2011
UNIVERSITY OF NAIROBI
4TH YEAR, DEPARTMENT OF MECHANICAL
AND MANUFATURING ENGINEERING
Email: alexkanyonga@gmail.com
Phone: 0725 011633

THE HYBRID FRIDGE 2011
Table of Contents
SECTION 1. INTRODUCTION ....................................................................................... 3
1.1
ABSTRACT ........................................................................................................................................... 3
1.2
OBJECTIVE ........................................................................................................................................... 4
1.3
INTRODUCTION .................................................................................................................................. 5
SECTION 2. OPERATION AND THERMODYNAMICS............................................. 6
2.1 PRINCIPLE USED IN AN ABSORPTION REFRIGERATION SYSTEM ......................................................... 6
2.2 A PRACTICAL ABSORPTION REFRIGERATION SYSTEM ......................................................................... 7
2.3 THERMODYNAMICS .......................................................................................................................... 10
2.3.1 CONDESER .................................................................................................................................. 10
2.3.2 HEAT EXCHANGER ...................................................................................................................... 10
2.3.3 EXPANSION VALVE ..................................................................................................................... 10
2.3.4 EVAPORATOR ............................................................................................................................. 10
2.3.5 ABSORBER .................................................................................................................................. 11
2.3.6 SOLUTION PUMP........................................................................................................................ 11
2.3.7 GENERATOR ............................................................................................................................... 12
2.3.8 CALCULATION OF COP ............................................................................................................... 13
2.4 PHYSICAL CHARACTERISTICS OF THE REFRIGERATION SYSTEM ........................................................ 14
SECTION 3. DESIGN AND CONSTRUCTION ......................................................... 15
3.1 CONSTRUCTION DETAILS .................................................................................................................. 15
3.1.1 REFRIGERANT CYCLE ................................................................................................................... 15
3.1.2 ELECTRICAL WIRING ................................................................................................................... 18
3.1.3 INSTRUMENTATION AND CONRTOL ........................................................................................... 18
3.2 PROJECT COST ESTIMATES ................................................................................................................ 19
SECTION 4. CONCLUSION .......................................................................................... 20
4.1 CONCLISION ........................................................................................................................................ 20
4.2 REFERENCES ....................................................................................................................................... 21
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THE HYBRID FRIDGE 2011
1.1 ABSTRACT
The project sets out with an objective to solve refrigeration challenges encountered in the agricultural sector in Kenya. It presents an easy and sustainable refrigeration system that can be easily adopted by fishermen, vegetable farmers among others to increase productivity and reduce waste.
The absorption fridge is unique type of refrigerator that uses thermal compression as compared to the conventional mechanical compression. It uses low quality heat, such as engine exhaust heat or solar heat, to provide energy for the refrigeration system. The refrigerant (ammonia in this case) is alternatively absorbed in the absorber and liberated from an absorbent medium in the generator.
This project presents a hybrid refrigerator that runs on two sources of heat: solar and electric heat. In the model presented, solar heat is harvested by heating circulating water that consequently heats the refrigerant. Electric heating is used in the system to fine tune and act as a backup, increasing reliability, accuracy and sustainability.
A simple system, comprising of an evaporator, absorber, generator, pump and condenser, is introduced to explain the principle of operation and the refrigeration cycle. Further, an advanced model is presented that takes care of refrigerant rectification necessary to make the system practical and more efficient.
A thermodynamic analysis is carried out for the whole system by taking flow across each component. Mass and energy balance are considered for the thermodynamic study.
Estimations are made in the system pressures, making it possible for the pump rating needed to be estimated as 145W. A coefficient of performance calculation is also presented.
In the design and construction consideration, using the Reynolds analogy, fluid flow rate is estimated at 0.1kg/s and hence used to the refrigeration capacity as 7kW. This is enough refrigeration muscle to theoretically freeze 100kgs of beef from 20 o C to -5 o C in two hours, assuming perfect insulation.
Construction parameters, both physical and electrical are proposed for optimum performance.
