Optimal Use
of Air Conditioner
May 2015
Introduction
The electric power is the most important requirement of modern contemporary life.
Advanced countries witness enormous progress in this area. The Kingdom of Saudi
Arabia, similar to other countries, had achieved tremendous leaps on the electric
power utilization and managed to cover most of its territories. These services moved
forward alongside great developments that the Kingdom is trying to accomplish in all
its regions. The state had spent billions of Saudi Riyals to establish power generating
plants, transmission and distribution substations aimed at delivering remarkable
electric power services to all its customers and providing comfort to the citizens and
residents of the Kingdom. Our valued customers, however, take the responsibility
for utilizing these services moderately and conscientiously so that the benefits
may cover all of their specific needs without waste or excessive use of this blessing
from God among other greatest graces that God has bestowed upon mankind and
avoiding extravagance or excessiveness in all aspects and affairs of life.
The amount of electricity consumed and the amount of money we paid for this
valued service are the results of our usage of electrical appliances. However, electric
power rationalization means reducing the electrical loads in power plants and
electric networks, thereby contributing to uninterrupted supply of electricity, saving
large sums of money, and preserving the environment. Rationalization of energy
consumption provides electricity to others. Air conditioning accounts for the largest
segment of power consumption; the statistics on this issue indicate that 60% of the
monthly power consumption during the summer months go for air conditioning, a
percentage that is too high.
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Definitions and Units
Air Conditioning:
This process is achieved by transferring heat energy from inside the room to the
outside by means of an air conditioner.
British Thermal Unit (BTU)
It is the standard thermal unit of measurement and is defined as the amount of
heat energy needed to raise the temperature of one pound of water (454 g.) by one
degree F (0.55 degree C).
Air Conditioning Capacity (by tons)
It means the ability to transfer 12,000 BTUs per hour. An air conditioner with a 1.5
ton capacity is capable of transferring 18,000 BTU per hour at a certain temperature.
Similarly, a 2-ton air conditioner transfers 24,000 BTU per hour, and so on.
Energy Efficiency Ratio (EER)
It is the result of dividing the maximum cooling capacity (BTU/hour) by the appliance’
total electrical input in watts which ranges between 5.4 to 11. The higher the ratio,
the more cost effective the appliance will be. By properly employing this ratio, we
can evaluate the appliance’ efficiency in terms of the consumed energy.
Types of Air Conditioners and their Components:
There are many different types of air conditioners. The following table shows the
most frequently used types with their approximate BTUs.
BTU
BTU/hour
Ton
Window Type Room A/C
12000-24000
1-2
Split Type Air Conditioner
18000-30000
1.5-2.5
Wheel Units
42000-120000
3.5-10
Compact Central Units
36000-192000
3-16
Central Air Handling Units
192500-741700
16-60
Type of AC System
10-1600
Central Units
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It is worthwhile noting that the above BTUs depend on the exterior temperature
upon which the design is made. For instance, the efficiency of a 24000 BTU/hr air
conditioner at 35C ambient temperature will be much more once it operates at 50C
external temperature.
As mentioned earlier, there are many types of air conditioners using refrigerants
which basically perform the same function and with almost the same components.
We shall look into the most common type, the window type air conditioner.
Window Type Air Conditioner:
• Window air conditioner consists of four main components:
1- The Compressor
2- The Condenser
3- The Evaporator
4- The Fans
It is installed and fixed externally so that the compressor, the condenser, and the
condenser fan are outside the building while the evaporator coil and evaporator fan
are directed to the inner side of the building.
Compressor
Low pressure vapor
High
Low
To the room
Exterior
temperature
45 C
High Pressure Vapor
Air from
inside the
room
25 C
Heat expel coil
55 C
35 C
valve
Inside the room
Outside the room
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Window Type Air Conditioner Operation Period:
The basic operation of an air conditioner can be summarized in the use of refrigerant as
the main assistant in transferring heat from and into the building. And as the summer
temperature inside the building is higher than the average human thermal level of
comfort, we operate the air conditioner to cool down the heat inside the building. The
compressor pumps the refrigerant to flow through the condenser coil where, with the
aid of the condensing fan, the heat-expel process takes place causing the refrigerant to
condense from gaseous state to liquid state. At this stage the refrigerant in liquid state
passes through the evaporator coil. It is at this point when the evaporator fan allows
indoor air to pass across the coil causing it to cool down. The cooled air is then delivered
to the inside of the room. As this happens, the liquid inside the evaporator coil absorbs
heat from the coil causing it to turn into gas state and returns to the compressor to
replicate the same cycle while the air conditioner is in operation.
