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A development of a portable air conditioning-heat pump unit using helical coil heat exchanger

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In the present energy crisis situation, maximization utilization of energy use is vital matter, especially an air conditioning unit which is one of the largest energy use in the home. The objectives of this paper are to: i) design and development of a portable air conditioning:-heat pump unit using helical coil heat exchanger, ii) improve the cooling performance of a portable air-conditioning heat pump unit, iii) enhance the heat recovery performance of the heat recovery system, and iv) improve the energy efficiency of the portable water-cooled air conditioning unit. In this research, a heat exchanger designed, working as water cooled condenser, consists of a shell and helically coiled tube unit which is fabricated by bending a 9.50 mm diameter straight copper tube into a helical-coil tube of twenty turns. Water and refrigerant R-22 are used as working fluids in shell side and tube side, respectively. The operation test results of the designed portable air conditioning-heat pump unit using helical coil heat exchanger, found that the unit worked satisfactorily. This paper then investigated the benefits of applying a helical coil heat exchanger for heat recovery of a portable air conditioning-heat pump unit. The unit with heat recovery system was set up for study at various water flow rates. The cooling performance, the heat recovery, and the energy consumption for different warm water flow rates were measured. The results show that the experimental unit when heat up the water by approximately 15-30°C at water flow rate of 0.5-2.0 l/min. The maximum achievable comprehensive COP was 5.13 when the water flow rate was set at 2.0 l/min. The COP of the designed air conditioning-heat pump unit is improved approximately 38% when compares to the typically air cooled counterpart. Moreover, according to the economic analysis, the unit is also economically attractive with the air conditioning-heat pump unit that has payback period of 4 months.
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A Development of a Portable Air Conditioning-Heat Pump
Unit using Helical Coil Heat Exchanger
T. Wessapan, T. Borirak, S. Teeksap
Mechanical engineering department,
Faculty of engineering, Eastern Asia University
Pathumthani, Thailand
e-mail: teerapot@eau.ac.th
N. Somsuk
Industrial engineering department,
Faculty of engineering, Eastern Asia University
Pathumthani, Thailand
e-mail: nisakorn@eau.ac.th
Abstract In the present energy crisis situation, maximization
utilization of energy use is vital matter, especially an air
conditioning unit which is one of the largest energy use in the
home. The objectives of this paper are to: i) design and
development of a portable air conditioning:-heat pump unit
using helical coil heat exchanger, ii) improve the cooling
performance of a portable air-conditioning heat pump unit, iii)
enhance the heat recovery performance of the heat recovery
system, and iv) improve the energy efficiency of the portable
water-cooled air conditioning unit. In this research, a heat
exchanger designed, working as water cooled condenser,
consists of a shell and helically coiled tube unit which is
fabricated by bending a 9.50 mm diameter straight copper
tube into a helical-coil tube of twenty turns. Water and
refrigerant R-22 are used as working fluids in shell side and
tube side, respectively. The operation test results of the
designed portable air conditioning-heat pump unit using
helical coil heat exchanger, found that the unit worked
satisfactorily. This paper then investigated the benefits of
applying a helical coil heat exchanger for heat recovery of a
portable air conditioning-heat pump unit. The unit with heat
recovery system was set up for study at various water flow
rates. The cooling performance, the heat recovery, and the
energy consumption for different warm water flow rates were
measured. The results show that the experimental unit when
heat up the water by approximately 15-30°
°°
°C at water flow rate
of 0.5-2.0 l/min. The maximum achievable comprehensive COP
was 5.13 when the water flow rate was set at 2.0 l/min. The
COP of the designed air conditioning-heat pump unit is
improved approximately 38% when compares to the typically
air cooled counterpart. Moreover, according to the economic
analysis, the unit is also economically attractive with the air
conditioning-heat pump unit that has payback period of 4
months.
Keywords— air-conditioning; heatpump; helical coil; heat
exchanger; heat recovery
I. INTRODUCTION
Due to the present world’s energy crisis and its related
environmental issues as well as increasing trend of fossil fuel
prices, therefore, maximization utilization of the energy use
is vital matter. Regarding energy used in household, heating
and cooling is the largest energy use in the home, and water
heating is the second largest energy use in the home [1].
