Study on Waste Heat Potential of Commercial Refrigerator
Condenser
Sulastri Panggabean
1
, Dewi Marina Sibarani
1
, Riswanti Sigalingging
1
and Adian Rindang
1
1
Agricultural Engineering, Faculty of Agriculture, Universitas Sumatera Utara, Medan, Indonesia
Keywords: Waste Heat, Condenser, Commercial Refrigerator.
Abstract: The waste heat from the commercial refrigerator came out from the heat released by the condenser. The
released heat had the potential to be reused. The heat potential was suitable to be used for drying
agricultural products that do not require too high temperatures or sensitive to high temperature such as
materials containing volatile substances for example Curcuma rhizome. The amount of enthalpy and heat
potential presented in the waste heat before doing modification is 94.29 kJ.kg
-1
and 1.336 kJ.s
-1
. By doing a
little modification on the condenser such as moved the condenser to the backside and added partitions, the
enthalpy can be increased as much as 108.69 kJ.kg
-1
(increased up to 15.27%) as well as the heat potential
as much as 1.723 kJ.s
-1
(increased up to 28.92%).
1 INTRODUCTION
There are several factors that influence the
agricultural product processing activities as well as
other processing industry. One of them that holds
great impact is the availability of energy during
those activities take place. That energy can be either
thermal energy, electrical energy, chemical energy,
mechanical energy, and others, which derived from
various energy sources. Based on the source, the
energy can be classified into two groups namely:
fossil energy (diesel, petrol, kerosene or gas) and
non-fossil energy (wind energy, water energy,
biodiesel, biogas, bio-ethanol, etc). For the time
being, fossil energy is still the main choice in the
processing industry in Indonesia, although the latter
not less than the first and has started to increase in
utilization. Among the energy sources that have
been mentioned earlier, there are other sources of
energy that can still be exploited but tend to be
ignored because they are considered no longer
useful, which is the energy that derived from waste
or by-product of the utilization of fossil and non-
fossil energy when it is converted to another form of
energy or when used for a process. Among the
energy that comes from a by-product of a production
process is wasted heat which is the unused output
from a production process and usually discharged
into the environment.
Utilization of waste heat into a source of energy
that can be reused for another process has several
positive impacts on the environment. First, the heat
that usually discharged to the environment which is
at a temperature above the ambient temperature,
could be one of the factors that led to the increase of
the environment temperature, can be reduced
because the heat was used for other processes before
discharged. Secondly, the aforementioned energy
usage savings, which are certainly along with cost
reductions for energy inputs. Thus, we can reduce
the cost of production because some energy required
comes from the waste that was previously about to
be disposed of. Third, it has good environmental
impacts, especially on the effects of fossil fuel
exploration.
With the enormous benefits of reusing waste
heat, it certainly has a new impact on future industry
development. However, a more in-depth study of
waste heat recovery is needed, such as: the quality of
heat that can still be utilized, the type of activity that
can exploit the heat potential possessed from waste
heat, additional measures that must be done so that
the waste heat can be utilized optimally, and how
much benefit is gained by wasted heat recovery.
There are some activities that produce heat as a
by-product, such as heat generated due to processing
at the factory, heat emitted by vehicle radiators, and
heat released by the condenser in the cooling system.
The amount of waste heat from the factory is high
Panggabean, S., Sibarani, D., Sigalingging, R. and Rindang, A.
Study on Waste Heat Potential of Commercial Refrigerator Condenser.
DOI: 10.5220/0010071700090013
In Proceedings of the International Conference of Science, Technology, Engineering, Environmental and Ramification Researches (ICOSTEERR 2018) - Research in Industry 4.0, pages 9-13
ISBN: 978-989-758-449-7
Copyright
c
2020 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
9
because usually, the heat comes from the
sterilization or the steaming process at very high
temperatures while the waste heat of motor vehicles
(such as cars or tractors) is classified as average. In
addition to both types of heat, there is still a low
waste heat from the condenser in the cooling system.
