International Journal of Emerging Engineering Research and Technology

Volume 6, Issue 6, 2018, PP 17-24

ISSN 2349-4395 (Print) & ISSN 2349-4409 (Online)

Design and Construction of Split Unit Air Conditioner

Akusu O.M., Salisu, S., and Akinfaloye, O.A.
Department of Mechanical Engineering, Petroleum Training Institute, Effurun, Nigeria
*Corresponding Author: Akusu O.M. Department of Mechanical Engineering, Petroleum Training
Institute, Effurun, Nigeria.

ABSTRACT
This project study is applicable to the field of heating, ventilation and air conditioning. The design and
construction of a split unit air conditioner was carried out to achieve a suitable comfort in an office
environment. After a study of existing air-conditioners and survey for availability of materials, the design
concept of the split unit air-conditioner was achieved. And the following standard part were estimated as;
compressor power rating 2.5hp, condenser power 8KW, evaporator power 5.85KW and power rating of
blower as 120watts. And with a working fluid of refrigerant R410A which is weak compared to refrigerant
R22 but less hazardous to the environment. The split unit air conditioner was tested for conformance to
specification and it was satisfactory.
Keywords: Design, construction, air conditioner, compressor power rating, refrigerant

INTRODUCTION cooled as a fan blows it over the evaporator. On

the exterior the heat drawn from the interior is
Air conditioning is the process of altering the
dissipated into the environment as a second fan
properties of air (primarily humidity and
blows outside air over the condenser. A large
temperature) to favorable conditions, typically house or building may have several such units,
with the aim of distributing the conditioned air allowing each room to be cooled separately.
to an occupied space is to improve comfort. In
the most general sense, air conditioning can The central unit air conditioning unit is for
refer to any form of technology humidification, cooling big building houses, offices, entire
de-humidification, heating, cooling, cleaning, hotels, cinema hall, and factory etc. If the whole
ventilation, or air movement that modifies the building is to be air condition, HVAC engineers
condition of air [1-3]. In general, the air conditioner find that putting individual units in each of the
is a device that lowers the air temperature. The room is very expensive initially as well in the
cooling is most done using a simple refrigeration long run. The central air conditioning unit is
cycle, but sometimes the evaporation is used, comprises of huge compressor that has the capacity
commonly for the comfort of cooling in buildings to produce hundreds of tons of air conditioning.
and motor vehicles [4-5]. In construction, a The split unit air conditioning system comprises
complete system of heating, ventilation and air of two parts the outdoor unit and indoor unit.
conditioning is referred to as "HVAC" [6]. Air The outdoor unit, fitted outside the room, house
conditioning can also be provided by the simple component like the compressor, condenser, and
process called free cooling which uses pumps to the expansion valve. The indoor unit comprises
circulate a coolant (typically or a glycol mix) the evaporator, and cooling fan. In the split
from a cold source, which in turn acts as a heat system, one does not have to make any slot in
sink for the energy that is removed from the the wall of the room.
cooled space [7]. However, considering the fact that Nigeria is
Generally, air conditioner can be classified into located in a tropical region which is characterized
[8-9]; window unit air-conditioners, central unit by excessive high temperature and highly humid, it
air-conditioner, and split unit air-conditioner. In became necessary to develop a mechanical system
this air conditioner, all the component, namely; which can help to reduce the hot the ambient
the compressor, condenser, expansion valve temperature within a confined space for human
evaporator and cooling coil are enclosed in comfort. In this research work, we carried out
a single box. Window unit air conditioners are the design and construction of split unit air
installed in an open window. The interior air is conditioner.

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Design and Construction of Split Unit Air Conditioner

