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REFRIGERANT CHARGE AMOUNT IN HEAT PUMP SYSTEMS AND EVALUATING
OPTIMAL AMOUNT OF GAS
Conference Paper · September 2015
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ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
REFRIGERANT CHARGE AMOUNT IN HEAT PUMP SYSTEMS AND EVALUATING
OPTIMAL AMOUNT OF GAS
Faraz AFSHARĠ*, Ömer ÇOMAKLI**, Nesrin ADIGÜZEL***, ġendoğan KARAGÖZ****
* Atatürk Üniversitesi, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
faraz.afshari@atauni.edu.tr
** Atatürk Üniversitesi, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
ocomakli@atauni.edu.tr
***Kafkas Üniversitesi, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
nesrin_ozdemir25@yahoo.com
**** Atatürk Üniversitesi, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
skaragoz@atauni.edu.tr
Abstract: The refrigerant charge amount is one of very important factors in heat pumps and cooling systems that
generally affect condensing pressure. Heating and cooling capacity of these systems could increase with gas charge
amount. However, there is an ideal charge amount for the best coefficient of performance (COP). On the other side,
compressor power varies with the refrigerant amount in a system. This study has focused on optimization of the
charge amount in a heat pump using several refrigerant as R134a, R404a and R22, also stepwise gas rising have been
observed in concerned outcomes as p-h, T-s and COP diagrams. Compressor consumption (w), coefficient of
performance and condenser outlet heat (Qh) has been measured in different levels of gas amount.
Keywords: Refrigerant gas, Heat pumps, Charge amount, COP, P-h and T-s diagrams.
ISI POMPA SĠSTEMLERĠNDE SOĞUTUCU GAZIN ġARJ MĠKTARI VE GAZIN
OPTĠMUM TUTARININ DEĞERLENDĠRMESĠ
Özet: Isı pompası düşük sıcaklıktaki bir ortamda bulunan ekonomik değeri olmayan ısıyı, kullanılmak üzere daha
yüksek sıcaklıktaki bir ortama pompalayan ve bu işi yapmak için pompalandığı ısıya daha az mekanik iş harcayan
bir sistemdir. Soğutucu akışkan miktarı ısı pompalar ve soğutma sistemlerinde çok önemli faktörlerden biridir ve bu
sistemlerin Isıtma ve soğutma kapasitesi gaz şarj miktarı ile artabilir, Ancak, performans katsayısı için (COP) ideal
bir şarj miktarı bulunmalıdır. Sistemde kompresör gücü (w), alınan ve atılan ısı (Q h,L) soğutucu gaz miktarı ile
değişmesi hesaplanmıştır. Bu çalışmada R134a, R404a ve R22 soğutucu gazları kullanarak şarj tutarının
optimizasyonu araştırılmıştır. Ayrıca, gaz miktarının artışıyla pH, Ts ve COP diyagramları ve ilgili sonuçlar
gözlemlenmiştir.
Anahtar Kelimler: Isı pompası, Soğutucu gaz, Şarj miktarı, COP, P-h ve T-s.
which has the maximum COP (coefficient of
performance) value is water to air type with 3.94 and
followed by water to water type with 3.73, air to air type
with 3.54 and air to water type with 3.40. In order to
investigate the performance of the solar-ground source
heat pump system in the province of Erzurum having
cold climate, an experimental set-up was constructed. In
this study, the performance of the system was
experimentally investigated. The experimentally
obtained results are used to calculate the heat pump
coefficient of performance (COP) and the system
performance (COPS). The coefficient of performance of
1. introducion
In recent years, the use of clean and renewable energy
sources such as solar, wind, geothermal and biomass
energy has received considerable attention for industrial
and domestic applications (Çomaklı Ö., et al, 1996).