The heat from a cooling system derived from the
cooling cycle as a heat discharged to the
environment as a result of rising temperatures due to
the compression process of the compressor. The
cooling cycle includes: compressing refrigerant into
the condenser by the compressor, discharging the
heat from the condenser to the environment,
throttling by the expansion valve, and absorbing the
heat from the surrounding by the evaporator and
then come back to the compressor, thus the cycle of
the cooling system occurred. Based on the purpose,
the cooling system could be divided into several
types, such as air conditioner (AC) for cooling room
and refrigerator for maintaining the freshness of
food or drinks (for cold storage purpose). The
refrigerator itself is divided into two types, namely
domestic refrigerator and commercial refrigerator
also known as showcase refrigerator.
The waste heat of an air conditioner and a
domestic refrigerator has been studied before
(Suntivarakon, et.al., 2009; Shinde, 2014;
Rahmanto, 2011; and Momin, 2014), but not for a
commercial refrigerator. Based on previous studies
(Suntivarakon, et.al., 2009; Shinde, 2014;
Rahmanto, 2011; and Momin, 2014), the potential of
heat that can be utilized is quite satisfactory. Given
that the objectives of a commercial refrigerator
(showcase) are slightly different from domestic
refrigerators, thereby resulting heat generation may
have different potential values. Therefore, a more in-
depth review of the potential for waste heat in the
showcase refrigerator is required.
The purpose of this paper was to get the heat
potential value that was still held by the heat of the
condenser and to propose the type of activity that
was suitable based on the potential.
2 METHODOLOGY
The research was conducted on a one-door
commercial refrigerator AGATE-300 model with
R600a refrigerant type. The initial data on the
refrigerator before and after modification were taken
during 6 hours. Preliminary data required include
refrigerant temperature leaving the condenser,
temperature and RH of air around the condenser, the
temperature in the cold region of the refrigerator,
and the temperature and RH of the environment. The
data will be used to calculate the potential value of
waste heat, compression work, refrigeration effects
and coefficient of performance before and after
modification. Modification was made to the
condenser to concentrate the condenser waste heat
so that the heat can be utilized more centrally.
3 RESULTS AND DISCUSSIONS
The cooling process in the refrigeration machine
occurs when heat from one region is absorbed by the
refrigerant and releases the heat to another region.
This refrigeration process runs with the help of
refrigerant passing through the coil. This process
begins with the flow of the refrigerant with the aid
of a compressor from the evaporator (conducting
heat absorption) to the condenser (releasing the heat)
(Ashby, 2006). This process can be understood more
clearly with the aid of pressure-enthalpy diagrams of
the vapor refrigeration compression cycle (Figure 1)
(Stoecker and Jones, 1987).
Figure 1: The standard vapor compression cycle in the
pressure-enthalpy diagram.
There are some important parameters in
refrigeration system that need to be known, such as,
the refrigeration effect, the compression work, and
the coefficient of performance (COP).
How much compression work during the
ongoing refrigeration cycle is described as (Stoecker
and Jones, 1987):
(1)
The effect of the refrigeration system is
expressed in how much heat is released during the
refrigeration cycle and described as (Stoecker and
Jones, 1987):
ICOSTEERR 2018 - International Conference of Science, Technology, Engineering, Environmental and Ramification Researches
10
(2)
The coefficient of performance (COP) signifies
the achievement value of the vapor compression
cycle is described as (Stoecker and Jones, 1987):
(3)
The waste heat from the condenser has the
potential to be exploited. For example waste heat
from an air conditioner used for drying clothes with
COP between 2.66 to 3.45. Hot temperatures dispose
of condensers vary between 41.9 to 42.6
o
C. Drying
rate of 1.1 kg.h
-1
without an additional fan and 2.26
kg.h
-1
with an additional fan. The heat potential
output of its air conditioner was 12,648 BTU.h
-1
or
equivalent to 3.71 kJ.s
-1
(Suntivarakon, et.al., 2009)
and for drying potato chips with COP of 2.64 to
3.26. Hot air temperature of 33.88
o
C to 44.05
o
C.