MATERIALS AND METHOD Table2. Indoor Unit Components

The split unit air conditioner consist of two SN Indoor unit

assemble units separated from each other, but 1 Evaporator
interconnected by refrigerating piping. The two 2 Blower
units are: 3 Blower motor
4 Blower mounting bracket
 Indoor unit 5 Electronic control unit
6 Cabinet
 Outdoor unit 7 Air filter
Table1. Outdoor and Indoor Unit Components 8 Fins or louvers(vertical and horizontal)
9 Display
SN Outdoor Unit 10 Infared signal receiver
1 Compressor 11 Remote controller
2 Condenser 12 Air
3 Fan
4 Fan motor Design Specification
5 Capillary tube Given consideration to constraints imposed by
6 Grill costs of material and availability, construction
7 Motor mounting bracket difficulties, operating conditions and design
8 Cabinet limits; the following design specification listed
9 Capillary in Table 3 were made.
Table3. Design specification
S/N Specification Description/Dimensions
1. Room size 5.2m x 4.6m x 2.7m
2. A/C unit type Ductless mini-split type
3. A/C rating 2.0 horse power
4. Compressor type Variable frequency drive (VFD)
5. User control Wireless remote control
6. Weight Indoor unit:9kg Outdoor unit:38kg
7. Dimensions Width x height x depth
Indoor unit: 0.79m x 0.25m x 0.28m Outdoor unit:0.78m x 0.55m x 0.290m
8. Power input 220-240v 50hz A.C
9. Space conditions Indoor unit: 20oc dry bulb temperature Outdoor unit: 30oc dry bulb
temperature
10. Special feature Self-diagnostic function
11. Refrigerant R410a (CHCLF3)
12. Copper pipe 0.00635m and 0.0127m

Design Consideration The cooling loads consist of the following:

Air-conditioning system design is governed by  Heat gain through the building wall
either thermal comfort condition or special  Heat gain through the ceiling
requirement for material or processes. This air
 Heat gain through the window
condition is basically design for office
application or residential application, thus only  Heat gain through door
thermal comfort if considered. Hence, small  Heat gain due to air infiltration
function in temperature and humidity are tolerated.  Internal heat gain due to equipment in
The outdoor and indoor surface heat transfer
 building space.
coefficient was considered to be 22.7w/m2K and
7.42w/m2K respectively Calculation of Areas in Building Space
Design Calculation Height of wall
The calculation of cooling load is a very vital Height of windows
factor in determining the appropriate air Height of doors
conditioner. The cooling load is defined as the Area of Glass Window (AGW)
rate at which heat is removed from the conditioned
space in order to maintain a constant air space AGW = Lw × Hw (1)
temperature. where,

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Design and Construction of Split Unit Air Conditioner

Lw =Length of window= 1.3m Area of concrete wall

Hw = Heigth of window =1.4m WA = WL × WH
AGW = Area of glass window where,
Area of Door WA =Area of wall
DD = DL × DH (2) WL = Length of wall in (m)
where, WH = Heigth of wall = 2.7m
DD = Area of door Calculation of Area of Concrete Wall
DL = Length of door = 0.78m Table 4 shows the calculated area of concrete
DH = Height of door =2.1m wall
Table4. Calculated Area of Concrete Wall
Wall dimension Length of Wall (m) Height of wall ( m) Area of wall (m2)
AB 5.2 2.7 14 04
BC 4.6 2.7 12.42
CD 1.8 2.7 4.84
DE 0.6 2.7 1.62
EF 1.6 2.7 4.32
GH 1.8 2.7 4.86
WA  42.12m2
* FG =ED and BC = HA
Overall Heat Transfer Co-efficient Heat Gain through Concrete Wall
1 xw 1
OHT = 1/(ho + kw + h1) (3) HGCW = OHT × TACW× ∆T (5)
where,
OHT = overall heat transfer co-efficient of
OHT = Overall heat transfer coefficient
building space and wall
TACW = total area of concrete wall
Ho = outdoor surface heat transfer coefficient
T = outside and inside temperature difference
hi = Indoor surface heat transfer coefficient
Estimation of Internal Heat Gain
xw = Thickness of concrete wall
The internal heat gain are due to occupants such
kw = Thermal conductivity of concrete wall and
as light, appliances, and equipment within the
ceiling
air-condition space.
Table5. Internal Heat Gain Computations
Heat gain by occupant =115W Number of average occupant = 4 Total heat from occupant =115 x 4
= 460W
Heat gain by light(bulb) Number of light bulb =2 Total heat from light = 60 x 2
60watts =120W
Heat gain from appliances Cpu =55W Monitor =55W Total heat from appliance =
Printer =440W 55+55+440 = 550W
Total internal heat gain = 1130W
Estimation of Heat Gain due to Air Inflation Qi = heat gain to air infiltration
Using the air change method, heat load due to B = Density of air
air changes and other infiltration is estimated VC = Rate of air infiltration/change
by Qi = BVCT (6)
T = Air temperature difference
where,
Table6. Heat Load Analysis
S/N Heat gain type Q (W)
1. Heat gain through concrete wall 1604.8
2. Heat gain through concrete ceiling 947.9
3. Heat gain through door 87.41
4. Heat gain through glass window 1537.8
5. Internal heat gain 1130
6. Heat gain through air infiltration 14.7
Total heat load = Q = 5322.61

