenoid valve opens if any.

1-b) Check on the sight glass (upstream of the expansion valve) that the bubbles disappear progressively, indicating a correct refrigerant charge and without non condensable gas. If the humidity indicator changes colour, indicating the presence of humidity, replace the filter-drier cartridge if the latter is of the replaceable type. Checking the sub cooling after the condenser is recommended. 1-c) Check that, when the cooling load has been balanced by the capacity of the unit, the chilled liquid is at design temperature.

2) Check the current values per phase on each compressor motor.

3) Check the current values per phase on each fan motor.

4) Check compressor discharge temperature.

5) Check compressor oil pump temperatures (semi-hermetic reciprocating compressors).

6) Check suction and discharge pressures and compressor suction and discharge temperatures.

7) Check chilled liquid entering and leaving temperatures.

8) Check outdoor air temperature.

9) Check liquid refrigerant temperature at the condenser outlet.

The function of these devices is to ensure a level of head pressure compatible with proper unit operation. An increase in outdoor air temperature increases head pressure, and this is maintained at its required value by fan operation.

This function only exists on units designed for brine or glycol/water chilling for which the freezing temperature depends on the concentration of the solution. Whatever type of device is used (see case 1 and 2), cut-out by the antifreeze function causes immediate unit stoppage.

CASE 1: Antifreeze thermostat

This device monitor chilled liquid temperature at the evaporator outlet. It triggers when the temperature goes below the minimum value (+ 4 C for water).

CASE 2: Antifreeze pressure switch

This monitors evaporating pressure of the refrigerant. It triggers when the temperature goes below the preset minimum value.

Electronic or cam type anti-short cycle relay:

This device limits the number of compressor start ups. Compressor motor thermal protection: This device stops the motor if winding temperature rises too high and enables it to start up again when temperature drops back to a normal value.

Fan over current protection:

Circuit breaker designed to stop the fan motors in the event of phase over current in relation to the permitted value.

Compressor motor over current protection:

Circuit breaker designed to protect each motor winding against accidental over current.

Indicator lights:

The electrical control box is fitted with indicator lights enabling visualization of the state of operation or non operation of a function or given circuit.

There is also an indicator to show that the unit is powered up, an emergency stoppage indicator for each compressor, an indicator to show stoppage of the compressor via the regulating system (through the main control thermostat which is sensitive to chilled water temperature), a run light per compressor, and a general fan default stoppage indicator (on air cooled units).

Chilled liquid pump interlock:

This interlock is made only if the pump is supplied with the liquid chiller. As soon as the unit is powered up and the remote on/off for the unit is validated, the pump starts running. Prior operation of the pumps is mandatory for compressor operation.

Flow switch for the chilled liquid :

This control device initiates unconditional unit stoppage as soon as the flow of chilled liquid (water, brine, etc…) ensured by the pump becomes insufficient, since this could cause rapid evaporate freeze up. When the contact opens due to a lack of flow the unit must stop immediately.