Energy Saving Motors

To ECM or Not?

One of the biggest considerations when choosing any new HVAC equipment with a fan (e.g. hot air furnaces, air conditioning equipment) is whether to select a system with an ECM (Electronically Commutated Motor).  An ECM-enabled system offers two principal advantages.  First, the mechanical configuration of the motor and electronic control make ECMs up to 65% more efficient than standard fan motors (significantly less electricity consumption).  Second, the built-in electronic control allows for an unlimited number of speed settings.  This means that the fan speed for ECM systems can be continually adjusted to provide the correct amount of airflow; much like a car can be operated at different speeds to meet traffic conditions.

At first glance, it might seem that the enhanced efficiency and greater adjustability of ECMs would make them the best possible option.  However, in many situations, the use of an ECM presents distinct challenges.  In fact, in 2008 Labrador Services was only able to install ECM systems in just over 50% of all projects.

Why?  Primarily because ECM-enabled systems can be noisier and have problems with erratic air flow when they are connected to improperly-sized or inappropriately- configured ductwork.  This is especially problematic in older homes and buildings with duct work that was originally designed for low-speed, high-temperature fan systems.  In addition, some newer structures with poorly designed or shoddily constructed ducts can also lead to complications. Unfortunately, many structures fall into one of these categories. A costly, system-wide overhaul is often required to ensure the proper function of an ECM.

Another complication for ECM units is that, in many cases, they cannot be used in zoned systems (although not always—see “A Better Control Strategy for ECM Motors” below for more details).  Zoned systems utilize multiple thermostats and duct branches to create variable temperature control within areas or rooms within a home or building.   The benefits of such systems, namely energy savings and improved temperature regulation, can be essentially negated by the introduction of an ECM.  If only one zone or a small percentage of the zones need air, the speed controls of an ECM are not sophisticated enough to keep the fan at the appropriate setting.  This results in a phenomenon known as “over-speeding,” inevitably leading to noise and airflow problems.

A Better Control Strategy for ECM Motors

Although it is an overly technical topic, we believe that the control and regulation of ECM-based systems is one of the top ten environmental/energy issues today.   Given the prevalence of fan-based heating and air conditioning systems in the US and throughout the world, a widespread transition to ECM-based systems provides enormous potential for energy savings.  What’s more, when utilized properly, ECM-based systems offer best-in-class comfort in most living spaces.  Unfortunately, ECMs are all too often paired with outdated speed-setting technology, resulting in noise and air flow challenges.  A solution may, however, be close at hand.  ECM motors are actually very similar to the variable speed motors used in commercial buildings.  Variable speed motors are typically speed-indexed based on system air-pressure; return air temperature or staging controllers.  If these control technologies were offered for ECM motors, the use of these motors would surely increase, yielding tremendous energy savings across the board.