10 ton Carrier Cond on a 7.5 AHU

[Six]

With a 7.5 ton TXV. R410A

This is on sight at a rig on a SCR house.

Curious as to why they would size these units like this.

[Cooked]

Doesn't seem like a good idea.

[Six]

Im tryinf to wrap my head around it. Brand new equipment from a major manufacturer of Drive houses.

High head, low suction, managed to with some adjustment get decent superheat.

Some tool pusher said they've always been like that ?

At least install a ERV on the damned thing.

[Dallas Duster]

Im tryinf to wrap my head around it. Brand new equipment from a major manufacturer of Drive houses.

High head, low suction, managed to with some adjustment get decent superheat.

Some tool pusher said they've always been like that ?

At least install a ERV on the damned thing.

Does it pull in any outside air?

[AddMore22]

Does it pull in any outside air?

No... No inside air.

Are you sure it's 10 ton comp? Is it a wall pack or split?

If It is a split , is the ahu broke into stages?

[Six]

Does it pull in any outside air?

No it's on a Natural Gas Drilling Rig. It's a trailer sized building where all the VFDs ,breakers, PLCs and disconnects are located. It's basically sealed with the exception of the occasional rig hand walking through.

Checked data tags, 120k Condensers and 90K AHUs.

Because of the drives they usually operate under a decent amount of load. According to a couple a rep from the company that builds the houses it's done for high Ambient reasons......huh ?

I responded with that doesn't make any sense and they're are better ways of doing that.

Who knows.

With it running it's what you would expect from a system that's that mismatched with an oversized compressor.

I told him if you " HAVE " to do this install ERVs.

[flange]

sometimes they go for colder coil to get lower dewpoint coming off of it. this changes performance. look at submittals. on units with outside air or infiltration issues. I have seen 2000 cfm air handlers mated to 12 ton condensers, delivering 45 degree air

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What rig is it? On SCR houses the cond. units are right near the large transformers and 9 times out of 10 it's Insanely hot back there. Perhaps they over sized to adjust to the outside heat.... Does it have a receiver ?

Is is a specific systems ?
Or a Custom Cooling Controls?

[AddMore22]

Attachment 272771

[Six]

What rig is it? On SCR houses the cond. units are right near the large transformers and 9 times out of 10 it's Insanely hot back there. Perhaps they over sized to adjust to the outside heat.... Does it have a receiver ?

Is is a specific systems ?
Or a Custom Cooling Controls?

Not a Custom Cooling Controls unit. Not a pressurized room either.

Sure they're located next a big Xformer and a huge set of brake resistors...I think that's what they are.

They absorb reverse EMF when the motors spool down and stops. Discharges the excess heat through louvers.


Oh and No receiver. Just your basic commercial grade 3 phase mismatched unit.

High load inside and high load outside is the typical application.

I guess the reason could be High Ambient but like I said there are better ways to address high ambient issues. How about installing a condensing unit rated for more than 90 degrees Fahrenheit ?

They're actually moving away from the splits and going with "homemade" wall mount and package units.

Made in Houston and not even UIL approved. I think the homemade ones are made by a company called "Mustang" I could be wrong.

Got a good look at one of them the other day.

Just a hodge podge of motors, coils, contactors and a Copeleand compressor. Whatever Johnson Supply carries.

I mean that. It looks like they went on a shopping spree through Johnson supply and then went back to the shop and built a A/C unit.

Complete junk IMO. Its the inevitable consequence of letting the bean counters call the shots.

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Lol... The company I work for builds custom units for that exact reason .... I do not work in shop, so I don't know all the details.

[Six]

You work offshore right ?

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Most of the time

[Six]

Hmmm..do you work for custom ?

[Six]

Compessor being oversized runs higher head under normal loads.

High ambient and high load doesn't improve that. Its just a bad idea.

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I work for Nance.

And I'm not sure for the reasoning behind that other then some engineer pencil whipping something.

[Six]

Can you do a fellow SCR AC tech a solid and ask around. Maybe you could gwt a better answer than I did.

410A pressures were 410 discharge with 90 suction. 90. Thats well below freezing and ambient was over a 100 and return at 78.

Crazy.

[AddMore22]

Huh.... Is it a scroll? And no kind of staging or unloading junk? What drilling company?

[hcong]

What makes the AHU a 90K btu unit? Is the AHU a furnace or just a fan with coils? You should see what the fan CFM rating is...

I can think of a few reasons...

1. They need 120K of cooling but only need around 3000 CFM, possibly lowering the CFM to get more latent cooling.

2. They have minimal duct work and thus have low static pressure loss so they can get a smaller AHU with a smaller fan but that smaller fan can still meet the 4000 CFM.

3. They made a mistake.

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Fan coil.