Heat Recovery System in Domestic Refrigerator

International Journal For Research & Development in Technology
Volume: 2, Issue: 2, AUG-2014 ISSN (Online):- 2349-3585
16 Copyright 2014- IJRDT www.ijrdt.org
Heat Recovery System in Domestic Refrigerator
Reny Varghese1
, Nithin Raju2
, Rohit M3
,
Roshan Thomas Antony4, Tom Mathew5
12345
Saintgits College of Engineering
Department Of Mechanical Engineering, Saintgits College of Engineering, Kottukulam Hills, Kottayam
Abstract - Refrigeration is a process in which work is
done to move heat from one location to another.
Refrigeration technology has rapidly evolved in last
century from ice harvesting to temperature controlled
rail cars. Most widely used current application of
refrigeration is for air-conditioning of homes and
public buildings. During refrigeration, heat from the
refrigerant is dissipated for the successful completion
of a refrigeration cycle. In normal household
refrigerators, the heat from the refrigerant is removed
using a condenser where the refrigerant cools and the
air surrounding the condenser heats up. The strategy
of how to recover the dissipated heat to develop a
waste heat recovery system is relevant. The energy lost
in waste heat cannot be fully recovered. However,
much of the heat can be recovered and the loss can be
minimized by adopting different measures. Hot air can
be used for space heating, industrial drying,
preheating aspirated air for oil burners, or any other
application requiring warm air. The purpose of this
project is to demonstrate the technical feasibility of a
heat recovery system to recover waste heat from the
condenser in the refrigerator and to reuse it for
heating application.
I.INTRODUCTION TO WASTE HEAT
RECOVERY SYSTEM
Waste heat is generally the energy associated with the waste
streams of air, gases and liquids that leaves the boundary of
the system and enter into environment. Waste heat which is
rejected from a process at a temperature enough high above
the ambient temperature permits the recovery of energy for
some useful purposes in an economic manner. The essential
quality of heat is not the amount but its value. Waste heat
recovery and utilization is the process of capturing and
reusing waste heat for useful purposes. Not all waste heat is
practically recoverable. The strategy of how to recover this
heat depends on the temperature of the waste heat sources
and on the economics involves behind the technology
incorporated.
In most cases household refrigerators use air-cooled
condensers. Generally, the heat from the condenser side is
dissipated to the room air. If this heat is not utilized it simply
becomes the waste heat. We have explained that the most
efficient way of heating water is with the help of heat pump.
Because, if we use fossil fuels to heat the water then it will
lead to global warming. If we use electricity, the cost for the
energy consumption by the heater (geyser) will be greater
than that of a heat pump. The household refrigerator can also
be used as a heat pump by retrofitting a water-cooled heat
exchanger to the conventional air-cooled condenser by
making a bypass line, which can recover the heat from the
condenser and utilized for the water heating purpose. The
recovered heat is then used in several heating applications.
The fabricated system can result in energy saving due to the
non-usage of electrical energy for heating purposes and cost
saving by combining both utilities (refrigeration and heating)
in one system.
In minimum constructional, maintenance and running cost,
this system is much useful for domestic purpose. It is
valuable alternative approach to improve overall efficiency
and reuse the waste heat. The study has shown that such a
system is technically feasible and economically viable.
No external devices are used in this system other than the
refrigerator. This is the main cost reduction factor as the
investment made in the refrigerator was the only major cost.
Condenser coil is placed inside the hot chamber and the
evaporator is moved from top chamber to the bottom
chamber.
For this project, a domestic refrigerator of 210 L capacity is
used. The top chamber is used as the hot chamber and the
bottom chamber is retained as the cold chamber. The
refrigerating unit rejects considerable amount of heat to the
atmosphere through its condensing coil unit. So, by suitably
retrofitting the heat recovery system in the unit, waste heat is
recovered. This heat is used to keep snacks and food warm, to
heat the water which can be further used in health care
centers, schools and industrial processes, to wash the cans in
dairy by hot condensate, to dry clothes, grains etc. thereby
saving significant amount of energy
The following are some of the applications of the
heat recovery system:
1. Space heating.
2. Industrial drying.
3. Maintaining temperature of substances up to 50 0C.
4. Keep snacks and food warm.
5. Used in health care centers, school etc.
6. To wash the cans in dairy by hot condensate.
7. To dry clothes, grains etc.
8. Any other application requiring warm air.

