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Measurement of refrigerant mass distribution within a R290 split air conditioner
Accepted Manuscript Measurement of Refrigerant mass distribution within a R290 Split Air Conditioner Tingxun Li, Jian Lu, Lei Chen, Dongcai He, Xiaozhou Qiu, Hongyao Li, Zhen Liu PII:
S0140-7007(15)00141-3
DOI:
10.1016/j.ijrefrig.2015.05.012
Reference:
JIJR 3049
To appear in:
International Journal of Refrigeration
Received Date: 5 March 2015 Revised Date:
2 May 2015
Accepted Date: 23 May 2015
Please cite this article as: Li, T., Lu, J., Chen, L., He, D., Qiu, X., Li, H., Liu, Z., Measurement of Refrigerant mass distribution within a R290 Split Air Conditioner, International Journal of Refrigeration (2015), doi: 10.1016/j.ijrefrig.2015.05.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Measurement of Refrigerant mass distribution within a R290 Split Air Conditioner Li Tingxun a,1, Lu Jian a, Chen Lei a, He Dongcai a, Qiu Xiaozhou a, Li Hongyao a, Liu Zhen b
b
Midea Group, Foshan 510725,China)
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Abstract:
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(aCollege of Engineering, Sun Yat-Sen University, Guangzhou510006,China;
R-290 (propane) has been chosen as one of the most potential next generation working
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fluids of RACs because of its favourable environmental and thermo-physical properties. However, its use is hindered by its flammability and resulting concerns on safety. In addition, the charge mass is limited strictly by the standards which would impact RAC’s heating performance. In this paper, refrigerant mass distributions within a R290 split type air
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conditioner were experimentally investigated at both static and dynamic state, in which the liquid nitrogen method (LNM) was used to determine the refrigerant mass inside the
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components of the circuit. The distribution of refrigerant that changes with temperatures and compressor speed were also measured and discussed. The results can assist with improving
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the design of the products (performance improvement, safety measures, etc.) and providing data for further theoretical study and simulation analyses.
Keywords: R290, Air conditioner, Refrigerant, Distribution
1
Corresponding author
E-mail address: [email protected] (Li. Tingxun) 1
ACCEPTED MANUSCRIPT
ODP
ozone depletion potential
GWP
global warming potential
LNM
liquid nitrogen method
OMM
on-line measurement method
IDUH
indoor unit heat exchanger
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Nomenclature
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ODUH outdoor unit heat exchanger
the mass of sampling cylinder before collecting (g)
W2
the mass of sampling cylinder after collecting (g)
W3
the mass of the sampling cylinder after collecting and Vacuuming (g)
W
the mass of the refrigerant in the sampling cylinder (g)
DB
dry-bulb temperature
WB
wet-bulb temperature
WT
the total mass of the refrigerant in each component of the system (g)
WC
the mass of refrigerant charge (g)
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EP
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W1
Greek symbols Ɛ
the deviation of the total refrigerant charge
2
ACCEPTED MANUSCRIPT 1. Introduction Hydrocarbon systems are commercially available in a number of low charge air conditioning applications, such as small split, window and portable air conditioners. When
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used to replace traditional RAC working fluid R22, R290 has performance characteristics that tend to yield higher energy efficiency and lower cooling and heating capacity. In terms of improvements in system COP in split type and window air conditioners with R290, values
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range from around 5% to 15%. For example, Padalkar et al. (2010) indicated up to 14%
found 10
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higher efficiency of R290 than R22. Wu et al (2012) tested a R290 window type RAC and 〜15% higher efficiency. The main difficulty for R290 is its high flammability,
which creates safety concerns in application, installation and field service. Standards limit the charge of R290; for example, IEC-60335-2-40 includes a formula to determine the maximum
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allowable charge in a specific application (Li, 2014). In order to extend the capacity range, charge reduction techniques can be applied, which reduces the refrigerant non-circled or useless for heat transferring. For instance, some refrigerant is dissolved in the oil and some is
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held in the accumulator. From this point of view, understanding precisely how refrigerant is
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distributed among all circuit components is useful for system optimisation and industrialisation of R290 products. Liquid nitrogen method (LNM) and on-line measurement method (OMM) are used to
determine refrigerant mass inside the components of the refrigeration system. With LNM, the refrigerant is drawn into a sampling cylinder with the low pressure caused by the low temperature of liquid nitrogen at atmospheric pressure; the refrigerant mass is the difference between the weight of the sampling cylinder with refrigerant and that without refrigerant.
3
ACCEPTED MANUSCRIPT LNM has a high accuracy, but is time-consuming and will consume substantial amounts liquid nitrogen. With OMM, the heat exchanger is weighed directly. It is convenient and not as time consuming, but the accuracy is lower.
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Tanakaet al., (1982) studied on the dynamic characteristics of a heat pump system through experiment; Belth et al. (1986, 1988) proposed a method of using the leverage to quickly measure the change of refrigerant mass in the refrigeration system
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during the start-up and shut-down process, obtained the transient refrigerant mass
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flow rate in each component of a heat pump system. Mulro and Didion (1985) measured refrigerant migration in a split-unit air conditioner. Ji Chang-fa and Liu Shun-buo (2002) tested the distribution of refrigerant in the system of inverter air conditioner under steady conditions. Guoliang Ding et al. (2009) presented a
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quasi-on-line measurement method for measuring refrigerant mass inside heat exchangers of an R410A inverter air conditioner under steady conditions. However, there are no published literatures about the characteristics of refrigerant distribution
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inside an R290 inverter air-conditioning system. The purpose of this paper is to use
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liquid nitrogen method (LNM) to measure refrigerant distribution inside an R290 inverter air condition system. In this paper, the experimental method is first described and then the results are
presented and discussed. In particular, the investigation considers distribution under different operating modes (heating, cooling and powered off), local temperature conditions and duration after start-up. 2. Experimental method 4
ACCEPTED MANUSCRIPT The experiment was carried out in an enthalpy-difference laboratory, in which the temperature and humidity can be well controlled, ensuring the accuracy of the test conditions. An R290 inverter air-conditioning system is chosen to do this experiment.
