RTU's, economisers, and fan cycling

[targetman]

Just wondering how many guys find the need to add fan cycling to units with economisers. I can say that the last two companies that I worked for never did. But, it's the normal practice with the current employer. I'll wait for some imput, then I'll show you what I found today.

[klrogers]

Most of the popular two stages units will run one stage of mechanical cooling as the second stage of cooling when in economizer mode. So I would say that condenser fan cycling should be used.

Kevin

[toptwo]

A fan cycler should be used when the compressor will run in low ambient conditions to keep the saturation temperature in the condenser up.

[chillerout1]

trane units with microcontrols and new trane units with microcontrols are good down to zero degrees f dont really need them here on trane package units with economisers carriers sometimes need them when second stage (#1) comp[ressor comes on depending on application

[targetman]

Most of the popular two stages units will run one stage of mechanical cooling as the second stage of cooling when in economizer mode. So I would say that condenser fan cycling should be used.

Kevin

Alot of package units do not come with fan cycling, but can be added as an accessory. Have you ever added fan cycling when it did not come that way from the factory.

[2sac]

Alot of package units do not come with fan cycling, but can be added as an accessory. Have you ever added fan cycling when it did not come that way from the factory.

Yes,
I'd recommend rather than breaking 1 leg of line voltage, install a contactor and break both legs at the same time(providing it's single phase) to extend motor life. If you're going to run in low ambients you should probably install a crankcase heater also.

[ascj]

I'll assume you mean condenser fan cycling to control head pressure......

One gripe I have is alot of the older/new cheap small tonage units had no mechanical cooling lockout. There is no reason to be running mechanical cooling under 45-50 degrees with a unit that can provide 100% economize air.

Most RTU's don't need any fan cycling running into 45-50 degree ambient cooling. So you should be locking out mechanical cooling. And if don't have it, then add it.

What application do you need 100% economize and sub 45 degree ambient mechanical cooling?

[targetman]

It's a problem child Carrier. It serves a clean room at an oil refinery. Drums are filled in the room and it's hot. I have not been with the company long and it's not my account. I do know that circuit 2 is tripped on high head pressure all summer long. The compressor had been changed before and a suction drier shell installed. The Boss sent me to change the compressor again yesterday. He thought that the compressor was going bad and thats why it was always tripped on high head.

My point is that this company always adds some sort of fan cycling to RTU's. And the Tech that had this account did it his own way. It's a 50TJ024 from 2000. I'll also add that he bypassed the CLO's and added his own pressure switches complete with tattle tales. Here is a picture off the number 2 compressor section. See anything wrong?

[master wong]

how does a compressor going bad trip a high head switch, it sounds like your condenser coil needs cleaned, may be one of those double coils that need to be seperated to be cleaned.

And for low ambient controls on a RTU that is common around here to deal with our humidity problems on cooler days that keep us from using economisers.

[Dallas Duster]

I'll assume you mean condenser fan cycling to control head pressure......

One gripe I have is alot of the older/new cheap small tonage units had no mechanical cooling lockout. There is no reason to be running mechanical cooling under 45-50 degrees with a unit that can provide 100% economize air.

Most RTU's don't need any fan cycling running into 45-50 degree ambient cooling. So you should be locking out mechanical cooling. And if don't have it, then add it.

What application do you need 100% economize and sub 45 degree ambient mechanical cooling?

What if it`s raining outside?

[hvacpope]

anybody using ICM326 head pressure controls? http://www.icmcontrols.com/ProdImages/ig_LIAF094.pdf

installed a few, like them better than just a fan cycling swt, they work similar to a Carrier MotorMater but are less $$$.

[Dallas Duster]

anybody using ICM326 head pressure controls? http://www.icmcontrols.com/ProdImages/ig_LIAF094.pdf

installed a few, like them better than just a fan cycling swt, they work similar to a Carrier MotorMater but are less $$$.

Wouldn`t work on this unit but I would use a pressure switch thou.

[qwerty hvac]

anybody using ICM326 head pressure controls? http://www.icmcontrols.com/ProdImages/ig_LIAF094.pdf

installed a few, like them better than just a fan cycling swt, they work similar to a Carrier MotorMater but are less $$$.