The air conditioner cooling capacity was about
2.734 ± 0.023 kJ.s
-1
(Rahmanto, 2011). The waste
heat of domestic refrigerator condenser can also be
used to heat water up to 47
o
C (Shinde, 2014) to
52
o
C (Momin, 2014).
Analysis of the heat potential of condenser
output begins with the measurement of the
temperature and humidity of the output air from the
refrigerator condenser as well as the environmental
air that described as (ASABE, 2006):
e
o
(T) = 0.6010 exp
17.27 T
T+237.3
(4)
Pv = e
o
(Twet) – γpsy (T – Twet)
(5)
RH = 100 x (Pv / e
o
(T)
(6)
In this case: e
o
(T) is saturated vapor pressure at
air temperature (kPa), Pv is actual vapor pressure
(kPa), e
o
(Twet) is saturated vapor pressure at wet
bulb temperature (kPa), Twet is wet bulb
temperature (
o
C), T is dry bulb temperature (
o
C),
γpsy is the psychrometric constant (0.06738 at
1atm), and RH is relative humidity of air.
Air specific humidity is described as (Cengel and
Boles, 2002):
ω = 0.622 x
(7)
In this case: ω is specific humidity (kg.kg
-1
), and
P is the atmospheric air pressure (kPa).
The enthalpy of air before and after passing
through the condenser is described as (Cengel and
Boles, 2002):
h = 1.005 T + ω(2501.3 + 1.82 T)
(8)
In this case: 1.005 is specific heat of dry air at 1
atm (kJ.kg
-1
), 2501.3 is air coefficient, and 1.82 is
specific heat of air (kj.kg
-1
K
-1
).
The specific volume of air passing through the
condenser is described as (Singh and Dennis, 2009):
(9)
In this case: Vs is the specific volume of air
(m
3
.kg
-1
).
Airflow rate pass through the condenser is
described as (Cengel and Boles, 2002):
V = v x A
(10)
In this case: V is air flow rate (m
3
.s
-1
), v = air
velocity (m.s
-1
), and A is surface area (m
2
).
The potential heat of the condenser is described
as (Cengel and Boles, 2002):
Q =
V
V
s
(11)
In this case: Q is heat (kJ.s
-1
), h
2
is the enthalpy of
air after passing through the condenser (kJ.kg
-1
), and
h
1
is the enthalpy of air before passing through the
condenser (kJ.kg
-1
).
3.1 Waste Heat Potential of
Commercial Refrigerator
Condenser
Based on observation, the following data (Table 1)
were obtained:
Table 1: Initial observation data (before modification).
Parameters
quantity
T ambient db
28.78
o
C
T ambient wb
26.96
o
C
T air from condenser db
33.39
o
C
T air from condenser wb
29.25
o
C
RH of air from condenser
73.57 %
Velocity of air leaving condener
5 m.s
-1
Study on Waste Heat Potential of Commercial Refrigerator Condenser
11
From the potential value obtained from
observation and calculation, it is advisable to utilize
the heat potential for the drying process of curcuma
chips. Given that, to dry the curcuma requires a
temperature between 40
o
C – 60
o
C (Sapei, et al,
2017). This is due to the presence of essential oils in
those rhizomes that would be lost if dried at high
temperatures.
Based on Table 1 and by using Equation 8 and
11, the enthalpy and the waste heat potential from
commercial refrigerator condenser could be
calculated and obtained respectively 94.29 kJ.kg
-1
and 1.336 kJ.s
-1
. This amount of energy can be used
for draying agricultural product such as curcuma
rhizomes. If all of the energy used for draying in 6
hours then the amount of curcuma chips that can be
dried as much as 13.2 kg, with the assumption that
all of energy used for drying or there are no energy
loss during drying process (efficiency is 100%),
90% of initial water content, and 7% of desired
water content.
