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View Full Version : Trane Intellipak 75 ton high pressure trips



michaele
25-07-2012, 10:57 PM
We have a 4 year old building with 2- 60 ton Intellipaks and 1- 75 ton Intellipak on the roof. Last year we had some very hot weather and we had a problem with the 75 ton unit tripping out on high head when the ambient temp hit 108. This happened many tmes. The condenser coils were kept clean with a pressure washer. The refrigerant charge was perfect. The 2- 60 ton units never tripped. Trane's solution was to have us buy 6 larger hp condenser fan motors and 6- 5 blade condenser fans. Along with pressure switches with a higher setting. This was going to cost over $10,000.00 dollars for the one unit. If I shut down about half of the vav's on that unit, it will run over 108 degrees. This year we have even hotter weather and the same thing is happening. I read the specs for both the 60 and 75 ton units and discovered they all have the same number and size of condenser fan motors and fans. To me it seems like they are trying to remove an additional 180,000 btu's of heat from the refrigerant of the 75 ton unit using the same amount of air flow they have on the 60 ton units. The 60 ton units have not ever tripped. Does this seem like a design flaw?

The Viking
25-07-2012, 11:18 PM
Design flaw or intelligent design, that is the question.

You will find that the manufacturers are trying to use the same parts wherever possible in order to reduce the costs of manufacturing as well as keeping spares.
The big question is to what ambient temperatures the units were designed and also what duties (as % of their capacities) they are working with.

You will probably find that the condensor coil on the 75 is larger than on the 60 and that's why Trane has calculated that they will cope with the same airflow across it.

There are 3 main causes for nuisance HP trips at hot weather (when the condensor coil is clean and the fans are working):
- Non condensable gases (air or OFN) in the system.
- Operating on greater load than it were designed for.
- Operating at higher ambient temperature than it were designed for.
(Not to mention external restrictions of the airflow)

:cool:

.

install monkey
25-07-2012, 11:25 PM
or in my case the idiot who looked at a trane rtad108 didnt notice 1 tripped breaker on the condenser fan and the other fan disconnected, so above 24deg both systems shut down- customer has now accepted the wuote to replace 2 fans- so all 6 will be operational-until the other 4 fail!

The Viking
25-07-2012, 11:25 PM
Second thought,

If Trane were suggesting HP switches with a higher cut out pressure, is the current ones operating OK or cutting out below MOP?
Otherwise why change?
And if Trane is proposing to raise the MOP, why bother with changing the fans until you know how well it will operate on the new higher MOP?

.

install monkey
25-07-2012, 11:30 PM
probably cheaper and easier limiting the capacity to 80% -got to be better than spending $10,000

serviceman
26-07-2012, 04:47 PM
during my time at trane, the most common problem is that these units had obstruction of the filter dryer, even on new machines or initial start

michaele
30-07-2012, 08:00 PM
Second thought,

If Trane were suggesting HP switches with a higher cut out pressure, is the current ones operating OK or cutting out below MOP?
Otherwise why change?
And if Trane is proposing to raise the MOP, why bother with changing the fans until you know how well it will operate on the new higher MOP?

.
The current switches are operating just fine and I have already decided to try that.

michaele
30-07-2012, 08:00 PM
during my time at trane, the most common problem is that these units had obstruction of the filter dryer, even on new machines or initial start
These machines have no LL filter driers.

michaele
30-07-2012, 08:02 PM
probably cheaper and easier limiting the capacity to 80% -got to be better than spending $10,000
At 80% that area gets too hot for the peaople and computers.

michaele
30-07-2012, 08:07 PM
Design flaw or intelligent design, that is the question.

You will find that the manufacturers are trying to use the same parts wherever possible in order to reduce the costs of manufacturing as well as keeping spares.
The big question is to what ambient temperatures the units were designed and also what duties (as % of their capacities) they are working with.

You will probably find that the condensor coil on the 75 is larger than on the 60 and that's why Trane has calculated that they will cope with the same airflow across it.

There are 3 main causes for nuisance HP trips at hot weather (when the condensor coil is clean and the fans are working):
- Non condensable gases (air or OFN) in the system.
- Operating on greater load than it were designed for.
- Operating at higher ambient temperature than it were designed for.
(Not to mention external restrictions of the airflow)

:cool:

.
The condenser coils on both units are the same size, face area, tube size, fins per inch. I have had gauges on and did not really consider the possibility of non condensables because at the time it was 2 years old and had a factory start up. I do remember the LL gauage fluttering but I dint have oil filled gauges on it. Maybe I should check into that some more.

install monkey
30-07-2012, 08:54 PM
ur sure the condenser heat rejected off the fans isnt shortcycling causing a higher head pressure?
running at 80% capacity will keep it running for longer without you having to reset it- once tripped youve lost 30% of your total cooling capacity, by limiting to 80% your running at around 85% capacity

serviceman
30-07-2012, 10:46 PM
you could provide readings of the machine work? or photos of the machine