Furnace: DC Motor Cost Savings

[plexus]

Hi. does anyone have real cost savings data between a dc motor furnace (ecm) and AC variable speed? i am trying to decide if i should spend the extra money on an ecm motor furnace.

oddly the "unit amps" listed in the rheem RGFD specs (ecm) says 8.7 and the RGRK specs (ac variable speed) "motor full load amps" says 6.8. too bad the two dont have the same specs so i can compare.

my main issue is with potential repair costs: the ecm furnace parts costs are crazy high compared to the AC furnace. but will the cost savings in energy make up for it? thats what i am looking for

brett

[Gunnery Sergeant Hartman]

You don't go with a variable speed for "cost savings" only.
You will get your money back in comfort 10 fold.
Increased dehumidification in the summer means you can set the t-stat a few degrees warmer and still feel comfortable.
More even temperatures throughout your home for comfort.
Couple your system with a high efficiency air cleaner and you can leave the fan run 24/7 for a fraction of the cost of a standard blower.

Look at the big picture and get an extended warranty for peace of mind if you're worried about service bills.

[beenthere]

A VS motor can save you enough in electric to cover the difference in replacement cost.
Weather it will or not depends on many things. System static pressure. The higher the static, the more electric it uses.
Weather or not you run your fan 24/7. If you do, it will save you money.
Length of heating and cooling seasons. The moe you use the blower the more it can save you. Mild heating and cooling season, you won't save much.

As above. VS blowers are comfort enchancements to your system design.

[bob hubbard]

heres a link you can try . Set everything the same but use the vs option on one and use the standard motor on the other . Do both coolin hours and heating hours to find the savings . Let us know how yours comes out . http://www.hvacopcost.com/

[plexus]

hello thanks for your answers! my question wasnt with respect to single speed vs variable speed. i was asking the difference between an AC motor and DC in terms of power draw.

what is the difference, typically, between the power draw in amps or watts between a modern furnace that uses an AC motor vs a DC motor, running at the same speed, say, the highest.

this appears to me to be the only real cost savings between the two types of furnaces. since the parts costs for a DC furnace are drastically higher, i want to determine the net potential cost of each system assuming a break down requiring a parts replacement.

this will then help me to determine if i want to get a DC furnace or not. i understand that stages, modulation and variable speed are about comfort more than about savings.

the two furnaces in question are the rheem 2-stage variable speed AC and the rheem modulating.

again, i GET that modulation/stages provide comfort. what i am trying to work out is operating + maintenance costs.


brett

[hvaclover]

There is a definite cost saving in the VS motor.

But like the the other guy said, that all depends on how it is applied.

I can tell you that from a training seminar an engineer did all the math

(Which I will admit is above my head) and with the motor running 24/7 it cost about as much as a 100 watt bulb.

Using an AC multi speed motor left to run 24/7 would cost as much to run as a 20cu ft side by side refrigerator freezer.



I am over simplifying but that's a good basic analogy

[beenthere]

What your refering to as a single speed, is a standard PSC motor.
What your calling a DC motor, is a variable speed motor.

If order to have savings with a VS/(DC) blower, your duct static can't be too high, or it will use more electric.
If your duct work is sized right, the VS motor will use about half as much electric as the single speed.


Rheem doesn't have a variable speed AC motor.
I think your confusing a multispeed, with variable speed.
A Multispeed motor is a standard PSC motor.

[hvaclover]

Thanks for the heads up Bennthere. I forgot to mention that was on continuous fan operation which is the lowest rpm on the VS motor.

[RoBoTeq]

hello thanks for your answers! my question wasnt with respect to single speed vs variable speed. i was asking the difference between an AC motor and DC in terms of power draw.

what is the difference, typically, between the power draw in amps or watts between a modern furnace that uses an AC motor vs a DC motor, running at the same speed, say, the highest.

this appears to me to be the only real cost savings between the two types of furnaces. since the parts costs for a DC furnace are drastically higher, i want to determine the net potential cost of each system assuming a break down requiring a parts replacement.

this will then help me to determine if i want to get a DC furnace or not. i understand that stages, modulation and variable speed are about comfort more than about savings.

the two furnaces in question are the rheem 2-stage variable speed AC and the rheem modulating.

again, i GET that modulation/stages provide comfort. what i am trying to work out is operating + maintenance costs.


brett
You are asking a question in a manner that is difficult to answer. Figure out what it is you really want to know and ask that question without the additional parameters.

