"Custom" Air Handling Units

[lowedogg]

These days, everyone claims to have a custom air handler. Even Trane, York, and Carrier are calling some of their stuff custom. Then there is the whole pack of guys with sort-of customizable, pre-engineered equipment (aka: Engineered Air, Munters) that call their units totally custom. How is one to distill the truly custom unit manufacturers (aka: Buffalo Air Handling, Mammoth) anymore without actually having had some prior experience with them on a project?

One can always write a very tight spec and used hard dimensioned air handler drawings in the contract documents, but listing the acceptable manufacturers can save a lot of headaches and uneccessary battles during construction. How do you find out who is really providing a custom unit?

 

[lownox]

Tough question, but I ponder that it comes down to how much crap is stuffed into the unit.

Some companies will manufacture a unit with the only customizations being pully sizes and air volume (blower size). While companies like Des Champs will build you just about anything that you want... dehum, heat recovery, cooling, heating (gas or hot water), etc...

Main limitation is what they are allowed to build based on the agency listing associated with the unit. For example, direct fired heat is tested to ANSI Z81.4... while a generic cooling unit may only be tested to UL1995.

Very tough question. I can't wait to see more replies to this one. Could be some good insight coming.

 

[KiwiMace]

If the unit does what you want, who cares?

The ideal situation would be that for every scenario, there would be a mass produced packaged air-handler that met every requirement. As this is clearly impractical outside of a specific range of performance, manufacturers stack together pre-tested modules to meet the requirements and be as mass-produced as possible. In situations where this falls down, you get the custom units, which you then need to extensively factory and field test, dick around with the controls, leak test, align, etc.

My opinion is that it will be cheaper, easier and probably better to let the manufacturer provide a packaged, or modular system before you enforce a custom built-up AHU.

Also, one could argue that a specific arrangement of modular units could be considered 'custom'.

 

[UtilityLouie]

One of pro's of the custom units is the unit base. Typically the "custom" units from a Temptrol, Huntair, Ventrol, Governair, etc have a base made from a structural shape. The others typically have a base made from sheet metal formed and welded into a shape...\

Other differences I've noticed are:
- Custom manufacturers truly offer any material type/thickness in the construction. Commercial "custom" units are typically limited by the forming ability of their equipment (i.e. 14 ga floors instead of 12 ga floors).
- Custom manufacturers offer limitless size options because they purchase coils for the unit itself. Commercial "custom" seem to still try to fit to their standard coil sizes to keep their costs down.
- I've purchased Commercial "custom" with a Wing integral F&B vertical steam coil in it AND I've purchased a custom unit with the same style of coil. There was a WORLD of difference. We had racking problems with the F&B dampers in the commercial unit and we could never discern why (installed poorly, handled poorly, poor initial quality, pipe stress on the coil connections). We investigated all the possibilities we could think of... With the custom unit, it worked right from day 1...

If you're looking for a basic unit with low airflow in a standard install, commercial custom is probably OK. If you have any special requirements, require something other than manufacturer standard equipment, size constraints, weird inlet or outlet connections, extra equipment, etc... custom is the only way to go.

 

[lowedogg]

Well, if you have an application that does require a custom unit, then it is in the engineer's (and client's) best interest to limit the competition to custom unit manufacturers.

If you get nominal sizing rather than custom sizing and you have a very specific set of requirements and tolerances, then chances are pretty good that you will not get what you need on the job. A modular manufacturer will beat a custom manufacturer on bid day every time. It would be pretty crappy to work with the custom guy to design the job and then let a modular guy come in and take it away.

There is a right and wrong time to use a custom unit. My question is not "should I be using a custom unit" but rather "how do I get the custom unit on the job without having to reject 20 submittals". Like I said, a tight spec will get it done in the end, but that manufacturer list will save us all a lot of heartburn.

 

[KiwiMace]

If there are specifications that need to be met, then you need to specify them or neither a custom or non-custom manufacturer will give you what you want.

However, I am agreed that the generic manufacturers would be inclined to offer a product anyway, meeting the performance and possibly not the details.

The only way you can possibly avoid this is to be very clear in your documentation about what is important, and call ahead to see what your suppliers want to offer before sending them an RFQ.

 

[ChrisConley]

If you really just want to get rid of the modular guys, find something they can't do and hard spec it.

For instance, most of the modular guys can't do custom paint. Custom paint (epoxy, colour, whatever) is a relatively inexpensive add ($1000 per unit depending) but most of the modulars can't do it.

The hard part is also explaining why you need the custom paint without saying :because I don't want a modular unit.

 

[Jabba007]

Simply control the bidders with a list of acceptable Manufacturers, then have the spine to tell everyone else "No."

Jabba

 

[HVAC68]

How do you define a "custom" unit ???

There are manufacturers who can make AHUs practically to a particular length to the mm They can add any section that you want. In fact, the software program allows one to actually "engineer" and "custom-build" an AHU - obviously within certain parameters. Materials of construction, motor makes, filter makes, etc., etc., can all be "custom-built" too.

Finally, it all boils down to what you want and how you specify the same so as to get a commercially viable and optimum quote.

HVAC68

 

[daly1]

custom ahu's used to onlyb use thermal breaks in the wall construction. Is that still something that spearates the MCC from the Des Champes--or does everyone do thermal break now?

 

[willard3]

Custom units are specified when you have custom requirements, ie, special fan, coil, heat recovery, filter, resistance to corrosion, low noise, bearing life, drive type, geometry and etc. By the time you get here with the rep for the Buffalo unit (for example), you pretty much have a dimensioned drawing. The factory will send you a dimensioned drawing with your requirements that you will import to your drawings.

Write a careful specification and enforce it. You are the Engineer of record and the rep from the commercial vendor is not.

The commercial unit will not meet the spec or comply with the drawings: what's the problem? Reject submittals that do not comply with the contract.

 

[AbbyNormal]

Engineered Air will custom build whatever type of air handler you want. Carrier will use their Racan division to do whatever you want, Trane will do the same.

With something like a Trane MCC series, they are stuck with basic module sizes, they gve you a couple blower sizes and you can mix and match whatever type of module you want. Trane will have a couple coil sizes, then give you more or less rows and fins etc, even the magic fins and the 'turbulators'. I believe Trane has their custom build division that is not constrained by the limits of the MCC series.

Engineered Air will alter their cataloged cabinet size, alter the face area of the coil as needed along with rows and fins, put in whatever type of fan wheel is needed, all the bells and whistles you want. I spent a few years in the design department there, can be a lot more work designing up a custom air handler than a custom packaged heat/cool unit for the roof.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

EngA will build stuff from the ground up as well. You want a penthouse on top of a paper mill with a couple 3 million Btu boilers inside, large diamter heat wheels and 150 hp plug fans you got it.

On their gas fired equipment the designs are going to revolve around some standard size heat exhcangers, but it can still be highly customized even with the standard heat exchangers.

It is pretty easy to write a spec to preclude modular equipment by say Trane, however you may have to reject about 3 rounds of submittals before the trane rep finally says uncle

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[HVAC68]

Saiver, Italy manufactures one of the finest AHUs in the industry and they can be custom-built. The selection program is so powerful that you can actually select the physical dimensions of the unit yourself - obviously, within certain constraints to meet good engineering practices.

HVAC68