Is there a way to work out operating pressure?

[Jackmate]

Hey everyone, new to the forums. I was just wondering if there's a standard way to work out operating pressures. Basically I'm asking if there is a formula to follow to work out operating pressures on different forms of refrigeration. Thanks in advance

[Rob White]

.

Refrigerant pressures are directly affected by refrigerant temp.

You need to understand the basic principles of a refrigeration system
and then that information would be used to tell you the pressures.

Its all to do with temperature / Pressure relationships of the refrigerant.

Different refrigerants work at different pressures which is why some refrigerants
are better at low temperature or some refrigerants are better at high temperature
than others.

The first thing to know is that in most (vapour compression) systems the refrigerant is
in one of two states.

It is either in liquid form or it is in vapour (gas) form and your gauges only shows
the point where the refrigerant changes from a vapour to a liquid or from a liquid to a vapour.

In the system we absorb and reject heat and the places where that is done is inside
the evaporator and condenser.

In the evaporator we "evaporate" the liquid and change it to a vapour.
In the condenser we "condense" the vapour and change it to a liquid.

Your gauges show the pressure and the temperature that, that happens at.

https://www.google.co.uk/search?q=pressure+temp+refrigerant+chart&oq=Pressure+temp+of+refriger&aqs=chrome.1.69i57j0l5.16809j0j8&sourceid=chrome&es_sm=93&ie=UTF-8

http://www.agas.com/upload/product/071203033235_1074.pdf

Regards

Rob

.

[sterl]

Basically:

You reject heat at the condenser. For a change of state refrigerant, that means its saturation temperature needs to be higher that the temperature of your cooling medium. If your cooling medium is air and weather data says that 1% of a year you will hit 35-deg. C ambient, the refrigerant in the condenser will need to be somewhat warmer than that. Buy a whole bunch of condenser, and you might get it to work at 38 Deg C....For more practical circuits something like 43 to 47 Deg C would be expected. Of course if you can reject that heat to well water at 25 Deg C. you can operate at a lower condensing temperature. And whatever that temperature is, there is a corresponding saturation pressure, presuming a singular pure fluid.

The opposite prevails on the evaporating side: for the refrigerant to absorb heat from whatever it is you are trying to cool, the refrigerant needs to be at a lower temperature than the cooled medium. There's a lot more considerations and variations dealing with the evaporating side, but if you are trying to make a 0-deg. C space, you will need to "suck" hard enough to maintain the refrigerant at least a few degrees colder. With that lower temperature corresponds a saturation pressure.....

[nike123]

At start of this forum section you have sticky thread named Refrigeration 101. Try to read that whole thread before next question.
http://www.refrigeration-engineer.com/forums/showthread.php?19701-Refrigeration-101

[nike123]

Formula is:
te=wet bulb temperature of air at evaporator inlet - TD of evaporator => convert that in to saturation pressure of used refrigerant
tc=dry bulb temperature of air + TD condenser =>convert that in to saturation pressure of used refrigerant