Why are the heating/cooling units in the southwest located on the roof

[jasno999]

I noticed on a trip out to Las Vegas that all of the residential areas have homes with what looks like the air conditioning unit located on the roof.

Are these air conditioning units that I am seeign on the roofs of the houses? If so why are they located there?

If not what are they? (Solar hot water heating???)

 

[RossABQ]

Those are swamp coolers, evaporative cooling units (no heat).

 

[IRstuff]

Some might be, but not all.

The problem may be getting more efficiency out of the exchanger. The ground is quite hot during the day and the air is generally stagnant. Putting the exchanger 30 ft into the air may result in getting a better air flow and better efficiency.

TTFN

FAQ731-376

 

[simsd]

I thought it was just a matter of room and convenience?

 

[IRstuff]

A condenser only occupies about 6 sq. ft., hardly challenging, even with today's micro lots, not to mention the added weight and plumbing and power needed to facilitize such an installation. There has to be a more engineering oriented requirement.

TTFN

FAQ731-376

 

[MintJulep]

My initial thoughts were similar to IRstuff's.

It might also be to get the coils away from wind-driven sand, which can be quite abrasive to aluminum fins.

 

[RossABQ]

There are two things that motivate builders: cheap and easy. With a typical swamp cooler system, the return air duct for the heating system is used as the distribution ductwork for the evap air cooling. Guillotine dampers are used seasonally to isolate the cooler from the RA header. It saves a bunch of ductwork to put the cooler on the roof, as the heating RA duct is in the attic.

I believe in Las Vegas, most people have both a swamp cooler and a refrigerated air system. The evap coolers give you cheap cooling up to the mid 90's, and the refrig system is used for truly hot days.

 

[PoorRod]

I don't think having both a swamp cooler and a refrigerated air system on a house is commom. There would be too many people who would run them both on a hot day, not understanding how they work. With the huge latent load, they would literally be pouring money down the drain in the form of condensate.

On the other hand, I have seen the two systems mixed before on a dining facility. Evaporative cooling was used in the kitchen as make up air for the exhaust hoods, and the dining are was refrigerated air. The key is to maintain the kitchen at a negative pressure so the air from the evaporative cooler never gets to the AC coils.

 

[BronYrAur]

I've seen these too and I don't remember seeing any water piping. I asked a friend who lives in Pheonix and he thought it was because most houses don't have basements. That's where most furnaces (or fan coils) are located in Northern IL. You never see residential rooftops here. It's probably just the cheapest option since you have no refrigeration piping, etc. Most of the units I saw were just "thrown" up on pitched roofs with cheap angle iron frames to level out the slopes.

 

[RossABQ]

Most of the units I saw were just "thrown" up on pitched roofs with cheap angle iron frames to level out the slopes.

The tell-tale sign of a swamp cooler on the roof is massive streaks of white salts running down the roof. Did you see that? If not, it definitely isn't a swamp cooler; sooner or later they always overflow! The stain is permanent too.

 

[AbbyNormal]

Roof top be hotter than the ground

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

 

[KiwiMace]

make it harder for all the dried out compulsive gamblers to steal all the copper.

 

[walkes]

It also may depend on the construction constraints. No basements for fans etc. because it may be too expensive to excavate. Closet mounted furnace/fan takes up floor space, so an attic or roof mounted unit that is out of the way may be their best solution, probably a pain in the butt the maintain for your regular homeowner though.

 

[berkshire]

Another interesting design constraint,
a local school has about 10 Carrier slimline units mounted on the roof, to stop the kids from kicking the condenser coils.
B.E.

 

[MarauderX]

The units seem to be mounted high for a number of reasons. The blower section is often close by in the attic, limiting the piping run. Setting the unit on the roof keeps it away from dust as well as give you some space back. The unit sitting in the sun is the same on the roof as it is on the ground... not much efficiency difference in the dry heat of the southwest.

And no they typically aren't 'swamp' type.

In other regions many units are on the ground because the main coil & blower section is nearby in the basement.

http://www.vanderweil.com

 

[FoMoCoMoFo]

those are usually heat pumps, done that way because its cheapest. you will also see whole subdivisions using split systems (condenser on a pad on the ground) sometimes it gets enclosed on 3 sides by house and a short L shaped wall, occasionally just by dumb luck its on the north side of the house. most home builders and buyers just don't care. a swamp cooler works great (PHX AZ. right now @ 1:18 PM - 109deg. 5% RH ) but you almost never see them in new homes. the people in those houses you saw are probably paying $300 +or- a month elec. bills this time of year.