To hot to run!

[mike robinson]

The college where I work has a 80 ton air cooled trane chiller that is on the science building with 100% outside air. [no return] The problem I am having is this machine will not run in this 108-110 tempture I have been running it at sundown till about 12 noon when it goes down on oil high temp which is above 170 degrees . All fans are running the coils are clean . I have been told that this is all it is going to do due to 100% outside air . My question is anybody got any ideas ? By the way I am located in southern Oklahoma.

[Southern Mech]

I am gussing RTAA chiller? have you used a pressure washer on the coils? I have had them so impacted I had 2 guys 1 crawled inside and 1 out to flush the coils. what were some of your readings, did you check H2O flow?

[mike robinson]

I am gussing RTAA chiller? have you used a pressure washer on the coils? I have had them so impacted I had 2 guys 1 crawled inside and 1 out to flush the coils. what were some of your readings, did you check H2O flow?

I will have to get back with you on all the information.

[929rc51]

IF it is an RTAA they are good up to 115*F inlet air. Have you actually checked your inlet air temp? Also what is your discharge pressure/temperature? If your pulling 100+*F air through your chilled coil its going to drive your discharge up as well so do you have a design issue? Check water flow and air flow across coil and barrel. Give us some numbers and design specs.

[Southern Mech]

I will have to get back with you on all the information.

if you are going back to the job, please take a gas pressure washer with you, and some coil cleaner, stay 10'' from coil make the spray be vertical with the fins and go slow. with someone on top looking down through the fans should see the water comming through the coil, if not youll see the dirt running out.

[GRANTBRYAN]

I've got the same problem going on with a RTAA. Its located close to the building and it's recirculating the leaving air. With the higher than normal temps here it shuts down on the high oil temp and high pressure on the really hot days (100+)

[ryan1088]

if you are going back to the job, please take a gas pressure washer with you, and some coil cleaner, stay 10'' from coil make the spray be vertical with the fins and go slow. with someone on top looking down through the fans should see the water comming through the coil, if not youll see the dirt running out.

Goodway machines are nice if you have one but if you don't have that, you can make a wand to hook to your water hose to give you great pressure. Take 3/4" copper, ball valve, 1/2 copper, 3/8 copper and adapters to hook to the garden hose. Put a cap on the end and drill 3 or 4 small holes (1/8 ") in the cap and you would be surprised how well you and someone on the other side of the coil can do. Saturate both sides then chemically clean.

[mike robinson]

if you are going back to the job, please take a gas pressure washer with you, and some coil cleaner, stay 10'' from coil make the spray be vertical with the fins and go slow. with someone on top looking down through the fans should see the water comming through the coil, if not youll see the dirt running out.

Southern Mech don't run off it willbe Monday evening before I can get back with the information. I am trying to take the weekend off I got to have a break been going like a bat out of hell since the last of May with no end in site on top of that school starts in one week.

[cperk]

If worse comes to worst put a water sprinkler on each side to keep it online. I have never used a pressure washer to clean an RTAA coil. We always use a firehose, and open the nozzle up where it is more volume than pressure so you don't bend the fins. I bet if I used a pressure washer the coil would look like a smooth block of aluminum.

[Southern Mech]

If worse comes to worst put a water sprinkler on each side to keep it online. I have never used a pressure washer to clean an RTAA coil. We always use a firehose, and open the nozzle up where it is more volume than pressure so you don't bend the fins. I bet if I used a pressure washer the coil would look like a smooth block of aluminum.

I have 4 - RTAA's and 15- RTAC chillers under contract, I clean coils every other month. with a pressure washer. not saying it wont bend the fins, you can't be stupid about it either.

[Cowpoke]

IF it is an RTAA they are good up to 115*F inlet air. Have you actually checked your inlet air temp? Also what is your discharge pressure/temperature? If your pulling 100+*F air through your chilled coil its going to drive your discharge up as well so do you have a design issue? Check water flow and air flow across coil and barrel. Give us some numbers and design specs.

Yeah he's right about the RTAA design temp. I don't believe this heat is too much for the RTAA chillers. I am in Texas and we have had 105+ for many days. I can't even keep up with the days in a row we have had over 100. I work on a military base and we have many of these chillers around. They have been running fine. I have one now that is going off on oil temp. Condensers are clean and all fans running, but have a bad oil temp sensor. If the chiller has the proper clearance, then I wouldn't think it is because of the heat. More than likely you have another problem.

[R123]

If worse comes to worst put a water sprinkler on each side to keep it online. I have never used a pressure washer to clean an RTAA coil. We always use a firehose, and open the nozzle up where it is more volume than pressure so you don't bend the fins. I bet if I used a pressure washer the coil would look like a smooth block of aluminum.