The compressor pumps the refrigerant for longer periods as long as the temperature
inside the room is higher than the desired temperature. The preferred temperature
level can be freely set using a regulator called the thermostat. Thus, if we know that the
compressor has a power consumption rating of 2,400 watts and that the air conditioner
fan is rated at 200 watts, we can assume that the compressor’s power consumption in one
hour is equal to that of the fan’s power consumption in over 12 hours. We then realize that
the common cause of high electric bill from one month to another in the summer months
is the compressor’s running time. When the ambient (external) temperature is high e.g.
at 45C level, it follows that the difference between the desired room temperature (25C)
temperature and the ambient temperature will be high. And in order to decrease the
difference in temperatures, the compressor has to run longer.
Likewise, if a given ambient temperature is less than 35C, the resulting difference between
the desired room temperature and the ambient temperature will be less. In this example,
the power consumption is lower than the previous example.
This difference can be well illustrated by approximation based on the compressor’s
capacity of 2.4 KW and the fan capacity of 0.2 KW as follows:
At 45 C Temperature
Compressor Capacity (Watt)
Period Compressor On
Fan Capacity
Operation Hours
5
Period Compressor Off
At 35 C Temperature
Period Compressor Off
Compressor Capacity (Watt)
Period Compressor On
Fan Capacity
Operation Hours
Temperature
At 45 C
At 35 C
Ratio of compressor’s running
time against the total air
conditioner’s operating time
85%
55%
Number of Operating Hours
12 Hours
12 Hours
Power consumed during this
period (the shadowed area in
the figure)
(12x2.4x.0.85) +
(0.2x12) = 26.88 KWH
(12x2.4x.0.55) +
(0.2x12) = 18.24 KWH
Power consumed during the
month
26.88x30 = 806 KWH
18.24x30=547 KWH
Cost of power consumpton for
Residential Category at 5 halalas
per KWH
806x0.05 = 40.3 Riyals
547x0.05= 27.35 Riyals
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From the preceding example, we can conclude that the daily power consumption
of an air conditioner at 45C temperature is higher by about 48% than the daily power
consumption of the same air conditioner at 35C. This is due to the compressor’s long run
time at 45C which accounts for about 85% of the air conditioner’s total operating time.
On the other hand, at 35 C level, the compressor run time accounts for about 55% of
the total operating time. This is reflected on the monthly bill i.e. the higher the ambient
temperature is than the degree of desired comfort cooling, the higher the bill will be. That
is exactly what happens in the summer months.
Significance of the Energy Efficiency Ratio (EER)
The air conditioner’s Energy Efficiency Ratio (EER) is the ratio of the cooling capacity in
BTU/hr to the power input or power consumption of the appliance in “WATTS.”
To illustrate the significance of EER and its impact on the monthly electric bill, we present
to our valued customers the following example of comparing two air conditioning units
run by refrigerant and operating under the same conditions in terms of:
- Capacity: 18000 BTUs
- Operating time: 12 hours per day
- Cost for each of the 1st and 2nd customer categories: 5 Halalas/KWH for the
residential sector
- EER of the first unit: 7.5
- EER of the second unit: 5
Unit One: EER = 7.5
Unit Two: EER = 5
Consumed power:
18000÷7.5 = 2.4 KWH
Consumed power:
18000÷5 = 3.6 KWH
Daily power consumption:
2.4x12=28.8 KWH
Daily power consumption:
3.6x12 = 43.2 KWH
Monthly power consumption:
28.8x30 = 864 KWH
Monthly power consumption:
43.2x30 = 1,296 KWH
Power cost based on the first and
second customer categories:
864x0.05 = 43 Riyals
Power cost based on the first and
second customer categories:
1,296x0.05 = 65 Riyals
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The higher the air conditioner’s EER, the
less electricity it will use to do its job. The
abovementioned example illustrates an
increase of power consumption cost to
about 50% in air conditioning unit with
low EER. Thus, we recommend that the
customer, when buying an air conditioner,
look for a model with a high energy
efficiency rating even at a higher price
than getting a cheaper unit with low EER.
A/C EER
Consumption decreases
the higher the EER is
The Thermostat
The thermostat knob-dials of air
conditioners are numbered in various
ways; some are numbered 1-7, others
are from 1-10, and still other dials
are numbered using different scales.
They differ from one A/C to another.
Yet, every scale means a certain
degree of temperature. Therefore, it is
recommended to turn the thermostat
dial to medium setting for a moderate
cooling effect and reasonable power
consumption. However, the usual desired
thermostat setting is between 18-32C for
comfort cooling and moderate energy
consumption.
On/Off Ventilation Switch
This is the switch that opens/closes the
air conditioner’s vent that switches it
between using outside air and recycling
indoor air. It is recommended that it be
set in the OFF mode unless there are
fumes you wish to expel from the room.
