multiple HVAC vs. zoning

[Nonny]

We've been looking at homes here in the Las Vegas area and I've noticed something that seems different from other areas where we've lived. In many of the newer homes we've visited, there are

2, 3 and even 4 furnaces, each with split A/C units; I would have expected to find just 1 or perhaps 2 units and then zone dampers. Which would be considered to be a superior system?

One thought is that its possibly considered more energy efficient to install (4) 2-1/2 ton to 4 ton units than to install a couple

4-5 ton units and then have dampers up in the attic, where it's both hotter than Hades and difficult to reach for maintenance. Could this be possible? I find it difficult to believe that purchasing and installing 4 furnaces and A/C units is less expensive than one or two larger ones with zoning.

Would a system with 3-4 individual, smaller, units give better humidity control (hint: it's 6% RH here today), better energy use or better energy management? The systems we've seen are all on a typical VAR meter and not a TOU/Demand meter.

What gives?

Nonny

[Oren]

Single or two story?

A local fireman (Captain) built 5000 s.f.. single story with just two AC units. The master side had a separate unit and the children / guest side had a unit. It was "zoned". (multi t-stats) He did the same for _three_ tank less water heaters -- a heater for the kitchen demand (zoned) (Hendersen, NV).

If you write children's book, four units may be needed for such a large home (Las Vegas)

[swarga]

Nonny,

A zoned system would be better depending on the home. Most builders in Vegas, (just like here in the Phoenix area) put in the cheapest ac units they can buy.

An air conditioning system that can respond to zoned controls would cost more, require skilled labor to install the system including the duct work and someone would actually have to perform the calculations to determine what the right amount of air is for the home and then balance the air.

They way they do it is cheaper for them in the long run, not cheaper for you.

Good zoned systems work very well, however I have seen several where they left a zone or two disconnected.

The attics are hot but insulating the duct itself is one way to combat that issue.

Trane has a system that I really like, it works like a 2 ton unit when the load is light and when the load is great it is a 5 ton system.

If the builder had installed two of these instead of 3-4 small units you may have saved money on energy.

Since your in Vegas look up Frank Vigil, he taught building science for years and worked with some AC companies to help them become more energy efficient, however he is now playing photographer as the contractors are interested in making money, not saving you money.

------------------------------------- Scott Warga ACSI American Construction Specialists & Investigations Arizona

------ _o

---- _ \

[gfretwell]

I have 3 A/C systems in my house. One central system would probably do the whole thing but I just use that to keep the house livable (set fairly high and on a timed thermostat that goes higher). Then at night we have a separate mini-split in the bedroom we only use when we are sleeping, set pretty low. The 3d is in the back room that we seldom use and do not really air condition unless the kids are here. Mini splits are getting so cheap, the payback is fairly fast and Obama will give you 30% back right away.

[jamesgangnc]

Surprisingly the price difference is not significant. The low volume on zone equipment keeps it's price high while the high volume of regular systems keeps their price down. Also it's harder to find service guys that really know what they are doing with zone controls.

3 or 4 seems excessive but I prefer several independent systems my self because when one is broken you still have some conditioned air in part of your house. Gives you time to shop for a good service guy and a reasonable price. When you only have one and it's January you pretty much are at their mercy.

[keith]

Got a good site for more information? These sound like a reasonable option for the currently unfinished space over my garage that I'm in process of converting into my shop. I was just going to tap into the upstairs air handler (it's in the area, already), but this may be an even better solution because it would help keep dust out of the res of the house. Perhaps simpler, too.

[jamesgangnc]

Just search, you'll find plenty of them. I don't think they are all that cheap yet though. However if you're making an upstairs shop having it's own system is probably a good idea in general.

[ransley]

Where is it 6% RH, maybe in the desert so humidity control isnt an issue but that sounds just to low to me, here its 91% RH inside, so I just turned on my AC to get it to near 60%. If humidity is an issue more units could help by just running one, but each each system uses electriicity even when not in use, and 4- 1/2 Hp motors will be alot less efficent than one 2 hp motor I would guess. If you got the expensive VSDC motor I would think one unit could be zoned, but get the 10-15 yr extra warranty

[Roger Shoaf]

If you are in Vegas, another idea would be to think about swamp cooling. With low humidity, these units will cool the house cheaper than AC.

[keith]

I see plenty of them, but there is little real information (or perhaps too much, spread all over). I'd like to know what the installation is like. What sorts of infrastructure has to be in place. Is it a DIY sort of thing? I see some have done it themselves and then had an HVAC tech charge the thing.

As far as "cheap", they look to be in the $1K region. Just as a guess, I should be able to get by with a ton (400 sq.ft., perhaps). I hadn't considered this sort of thing before because deed restrictions forbid window units. This would be a natural for the shop, but I want to be able to convert the space to another bedroom down the road (I may move and a fourth bedroom would be a selling point in a 3-1/3 bath house ;-).

[chaniarts]

pretty easy. a small pad on the ground or screwed into a platform on a balcony or the roof (if flat). you need about a 2" diameter hole in the wall for the tubes, and i think a 20 or 30amp 240v line. you need a cutoff switch in a box within reach of the outside unit.