superheat calculation 1

[atom123]

i am using a software to simulate a refrigeration cycle and i need to feed the superheat value in the compressor data. how do i calculate the superheat from the compressor catalogue data( return gas temp. is mentioned in compressor catalogue). Is this value different from evaporator superheat?

 

[imok2]

A/C with a Thermostatic Expansion Valve (TXV) is charged to the sub-cooling of the liquid line leaving the condenser because the superheat is fixed. The superheat is fixed at 8 to 12 degrees in most residential air conditioning systems taken at the evaporator outlet. If taken at the compressor suction line it could pick up another 3 to 7 degrees dpending on the pressure drop, and the temperature in which it runs.

A/C with a “fixed orifice” is charged to the superheat of the suction line leaving the evaporator. Superheat is the gas temperature above the saturated temperature.
Superheat can be split into two types of heat:
(1) Superheat of the evaporators and
(2) Total superheat entering the compressor.

The evaporators superheat must be figured at the evaporator outlet not at the compressor inlet. Total superheat is figured at the compressor inlet.

 

[gepman]

To expand on what [/u]imok2[/u] has said the superheat in the evaporators is sometimes called "useful" superheat since it actually contributes to the refrigeration effect of the refrigeration system while superheat picked up in the suction line after the evaporator does not contribute to the refrigeration effect of the sytem (unless the suction line is located in the refrigerated space) since any heat gain in the suction line comes from the ambient environment not the refrigerated space. Most of the software that I have for small compressors (Copeland, Bitzer, Maneurop, Carlyle) allows for separate values for evaporator superheat and total superheat.

You probably have a DX (direct expansion) system as [/u]imok2[/u] has answered since your catalog mentions constant return gas temperature which most industrial compressors won't mention. There are some supermarket refrigeration systems which have long suction lines which can pick up considerable superheat and are sometimes modeled as constant return gas. If by chance you have a liquid recirculation system the total superheat is usually very low if any. If you have a flooded system you won't have any useful superheat but you may have a couple of degrees in the suction line mostly due to pressure drop of one to two pounds.

The superheat is important for the refrigeration cycle calculations for two reasons:

1) The useful superheat contributes to the refrigeration effect of the system.
2) All superheat reduces the mass flow capacity (and therefore the refrigeration capacity) of the compressor since it decreases the density of the gas which reduces the mass of gas which can be brought into the constant volume suction of the compressor.

 

[AbbyNormal]

use 15F of superheat,

Take the "V" out of HVAC and you are left with a HAC(k) job.