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The rated cooling capacity and heating capacity is 2.6 kW and 4.2 kW, respectively. As shown in Fig. 1, the air conditioner was reconstructed as follows. (1) Solenoid valves and stop valves were installed at the two sides of the evaporator, the condenser,
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the compressor and accumulator. The inner diameter of the valves was same as that of
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the pipes in order to minimise the pressure drop of the valves. (2) Check valves were installed in each pipe in order to prevent the reflux of refrigerant. Thermocouples were arranged along the heat exchangers, the compressor, the accumulator and the 4-way valve. Six sampling cylinders were used to collect the refrigerant of the
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components, the liquid pipe and the vapour pipe, respectively. The IDUH in the Fig.1 was indoor unit heat exchanger that worked as evaporator for cooling and condenser for heating. The ODUH was outdoor unit heat exchanger. The liquid lines were the
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pipes between of ODUH and IDUH, whiles the gas lines were the pipes from the
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IDUH to the accumulator and the ones from compressor to the condenser.
5
ACCEPTED MANUSCRIPT Fig. 1 Schematic diagram of the experimental apparatus.
A balance with 4.1 kg range and ±0.1 g precision was used to measure the weight of the sampling cylinder. The physical parameters of the system components are listed in Table. 1.
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Table 1Specifications of the test apparatus parameters Compressor Type
Rotary DC inverter compressor
Displacement
17.9 cc / rev
Free volume (cm3)
993.6
3
200 Heat exchangers Condenser
Type
Evaporator
Finned-tube 3
Volume (cm )
Finned-tube
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740
Tube material Tube length (mm) Tube outer diameter (mm) Tube inner diameter (mm) Tube Spacing (mm)
650
Copper
Copper
875
605
7
7
6.59
6.59
21
21
2
2
24
30
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Number of tube row Numbers of tubes
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Oil quantity (cm )
Accumulator
3
Volume (cm )
440
Pipes
Compressor to condenser
Evaporator to accumulator
5.5
1.2
5.8
5
9
9
107.9
76.3
368.8
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Length (m)
Liquid pipe
Diameter (mm) 3
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Volume (cm )
Remark: the volumes of the components were determined by calculation.
The schematic of LNM was shown as Fig. 2.The operation steps of LNM were
(1) Vacuum the sampling cylinder and weigh it as W1. (2) Connect the sampling cylinder to the sampling port, open the adjust valve 2 and evacuate the connecting pipe and then close the valve. (3) Start the air conditioner and keep running until reaching the test condition, then simultaneously shut off both the air conditioner and all solenoid valves. (4) Place the sampling cylinder into the liquid nitrogen tank and 6
ACCEPTED MANUSCRIPT open the valve 1 and valve 3, allowing the refrigerant to flow into the sampling cylinder from the section. (5) When nearly all refrigerant flow into the sampling cylinder (normally taking about 60 minutes), close the valve 1 and the valve 3. (6)
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Disconnect the sampling cylinder from the sampling port, defrost the surface of the sampling cylinder, and weigh it as W2. (7) Open the valve 1 on the sampling cylinder,
W3. The collected mass of refrigerant W is: 1
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W = W2 – W3.
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and exhaust the refrigerant slowly, then vacuum the sampling cylinder and weigh it as
It should be noted that the reason why the refrigerant mass W was calculated as Eq. (1) was that a small amount of oil in the compressor might be distributed among the refrigeration system, and very small amount of oil might flow into the sampling
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cylinder with the refrigerant, the quantity of the oil must therefore be subtracted.
Fig.2Scheme and photo of refrigerant sampling rig.
This paper experimentally investigated the refrigerant distribution inside the R290 inverter air conditioner at both static and dynamic states under cooling mode and heating mode. The distribution is affected by many factors such as flow rate of the refrigerant, temperature and running mode. The speed (frequency) of the compressor, 7
ACCEPTED MANUSCRIPT the refrigerant charge mass and the working condition temperatures were used to configure the test conditions as in Table 2. The tests No.1, 2, 3, 8, 9 and 10 were used to study the effect of condition temperatures on the refrigerant distribution where the
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opening of the electronic expansion valve was fixed. With tests No.1 and No.8, the electronic expansion valve setting was adjusted to achieve the best performance (COP).Tests No.1, 4, 5, 8 and 11 were intended to investigate the influence of charged
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refrigerant mass where the electronic expansion valve had been adjusted to optimise
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the system performance. The tests No.1, 6, 7, 8, 12 and 13 were used to research the distribution of the refrigerant affected by the compressor frequency. It should be noted that the tests No.14 and 15 were performed when the system was powered off under cooling or heating mode. For these tests the air conditioner was kept running to a
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stable operating condition and then stopped while the solenoid valves were kept open to let the refrigerant flow freely in the circuit, whilst the indoor and outdoor temperatures were kept constant. The solenoid valves were closed to isolate the
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sections after the circuit had been allowed to stagnate for 90 minutes. Table 2 Tests at steady conditions Outdoor Temperature
Refrigerant
Compressor
DB ( ) /WB ( )
DB ( ) /WB ( )
charge (g)
frequency(Hz)
Cooling
27/19
35/24
300
45
Cooling
27/19
27/24
300
45
Cooling
27/19
43/26
300
45
Cooling
27/19
35/24
245
45
5
Cooling
27/19
35/24
360
45
6
Cooling
27/19
35/24
300
23
7
Cooling
27/19
35/24
300
75
8
Heating
20/15
7/6
350
94
1 2 3 4
Mode
Indoor Temperature
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No.
9
Heating
20/15
2/1
350
94
10
Heating
20/15
-7/-8
350
94
11
Heating
20/15
7/6
270
94
8
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Heating
20/15
7/6
350
33
13
Heating
20/15
7/6
350
62
14
Power off
27/19
35/24
300
/
15
Power off
20/15
7/6
350
/
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3. Results and discussion The test results under steady conditions were summarized in Table 3. The deviation of the total refrigerant charge, Ɛ, can be estimated by Eq. (2).
× 100 %
(2)
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Ɛ=
Where WT is the total measured weight of the refrigerant in each component of the
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system, WC is refrigerant charge. The refrigerant was charged by a charge machine (GALILEO Fr igus K12) that the accuracy is ±0.5 gram. The accuracy of the balance is ±0.1 gram. Since the collected mass is sum of the five components, namely ±0.5 gram in total.
Therefore, the biggest uncertainty both of the charged and collected
is about 0.41 per cent.