Paper Title:- Heat Recovery System in Domestic Referigerator System(Vol.2, Issue-2) ISSN(O):- 2349-3585
II. OPERATION PRINCIPLE
Compression refrigeration cycles take advantage of the fact
that highly compressed fluids at a certain temperature tend to
get colder when they are allowed to expand. If the pressure
change is high enough, then the compressed gas will be hotter
than our source of cooling (outside air, for instance) and the
expanded gas will be cooler than our desired cold
temperature. In this case, fluid is used to cool a low
temperature environment and reject the heat to a high
temperature environment.
The Vapour Compression Cycle uses energy input to drive a
compressor that increases the pressure, the pressure of the
refrigerant, which is in the vapour state. The refrigerant is
then exposed to the hot section (termed the condenser) of the
system, its temperature being higher than the temperature of
this section. As a result, heat is transferred from the
refrigerant to the hot section (i.e. heat is removed from the
refrigerant) causing it to condense i.e. for its state to change
from the vapour phase to the liquid phase (hence the term
condenser). The refrigerant then passes through the
expansion valve across which its pressure and temperature
drop considerably. The refrigerant temperature is now below
that existing in the cold or refrigerated section (termed the
evaporator) of the system, its temperature being lower than
the temperature in this section. As a result, heat is transferred
from the refrigerated section to the refrigerant (i.e. heat is
absorbed by the refrigerant) causing it to pass from the liquid
or near-liquid state to the vapour state again (hence the term
evaporator). The refrigerant then again passes to the
compressor in which its pressure is again increased and the
whole cycle is repeated.
Figure shows Vapour Compression Refrigeration Cycle
Figure 2.1 shows a typical vapour compression refrigeration
system that can be broken into the different processes as
explained below:
Process 1–2
Low-pressure liquid refrigerant in the evaporator absorbs
heat from its surroundings, usually air, water or some other
process liquid. During this process it changes its state from a
liquid to a gas, and at the evaporator exit is slightly
superheated.
Process 2–3
The superheated vapour enters the compressor where its
pressure is raised. The temperature will also increase,
because a proportion of the energy put into the compression
process is transferred to the refrigerant.
Process 3–4
The high pressure superheated gas passes from the
compressor into the condenser. The initial part of the cooling
process de-superheats the gas before it is turned back into
liquid. The cooling for this process is usually achieved by
using air or water. A further reduction in temperature
happens in the pipe work and liquid receiver, so that the
refrigerant liquid is sub-cooled as it enters the expansion
device. The condenser has to be capable of rejecting the
combined heat inputs of the evaporator and the compressor.
In other words: (1 – 2) + (2 – 3) has to be the same as (3 –
4).
Process 4-1
The high pressure sub-cooled liquid passes through the
expansion device, which reduces its pressure and controls the
flow into the evaporator. There is no heat loss or gain through
the expansion device.
The four basic components of the vapour compression
refrigeration system are:
1. Evaporator
In evaporator, refrigerant in liquid form will absorb
heat from the cold chamber causing it to evaporate. This is
done at a low temperature. So, a low pressure has to be
maintained in the evaporator. This heat absorption produces
cooling in a refrigerating process. If a refrigerant is allowed
to expand through the expansion valve, heat will be taken up
from the surrounding air and evaporation of the refrigerant
will occur.
2. Compressor
The compressor increases the pressure of the refrigerant
flowing from the evaporator (drawing in low- pressure, low-
temperature saturated vapour) and to that existing in the
condenser (i.e., delivering high pressure and high temperature
vapour to the condenser). The refrigeration process is a
closed circuit process. To maintain a lower pressure and
lower temperature inside the evaporator, it is necessary to
remove vapour. The compressor sucks vapour away from the
evaporator. If the load on the evaporator rises and the
refrigerant evaporates quicker, the pressure and temperature
in the evaporator will rise. Refrigerant leaves the evaporator
enters the compressor where it becomes compressed.
Compression is carried out as in a petrol engine by the
movement of a piston. The compressor requires energy to
increase the pressure. This increase is transferred to the
refrigerant vapour and is called the compression input.
Because of the compression input, vapour leaves the
compressor at a different pressure and the extra energy
applied causes superheating of the vapour.
3. Condenser
The high pressure, high temperature (superheated or
saturated) vapour that enters the condenser has heat removed
from it and as a result it is condensed back into a liquid
phase. The refrigerant gives off heat in the condenser, and
this heat is transferred to a medium having a lower
temperature. The amount of heat given off is the heat

