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.