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mass is 0.204 per cent. The uncertainty of the deviation is calculated as Eq.(3) and it
∆Ɛ
∆( )
+
∆
(3)
EP
Ɛ
=
The maximal deviation of the total refrigerant charge is 2.31%, which indicated that
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the liquid nitrogen method was accurate enough. It could be found that most of the tests had negative deviation. The reason for it was that there were still refrigerant left in the components. For test No 11, the deviation was positive for which the reason might be some oil flowed into the cylinder or the cylinder was not totally blow-dried and some water was left on the cylinder surface. Table 3 Refrigerant distribution results under steady conditions Refrigerant mass distribution (g)
Deviation
No. ODU
IDU
C
Liquid
A
9
Gas
Charged
Collected
(%)
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138.4
43.7
79.4
16
15.6
300
293.1
-2.30
2
134.7
51.5
73.6
27.7
9.2
300
296.7
-1.10
3
137.6
45.5
80.4
25.2
10.8
300
299.5
-0.17
4
122.1
26
63.1
24.5
7.2
244
242.9
-0.60
5
189.7
45.8
78.6
40
8.2
360
362.3
0.64
6
112.4
47
99.1
24.3
13.6
300
296.4
-1.20
7
140.8
36.6
73.6
31.6
17
300
299.6
-0.13
8
47.6
161.3
68.3
64.5
6.4
350
348.1
-0.54
9
73.5
140.4
66.7
60.2
7.2
350
348.0
-0.57
10
66.5
116
114.8
40.8
5.7
350
343.8
-1.77
11
59.4
103.1
64.8
36.9
6.1
270
270.6
12
81.4
115.4
105.2
33.5
10.5
350
346.0
-1.14
13
58.2
142.9
79
57.5
6.5
350
344.1
-1.69
14
21.5
197.6
64.7
4.6
7.9
300
296.3
-1.23
15
285
10.3
341.9
-2.31
34.6
2.9
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1
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lines
9.1
350
0.22
3.1 Influence of the ambient temperature
When the system was powered off, the refrigerant distribution was largely
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influenced by the external temperature conditions. For example, most of the refrigerant (about 66%) was located in the indoor unit heat exchanger when the indoor
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and outdoor temperature were 27°C and 35°C respectively. When the indoor and outdoor temperature were changed to 20°C and 7°C, respectively, the outdoor unit
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heat exchanger held most (82%) refrigerant. This variation is evidently dictated by the location of the lowest temperature, which results in the local state of the refrigerant being saturated and thus forming a liquid reservoir where refrigerant would condense at lower temperature. For heating mode, the refrigerant mass in the indoor heat exchanger (the evaporator that acts as a condenser for heating mode) was decreased as the outdoor temperature lowers (Fig.3),while more refrigerant accrued in the outdoor components 10
ACCEPTED MANUSCRIPT (compressor, condenser and liquid pipe). This observation is expected since refrigerant density is higher at lower temperature. In addition, more refrigerant was solved in the compressor oil as its temperature decreases. Conversely, under cooling
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mode the outdoor temperature had little effect on the distribution of the refrigerant (Fig.4). The most probable reason is (1) the state of the inlet of the compressor was almost same when the out temperature was changed from 27
to 35
;(2) the
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refrigerant density in the condenser decreased slightly (the density is 488kg m-3 for 45 and 438kg m-3 for 55
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) ;(3) since inlet of the compressor was almost same, the oil
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temperature changed slightly and the oil solubility was almost same.
Fig.3 Refrigerant distribution of heating mode at different outer door temperature (The tests for 7 were No.8 and N0.10 respectively)
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and -7
Fig.4 Refrigerant distribution of cooling mode at different outer door temperature (The tests for 27
11
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43
were No.2 and N0.3 respectively)
3.2 Influence of the compressor speed By increasing the compressor speed, the refrigerant mass under cooling mode
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increased in the condenser and decreased in the evaporator, compressor and accumulator (Fig.5). The reason was that the opening of electronic expansion valve was fixed, which was optimized for the test No.1 that the compressor’s frequency was
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45Hz.Theoretically, a larger expansion valve opening is needed for higher compressor
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speed in order to maintain the inlet superheat of the compressor and achieve the best system performance. Therefore, the expansion valve opening was too large for 23Hz and the throttling effect was poor. It resulted in lower vapour ratio at the outlet of the evaporator in that it was flooded with excess liquid, whilst more liquid flowed into the
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EP
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accumulator. The effect was the opposite for 75Hz.
Fig.5 Refrigerant distribution with different compressor speeds in cooling mode. (The tests for 23Hz, 45Hz and 75Hz were No.6, No.2 and No.7 respectively.)
12
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Fig.6 Refrigerant distribution with different compressor speeds in heating mode. (The tests for 33Hz, 62Hz and 94Hz were No.12, No.13 and No.8 respectively)
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Different company have different control logic to adjust the opening of the expansion valve, for example, the opening might be adjusted with the discharging temperature. Both the compressor speed and the expansion valve’s opening will determine the refrigerant mass flow of the circuit and then affect the refrigerant distribution. In order
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to investigate the compressor speed’s influence to refrigerant distribution individually, the expansion valve’s opening was fixed in this tests. In fact, there are lots of variable
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speed type RACs in the market use capillary tube but not expansion valve, which means that different compressor speeds have same expansion valve opening. For
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heating mode, the opening of the electronic expansion valve was optimized and fixed for maximum frequency (94Hz) in this work. This meant that the throttling was insufficient for other lower frequency (33Hz and 62Hz). Due to the same reasons as with the cooling mode, more refrigerant would accrue in the accumulator and condenser (the condenser in Fig.6 in fact was outdoor heat exchanger and worked as evaporator for heating mode). The liquid pipe held more refrigerant whilst gas pipe held less mass for faster compressor speed. The reason for this is that lower 13
ACCEPTED MANUSCRIPT compressor speed would result lower condensing pressure and less mass flow rate. The outlet of the IDUH might be not subcooled but two phases for lowest frequency
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and there would be vapour in the liquid lines.