In conclusion, financial considerations are made to estimate the cost of the system at Ksh
17,000.
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THE HYBRID FRIDGE 2011
1.2 OBJECTIVE
In fabricating a hybrid refrigerator using ammonia absorption, this project seeks to solve the refrigeration challenges faced by majority of farmers who operate on small scale. These may include: fishermen, vegetable farmers and vendors, flower famers and small scale butcheries among others.
Kenya, being primarily an agriculture-based economy, needs a lot of refrigeration to increase productivity and reduce wastage. This project thus fills in the conspicuous gap in the agriculture chain of production.
The refrigerator considered in the design is small (about 50×50×100 cm) and is thus considered sizable for domestic and subsistence use.
Finally, this project seeks to reduce the cost of refrigeration. With little operating costs, and good sustainability, refrigeration can be considered universal.
Other applications of the hybrid refrigerators may include:


 rural refrigeration of medicine in hospitals that operate far away from the national grid,
use by the UN to refrigerate vaccination medicine in the hotter parts of the country e.g., northern Kenya, preservation of laboratory supplies in secondary schools and research institutes in parts of the country not served by the national grid
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THE HYBRID FRIDGE 2011
1.3 INTRODUCTION
Ammonia refrigeration: the hybrid
A refrigerator can be defined as a heat pump that absorbs heat from one part (refrigerated space) and liberates that heat to the environment.
Ammonia absorption is an old type technique used in refrigeration. It was most famous in the
United States, where it was used to make ice boxes that were used for camping as well as for domestic use. Its operation was however intermittent, inaccurate and unreliable.
This project presents an innovative and interesting dimension by making the system hybrid.
Thus it can use both electric power as well as solar heat, for more reliability, smooth continuity and sustainability. Electric power can either be battery and photovoltaic cell powered, or grid powered, while the solar heating is harvested by circulating water.
Environmental and economical impact:
As the world becomes more self-aware of the changing climatic conditions caused by global warming, it is vital to reassess our dependence on the burning of fossil fuels to gain energy. This reassessment, spear headed by international environmental agencies such as UNEP, has to be complemented by scientists, technologists and engineers. One such way, is in the use of solar heat for refrigeration.
Kenya, being largely an agricultural country, has high demand for refrigeration, with applications ranging from fishing, dairy, horticulture, and vegetable farming among others. This need for refrigeration is indeed a challenge for the rural small scale farmers, who have little turnover and limited access to the national electricity grid. However, the presence of abundant solar heat presents a ready source of energy for refrigeration.
This project thus seeks to hit the proverbial two birds with one stone. On one hand, it seeks to use a non pollutant refrigerant (ammonia), while using the solar heat as the source of energy, and on the other hand it solves refrigeration problems for farmers, thus impacting positively on the economy of our country.
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THE HYBRID FRIDGE 2011
2.1 PRINCIPLE USED IN AN ABSORPTION REFRIGERATION SYSTEM
An absorption refrigerator is one that uses a heat source, such as solar heat, to provide energy to the cooling system. The refrigerant is alternatively absorbed and liberated from an absorbent medium. The refrigerant used in this project is ammonia while the absorbent is water.
Referring to the system illustrated in figure 1, ammonia leaves the evaporator at low pressure at state 1 and enters the absorber. The ammonia is rigorously absorbed in the weak solution of ammonia and water. Heat released during the process is dissipated to the circulated cooling water and the solution is maintained at a constant temperature.
The liquid which leaves the absorber at stage 2 is high in ammonia concentration. This binary liquid mixture is compressed by a pump to state 3. At the generator, heat from the sun warms the liquid to saturation temperature and drives out of the solution the ammonia. The nearly pure ammonia gas passes to the condenser at stage 6 where it is cooled to liquid. The liquid ammonia then expands through the throttle valve and flow to the evaporator, where it evaporates producing the refrigeration effect. Vapor ammonia from the evaporator at stage 1 eventually returns to the absorber. The weak solution, left in the generator after ammonia is driven out, flows through the regulating valve which drops the pressure to that in the absorber.