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Design and Construction of Split Unit Air Conditioner

Estimation of Coefficient of Performance of Sensible Heat Removed From the Air (SH)
the System (COP)
Sensible heat removed from the air (SH) =
Considering 390C and -150C as the condenser 𝑀𝑎 (ℎ3 -ℎ2 ) (13)
and evaporator temperature respectively; using
refrigerant R410a. The T-S of the process is Sensible Heat Factor (SHF) Of the System
shown in Fig. 1. 𝑆𝐻
SHF = = SH +LH
(14)

Material Requirements and Selection

This section of the project involves detail and
proper consideration of material properties,
availability and likely limitations they may
impose on the design. The main goal of material
selection is to minimize cost while meeting a
Fig1. T-S diagram of refrigeration cycle design performance goal; hence, material
selection is fundamental to the design success.
Calculation for Mass Flow Rate
In material selection, certain requirements are
QT = m (h1 − h4 ) (7) put into consideration. These include:
where,  Economic requirement
QT = Refrigeration capacity or evaporator  Availability requirement
m = Refrigerant mass flow rate
 Service requirement
h1 = Enthalpy of refrigerant at inlet to
compressor  Fabrication requirement
h4 = Enthalpy of refrigerant at inlet to Economic Requirement
evaporator
Under economic requirement, the cost of a
Calculation for Compressor Power material including cost of manufacture and
𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟 𝑟𝑎𝑡𝑖𝑛𝑔 𝑊𝑜 = 𝑚(ℎ2 − ℎ1 ) (8) assembly is taken into consideration. Also, it is
Calculation of Heat Rejected By Condenser important to note that the vital criteria should
QC = m(h2 − h1 ) (9) not be the initial cost of material, but the life
cycle cost or cost effectiveness. It is usually
where, more cost effective to collect a material that will
QC = Heat removed by condenser produce an extended life of the product.
m = Refrigerant mass flow rate Availability Requirements
h2 = Enthalpy of refrigerant at inlet to condenser
The availability of material as well as spares
h3 = Enthalpy of refrigerant at outlet of plays an important role in material selection. It
condenser will reduce the total cost of the project
Volume of Air Flow Service Requirement
If the time taken for cold air from the external Under service requirement, consideration is
surface of the evaporator to fill the cooling given to physical mechanical, thermal, electrical
space of a given capacity, then the maximum air properties etc., of a material in order to
flow is given as;
determine its functionality for selection. Other
volume important consideration in service requirements
Q= time
(10)
are operational environment, and servicing
Capacity of the humidity (mass of water) requirements such as;
removed per hour
Physical properties: These include colour,specific
𝑀𝑎 = (𝑤1 –𝑤2 ) (11) weight,density, lustre etc.
Latent Heat Removed From the Air (LH) Mechanical properties: These tensile strenghth,
Latent heat removed from air (LH) = 𝑀𝑎 (ℎ1 -ℎ3 ) hardness ,ductility,impact strength, wear resistance
(12) etc.

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Design and Construction of Split Unit Air Conditioner

