Hi guys. Sorry for the naive questions but now that I have built my own chiller I start understand some thing better so I have some questions.
1) How much should the low-side pressure before I have too much refrigerant inside?
2) When we say that there is a vacuum in the low-side or that the low-side 7" or 8" or whatever Hg what does that mean?
3) Should we charge a system by just watching the evap temp (or the frost on the evap) or with the low-side pressure?
Thats it. Thanks in advance
1. Not sure
2. Its what the pressure gauge reads.
3. I charge based on the temps, but there is probably formulas for each refridgerant and how much pressure would be ideal for X watts of heat.
For those of you about to post:
concerning number 2. I can see that its what pressure gauges says. But mine has Hg's only below 0. Does that mean that the low-side pressure is below zero?
0 is supposed to be 1ATM IIRC, and the MMHG is how far below one ATM the pressure is. I'm pretty sure is based on how much murcury expands under pressures that low, it might be something else, but its based around mercury obviously. 1ATM=760MMG, its around 30 inches if I converted it correctly.
EDIT: my ISP is getting really slow right now, it took like 15 minutes for the post to get posted after I clicked the post link.
Last edited by craig588; 09-04-2004 at 02:42 PM.
For those of you about to post:
i don't think u should care about the pressure at all, i mean...maybe for safety reasons...and to make sure u didn't add too much, but just keep adding gas until u get frost...then add tiny more until u get really good temps..once they start dropping..u know u added too much
i don't think manifolds guages read in hg do they?..i thought they read in psi
The low side (blue) gauge on a manifold usually reads from 30" hg to 120 psi. Inches of mercury measures the vacuum (if present) on the low side of the system. Operating the low side in a vacuum means the boiling point of the refrigerant is lower (meaning lower temps). I think 29.97" of mercury is a theoretically perfect vacuum.
My best advice would be to charge the system while under load until you get the lowest possible evap temp and then stop there, it seems to work for me.
Last edited by gkiing; 09-04-2004 at 08:15 PM.
1) ??? Depends upon design temperatures.Originally posted by JohnFish
Hi guys. Sorry for the naive questions but now that I have built my own chiller I start understand some thing better so I have some questions.
1) How much should the low-side pressure before I have too much refrigerant inside?
2) When we say that there is a vacuum in the low-side or that the low-side 7" or 8" or whatever Hg what does that mean?
3) Should we charge a system by just watching the evap temp (or the frost on the evap) or with the low-side pressure?
Thats it. Thanks in advance
2) A vacume is just that a vacume. When we say 4 " hg that is a refrence for below atmosphere. Using a mecury (hg) manometer (Basically a tube sealed at one end filled with mecury adn flipped upside down) at sealevel we would have 0 psi actual barametric pressure is also read in inches of mecury so if we have 30 inches that is atmospheric pressure.
3) None of the abouve charge to a refrence value Like 4 " hg and then add or remove refrigerant as nessassary depending upon superheat Shoot for 10 to 12 a few inches from the evaporator.
ok guys. thx.
chilly, as far as i remember, superheat is the heating of vapor after evaporation, right? But how can I measure superheat 10" from the evap?
Last edited by JohnFish; 09-04-2004 at 11:35 PM.
Actually a few inches from the compressor is good, measure the pressure in the suction line convert that to temperature using your P/T chart. Subtract from this your actual measured temperature 3 inches from the compressor or so. This is your superheat. Superheat is the amount the vapor is heated above it's saturation point.
YYEEEEEEEEAAAAAAAAAAAAH. Now I got it. I ll test that as soon as finish some mods in my chiller box. Thanks so much chilly.
what figure of supa heat should we aim for?
10 to 12 this will keep too much liquid from enterintg the compressor I have seen freezers as low as 6 and as high as 18 but at 18 the compressor will run hot.
cheers
what about sub cooling on the high side
what is the ideal figure?
u know, there's never been a def figure i don't think...weird, but this is def worth remembering....man, its so mindbogelling how there's...so many factors to how cold u can get
We haven't even gotten started, I have been simplifying things immensely.
ok i guess there is no def figure but whats a good sub cooling figure to aim for?
Last edited by kayl; 09-14-2004 at 08:42 AM.
5 to 8 degF subcooling that is dependant on ambient conditions condenser size load and refrigerant flow. There are a lot of interdepent variables in refrigeration systems.
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