ECM Air Handler Fans

Home owners who use an HVAC system with a central air handler fan can realize significant energy savings by using a fan with an electronically commutated (ECM) motor. Savings will be even larger for homeowners who run the HVAC fan continuously or frequently to filter the air or to bring in and circulate fresh air as part of a whole-house ventilation system. Because they are variable speed and can adjust their speed up or down to meet load, ECMs can operate on as little as 80 watts of electricity. In contrast, permanent split capacitor (PSC) engines are single-speed motors that typically consume between 500 and 550 watts when providing heating and cooling (Michael 2009).

Until recently PSC motors have been the most popular fan motor for furnaces, air handlers, condensing units, and packaged units. They are known for their simplicity, reliability, and low cost. However, these alternating current (AC) induction motors have inherent inefficiencies; they are at best 60% efficient and they generate excess heat which must be dealt with. PSC motors are not programmable and their motor speed cannot be easily varied.

ECM technology is based on a direct current (DC) design that is inherently about 80% efficient, compared to the 60% efficiency of a PSC motor, and they run cooler than PSC motor designs (Holliday 2011). The brushless design eliminates failures caused by worn brushes and commutators. ECM fans use about 400 watts in cooling mode and about 80 in continuous fan mode (Michael 2009). Because of their variable speed, they can run at low speeds for much of the time while PSC motors are typically on high speed all the time, so annual operating costs for ECMs can be 25% to 75% lower (Minnesota Power 2015).

The ability of ECMs to ramp up and ramp down slowly adds to their quiet operation and enhances their dehumidifying ability, especially when combined with a two-stage compressor and dehumidification controls. In dry climates, the ECM motor can be programmed for cooling at high speed followed by continued running of the fan at the end of the cooling cycle at a lower speed and watt draw to evaporate the water off the coil. In a wet climate, the controls are set differently for lower speed cooling, which provides more dehumidification in cooling mode, with the fan going off at the end of the compressor cycle to allow the coil to drain. Even when the system is set to “constant fan,” the fan still shuts down for 20 minutes at the end of the compressor cycle so the coil can drain. In climates that are sometimes dry and sometimes wet, an indoor thermidistat can be installed that will enable the motor controls to switch from dry climate programming to wet climate programming depending on the indoor conditions (Holliday 2011).

New HVAC equipment with ECMs installed typically costs 40% to 60% more than non-ECM based equipment (Michael 2009). Inexpensive replacement ECM motors can be installed to replace PSC motors in existing equipment (not recommended on equipment more than 10 years old per Michael 2009) while offering many of the benefits of ECMs, including high efficiency, variable speed, and quiet operation, at a lower cost.

Building America researchers note that ECM motors can reduce fan energy consumption by 50% or more over PSCs as long as the duct system is properly installed and constructed to eliminate excessive airflow resistance (Rudd 2011).

Both IECC 2012 and the ENERGY STAR Certified Homes program require the use of an ECM fan motor if the home’s HVAC air handler will be used to distribute fresh air as part of a whole-house ventilation system. See the guide Whole-Building Delivered Ventilation for more information. Alternately, ENERGY STAR permits non ECM fan motors, if the HVAC system has controls that will reduce the standalone ventilation run-time by accounting for hours when the HVAC system is heating or cooling, while meeting code-required ventilation levels, such as those specified in ASHRAE Standard 62.2-2010/2013, Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings. See manufacturers’ instructions for installing and setting the timer, damper, and controls. 

Figure 1 shows a central-fan-integrated ventilation system that uses the air handler fan to distribute fresh air ducted directly to the return side of the air handler from outside. When the central air handler fan uses an ECM motor, the motor power draw will be about one-fourth of what it would be with a PSC motor when the system is operating in “fan-only” mode for ventilation.

Figure 1 – Using an ECM motor rather than a PSC motor in air handler fan used for central fan integrated ventilation can cut fan energy use by 25% to 75%.

Compliance

ASHRAE 62.2-10/13  
Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings. This ventilation standard by the American Society of Heating, Air-Conditioning and Refrigeration Engineers (ASHRAE) defines methods for determining the minimum levels of ventilation needed to provide acceptable indoor air quality in low-rise residential buildings.

2009 IECC 
Section 403.5 Mechanical ventilation (Mandatory). Automatic or gravity dampers are installed on all outdoor air intakes and exhausts.

2012 IECC 

R403.5 Mechanical ventilation (Mandatory). The building must have ventilation that complies with the International Residential Code or International Mechanical Code. Outdoor air intakes and exhausts must have automatic or gravity dampers that close when the ventilation system is not operating.

R403.5.1 Whole-House mechanical ventilation system fan efficacy. Mechanical ventilation system fans should meet the fan efficacy requirements shown in IECC Table R403.5.1. Exception: Where mechanical ventilation fans are part of the tested and listed HVAC equipment, they should be powered by an electronically commutated motor.

2015 IECC

R403.6 Mechanical ventilation (Mandatory). The building must have ventilation that complies with the International Residential Code or International Mechanical Code. Outdoor air intakes and exhausts must have automatic or gravity dampers that close when the ventilation system is not operating.

R403.6.1 Whole-House mechanical ventilation system fan efficacy. Mechanical ventilation system fans should meet the fan efficacy requirements shown in IECC Table R403.6.1. Exception: Where mechanical ventilation fans are part of the tested and listed HVAC equipment, they should be powered by an electronically commutated motor.

ACCA Manual S
Size the heating and cooling equipment including the HVAC fan in accordance with the guidelines described in ACCA Manual S, Residential Equipment Selection.

ACCA Manual J
Perform building heating and cooling load calculations as described in ACCA Manual J, Residential Load Calculation.

ENERGY STAR Certified Homes 

ENERGY STAR Certified Homes (Version 3.0, Revision 08), Rater Field Checklist, 7. Whole-House Mechanical Ventilation System, 7.5. If system utilizes the HVAC fan, then the specified fan type is ECM/ICM (4.7) or the controls will reduce the standalone ventilation run-time by accounting for hours when the HVAC system is heating or cooling.

DOE Zero Energy Ready Home
The U.S. Department of Energy (DOE) Zero Energy Ready Home National Program Requirements requires (Exhibit 1, and 6) that all homes meet ENERGY STAR Certified Homes Version 3 or 3.1 and the U.S. Environmental Protection Agency Indoor airPLUS Construction Specifications

EPA Indoor airPLUS
The U.S. Environmental Protection Agency (EPA) Indoor airPLUS Construction Specifications requires homes to meet the ENERGY STAR Certified Homes requirements. Additional advisories include the following.

4.5 Mechanical Whole-House Ventilation
Advisory: Outdoor air ducts connected to the return side of an air handler should be used as supply ventilation only if the manufacturers’ requirements for return air temperature are met (e.g., most manufacturers recommend a minimum of 60 degrees Fahrenheit air flow across furnace heat exchangers).