compressor cooling capacity 1

[vinod68]

hi all,
i am trying to design a condensing unit.
how do i calculate the cooling capacity of the compressor when the compressor hp is known.
i will be using the hermatic compressors of 1/4 to 3/4 hp.

 

[psychro]

Vinod
The compressor does not have cooling capacity but a compression ratio. The compression ratio shall be selected depending on the refrigerant flowrate and the temperature limits of the refrigeration cycle.
Also, an hermetic compressor is less efficient than a semihermetic one. The evaporator has a cooling capacity based on the temperature of the room,heattransfer area and the temperature of the refrigerant and its flowrate.

 

[vinod68]

hi jcpp16674
i agree the compressor is only going to compress the low pressure refrigerant gas to high pressure gas.
then how do i select the evaporator capacity in kcal/hr or watts/hr

 

[azertyuiop]

You start by defining your evaporator. The evaporator at his working conditions , will evaporate a choosen liquid refrigerant to a certain low gas pressure , cooling the ambiant atmosphere in contact with the evaporator , during this process. This low gas pressure is then aspired by your compressor and compressed into a hot high pressure gas. The condensor will cool down this hot high pressure gas , condensing it into high pressure liquid refrigerant. This liquid refrigerant is then flowing toward your evaporator. The process can then restart.

I have the feeling that you are not very well versed in HVAC , and need to upgrade your knowledge of it before venturing further into this matter. You are asking very basic questions typical of a first grader , which is not the subject of this website. Read some books and come back ?

 

[greenaire]

Hi, I agree with azertyuiop (Mechanical).
There is no such way you intend to do.

 

[vinod68]

yes. the hvac is a bit new to me as i have been more in the petrochemical and process engineering. anyway i have been reading quite a bit.
the main question that has been of interest to me had been that some of the compressor manufactureres mention compressor hp with cooling capacities in their catalogues. i wanted to how the two is calculated or corelated(for a hermatic compressor either cooling or freezing).
can any one help.

 

[lilliput1]

Hire an HVAC Engineer or purchase a new unit rated for the duty required. You can blow your head off fooling with a compressor!

 

[psychro]

Reading at catalogs can be quite confusing because most manufacturers make a lot of assumptions and sometimes a lot of mistakes. Try to understand well the basics before looking at catalogs.
The information I think you need is the following:
1. COP -heat absorbed at the evaporator divided by the power of the compressor.
Find out the COP of the existing unit or select an attainable one from the catalog. Determine the cooling capacity of the unit multiplying the COP by the power of the compressor. Catalogs stating cooling capacity to a compressor is misleading. Compressors do not cool. Evaporators do. However compressors are neccesary for vapor-compression cycles.
I hope this will work for you.
Good Luck!

 

[greenaire]

As a rule of thumb, one ton of refrigeration need 1hp comperssor.

 

[r22]

You're going at it backward. You first decide the temperature requirements, ie:high, low, or medium, temperature. This will determine the saturation temperature required in the evaporator, the type of refrigerant, the compressor type, once again, low, medium or high temp. Low temp compressors must tolerate high compression ratios with minimal suction gas coming back to provide cooling.
So the compressor itself is determined by the task and so is the refrigerant type. Tonnage required goes up as temperature goes down.
Then the R value of the container and the load presented by the product. It's not much different for air conditioning.

Horsepower means very little unless taken within a temperature range.The lower the temp requirements the higher the horsepower required since you need a bigger compressor to move adequate amounts of suction gas at low back pressures. The amount of refrigerant circulating per minute goes down as compression ratio goes up and box temperature falls.

There is tables and charts for all this stuff.
Make the person selling the equipment to you, show you his selction criteria or have him double check yours. If he's good he won't mind.