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Desert Air Cooler - How It Works
The desert air cooler is the lowest energy
consuming unit. It is typically used in the
hot and dry areas to cool down the air
inside buildings or open halls. It works
by pulling in the outside air by a fan and
then passing it through water-saturated
straws. As the air passes the wet straws,
evaporation takes place thereby causing
the temperature to cool down. The cool
air is then blown in the room/building by
the fan.
Water-saturated straws
Fan
41 C
20% relative humidity
27 C
40% relative humidity
Desert A/C Power Consumption
Illustrative Drawing of the Desert A/C
By comparing this air cooling device to
air conditioners (A/C), we find that A/Cs
using refrigerants consume 8 times as
much electricity than that of the desert
air cooler. This proves that the desert air
cooler has low power consumption rate,
as shown on the following example.
Comparison Aspect
Air Conditioner
Desert Air Cooler
Room Area(m2)
25
25
Capacity
18,000 units
1/3 hp
Daily operating hours
12
12
Air conditioner power
consumption based on 45C
ambient temperature which
accounts for 85% of the total 12
hour running period.
(12x2.4x0.85) +
(0.2x12) = 26.88 KWH
0.25x12 = 3 KWH
Power consumed per month
26.88x30= 806 KWH
3x30=90 KWH
Cost of power consumption
using the tariff rate for
Residential Sector equivalent to
5 Halalas per KWH
806x0.05= 40 Riyals
90x0.05= 4.5 Riyals
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The example illustrates the importance of using desert air cooler during the summer
season due to the significant savings it offers on power consumption as compared to
a conventional air conditioner while taking into consideration the adequacy of water
supply in a manner that does not go against policies on water conservation.
Methods of Raising the Efficiency of Desert Air Cooler
- Prevent accumulation of salts, dusts, and suspended particles by periodically changing
the straws to improve the air cooler’s efficiency.
- Check and lubricate the water pump periodically.
- Use the desert air cooler in open places such as halls and kitchens.
Optimal Utilization of the A/C Systems.
Valued customer:
Listed below are special guidelines on the proper use of all types of air conditioning
units to reduce power consumption and subsequently reduce the payable value of the
electric bill.
1- Choose the right capacity and size of the air conditioner that best fit the size of the
room. Cooling 1 m2 of an uninsulated building requires about 800 BTUs, but only 600
BTUs required for an insulated building.
2- Buy the air conditioner with high EER to get more cooling output and lower power
consumption. The study had proven that the A/C power consumption is reduced by
40% when its EER is raised from 5 to 7 at the same ambient temperature.
3- Maintain and clean the A/C unit once every year, at least, as the accumulation of dusts
and sands reduces its efficiency.
4- Clean the air filter once every two weeks, as the accumulation of dusts and other
particles impedes the passage of warm air from inside the room to the outside. As
a result, the power consumption increases and the electricity bill correspondingly
become higher.
5- Shade the air conditioner and lessen its exposure to the sun, as studies found that air
conditioners with proper shading can be more efficient.
6- Set the thermostat at a moderate setting of 25C to reduce the temperature difference
between ambient temperature and the desired temperature. This will in turn shorten
the compressor’s operating time and reduce energy consumption. Further, if the
thermostat is set at higher degree, ice will form on the evaporator coil which then
impedes air circulation inside the room.
7- Keep furnishings away from the air vents of the cooling system. Blocking the air flow
impacts the functionality of the air conditioning system and leads to excessive power
usage.
8- Use thermal insulation and double-pane glass to prevent heat loss through windows.
In this regard, an insulated window is a good complement to thermal insulation in the
building.
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9- Install the air conditioner on the outer part of the room that has a constant flow of air
to help dispel the heat coming from the unit to increase its efficiency. Avoid installing
ACs in enclosed locations e.g. skylights and narrow spaces.
10- Turn off the air conditioner when leaving the building so as not to unnecessarily
consume excessive amount of energy.
11- Seal the side openings or edges of the air conditioner to prevent air leaks. Preferably,
apply in place insulation materials such as cork to prevent heat exchange.
12- Keep all windows and doors closed when air conditioning is on in order to maintain
the desired air conditioning temperature and to keep warm air from entering the
room. Further, we recommend the use of automatic door closers at building entrances
that are more exposed to the exterior air.
13- Reduce ventilation when the central air conditioner is taking in more exterior air than
required. In the case of window type air conditioner, keep the ventilation switch to off
mode most of the time.
14- Use curtains or window blinds to prevent solar heat from penetrating the inside of the
house during summer season.
15- In case of power outage, switch off the air conditioner in order to reduce the load and
leave one light on to indicate that power has been restored.
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