Single phase vs. three phase air conditioning

[Big Al]

I have a house with both single and three phase electric. I'm thinking of adding air conditioning. Pros and cons of three phase?? It's a small house, two tons should be enough.

Al

[Bob]

Your average residential HVAC technician will have a harder time working on it, and parts may be harder to get.

[Bob]

Meant to say: "Your average residential HVAC technician will have a harder time working on

3 Phase, and parts may be harder to get."

[Stretch]

Al, I doubt you will find many 2-ton Three phase units available. Most three phase units are 3 ton & up. Go single phase.

Stretch

[Bob]

Good point. I just looked at the Rheem/Ruud specs and 3 tons is the smallest with 3 Phase. When you get into higher SEERs, there's nothing 3 Phase.

[Big Al]

I found a two and a two and a half ton. What about operating costs? Is three phase more efficient or less expensive to run? My three phase is one cent a KW more than single phase.

Al

[John Hines]

Not enough to offset that over the life of the unit.

[SQLit]

Let your contractor choose what is best after doing the manual calculations. What voltage is the service? Are you saying on a small house you have 2 services? Check with your utility for rebates and deals offered. Mine has deals all of the time.

I am unaware of any 3 phase units that small. The smallest I have ever seen is 3 tons. No over is not a good idea.

[Bob]

If your 3 Phase "is one cent a KW MORE than single phase", why would you want 3 Phase. If you have extra money you want to spend, PayPal me some. What brand of 3 Phase comes in 2 ton?

[Big Al]

calculations.

The three phase is 200 Amp, 240 volt. I didn't look at the single phase to see what current it is. Two separate meters, and two separate services but billed on one account. I'm the only house with three phase power in the neighborhood. That can't be good:(

Al

[Tekkie®]

Big Al posted for all of us... I don't top post - see either inline or at bottom.

Are you SURE you have three phase? How many wires coming in the house?

[Big Al]

Yes I'm sure. Four wires come in.

Al

[MC]

I have work in commercial field. Many problems could have is a brownout or other problem on one of the phases which when other phases still have power could damage the compressor motor. We had to many time have phase protection on the power to these units that if a problem happed as such would kill power for all phases. The equipment can be costly and therefore may not be worth it for residential use.

[hallerb]

i seriously doubt he has 3 phase, more likely 3 wires coming in. unless he lives in a commercial area.

yeah phase failure imbalance can cause all sorts of troubles, with wild voltage swings. company I used to work for had that trouble, the company copiers didnt like 30 volt changes:( We sold copiers and I was one of the techs, it was a ongoing trouble finally sloved when the company went out of business....

[CJT]

I think that's pretty unusual, so I'm curious what you use it for (other than considering using it for AC).

[~^Johnny^~]

Not with Copeland compressors.

I have built 2-ton DH's withe Copeland (coplemetec) pumps, rated at 3 HP, R-12, 2 tons, medium-to-high temp.

Of course, that was many years ago, and these were salvaged from commercial units.

But three phase exists all the way down to fractional horsepower, if you need it. Price is the main stickler. Go with what is cheaper (and cheaper to repair/replace, etc).

The reason you don't see too many residential 3-PH units under 5 tons, is 3-PH power is rare in residential services, so there is little call for it. But 3-PH motors and compressors are readily available, all the way down to two tons or less. Fifteen to Thirty years ago,

3-PH motors were generally cheaper than single PH. Now, I dunno. I don't do it no more.

Grab the latest Grainger catalog, and see what compressors are available, and for what prices.

[~^Johnny^~]

Nope. It's easily "hacked together" (for lack of a better term). Grab an "artificial neutral", by connecting three equal resistors in a WYE. Run the node of the WYE (the "artificial ground) through a current sensor, to the real ground, or neutral. A preset unbalance will develop a current offset from artificial neutral to real neutral or ground, and trip the protective relay which will open the mag (contactor)

A few bucks worth of Radio Shack parts, and a 16 year old nerd down the street are all you need.

[RP]

Or you could just buy one. All of our 3 phase units come with phase protection consisting of a 2.5" x 2.5" card with very few components mounted on it. Cost about 15 bucks apiece. How many do you need? BTW, they will be marked up before you get them :)

Richard Perry

[Stretch]

John Wrote

"Not with Copeland compressors.

I have built 2-ton DH's withe Copeland (coplemetec) pumps, rated at 3 HP, R-12, 2 tons, medium-to-high temp.

Of course, that was many years ago, and these were salvaged from commercial units.

But three phase exists all the way down to fractional horsepower, if you need it. Price is the main stickler. Go with what is cheaper (and cheaper to repair/replace, etc).

The reason you don't see too many residential 3-PH units under 5 tons, is 3-PH power is rare in residential services, so there is little call for it. But 3-PH motors and compressors are readily available, all the way down to two tons or less. Fifteen to Thirty years ago,

3-PH motors were generally cheaper than single PH. Now, I dunno. I don't do it no more.

Grab the latest Grainger catalog, and see what compressors are available, and for what prices. "

John,

Yeah he could build his own air conditioner from parts he got at Grainger. But he wants to BUY one that is already made, from Lennox or Trane or Carrier, etc. THEY don't make many 3 phase units less than three ton. THAT was the question. I realize it COULD be done, but a homeowner isn't likely to do it, it would make no economic sense. I don't make my own units either. cheaper and easier and better to buy one from a major manufacturer.

Stretch

[MC]

When my brother had his house built, he wanted 400 amp service which was not as common then as now, Utility company had to use four wire entrance as the only type they had that would suffice for that amperage. One of the wires was not used.