Typical superheat and subcools for R134a based air-conditioning unit

[akr768]

We have a residential R134a air-conditioning system coupled with a R134a based heat engine. The engine and the compressor are mechanically coupled. Based on our tests, the cooling output produced is about 0.07 kW (air side) and the system efficiency is about 2% (at 35 C outdoor temperature). We tested at 35 C and 25 C outdoor temperature. Ideally, the system efficiency should have increased at lower outdoor temperatures, but there wasn't any. However, the curious part is at 25 C outdoor, the refrigerant temperature can drop as low as 8 C at the evaporator inlet, but the cooling output did not increase. I suspect evaporator fan might not be operating correctly. Please let me know your thoughts.

Question 1: Is that evaporator superheat at 25 C outdoor very high?
Question 2: What are the typical superheats and subcools?

Note: AC side refrigerant charge is about 0.45 kg.

Here are the some of the plots representing the sueprheats and subcools at 35 C and 25 C respectively.

 

[itsmoked]

How do you get these graphs out of a system you don't know if air is flowing thru the evaporator??

Yes, a dead evaporator fan would prevent cooling but more likely would be an iced-over evaporator. 2% efficiency is an abomination to nature.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[akr768]

Thanks for your reply. There is air flow, but I'm thinking it is not running at the rated capacity. Measured air flow across the evaporator is about 0.048 kg/s in contrast to evaporator's rated flow rate of 0.09 kg/s. Flow rate was calculated using measured flow velocity in a rectangular box. Pressure and temperatures are being measured and logged.