HVAC Electrical Specifications

[wilsonv]

Hi, may be I'm missing something. Sometimes when I asked for the electrical specifications/requirements on an HVAC unit condensing/AHU, the people give me the tons. Like 4 tons 15 tons. Is there any way that you can size the min/max protection on these units just having the capacity in tons?. If no what may be the reason on refering to the capacity in tons when all I need is to protect the motor/compressor?. Just in case I'm not interested on converting tons to watts or BTU.
Thank you.

 

[HVACctrl]

I think they need to give you electrical specs on the compressor, fan, etc... or, better yet just the overall electrical specs on the unit. THere may be some what to SWAG electrical requirements knowing the tonnage, but I'm not really sure it is precise enough- if it exists.

Ed

http://www.engineerboards.com

 

[imok2]

Most all units should have a brochure with it or is avialible from the mfg on the Internet, but you need the model number and make unless they quite old( like before the Internet was popular)

 

[Yorkman]

It sounds like the individual has a misunderstanding of your requirements. The tonnage of an AHU or condensing unit will not provide you with the data you need. Tonnage won't tell you how many condenser fans it has, the number of compressors, if the compressors are part wind or across the line start, single point or dual point connection. You're right in questioning that type of response.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[quark]

You guys hit the nail on the head. In this abbreviation era, people have less time for all things. Worst part is that I still hear some engineers estimating the characteristics of a pump by HP. I hope you guys are not so unfortunate as I am.

 

[wilsonv]

Thank you all. That is my understanding too, but I just want to double check with the experts.

 

[KiwiMace]

Note also that converting the tons to kW directly will give you a wildly high figure by around 4 to 6 times actual consumed power. The multiplication factor (COP) varies for each unit. Reiterating imok2; Get the model, look up the manual.

 

[trashcanman]

Do not accept such garbage. Request in writing the electrical cut sheets for the HVAC equipment. CYA.

 

[KiwiMace]

Having the mechanical engineer produce the electrical specification sheets for the electrical engineer is a very common practice in consulting circles. I am often at a wonder why the electrical engineers in a building services practice desire to distance themselves from the mechanical equipment for which they supply service. Given all the time that the sparkies should have on their hands from not having to produce real drawings, you'd think that they'd be looking for something to do.

 

[HVAC68]

As a practicing HVAC engineer, I always give the electrical engineers the feeder list.

i.e. no. of each equipment and the rating of each.

Insist on this.

For bigger equipments, there may be 2 power inputs for a single chiller, in some instances.


HVAC68

 

[MintJulep]

UL Standard 1995, paragraphs 35, 36 and 37 lists the information that should be included on HVAC equipment nameplates.

The list includes everthing electrical types should need to know to size wires, starters and protection.

 

[imok2]

Thank you all. That is my understanding too, but I just want to double check with the experts.

Gee, I think I just got a promotion! :>)

 

[quark]

From expert to which position

 

[wilsonv]

well earned imok2, but the pay check did not have the same luck... quark is from the mechanical engineers. Like I said before I just want to be sure that I'm not missing a detail on the HVAC system.

Thank you all for your help.

 

[stanlsimon]

There are rules of thumb that will get you into the ballpark for schematic design developement type drawings. 1.2kw/ton will get you a conservative running load amps (RLA) for general applications. However real construction documents require more specific information.

An HVAC unit may have multiple components including but not limited to compressors, fans, heaters, controls, etc. Starting current (which is close to locked rotor amps(LRA)) of unit components may be 5 times component RLA so take a look at voltage drop under starting conditions. If feeders are sized only for MCA then starting voltage drop can be so bad that a compressor will stall. Reciprocating compressors have an especially high initial amp draw.
Generally heating components will not operate at the same time as cooling, but this is not always true. Demand the catalog electrical cutsheets and a wiring diagram that shows the field wiring. The manufacturer may supply a disconnect, but it may arrive lying in a box and require installation.

After all is said remember that competive bidding allows substitutions that will give you a different manufacturer and of course varying ampacities, that is why the electrical guys get the big money.