Fast urbanization caused by industry revolution made to
emerge the idea finding a remedy to human needs from a
centre in addition to the social services like water supply,
sewer system, public transportation and district heating
system. In a study, results show that the heat pump unit
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ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
the heat pump and system were found to be in the range
of 3.0-3.4 and 2.7-3.0, respectively. This study also
shows that this system could be used for residential
heating in the province of Erzurum being a cold climate
region of Turkey (Çakır U., 2013, Bakirci K., et al,
2011). In some studies, the aim of the study is to select
working fluids which have excellent performance and
are environment friendly for moderately high
temperature heat pump (Pan L., et al, 2011). A domestic
heating system has been designed, constructed and
tested. The evacuated tubular solar collector has been
used to achieve higher collector efficiencies. The effects
of evaporation temperature on the heating capacity and
performance of the system have been investigated
(Çağlar A, ve Yamalı C., 2012,). Thermal performance
analysis of a direct expansion solar assisted heat pump
was investigated by Kong X. and friends (Kong X., et al,
2011). Many studies aimed at minimizing the charge in a
refrigerating machine were thus developed. On a global
level, reduction of refrigerant charges must not affect
energy aspects while respecting environmental
constraints. Independently of the choice of refrigerant,
environmental and or safety issues can be minimised by
reducing the amount of refrigerant charge per heat pump
or refrigeration system (Fernando P., et al, 2004, Choi
H., et al, 2012). The system refrigerant charge are
believed to have a great effect on the cycling thermal
performance. In CO2 heat pump, the CO2 system shows
a large variation of the performance according to
refrigerant charge. In a study has been reported that, the
performance of the CO2 heat pump was measured and
analyzed by varying the refrigerant charge amount at
standard cooling condition. In addition, the performance
sensitivity of the CO2 system as a function of refrigerant
charge was compared to those for the R22, R410A, and
R407C systems (Zhang D., et al, 2014, Cho H., et al,
2005). The refrigerant charge amount is a key factor for
heat pump system optimization, and normally
determines the condensing pressure, which affects the
subcooling at the exit of the condenser. Heating capacity
increases as subcooling increases, however, there is an
optimum charge amount for the best coefficient of
performance (COP) (Corberan J., et al, 2008). Charge
optimisation study of a propane heat pump, optimal
refrigerant charge of a water-to-water heat pump,
Refrigeration systems with minimum charge of
refrigerant, analysis of gas mixtures are some the studies
that show the importance of the charge amount in the
heat pump system (Corberan J., et al, 2011, Kim D., et
al, 2014, Çomaklı Ö., et al).
aluminum fins air source evaporator, an expansion valve,
and a water-cooled copper pipe body type condenser.
The condenser and evaporator were used to transfer heat
from the refrigerant to water and air to refrigerant
respectively and so air was as a heat source and water
was sink for the constructed heat pump. Temperatures in
the test setup were monitored at the selected locations
using T-types thermocouples, and refrigerant pressures
were also measured in the locations as shown in figure.
Compressor power consumption calculated by using
voltage and amperage measured by a digital
amperemeter. A volumetrical flow meter was set up to
obtain flow rate of the condenser cooling water. all
sensors was calibrated to decrease uncertainties during
experimantal tests (Karagöz Ş., 2002).At first level 2000
gr refrigerant, and then in a 200-300 gr increments of the
gas was added into the system to find out maximum
COP respect to the gas amount. A total of 7 Tests
performed in each stage (4 tests for different condenser
water flow and 3 tests for different evaporator air
temperature).
Fig 1. Schematic diagram of the air-to-water heat pump
experimental setup.
Based on the tests, it was found that the full charge of
R134a,R404a and R22 refrigerants for the heat pump
unit was 5800 gr, 5200 gr, 6200 gr respectively. Heating
capacity was calculated using condenser water flow rate
and temperature difference between inlet and outlet. To
confirm the calculation, the capacity was also
determined by refrigerant flow rate and enthalpy
difference between condenser inlet and outlet.
3. Results and discussion
2. Experimental setup and test procedure
Fig. 2,3. shows the variations of the R134a refrigerant
heating capacity and COP as a function of refrigerant
charge at the four different water flow. Gas amount has
increased from 2000 gr upto 7000 gr and in every stage
water supply has been increased in four levels. For
overcharged conditions, the COP was reduced due to a
decrease of the temperature difference between the
refrigerant and the water and compressor power
consumption with increasing gas amount. For
designed heat pump was to measure the performance and
effeciency of AWHP system to investigate different
types of refrigerants under various operating conditions.
Fig. 1 is shown a schematic of the heat pump unit have
been use in this experimental study. In the system
several fluids were used including R134a, R404a and
R22. As shown in the figure, designed heat pump
consists of a reciprocating compressor, copper pipe with
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ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
undercharge conditions, the capacity dropped due to a
reduction of refrigerant flow rate and compressor
efficiency.
