Trane SCXG-SVX01B-EN manual Waterside Components, general Operation information, Water Purge

general

Operation information

Waterside Components

Waterside components consist of water piping, water valves, water flow switch option, water cooled condensers (SXWF only), and the economizer option.

Water Purge

This user-definable feature allows the user to select a purge schedule to automatically circulate water through the economizer and condensers periodically during non-operational times. This allows fresh chemicals to circulate in waterside heat exchangers. This feature is on all units and is defined at the HI.

Water Piping Options

Water piping is factory-installed with left- hand connections on units without a waterside economizer. Units can be ordered with either basic piping or intermediate piping. Also, units with waterside economizers can be set for either variable or constant water flow at the HI. See Figures O-GI-3, O-GI-4, and O- GI-5 for detailed piping configuration information.

With compatible piping configurations, the unit can be configured to provide:

1.Constant water flow with basic or intermediate piping or

2.Variable water flow (head pressure control) with intermediate piping only.

Constant water flow is for condenser pumping systems that are not capable of unloading the water-pumping system. Variable water flow maximizes energy saving by unloading the water pumping system.

Basic Water Piping

This option is available on units without a waterside economizer and with condenser water applications above 54°F (12.2°C) that do not require condensing pressure control. Left hand water connections and piping are extended to the unit exterior. Manifold piping is factory installed.

Intermediate Water Piping This option provides condensing temperature control when the unit is configured (user defined at the HI) for variable water flow with or without a waterside economizer. A two-way modulating control valve is wired and installed in the unit to maintains a specific

range of water temperature rise through the condenser when entering fluid temperature is less than 58°F (15°C). This option allows the compressor to operate with entering fluid temperature down to 35°F (2°C). The minimum valve position to maintain minimum condenser flow rates is user-defined at the HI. This valve drives closed if the unit shuts down or if a power failure occurs.

Water Flow Switch Option

A water flow switch is factory installed in the condenser water pipe within the unit. Whenever the flow switch detects a water flow loss prior to or during mechanical cooling, compressor operation locks out and a diagnostic code displays. If water flow is restored, the compressor operation automatically restores.

Water-Cooled Condensers

Units that are set up for variable water flow will modulate a water valve to maintain a user-defined condensing temperature setpoint. Condensing temperature will be referenced utilizing factory installed sensors located at each condenser.

Table O-GI-8. Condenser water piping

connection	sizes
unit size	inlet pipe	outlet pipe
SXWG 20, 25,	2 1/2 NPT	2 1/2 NPT
30, 32, 35

Waterside Economizer Option

The waterside economizer option takes advantage of cooling tower water to either precool the entering air to aid the mechanical cooling process or, if the water temperature is low enough, provide total system cooling. Waterside economizing enables when the unit’s entering water temperature is below the unit’s entering mixed air temperature by a minimum of 4°F plus the economizer’s approach temperature. The approach temperature default is 4°F. Waterside economizing disables when the unit’s entering water temperature is not below the unit’s entering mixed air temperature by at least the water economizer approach temperature. The approach temperature defaults to 4°F.The economizer acts as the first stage of

cooling. If the economizer is unable to maintain the supply air setpoint, the unit control module brings on compressors as required to meet the setpoint.

The waterside economizer includes a coil, modulating valves, controls, and piping with cleanouts. The coil construction is ½- inch (13 mm) OD seamless copper tubes expanded into aluminum fins. The evaporator and economizer coils share a common sloped (IAQ) drain pan. Drain pan options are either galvanized or stainless steel, and are insulated and internally trapped.

The waterside economizer coil is avail- able with either a two or four row coil, with no more than 12 fins per inch. The tubes are arranged in a staggered pattern to maximize heat transfer.The coil has round copper supply and return headers with removable cleanout and vent plugs. The optional mechanical cleanable economizer has removable cast iron headers to allow easy mechani- cal cleaning of the tubes. The waterside working pressure is rated for 400 psig (2758 kPa).

Waterside Economizer Flow Control Units equipped with a waterside economizer can be set from the human interface panel for variable or constant water flow.

Constant Water Flow

Two-way modulating control shutoff valves are wired, controlled, and installed in the unit. One valve is located in the economizer’s water inlet, and the other is in the condenser bypass water inlet. When the waterside economizer enables, the two-way valves modulate to maintain the discharge air temperature setpoint. As the economizer valve opens, the condenser bypass valve closes, and vice versa. Full water flow is always maintained through the condensers. Both valves will close in the event of a power failure.

Variable Water Flow

Two-way modulating control shutoff valves are wired, controlled, and installed in the unit. One valve is located in the economizer’s water inlet, and the other is in the condenser water inlet. When the economizer valve is active, the condenser bypass valve closes. The

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