3.3 Influence of the charge mass
From the data in Table 3, it can be concluded that the refrigerant in the heat
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exchangers accounts for about 55% to 60% of the total charge when in steady cooling
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or heating mode. By increasing the refrigerant charge, the refrigerant mass in the heat exchangers increased. If the system is over charged, the condenser (ODUH for cooling and IDUH for heating) will held more refrigerant (Fig.7 (b)).However, the ratio of the refrigerant in the heat exchangers (ODUH and IDUH together) changed
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little. The refrigerant in the ODUH and the IDUH were 50.0 ± 2.8% and 12.0 ± 2.9% of the whole charge at cooling mode (Fig.7 (a)) and 18.0 ± 4.3% and 42.0 ± 4.3% at
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heating mode respectively (Fig.8).
a Refrigerant mass ratio of components
14
b
Refrigerant mass of components
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Fig.7 Refrigerant distribution with different charge mass at cooling mode (The tests for 360g, 300g and
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245g were No.5, No.1 and No.4 respectively)
Fig.8 Refrigerant distribution with different charge mass at heating mode (The tests for 350g and 270g
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were No.8 and No.11)
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3.4 Refrigerant transition during start-up In order to investigate the refrigerant transition during start-up, several tests were
carried out, whereby the operation was terminated at different durations after start-up; thereafter the refrigerant mass was measured within each component. The tests conditions were listed in Table 4 (start-up cooling mode conditions is as test No. 14 and start-up heating mode is as test No.15 in Table 2). The test results are listed in Table 5. 15
ACCEPTED MANUSCRIPT Table 4 Tests of start-up Refrigerant charge (g)
Time after start-up (min)
1
Cooling
300
0
2
Cooling
300
0.5
3
Cooling
300
1
4
Cooling
300
2
5
Cooling
300
5
6
Cooling
300
7
Heating
350
8
Heating
350
9
Heating
350
10
Heating
350
11
Heating
350
12
Heating
350
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Mode
40 0
0.5 1
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2
5
40
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No.
Table 5 – Refrigerant distribution results under start-up Refrigerant mass distribution (g) NO
IDU
C
A
Pip A
Pip B
Total
deviation (%)
1
21.5
197.6
64.7
4.6
7.9
296.3
-1.23
2
124.4
12.6
128.6
20.3
6.9
292.8
-2.40
3
134.5
10.7
26.2
6.4
293.6
-2.13
4
132.5
10
119.1
20.4
6.2
288.2
-3.93
5
155.5
28.7
71.7
33.4
8.5
297.8
-0.73
6
138.4
43.7
79.4
16
15.6
293.1
-2.30
7
285
10.3
34.6
2.9
9.1
341.9
-2.31
8
74.9
59.9
188.8
14.2
8.4
346.2
-1.09
9
26.1
104.5
164.9
33.2
18.4
347.1
-0.83
10
20.4
113.5
170.2
36.5
6.8
347.4
-0.74
11
45.8
EP
.
ODU
Total
139.3
86.6
61.9
15
348.6
-0.40
79
57.5
6.5
344.1
-1.69
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58.2
115.8
142.9
The trend in the charge distribution within the circuit during start-up for cooling mode and heating mode is shown in Fig.9 and Fig.10, respectively. The point that time was zero (t = 0 minute) was for shutdown mode and the point (t = 40 minutes) represented stable operation condition. As shown in Fig.9, almost all of refrigerant was drawn out of
the
evaporator
and
rapidly
transferred 16
into
the
condenser
and
the
ACCEPTED MANUSCRIPT accumulator/compressor within the first half-minute. After two minutes, the refrigerant mass in the compressor and accumulator decreased, as the refrigerant separated from the compressor oil and further migrated into the condenser, evaporator
became stable (i.e., full of saturated liquid).
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and piping. The refrigerant in the liquid pipe increased gradually until the state
For heating mode, most of the refrigerant was initially located in the condenser.
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Similar to cooling mode, refrigerant rapidly flowed out of the condenser and into the
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accumulator/compressor and evaporator. After one minute, the refrigerant mass in the condenser and evaporator increased and reduced in the compressor/accumulator
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gradually towards a stable state (Fig.10).
Fig.9 Refrigerant transition during start-up at cooling mode
17
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Fig.10 Refrigerant transition during start-up at heating mode
4. Conclusions
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(1). LNM is an accurate method for refrigerant mass measurement and the deviation of this experiment ranges from 0.13% to 3.93%. LNM was suitable for the refrigerant mass distribution measurements within the circuit components. (2). The refrigerant in the heat exchangers was about 60% of the whole charge at steady conditions, whether in cooling or heating mode.
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(3). When the system was powered off, most of the refrigerant would accumulate in the heat exchanger that experienced the lower temperature. For cooling mode, the working temperature had little effect on the distribution of the refrigerant. For
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heating mode, the refrigerant would move from the indoor unit into outdoor units as the ambient temperature decreases.
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(4). Increasing the compressor speed (frequency), the refrigerant mass in the condenser increases and that in the evaporator and the compressor/accumulator decreases under cooling mode. On the contrary, the refrigerant mass in the evaporator decreases for heating mode with the compressor speed.
(5). With the increase of the refrigerant charge, the refrigerant mass in the heat exchangers increases, but the distribution ratio of the refrigerant in the heat exchangers changes little. (6). During start-up, the refrigerant flowed out from the heat exchanger that initially had lower temperature into the compressor/accumulator and the heat exchanger that initially had higher temperature rapidly within first half minute. After two 18
ACCEPTED MANUSCRIPT minutes, the refrigerant in the heat exchangers increased gradually to stable condition while the refrigerant in the compressor and accumulator reduced.
Acknowledgement
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This project was supported the HCFC phase out management plane in room air conditioning sector technical assistance fund (China), FOSHAN Major Biding Research Program for
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Domestic and Abroad 2013AH100023 and Midea Group.
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Ding, G.L., Ma, X.K., Zhang, P., Han, W.Z., Shinichi K., Takahiro Y., 2009. Practical methods for measuring refrigerant mass distribution inside refrigeration system. Int. J. Refrigeration. 32, 327-334.
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pump. Int. J. of Refrigeration. 11, 298–304 Belth, M.I., Tree, D.R., 1986. Design and preliminary analysis for measuring transient mass rate of flow in unitary heat pumps. ASHRAE Transactions. 92(1B), 843-853.
Janssen M.J., 1989. Cycling losses in cooling circuits, MSc Thesis, Eindhoven University of Technology.
Mulroy, W.J., Didion, D.A., 1985. Refrigerant migration in a split unitary conditioner. ASHRAE Transactions. 91, 193–206. Tanaka, N., Ikeuchi, M., Yamanaka, G., 1982. Experimental study on the dynamic characteristics of a heat pump. ASHRAE Transactions. 88, 323–331 Padalkar, A., Mali, K., Rajadhyaksha, D., Wadia, B., Devotta, S., 2010. Performance assessment of air 19
ACCEPTED MANUSCRIPT conditioners with HC-290. 9th IIR-Gustav Lorentzen Conference on Natural Working Fluids. 671-677. Li, T.X., 2014. Indoor leakage test for safety of R-290 split type room air conditioner, Int. J.
