simple suction/ head pressure

[chill one]

please help i keep getting told different things by diffrent people, but can some one please explain in degrees celsius and psi, the correct way to measure the head pressure adn suction pressure, of air conditioning, fridges, so 0 degrees to 7 and freezer down to minus 20
i think head pressure is ambient temp plus between 15- 19 degrees but i get told different every time, tahnks for your help.

[nike123]

Here is answer to me from lana



Here are some figures :

Tai ----- air entering temperature
Tao -----air outlet temperature
Te ------Evaporating temperature
Twi ------water entering temperature
Two-------water outlet temperature
Tc---------condensing temperature



Air conditioning (evaporator) :
Tai-Tao = 8 to 10 °C
Tai-Te=16 to 20°C
Tao-Te=8 to 10°C

Refrigeration (evaporator) :
Tai-Tao = 3 to 5 °C
Tai-Te=5 to 10°C (evaporator TD) take low TD for high relative humidity
Tao-Te=3 to 5°C

Water Chiller (evaporator) :
Twi-Two=5°C
Twi-Te=10°C (evaporator TD)
Two-Te=5°C

Air cooled condenser :
Tao-Tai=5 to 10°C
Tc-Tao=5 to 10°C
Tc-Tai=10 to 20°C (condenser TD) take low TD in design for hot climate so the condenser will be bigger.

Water cooled condenser :
Two-Twi=5°C
Tc-Two=10°C
Tc-Twi=15°C (condeser TD)
Knowing these values you simply make calculation.
Evaporation pressure should be as follow: temperature of air entering to evaporator -TD of evaporator converted to pressure of used gas.

Condensation pressure should be as follow: temperature of air entering to condenser + TD of condenser converted to pressure of used gas.


http://www.refrigeration-engineer.com/forums/showthread.php?p=99063#post99063