Air conditioning units are designed to remove heat from
interior spaces and reject it to the ambient (outside) air [2].
Waste heat rejected from the air conditioning units, which is
a large quantity, can be recovered and applied for use in
another system such as a water heating system [3].
From an energy conservation standpoint, it would be
desirable to reclaim this waste heat in a usable form. The
best and most obvious form of heat recovery is for heating
water. Water heating system from waste heat recovery of an
air conditioning unit, which is one of the most cost effective
energy conservation, has the same concept as heat pump [4-
5], which operates on vapor-compression cycle to pump
energy from surroundings into water. The heat pump water
heater is a promising technology in both residential and
commercial applications due to its improved energy
efficiency and its improved air conditioning performance [6].
Typically commercialized window type air conditioning
unit have rather big size. Recently, portable air conditioning
units, which have the smaller size, have been designed for
providing cooled air and for being movable to be used in the
desired area.
Our previous research studied the use of a combined
water-cooled condenser and a conventional split type air
conditioning unit [7]. In this research, the portable air
conditioning-heat pump unit using helical coil heat
exchanger makes use of both heating and cooling systems, to
maximization utilization energy use by using the waste heat
recovery of an air conditioning unit, for warming water.
Considering the helical heat exchangers, they are
extensively applied in many applications such as utilization
of heat recovery systems [8], due to high heat transfer
coefficient and compact structure. Recently, there have been
some scholars, who study in the use of helical heat
exchanger for recovering waste heat recovery of the
domestic water cooled air-conditioners [9]. However, there
are no reports of using the helical heat exchanger with
portable air conditioning unit, to improve the cooling
performance of a portable air-conditioning heat pump unit,
and to enhance the heat recovery performance of the heat
recovery systems.
Therefore, the objectives of this paper are to: i) design
and development of a portable air conditioning:-heat pump
unit using helical coil heat exchanger, ii) improve the cooling
performance of a portable air-conditioning heat pump unit,
V5-186
978-1-4244-6350-3/10/$26.00
c
2010 IEEE
iii) enhance the heat recovery performance of the heat
recovery system, and iv) improve the energy efficiency of
the portable water-cooled air conditioning unit.
The portable air conditioning-heat pump unit with helical
heat exchanger was fabricated and was then taken to test in
laboratory. The tests are done at the water flow rates ranging
between 0.5 and 2.0 l/min. In the experiments with full load
condition, the cooling performance, the heat recovery, and
the power consumption for different water flow rates were
measured and evaluated.
II. T
HEORY
A. Basic Refrigeration Principles
Refrigeration is the process of extracting heat from a
space and rejecting that heat typically to the surroundings.
The devices that produce refrigeration are refrigerators or
air conditioning units and heat pumps. Both air conditioning
units and heat pumps are basically the same devices, but
differ in their function. Air conditioning unit is used to
maintain the space at low temperatures by absorbing heat,
and extract that heat into a higher temperature environment.
On the other hand, the role of the heat pump is to maintain a
heated space at higher temperatures.
Most air conditioning units consist of four major parts:
compressor, condenser, expansion valve and evaporator.
These components form a complete refrigeration cycle. Each
of them has an important role within the cycle. The four
major steps of the refrigeration cycle are compression,
condensation, expansion and evaporation.
B. The Coefficient of Performance
The coefficient of performance (COP) is a measure of
the efficiency of refrigerators and heat pumps. The
definition of the COP is the efficiency ratio of the amount of
heating or cooling provided by a heating or cooling unit to
the energy consumed by the system. The equation of
calculating the coefficient is as follows:
For a refrigerator or an air conditioning unit, as in (1)
innet
L
orrefrigerat
W
Q
COP
,
=
(1)
For a heat pump, as in (2)
innet
H
pumpheat
W
Q
COP
,
=
(2)
Where
L
Q
is the cooling effect or the desired output for
the refrigerator,
H
Q
is the heating effect or the desired
output for the heat pump, and
innet
W
,
is the energy that is
needed to run the air conditioner or heat pump.