3
7000
6000
2,5
5000
2
2000 gram
2000 gram
Qh (watt)
3000
COP
3400
1,5
3800
4200
3000
4000
3400
3800
3000
4200
4600
4600
5000
1
5000
2000
5400
5400
5800
5800
6100
0,5
6100
1000
6400
6400
0
0
water flow rate kg/s
water flow rate kg/s
Fig 2. The effect of the refrigerant charge and water flow rate
Fig 3. The effect of the refrigerant charge and water flow rate
on the COP.
on the heating capacity.
3
2,5
COP
2
0,049281 kg/s
1,5
0,065708 kg/s
1
0,09857 kg/s
0,131433 kg/s
0,5
0
2000
2500
3000
3400
3800
4200
4600
5000
5400
5800
6400
7000
Gas amount (gr)
Fig 4. COP increasing due to gas amount in different water flow rate for 134a refrigerant.
flow rate for 134a refrigerant.
3
3
7000
2,5
6000
5000
COP
2
4000
1,5
3000
1
2000
0,5
Qh - Compressor power (watt)
ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
1000
0
0
1800
2800
3800
4800
5800
6800
Gas amount (gr)
cop
compressor
consumption
kompresör
güçpower
masrafı
Qh (ısıtma kapasitesi)
Fig 5. Heating capacity, compressor power and COP diagram for increasing R134a refrigerant
flow rate for 134a refrigerant.
3
2,5
COP
2
1,5
COP R134a
COP R404a
COP R22
1
0,5
0
2000
2400
2800
3200
3600
4000
4400
4800
5200
5600
6000
6400
6800
7200
gas amount (gr)
Fig 6. COP increasing due to gas amount for three different gases
in 0,131433 kg/s water flow rate
4
7600
ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
8000
7000
Qh (watt)
6000
5000
4000
R134
3000
R404
2000
R22
1000
0
2000
3000
4000
5000
6000
7000
8000
gas amount (gr)
Fig 7. heating capacity increasing due to gas amount for three different gases
in 0,131433 kg/s water flow rate
It was presented that compressor worked in very
different condition for various refrigerants and charge
levels. input and discharge pressures and temperatures
was compared and it was revealed that R22 caused
higher temperature than others in the discharge line. On
the other hand R404a preduced most pressure between
gasses in the output of the compressor. Fig. 8 and 9 are
shown differences between input and output temperature
and pressure respect to the gas charge amount in
constant test condition. (ΔT and ΔP are differences
between compressor inlet and discharge temperatures
and pressures.) as shown in the fig. 8, R22 resulted more
temperature difference following by R404a and R134a.
in the other diagram R404a revealed more pressure
change inside Compressor compartment which is related
to the properties of refrigerant such as specific volume,
liquid density and vaporization latent heat.
1000
900
R134a
800
R404a
ΔP (kpa)
700
R22
600
500
400
300
200
100
0
2000
3000
4000
5000
6000
7000
gas amount (gr)
Fig 9. Pressure difference between compressor input and
discharge line for three gases with increasing charge amount
100
R134a
90
R404a
80
R22
ΔT °C
70
60
50
40
30
20
10
2000
3000
4000
5000
6000
7000
gas amount (gr)
Fig.8. Temperature difference between compressor input and
discharge line for three gases with increasing charge amount
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ULIBTK’15 20. Ulusal Isı Bilimi ve Tekniği Kongresi
02-5 Eylül 2015, BALIKESİR
Fig 10. Heat pump cycle in Enthalpy-Pressure diagram for three gases when charge quantity is 5400 gr
(water flow rate was constant equal to 0,131433 kg/s).
4. Conclusions
References
The amount of refrigerant gas in the heat pump unit is
very important
parameter
influencing system
performance. In this study the experiments were
conducted by varying refrigerant charge amount and
effect of the water flow rate and evaporator air
temperature on the system capacity. Undercharge or
overcharge of refrigerant decrease performance and
deteriorated system reliability. The COP quantity
improved significantly with the rise of refrigerant charge
up to optimal charge, but it slowly decreased as the
refrigerant charge increased beyond optimal charge. In
this study, every three gases have different COP in every
stage. Also R22 refrigerant has more heating capacity
than two others. Compressor in the heat pump unit
worked in different conditions due to several parameters,
the refrigerant charge and gas type is two important
parameters that cause to change in inlet and discharge
temperature and pressure.
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