absorbed by the refrigerant in the evaporator plus the heat
created by compression input. The heat transfer medium can
be air or water, the only requirement being that the
temperature is lower than that which corresponds to the
condensing pressure. The process in the condenser can
otherwise be compared with the process in the evaporator
except that it has the opposite “sign”, i.e. the conditional
change is from vapour to liquid.
4. Expander
The high-pressure liquid from the condenser is expanded
through an expander which is a capillary tube or an
expansion valve, allowing pressure to drop to the existing
pressure in the evaporator. Pressure in the receiver is much
higher than the pressure in the evaporator because of the
compression (pressure increase) that has occurred in the
compressor. To reduce pressure to the same level as that of
evaporating pressure, a device must be inserted to carry out
this process, called throttling, or expansion and the device is
therefore known either as a throttling device or an expansion
device. Ahead of the expansion valve the liquid will be at a
temperature lesser than the boiling point. By suddenly
reducing pressure a conditional change will occur and the
liquid begins to boil and evaporate in the evaporator.
In our sudy, we used a double door refrigerator. The upper
chamber was converted to a heat chamber by replacing the
evaporator coils with the condenser unit (Fig 2.2). The
evaporator is placed in the lower chamber. In a conventional
refrigerator (double door) the cold air from the upper
chamber is blown to the lower chamber with the help of a
fan. In our study the upper and lower chamber are separated
by insulating it with thermocol (polystyrene). The heat
released by the condenser is blown into the hot chamber
using a fan
Figure shows Vapour Compression Refrigerator Systematic
Diagram
The compressor consists of two charge lines and one
discharge line. The evaporator is connected to one of the
charge lines of the compressor. The discharge line of the
compressor is connected to the condenser placed inside the
hot chamber. The other end of the condenser is connected to
a second condenser placed on the body of the refrigerator.
Then it is connected to expansion valve and then to the inlet
of evaporator which is placed inside the bottom chamber. All
the connections are made using Copper tubes.
III DESIGN PARAMETERS
Since the concept gives brief idea about utilizing waste heat
at domestic level, it is decided to use a “Videocon” second
hand double door working domestic refrigerator of capacity
210 liters. Parts of the domestic refrigerator is listed below.
1. Compressor
2. Condenser
3. Capillary Tube
4. Plate type Evaporator (Freezer)
5. Insulated Chambers
The two chambers of the refrigerator is insulated
with thermocol of which one chamber is used for utilizing the
waste heat from refrigerator and the other chamber for
keeping the substances cool. These are the insulated
chambers used in the design.
IV PERFORMANCE ANALYSIS
Heat recovery system is used to utilize waste heat
from the condenser of the refrigerator. The effort is to
increase maximum temperature output inside the hot
chamber. There are various parameters which affects the
temperature variation. In the present study, the temperature
change with respect to different parameters like time, volume
of chamber and load is studied.
1. Analysis of Temperature variation in Hot and Cold
chambers with Time
This analysis was conducted under the atmospheric
temperature of 33.2 0C.
Figure shows Temperature-Time plot (without load)
From the analysis of temperature variation with
respect to time, it is seen that the maximum temperature
reached by the hot chamber is 50.8 0
C. On further increase in
time, the temperature remains a constant. But it is observed
that the temperature in the cold chamber is decreasing with
respect to time and reaches a constant value of -10.9 0
C.
2. Analysis of Temperature variation in Hot chamber
with Volume of chamber
Temperature of the hot chamber was reduced so as
to increase the temperature inside the chamber. This was
-20
-10
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Temperature,0C
Time, min
cold
chamber
temperature
hot chamber
temperature

done using thermocol, which is used as an insulating
material.
In the study, the depth of the chamber was reduced
by 9.6cm. This has increased the temperature inside the
chamber by about 4.8 0
C.
3. Analysis of temperature variation in hot chamber
with constant load
Study is conducted considering a copper pot filled
with 1200g of water kept inside the cabin and temperatures
are noted after specific interval of time.
Figure shows Temperature-Time plot (with load)
From the analysis, the following are the observations:
Mass of water in the pot, m
= 1200 gm =1.200 kg
Specific heat of water, Cp = 4.184 KJ/Kg K
Initial temperature of water
= 260
C
Final temperature of water
= 420
C
Time required for reading,
Δt = 135 min
Heat Absorbed By Water, Q
= m x Cp x ΔT/Δt
= 9.92 J/s
Heat recovery achieved, Q
= Heat Absorbed by Water
= 9.92 W
For Refrigerator of 210 liters capacity, given data from
Videocon Ltd manual:
Refrigerator cooling capacity
= 85 kcal/hr
= 85×4.187×1000/3600
= 98.859 W
Power required for running the compressor
= Work done on refrigerant
= 1/8 HP
= 1/8×746
= 93.25 W
COPactual
compressorbydoneWork
orrefrigeratinextractedHeat
=
93.25
98.859
=
= 1.06
Condenser heat is utilized, which is the part of compressor
work. Hence COP of system will improve.
achievedrecoveryHeat-compressorbydoneWork
ionrefrigeratinextractedHeat
=
COPimproved
9.92-93.25
88.392
=
= 1.19
Percentage Improvement in COP
100×
COP
)COP-(COP
=
improved
actualimproved
100×
1.06
1.06)-(1.19
=
= 12.26 %
V EXPERIMENTAL PROCEDURE
Table shows List of Equipments
Conventional domestic refrigerators have chambers which are
insulated using polyurethane along with plastic. This insulation
is retained in our study. Thermocol is another insulating material
used which is mainly used in our study for reducing the cubic
capacity of the chambers without affecting its performance.
20
22
24
26
28
30
32
34
36
38
40
42
44
0 30 60 90 120
Temperature,0C
Time, min
Hot
chamber
temperature
Sl.
No.
Equipment Type/Material Speci
ficati
on
1. Refrigerator
1. Compressor
2. Condenser
3. Evaporator
Domestic Type
Hermetically
Sealed
Copper, Air cooled
Plate Type
210L
1/8th
HP
2. Refrigerant R-134a
3. Chambers
1. Hot
Chamber
2. Cold
Chamber
Thermocol
Insulated
Thermocol
Insulated
24cm
×
40cm
×
27cm
78cm
×
46cm
×
48cm

