QwikSEER White Paper

ManualsBrandsQwik Products ManualsHVAC ControlsQwikSEER+ WattSaver

QwikSEER+ Theory of Operation and Retrofit Potential

Mainstream Engineering Corporation

Rockledge, FL 32955

http://www.qwik.com/products/qwikseer/index.jsp

Prepared by Robert P. Scaringe and R. Paul Roth

March 2013

Introduction

Three motor types are primarily used in residential air handlers: permanent split capacitor (PSC),

X-13, and electrically commutated motor (ECM). If selected properly, all three are capable of

delivering the required airflow. However, the three choices vary in price and energy

consumption. The ECM motor is the most efficient and most expensive, while the PSC is the

least efficient and least expensive.

The ECM and X-13 motors will indisputably decrease the electric bill when compared to a PSC

motor that is providing the same airflow. However, an efficient blower motor that is providing

more airflow than is required can waste more energy than a less efficient blower motor providing

the correct lower airflow.

The two challenges addressed in this paper are first determining under which environmental

conditions the fan speed can be lowered to reduce energy consumption, and second determining

if the higher cost, increased complexity, and potentially lower reliability of the ECM or X-13

motor is worth the investment.

To understand the components involved in these challenges, the types of motors and thermostats

used in residential air handlers are described in the next section, followed by a section that

describes the environmental effects of conditioned airflow rate on efficiency. Finally, the last

section shows how Mainstream’s QwikSEER+ WattSaver control board can meet the challenge

of providing the most efficient fan speed that can save money by changing with environmental

conditions without the increased complexity of an expensive, continuously variable speed motor.

Motor Types

This section describes the three most commonly used motor types for residential air handlers:

permanent split capacitor (PSC), X-13, and electrically commutated motor (ECM).

PSC Motors

A PSC motor is a fixed-speed, asynchronous motor that operates on alternating current power.

PSC motors in residential air conditioning systems typically have between three and five speed

taps. These speed taps are connection points for electrical power and determine the blower speed.

When installing a residential air conditioning system, the HVAC technician selects one of the

possible blower speeds by connecting the power input to one of the speed taps. It is important to

understand that although blower motor speed is constant, actual airflow, typically measured in

Cubic Feet per Minute (CFM) is dependent on the pressure drop in the system. Clearly, the ideal

blower speed selection for a given system is different for different installations due to differences

Summary of content (7 pages)

PAGE 1
QwikSEER+ Theory of Operation and Retrofit Potential Mainstream Engineering Corporation Rockledge, FL 32955 http://www.qwik.com/products/qwikseer/index.jsp Prepared by Robert P. Scaringe and R. Paul Roth March 2013 Introduction Three motor types are primarily used in residential air handlers: permanent split capacitor (PSC), X-13, and electrically commutated motor (ECM). If selected properly, all three are capable of delivering the required airflow.
PAGE 2
in the pressure drop in the ductwork. conditions. The ideal flow rate also varies with environmental A PSC blower motor is less efficient than ECM or X-13 motor. expensive and most reliable motor due to their simplicity. They are also the least ECM Motor An ECM motor is a brushless, direct current (DC) motor with an internal microprocessor that manages commutation, resulting in synchronous operation over a range of speeds.
PAGE 3
the compressor contactor, 24 VAC across the W (white) and C activates the heat contactor, and 24 volts across either O (orange) or B (blue) to C actives the heat pump reversing valve. In addition, 24 VAC is continuously supplied to the thermostat, if needed, via R (red) and C wires. Digital Thermostats On a digital thermostat, 24 VAC is still supplied to the thermostat via the R (red) and C (common) wires; however, all commands from the thermostat to the system are via two or more digital lines.
PAGE 4
evaporator coil only increases the compressor lift by about a degree or less (i.e., lowers the evaporator temperature by 1 degree or less), then we have found that the savings in power consumption by the blower motor is greater than the increased power consumption of the compressor, the difference being the energy saved. This is in part because the motor power curve for the compressor is relatively flat, that is an unloaded compressor motor draws almost the same power as a loaded motor.
PAGE 5
Constant Torque ECM or X-13-type Motors Constant torque ECM or X-13-type motors have multiple torque settings instead of speed settings. These motors are typically operated at a single torque setting, and as a result, can provide a relatively constant airflow even as installation conditions change. Besides being more efficient than PSC motors, the actual airflow achieved in an installation is more likely to be the design airflow specified by the manufacturer.
PAGE 6
Unfortunately, HVAC installers do not perform efficiency optimization tests when selecting the appropriate airflow rate, so there is no way to know if the blower is operating at the conditions that optimize system performance. Even if HVAC technicians could perform a system efficiency optimization test when selecting the blower setting, the optimal blower airflow can change over time because of environmental changes.
PAGE 7
and potentially lower the reliability. QwikSEER+ can be installed in an existing system with a PSC motor and analog thermostat to enhance efficiency and humidity removal. QwikSEER+ along with a PSC motor can also be installed in any system with a failed ECM or X-13 motor that uses an analog thermostat. Figure 1. Percentage improvement in EER with QwikSEER+ control board (using 14 SEER Straight Cool and 14 SEER combined AC–furnace, return air: 80 °F, 51% RH) Figure 2.