Testing Setup

I am planning to create a testing setup as follows:


Small building with two separate chambers, one for the condenser and one for 1-3 evaporators, and an instrumentation board.
The condenser and evaporators will be expelling their air to the outside and a volumetric flow and humidity measurements will be taken.
The chambers will have a heater supplying air to the chamber with a thermostat in each to ensure that the temp in the chamber is maintained, and also there will be a humidity measurement in the chambers.
Analog pressure gauges at each component's entrance and exit, along with thermocouples on the outside of the refrigerant lines.
Variable speed motor to drive the compressor just outside the small building.

I will be able to determine the btu rating of the entire system by using both the refrigerant, and the temperature and humidity change across the evaporators. I was also thinking of monitoring the btu input of the heater to the evaporator enclosure so that I know if the temperature is constant, this will be another verification of the system performance.

I was planning on the chambers being approximately 16 cu ft or so. Do you think that this will be large enough?

This system will be mostly analog with just steady state readings being measured, but I want it to have the ability to be upgraded to a DAQ type setup in the future.

Thanks in advance for any help, concerns, or comments.

This will be used for tesing moble A/C systems.

Also, a rotameter will be used to measure the refrigerant flow rate through each of the evaporators and the compressor suction line.

Hi cwells
It would be helpful if we had a little more info to give a more accurate answer - what sort of portable ac units are you testing, size of test boxes will depend on load etc. Would be best to log all data then analyse from graphs. You may need to test under varying conditions like condenser with cold or hot / humid or dry conditions which will require variable capacity compressor & fans & or heating inputetc. A few simple line drawings could help too. I assume you will plot data on psychometric, enthalpy & power charts for both test unit & unit being tested?

Cwells, your specifications are strange and need a little more thought or care.

I suppose the evaporator is NOT “expelling the air to the outside” moreover there is no outside, you are operating inside the lab, …or I did not understand!

The evaporator enclosed in a chamber with insulation good enough or walls heated to prevent condensation will allow you to keep the conditions of humidity in the evaporator enclosure. All water condensed by the evaporator is measured and sprayed back in the enclosure.

You only need then a heater to keep the room temperature constant.

If you want to start with low temperature ambients then you may need a second evaporator in this enclosure or you may use the same evaporator you will test to bring the room to initial conditions.

In the condensers enclosure you will need an extra evaporator to keep the conditions of the condenser constant taking the same precautions not to condense on any inside surface if you will try high RH tests.

Sorry, I was a little vague when describing the testing setup.

The a/c systems that will be tested are on the range of 15,000 to 40,000 btu/hr. They are designed to be used in aircraft in a variety of environments. The condenser chamber will need to be able to mantain a temperature range of approximatley 70 to 120 F. The evaporator chamber will need to be able to maintain a temperature of approximately 60 to 80 F.

The seperate chambers need to be large enough so that the temperatures do not fluctuate to rapidly during testing.

The testing building will be an pre-manufactured shed, and I was planning on expelling the air from the evaporator and condenser to the outside of the building so that I can determine if the system can keep up with the required load under steady state conditions. Also, I can determine the actual capability of the system, as well as determining a refrigerant servicing amount for each system under the designed conditions.

Discharging the air to the outside means you have to feed the same amount to the test chamber or the air flow of the evaporator will vary.

In my modest opinion trying to keep the pressure and chamber temperature and humidity feeding outside air in real time is complicated.

Repeating my previous post:

Instead you can discharge the evaporator air to the same room through a resistor and a humidifier (you can spray the same water the evaporator condensed) and the power of an electric heater (which is easy to measure) can tell you exactly the heat capacity of the evaporator.

Some things you should ensure:
- not to introduce a high pressure drop in the discharge of the evaporator or you’ll be tampering with its nominal airflow.
- Not let any surface within the room go below the dew point of the air in the room or you’ll need more sophisticated control. This is better achieved by insulation.

The condenser air you may discharge after measuring as unless you need air in conditions far different from ambient conditions. In this case you’ll need to enclose it together with another (non condensing) evaporator to keep the room conditions constant.

I think this is the easiest way.

Good luck with your project!

Hi Cwells,

I have to do a similar type of testing. So wanted to ask you, how are you planning to create the test conditions in the test chamber. I am stuck with the calculations required to create the test conditions...
Any information regarding the calculations, would be appreciated.
Thank you in advance....

So I am having trouble using the rotometer to measure the flow rate of the refrigerant in the suction line. According to the temperature measurements, the refrigerant is leaving as a superheated gas as it should be, but the fluid passing through the guage is a liquid. The temperature measurement at the inlet of the condenser shows that is is a gas again. The fluid is expanded as it is passed through the rotometer, but this should only make it more superheated due to this being an isentropic expansion process. Any ideas on why this would be happening? The link to the meter is provided below.

http://www.omega.com/ppt/pptsc.asp?r...000&Nav=greb02

I meant to say isenthalpic not isentropic.