Since the less energy is needed to move heat than to
create it, the effective water-heating efficiency of the unit
system will be greater than 100%. The COP value greater
than 1.0 can be achieved especially when the unit is
removing heat from an object that is cooler than the
ambient. Therefore warm water heating from waste heat
recovery of the unit by letting the water flows through the
condenser.
One of the key factors that affect the COP value is the
high temperature or pressure during condensation. If the high
temperature or pressure during condensation is lower, it will
lower the power used of the compressor and the energy will
save more.
III. D
ESIGN AND TEST
A. Designing the Unit
The portable air conditioning-heat pump unit with helical
heat exchanger is designed by concept of maximization
utilization of an air conditioning unit. All components are in
a same body structure. The unit is on wheels for easy
mobility. It is designed for use the air conditioning system
and warm water heater at the same time. Water heating
system from waste heat recovery of the condenser uses a
helical coil heat exchanger to transfer heat to water. Fig. 1
illustrates the schematic of an air conditioning-heat pump
unit.
Figure 1. The schematic diagram of the air conditioning-
heat pump unit.
From Fig. 1, the process starts with vaporization of the
refrigerant in the evaporator. This is complete at point 1.
Compression is used to raise the pressure of the refrigerant
by compressor, point 2, so that it can condense at a higher
temperature. When the entire vapor has condensed, point 3,
the pressure is reduced in an expansion valve, and the
refrigerant is returned to its original condition 4.
When superheat R-22 transfers the heat to the water that
flows through condenser in condenser case, it will be
condensed to liquid. The water temperature that flows
through copper tubes in condenser will get higher than inlet
water temperature and the obtained warm water then flows
out from condenser via outlet pipe.
The portable air conditioning-heat pump unit with helical
heat exchanger can provide warm-water as a by product of
air-conditioning, which will help to improve the total
coefficient of performance of the unit and reduce water-
heating energy cost. The heat exchanger designed, working
[Volume 5] 2010 2nd International Conference on Computer Engineering and Technology V5-187
as water cooled condenser, consists of a shell and helically
coiled tube unit which is fabricated by bending a 9.50 mm
diameter straight copper tube into a helical-coil tube of
twenty turns. Water and refrigerant R-22 are used as working
fluids in shell side and tube side, respectively.
The unit with helical heat exchanger is designed on
wheels to ease mobility, in small size. It may be used as
stand alone unit or as a supplement unit to other air
conditioning systems. It is appropriate for the household
section, and some commercial buildings where need to use
conditioning air and warm water at the same time or to use as
pre-heater for water.
Fig. 2 and Fig.3 illustrate the components of the portable
air conditioning-heat pump unit with helical heat exchanger.
Figure 2. Front view of the unit.
Figure 3. Side view of the unit.
Legend:
1. Evaporator
2. Control box
3. Fan
4. Inlet and outlet water tubes
5. Heat exchanger case
Specification of the unit
BTUs 9,000
COP 3.3-5.1 depend of water flow rate
Water flow rate 0.5-2.0 l/min
Kilowatt input 0.65 kW
Voltage/Hz/Phase 220V / 50Hz / 1 Phase
Weight 50 kg
Size L 70 cm, W 50 cm, H 40 cm
The helical heat exchanger consists of a shell and a
helically coiled finned tube unit. The copper coil is
constructed by bending a 9.5 mm diameter straight tube into
a helical-coil of twenty turns. The diameter of helical-coil is
150 mm. The dimensions of the helical coil are shown in
Table I.
T
ABLE I. D
IMENSIONS
O
F
T
HE
H
ELICAL
-
COIL
H
EAT
E
XCHANGER
Parameters Dimensions
Outer diameters of tubes, mm
Inner diameters of tubes, mm
Diameters of helical coil, mm
Number of coil turns
Helical pitch, mm
Width of shell, mm
Length of shell, mm
Total length of helical coil, mm
9.50
9.30
150
20
20
250
420
10,000
B. Performance Testing Method
The test unit consists of a refrigerant loop, tap water
supply system, and data acquisition system. And the helical-
coil heat exchanger consists of a shell and helically coiled
unit (Fig.4). The test unit and the connections of the water
sullied piping system are designed such that parts can be
changed or repaired easily. An instrument for measuring and
control of room temperature, refrigerant pressure and air
flow rate is installed at all important points in the circuit. The
room temperature is adjusted to the desired level and
controlled by temperature controller. The flow rates of the
water are controlled by adjusting the valve and measured by
the flow meters.