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Refrigeration. 40 , 380–389.
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Research Highlights
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1. LNM is first used to measure refrigerant distribution in a R290 air conditioner 2. The influence of compressor speed, refrigerant mass and temperature is measured.
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3. The refrigerant distribution transient behavior is investigated
S0140-7007(15)00141-3
DOI:
10.1016/j.ijrefrig.2015.05.012
Reference:
JIJR 3049
To appear in:
International Journal of Refrigeration
Received Date: 5 March 2015 Revised Date:
2 May 2015
Accepted Date: 23 May 2015
Please cite this article as: Li, T., Lu, J., Chen, L., He, D., Qiu, X., Li, H., Liu, Z., Measurement of Refrigerant mass distribution within a R290 Split Air Conditioner, International Journal of Refrigeration (2015), doi: 10.1016/j.ijrefrig.2015.05.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Measurement of Refrigerant mass distribution within a R290 Split Air Conditioner Li Tingxun a,1, Lu Jian a, Chen Lei a, He Dongcai a, Qiu Xiaozhou a, Li Hongyao a, Liu Zhen b
b
Midea Group, Foshan 510725,China)
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Abstract:
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(aCollege of Engineering, Sun Yat-Sen University, Guangzhou510006,China;
R-290 (propane) has been chosen as one of the most potential next generation working
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fluids of RACs because of its favourable environmental and thermo-physical properties. However, its use is hindered by its flammability and resulting concerns on safety. In addition, the charge mass is limited strictly by the standards which would impact RAC’s heating performance. In this paper, refrigerant mass distributions within a R290 split type air
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conditioner were experimentally investigated at both static and dynamic state, in which the liquid nitrogen method (LNM) was used to determine the refrigerant mass inside the
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components of the circuit. The distribution of refrigerant that changes with temperatures and compressor speed were also measured and discussed. The results can assist with improving
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the design of the products (performance improvement, safety measures, etc.) and providing data for further theoretical study and simulation analyses.
Keywords: R290, Air conditioner, Refrigerant, Distribution
1
Corresponding author
E-mail address: [email protected] (Li. Tingxun) 1
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ODP
ozone depletion potential
GWP
global warming potential
LNM
liquid nitrogen method
OMM
on-line measurement method
IDUH
indoor unit heat exchanger
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Nomenclature
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ODUH outdoor unit heat exchanger
the mass of sampling cylinder before collecting (g)
W2
the mass of sampling cylinder after collecting (g)
W3
the mass of the sampling cylinder after collecting and Vacuuming (g)
W
the mass of the refrigerant in the sampling cylinder (g)
DB
dry-bulb temperature
WB
wet-bulb temperature
WT
the total mass of the refrigerant in each component of the system (g)
WC
the mass of refrigerant charge (g)
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W1
Greek symbols Ɛ
the deviation of the total refrigerant charge
2
ACCEPTED MANUSCRIPT 1. Introduction Hydrocarbon systems are commercially available in a number of low charge air conditioning applications, such as small split, window and portable air conditioners. When
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used to replace traditional RAC working fluid R22, R290 has performance characteristics that tend to yield higher energy efficiency and lower cooling and heating capacity. In terms of improvements in system COP in split type and window air conditioners with R290, values
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range from around 5% to 15%. For example, Padalkar et al. (2010) indicated up to 14%
found 10
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higher efficiency of R290 than R22. Wu et al (2012) tested a R290 window type RAC and 〜15% higher efficiency. The main difficulty for R290 is its high flammability,
which creates safety concerns in application, installation and field service. Standards limit the charge of R290; for example, IEC-60335-2-40 includes a formula to determine the maximum
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allowable charge in a specific application (Li, 2014). In order to extend the capacity range, charge reduction techniques can be applied, which reduces the refrigerant non-circled or useless for heat transferring. For instance, some refrigerant is dissolved in the oil and some is
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held in the accumulator. From this point of view, understanding precisely how refrigerant is
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distributed among all circuit components is useful for system optimisation and industrialisation of R290 products. Liquid nitrogen method (LNM) and on-line measurement method (OMM) are used to
determine refrigerant mass inside the components of the refrigeration system. With LNM, the refrigerant is drawn into a sampling cylinder with the low pressure caused by the low temperature of liquid nitrogen at atmospheric pressure; the refrigerant mass is the difference between the weight of the sampling cylinder with refrigerant and that without refrigerant.
3
ACCEPTED MANUSCRIPT LNM has a high accuracy, but is time-consuming and will consume substantial amounts liquid nitrogen. With OMM, the heat exchanger is weighed directly. It is convenient and not as time consuming, but the accuracy is lower.
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Tanakaet al., (1982) studied on the dynamic characteristics of a heat pump system through experiment; Belth et al. (1986, 1988) proposed a method of using the leverage to quickly measure the change of refrigerant mass in the refrigeration system
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during the start-up and shut-down process, obtained the transient refrigerant mass
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flow rate in each component of a heat pump system. Mulro and Didion (1985) measured refrigerant migration in a split-unit air conditioner. Ji Chang-fa and Liu Shun-buo (2002) tested the distribution of refrigerant in the system of inverter air conditioner under steady conditions. Guoliang Ding et al. (2009) presented a
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quasi-on-line measurement method for measuring refrigerant mass inside heat exchangers of an R410A inverter air conditioner under steady conditions. However, there are no published literatures about the characteristics of refrigerant distribution
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inside an R290 inverter air-conditioning system. The purpose of this paper is to use
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liquid nitrogen method (LNM) to measure refrigerant distribution inside an R290 inverter air condition system. In this paper, the experimental method is first described and then the results are
presented and discussed. In particular, the investigation considers distribution under different operating modes (heating, cooling and powered off), local temperature conditions and duration after start-up. 2. Experimental method 4
ACCEPTED MANUSCRIPT The experiment was carried out in an enthalpy-difference laboratory, in which the temperature and humidity can be well controlled, ensuring the accuracy of the test conditions. An R290 inverter air-conditioning system is chosen to do this experiment.
