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 vivekkumarmishra2003 January 25, 2010 08:11

Doubts in HVAC

Hello All,

I have certain doubts related to automobile air conditioning. I am expecting clarrification from all of you who have good working knowledge of automobile air conditioning process.

The problem in automobile air conditioning is the cool down performance i.e. the gradient in temperature drop in first 20 minutes,My suggestion is to increase the air flow across the condenser by means of providing a high air flow rate fan, to justify this i want to measure the improvement theoritically. but before i can proceed i want clarrifications on :

a) Is the proposal and the logic behind the suggestion which is " The higher flow rate across condenser will cause an increased heat rejection rate at condenser which will decrease the cool down time but will not affect the overall temperature of the passenger compartment as the temperature is governed by the Thermistor situated on the evaporator which cuts off the compressor at a pre defined temperature of the discharge air" ,correct ?

b) - I am planning to show the improvement by means of calculating the heat rejection at existing air flow and will show the heat rejection at (assumed) increased air flow, can i do this comparison when the vehicle is idling i.e. engine rpm is fixed so the mass flow rate of the refrigerant in the AC system is fixed ?

c) - Also i believe that an increase in heat rejection will increase the net refrigeration effect (NRE) inside the passenger compartment i.e. for a given mass flow of refrigerant the heat removed from the passenger compartment will be higher thus time require to cool down the passenger compartment will go down, is my deduction is in right direction ?

d) - For a given condenser the overall heat transfer coefficient U in the formula( Q = U x A x TD ) will change at increased flow rate only because of increased convection because for a given condenser conduction and radiation will remain same. Is this assumption right ?

e) - In steady state simulation the cool down performance of the vehicle can not be simulated, is this deduction right?

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