Direct Expansion (DX) versus PTAC's

Mechanical & Electrical Plan Vignette and Multiple Choice

Direct Expansion (DX) versus PTAC's

Postby vrcat25 » Mon May 08, 2017 1:06 pm

Is there a difference between a DX system and a PTAC? Also, what would be a good source that explains all of the different HVAC systems along with their pro's and con's? Would MEEB be the best source for this?
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Re: Direct Expansion (DX) versus PTAC's

Postby corbismyhomeboy » Tue May 09, 2017 5:14 am

Check the book Mechanical and Electrical Systems in Buildings. It's listed in the BS NCARB guide. There are tons of diagrams that are extremely helpful! The book may or may not have a pros cons thing like you're looking for but the diagrams are helpful nonetheless.

Also check Jenny's notes for a chart - I remember reading over a chart in her notes that lists different types of systems and their differences.

Not sure there is really a pro con list like what you're looking for because it really just depends if a system fits your clients needs, building, occupancy, etc., so a pro for one might be a con for another. There is no "best" system, just a bunch of options you can mix and match.
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Re: Direct Expansion (DX) versus PTAC's

Postby vrcat25 » Tue May 09, 2017 5:44 am

corbismyhomeboy wrote:Check the book Mechanical and Electrical Systems in Buildings. It's listed in the BS NCARB guide. There are tons of diagrams that are extremely helpful! The book may or may not have a pros cons thing like you're looking for but the diagrams are helpful nonetheless.

Also check Jenny's notes for a chart - I remember reading over a chart in her notes that lists different types of systems and their differences.

Not sure there is really a pro con list like what you're looking for because it really just depends if a system fits your clients needs, building, occupancy, etc., so a pro for one might be a con for another. There is no "best" system, just a bunch of options you can mix and match.


Thanks Corb! I actually already have a copy of "building technology mech and elec systems" by stein. It's the second edition so i'm not sure how up to date it is. I did find some of the advantages of DX, ALL AIR VAV and dual duct high velocity systems, etc. For example, a dual duct high velocity is flexible and can heat and cool at same time but it's inefficient and expensive. I'll take a look at BTMES and see if it has a more in depth explanation because what i found in Ballast is a little too general.

As for DX vs PTAC, are they the same thing?
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Re: Direct Expansion (DX) versus PTAC's

Postby corbismyhomeboy » Wed May 10, 2017 11:07 am

As far as I know, DX is like a rooftop unit with ductwork running to different rooms where PTAC is fully contained system that only serves one room like what is in a hotel room.
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Re: Direct Expansion (DX) versus PTAC's

Postby vrcat25 » Wed May 10, 2017 12:29 pm

corbismyhomeboy wrote:As far as I know, DX is like a rooftop unit with ductwork running to different rooms where PTAC is fully contained system that only serves one room like what is in a hotel room.


hmmm...the ARE review manual says about DX "this is a self contained unit that passes nonducted air, which is to cooled, over the evaporator and back into the room." Also, "Direct expansion units can be through wall types, roof mounted or packaged."

The "through wall types" kinda thru me of and you're right that they can be roof mounted, but they also say that they are "self contained". I understand what a PTAC is, but i'm still confused with a Direct Expansion. Thanks for trying. I'll check out a few other sources.
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