Evaporator performance question
Evaporator performance question
(OP)
I have two freezer evaporators (134a) which are identical by design (geometry). However, when I test these for energy, one of them always consumes more kWh. I am pretty sure that I am doing the test right, but I just can't tell why do I get different results? Any ideas?
Thanks,
Thanks,





RE: Evaporator performance question
Do you actually know whether the variance is outside of the norm?
Why would you expect the wear and actual construction to be identical?
TTFN
RE: Evaporator performance question
RE: Evaporator performance question
Could you be more detailed in the test numbers are the pressures, superheats, and amount of subcooling the same, do you know for sure they are both seeing the same load? Are these reciprocating or scroll type compressors. Are they feed from the same electrical service is it an issue with power factoring? 25% is a pretty big difference.
Have you tried to plot their performance on a pressure enthalpy diagram maybe something will stand out there.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Evaporator performance question
There has to be some difference between the two.
Ed
www.engineerboards.com
RE: Evaporator performance question
RE: Evaporator performance question
RE: Evaporator performance question
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Evaporator performance question
RE: Evaporator performance question
Hard to detect but a true fact.
If the tubes are not swedged to the fins properly you can expect inconsistent and very poor performance. Stick to the manufacture that provide the better performing coil. Some manufactures draw a mandrill through the tube (best) others use hydraulic pressure to expand the tubes (a poor method <MHO>).
Good Luck
Best regards
pennpoint
RE: Evaporator performance question
RE: Evaporator performance question
If you compared a rough surface to a smooth surface I'd say it's likely that the rough suface might have an extended surface area, providing a greater rate of heat transfer. As long as the air flows across both coils was measured and found the same.
I would caution that with a rough surface you might see a greater air flow resistance and reduced air flow, for accuracy I'd want to verify the air flows as being the same. That way you could calculate the heat transfer of both styles and be assured that you were comparing true coil performance, and not a greater [&Delta]H because of reduced air flow.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Evaporator performance question
thanks for returning to this forum with some details to your findings. It's always good to hear the outcome of an investigation.
OOpps I see I made a typo I wanted ΔH not, [&Delta]H. Oh well you got the drift.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
RE: Evaporator performance question
RE: Evaporator performance question
On the other hand, I immersed both evaporators into a water tank and then pull them out. The one evaporator with a rougher surface retained much much more water than the one with a smooth surface finish. Can you imagine these two evaporators running in a freezer, these parts sweat pretty much and if that water doesn't drain off the surface, it will remain on evaporator and end up freezing. I think this is one of the cons of rough surface. Also, rougher surface means poor surface contact with fins as well, you would want to create snug fit and it is easier with a smoother surface. Anyways,these are just my opinions ofcourse, any suggestion, comments are most welcome.
RE: Evaporator performance question
RE: Evaporator performance question
RE: Evaporator performance question
This is all speculation, as you have yet to give any body here any real numbers to work with.
design CFM
entering DB WB temperatures
leaving DB WB temperatures
load in the space BTU/Hr
type of refrigerant
suction pressure
discharge pressure
superheat
subcooling
With some additional data maybe we could come up with some ideas.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI