Maybe someone can answer this.
Why is it that all forced air gas furnaces in the united states are driven by 110v half-phase motors?
It makes no seance to me, 220v motors are by their very nature more energy efficient.
There is no difference in efficiency. Many motors are 110 or 220 just by switching wires around. There could be a savings in wiring costs if it was a long run to the motor.
Not actually, in a split-phase system inductive loads (i…e.: motors, etc.) actually draw twice their rated power from the grid.
While the meter only records in watts it does not take into account the actual power-factor, good for the customer, but bad for the grid and the environment.
Look up specs on 1/2 hp 110v and 220v motors, you should see a difference.
BTW: Thank you for commenting.
What is a half-phase motor?
AFAIK, they are 110v (or 120v) because that’s the standard in the US. I didn’t think there was any difference between 110v and 220v motors–the amps will be different but the wattage is the same.
This isn’t a 120 versus 240 volt question, it’s a single-phase versus 3-phase question.
My understanding is that single-phase motors are only woefully inefficient compared to 3-phase motors when they’re used below their design load, otherwise they perform similarly. There’s also many different designs of single-phase motors and various uses of capacitors to correct power factor and improve startup. Many commercial rooftop HVAC units that have 3-phase compressors still have single-phase indoor blower and condenser fan motors.
The reason is cost.
Small single-phase motors are cheaper and the wiring is simpler. In cheap/simple residential or small commercial systems (which are unlikely to have variable speed blowers) those upfront dollars matter to the buyer. Also the electrical draw may not even be reported for the blower on Energy Guide labels since they’re more concerned about gas usage for heating or the compressor for cooling. The other factor is that 3-phase service for residential is basically unheard of in North America (Europe seems to have some of this but it’s definitely not universal).
This is the biggest roadblock for 3-phase motors in a residential setting in the US. 3-phase power only goes to commercial/industrial sites, and even there, the smallest motors aren’t typically 3-phase because of the cost reasons you mentioned.
If you want 3-phase power in your home (suppose you bought an industrial lathe at an auction and you’re setting it up in your garage), you need a 1-phase to 3-phase inverter. Many years ago that was just a 1-phase motor running on 220 from your house’s wiring, and powering a 3-phase alternator that fed your lathe what it needed. These days, you can buy a solid-state 1-to-3-phase inverter to do the same job.
Here for example is a high-powered 1-to-3-phase motor/alternator inverter.
I don’t suppose there’s anything stopping you from getting 3-phase service to a house, assuming of course that you have 3-phase primary distribution wiring out at the street. The problem is that the power company will have to do a special drop just for you with a 3-phase transformer (or three single-phase transformers), so they’re likely going to bill you as if you were a commercial operation, and they may also slap a demand meter on you as well, so there’s not going to be any cost savings for sure.
I remember reading an article about the UK being behind the rest of Europe in providing 3-phase power to homes. It seems that 3-phase 4-wire 230/400v service is fairly common in much of Europe for newer construction. Norway, France, and Belgium have some older 3-wire service with no neutral, and Denmark uses 5-wire with separate neutral and ground wires. In homes that don’t have 3-phase service, they still have 3-phase secondary distribution at the street.
Typical power factors for consumer grade motors are much higher then 50% - 75 to 80% on the low end. But they aren’t any different for 110 vs 220 motors. Power factor for a large factory can be corrected with power capacitors but it is hardly worth it to correct a single motor.
That’s often not the case in the U.S. Some areas have it, some don’t.
It’s fairly common in residential neighborhoods for them to use one phase for one street, the second phase for the next street over, and the third phase for the next street after that. There’s three phase at the end of the neighborhood, but only one phase on any given street.
There are some older neighborhoods in New York City and Chicago where three phase is run down the street and each house gets two out of the three phases. It’s rare, but there are some. It’s easy to tell if you have this type of service since you’ll have 120/208 service instead of 120/240.
I wasn’t aware that three phase was so common in Europe. I guess it shouldn’t surprise me, given the population density. Thanks for the info.
Eh, not really that bad. Most residential service has a power factor well above 0.9 and the power company monitors the overall power factor of distribution lines and switches capacitors on and off the line during the day to correct the power factor anyway.
Many areas are going to smart power meters. Not only do these “phone home” so that billing is all automated (no more sending anyone out to read the meter), but they also measure all kinds of things, like the actual voltage at the service and the power factor. They only bill on the watts, but they use the power factor to make more efficient switching on the power factor correction capacitor banks elsewhere on the line.