The fact is that a variable speed blower is going to save energy usage, usually about a fifth of the energy used by an AC motor. As mentioned, there are other factors for comfort and energy savings that are not directly associated with the direct energy usage.

Your inquiry is "is it worth it to pay the additional cost for a variable speed blower" and the answer has been given; yes it is.

[plexus]

thanks for your replies. i will try and be more specific. i can choose to go with a 2-stage PSC motor rheem furnace or their modulating ECM+ model. the additional upfront cost is a bit limiting but doable if i can justify it. the issue for me is the cost of parts. i will be getting a 10 year p/l warranty regardless but if the furnace lasts longer, i am concerned about the difference between replacing a $1000 blower vs a $400 blower in the simpler PSC motor model.

my house is small, 1200 sq ft, 2 story and the exiting ductwork will not be changed and is c.1975 when the existing furnace was put in.

should i just not worry about it and spend the extra money and get the modulating ECM furnace or should i stay away on the Keep It Simple Stupid principle?

the existing furnace is fine for me in terms of comfort so anything more is great. i am sure a mod/vs furnace is potentially amazing in term of comfort but for me right now costs are the biggest issue.

also resale value - if i sell the house will a potential buyer say "oh great they have a good but simple furnace installed that is more matched to the house" or "too bad they didnt put in a top of the line" or "fantastic! they have a modulating furnace installed" or "oh no, they have one of those variable speed furnaces installed thats going to cost an arm and a leg to maintain"...

what are your professional experiences with the rheem modulating furnace vs the 2-stage? i guess that will tell me more accurately than anything how reliable these things are in the long run.

brett
brett

[hvaclover]

Reem makes a good dependable mod furnace.
But the more bells and whistles....well, you know what I mean.

My opinion is this: If Modulating furnaces are THAT good, why aren't more mfrs making them?
The only other one who makes a mod is York, and the technology they use is slightly diff from Reem.



The fact is that the price of gas is going to do nothing else but INCREASE.

So on the face of it I would say that a ROI calculated today might not look favorable in today's dollars, but with the price of gas going up all the time
the payback will probably grow more to your favor each year.

But is that mod furnace going to eat you alive in repairs?

Personally I would not take the chance since there are only two mfgs using that technology.

ECM motors on 90% furnaces have been available since the late 80's and early 90's from Heil and others.

Everyone sold was recalled by Heil and the other mfrs had their problems too..

Here we are in 2008 and now they are as common as cars on the road.

I would suggest a 2stg vs 95% furnace. They are priced with in range of most folks income, and even if you have to get a loan to afford one I would recommend it, as the reliability of these type furnace are thru the roof.

The Ecm is always going to be the most expensive part, but gas prices will be so high they will make the investment worthwhile.

[beenthere]

The Rheem mod, has a lifetime replace the furnce if the heat exchanger fails warranty.
Not sure if it can be transfered to a new owner.

ECM motors seldom fail. Its usually the module when their is a failure. The module is a lot less then the motor and module.(can't get the motor without the module.)

The mod is a comfort furnace. So don't buy it for savings.

Most home buyers would like a top of the line furnace already in the house their buying.

[hvaclover]

The Rheem mod, has a lifetime replace the fence if the heat exchanger fails warranty.
Not sure if it can be transferred to a new owner.

ECM motors seldom fail. Its usually the module when their is a failure. The module is a lot less then the motor and module.(can't get the motor without the module.)

The mod is a comfort furnace. So don't buy it for savings.

Most home buyers would like a top of the line furnace already in the house their buying.

Only thing I see wrong with that is what history has taught us.

Luxaire made a product called a "HEAT PIPE" furnace. Life time warranty.

They all went defective and customers had to settle for a lower quality replacement furnace.

Lennox Pulse. Sweet piece of technology: Heat Exchanger were bad in a high percentage. Government action forced replacement (I think it was a forced government recall, not 100% sure. But a huge recall happened) and again the customers got a replacement that was no where good as the original.

Lifetime warranties on heat exchangers are great and companies do honor them.

But the 90%years I put in 20 years ago are no where near as good as whats available to day.

I have had some heat exchangers go bad on me and in most cases the customer wants the newer technology.

[hangfirew8]

Only thing I see wrong with that is what history has taught us.

Interesting information, but I understand the Rheem Mod is already a decade old. Seems to me, if some huge recall were to happen to it, there would already be rumblings.

On the contrary, the only complaints I here are from pro's trying to sell competitor's units.

