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Hi all i am fairly new to HVCA
I was wonering if any one would help explain a query i have. I am aware of the target superheat caculation but i have just got the hvac buddy android app which calculates target superheat i input in the following info. R wet B 16.7c, out door dry 23.9c it gives a target of -4.0 but i dont understand how it can be a negative value should the target be around 8.5 Thanks for any help
Based on the info you provided, that app is garbage.
Here are a couple articles to assist you:
http://www.achrnews.com/articles/96890
http://www.emersonclimate.com/Docume...re-article.pdf
Quote:
Originally Posted by todd86
I'm not sure how that app is supposed to work but Superheat is the calculation
of the gauge temperature (as near to the evap as possible) and actual measured
temperature of the suction pipe out of the evaporator.
It has nothing to do with ambient temperatures.
Regards
Rob
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How To Measure Superheat ?
Superheat: the heat added to refrigerant vapor after the vapor has changed state. Simple as this may seem, many hvacr technicians don't fully understand superheat or it's importance in relation to a refrigeration system.
Ordinarily, service technicians are concerned with superheat readings taken at two different places in the refrigerant system: at the outlet of the evaporator coil and at the compressor, 8 to 12 inches from compressor on the suction line
Finding superheat at the evaporator coil or at the compressor is relatively easy. First, the technician must use his or her compound (low side) gauge to get the boiling or evaporating pressure of the coil. Next, we have to convert this pressure to its corresponding temperature with the use of a pressure/temperature chart.
(Note: All pressure temperature charts are not the same. Some have the psig reading in the column to the far left and you have to look under the correct refrigerant to find the corresponding temperature. Others have the temperature reading in the far left column and you have to look under the correct refrigerant to find the right pressure.)
On an R-12 system, if the evaporating pressure is 21 psig, converting this to temperature you get 20 You now have to find the temperature of the suction line at the outlet of the evaporator coil. To do this, you should use a good strap-on thermometer. Most wholesalers carry thermometers designed specifically to take temperature measurements from refrigerant lines. Be sure to properly insulate the temperature sensing element to insure an accurate reading.
As an example, let's say the suction line temperature at the evaporator outlet is 27° F. You then subtract the temperature you converted from the pressure reading at A, which is 20° F, from the temperature of the line at B, which is 27° F On this particular sys-tem the superheat at the evaporator coil is 7° F: that is, 27° F * 20° F = 7° F superheat.
The procedure for calculating compressor superheat is similar. Using your thermometer, find the temperature of the suction line 8 to 12 inches from the compressor In our example, this temperature is 47° F. From this subtract the temperature you found from the pressure/temperature chart at location A in The superheat at our compressor is 27° F: 47° F * 20° F = 27° F superheat.
Rajasthan Tour
India Tour
The application is asking you for the DB and WB in order to determine what the enthalpy or total heat load of the air is so it can suggest your target superheat.
It's telling you that your actual SH is 4.0K below the Target SH. IOW the system is a bit overcharged. The Target SH will be shown in the box directly under the word "Target".Quote:
Originally Posted by todd86