Industrial and business customers on the other hand are expected to provide their own power factor correction, and they get charged out the wazoo if their power factor drops too low.
For whatever reason, all of the old neighborhoods I lived in in Melbourne.au were wired 3-phase to the street (2 phase to the home). None of the new neighborhoods (or even new homes in old neighborhoods) are wired 2-phase to the home. (We don’t use split-phase at all).
I notice that large parts of Europe (used to?) think that apartment living is a ‘normal’ way to live. 3 phase supply is common to apartment buildings.
I just had my furnace replaced last month, it was 50 years old and we just had that really cold snap so it wasn’t completely surprising. The new furnace has a variable speed DC motor that draws as much power as charging a phone. Plus the improvements in burner and pilot-less technology over the last half century, I’m going to save so much money next winter, but not enough to offset the cost.
Draw a sine wave with a line indicating 0v, in a split phase system one leg gets the top and the other gets the bottom, essentially each get a bump of voltage. from 0v to 110-120v for 1/30th second with gap of 1/30th second in between.at 0v; think of it as spinning a wheel by striking it along it’s diameter ((you’re applying force in only one direction) vs. cranking a wheel with a handle set at it’s diameter(you’re applying force in 2 directions). U.S. standard is 110v to 220v with an allowance of +/-7v for unbalanced loads so anything residential can expect power ranging from 103-127v before a breaker might trip.
Amperes are the amount of energy being used, watts represents how much force the energy pushed at.in eather direction.
You are correct, 3 phase motors are most often vastly more efficient than single phase and split phase motors, however in a small grid (i.e.: residential) situation 3 phase power introduces the need for extremely complex power management.
Typically single phase motors tend to run ~20% more efficiently than motors running on one half phase and run cooler in the process.
The root tenon of my question is why in the case of gas furnaces the blower motors are at 110v and yet in the case of most electric furnaces they run at 220v.
Unless the residential user is using or attempting to use alternative energy sources.
The brave new age of alternative energy does come at a price, load balancing and power factor become real first person issues and the demand for aspirin goes up.
Yup, that’s the imbalance in George Westinghouse’s KWM.from the get go.
Not sure on your numbers, I have seen residential panels loaded so badly as to echo the old fuse boxes that often placed lighting on one leg and load on the other.
Yuck!, I wouldn’t to have to deal with that wiring.
3 phase for everyone crosses the line from complex math to math theory of modeling behavior within a chaotic complex system and I don’t think most electricians are willing go get a doctorate in mathematics to do their job.
It’s long over due that HVAC systems actually provide heating/cooling/humidity regulation on a per room basis.
The downside is that your HVAC technician will most likely charge a higher rate for their services to offset the cost of additional education.
This was difficult to parse, but it sounds like you’re describing the voltage on each leg as an intermittent sine wave, which is not the case.
Two 120 V AC lines are supplied to the premises which are out of phase by 180 degrees with each other (when both measured with respect to the neutral), along with a common neutral. The neutral conductor is connected to ground at the transformer center tap. Circuits for lighting and small appliance power outlets (ie. NEMA 1 and NEMA 5) use 120 V circuits - these are connected between one of the lines and neutral using a single-pole circuit breaker. High-demand applications, such as air conditioners, are often powered using 240 V AC circuits - these are connected between the two 120 V AC lines. These 240 V loads are either hard-wired or use NEMA 10 or NEMA 14 outlets which are deliberately incompatible with the 120 V outlets.
IOW, the voltage on each leg of a split-phase system is a complete sine wave. If you want 110 volts, you wire your device between one leg of the system and neutral. If you want 220 volts, you wire your device between one leg of the system and the other leg. In each case, the device sees a complete sine wave of voltage across its terminals; the only difference is the magnitude of the voltage.
This is completely wrong. Amps are not the amount of energy being used, and watts do not represent force. Let’s start with the basics.
There is a fundamental unit of electrical charge called the coulomb (C). It’s the amount of electrical charge carried by 1.602 x10^19 electrons.
The ampere (A) is the fundamental unit used to measure the flow of charge in a conductor, and it is equal to one coulomb of electrical charge flowing past your measurement point every second: 1 A = 1 C/s.