Thermal properties: These include thermal  Rigidity

expansion, thermal cinductivity, thermal stress,  Flexibility
thermal resistance etc.
 Ductility
Electrical properties: These include conductivity,
 Malleability
resistivity etc.
 Machinability
Fabrication Requirement
 Weldability
Fabrication requirement give consideration to
materials properties which gives an indication of Material Selection
the suitability of a material for construction of a Having considered the factors stated above and
product. Material properties which are considered the design purpose, various materials were
under fabrication requirements are: selected. The materials are highlighted below:
Table7. Material Selection
S/N Components Materials Description
1. Refrigerant R410a Its latent heat at -150C is 218kj/kg
(Monochlorodifluoro It has a boiling piont of -40.80C
methane) It has a moleculer weight of 86.5
It has an oxygen depleting potential (ODP) of 0.05
Its evaporator and condenser pressure at standard ton of
refrigeration are 2.9 bar and 11.9 bar respectively
2. Cabinet Galvanized steel High resistance to corrosion
Good tensile strength
Possesses good ductility
3. Refrigerant tubing Soft copper tubing and high resistance to corrotion
(indoor-outdoor aluminium fins It is ductile
connection) It is non-magnetic material
It can be easily bent and joined together.
4. Air filter Cellulose fibre and Cellulose fibre possesses a high dust resistance
frame The wire frame possesses a rigid surface for attaching fibre
5. Capillary tube Fixed length copper Its small diameter enable pressure drop.
tubing It produces a pressure proportional to its length and inversly
proportional to its inner diameter
6. Fan (indoor unit) Drum type cross- flow It produces efficient air flow at high pressure
fan It produces an air flow tranversely across the impeller, moving
pass the blade time
It uses an impeller unit forward curved blades
It has a lond length relatively to its diameter
It is suitable for application where laminar flow is considerable
in order to reduce noise.
7. Fan(outdoor unit) Propeller type axial It is suitable for handling large air volume
flow fan It produces a flow of air in a direction parallel to the axis of
rotation.
8. Compressor Hermetically sealed It consist of a motor and compressor coupled together by a
reciprocating common shaft inside a welded steel dome.
compressor It is powered by electricity
In this type of compressor it is difficult to access the compressor
and motor assembly.
It is suitable for application requiring small displacement
volumes and high condensing pressure.

Fabrication Procedure  Avoidance of exposure of the A.C unit to

direct sunlight.
Under this section the installation of various
components that comprise the air-conditioning Installation of the Mounting Plate
unit will be discusses. Various considerations Using a level, the mounting plate was placed in
during this procedure are: a perfect square position vertically and
horizontally.
 Provision of an easy means of draining away
 Using a drill, 32mm deep holes were drilled
condensed water. in the wall to fix the mounting plate.
 Utilization of a wall surface that is not  Plastic anchors were inserted into the holes
subject to vibration for the indoor unit. and the mounting plate was fixed using the
 Proximity of an appropriate electric socket tapping screws.

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Design and Construction of Split Unit Air Conditioner

Mounting of the Indoor Unit  The flare nut was screwed to the indoor unit
After completing the above, the indoor unit was coupling and the connections were
mounted onto the upper part of the mounting tightened using two wrenches.
plate. The lower part of the indoor unit was then Bleeding the Refrigerant Circuit
pressed tightly against the mounting plate.
 Having connected the indoor an outdoor
Outdoor and Indoor Unit Assembly
units, air and humidity were bled from
Drilling for Wall Piping the refrigerant circuit using a vacuum; as
 Considering the position of the mounting explained below;
plate, a drill was utilized to drill a hole in the
 The cap from the outdoor unit service port
wall for the piping. The drilling was done such
was removed
that the hole sloped towards the exterior.
 The vacuum pump 1ose was connected to the
 Also, a flexible flange was installed through
service port
the hole the keep it intact and clean.
Electrical Connections  The vacuum pump was operated until an
absolute vacuum of 10mHg was reached
 Having selected wire size suitable to the
electrical power input and safety requirements,  The vacuum pump was stopped and the
the cable wires were connected to the screw joints were checked for leaks using liquid
terminals. soap.
 A plug connection was made available and Piping Insulation and Protection
an efficient earthing connection was ensured.
The piping connection was covered using an
Refrigerant Piping Connection insulating material. The piping was then inserted
 Firstly, the piping was run in the direction of to the plastic slots fixed to the wall.
the wall hole. Then, the copper pipes,
drain pipes and power cables were bound RESULTS AND DISCUSSION
together with a tape. The performance test results are shown in Table
 The pipe cap of the indoor unit connection 8. The AC was tested in airtight apartment to
pipe was removed and a flare nut was avoid leakage. The duration of the test lasted for
inserted to create a flange at the extreme and three hours. The temperature of the room before
of the connection pipe. testing was 26oC and 18oC after testing.
Table8. Performance Test Result Analysis
S/N Description Observed Quantity/Quality
1. Room features Air tight
2. Duration of Test Three hours
3. Temperature of room before test 26oC
4. Temperature of room after test 18oC
5. Numbers of persons in the room Four
6. Relative humidity before test 70%
7. Relative humidity after test 55%
8. Position of regulator High cool
9. Room size 6.4m x 4.6m x 2.7m
10 Other items in the room Table, Chairs, Computer, Photocopy Machine
The indoor and outdoor components of the through an inlet grill located above the evaporator
conditioning unit are interconnected to achieve unit. The air in the unit passes through a filter
control of ambient conditions of a space to suite media which removes dust from pother allergens.
user requirements. In the interior, air is cooled The cleaned air then passes through the surface of
by means of a fan which blows it over the the evaporator coils where it is cooled to user
evaporator. At the exterior, air is heated as a requirement.
seconds fan blows it over the condenser. Thus, a
Finally, the fan forces the cooled air through the
cycle is formed which draws heat from the room indoor unit louvers into the room. It was
and discharge to the environment. The process observed that the outdoor unit powered by
which makes up the air conditioning cycle electric motor was able forces outside air into
comprises the following. The fan powered by the condensing unit through the side grill. The
electric motor forces air into the indoor unit air in the unit is blown over the surface of the