It mixes with the solution remaining in the absorber and the cold ammonia vapor coming from the evaporator.
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7
Heat removed from system
6
THE HYBRID FRIDGE 2011
Solar heat added to the system
3
4
5
8
1 2
Heat absorbed from surrounding, producing the refrigeration effect
Figure 1.
Cooling water circulating as heat is rejected from system
This system is simplified, since an ammonia-water system needs to have a rectification column and a dephlegmator (reflux condenser) to take care of water that is undesirably evaporated in the generator.
2.2 A PRACTICAL ABSORPTION REFRIGERATION SYSTEM
This is similar to the previously described absorption refrigeration system with some rectification to achieve 99.9% ammonia at the entry to the condenser. In addition, two heat exchangers are introduced to improve overall efficiency and minimize heat loss from the system. Some observatory instruments are added to the system for study, though these may be omitted in a commercial version of the refrigeration system.
Figure 2 illustrates the practical version of the absorption refrigeration system.
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Heat rejected
THE HYBRID FRIDGE 2011
Cooling water cools dephlegmator
Solar heating
Heat absorbed from the surrounding produces the refrigeration effect
Cooling water circulates cooling the absorber
Figure 2
At stage1, vapor ammonia enters the condenser and is cooled while at high pressure to liquid ammonia at stage 2. It then passes through the heat exchanger 1, where it is sub cooled as it exchanges heat with cool ammonia from the evaporator. The liquid ammonia at stage 3 then
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THE HYBRID FRIDGE 2011 expands in the expansion valve, where pressure drops to the evaporator pressure at stage 4.
Once in the evaporator, the ammonia evaporates absorbing heat from the surrounding, and producing the refrigeration effect. This evaporated ammonia, at stage 5 passes through the heat exchanger 1 where it gets super heated to stage 6 and ends up in the absorber.
In the absorber, the super heated ammonia from the evaporator mixes with the weak solution from the generator, in an exothermic reaction, to form a high concentration ammonia solution.
Cooling is needed in the absorber to maintain the temperature as the absorption produces heat.
The strong solution from the absorber at stage 7 is pumped to higher pressure at stage 8 and enters the heat exchanger 2. In this stage, the strong solution from the pump is pre heated while the hot weak solution from the generator gets cooled. This is a measure taken to reduce heat loss from the system, and increase efficiency.
The pre heated solution at stage 9 ends up in the rectification column connected to the generator. In the generator, ammonia refrigerant is generated and as it rises, it gets in contact with the descending pre heated strong solution. While in contact, the high concentration ammonia gets more enriched from strong solution. The vapor ammonia then emerges at stage
13, and enters the second stage of the rectifier. At this stage, the ammonia vapor contains 5-
10% water vapor. In the dephlegmator, the water vapor present is cooled by cooling water and it descends resulting in high concentration of pure ammonia. Proper design of the rectifier should achieve 99.9% ammonia. The rectifier is made in the form of a packed bed, a spray column or a perforated plate column. This pure ammonia then moves to stage 1 and the circuit is complete.
After evaporation, the weak solution left in the generator flows out at stage 10, through the heat exchanger 2, to stage 11. The weak solution at high pressure passes through the expansion valve to drop the pressure to absorber pressure at stage 12.
The [P] and [T] symbols in the figure 2, show the position of pressure and temperature gauges for the purpose of monitoring and data measurement.
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THE HYBRID FRIDGE 2011
2.3 THERMODYNAMIC ANALYSIS
In thermodynamic analysis, the principle of mass and energy balance is taken across each component. Each component is to be considered as a control volume while heat and work interaction are taken into account. Further, an assumption that unit mass of ammonia and unit mass of water are in circulation is to be made. This simplifies calculation.
1.
Condenser
In the condenser, only ammonia refrigerant is present.
