Replylook at this
Professional Member
hey i just recently started working for a hospital. they have two trane low pressure chillers i believe(200 ton and a 300 ton) and a 150 ton carrier chiller. I went to hvac school but never learned anything about chillers besides what i read in our book on my own. I learned a little in the short time i've been with the hospital. Us maintenance guys don't really get to do much work on the chillers. Usually trane technicians are called in. I still want to expand my knowledge on them though because they interest me so much more than regular residential units or rooftop units. Wondering if you guys have any suggestions of books i could read or articles? I'm hoping to get the manual on the chillers at the hospital so i can read them. Any help or advice or words of wisedom would be much appreciated. Hoping to maybe get good enough with them that i could do a majority of the maintenance on them and what not. Thanks!!
Professional Member*
look at this
It`s better to be silent and thought the fool; than speak and remove all doubt.
Professional Member
i have seen that book on the barnes and noble website. only problem is the nearest barnes and noble to me is an hour away. ill have to read some of that on here. haha be nice to sit here and read the whole thing for free but i just cant sit at computer that long and read.
Professional Member
Check with your local Trane office. They usually have classes for their customers. Ask the Trane technicians questions when they are on site. Most importantly be patient and don't get frustrated. It takes years to learn. Read the document dandyme posted.
Professional Member*
Happy reading!
Professional Member
thanks for the advice and the articles guys! hell, keep em coming if anyone has anything different! haha ill spend my whole weekend reading if i have to.
Professional Member*
I would also get the exact model numbers off the chillers that you currently work on. So maybe some one on here can send ya the IOM's. Nothing like learning on what you get to see.Originally Posted by Scotty58
Professional Member*
Just print it off then.
Professional Member
Here are a couple that I have found to be a big help.
Professional Member
I doubt you will be asked to actually fix a chiller. Most hospitals don't want the maintenance guys tearing down units.
Mostly you need to know what a chiller requires in order to be able to start. You need to prove flow through evaporator and condenser. This is usually done with differential pressure switches. They are connected to the chill water and condenser water lines with tubing. Often they will stop up where the nipples screw into the larger piping. Next you need to prove the chiller is unloaded. You should be able to see a mod motor that moves the vanes. Depending on your chiller the linkage may make a limit switch or it might be a little more complicated. Take a look and see if you can find the parts. Ask your Trane tech. Sometimes the limit switch pulls in a relay that can go bad.
Then you have the regular maintenance items like brushing the tubes. Learn how to determine the "approach" as it will give you an idea of how clean the tubes are and what is normal for your machine. The importance of water treatment can't be over stated. Ideally you would want to know how to do your own testing.
More important is to understand that the chiller is part of a system. You have the chill water pumps, AHU's, and the flow rates through them. Neglecting proper flow rates and heat gain from dirty coils and improper installation and balancing will compromise things. Same thing on the cooling tower side. Something as simple as a float valve hanging up, dumping water out of the tower, will greatly affect water chemistry. A couple/few days of that is all it might take to start scale formation. Then efficancy goes to crap in a hurry.
Learn to catch problems early before they become a problem. Learn how all the parts work together.
Professional Member
No, it's correct as stated. Once the pressure reaches 60 PSIG the switch closes proving flow. If the pressure drops below 20 PSIG then the switch opens telling the BAS that there is no flow (or insufficient flow). Usually a flow protection device is wired directly to the chiller control pane.l (So the BAS isn't responsible for shutting the chiller down.)
Professional Member*
Probably should be talking PSID (D for Differential), vs PSIG (G for gauge). I think that is reason for the confusion.
Last edited by Nuclrchiller; 11-08-2012 at 12:17 PM. Reason: clarified with "probably".
Professional Member
Shockwave, remember it is a "differential" switch so it isn't looking for just 60 psi. It is looking for 60 psi "difference" between suction and discharge side of the pump.
I'm going to bet the "20 psi" isn't "cut out". Instead it should be the switch differential.....meaning once you reach a diifference of 60 psi between suction and discharge the switch changes state (say it closes).....once the difference drops by 20 psi the switch changes state again (in this case it opens)....as in 40 psi difference between suction and discharge on the pump.
Without more info I can't guess what its purpose is in your BAS. I doubt it is used to stage a chiller on/off as each chiller should have its own differential pressure switch. Likely it is just used to activate an alarm to let you know the pump isn't performing at desired level (for any number of reasons).
Professional Member
We use dp switches, or other methods, to prove the pump is working in our building control systems. In a lead/lag setup if the pump is not proven within a reasonable time frame then the next pump is called for, and it needs to prove its operation. It also generates an alarm on the "failed" pump. That alarm is sent to 'He who needs to know'.
Professional Member
DP switches aren't the only way to prove flow through a chiller condenser or evaporator. There are also mechanical paddle switches and thermal dispersion sensors like those made by IFM Electronic. All 3 of them are very common and are still widely used. They are also selected for different applications. I prefer IFM sensors or mechanical paddle switches in places where the static pressure in the system is too high to use a standard DP. DP switches all have a "proof pressure", which is the highest differential pressure either of the bellows can be subjected to without damaging the switch. Switches with a high proof pressure are usually much more expensive than the standard ones. DP switches also suffer from setpoint drift pretty badly after a few hundred cycles. I typically pull them and re-set them with nitrogen once a year. As was mentioned previously, the piping that goes to the DP is also a maintenance item. It frequently needs to be cleaned out.
Some manufacturers will even tell you that their chillers are smart enough to not need a flow proving device at all.
Don't pick the fly crap out of the pepper.
Professional Member
you could always print it?
true knowledge exists in knowing that you know nothing.
Professional Member
The most important thing you need to know about chillers is, that water freezes at 32°F and static water freezes far quicker then anything else. Therefore never charge a water chiller with liquid refrigerant at saturation temperature below that magic point, never do that with static water on cooler and condenser and never bypass the flow protection device (of course the HP switch as well).
"Quality exists, when the price is long forgotten."
Henry Royce
Professional Member
remember that dp switches on pumps prove that the pump is RUNNING. they do not prove that the pump is FLOWING. i have been to many jobs where the bas techs use dp switches to prove the pump is flowing (which is incorrect) and then start the chiller. i mostly don't like them on anything (pumps or chillers) because the piping to the switch does not have any flow in them and over time, crud fills up the piping making the switch fail.
a fun example with dp switches on pumps: close 1 isolation valve to the chiller (with the chiller off) then manually start the chilled water pump...the switch will make...do this in front of the bas tech and ask them to explain why this is happening. 95% of the bas techs will say that the switch has failed and needs replaced!
ifm effectors have been my favorite for about 5 years now....they are great if selected properly and installed properly.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
Professional Member
They are old tecnology. We typically use VFD's and pressure transducers, as well as flow meters, but his question was about why he had a DP switch going to his BAS. Question answered?
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