Energy Saving Scope for Air Conditioners
Energy Saving Scope for Air
Conditioners
Darkness
is absence of light. Similarly cool means absence of heat. So cooling is
expelling heat from any space. Air conditioning systems are intended to evacuate
heat from specific area called controlled area. Chill water plant, central ac
plant and package units are installed for cooling big premises. For homes and
offices, small units of 1 to 2 tones capacity are used. Window units used
earlier are now obsolete and now split units are most common. Normally cooling area
is a close room and air inside is circulated by AC.
Flow
of heat from higher temperature to lower temperature side is natural. But duty
of air conditioner is to transfer heat from room at lower temperature to outside
atmosphere at comparative higher temperature. This requires some trick to
accomplish the objective.
The
process required for cooling the room is similar to removing splashed water on floor
of the room. This is done by spreading loose mop over the water. The loose mop
absorbs some water. It is than taken outside side where water is to be released.
Than mope is squeeze to release the water. The process is repeated continuously
and successively water is removed from the floor.
The
role of refrigerant is similar to mop in AC. In the inner unit, liquid
refrigerant is released through expansion valve. So its pressure drops and cools
down below the room temperature. Blower forces air over evaporator coils while
cooled refrigerant is allowed to flow through the coils. Here refrigerant
absorbs heat from air and evaporate and turn into gaseous form whereas the air
loose heat and cool down. This cold air is distributed from bottom vent in the
room. Air temperature increase a bit after interaction with the occupants and
move upward. This air is taken in the AC from top for further cooling and
circulation continues. Refrigerant gas from inner unit is drawn by outer unit
and compressed to high pressure. So it is heated up to temperature higher than
ambient and sent to condenser coils. Air forced by the fan over the condenser
coil takes heat of refrigerant to atmosphere and cool down to liquid. The
process of circulation of refrigerant continues. In this way heat from the room
is successively thrown out.
There
are three motors in AC for above function.
Compressor Motor
Used
for compression of refrigerant. This motor is of highest rating amongst the three.
Thermostat controls start and stop of this motor during AC is ON
Condenser Fan Motor
Fan
forces air on condenser coils to cool down refrigerant. This fan works only
when compressor is operating.
Both
above are in external unit.
Blower Motor
Blower
in internal unit circulates cold air in the room. Comparative hot return air is
taken from top opening through filters and passed over evaporator (cooling
coils) where loose heat and cool down. This cold air is distributed in the
room. This motor runs continuously till air conditioner in ON.
Motor
for air vent diverter is very small and its energy consumption is
insignificant.
The
role of thermostat in inner unit is very important. Desired temperature can be
set by operator. When room temperature falls below the set value, further
cooling down is suspended by cut off supply to compressor and condenser fan. After
some time compressor and condenser fan are restarted by thermostat control when
room temperature go up the set value. When temperature setting is low, compressor
and condenser fan run longer to attain that temperature level. But in case of high
temperature setting running time is shorter and off time is longer. This means thermostat
temperature setting controls the running pattern of compressor and fan. Energy
consumption by AC depends on temperature setting. It is estimated to have about 5% reduction in energy consumption by increasing
temperature setting by 10C.
AC
is meant to combat uncomfortable surroundings due to high temperature.
Objective is to bring down temperature and humidity to comfortable level. It may
be ridiculous to have very low temperature that is uncomfortable and expensive.
The comfortable temperature zone is in the range of 240C to 280C
depending on metabolic rate of occupant.
But
due to ignorance, misconception or impatience, AC operated with low temperature
setting. Person experience poor cooling effect when AC is started after entry
in the room from outside hot atmosphere. Actually he is carrying lot of heat
from hot atmosphere outside. On starting the A/C, its function to vacate heat
is stated but AC is not magical device that instantly change temperature from
350C to 250C. Temperature drop is in
process and may take some time. But without waiting, setting is reduced to
minimum and then forgets or ignores to reset it. Eventually lower setting
continues throughout the AC operation and results in over cooling. Actually cooling
cannot be fast by reducing temperature setting. Once decide appropriate setting
and as far as possible it should not be disturbed.
This
problem of poor cooling at the time of entry can be overcome by advance start
of AC using facility of IOT. Some air conditioner has this facility of remote
operation by mobile. Or simple way is to instruct assistant to start air
conditioner in advance.
Similar
in bed room setting is kept very low for fast cooling. Late night temperature
drops very low and use blanket. Use of sleep mode function enables automatic
raise of setting in steps at late night. Increasing setting from 200C to 260C results in 30% saving of energy. So most important
tip is to have proper temperature setting. Other tips are as under.
Installation
External
unit
It should also have
the similar arrangement for free air flow. There has to be sufficient space on
back, top and sides of the unit. Condenser has to discharge maximum heat of
compressed refrigerant to atmosphere. Direct sun rays on condenser will add
heat. So cooling and condensing of refrigerant may not be perfect as expected and
reflect in performance. During operation of AC external unit should remain in
shed. Mostly AC is operated in afternoon and night hours. Therefore external
unit may be installed on east side wall or provide shed such that it protect
from sun rays but air flow is not blocked.