Mass balance: 𝑚̇
1
= 𝑚̇
2
= 𝑚̇
Where 𝑚̇ = mass flow rate of the refrigerant
Energy balance: 𝑄
𝐶
= 𝑚̇(ℎ
1
− ℎ
2
)
Where 𝑄 𝑐
= heat rejected by generator, while ℎ
1
, ℎ
2
= enthalpy at stages 1 and 2.
In the actual situation, the values of pressure and temperature are measured and used to determine enthalpy and heat rejected.
2.
Heat Exchanger 1
Mass balance: 𝑚̇ = 𝑚̇
2
= 𝑚̇
3 𝑚̇ = 𝑚̇
5
= 𝑚̇
6
Since the two fluids do not mix, there are two mass balance equations
Energy balance: 𝑄 ℎ𝑥
= 𝑚̇(ℎ
2
− ℎ
3
) = 𝑚̇(ℎ
5
− ℎ
6
)
I.e. assuming no heat loss in the heat exchanger
3.
Expansion valve
Mass balance:
Energy balance: 𝑚̇
3
= 𝑚̇
4
= 𝑚̇ ℎ
3
= ℎ
4
4.
Evaporator
In the evaporator, only ammonia refrigerant is present.
Mass balance:
Energy balance: 𝑚̇
4
= 𝑚̇
5
= 𝑚̇ i.e. only ammonia refrigerant is in the evaporator.
𝑄 𝑒
= 𝑚̇(ℎ
4
− ℎ
5
)
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THE HYBRID FRIDGE 2011
Where 𝑄 𝑒
is the heat absorbed producing the refrigeration effect. The values of pressure and temperature are used to determine the enthalpy and heat absorbed.
5.
Absorber
In the absorber, ammonia vapor mixes with weak solution from the generator.
Mass balance: 𝑚̇ + 𝑚̇ 𝑤𝑠
= 𝑚̇ 𝑠𝑠
Where 𝑚̇ 𝑤𝑠
, is the weak solution mass flow rate (assumed to be water flow rate) 𝑚̇ 𝑠𝑠
, is the strong solution flow rate (summation of the water and ammonia flow rates)
Energy balance: 𝑄 𝑎
= Heat into the absorber – Heat out of absorber
𝑄 𝑎
= 𝑚̇ℎ
6
+ 𝑚̇ 𝑤𝑠 ℎ
12
+ 𝑚̇ 𝑠𝑠 ℎ
7
Where 𝑄 𝑎
= heat rejected by evaporator
6.
Solution Pump
Mass balance:
Energy balance: 𝑚̇
7
= 𝑚̇
8
= 𝑚̇ 𝑠𝑠
𝑊 𝑝
= 𝑚̇ 𝑠𝑠
(ℎ
8
− ℎ
7
)
Where 𝑊 𝑝
= is the work done by the solution pump.
However pump work needs to be calculated before the actual absorption refrigerator is made.
An assumption is made that the solution is incompressible; hence the following alternate formula is used;
It is noted that :
8
𝑊 𝑝
= − ∫ 𝑣 𝑑𝑝 = (𝑃 𝑐
− 𝑃 𝑒
)𝑣 𝑓
7
𝑃
8
= 𝑃 𝑐
= Condenser pressure
𝑃
7
= 𝑃 𝑒
= Evaporator pressure
Assuming that the flow rate 𝑣 𝑝
= 100 milliliters/s = 1×10 -4 m 3 /s
The typical maximum pressure in an ammonia absorption refrigerator is 1980kPa and minimum pressure is 480kPa, therefore the power rating of the solution pump is calculated as follows:
𝑊 𝑝
= (𝑃 𝑐
− 𝑃 𝑒
)𝑣 𝑝
= (1930 − 480) × 10 3 × 0.0001 = 145 𝑤𝑎𝑡𝑡𝑠
Therefore a pump with an output of 145watts is to be selected.
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THE HYBRID FRIDGE 2011
7.