-HF

[FRE]

My knowledge of what is available in furnaces and air handlers is limited. However, I do know quite a bit about motors, so perhaps I can contribute something in that area.

PSC (permanent split capacitor motors) are more efficient than shaded pole motors, but I think that shaded pole motors are no longer used anyway. The PSC motors used with blowers often have tapped windings which typically provide 3 or 4 speeds. Generally the motors have 6 poles providing a synchronous speed of 1200 rpm but, because there are not synchronous motors, there is always some slip resulting in a speed somewhat below 1200 rpm. When a lower speed tap is selected to make the blower run more slowly, efficiency is reduced because of the increase in slip. However, because the power required to drive the blower varies with the cube of the speed, running it at a lower speed would reduce the power required even though the motor is less efficient at the lower speed.

The efficient variable speed blowers control the speed by other means. Some use brushless DC motors. Actually, the motors aren't really DC; there is an inverter built into the motor so that the motor is actually running on AC even though DC is provided to the motor assembly. Generally the motors are permanent magnet synchronous motors. They are very efficient at all speeds and generally the speed is controlled by varying the DC voltage to the motor assembly.

Another method to control blower speed uses an ECM (electronically commutated motor) controlled via an external 3-phase inverter and the speed is controlled by varying the AC frequency. Another type of motor that uses an external inverter is the VSR (variable switched reluctance) motor. The VSR motor itself is very simple and has no windings on the rotor. It too is controlled via a variable frequency inverter.

The shaded pole motor is horribly inefficient but cheap to manufacture. The PSC motor is considerably more efficient than the shaded pole motor. The other motors are considerably more efficient than the PSC motor at all speeds and, when the speed is controlled appropriately, will provide more satisfactory performance for the HVAC system. However, the initial cost is greater and it may be that the electronics involved could reduce the reliability. On the other hand, they've been around for a long time and it may be that that has provided sufficient time to work out the bugs and make them reliable.

Others know more than I do about how these devices are used with HVAC systems.

[House]

Fairly good analysis of energy saving blower motors. It's five years
old so the utility rates used in the calculations are a bit low.
Good read though.

http://www.aceee.org/pubs/a033full.pdf

[hvaclover]

My knowledge of what is available in furnaces and air handlers is limited. However, I do know quite a bit about motors, so perhaps I can contribute something in that area.

PSC (permanent split capacitor motors) are more efficient than shaded pole motors, but I think that shaded pole motors are no longer used anyway. The PSC motors used with blowers often have tapped windings which typically provide 3 or 4 speeds. Generally the motors have 6 poles providing a synchronous speed of 1200 rpm but, because there are not synchronous motors, there is always some slip resulting in a speed somewhat below 1200 rpm. When a lower speed tap is selected to make the blower run more slowly, efficiency is reduced because of the increase in slip. However, because the power required to drive the blower varies with the cube of the speed, running it at a lower speed would reduce the power required even though the motor is less efficient at the lower speed.

The efficient variable speed blowers control the speed by other means. Some use brushless DC motors. Actually, the motors aren't really DC; there is an inverter built into the motor so that the motor is actually running on AC even though DC is provided to the motor assembly. Generally the motors are permanent magnet synchronous motors. They are very efficient at all speeds and generally the speed is controlled by varying the DC voltage to the motor assembly.

Another method to control blower speed uses an ECM (electronically commutated motor) controlled via an external 3-phase inverter and the speed is controlled by varying the AC frequency. Another type of motor that uses an external inverter is the VSR (variable switched reluctance) motor. The VSR motor itself is very simple and has no windings on the rotor. It too is controlled via a variable frequency inverter.

The shaded pole motor is horribly inefficient but cheap to manufacture. The PSC motor is considerably more efficient than the shaded pole motor. The other motors are considerably more efficient than the PSC motor at all speeds and, when the speed is controlled appropriately, will provide more satisfactory performance for the HVAC system. However, the initial cost is greater and it may be that the electronics involved could reduce the reliability. On the other hand, they've been around for a long time and it may be that that has provided sufficient time to work out the bugs and make them reliable.

Others know more than I do about how these devices are used with HVAC systems.

Anybody as a student who attended a good HVAC school knows all that theroy, but I think it is too deep to present to an HO>

[beenthere]

Too much for some. Others would like to hear that info.

In the end though, if the info makes or breaks the sale, is what matters.

[plexus]

Too much for some. Others would like to hear that info.