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The rated cooling capacity and heating capacity is 2.6 kW and 4.2 kW, respectively. As shown in Fig. 1, the air conditioner was reconstructed as follows. (1) Solenoid valves and stop valves were installed at the two sides of the evaporator, the condenser,
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the compressor and accumulator. The inner diameter of the valves was same as that of
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the pipes in order to minimise the pressure drop of the valves. (2) Check valves were installed in each pipe in order to prevent the reflux of refrigerant. Thermocouples were arranged along the heat exchangers, the compressor, the accumulator and the 4-way valve. Six sampling cylinders were used to collect the refrigerant of the
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components, the liquid pipe and the vapour pipe, respectively. The IDUH in the Fig.1 was indoor unit heat exchanger that worked as evaporator for cooling and condenser for heating. The ODUH was outdoor unit heat exchanger. The liquid lines were the
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pipes between of ODUH and IDUH, whiles the gas lines were the pipes from the
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IDUH to the accumulator and the ones from compressor to the condenser.
5
ACCEPTED MANUSCRIPT Fig. 1 Schematic diagram of the experimental apparatus.
A balance with 4.1 kg range and ±0.1 g precision was used to measure the weight of the sampling cylinder. The physical parameters of the system components are listed in Table. 1.
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Table 1Specifications of the test apparatus parameters Compressor Type
Rotary DC inverter compressor
Displacement
17.9 cc / rev
Free volume (cm3)
993.6
3
200 Heat exchangers Condenser
Type
Evaporator
Finned-tube 3
Volume (cm )
Finned-tube
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740
Tube material Tube length (mm) Tube outer diameter (mm) Tube inner diameter (mm) Tube Spacing (mm)
650
Copper
Copper
875
605
7
7
6.59
6.59
21
21
2
2
24
30
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Number of tube row Numbers of tubes
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Oil quantity (cm )
Accumulator
3
Volume (cm )
440
Pipes
Compressor to condenser
Evaporator to accumulator
5.5
1.2
5.8
5
9
9
107.9
76.3
368.8
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Length (m)
Liquid pipe
Diameter (mm) 3
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Volume (cm )
Remark: the volumes of the components were determined by calculation.
The schematic of LNM was shown as Fig. 2.The operation steps of LNM were
(1) Vacuum the sampling cylinder and weigh it as W1. (2) Connect the sampling cylinder to the sampling port, open the adjust valve 2 and evacuate the connecting pipe and then close the valve. (3) Start the air conditioner and keep running until reaching the test condition, then simultaneously shut off both the air conditioner and all solenoid valves. (4) Place the sampling cylinder into the liquid nitrogen tank and 6
ACCEPTED MANUSCRIPT open the valve 1 and valve 3, allowing the refrigerant to flow into the sampling cylinder from the section. (5) When nearly all refrigerant flow into the sampling cylinder (normally taking about 60 minutes), close the valve 1 and the valve 3. (6)
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Disconnect the sampling cylinder from the sampling port, defrost the surface of the sampling cylinder, and weigh it as W2. (7) Open the valve 1 on the sampling cylinder,
W3. The collected mass of refrigerant W is: 1
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W = W2 – W3.
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and exhaust the refrigerant slowly, then vacuum the sampling cylinder and weigh it as
It should be noted that the reason why the refrigerant mass W was calculated as Eq. (1) was that a small amount of oil in the compressor might be distributed among the refrigeration system, and very small amount of oil might flow into the sampling
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cylinder with the refrigerant, the quantity of the oil must therefore be subtracted.
Fig.2Scheme and photo of refrigerant sampling rig.
This paper experimentally investigated the refrigerant distribution inside the R290 inverter air conditioner at both static and dynamic states under cooling mode and heating mode. The distribution is affected by many factors such as flow rate of the refrigerant, temperature and running mode. The speed (frequency) of the compressor, 7
ACCEPTED MANUSCRIPT the refrigerant charge mass and the working condition temperatures were used to configure the test conditions as in Table 2. The tests No.1, 2, 3, 8, 9 and 10 were used to study the effect of condition temperatures on the refrigerant distribution where the
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opening of the electronic expansion valve was fixed. With tests No.1 and No.8, the electronic expansion valve setting was adjusted to achieve the best performance (COP).Tests No.1, 4, 5, 8 and 11 were intended to investigate the influence of charged
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refrigerant mass where the electronic expansion valve had been adjusted to optimise
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the system performance. The tests No.1, 6, 7, 8, 12 and 13 were used to research the distribution of the refrigerant affected by the compressor frequency. It should be noted that the tests No.14 and 15 were performed when the system was powered off under cooling or heating mode. For these tests the air conditioner was kept running to a
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stable operating condition and then stopped while the solenoid valves were kept open to let the refrigerant flow freely in the circuit, whilst the indoor and outdoor temperatures were kept constant. The solenoid valves were closed to isolate the
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sections after the circuit had been allowed to stagnate for 90 minutes. Table 2 Tests at steady conditions Outdoor Temperature
Refrigerant
Compressor
DB ( ) /WB ( )
DB ( ) /WB ( )
charge (g)
frequency(Hz)
Cooling
27/19
35/24
300
45
Cooling
27/19
27/24
300
45
Cooling
27/19
43/26
300
45
Cooling
27/19
35/24
245
45
5
Cooling
27/19
35/24
360
45
6
Cooling
27/19
35/24
300
23
7
Cooling
27/19
35/24
300
75
8
Heating
20/15
7/6
350
94
1 2 3 4
Mode
Indoor Temperature
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No.
9
Heating
20/15
2/1
350
94
10
Heating
20/15
-7/-8
350
94
11
Heating
20/15
7/6
270
94
8
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Heating
20/15
7/6
350
33
13
Heating
20/15
7/6
350
62
14
Power off
27/19
35/24
300
/
15
Power off
20/15
7/6
350
/
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3. Results and discussion The test results under steady conditions were summarized in Table 3. The deviation of the total refrigerant charge, Ɛ, can be estimated by Eq. (2).
× 100 %
(2)
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Ɛ=
Where WT is the total measured weight of the refrigerant in each component of the
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system, WC is refrigerant charge. The refrigerant was charged by a charge machine (GALILEO Fr igus K12) that the accuracy is ±0.5 gram. The accuracy of the balance is ±0.1 gram. Since the collected mass is sum of the five components, namely ±0.5 gram in total.