The joule (J) is the fundamental unit of energy in the SI measurement system, and it’s equal to one Newton of force (about .225 pounds) moving over a distance of one meter: 1 J = 1 N*m.
The watt (W) is the fundamental unit of power in the SI measurement system, and it’s equal to one joule of energy per second: 1 W = 1 J/s.
The volt (V) is the fundamental unit used to measure electrical potential, and it is equal to one joule of energy per coulomb of electrical charge: 1 V = 1 J/C.
If you look at how all those units combine, you can see why we multiple current and voltage to obtain power:
P = X amps * Y volts
P = X (C/s) * Y (J/C)
The coulomb units cancel out, and we’re left with J/s, or watts.
A typical residential HVAC blower is on the order of 500 watts, and runs maybe a 30% duty cycle (averaging year-round). Figure a kilowatt-hour costs 16 cents, so total cost of operating the blower motor is $210 per year. Let’s imagine a blower motor running on 220V uses 10% less power, saving me $21 per year.
If I’m a homeowner looking to replace my old furnace (which ran on 110V), and there’s a new model of furnace that will save me less than two dollars a month, but will require an electrician to run 220V wiring over to it for an extra $500, I’m not gonna buy that furnace.
Electric furnaces (i.e. ones that use electricity for heat production) require 220V service because of their high power consumption, so if you’re using an electric furnace you might as well also make the blower motor 220V.
A small nitpick: what you have is not a conventional DC motor. It’s a “brushless DC” motor:
They are handy in part because it’s easier to implement variable speed operation with them than it is with standard AC induction motors, which facilitates multiple furnace heat settings and allows for quiet, unheated circulation of house air at a lower blower power setting. They are also more efficient and quieter than conventional DC motors.
Can do. How much money have you got? You’ll need temperature and humidity sensing in each room where you want independent control, and you’ll need hardware to put the heat/humidity wherever the control system wants it to go. These systems already exist, but most folks don’t find them to be worth the investment; they just put one thermostat/hygrometer somewhere in the middle of the house, and move the dampers in various ducts to adjust local air flow rates so the temperature is reasonably even.
It’s very common in older neighborhoods in New York City for apartment buildings to receive 3-phase service with each apartment getting two of the three phases. When I lived in Brooklyn I had to run my 240v electric dryer extra long because it was really only getting 208v. An HVAC contractor I chatted with mentioned that this is also sometimes a pain point with big air conditioners.
As an interesting note - the distance from Sault Ste Marie to Wawa in Northern Ontario is 200km, which may be iffy for some electric cars - Tesla wanted to put a supercharger in Bechwana Bay part way north, but the only power there is 208V one phase, so inadequate for a charger. As a result, it’s an iffy stretch in winter. They did put some slow chargers, but with 208V instead of 240V it’s a little slow. An entire region was fed with only one phase, since the only occupant was one gas restaurant. This is because there is essentially nothing in that stretch of road. In the north, when they say “nothing” they mean “nothing”.
Most new furnaces in Canada will have the DC brushless motors, so really the power source makes no difference. The only real 240V appliances in a typical home would be dryer, oven, and A/C if applicable. Any electric furnace instead of gas would use 240V also. (and for me, I have a car charger). But generally, all appliances in N. America run on 120V AC so there’s no great incentive to feed 3 phases into homes; 240V 2 phases seems to be adequate. My panel has one of the phases down each side, and half the load on each side.
Perhaps it’s like the chicken and the egg. There’s no supply because there’s no demand. There’s no demand because there’s no supply. There’s no reason to change because people don’t typically have appliances where 110V is inadequate, or only 2 phases and 240V is inadequate. I suppose there’s marginal savings to be had if they were to go to 240V (single phase) like the rest of the world, since the current is lower so I assume you could use less copper in the conductors - but severely disrupting and confusing the electrical device market for marginal savings is probably not worth it.
As for 3-phase: I worked in an old office building once where there were 3 phases and florescent tube lights. A salesman came by once trying to sell a dimming option for these lights. The electrical engineer hit the roof and said “no F***ing way!!” The device monkeyed with the power sine wave (clip, to a variable width pulse square wave, if I recall) to reduce power to allow dimming while keeping 120V. The EE pointed out this would put the amperage out of phase with voltage. The problem is the building had been wires with common neutrals, on the assumption this would never happen. the risk was the neutrals could end up with additive current from multiple phases, and burn out (or burn down the building)