In the end though, if the info makes or breaks the sale, is what matters.

exactly. im a home owner and i want this information. i have spend considerable time researching furnaces because i want to understand what is involved and make a decision i am comfortable with. i also want to have knowledge around some of these details to protect myself from false information or faulty opinions because after all, i am the one that is going to have to live with the machine and installation, not the contractor or manufacturer.

i think buying an extended warranty is a good way to mitigate risks as well.

brett

[beenthere]

An extended parts and labor warranty are always smart investments.(factory/third party)

[hvaclover]

Too much for some. Others would like to hear that info.


I'd agree if the prospects you are servicing and selling to are all engineers and/or employed in technology based career.

But that is not the case. Not every prospect is going to be a technically oriented person or engineer, just as every one is not going to be a doctor or lawyer.

By saying "Too much for some. Others would like to hear that info" leads me to think you feel the majority of prospects would want this info.

I go into great detail on equipment as my selling approach is based on selling the mechanic of the install. When a customer wants the theoretical workings
of the equipment I will gladly indulge that person. Otherwise I stick to analoies that folks can relate to in every day life.

Analogies work best on HOs who don't want to hear OHMS law or what the "Wet Time" of a furnace is, or how the AC current is converted to half wave DC current.
Your market may be different than mine, but I don't think you use such technical speak on every sales call unless you are selling HVAC systems on the International Space Station:D:rolleyes:

[a0128958]

Plexus:

Here's some data for you to illustrate power consumption for a VS motor. I don't have example data for a PSC motor.

This data is from a WaterFurnace 3-ton 2-speed compressor variable-speed fan motor Envision unit. It's a 230V ECM2 variable-speed motor.

While the range of data is reflective of the ECM2 motor overall, the specific values are dependent on specific installation. Current draw is shown as a range, as the draw is dependent on static pressure. This data is from a zoned unit, and thus the static pressure varies as a function of the zone damper positions.

ECM2 motor (only) current draw:
0650 cfm: 0.15 - 0.36 amps (200-395 rpm)
0750 cfm: 0.19 - 0.54 amps (263-465 rpm)
0850 cfm: 0.24 - 0.76 amps (270-519 rpm)
1000 cfm: 0.32 - 1.12 amps (308-625 rpm)
1100 cfm: 0.43 - 1.54 amps (333-678 rpm)
1200 cfm: 0.56 - 2.25 amps (363-779 rpm)
1300 cfm: 0.67 - 1.04 amps (385-508 rpm)
1400 cfm: 1.02 - 1.30 amps (472-555 rpm)
1500 cfm: 1.02 amps (454 rpm)

Again, this data should be used just to get an idea of power consumption for an ECM2 motor - the variability shown above is reflective of static pressure changes, and, the Intellizone controller limiting upper speeds to lower static pressure scenarios.

Hope this helps.

Best regards,

Bill

[plexus]

Plexus:

Here's some data for you to illustrate power consumption for a VS motor. I don't have example data for a PSC motor.

This data is from a WaterFurnace 3-ton 2-speed compressor variable-speed fan motor Envision unit. It's a 230V ECM2 variable-speed motor.

[snip]

Hope this helps.

Best regards,

Bill

yes thats very helpful! i see the current draw is quite low. lower than i expected actually. i understand that the static pressure affects these units but still as a guideline. i can see why its possible to run an ECM motor on low 24/7 without too much utility cost.

[beenthere]

As I said in my post, its too much for some.

You have to feel out each individual customer. You can't group all customers together, no more then you can group all HVAC contractors together

[a0128958]

... i can see why its possible to run an ECM motor on low 24/7 without too much utility cost.

Yes, if I were to run my ECM2 motor "on low 24/7" it would cost me roughly .15A * 230V, or approximately 34 watts. Including the standby power consumption for the Envision, at about 30 watts, the total adds up to the advertised "run the fan on ON for about the cost of a 60 watt light bulb" (paraphrasing). So it can be measured, and verified, that yes, running an ECM2 motor on the lowest setting is about the same as the light bulb. So if this is what you were looking for independent confirmation of, you're all set. Indeed, the ECM2 motor is 'the real deal.'

But, in my individual case, I don't run my blower motor 24/7 because I don't live in an arid climate (I live in Dallas area). See the numerous threads on this site that address the increased humidity levels that can occur when the blower motor is running with an evaporator coil all loaded up with water without the compressor simultaneously running. In fact, this was the case for me, and I actually measured the RH increase. So for my geographic location, while the advertising of a cost savings of a VS motor running 24/7 is 'catchy,' it's not as comfortable due to increased RH.