Heat Ingress
 |
Avoid this |
 |
Avoid this |
Air
conditioners are used when outdoor is very hot. If this external heat enters
the room, the machine has to draw out this additional heat also to attain desired
temperature. This results in longer time running of compressor consuming more
energy. Therefore all efforts have to be made to restrict the entry of heat in
the room.
If
the room is on top floor, the terrace is heated by sun rays and the heat is transfer
to room by conduction. This can be avoided/minimize by painting terrace with
white glossy paint or providing mosaic of light colored glassed tiles pieces.
This reflects run the rays. Also green net at about two/three feet above the
terrace may prevent sun rays heating the terrace. Room ceiling can have
thermocol lining as heat insulator or false ceiling wherein trapped air acts as
insulator.
Wall
of the room facing the sun is heated by sun rays and transfer to room by
conduction. This can be eliminated by painting outer side of wall with light
color glossy paint. Inside of wall can have wooden or thermocol lining as
insulator covered by decorative wall paper.
Glass
window of the room can have sun ray control film. Window can have double glass
(inner and outer). Air trapped between glasses acts as thermal insulation. Light
color cotton curtain on window also block radiation.
Cold
air leakage and entry of hot air from outside has to be controlled by blocking openings.
Doors and windows should remain closed when air conditioner is operating. Door seal
and door closer should be installed. Air curtains or automatic door open/close
device or air buffer at gate is suitable where frequent entry/exit.
Capacity
of air conditioner depends on air volume (room size), numbers of occupants
(persons in the room) and heat load (heat ejected by gadgets in room). AC of
lower capacity than required could not cool down to temperature setting. So compressor
runs continuously without rest and has probability of failure. Similar
condition occurs where room is open to kitchen, other room or up stair.
Care
Air
filters of internal unit should be clean periodically. Reverse air blowing
through condenser and evaporator coils to remove blockages by deposition of
dust etc. Air flow is restricted due to blockages resulting in slow cooling leading
to longer compressor operation. Check leakages of refrigerant from joints using
soap solution. When cooling is very poor than normal, gas pressure to be checked
and top up if required. See that air path of external unit is not blocked by
bird nest, paper or polyethylene piece.
Always
check that temperature setting is not disturbed by someone. Also see that AC is
switched off while leaving the room. Occupancy sensors are useful to avoid
wasteful running of air conditioner in absence of occupant. Check that doors
and windows are properly closed. Do not encourage anyone to stand in open door and
talk. Iron or hot plate / stove should not be used in the air conditioned room.
It has dual disadvantage. It adds undue heat load increasing energy consumption
of AC. Also part of the heat generated by iron or hot plate is taken away by
air conditioner and hence iron or plate takes more time to heat up and consuming
more energy. Stove consumes oxygen and emits carbon dioxide in the closed room
and lead to serious condition.
Caution.
About
6 to 8 hours are spent in bed room. While AC is on doors and windows are
closed. Oxygen is consumed and carbon dioxide is released due to breathing of
occupants. Condition may be worst during last segment of the night. So it is
better to have small vent in AC bed room to maintain proportion of oxygen and
carbon dioxide by diffusion through it.
While
AC is on the doors and windows of the car are closed. AC operated in air
circulation mode for effective cooling. The volume of air in car is less and
number of passengers may be more as compared to bed room. Proportion of oxygen is
reduced and carbon dioxide is increased due to breathing. Occasionally it is observed
that passengers feel weary after long travel even though it was comfortable
with AC. It is worth to change circulation to fresh air mode for about a minute
every hour.
Star
Rating
Star
Rating is compulsory by low for air conditioners. Star label has Energy
Efficiency Ratio (EER). More stars means more efficient machine having higher
EER that consume less power.
One
ton cooling capacity equals 3518 watts.
Power
consumption = cooling capacity ÷ EER
AC
of 1.5 ton capacity and EER 3.3 has average power requirement = 3518 × 1.5 ÷
3.3
=
1599 Watts means 1.599 Units per Hour.
High
star rated AC are costly. But additional cost is set off by reduction in
electricity bill for AC. This gain in bill depends on expected numbers of hour
of utilization of AC in the year. It is worth to opt for higher star AC for
office or bed room wherein AC operated for more hours but for guest room AC
utilization may be limited.
Up to 40% energy saving is possible by adopting
applicable measures as above.
Air
conditioner is highest energy consuming domestic gadget compare to geyser and
fridge. Scope for energy saving is also high as above. Maximum benefit can be
availed by implementing applicable measures as discussed here above. In
addition to personal benefit, it is also our moral duty to contribute
conservation of scarce entity like electricity and indirectly be instrumental
in control of Green House Gases and ultimately Global Warming.