Experimental Investigation; optimum charge R290 for

Split Unit Air Conditioning

The use of Hydrocarbon (R290) as an drop in for split type air conditioning is widely proposed by the local supplier with reason of Malaysian commitment to Montreal and Kyoto Protocol. There are many experimental investigation in the past showed that there is a drop of total charge (40% to 60%) and running amp by 50% due to its low density of refrigerant compares to R22 (1.013 bar at boiling point) : 4.706 kg/m3 for gas, (1.013 bar at boiling point) : 1413 kg/m3 for liquid and R410a (3.0 kg/m³ for gas, 1040 kg/ m³ for liquid). To define the optimum charge for the unit, several test were carried out under control environment and actual ambient condition. The result showed that there is significant drop of total charge and running amp.

Abstract

In Malaysia almost 90% of air conditioning system still using R22 as refrigerant, and 100% still using R22 for split air conditioning system.

Early 2009 the air conditioning manufacturer start to promote R410a as replacement but with extra cost for installation due to its high working pressure. This also due to Government decision to stop the use of R22 for all new system start Jan 2010.

When the concern of ODP and global warming increases the independent supplier for the refrigerant start proposing Hydrocarbon as an alternative. WHY R290 ?

Reported that 80 g of LPG showed that the best performance compared to that R12. Akash and said.

Jung et al experimented with R290/R600 (in ratio of 60:40, by mass fraction) as an alternative to R12 for domestic refrigerators and reported that COP and energy efficiency improves by 2.3 and 4%

Introduction

R290 is pure propane, a hydrocarbon and efficient naturally occurring refrigerant with similar properties to R22.

No ozone depletion potential, ODP = 0 Low Global Warming Potential, GWP = 3 Environmentally safe but highly flammable. In the case of leakage, the full hydrocarbon

quantity does not exceed the lower flammable limit during normal working condition. M.Mohanraj et al.

Item R22 R290 R134a R404A R600a

Pressure O 0 + - +

Pressure ratio low back pressure (LBP) O + - O -

Discharge temperature - + + + +

Volumetric capacity + + - + -

Capacity loss O O O - O

COP O O O - +

Table below provides a summary of the thermodynamics of R290 as compared to R22, R134a, R404A, and R600a under the chosen conditions.

Legend: 0 = acceptable; + = good; - =

problematic.

Summing up the different thermodynamic aspects, R290 could be used as replacement for R22 in many commercial refrigerated MBP and LBP applications. R290 is the only candidate, which comes close to R22, in some aspects even outperforming it. The lower pressure ratio and lower discharge temperature even allow for use in certain applications where R22 is problematic. Heinz Jurgensen, Danfoss Compressor GmbH

R22 R 290

Boiling point = - 40.7 ⁰C

Density = 3.66 kg/m³ at 15⁰C, gas

ODP = 0.055 GWP = 1810

Boiling point = -42.09 ⁰C

Density = 1.83 kg/m³ gas, 583 kg/m³ liquid.

ODP = 0 GWP = 3

R410A

Binary Blend of hydroflourocarbon or HFC compounds, 50% of R32 and 50% of R125

Boiling Point = -48.5 ⁰C Density = 3.0 kg/m³ gas,

1040 kg/m³ liquid No chlorine content, no

ozone depletion potential, ODP = 0

GWP = 1725

The review and experiments has showed that R290 is the good alternative which come close to R22 in some aspect. The increasing use of flammable refrigerant such as isobutene R600a in house appliances also can be an indication of it is safe to use hydrocarbon as a direct replacement for split air conditioning system, but the total amount of charge will be very critical. Some manufacture only limit the charge up to 150g and service technician must be trained in safe handling procedure.

The schematic diagram of split air conditioning unit experimental setup with the total capacity of 10000 btu is as shown in Fig 1. Its consist of indoor unit installed in control ambient room with artificial sensible load varies from 1000 watt to 5000 watt. The air cooled condensing unit is installed in open ambient condition. The system using capillary tube to control the amount refrigerant to match the system capacity.

Experimental Setup

Indoor Unit

Air Cooled Condensing Unit

Control Environment room

Fig 1

To measure the parameters related to the experiment, 12 temperature point (type K temperature sensor), low pressure and high pressure gauge are fix on the system.

All measured data will be plotted on the PH chart using cool pack.

Refer Fig 2

Fig 2

During the experiment, the temperature inside the room was maintained at 24⁰C to 26⁰C, which was monitored by digital thermometer with an accuracy ± 0.5 K

A 20 numbers of 100 watt each bulb was connected to power supply in order to maintain the room temperature and also as an artificial load for the system.

Initially, the system was flushed with nitrogen to eliminate impurities, moisture and other foreign materials inside the system, which may effect the accuracy of the experimental result.

Next the system was evacuated until its reach 1000 micron and break the vacuum using nitrogen.

And then evacuated the system again until its reach 500 micron and break the vacuum with nitrogen.

The system is evacuated for the 3rd time until its reach 250 micron to ensure that the system is leakage free and no moisture inside.

Experimental Procedure

The system is charged with R290 start with 200 g, 240 g, 260 g, 280 g, 300 g, 320 g, and 340 g.

At the same time 20 numbers of 100 watt bulb is on to create the load.

On every charging process , 30 minutes time frame is allowable for the system to stabilize and all reading is recorded.

In order to reduce the experimental uncertainties, experiments is repeated for 3 times and average value were considered.

Experimental Procedure

Result and discussionExperimental data obtained from

the different charge amount are as follow.

200 220 240 260 280 300 320 3407.700

7.800

7.900

8.000

8.100

8.200

8.300

8.400

COP vs CHARGE

Result and Discussion

48.53 49.36 48.73 45.40 41.86 39.60 39.23 39.307.700

7.800

7.900

8.000

8.100

8.200

8.300

8.400

COP vs DISCHARGE

Result and Discussion

Base on the chart COP vs. Charge and chart COP vs. Discharge plotted; found that the trend of COP increasing when the charge is added until it reach the maximum point and then gradually going down. The maximum point on chart is the optimum point where; the total charge by mass is optimum.

Result and Discussion

7.93 8.01 8.3 8.27 8.26 8.24 8.24 8.240

2

4

6

8

10

12

SH VS COP

Result and Discussion

From the chart plotted; superheat vs. COP the optimum charge at 240g and its give superheat = 8.3 ⁰C

If we take Superheat as checking criteria; the normal value for superheat for an air conditioning application is somewhere 5⁰C to 10⁰C, Air conditioning Installation Manual by Kotza.

Result and Discussion

For further discussion, even the optimum charge is found from the experiments, the evaporating temperature found to be very high 14.6⁰C,

For air conditioning application the temperature for evaporation is 5⁰C and condensing temperature is 45⁰C.

For the result above and requirement stated show that there is an accurate result due to system setup.

Even the manufacturer claim that R290 is suitable as direct replacement for R22 and R410A (in the case of this experiment), we found that minor modification need to be done on the system.

Suitable capillary tube should be change and follow with further investigation.