AC myths 3: Not AC and fan together
Thursday 15 September 2011, 1.00pm HKT
(Continued from Part 2)
In this third part, we continue our AC myth-busting by looking at why using the AC and fan together is all wrong, despite the strong temptation to do so.
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If 25°C (77°F) is too warm for you, run an electric fan on high with the AC set no cooler than 25°C. This will provide optimal efficiency to augment AC cooling.
Rubbish! If you are ever concerned about maintaining a low carbon footprint (and who isn’t?), this is exactly the way to skyrocket your carbon footprint — and your electricity bill.
Running your fan like that is crazy. You can factualise all day long, calculationalise endlessly, citationise everything, statisticise all the time — but you’ll be no wiser about your expenses. Until the bills arrive.
FACT: The AC works at its rated power consumption level regardless of the thermostat setting.
Not strictly accurate in the absolute engineering sense, but true in a relative sense from a consumer point of view.
The garden-variety electric or ceiling fan uses around 60 watts an hour (just like a 60-watt lightbulb). The average split-type (wall) AC uses 650 watts an hour. That’s like 10 times the power consumption. Some people balk at this and use that ‘fact’ to talk trash.
Sure it’s 10 times greater. And it has to be.
THINK. The AC has to do several things — sucking in air, compressing, decompressing, cycling the refrigerant, cooling the air, running the fan motor, dehumidifying and other stuff. All the fan has to do is spin the propeller motor. Whaddaya expect, professah?
Be objective. Running a fan in addition to the AC is just adding on to your overall power usage whilst not making the ambient temperature appreciably cooler or more comfortable. As said already, modern ACs run at their manufactured power consumption level regardless of the temperature being set to.
The fact that a 650-watt AC uses 10 times the electricity of a 60-watt fan (and therefore higher running cost) is irrelevant. Running a high power-consuming appliance has to be more expensive than running a cheapo — that much should be obvious. It’s the number of hours you put the AC or fan to use that also determines the price of your electricity bills, dimwit.
If you want more, you use more, so you pay more. The AC is like your bitchy girlfriend: you like her cleavage, but you have to put up with her drama. Your mother never told you this?
FACT: ACs are designed to create their own air drafts for balanced cooling and dehumidification. Therefore, running a fan will throw the AC airflow out of whack.
Disrupting the AC airflow causes the AC to work that much harder. In effect, you’re driving your AC to early death.
It’s like the bathroom ventilation fan. What goes out, something must come in. Whenever you turn on the bathroom fan, you need to throw open at least one window for air inflow to balance out the air outflow. Since the air outflow is ‘assisted’ (by the fan), the air inflow must be of a greater margin than the outflow. Still with me?
Shut off all the windows or doors, and the bathroom fan causes a pressure difference between indoors and outdoors. Then, the fan labours against the lack of airflow (sometimes audibly so), and burns out sooner than usual.
The AC works roughly the same way, except that it does this by creating a closed system. Even my plumber knows this.
But why run another ‘cooling’ appliance (especially a fan) in conjunction with the AC? It makes no sense because of the above. Read some school-level physics, please.
FACT: The fan motor generates heat, and is counterproductive to the work of the AC.
You never thought of this, did you, genius?
For some people, a 25°C/77°F AC is sometimes unneeded altogether:—
“I find 25°C is a very comfortable temperature with [just] the fan on. And I grew up in Calgary [Canada] where 25°C is considered a hot summer day!” (Friend)
Use the AC as it was intended and it will do its job properly without using fans.
Trivia: American engineer Schuyler Skaats Wheeler (1860-1923) invented the electric fan in 1882 at age 22. A few years later, German-American inventor Philip Diehl (1847-1913) invented the electric ceiling fan by sticking blades to a sewing machine motor and attached it to the ceiling.
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Official recommendations on AC temperature settings
are only guidelines, not gospel.
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© The Naked Listener’s Weblog, 2011.
Images: Electric fan from author’s collection ♦ Chinese fan via Freaking News.