Heat Exchanger 2
Mass balance: 𝑚̇ = 𝑚̇
8
= 𝑚̇
9 𝑚̇ = 𝑚̇
10
= 𝑚̇
11
Since the two fluids do not mix, there are two mass balance equations
Energy balance: 𝑄 ℎ𝑥
= 𝑚̇(ℎ
8
− ℎ
9
) = 𝑚̇(ℎ
11
− ℎ
10
)
I.e. assuming no heat loss in the heat exchanger
8.
Generator , Dephlegmator and Rectification column
A control volume is taken across all these components to simplify analysis.
Q d
heat rejected at the dephlegmator
1
9
10
Q g
heat input at the generator
Mass balance:
Energy balance: 𝑚̇ 𝑠𝑠
= 𝑚̇ 𝑤𝑠
+ 𝑚̇
Q g
− Q d
= ṁ ws h
10
+ ṁh
1
− ṁ ss h
9
Since 𝑄 𝑔
is needed in the calculation of coefficient of performance (COP) it is assumed that 𝑄 𝑑
10 - 20% of 𝑄 𝑔
.
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17
18
19
20
11
12
13
14
15
16
4
5
6
7
1
2
3
8
9
10
THE HYBRID FRIDGE 2011
9.
Calculation of COP refrigeration effect
COP = work and heat input to the system
=
Q g
Q e
+ W p
Therefore, once the heat and work into the system are determined, as well as the refrigeration effect, the practical coefficient of performance can be calculated.
RESULTS TABULATION
After the construction and testing of the refrigerator is complete, the following table is to filled for mathematical analysis.
Point Temperature
℃
Enthalpy
[𝑘𝑗 𝑘𝑔 ]
Ammonia Concentration
[%𝑁𝐻
3
]
Pressure
(bars)
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THE HYBRID FRIDGE 2011
2.4 PHYSICAL CHARACTERISTICS OF THE REFRIGERATION SYSTEM.
As referred from ASHRAE REFRGERATION BOOK 2006, the following are the typical temperatures achieved in typical absorption refrigerator:
Absorber exit temperature : 40 o C
Generator exit temperature
Condenser exit temperature
Evaporator temperature
: 85 o C
: 55 o C
: -15 o C
1.
Flow characteristics:
The Reynolds number is given by the following expression:
Where
𝑅𝑒 =
𝑉𝐷 𝑣
Re: Reynolds number V: Velocity D: Diameter v: Kinematic viscosity
For laminar flow, the Reynolds number should be less than 600, and taking the kinematic viscosity as 1.1
× 10 -6 M 2 /s, and choosing pipes of 10mm internal diameter, a laminar velocity of about 100mm/s is achieved.
2.
Refrigeration load (capacity):
Using the proposed flow rate of 0.1kg/s, and specific and latent heat of ammonia being 4.448 kJ/Kg K and 1370kJ/kg respectively, the following calculations were made:
Therefore, the proposed refrigeration capacity to absorb heat to 0 o C is:
𝑅𝑒𝑓𝑟𝑖𝑔𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = {(𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 × ℎ𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 × 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑐ℎ𝑎𝑛𝑔𝑒)
+ (𝑙𝑎𝑡𝑒𝑛𝑡 ℎ𝑒𝑎𝑡 𝑜𝑓 𝑣𝑎𝑝𝑜𝑟𝑖𝑠𝑎𝑡𝑖𝑜𝑛 × 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒)}
= {(0.1 × 4448 × 15) + (0.1 × 1370)𝑘𝑊
= 7𝑘𝑊
To put this refrigeration capacity into perspective, at 7kW refrigeration capacity, it is possible to theoretically freeze 100 kilos of lean beef from 20 o C to -5 o C in about two hours.
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THE HYBRID FRIDGE 2011
3.1 CONSTRUCTION DETAILS
The pictures below show images of a typical absorption refrigeration system.
(Notice that ice forms on the evaporator)
3.1.1
THE REFRIGERANT CYCLE DESIGN
The refrigerant cycle consists of a generator, a rectifier, a condenser, an ammonia storage tank, an evaporator, an absorber and a pump.
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THE HYBRID FRIDGE 2011
I.
