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| Subject - 3 phase VS single Phase | |
| David Hyatt |
(This was an email directed to me any ideas?)Need a good second opinion or sixth since I have received conflicting information. Single phase vs. Three phase. We have a large 11000 sq ft home with no current hvac equipment. We want to equip it only once (estimate of 35 tons) and also correctly with no regrets in the years to come. The hvac contractors are not in agreement on the single or three phase equipment question. The electrical contractors are all in agreement that the initial start up will be more expensive with three phase but they are not sure if we can regain our intial investment over time through lower power consumption. The electic providers can't seem to shed much light on the subject. Can you? Do you think the commercial demand meter with three phase will save operation costs vs the residential single phase? Are there any formulas written on the subject? |
| kbsparky | Most utilities only have commercial rates, including demand charges for 3-phase service. I am not sure about demand charges being assessed on "residential" rates, and that one thing alone can make a significant difference in energy charges. Most Public Service commissions don't have such charges in their approved rate structures. Of course, there may be exceptions. While 3-phase units may have slightly lower energy usage, buying that energy at commercial rates with their accompanying demand charges can be quite expensive indeed. 
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| lctrc789 | I have seen only one application in a residential use where they used 3 phase power for a home and that home was a little larger then the home you are referring to. The initial cost was very expensive and the utility enginner had to OK the whole deal. I would recommend calling the utility company give the the total demnad load on this house and then see what they suggest. The homeowner will have to say yes or no here on the cost for the extra power and have the utility comany find out the difference in rates and costs, I have always dealt with the enginners and have never had a problem with them on this. The home I am refering to was 12,000 sq. feet with a pool, tennis court lights, outside lights, A summer house (if you could call it that) and two ponds. 4 Furnaces 4 central air units as well, Initially they wanted us to install a 800 amp disconnect single phase till they seen the total load demands and that did change their minds. |
| wareagle | David From my past experience the breaking point for 3 phase equipment has been a 5 ton unit and up. it may be 7 1/2 tonb and up now. Normally it the uitlity that decides. In your post you said "The electrical contractors are all in agreement that the initial start up will be more expensive with three phase but they are not sure if we can regain our intial investment over time through lower power consumption." If you are expecting to save money on the electric bill by using a 3 phase unit you won't. You are buying BTU's. The cost will be the same for an equal BTU machine. |
| wareagle | quote: |
| JimmyDee | Primary savings from the 3 phase system come from the cost of compressor motors for air conditioning. 3 phase is also less expensive to repair. Jim |
| wareagle | see new post |
| JimmyDee | quote: Where??????  Jim |
| PEI | I pretty much agree, that you are buying BTUs and there will be negligible difference in KW usage. So, if you were buying "x" amount of kilowatts, where is the price break - in single or 3-phase ? That will put you at the mercy of your power company's rate structure. But, one thing no one has mentioned, do you have the 3-phase option at the street? If the power company has to bring it several blocks to your house, forget it! You may get an invoice for about $6,000 or more and possibly a transformer charge which may be double that. |