The EXV control logic has several overrides, which are also used to control the position of the EXV.

Approach between SST and LWT

Maximum Operating Pressure (MOP)

Approach — If the approach (pinch), which is the difference between leaving fluid temperature and saturated suction tem- perature, is equal to or less than the pinch set point then the EXV will not open any further even though discharge super- heat set point is not met. Pinch set point is calculated using suction superheat, discharge superheat and pinch offset. Pinch offset is used to adjust calculated pinch set point do to accuracy of transducers and thermistors.

MOP — The EXV is also used to limit cooler saturated suction temperature to 55 F (12.8 C). This makes it possible for the

EXV to maintain economizer superheat set point, which is ap- proximately 8° to 12° F (4.4° to 6.7° C). If the circuit capacity is less than 70%, the economizer EXV will be closed.

The economizer EXV has one override. If the discharge gas temperature exceeds 195 F (90.6 C) the economizer EXV will start to open. The EXV will be controlled to maintain discharge gas temperature at approximately 195 F (90.6 C).

If it appears that main EXV or economizer EXV is not properly controlling circuit operation to maintain correct super- heat, there are a number of checks that can be made using test functions and initialization features built into the microproces- sor control. See the Service Test section to test EXVs.

MAIN EXV CONNECTOR

chiller to start at higher cooler fluid temperatures without over- loading the compressor. This is commonly referred to as MOP (maximum operating pressure). If the SST is equal to or greater than the MOP set point then the MBB will try to control the EXV position to maintain the MOP set point.

The discharge superheat leaving the compressor is main- tained between approximately 18 and 25 F (10 and 14 C), or less. Because EXV status is communicated to the Main Base Board (MBB) and is controlled by the EXV modules, it is pos- sible to track the valve position. The unit is then protected against loss of charge and a faulty valve. During initial start-up, the EXV is fully closed. After an initialization period, valve position is tracked by the EXV module by constantly monitor- ing the amount of valve movement.

ECONOMIZER EXV CONTROL — The economizer EXV

6

ECONOMIZER EXV CONNECTOR

1

NAME PLATE

2

1

3

is controlled by the circuit EXV board. There is an economizer gas temperature thermistor and economizer pressure transducer located in the line, which runs from the economizer assembly to the compressor. The economizer pressure is converted to satu- rated temperature and is used to calculate economizer superheat. Economizer superheat equals economizer temperature minus saturated economizer temperature. The economizer EXV only operates during normal conditions when the capacity of the circuit is greater than 70%. Once the capacity of the circuit is greater than 70% the MBB will start controlling the economizer

5

4

LEGEND

EXV — Electronic Expansion Valve

1Fuse Plug Adaptor

2High Flow Access Fitting

3Filter Drier

4Main Expansion Valve

5Economizer Expansion Valve

6Brazed Plate Heat Exchanger

Fig. 42 — Economizer Assembly

1.

Cable

 

2.

Glass Seal

 

3.

Motor Housing

 

4.

Stepper Motor

 

5.

Bearing

 

6.

Lead Screw

 

7.

Insert

 

8.

Valve Piston

a30-4241

9.

Valve Seat

 

10.

Valve Port

 

Fig. 43 — Cutaway Views of the Electronic Expansion Valve

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Carrier 30XW150-400 specifications Economizer Assembly

30XW150-400 specifications

The Carrier 30XW150-400 series is a line of water-cooled chillers that exemplifies innovation, efficiency, and reliability in commercial cooling solutions. Designed for medium to large-scale applications, this series is ideal for a variety of settings, including commercial buildings, industrial processes, and chilled water systems.

One of the standout features of the Carrier 30XW series is its efficiency. The chillers utilize advanced variable-speed compressor technology, which allows the units to adapt to varying cooling loads while minimizing energy consumption. This technology not only reduces operational costs but also contributes to better environmental sustainability by lowering greenhouse gas emissions.

The 30XW series chillers are equipped with high-efficiency, scroll compressors that operate quietly and provide significant energy savings. By utilizing enhanced economizer controls, these units can achieve higher efficiency ratings, especially in part-load conditions. The result is an impressive Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER), making these units a smart choice for energy-conscious businesses.

In terms of reliability, the Carrier 30XW150-400 series features robust construction and an array of safety and monitoring systems. The units come with advanced diagnostics that help in quickly identifying and addressing any operational issues. This proactive approach ensures reliability and minimizes downtime, which is crucial for maintaining optimal temperature controls in critical environments.

Additionally, the chillers incorporate environmentally friendly refrigerants that comply with the latest regulations, making them a sustainable choice for modern commercial applications. Their compact design allows for flexible installation options, and the integrated control systems provide the ability to optimize performance based on specific building management demands.

User-friendly interfaces and remote monitoring capabilities further enhance the ease of operation, allowing facility managers to have real-time insight into performance metrics and system health. This level of control contributes to better maintenance planning and maximizes the lifespan of the equipment.

In summary, the Carrier 30XW150-400 series of water-cooled chillers combines advanced technology, energy efficiency, and reliable performance, making it an ideal solution for various commercial and industrial cooling needs. With its commitment to innovation and sustainability, Carrier continues to set the standard in the HVAC industry.