|
Ok, so we have discussed and demonstrated that the Airwatts published in a product brochure are not a good measurement of performance.
We also discussed that Airwatts are misleading not only because smaller motors can be hidden inside a large central vacuum system, but also because Airwatts in a working vacuum are much different than those promoted in a sales brochure.
What we would now like to introduce is two other performance terms you may encounter: Airflow (CFM) and Suction (Vacuum / Inches of Waterlift) which when applied together are used to determine Airwatts through a mathematical equation.
Before going further it is important that we remind you that the ONLY time Airwatts are a true measure of cleaning performance, is when they are measured at the END of your central vacuum hose (which no manufacturer does), not at their peak values taken at the motor without any Airflow performance loss.
In this exercise, we would like to demonstrate the significance Suction plays on 'real life' vacuuming and Airwatt performance where it actually matters. At the end of your vacuum hose!
 Imagine your central vacuum motor much like a Jet engine. Turbine propellers are spinning at thousands of RPM's per minute generating tremendous Vacuum and producing a tremendous amount of Airflow which is then exhausted outdoors. A central vacuum motor operates along the same principle. Vacuum is generated producing Airflow which is exhuasted from the motor.
Airflow which is measured in CFM (Cubic Feet Per Minute) whereas Suction / Vacuum which is measured in "Inches of Waterlift".
While the Airflow measurement tells how much Air the central vacuum motor can move, the Suction measurement tells how much maximum pull the motors is capable of. This is determined by sucking a 2" column of water vertically to its maximum height in inches, hence the term "Waterlift".
Unlike a car engine however where both Torque and Horsepower share a similar performance curve, a central vacuum motor is quite different. When Airflow is at its maximum performance at an open orifice of 2 inches, Suction is at it's weakest and vice versa, when Suction is at its maxium at sealed vacuum 0 inch orifice, there isn't any Airflow. This is illustrated in [Figure 1]
Like dust in the wind, it is the movement of air (Airflow) which carries dirt away and just like in nature, it is a difference in atmospheric pressure (Vacuum) that creates that movement of air. The stronger the Vacuum that is created, the greater the velocity of air that rushes to balance a pressure imbalance!
The amount and speed at which air travels (i.e. velocity) has a direct impact on your central vacuum's ability to move debris. In the case of a gentle ocean breeze versus a tornado or hurricane…this is the difference between drying your laundry and ripping your house off its foundation.
In [Figure 2] you will notice when you reduce the orifice size of the Airflow (such as using a crevice tool attachement) the result is an increase in airflow velocity as Suction increases. You might compare this to walking between two city skyscrappers on an otherwise calm day. Between the buildings you will experience a big increase in wind speed.
A typical household fan and a bathroom exhaust fan can produce a lot of airflow comparable to the output of a central vacuum, but neither is capable of generating enough Suction to create or maintain the Airflow velocity necessary to overcome the resistances found in a typical central vacuum system.
If you remember earlier, we introduced the term "Working Vacuum / Effective Orifice" which is what a central vacuum motor typically operates at when installed into a vacuum installation. Essentally, all the airflow robbing restrictions within the system make the motor operate as though it were being restricted by a 5/8" orifice which means the motor has to work harder. Motor RPMs (Revolutions per minute) increase, suction increases where conversely airflow decreases. Hence central vacuums using motors with higher Suction yeild higher end of hose Airwatts.
Of both Airflow and Suction, Suction plays the most impact on the end of hose Airwatts (the point where actual vacuuming take place). This is because within your central vacuum system, there are Airflow robbing restricitons from the hose, piping, elbows, filters or paper bag. Suction helps maintain Airflow by overcoming these restrictions as you will see in [Figure 3].
[Figure 3] represents an experiment designed to show the importance of Suction and how it impacts END of hose airwatts.
RED LINE: This line represents a system using two identical motors together in "Air Series" to create a central vacuum system with HIGH SUCTION with no improvement in Airflow. As you can see, the system with the highest END of hose Airwatts was also the system which had the highest SUCTION.
BLUE LINE: This line is extremely important in realizing the importance of Suction on end of hose Airwatts. The Blue line represents the same two motor system, but instead of installing the motors in "Series" to create high Suction, the motors are installed in "Parallel" to significantly boost Airflow performance with no increase in Suction. As you can see, despite a significant boost to the "Airflow" the system lacks the Suction necessary to maintain the Airflow velocity necessary to achieve high Airwatts.
YELLOW LINE: This line represents a system using a single motor. The Ametek/Lamb 116765 motor (the same as used in the Cana-Vac model 399 series) which produces unaugmented high suction and lower CFM. As you can see from [Figure 3], the single motor system performed almost equally as well as the two motor system installed in series because it has high suction which improves end of hose Airwatts.
CONCLUSION:
When shopping for your central vacuum, use the performance specifications according to the product brochure as a guide which should be taken lightly as to their cleanability. Remember, just because it has higher Airwatt's doesn't mean it is the best performing system for your home.
While we the consumer are driven by product specifications and use product pricing as a gauge of overall quality and value, you really cannot rely on brochure performance specifications or pricing to determine the system which offers the best motors, quality, longevity or value.
Know what you are getting, ask to see and for information about motor is inside! It's your money!!!
As for dual motor systems, be wary! Because of the deceitful nature of brochure Airwatts. Manufacturer's who utilize dual motor systems almost always simply add the Airwatts of both motors together to promote a system which shows tremendous Airwatts but it is not true. When adding a second motor be it in parallel (High CFM) or series (High Suction), the performance gain is never double! We'll discuss motors later.
|
(Figure 2)