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Design and Construction of Split Unit Air Conditioner

condensing coils and extracts heat from the high  Connect these suctions of the pump with
temperature refrigerant. The heated air leaves separate tank by rubber hose and discharge
through the front grill and the process is the pump to condenser water inlet with
continuously repeated. suitable connectors and rubber hose.
For efficient use of the AC, the following  Connect the condenser line back to the tank.
maintenance procedures are required; Fill the tank with the raw water. Start the
 Compressors repair should be carried out pump and circulate the water for about ten
only when it is ensured that the other parts of minutes through the condenser and make
the system are trouble free. sure that water does not leak from any of the
joint hose e.t.c. Make sure that adequate
 Minor repairs of the system can ordinarily be water is available in the plant room for
made without removing the compressor. cleaning the condenser after acid circulation.
 When the compressor is worn out  Add acid to the tank water at 1:6 ratios.
considerably, it gives out a lot of noise; this Circulate the solution for 6-8 hours and drain
means that the main bearing journals are out the acid thereafter. Flush the system with
worn out. In such a case, it is better to use a fresh water. Then circulate washing soda in
new or reprocessed/rebuilt compressor than the tank for half an hour flush the system
to attempt to repair. with fresh water once again.
The following procedures were followed to When air is cooled below its dew point temperature
check the efficiency of the compressor. (at 100% RH), it gives up the moisture and deposit
on the nearest cooler surface (the evaporator).
 Back seat the suction and discharge service
When the temperature of the evaporator falls
value and then remove the plug.
below 0oC, the moisture deposit on the surface
 Attach a pressure guage to the discharge of the evaporator freezes and form a coating of
service value and a compound guage to the frost. If this frost is not removed periodically, it
suction valve guage port. acts as an insulator and retards the heat transfer
 Start the compressor and throttle the rate between the air and the evaporator which
discharge valve until pressure head of 9 bars causes the compressor to run at a lower suction
is maintained. pressure. Also frost decreases the capacity and
 Close the system valve slowly and when it is efficiency of the system. The process of
completely closed, note the vacuum guage. removing the frost formed on the surface of the
evaporator by melting it is called defrosting.
 Check the discharge valve leakage only after the Several methods are used in defrosting an
compressor has been running long enough with evaporated but the manual defrosting method
the suction valve closed to remove any can be used in this system, where frost is
refrigerant which may be in the crankcase. allowed to melt off. This is the easiest and
 Replace or repair both the suction and discharge simplest for defrosting.
valve if found defective.
However, purging or removing of air from the
 In the compressor, if there are loose or broken evaporator and lines can also help in the
parts, replace the entire unit. maintenance of the evaporator and even the
The maintenance that may be caries out on the system at large. Through there are different
condenser is mainly that of de-scaling. The de- method used to remove air from the evaporator,
scaling of a condenser should be carried out but the one recommended for this project is the
only when it is firmly ascertained that there is a method that makes use of a separate vacuum
considerable scaling in the condenser. The scale pump to purge or remove the air.
formation prevents heat transfer from the refrigerant The following procedure should were followed
to the water and thereby results in high discharge to purge the system;
pressure which affects the performance of the
equipment immensely.  Close the suction valve and remove the
gauge port plug.
The following procedure is adopted to de-scale
the condenser;  Screw a pipe flare connector into the gauge
port and connect to the vacuum pump which
 Drain out the water from condenser after is then connected to compound gauge and
isolating it from rest of the water line. valves between the gauge and the pump.

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Design and Construction of Split Unit Air Conditioner

 Start the vacuum pump and open the suction REFERENCES

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