The Switch to EC Motors is On
New energy efficiency standards impact HVAC units for modular buildings and telecom structures.
New energy conservation standards taking effect next year will require changes to the specialty heating, ventilation and air conditioning systems used in modular classrooms, office buildings and telecom structures that house electronic equipment. In the meantime, the onus is on original equipment manufacturers to help their customers understand and comply with the new standards.
The HVAC units affected by the new U.S. Department of Energy standard (DOE), which takes effect in September 2019, are single package vertical air conditioners and heat pumps with cooling capacities of 65,000 Btu/h or greater.
Historically, these units were regulated under the DOE’s commercial air conditioner and heat pump category. Now separated into their own category with its own standards, these units must increase their energy efficiency ratio (EER) to 11, up from the current required EER rating of 10. The change is expected to cut cooling energy use by these users about 4% annually, compared to existing standards. Few, if any, legacy systems will meet this new rating by utilizing their existing induction motors.
Unlike most split residential HVAC systems—which locate their independently rated air conditioning motors outside and furnace motors inside—single package vertical units are all-in-one units that are rated according to their overall system efficiency. These commercial units are distinct for another reason: they typically have one blower and two (rather than one) condenser fan motors.
These differences matter. Most notably, they give OEMs more levers they can pull to address and meet the new efficiency standards and their engineering teams are evaluating every conceivable option to satisfy this new requirement at the best possible cost.
HVAC industry looks to more efficient EC blower motors
In most cases, OEMS are focusing first on blower fan motors. For one thing, they are installed indoors and, therefore, do not require the same protections from dust and water as condenser motors, which require an IP rating greater for outdoor use. They are, therefore, less expensive.
There is another compelling reason for focusing on blower motors. They are one of the biggest energy consumers in an HVAC system. As “low-hanging fruit,” they have been a primary target for efficiency improvements.
Most blowers in these units currently use permanent split capacitor (PSC) motors, which operate at 60% to 65% peak efficiency. To meet the new standards, blower OEMs have been upgrading these motors with more efficient EC—electronically commuted—motors, which operate between 80% and 85% efficiency, depending on the version selected.
A dual shaft blower ECM with a remotely mounted control offers a 20 point improvement in efficiency over standard dual shaft PSC blower motors.
EC motors have electronic speed and torque controls built in, which enables the drive to maintain airflow during environmental changes, such as static pressure drops. This makes it possible to achieve approximately 20 percentage points more efficiency than single-phase PSC motors, even at peak conditions.
To see why EC motors are a natural upgrade, it’s important to understand the fundamental differences between PSC and EC motors.
A PSC motor is an induction motor that is driven by line voltage. The design targets a specific load at a specific static. The speed at which the motor actually operates depends on the fan load, installation and static pressure. This dependency causes the motor efficiency to fall off drastically when operating outside the designed load and static window.
EC motors, on the other hand, utilize brushless permanent magnet (BPM) motor technology and are integrated with a tuned AC Drive. Because they use electronics to control the voltage and current applied to the motor, EC motors do not waste power inducing the rotor field like induction or other motor types. They allow speed to vary according to the unit’s need for constant torque or air flow.
There are many other benefits to migrating to EC motors. Among them:
More efficient design process: To design a PSC motor for a single package vertical unit blower, the OEM must define to the motor manufacturer the precise speed and power at which it wants the motor to operate. The motor manufacturer then designs a motor to those specifications and sends a sample to the furnace OEM for testing. Since the motor is load dependent, the motor design may need to be tweaked to meet the desired performance based on actual testing, requiring the manufacturer to create a new sample. It could take several design iterations—and perhaps even a blower wheel modification—to achieve the desired results.
With EC motors, blower OEMs eliminate the back-and-forth needed to achieve desired performance. With the assistance of development hardware and software, motor performance changes can be programmed in real time, resulting in significant reduction in the weeks or possibly months of development time for the induction motor.
Easier installation and integration: Because these motors are driven by electronics, it is also possible to program their speed and torque through the electronic controller incorporated into the motor. That is good news to OEM product developers, who can simply define the desired torque and speed settings they want in a motor. The motor drive is plugged into their lab development computer using a programming tool. Lab development software is utilized to set the desired constant torque, speed or airflow. The programming tool then communicates to the motor, and the program is stored on the electronic drive. The motor can then be tested in the unit for validation. If the motor needs to be tweaked for desired airflow, the motor can simply be reprogrammed.
EC motors have the same size diameter as a standard furnace PSC motors, and therefore can be incorporated into most blowers without additional design changes.
Improved reliability: An integrated EC drive/motor system that has been precisely tuned can reduce common VFD-related issues, such as electromagnetic interference and corona discharge, which can produce radio and television noise and disturbance. In addition, EC motors are not prone to overheating and do not require additional measures to offset heat generation.
Flatter efficiency curve: A blower motor will typically cycle through several stages while in use. These stages are usually pre-determined by the motor manufacturer or a preprogrammed controller. When it is first started up, for example, it will likely run at a lower speed to remove humidity or circulation mode. During heating or cooling mode, the motor will accelerate to the operating speed designated for the application or unit.
When looking at a PSC efficiency curve, peak efficiency is achieved at a single speed, and drops off quickly as you move away from this optimal condition. In comparison, a BPM efficiency curve is higher and considerably flatter over a broad operating range. The difference in efficiency curves illustrates the BPM motor’s greater operating efficiency over a larger range versus the PSC. This operating range includes circulation speed, which is a low efficient operating point for PSC motors, and the largest improvement with the switch to BPM technology.
Value to the distributors, after-market and end-users
While OEMs are most immediately impacted by the new single package vertical unit regulations, distributors, HVAC contractors and other after-market companies should find that their own operational efficiency will improve with the switch.
Primary EC motor ratings can be shipped to distributors preprogrammed. Moreover, for greater customization the distributors are provided with tools that allow preprogramed EC motors to be reprogramed to match the performance of the original motor.
Looking ahead: collaboration is key
EC motors on the market today can help HVAC OEMs meet the new performance regulations. That’s the good news, but it’s not good enough.
To mitigate the cost impact to the end-customer created by switching to EC motors, OEMs and motor manufacturers need to partner in open collaboration for even better solutions.
A standard 82% efficient EC motor, for example, may be overkill to meet the new regulations. Instead of offering a single level of efficiency, multiple efficiency tiers may be needed to meet performance and cost targets in the redesign process. Some systems, particularly higher tonnage units, may not be able to achieve the necessary 11 EER rating using the blower motor alone, and in turn must also upgrade their condenser motors. Some states may invoke even higher standards that require great energy efficiency.
It’s clear that the EC motor will be the driving motor technology once the new regulations are implemented. However, further innovation is prudent to create the best value for the market. Single package vertical unit OEMs will benefit by collaborating with motor companies, as well as blower wheel and blower housing manufacturers. It will help them achieve more success in developing finished products that both meet regulatory efficiency standards AND customer pricing demands.