INCREASING THE AIR FLOW OF AN AIR CONDITIONER
Purchasing an air conditioner is relatively easy for the average person who simply wants
to cool the family home. In these instances, you can generally walk into the appropriate
store and buy a suitable sized unit off the shelf. However, what happens if you add an
extra room or two to your house? Will your existing air conditioner cope with the house
extensions, or will you have to go to the expense of buying a larger one? There is a third
Similarly, when installing air conditioning into larger buildings it is not always as simple
as buying a standard sized unit. One could of course buy a larger unit than is required;
however, this is somewhat inefficient in terms of energy consumption and running costs.
Often air conditioning firms will select an air conditioner that will go close to meeting
their demands and then they will modify the unit.
In this investigation you will investigate the mathematics involved in the modification of
an air conditioning unit to provide the volume of air required for a particular building.
1. Using the floor plans that have been supplied below, calculate the floor space (area)
of the building. Give your answer in square metres.
2. Working on the requirement that we need approximately 10 L/m2, what volume of air
is required to cool the building?
3. The air conditioner that comes closest to your requirements, and which you have
decided to purchase, has the following specifications.
Air flow 1800 litres/sec
Motor speed 1420 RPM
Motor pulley size
(Driving pulley – d)
Fan pulley size
(Driven pulley D)
(Maximum amps able to be drawn by 3.5 amps
existing motor is 4.72 amps)
Distance between pulley centres 210 mm
Does this air conditioner deliver the volume of air that you require for the office
building? Does the air conditioner that you have purchased need to be modified? How
much extra air does the conditioner need to output?
Office Floor Plan
Female Male Lunch room
Using the specifications of the air conditioner that you have purchased, carry out the
necessary calculations so as to modify the air conditioning unit to meet the needs of the
building under consideration.
1. Calculate the size of the new Driven pulley (D) that you require.
a) Select the nearest commercially available pulley from the catalogue.
b) Using the size of this pulley check the actual air flow that would be achieved.
c) Do you achieve the air flow that you required in part 1(b)?
d) What percentage difference is there between your required air flow and the actual
air flow? In your opinion, is this difference acceptable?
2. a) Calculate the new amount of current that is now drawn upon by the air
b) Is this figure beneath the maximum limit of the air conditioning unit that you have
selected for purchase?
3. a) Using the new pulley size that you calculated in part 2(1), calculate the new belt
size that you will need to fit the new pulley system.
b) Select the belt size, from the catalogue, that is closest to your requirements.
c) Given that the belt you have selected will not fit perfectly, you will most likely
need to increase/decrease the Centre distance, which is the distance from the
centre of the driving pulley to the centre of the driven pulley.
Calculate the new Centre distance that you require.
d) The motor, which the driving pulley is attached to, is generally on a sliding tract
and therefore can be moved, within reason. In your opinion, do you think that
your answer to part (c) is reasonable?
PART 3 - Research
Consider a large office block where ducted air conditioning has often been installed. In
these cases the temperature is often controlled from one location and individuals sitting in
their offices cannot do anything if they get too cold or too hot.
What happens if there is a sudden influx of people into the building and therefore an
increase in overall body heat, which places extra demands on the air conditioning
What happens if the weather conditions outside suddenly change and it becomes hot
or cold inside the building as a result?
What if there has been very little movement in or out of the building, during a
particular part of the day, resulting in very little air escaping through the opening of
In the above case, the concentration of air often builds up and the people inside
freeze. What happens to the air conditioner in these situations?
How can these different scenarios be planned for, and/or overcome, on a day to day basis.
Using the Internet, or other sources, find out as much as you can about the workings of an
air conditioning unit, and its associated ducting, in order to answer the above questions.
Are there any other factors that can have an affect on the efficiency of the air
conditioner? (Some key words to look for might include ‘dampening’, ‘static’, and
Air flow verses driven pulley size
where Q2 is the required air output, Q1 is the existing air output, D2 is the size of the
required new driven pulley, and D1 is the current size of the driven pulley.
where HP2 is the new current and HP1 is the old current. ( D1 and D2 are as above.)
New belt size.
D d 2 1.57 D d
where C is the current distance between pulleys, D is the size of the new driven pulley
required, and d is the size of the driving pulley.
C A A2 B
D d 2
Notes to myself:
Check the Internet first before deciding on whether to include part 3 or not. Also check if
the three key words come up or not. If not, delete the last sentence.