Don't put a water sprinkler on the coils unless you are planning on replacing the coils anyway and you are trying to keep the chiller online until the new coils come in. Putting a sprinkler on will load the coils up with calcium and ruin them.

[deltap10]

May be another problem. Check for cond. air side issues if coils are clean. Too much chemical cleaning can degrade heat transfer. Look for fins flaking off. Check design specs. If chiller holds setpoint it may still be overloaded. Full load amps OK? May have to reduce load on chw side by reducing OA or flow through chiller. If unit is on a roof maybe sprinkler roof surface around chiller without getting chiller wet.

[ga1279]

Mike Robinson- I have had situation at several plants in the Houston area. As they all use 100% outside air for the labs. I would suggest looking at the original design criteria. Unfortunately ASHRAE is still using 95*F as the design temperature in Houston. Unfortunately again when the outside air temperature rises to 100*F you are 6% over design, at 104*F you are 12% above design I had one that the Trane start-up mechanic through his hands up at the start-up as he could not keep it running in the heat. It was a 200 ton RTAA and it wouldn't even try to load with out shutting down. What I had to do was 1) to get it running was jump out the flow switch and reduce flow rates as it is hard to produce 44* water when you have 90* water entering. I adjusted the flow to maintain a 10* delta "T" and as the return water cooled down I would open the valves alittle at a time. 2) We installed a by-pass secondary loop with a 3-way valve preset to only allow the minimum flow rate from a design flow of 500 GPM, to 220 GPM, just enough to make the flow switch contacts, which is the minimum flow allowed for this evaporator and as the return chill water dropped a little it would start to close off by-pass mode and allow more water flow through the chiller. When I had the flow switch jumped out I was always there, at the customers and Trane's expense as this was a combination of the plant engineers and Trane's engineers fault. Until the firm I was working for had installed all the necessary controls to achieve our permanent solution-GEO

[mike robinson]

Mike Robinson- I have had situation at several plants in the Houston area. As they all use 100% outside air for the labs. I would suggest looking at the original design criteria. Unfortunately ASHRAE is still using 95*F as the design temperature in Houston. Unfortunately again when the outside air temperature rises to 100*F you are 6% over design, at 104*F you are 12% above design I had one that the Trane start-up mechanic through his hands up at the start-up as he could not keep it running in the heat. It was a 200 ton RTAA and it wouldn't even try to load with out shutting down. What I had to do was 1) to get it running was jump out the flow switch and reduce flow rates as it is hard to produce 44* water when you have 90* water entering. I adjusted the flow to maintain a 10* delta "T" and as the return water cooled down I would open the valves alittle at a time. 2) We installed a by-pass secondary loop with a 3-way valve preset to only allow the minimum flow rate from a design flow of 500 GPM, to 220 GPM, just enough to make the flow switch contacts, which is the minimum flow allowed for this evaporator and as the return chill water dropped a little it would start to close off by-pass mode and allow more water flow through the chiller. When I had the flow switch jumped out I was always there, at the customers and Trane's expense as this was a combination of the plant engineers and Trane's engineers fault. Until the firm I was working for had installed all the necessary controls to achieve our permanent solution-GEO

Update Well I went back on saturday took power washer and washed front side of the condenser then I pulled all the fan guards and power washed the coils from the other side. Boy did I see alot of dirt come out by looking at it you would think it was clean but it wasn't. I sarted chiller up sunday about noon it has been on line ever since. It holds 45* water untill about noon then creeps up to about 51 not to bad for these hot days the oil temp on a is 161 and on b is 156 all is well right now. Thanks for all the info everybody maybe I can repay it some day.

[Southern Mech]

Update Well I went back on saturday took power washer and washed front side of the condenser then I pulled all the fan guards and power washed the coils from the other side. Boy did I see alot of dirt come out by looking at it you would think it was clean but it wasn't. I sarted chiller up sunday about noon it has been on line ever since. It holds 45* water untill about noon then creeps up to about 51 not to bad for these hot days the oil temp on a is 161 and on b is 156 all is well right now. Thanks for all the info everybody maybe I can repay it some day.

there you have it, nobody believs me about these coils, even in our office. I just talked to 5 techs this morning with similar issues, all won't clean the coils, I just tell them they are 4'' thick, a water hose won't cut it. let alone on a chiller with sub par service in the past.

[ga1279]

Mike Robinson- Glad to hear it all worked out for you, if you do reduce your flow a bit you can also loose your late afternoon problem. Lower GPM higher delta "T" . In my case though this was a brand new unit, fresh from the retired bikers factory in Pueblo, CO. It obviously needed another 100 tons during the summer heat. No engineer from the plant or the Trane office would admit the unit was undersized. So, we used some tactics that were above and beyond. The Trane tech who tried to do the original start-up asked the magic question. Who's crazy design idea was this? I got to tell him the name of the Trane sales engineer, priceless.-Geo