Variable Speed Motors

Electronically commutated motors are widely described as variable speed motors. In truth, most blower motors used in air conditioning are variable speed, including shaded pole and PSC motors. Muliple tap shaded pole and PSC motors are designed specifically to vary their speed based on the tap that is powered. All induction motors vary their speed depending on the load. An increase in load will result in decreased motor speed. What makes ECM motors unique is their ability to vary their speed intelligently in response to the load. They are often used to vary motor speed to maintain constant airflow. To do this, the motors are programmed to match the performance of the blower on which they are mounted. When the airflow through the blower is restricted, the motor responds by speeding up enough to keep the blower CFM the same. In truth, a common PSC blower motor also speeds up when the air through the blower is restricted. However, it does not speed up enough to offset the loss of airflow caused by the restriction, so the airflow decreases. The PSC motor is just responding the way any induction motor does to a decreased load. On a blower with a PSC motor, an airflow restriction causes a decrease in airflow and in motor amp draw because it is not under as much load. A blower with a constant CFM electronically commutated motor will still move the same amount of air by increasing the speed enough to overcome the restriction. Because the motor is doing more work, the amp draw will increase. This is why good duct design and clean filters are important to ECM equipment. The blower motor on a new system with an ECM motor may actually draw a higher amp draw than the old PSC blower it replaced if it is connected to a restrictive duct system.  The popular X13 motors by Genteq are constant torque ECM motors. They vary their speed to maintain a steady torque output. When the blower airflow is restricted, the X13 ramps up its speed to maintain the same torque output. This will usually not be enough to completely overcome the restriction, but it will not be producing less torque when the system needs more torque, as is the case with a PC blower. Airflow still drops off, but not as much as with a PSC blower motor. A few systems use an external pulse width modulated signal to the motor to create a feedback loop that maintains an external measured system condition, such as static pressure in a duct system. 

NIOSH Safety Resources

The National Institute for Occupational Safety and Health (NIOSH) is the federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness.

The NIOSH web site has many excellent safety resources that your students can view or download. The site is large, so finding what you are looking for can sometimes be difficult, but it is worth the effort. You can find many excellent publications in their  directory of publications. Click on the “Directory of Publications and Products” link on the bottom left side of their main page. There is  a search bar to enter subjects you want to research. These are all free to download or view. Smaller documents can make excellent class safety handouts. Larger documents are more like small text books. For example the Electrical Safety Student Manual is really a book in pdf form. It is really good. One word of caution -  it shows graphic pictures of electrical burns and injuries, not cartoons. However, I find that after viewing the results of a severe electrical burn, students are far more likely to be careful in the lab.It is really too big to print and hand out, but it can be downloaded and shared as a pdf, allowing students to view it on a computer.Other publications available through the NIOSH site are

Electrical Safety Page

Protecting Worker from Heat Illness

Pocket Guide to chemical Hazards

NIOSH Safety Videos

Arc Flash Awareness Video

NIOSH Fact Sheets

   

Document Your Abilities

It is common for people who work in the HVACR industry to have very little documentation showing their proficiency. Many have never been to any formal school, others started and did not finish. Although there are now many certified techs, there are more that are not certified. This does not necessarily mean that they cannot perform their jobs, but that they have not taken the time to document their abilities. Often, the explanation is “I have been doing HVACR for 15 years and that is worth more than any piece of paper.” I would be the last to suggest that experience does not count – it does. But without a diploma or certification, how does a prospective employer know what you can do? In a tight job market, credentials matter. Many places examine resumes first to determine whom they want to interview. With no credentials, your chance of even getting an interview is slim. If you are one of the many HVACR workers without credentials, my suggestion is that you make documenting your abilities a priority. Chances are, there is a school somewhere near you that teaches HVACR. I am not suggesting that you quit working to go to school. It is often possible to do both. If you do not have any professional certifications from NATE, RSES, or HVAC Excellence you should work on obtaining professional Certification. Yes, it can take some time to go to school or study for a professional certification exam, maybe even a matter of years. Rather than focus on the length of the road, concentrate on the destination. One or two years will pass whether or not you are doing anything to improve your position. The question is, at the end of the time, where will you be? Will you be graduating with a diploma that documents your ability and opens doors, or will you still be right where you are today?