AC Consumes Fuel, Fact Or Myth?

“I no wan waste my fuel; if you dey hot wind down abeg…”
If you use public transport regularly or have ever used one, you’ve probably heard those words. And even if you haven’t (very unlikely), you might want to find out if the age-long myth has some truth to it…

First, what does AC mean?Air conditioning/air conditioners (AC) work by dehumidifying a place crammed with heat, thereby enhancing comfort. In a car, it removes moisture from the air and makes the vehicle conducive for its occupants. A vehicular air conditioning system has the following components: compressor, condenser, expansion valve (or orifice tube), accumulator (or receiver dryer) and evaporator.

How an AC functions

Essentially, an AC system is closed, that is, it is a looped system that involves taking in hot air, cooling the air internally, dispersing the cooled air, taking more air, recycling the air and repeat.

Usually, the process begins with the compressor which essentially powers the whole system. It enables the condenser to convert refrigerant into a condensed liquid. The receiver dryer removes moisture and dirt from the liquid and the evaporator returns it to its gaseous state; only much cooler. Air from the AC is then passed into the car; the rate at which this works is a function of the orifice tube or expansion valve. Interestingly, the air inside the car is also collected via the refrigerant and sent to the condenser to repeat the whole process again.

Windows down or AC on?

When it comes to the decision of “AC on or windows down”, there is a caveat – switching on the air-conditioning of a car can either consume or economise the fuel. However, this is solely dependent on the distance and speed driven.

Driving at a relatively low speed or below 45 MPH within streets or around town, in traffic, it is advisable to switch the air conditioner off and roll down the windows. This is one quick way to reduce fuel consumption. The reason is not far fetched- there is less aerodynamic drag when you’re driving slow. Aerodynamics relates to the study of how air moves around objects as well as the forces exerted by air in relation to the object. Drag is an opposing force or air resistance exerted upon an object in motion.

Research shows that driving at a speed greater than 45MPH, it is better that your windows are rolled up and your air conditioner is turned on. This is a great way to lower your fuel consumption. This is because when driving at high speeds, the wind entering your car will create a drag (called aerodynamics- wind resistance). This forces your car to work harder using more energy to push through the air in order to get to the same speed as when the windows are rolled up. Consequently, you burn more fuel because that extra energy comes from your fuel powered engine.

At the end of the day, it’s up to you…

However, as some studies have shown, it is not a one-size-fits-all approach resolution. Your fuel economy methodology varies with respect to weather, budget, car type and driving speeds. Additionally, it is also advised to park under shades in hot weather as your compressor has to work overtime when it is already heated up. This is because there is a direct correlation between outside temperature and your AC efficiency. More so, idling the vehicle with the AC running is not advised.

It is easy to see the advantages and disadvantages of both options. That is, to AC or not to AC. These have already been outlined above. What we will say though is that there is a direct correlation between AC utilization and fuel consumption. Nonetheless, in certain conditions this works favourably with respect to fuel economy. So really the decision is up to you. However, It is worth noting that too much heat in a car can lead to drowsiness or distracted driving. And we don’t want that.

Definition of some terms

  • Compressor: A compressor is a machine that is used to supply air or other gas at increased pressure. Also, it converts power using diesel or gasoline engine, into potential energy stored in pressurized air (i.e., compressed air).
  • Condenser: This is used to convert gas or vapor into a liquid state. They are special heat exchangers.
  • Accumulator or receiver dryer: this essentially removes dirt, moisture and debris from the condensed refrigerant; this prevents the system from malfunctioning.
  • Expansion valve or orifice tube: The expansion valve and orifice tube keep the AC flowing, essentially, their job is to control or regulate the flow of refrigerant through the evaporator.
  • Evaporator: this is the last stage in the ‘conditioning’ process. It essentially converts and cools the low pressure liquid to gas that is felt by passengers.
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