Please define "small temperature" in regard to HVAC
Please define "small temperature" in regard to HVAC
(OP)
I'm a chemical person not a mechanical person - please help me understand what the HVAC Chiller Mechanic is referring to when he speaks of "the small temperature" he refers to this differential (I assume) as a means of evaluating whether the condenser tubes are fouled due to poor water treatment and thus are inhibiting heat transfer. I did not think there was such a simplistic approach to determine if loss of efficiency was due to water treatment or via mechanical problems - refrigerant, bearings, pumps, etc.... We'd always pulled the end bell of the condenser and examined the tubes to make the determination if water treatment was the problem. Can anyone enlighten me?
Thanks!!
kbparham
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Thanks!!
kbparham
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RE: Please define "small temperature" in regard to HVAC
Usually they are designed such that there is one large "process" flow volume, in the AC part of HVAC work that would be the air supply going into the building, and a smaller flow, in your case, of refrigerant that is cooling that air.
Typically the air might enter the exchanger at 80ºF and exit at 68ºF, the difference being 12ºF. The smaller flow of refrigerant usually requires a much greater temperature difference to affect the larger air volume, so its entry temperature might be 48ºF and exiting at 87ºF. That difference being 39ºF.
The efficiency of the heat transfer process can be correlated to any changes in the differences between the air flow temps and refrigerant temps over time. As efficiency worsens, the temperature difference of each stream as it enters and exits would get smaller and smaller. You could correlate efficiency to either or both streams and it appears that your tech has correlated efficiency in his mind to what would be the temperature differential of the air flow in the above example, since that was the "small dTemp"
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RE: Please define "small temperature" in regard to HVAC
RE: Please define "small temperature" in regard to HVAC
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Please define "small temperature" in regard to HVAC
KBParham
RE: Please define "small temperature" in regard to HVAC
I'm not an hvac guy so I could be wrong, but I always thought that approach was more like the inlet coolant temperature and the outlet air temperature (in a typical AC system) ie a good (low approach) gets the air going out as close to the temperature of the coolant coming in. with an ideal heat exchanger producing air at the same temperature as the coolant coming in. I guess in a condenser the coolant temperature should be constant (more or less) is that the difference, or I'm I wrong here?
chad
RE: Please define "small temperature" in regard to HVAC
RE: Please define "small temperature" in regard to HVAC
Fair question/no foul! And you are right chadl in descibing the approach for a hydronic coil. It is a little different when relating it to a flooded evaporator or condenser.
Remember the inlet that you see at the cooling coil is actually the outlet that I see at the evaporator bundle. So my approach is figured differently. It just a matter of looking what the machine is trying to produce versus what your cooling coil is producing. Does that make sense?
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Please define "small temperature" in regard to HVAC
I appreciate the tip, but wanted to verify the information he provided. Just because your mechanic tells you something -- doesn't mean you should take their word as gospel right?? In any event, I wanted to know if this "diagnostic" was widely accepted, or an engineering "wives tale." I searched on the web at large for the term "small temperature" that he used and was unable to find any definitive information. It was then and only then that I opted to bother you guys on this forum. As it turns out I found that non condensables can also be responsible for the differential - not just condenser tube fouling as he had mentioned. The wide variety of responses on this forum is what makes it such an asset. I learn more from you guys as a group, than any one person could ever explain.
Thanks guys,
KBParham
RE: Please define "small temperature" in regard to HVAC
The approach can also be the wet bulb temp when talking about evaporative cooling towers. This is in relation to relative humidity and can allow the cooled fluid to go lower than the ambient temp.
RE: Please define "small temperature" in regard to HVAC
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