I have used them for strait A/C, can't remember the part number right now. They work very well.

[targetman]

Wouldn`t work on this unit but I would use a pressure switch thou.

There is a Penn pressure switch installed.

[Dallas Duster]

There is a Penn pressure switch installed.

Yeah I know and it`s only on circuit #1 so when circuit #1 fails #2 fails too. But that`s how ac go unless you put another switch on in parallel. But no reason to do this but then again your CLO`s are jumped out.

[targetman]

Yeah I know and it`s only on circuit #1 so when circuit #1 fails #2 fails too. But that`s how ac go unless you put another switch on in parallel. But no reason to do this but then again your CLO`s are jumped out.

Did you notice the piece of sheet metal added between the two compressors/fans? The two fans were split on two contactors. Pressure switch is tapped into circuit one. It's breaking the contactor coil for #2 condenser fan.

[Dallas Duster]

Did you notice the piece of sheet metal added between the two compressors/fans? The two fans were split on two contactors. Pressure switch is tapped into circuit one. It's breaking the contactor coil for #2 condenser fan.

I did see that but I just figured someone lost the panel and had one fabbed up. But yeah like that`s going to work, hope it wasn`t your guy.:bump:

[targetman]

I did see that but I just figured someone lost the panel and had one fabbed up. But yeah like that`s going to work, hope it wasn`t your guy.:bump:

Yea. I think it was Senior Tech knows it all.

[Dallas Duster]

Yea. I think it was Senior Tech knows it all.

Did he even try to put a stack on top to keep the fans from rebreathing?

[targetman]

No he did not. I'm thinking I'll be going back and trying to correct the whole mess.

[rucomfy101]

Just a thought, but you probably realized as I was reading your thread...
the field added panel between the CFM 1-2 has effectively cut your condensing coil surface in half, thus the high pressure trip.

[targetman]

Just a thought, but you probably realized as I was reading your thread...
the field added panel between the CFM 1-2 has effectively cut your condensing coil surface in half, thus the high pressure trip.

Thats coming out next time I'm there.

[MUNC]

On these units in the past, stopping one fan with contactor or switch and running the other really gets the stopped blade cooking backwards. When it calls I've seen the results of broken shafts,torn motor brackets,shorted motors ect,ect. Had one start and run backwards after one leg opened internally. Really like those ICM 3... fan cycling controls. Whould it not be better to just leave the sheet metal in if shutting down only one fan???
Just thinkin out loud here

[jjbergeron77]

Maybe I am not seeing the picture well but is that cap tube for the fan cycling switch pinched between the condenser coil and the condensing section divider?

[timebuilder]

Most of the popular two stages units will run one stage of mechanical cooling as the second stage of cooling when in economizer mode. So I would say that condenser fan cycling should be used.

Kevin


It's climate - dependent, IMHO.

I would install the low ambient controls because so often, while the econs are not being set up or checked out properly, there is a need to maintain head pressure when mechanical cooling inevitably does come on as that second stage call arrives.

Story time:

I find that the economizers are set by the installers, who often don't know Jack or the rest of his family.

A few months ago, I found two new Coleman-style York RTU's with some problems, and when I investigated I found two distinct mistakes:

1) the baro dampers were installed backward. Hot outsie air was blowing into the store wnenever the door opened.

2) The enthalpy sensors had never been moved from their shipping positions on the economizer structure. The econs were installed and plugged in, but that's it. No setup, and the enthalpy sensors were exposed to return air.

The reason: there was a BIG label right there telling the installer what to do. It was in..


(wait for it)



ENGLISH.

Okay, I had to vent.

[rucomfy101]

Take pride in what you do and in what you know and that you took the time to set it up the right way. Been there and done that.

[jjbergeron77]

I think the carrier condenser coils are split top and bottom, not left and right so if one fan was running on either side of the add on divider it would cool half of 1st stage condenser and half of 2nd stage condenser. Both stages have the refrigerant enter on the same side of the coil and travels full length to the return bends on the opposite side.