Application Notes: Optimizing Chiller Plant Performance

Optimizing Chiller Plant Performance

Background information on chiller optimization:

In most commercial facilities, the chiller plant represents a significant percentage of the total building electrical consumption and maximizing the efficiency of the chiller plant is a crucial part of managing the facility's mechanical system. Most building operators are unable to achieve maximum system efficiency because they do not have the data necessary to evaluate the success of measures implemented to improve efficiency. Several key factors make chiller optimization difficult:

Accurate chiller system assessments must account not only for the chiller operation, but also must look at the impact on the cooling tower, condenser water pumps and chilled water pumps.
Very few buildings have accurate system curve data to provide a guide for optimizing performance. The chiller manufacturers provide data on the chillers, the pump manufacturers provide data on the pumps and the tower manufacturers provide data on the towers, but there is rarely actual performance data which reflects the interaction of all components
To accurately assess the effects of changes made to plant operation, the total kW for all of the components must be measured and summed. This is typically expensive and often requires shutdown and rewiring of the chiller plant

Although these factors represent a significant challenge to the building owner, the use of installed automation systems and new Veris technologies provide an opportunity for payback of all installation costs within a year or less for most building owners. Measurement of a few simple variables combined with state-of-the-art power sensing products permits the building owner to implement a very successful program of chiller optimization in a relatively short time. Ongoing monitoring using graphics-based operator interfaces allows the operator to precisely determine the impact of changes in a timely and efficient manner.

Successful implementation requires the following:

Automated control system with analog inputs;
Graphical user interface for plotting multiple variables;
Entering and leaving condenser water temp (ECWT & LCWT) sensor(s) to measure the water temperature entering and leaving the condenser ;
Entering and leaving chilled water temp (EChWT & LChWT) sensor(s) to measure the entering and leaving chilled water temperatures at the evaporator;
Chilled water flow (in GPM) to calculate the tons of cooling;
Veris single phase power sensors for the chiller, pump(s) and tower electrical supply leads

Single phase power sensor theory of operation:

Mechanical loads such as chillers, pumps and cooling towers are balanced loads, which means that the power drawn by each of the three phases is equal. This provides an excellent opportunity for lowering installation costs by measuring the power on a single phase of the load and using software to determine the total power load. The sensor uses a split core, high accuracy current sensor combined with an integral voltage sensor and the associated circuitry to produce an analog output (4-20 mA) proportional to the power (kW) being sensed. This approach is superior to calculated methods using current sensors as the kW transducer captures power factor and voltage, providing a much higher level of accuracy than calculated values.

The VERIS 6200, 6300 and 6400 kilowatt transducers (KT's) represent the perfect solution to monitoring power on balanced loads such as motors. These transducers offer an excellent alternative to current sensors which do not capture power factor and thus can provide significant errors when used to calculate motor loads. The KT's are available in 3 sizes (300 A, 800A and 2400 A) with respective openings of 1.25", 2.50" and 2.50" x 7.75". Standard outputs are for pulse (kWH) and analog (kW). The KT's provide for easy installation directly in the motor control center or other electrical panel.

Installation instructions:

Turn off power to the motor(s)
Mount the KT so that the conductor wire to the load is approximately centered in the KT
Verify that the KT is oriented properly (i.e., the arrows on the label point in the direction of the load
Connect the voltage leads from the KT to the voltage source corresponding to the phase being sensed (Line to line for three phase loads). Insure that the device is fused per NEC requirements.
Connect the output leads to the analog input to the automation panel
Start the motor and verify that the power sensed by the KT is correct (within the expected range) by using a hand-held ammeter and voltmeter

The total kW for the system is calculated by summing the values determined above:

kW _total=kW_chiller+kW_pumps+kW_tower

Using this input data to measure power, the building operator can adjust the temperature differential on the condenser and chilled water loops while measuring the kW consumed by the total chiller plant (chiller, pumps and towers). By measuring the volume of water (GPM) flowing in the system and the DT of the chilled water supply, the user can calculate the efficiency of the system using the formula:

Efficiency = kW / Ton

Efficiency = kWtotal /[ (GPM * DT)/24]

Typical installation:

Applications are suggestions. Field applications vary; since manufacturer does not install the devices, it is up to the installer to ensure suitability and compliance to appropriate codes.