Figure 4. A schematic diagram of the helical-coil heat
exchanger unit.
T
esting was conducted with various inlet water flow rates
entering the test unit. In the tests, the water flow rate was increased
in small increments while the refrigerant flow rate and inlet water
temperatures were kept constant.
The controlled parameters and
measured parameters are shown in Table II.
V5-188 2010 2nd International Conference on Computer Engineering and Technology [Volume 5]
TABLE II
C
ONTROLLED PARAMETERS AND
M
EASURED
P
ARAMETERS
Controlled parameters
The room temperature is set at 25
o
C
Water inlet temperatre is set at 27
o
C
Water flow rate; 0.5, 1.0, 1.5, and 2.0 l/min
Measured Parameters
Power input; electrical power consumption is measured by
wattmeter to calculate the COP of the cooling system.
The interval time for heating water; the warm water temperature
at outlet pipe is measured to determine an appropriate interval
time that the warm water can be used.
Water outlet temperature is measured to calculate the water
heating system performance.
Inside and outside air temperatures are measured to calculate the
COP of the cooling system.
IV. R
ESULTS AND
A
NALYSIS
According to design and development of the portable air
conditioning-heat pump unit the results of the functional and
performance testing, it found that the unit can work
functionally and properly with the obtained performance is
improved as well as the warm water supplied from the unit is
in an utilization temperature.
A. Warm Water Temperature
Fig. 5 shows the warm water temperature from waste
heat of the unit at various water flow rate. It is found that
when the room temperature and inlet tap water temperature
are kept constant,
the outlet water temperature increases with
decreasing water flow rate. This is because the heat transfer rate of
the heat exchanger increases with increasing water flow rate.
For
comparison of temperature increased of water from the unit
with general water cooled condenser and the unit with helical
coil condenser, it is found that the temperature increased of
water, in case of using helical coil condenser with the unit, is
obviously greater than in the case of the unit with general
water cooled condenser.
0
5
10
15
20
25
30
35
0.5l/min 1.0l/min 1.5l/min 2.0l/min
water flow rate (l/min)
Water temperature increased (
o
C)
Water cooled condenser
Water cooled using helical coil condenser
Figure 5. The temperature increased of water from the
portable air-conditioning unit with the general water cooled
condenser and with the helical coil condenser.
B. The COP Value of the Unit
The data from the previous research show that, the
conventional air conditioning unit using air cooled
condenser used in the test performed the COP value at 2.82.
Fig. 6 shows the variation of COP of the unit with general
water cooled condenser and the unit with helical coil
condenser at various water flow rate compared to the
conventional air conditioning unit. As expected, the unit
with the water cooled condenser performed the better results
of COP values and at a specific temperature of water
entering the test unit, the COP depends directly on water
flow rate. This is because the heat transfer from the
refrigerant to tap water increases with increasing tap water
flow rates. Therefore, the COP of the unit also tends to
increase when water flow rate increases. Moreover, the
benefit of applying a helical coil condenser is to improve the
COP of the unit to 4.41 from using the general water cooled
condenser of 4.16 at water flow rate of 2.0 l/s.
0
1
2
3
4
5
conventional unit 0.5l/min 1.0l/min 1.5l/min 2.0l/min
water flow rate (l/min)
COP of Air-Conditione
r
Water cooled condenser
Water cooled using helical coil condenser
Air Cooled
Figure 6. The
COP values of the unit at various water flow rates
.
C. Payback Period Analysis
Cost for fabrication and installation of the helical coil
heat exchanger to the unit is approximately 10,000 Baht. The
useful life expectancy is estimated at 5 years. It is assumed
that the operating time at 8 hours a day. With the interest
rate 5% and electricity cost at 3.5 Thai Baht/kWh, payback
periods compared between the energy saving at various flow
rates are shown in Table II.