The waste heat potential can be raised if a
modification is made to the condenser. In addition,
this modification can also increase the number of
activities that can use the waste heat. Furthermore,
this needs to be done because in the default
condition the direction of the waste heat (air leaving
the condenser) leads to the front of the refrigerator,
making it quite difficult to exploit the heat potential.
In addition, the heat tends to spread in all directions.
The modification done by moving the condenser
position to the back of refrigerator and adding some
partitions outside the condenser. Adding partitions
could reduce the air velocity leaving the condenser
but it also increased the air contact time with the
condenser surfaces. Here are the data obtained after
modifications (Table 2)
Table 2: Observation data after modification.
Parameters
quantity
T ambient db
28.78
o
C
T ambient wb
26.96
o
C
T air from condenser db
42.12
o
C
T air from condenser wb
32.09
o
C
RH of air from condenser
50.28 %
Velocity of air leaving condenser
1.6 m.s
-1
After modification the enthalpy and the waste
heat potential respectively 108.69 kJ.kg
-1
and 1.723
kJ.s
-1
. The enthalpy can be increased as much as
15.27% and the the waste heat potential can be
increased as much as 28.92%.
With this amount of energy, then 16.7 kg of
curcuma chips will be able to be dried, with
assumptions that all of energy used for drying or
there are no energy loss during drying process
(efficiency is 100%), 90% of curcuma water content,
and 7% of desired water content.
Although this modification could improve the
quality of heat that can be utilized, this also changed
the value of COP, compressor work and
refrigeration effect.
3.2 Work of Compressor, Refrigeration
Effect, and COP
The work of a compressor from a refrigeration can
be calculated using Equation1 and using properties
of refrigerant R600a (ASHRAE, 2009). From the
calculation, the work of compressor before and after
modification obtained as follows (see Figure 2):
Figure 2: The work of compressor.
The refrigeration effect of a commercial
refrigerator can be calculated using Equation 2. Here
is the refrigeration effect before and after
modification (see Figure 3).
Figure 3: The refrigeration effect.
The COP of a commercial refrigerator can be
calculated using Equation 3. Here is the COP before
and after modification (see Figure 4).
ICOSTEERR 2018 - International Conference of Science, Technology, Engineering, Environmental and Ramification Researches
12
Figure 4: The coefficient of performance (COP).
The COP after modification (Figure 4) was lower
than before modification. This happened because the
work of compressor (Figure 2) has been increased
after modification although the refrigeration effect
(Figure 3) was almost constant. Nevertheless, the
average of COP was still relatively high, which was
above 4. The increase in the work of compressor
could occur due to modification made to the
condenser position and the partitions added on the
outside of the condenser which resulted in a reduced
air velocity passing through the condenser. Thus
made the compressor work more even though the
refrigeration effect was almost constant. This
illustrates the considerable influence on the
performance of irreversible heat transfer between the
refrigerant on the cold and warm region.
4 CONCLUSIONS
From the observation, it can be concluded that the
waste heat of a commercial refrigerator had potential
to be utilized for another process such as for drying
process. The potential heat also can be improved by
doing some modification in to the system. The
enthalpy and the potential heat presented in the
waste heat before doing modification respectively
was 94.29 kJ.kg
-1
and 1.336 kJ.s
-1
. Modifications
done to the condenser such as moved the condenser
to the backside of refrigeration and added partitions
on the outside of condenser. By doing modifications,
the enthalpy could be increased as much as 108.69
kJ.kg
-1
(increased up to 15.27%) as well as the
potential heat as much as 1.723 kJ.s
-1
(increased up
to 28.92%).
ACKNOWLEDGEMENTS
This research was funded by Universitas Sumatera
Utara in accordance to TALENTA of Universitas
Sumatera Utara, Research Contract of Fiscal Year
2018 No. 38 / UN5.2.3.1 / PPM / KP-TALENTA
USU / 2018 on March 16, 2018.
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Study on Waste Heat Potential of Commercial Refrigerator Condenser
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