Therefore, the biggest uncertainty both of the charged and collected
is about 0.41 per cent.
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mass is 0.204 per cent. The uncertainty of the deviation is calculated as Eq.(3) and it
∆Ɛ
∆( )
+
∆
(3)
EP
Ɛ
=
The maximal deviation of the total refrigerant charge is 2.31%, which indicated that
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the liquid nitrogen method was accurate enough. It could be found that most of the tests had negative deviation. The reason for it was that there were still refrigerant left in the components. For test No 11, the deviation was positive for which the reason might be some oil flowed into the cylinder or the cylinder was not totally blow-dried and some water was left on the cylinder surface. Table 3 Refrigerant distribution results under steady conditions Refrigerant mass distribution (g)
Deviation
No. ODU
IDU
C
Liquid
A
9
Gas
Charged
Collected
(%)
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138.4
43.7
79.4
16
15.6
300
293.1
-2.30
2
134.7
51.5
73.6
27.7
9.2
300
296.7
-1.10
3
137.6
45.5
80.4
25.2
10.8
300
299.5
-0.17
4
122.1
26
63.1
24.5
7.2
244
242.9
-0.60
5
189.7
45.8
78.6
40
8.2
360
362.3
0.64
6
112.4
47
99.1
24.3
13.6
300
296.4
-1.20
7
140.8
36.6
73.6
31.6
17
300
299.6
-0.13
8
47.6
161.3
68.3
64.5
6.4
350
348.1
-0.54
9
73.5
140.4
66.7
60.2
7.2
350
348.0
-0.57
10
66.5
116
114.8
40.8
5.7
350
343.8
-1.77
11
59.4
103.1
64.8
36.9
6.1
270
270.6
12
81.4
115.4
105.2
33.5
10.5
350
346.0
-1.14
13
58.2
142.9
79
57.5
6.5
350
344.1
-1.69
14
21.5
197.6
64.7
4.6
7.9
300
296.3
-1.23
15
285
10.3
341.9
-2.31
34.6
2.9
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1
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lines
9.1
350
0.22
3.1 Influence of the ambient temperature
When the system was powered off, the refrigerant distribution was largely
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influenced by the external temperature conditions. For example, most of the refrigerant (about 66%) was located in the indoor unit heat exchanger when the indoor
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and outdoor temperature were 27°C and 35°C respectively. When the indoor and outdoor temperature were changed to 20°C and 7°C, respectively, the outdoor unit
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heat exchanger held most (82%) refrigerant. This variation is evidently dictated by the location of the lowest temperature, which results in the local state of the refrigerant being saturated and thus forming a liquid reservoir where refrigerant would condense at lower temperature. For heating mode, the refrigerant mass in the indoor heat exchanger (the evaporator that acts as a condenser for heating mode) was decreased as the outdoor temperature lowers (Fig.3),while more refrigerant accrued in the outdoor components 10
ACCEPTED MANUSCRIPT (compressor, condenser and liquid pipe). This observation is expected since refrigerant density is higher at lower temperature. In addition, more refrigerant was solved in the compressor oil as its temperature decreases. Conversely, under cooling
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mode the outdoor temperature had little effect on the distribution of the refrigerant (Fig.4). The most probable reason is (1) the state of the inlet of the compressor was almost same when the out temperature was changed from 27
to 35
;(2) the
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refrigerant density in the condenser decreased slightly (the density is 488kg m-3 for 45 and 438kg m-3 for 55
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) ;(3) since inlet of the compressor was almost same, the oil
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temperature changed slightly and the oil solubility was almost same.
Fig.3 Refrigerant distribution of heating mode at different outer door temperature (The tests for 7 were No.8 and N0.10 respectively)
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and -7
Fig.4 Refrigerant distribution of cooling mode at different outer door temperature (The tests for 27
11
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43
were No.2 and N0.3 respectively)
3.2 Influence of the compressor speed By increasing the compressor speed, the refrigerant mass under cooling mode
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increased in the condenser and decreased in the evaporator, compressor and accumulator (Fig.5). The reason was that the opening of electronic expansion valve was fixed, which was optimized for the test No.1 that the compressor’s frequency was
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45Hz.Theoretically, a larger expansion valve opening is needed for higher compressor
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speed in order to maintain the inlet superheat of the compressor and achieve the best system performance. Therefore, the expansion valve opening was too large for 23Hz and the throttling effect was poor. It resulted in lower vapour ratio at the outlet of the evaporator in that it was flooded with excess liquid, whilst more liquid flowed into the
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accumulator. The effect was the opposite for 75Hz.
Fig.5 Refrigerant distribution with different compressor speeds in cooling mode. (The tests for 23Hz, 45Hz and 75Hz were No.6, No.2 and No.7 respectively.)
12
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Fig.6 Refrigerant distribution with different compressor speeds in heating mode. (The tests for 33Hz, 62Hz and 94Hz were No.12, No.13 and No.8 respectively)
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Different company have different control logic to adjust the opening of the expansion valve, for example, the opening might be adjusted with the discharging temperature. Both the compressor speed and the expansion valve’s opening will determine the refrigerant mass flow of the circuit and then affect the refrigerant distribution. In order
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to investigate the compressor speed’s influence to refrigerant distribution individually, the expansion valve’s opening was fixed in this tests. In fact, there are lots of variable
EP
speed type RACs in the market use capillary tube but not expansion valve, which means that different compressor speeds have same expansion valve opening. For
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heating mode, the opening of the electronic expansion valve was optimized and fixed for maximum frequency (94Hz) in this work. This meant that the throttling was insufficient for other lower frequency (33Hz and 62Hz). Due to the same reasons as with the cooling mode, more refrigerant would accrue in the accumulator and condenser (the condenser in Fig.6 in fact was outdoor heat exchanger and worked as evaporator for heating mode). The liquid pipe held more refrigerant whilst gas pipe held less mass for faster compressor speed. The reason for this is that lower 13
ACCEPTED MANUSCRIPT compressor speed would result lower condensing pressure and less mass flow rate. The outlet of the IDUH might be not subcooled but two phases for lowest frequency
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and there would be vapour in the liquid lines.
