View Full Version : Trane nightmare
06-26-2006, 10:59 PM
Im about to look at a job. Apparently Someone has installed 2 condensing units on 1 evaporator circuit. I've yet to see this set up.
I've seen multi evaps on 1 condensing unit all day long.
What are your opinions of using 2 10 ton condensing units (with compressors) with 1 20 ton evaporator. Sounds like a nightmare to me.
06-26-2006, 11:32 PM
Does the AHU have two circuits? If it has one, my concern would be oil return to both compressors. How is it piped? Controls? There are no nightmares, just scary salesmen. Is it operational now?
06-26-2006, 11:59 PM
The AH has (2) 20 ton circuits. Roof has (4) 10 ton trane condensing units. It is my understanding that 2 condensing units are piped to (1) 20 ton evap. I would emagine the only way this can be done is to join the two liquid lines and seperate the 2 suction lines at the units. They are running (1) 10 ton condensing unit on each 20 to curcuit currently. They cannot run 2 because they say the evap will freeze up.
The AH is a 1961 dinosar. My opinion is they should have installed a 15 ton condensing unit on each 20 ton evap circuit since the old evap does not have enough surface area as a new evap would, and a 2005 condenser is way more efficent than the unit designed in 1961.
This install supposedly took place this past november and this is the first summer they have ran.
The 10 ton systems have to be combined as one circuit to make 20 tons. Each unit should have its own liquid line feeding the expansion valve with a solenoid valve before feeding the liquid header. Furthermore each circuit (10 ton, 10 ton) will need an oil cross over line. Both condensers have to be level with each other.
In this situation piping practice is KING.
You may want to take a look at your expansion valve to verify it can handle that capacity range 10 to 20 tons.
The efficiency has nothing to do with it. When running full capacity make sure you VERIFY airflow. If this is an old air handler, and worn pulleys have been changed, then this system will have to be re-commissioned.
I just cant see how that is going to ever work well. How are you going to keep the charge correct between the two condensers with out alot of extra piping? Why not do the job correct?
06-27-2006, 07:08 PM
I have seen down here where they have taken a 10ton dual circuit evap coil and hooked up two 5 ton condenser's and seperated them as Y1 and Y2 and they work fine. But not piping them together on a single circuit i agree just replace it all and be done with it.
Sure rip it all out and re-do it, sounds easy but who will foot the bill? I kinda wish I had your customers.
Call the rep. of the unit and have the technical dept. send you some info on pipeing the system to a single evap. coil.
What type of units are these? Model# and Make.
06-27-2006, 07:29 PM
That is true that it will cost but you also have to evaluate what the customer wants becuase i dont know anyone who does this work for free much less how the manufacturers will respond with warranty claims if need be. If your customer wants it fixed correctly and safely you just explain all the options to them because it sux if you have to use your liability insurance even if its not your fault.
So basically what I'm saying is yes you can talk to tech reps and all and make the system work, but if the customer will do it replacement is the best option.
Follow cores good piping practice suggestion. There are a lot of dual cond circuit systems out there (eg. multiple 5H compressors on the same chiller barrel/ 1 circuit) Oil equalization is everything. If your txv's are sized right and your still concerned with low suction, throw in a hot gas bypass circuit.
07-22-2006, 12:02 AM
review the evaporator piping.It may be easier than you think to repipe it for four circuits.Alot of older larger tonnage evaps I have worked on run a header from liquid & suction to connect the circuits together.
07-22-2006, 05:17 PM
Replace the ahu with a 40 ton 4 circuit coil . Provide controls for 4 stages of cooling and possibly a humidity thermostat. Verify duct size, tubing size, and overall system operation before submitting proposal. If you try to modify system you will have compressor failures.
07-24-2006, 10:39 PM
make sure thier is a check valve installed in each liquid line and stage them like a 2 stage system and youll be fine.
charging has to be done with both units fully loaded.
07-24-2006, 10:48 PM
The chech valve does nothing to solve the problem with coil icing at full capacity. Poor heat transfer of a 1961 coil with electrolosis and mismatched equipment.
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