Figure shows cold chamber
Figure shows hot chamber
To utilize maximum heat, condenser is mounted
inside the insulated chamber. Two condensers are used in this
study. One of the condensers is placed in the hot chamber and
the other condenser is placed outside the refrigerator in contact
with atmosphere. This is constructed by ensuring the proper
working of the refrigerator. All the copper tube connections in
the refrigerator are joined by brazing.
Figure shows condenser mounting
VI CONCLUSIONS
A method to recover and utilize waste heat, in refrigerators is
studied. The presented project, attempted to recover the waste
heat from a 210 L refrigerator, for domestic purposes. The upper
chamber of the refrigerator was developed as a hot chamber, by
extension of the condenser coils, and the attachment of the upper
portion, towards the top surface of the lower chamber of the
refrigerator. The temperature variation in the hot chamber and
the cold chamber is studied considering the various parameters
like time, capacity of chamber and load.
From the results obtained, it is concluded that the
temperature in the hot chamber increases and that in the cold
chamber decreases with increase in time. As the atmospheric
temperature increases, since the loss of heat from the hot
chamber to the atmosphere decreases, the maximum temperature
within the hot chamber increases.
The variation in capacity of hot chamber was
obtained by employing the use of thermocol, and from the
obtained observations, we understand that the temperature within
the hot chamber increases, with decrease in cubic capacity. The
time taken for the hot chamber to attain any particular
temperature, without load, was lesser than with load in the hot
chamber. The COP calculated, may be higher than the actual
value, because of leakage of heat whilst the door is opened or
closed, the age of the refrigerator, and the physical condition of
the gasket.
From the results, it has been established that the
above mentioned method of heat recovery, can be designed and
developed for every household refrigerators, with the minimal
cost. Hence the reuse of waste heat paved way for maximum
energy conservation. This work can be enhanced by providing
better insulation which in turn minimizes the heat loss and
increases the efficiency of the system.
REFERENCE
[1] S.C.Kaushik, M.Singh., Feasibility and Design studies
for heat recovery from a refrigeration system with a canopus heat
exchanger, Heat Recovery Systems & CHP,
Vol.15(1995)665673.
[2] P.Sathiamurthi, PSS.Srinivasan, Studies on waste heat
recovery and utilization. Globally competitive eco-friendly
technologies engineering National conference, (2005)39.
[3] S. C. Walawade,B.R. Barve, P. R. Kulkarni, Design
and Development of Waste Heat Recovery System for Domestic
Refrigerator.
[4] P.Sathiamurthi, PSS.Srinivasan “Design and
Development of Waste Heat Recovery System for air
Conditioning Unit, European Journal of Scientific
Research,Vol.54 No.1 (2011), pp.102-110.
[5] F.N.Yu, K.T.Chan, “Improved condenser design and
condenser-fan operation for air-cooled chillers”, Applied Energy,
Vol.83 (2006) 628-648.
[6] B. E. Project „Waste heat recovery for domestic
refrigerator‟ Thesis submitted by Ms. Anjali Zalake, Ms.
Bhagyashree Adake, Dr. J. J. Magdum College of Engineering,
Jaysingpur.2011-12
[7] C.P. Arora, Refrigeration and Air conditioningPHI
Publications, 2010.

Heat Recovery System in Domestic Refrigerator

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