3.3 Influence of the charge mass
From the data in Table 3, it can be concluded that the refrigerant in the heat
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exchangers accounts for about 55% to 60% of the total charge when in steady cooling
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or heating mode. By increasing the refrigerant charge, the refrigerant mass in the heat exchangers increased. If the system is over charged, the condenser (ODUH for cooling and IDUH for heating) will held more refrigerant (Fig.7 (b)).However, the ratio of the refrigerant in the heat exchangers (ODUH and IDUH together) changed
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little. The refrigerant in the ODUH and the IDUH were 50.0 ± 2.8% and 12.0 ± 2.9% of the whole charge at cooling mode (Fig.7 (a)) and 18.0 ± 4.3% and 42.0 ± 4.3% at
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heating mode respectively (Fig.8).
a Refrigerant mass ratio of components
14
b
Refrigerant mass of components
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Fig.7 Refrigerant distribution with different charge mass at cooling mode (The tests for 360g, 300g and
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245g were No.5, No.1 and No.4 respectively)
Fig.8 Refrigerant distribution with different charge mass at heating mode (The tests for 350g and 270g
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were No.8 and No.11)
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3.4 Refrigerant transition during start-up In order to investigate the refrigerant transition during start-up, several tests were
carried out, whereby the operation was terminated at different durations after start-up; thereafter the refrigerant mass was measured within each component. The tests conditions were listed in Table 4 (start-up cooling mode conditions is as test No. 14 and start-up heating mode is as test No.15 in Table 2). The test results are listed in Table 5. 15
ACCEPTED MANUSCRIPT Table 4 Tests of start-up Refrigerant charge (g)
Time after start-up (min)
1
Cooling
300
0
2
Cooling
300
0.5
3
Cooling
300
1
4
Cooling
300
2
5
Cooling
300
5
6
Cooling
300
7
Heating
350
8
Heating
350
9
Heating
350
10
Heating
350
11
Heating
350
12
Heating
350
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Mode
40 0
0.5 1
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2
5
40
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No.
Table 5 – Refrigerant distribution results under start-up Refrigerant mass distribution (g) NO
IDU
C
A
Pip A
Pip B
Total
deviation (%)
1
21.5
197.6
64.7
4.6
7.9
296.3
-1.23
2
124.4
12.6
128.6
20.3
6.9
292.8
-2.40
3
134.5
10.7
26.2
6.4
293.6
-2.13
4
132.5
10
119.1
20.4
6.2
288.2
-3.93
5
155.5
28.7
71.7
33.4
8.5
297.8
-0.73
6
138.4
43.7
79.4
16
15.6
293.1
-2.30
7
285
10.3
34.6
2.9
9.1
341.9
-2.31
8
74.9
59.9
188.8
14.2
8.4
346.2
-1.09
9
26.1
104.5
164.9
33.2
18.4
347.1
-0.83
10
20.4
113.5
170.2
36.5
6.8
347.4
-0.74
11
45.8
EP
.
ODU
Total
139.3
86.6
61.9
15
348.6
-0.40
79
57.5
6.5
344.1
-1.69
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58.2
115.8
142.9
The trend in the charge distribution within the circuit during start-up for cooling mode and heating mode is shown in Fig.9 and Fig.10, respectively. The point that time was zero (t = 0 minute) was for shutdown mode and the point (t = 40 minutes) represented stable operation condition. As shown in Fig.9, almost all of refrigerant was drawn out of
the
evaporator
and
rapidly
transferred 16
into
the
condenser
and
the
ACCEPTED MANUSCRIPT accumulator/compressor within the first half-minute. After two minutes, the refrigerant mass in the compressor and accumulator decreased, as the refrigerant separated from the compressor oil and further migrated into the condenser, evaporator
became stable (i.e., full of saturated liquid).
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and piping. The refrigerant in the liquid pipe increased gradually until the state
For heating mode, most of the refrigerant was initially located in the condenser.
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Similar to cooling mode, refrigerant rapidly flowed out of the condenser and into the
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accumulator/compressor and evaporator. After one minute, the refrigerant mass in the condenser and evaporator increased and reduced in the compressor/accumulator
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gradually towards a stable state (Fig.10).
Fig.9 Refrigerant transition during start-up at cooling mode
17
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Fig.10 Refrigerant transition during start-up at heating mode
4. Conclusions
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(1). LNM is an accurate method for refrigerant mass measurement and the deviation of this experiment ranges from 0.13% to 3.93%. LNM was suitable for the refrigerant mass distribution measurements within the circuit components. (2). The refrigerant in the heat exchangers was about 60% of the whole charge at steady conditions, whether in cooling or heating mode.
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(3). When the system was powered off, most of the refrigerant would accumulate in the heat exchanger that experienced the lower temperature. For cooling mode, the working temperature had little effect on the distribution of the refrigerant. For
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heating mode, the refrigerant would move from the indoor unit into outdoor units as the ambient temperature decreases.
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(4). Increasing the compressor speed (frequency), the refrigerant mass in the condenser increases and that in the evaporator and the compressor/accumulator decreases under cooling mode. On the contrary, the refrigerant mass in the evaporator decreases for heating mode with the compressor speed.
(5). With the increase of the refrigerant charge, the refrigerant mass in the heat exchangers increases, but the distribution ratio of the refrigerant in the heat exchangers changes little. (6). During start-up, the refrigerant flowed out from the heat exchanger that initially had lower temperature into the compressor/accumulator and the heat exchanger that initially had higher temperature rapidly within first half minute. After two 18
ACCEPTED MANUSCRIPT minutes, the refrigerant in the heat exchangers increased gradually to stable condition while the refrigerant in the compressor and accumulator reduced.
Acknowledgement
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This project was supported the HCFC phase out management plane in room air conditioning sector technical assistance fund (China), FOSHAN Major Biding Research Program for
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Domestic and Abroad 2013AH100023 and Midea Group.
References
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Ding, G.L., Ma, X.K., Zhang, P., Han, W.Z., Shinichi K., Takahiro Y., 2009. Practical methods for measuring refrigerant mass distribution inside refrigeration system. Int. J. Refrigeration. 32, 327-334.
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ACCEPTED MANUSCRIPT conditioners with HC-290. 9th IIR-Gustav Lorentzen Conference on Natural Working Fluids. 671-677. Li, T.X., 2014. Indoor leakage test for safety of R-290 split type room air conditioner, Int. J.
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Research Highlights
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1. LNM is first used to measure refrigerant distribution in a R290 air conditioner 2. The influence of compressor speed, refrigerant mass and temperature is measured.
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3. The refrigerant distribution transient behavior is investigated