Water Source Heat Pumps

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Aquazone™ Water Source Heat Pumps - Fan Motor Innovation

Carrier’s commercial water source heat pumps (WSHP) offer a wide selection of fan motor options, from permanent split capacitor (PSC) motors and constant airflow electronically commutated motors (ECM). One our most popular options is the constant torque ECM motor, which is an ideal choice when both cost and efficiency matter.

How is a constant torque ECM different from a constant airflow ECM?

Constant torque ECMs are high efficiency, brushless DC motors similar to constant airflow ECMs but much less expensive. The constant torque ECM fan motors maintain constant torque, not constant airflow, as the system external static pressure (ESP) changes. Herein lies the main performance difference between the constant torque and constant airflow ECM. The actual amount that the airflow will vary with the constant torque ECM, however, is minimal.

The airflow of a 3-ton WSHP changes as ESP increases for each of the 3 fan motors. At low ESP, all fan motors provide relatively the same amount of airflow. As the ESP increases above 0.5 inches of w.g., the airflow from the PSC and constant torque ECM fan motors decreases. However, the decrease of the airflow in the constant torque ECM is minimal. Even as the ESP increases up to almost 1 inch w.g., the constant torque ECM air volume is still near 90% of design volume. Thus, with a minimal airflow reduction as ESP increases and a lower first cost, the constant torque motor is a perfect middle tier fan motor option.

What motor is the right choice for my WSHP?

Determining exactly what motor is the correct choice depends upon the specific needs of the application. To help with this, Table 1 is provided below to compare each of the 3 motor types available.

A PSC motor provides an adequate solution where first cost is the main concern. When efficiency and longevity are important, ECM motors are the best choice. Constant airflow motors excel at maintaining an exact volume of air, but at high first cost. If both efficiency and cost are important, turn to the constant torque ECM.

How quickly can an ECM payback?

Choosing either a constant torque or constant airflow ECM motor will help to reduce operating cost. While both types of ECM motors will have similar operating costs, constant torque ECM motors will have a lower purchase price, making it’s payback period more attractive than constant airflow ECM motors. Depending on the location and application, constant torque ECM motors can pay for itself in as little as two years. For example, when modeling a school in Atlanta, New York, or Los Angeles using Carrier’s 50PCH030 WSHP, the payback for the additional cost of a constant torque ECM over a PSC motor is as short as 2 years. Here, Carrier’s Building System Optimizer software was used to model the building’s energy costs.