The generator
The generator receives heat from two sources, solar and electric. The solar heat gets to the system via heated water while electric heat is delivered directly using an electric coil heater.
The generator is made of an insulated high pressure aluminum vessel.
II.
The rectifier
The rectification column is made of an indented wide tube that allows evaporated water to condense and trickle back to the generator. It should have enough length to allow complete rectification.
III.
The condenser
The condenser is used to facilitate cooling of the generated vapor ammonia back to liquid state.
It is made of long finned tubes that increase the surface area for heat rejection to the environment.
IV.
The ammonia storage tank
The ammonia storage tank is used to hold up the generated ammonia. Ammonia is then gradually released (via the regulation valve) to the evaporator for refrigeration. This storage tank should be well insulated to keep the ammonia in liquid state.
V.
The evaporator
The evaporator is made of thin walled and finned vessel that allows for maximum heat absorption from the refrigerated space. With the right construction design, is should achieve sub zero temperatures.
VI.
The absorber
The absorber column is made of a coiled tube and a perforated column that allow for maximum mixture between ammonia and the weak solution from the generator. The reaction in the absorber is exothermic; hence it is coiled for heat dissipation.
VII.
Heat exchangers
The system consists of two heat exchangers, one to pre heat and one to sub cool. The two heat exchangers are designed as shell and tube, both in counter current to maximize the efficiency of the system.
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THE HYBRID FRIDGE 2011
A schematic representation of the ammonia refrigeration cycle.
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THE HYBRID FRIDGE 2011
3.1.2
THE ELECTICAL WIRING
Electrical wiring takes care of electrical heating in the generator, pumping of the refrigerant, circulation of the solar heated water and lighting inside the refrigerator.
I.
Electrical heating.
A small thermostat is used in series with the electrical heating, to maintain the temperature inside the generator at a specified point. A simple immersion heater rated 500W, 240V should be sufficient.
II.
Refrigerant Pump
As calculated in the thermodynamic analysis, the pump needed is rated at 145W. This pump may be selected as one running on solar powered 12V D.C battery or the mains 240V. For this particular project, the former will be selected for experimental purpose.
III.
Hot water Pump
A small pump is selected to facilitate the circulation of the solar heated water. Rating of water pump may be varied, depending on the solar intensity. For preliminary design, the pump rating is selected as one similar to the refrigerant pump, i.e. 145W solar powered by a 12V D.C battery.
IV.
Internal Lighting
An electrical circuit is designed for the refrigerator cabinet lighting. As is in conventional fridges, a door operated switch will be used to turn on the light whenever the door is open and vice versa.
3.1.3
INSTRUMENTATION AND CONTROL
Temperature in the refrigerator is controlled by a regulator knob which controls the control valve from the ammonia tank (the rate of ammonia flow determines the temperature).
Both the solar heated hot water pump and the electrical heater thermostat are controlled by the level of ammonia in the storage tank. When ammonia has filled the tank, both the hot water pump and the thermostat are turned off. When more ammonia needs to be generated, both the pump and thermostat engage.
The circulation pump (responsible for pumping refrigerant round the loop) is controlled by the level of ammonia in storage tank. When the tank is full, the pump is turned off to save power.
When the level of ammonia in the tank is low, the pump is turned on to generate some more.
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3.2 PROJECT COST ESTIMATES
The total cost and estimates are tabulated as follows:
ITEM
Body casing material
Insulating material
Ammonia
Valves and Tubes and piping material
Electrical fitting
DESCRIPTION
 2.5 m 3 Steel sheets (3mm) for exterior
 2.5m
3 plastic for interior
 Miscellaneous body fittings

Approximately 10Kgs of insulating foam

5 liters of ammonia
 5m Ungalvanized steel tubes ( ¼ and ½ inch),
 3 stainless steel valves,
 3 two liter steel vessels (for ammonia storage absorber and generator)
 miscellaneous plumbing material

150W rated 12V D.C. motor pump
( 2 pieces),
 heating coil and thermostat (for electrical heating),

12V solid state battery with photovoltaic cell charger.
