Please walk me around the P's and T's in a typical A/C system.

[dbecker]

Hello,

I am a little bit confused. From what I understand, pressure shouldnt rise through a heat exchanger, temperature is what is controlled through it.

I was told from an AC technician that the pressure rises through a heat exchanger, I thought that was not possible since the gas is flowing and it will only rise in temperature as volumetric flow rate increases to keep mass flow and pressure constant.

Does anyone have a diagram of a typical home AC system with P's and T's at all the different thermodynamic stations?

R22 Saturates at 235 psi saturates at about 108F. Which means, that a condensor of 'whatever' size should have no problem bringing saturated gaseous R22 into a subcooled liquid state (assuming ambient is 85F here in florida).

So if the entrance to a condenser is 235 psi and 150F, it is superheated and then comes out of the condensor subcooled but at what pressure? Just because it goes down to 85F (assuming 100% heat exchange) do I need to compute vapor pressures of a subcooled liquid?

Thank you for your time,

- Dan

 

[MintJulep]

Pressure through the evaporator or condenser is "constant enough" if you're interested on the overall performance of a system.

That is to say, if you're drawing the cycle on a Pressure vs. Enthalpy chart, just go right ahead an draw horizontal lines.

http://www.alephzero.co.uk/ref/practcyc.htm

 

[imok2]

Go to google and down load ( pressure enthalpy without tears )

 

[chicopee]

Go on line and check out refrigeration cycle diagrams for different refrigerants. These cycles are idealized and at least you'll get an idea how they relate to real refrigeration and AC systems.
In reality, the refrigerant enters the cooling coil(or evaporator) as a saturated liquid(at a particular temperature and pressure),and it exists the cooling coil at a sligthly superheated state(correspondingly slightly lower temperature and pressure) before it enters the compressor suction side.
On the air side, there will be a pressure drop across the cooling coil fins.

 

[DrRTU]

This is a good document on P-H diagrams.

http://www.sporlanonline.com/5-200.pdf

 

[dbecker]

Thank you.