By heating water from waste heat of the unit at water
flow rate of 2.0 l/min, the amount of energy consumption
that can be saved is 5,954 kWh per year. And by improving
COP value by using water cooled condenser of the air
conditioning system, the amount of energy consumption that
can be saved is 2,154 kWh. Therefore, the total amount of
energy saved of the portable air conditioning-heat pump unit
is 8,109 kWh. However the amount of energy saved and
amount of the warm water obtained depend on application of
the unit.
[Volume 5] 2010 2nd International Conference on Computer Engineering and Technology V5-189
TABLE II
P
AYBACK PERIODS COMPARED BETWEEN THE ENERGY SAVED AT VARIOUS
FLOW RATES
Item Warm water flow rate (l/min)
0.5 1.0 1.5 2.0
Warm water
volume obtained
per day (liter) 240 480 720 960
Water
temperature
difference
ΔT(°C ) = T
out
T
in
32.4 24.7 19.5 14.6
Energy
consumption
saved per year
from improving
COP (kWh) 870 1,576 1,898 2,154
Energy
consumption
saved per year
from producing
warm water
(kWh) 3,303
5,036
5,964
5,954
Annual energy
saved cost
(Thai Baht) 14,607 23,147 27,518 28,382
Payback periods
(year)
0.72 0.75 0.38 0.37
V. CONCLUSIONS
This paper investigated the benefits of applying a helical
coil heat exchanger for heat recovery of a portable air
conditioning-heat pump unit. The unit with heat recovery
system was set up for study at various water flow rates. It
was found that the heat recovery system could improve the
coefficient of performance for cooling of the unit by 38% at
water flow rates 2.0l/min under full load conditions, and the
level of improvement increased with the tap water flow rate.
The results of this study clearly support widening the
application of heat recovery of a portable air conditioning
unit by using a helical coil heat exchanger to reduce energy
use for air conditioning and water heating in the general way.
Besides maximization utilization energy use by: using the
waste heat recovery of an air conditioning unit for warming
water; improving improve the cooling performance of a
portable air-conditioning heat pump unit; and enhancing the
heat recovery performance of the heat recovery system, this
portable air conditioning-heat pump unit with helical heat
exchanger is also appropriate for the household section, even
the commercial buildings where need to use conditioning air
and warm water at the same time or to use as pre-heater for
water. The unit is designed on wheels to ease mobility, in
small size. It may be used as stand alone unit or as a
supplement unit to other air conditioning systems. Finally,
according to the economic analysis, the unit is also
economically attractive with the air conditioning-heat pump
unit that has payback period of 4 months.
A
CKNOWLEDGMENT
The authors wish to express their gratitude to
Mr.Sitthichai Wanasit, Mr.Chawangkul Praprut, Mr.Suriya
Anchoo, and Mr.Ekachai Kulsuwan of mechanical
engineering department, Eastern Asia University to help us
on this research. Thanks to Eastern Asia University for many
supports.
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The success of the `Monergy' campaign has led to an improved level of energy awareness in many industries. The level of good housekeeping and the standards of thermal insulation have increased, and many heat-recovery schemes using heat exchangers have been installed. For further improvements to be made more sophisticated techniques are required and the efficient use of industrial heat pumps, when correctly applied, is for many industries the most cost-effective remaining option. Heat pumps often also carry other added benefits, such as easier process control and improved product quality. The author briefly describes mechanical-vapour-compression heat pumps and goes on to discuss rules for application and the various components of heat pumps. The author discusses three applications, i.e. dehumidifiers, malt kilns, and malt-whisky distillation
Heat Recovery from Air Conditioning Units
  • R E Jarnagin
R. E. Jarnagin, "Heat Recovery from Air Conditioning Units," Fact Sheet EES-26, Florida Cooperative Extension Service, University of Florida.
Technical Manual of Design for Lifestyle and the Future: Australia's guide to environmentally sustainable homes
  • C Reardon
  • S Woodcock
  • P Downton
Reardon C, Woodcock S, Downton P 2008: Technical Manual of Design for Lifestyle and the Future: Australia's guide to environmentally sustainable homes. Commonwealth of Australia www.yourhome.gov.au/technical/fs62.html (accessed 18 December 2009).