 Electrical wiring, lighting and miscellaneous
COST ESTIMATE
3000
1000
2000
4000
7000
17,000 TOTAL
The above project cost estimates are grossly approximated and are subject to change.
However, they represent a rough idea on the total cost of the system construction.
The project will be funded partly by my personal sources, and complimented by external sources.
The time frame from start to completion of the whole project is estimated at two to three months.
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4.1 CONCLUSION
The Kenyan economy is said to be 60 – 70 % agricultural based. Innovation should thus be focused on making the agriculture sector more productive and efficient, for faster realization of vision 2030.
The project has the objective to solve refrigeration challenges faced by farmers in Kenya. It takes advantage of the abundant solar energy in our country’s climate. Running primarily on heat from the sun and using ammonia refrigerant that is non pollutant, the hybrid refrigeration system has developed a solution to solve many refrigeration challenges.
The refrigeration system primarily uses solar heat to supply most of the energy, with electric heating stepping in to fine tune the system, making it more reliable and accurate. The system incorporates a rectifier that should theoretically attain 99.9% ammonia. In addition heat exchangers are used to increase efficiency. Further, calculations are made that estimate the pump rating at 145W and a refrigeration capacity of 7kW. A financial projection reveals a total cost of approximately Ksh. 17,000.
As is with any project, this one has both advantages and disadvantages. On the down side, the project relies on solar heat for refrigeration. This means that in absence of a source of heat, the refrigeration uses electricity which may not be available or uneconomical. In addition, the hybrid fridge uses a solar heater making it quite cumbersome for domestic installation. On the up side, the refrigerant uses ammonia which is ozone friendly. Further, in the presence of abundant solar energy, as is the case in Kenya, the refrigeration system is cheap and practical.
With almost negligible operating costs, refrigeration is considered universal for higher productivity and less wastage in the agricultural sector.
In conclusion, the hybrid fridge is recommended for fabrication and testing to study its performance, and subsequent feasibility for production.
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4.2 REFERENCES
[1] Dr. J. Nyang’aya, Department of Mechanical Engineering- University of Nairobi.
Lectures on REFRIGERATION CYCLES
[2] Indian Institute of Technology; AIR CONDITIONING AND REFRIGERATION Lectures
14,15,16,17. By Prof. M. Ramgopal, Department of Mechanical Engineering.
[3] Indian Institute of Technology Madras- REFRIGERATION CYCLES. By Prof U.S.P Shet,
Prof T. Sundrarajan and Prof. J.M. Mallikarjuna
[4] International Sorption Heat Pump Conference June 22-24, 2005; Denver, C.O, USA
ABSORPTION REFRIGERATION- AN EFFICIENT WAY TO USE WASTE HEAT AND SOLAR
HEAT.
[5] ASHRAE refrigeration Encyclopedia editions on: Fundamentals (2009), HVAC Systems and Equipment (2008), HVAC Applications (2007), Refrigeration (2006).
[6] MODERN REFRIGERATION AND AIR CONDITIONING-18TH EDITION-1211
[7] World academy of Science, Technology and Engineering; HEAT EXCHANGER DESIGN
[8] THERMOPHYSICAL PROPERTIES OF AMMONIA-WATER SOLUTIONS FOR THE DESIGN OF
ABSORPTION REFRIGERATION EQUIPMENT (formulation for industrial use)
M.Conde Engineering, Zurich, Germany.
[9] California Energy Commission- OPTIMIZATION OF SOLAR ABSORPTION CHILLERS
[10] Janilson Arcangelo Rossa and Edson Bazzo: Federal University of Santa Catarina Brazil,
Department of Mechanical Engineering
THERMODYNAMIC MODELING OF AN AMMONIA-WATER ABSORPTION SYSTEM
ASSOCIATED WITH A MICROTURBINE
[11] DESIGN AND RATING SHELL AND TUBE HEAT EXCAHNGERS; By John E. Edwards
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