Best regards,

Bill

[FRE]

Actually, I am a home owner and my degree is in business administration. So, if I can understand various types of electric motors, surely others can also.

[plexus]

Actually, I am a home owner and my degree is in business administration. So, if I can understand various types of electric motors, surely others can also.

on the other hand, not all HOs care. in fact i asked the contractors i interviewed about how other HOs deal with the myriad of information about havc. they all said that most people just go with someone they trust and trust what they bring into the house. most HOs dont do the level of research and knowledge gathering I did. hell at this point i even know more about some of the details than the HVAC contractors (i've pointed out some details they were not aware of around various things like exchanger construction to warranty details). but thats me.

so like that previous poster said, i can imagine that the contractors have to adjust their "pitch" based on what they know of the specific HO. the contractor i am dealing with has responded quickly to the myriad of questions i asked.

on the other hand, i asked at one point "what makes the difference between a good install and a bad install" and his answer was "the install will speak for itself" where-as another contractor brought up specific issues. i think that the first contractor was just trying to be concise and non-technical which is fine, but it wasnt what i wanted to hear. once i started asking specific questions about drains, vents and hook ups his answers were detailed.

brett

[hvaclover]

Actually, I am a home owner and my degree is in business administration. So, if I can understand various types of electric motors, surely others can also.

Do you think that the majority of persons in this country have a degree?

It is very arrogant and elitist of you to assume that every body does, because it assumes anyone who is degreeless is ignorant.

My customer base are people who work manufacturing jobs. How many degrees you going to find on an assembly line? These people have an intuative grasp of mechanics. When I present a system to them they don't want to hear it laid out in tech-speak, they want common every day language they can relate to.

[plexus]

Do you think that the majority of persons in this country have a degree?

It is very arrogant and elitist of you to assume that every body does, because it assumes anyone who is degreeless is ignorant.

My customer base are people who work manufacturing jobs. How many degrees you going to find on an assembly line? These people have an intuative grasp of mechanics. When I present a system to them they don't want to hear it laid out in tech-speak, they want common every day language they can relate to.

the point is that its probably more effective to gear the nature of your communication to the intended audience. "speak the users language" as we say in my field (usability). im sure hvac contractors have a challenge with this as there are so many different kinds of people that ultimately want the same thing: to make a decision they are comfortable with.

[hvaclover]

on the other hand, not all HOs care. in fact i asked the contractors i interviewed about how other HOs deal with the myriad of information about havc. they all said that most people just go with someone they trust and trust what they bring into the house. most HOs dont do the level of research and knowledge gathering I did. hell at this point i even know more about some of the details than the HVAC contractors (i've pointed out some details they were not aware of around various things like exchanger construction to warranty details). but thats me.

so like that previous poster said, i can imagine that the contractors have to adjust their "pitch" based on what they know of the specific HO. the contractor i am dealing with has responded quickly to the myriad of questions i asked.

on the other hand, i asked at one point "what makes the difference between a good install and a bad install" and his answer was "the install will speak for itself" where-as another contractor brought up specific issues. i think that the first contractor was just trying to be concise and non-technical which is fine, but it wasnt what i wanted to hear. once i started asking specific questions about drains, vents and hook ups his answers were detailed.

brett

You said a mouth full, but what stands out is the trust one generates between him and the prospect. A guy who grants me his work is gonna get my best shot. If they have the monetary means then I recommend accessories that add honest value and comfort to the job.

[beenthere]

About a year ago. I sold a 2 stage HP to a customer. First meeting was with teh wife. Second with the husband. Due to their work schedules they couldn't be there at the same time.

She wanted to know what the system could do for their house.
He wanted to know how it would do it.

Both were well educated, both wanted to know different things, that the other wasn'r concerned about.
Point, always be ready to explain, what you didn't think they wanted to know.

[jeff520]

hvaclover: "As a student anybody who attended a good HVAC school knows all that theroy, but I think it is too deep to present to an HO>"

That statement really annoyed me because it implies that attending a good HVAC school takes a student way above the understanding level of their average customer. To use an analogy, the best HVAC folks I have met in conjunction with my recent installation were about at the level of a good hospital nurse. Competent, capable, the result of considerable training, clearly professional folks, BUT not in the same class as skilled surgical nurses, and way below specialist surgeons.

The HVAC professionals meeting with customers need to appreciate that in many cases the customer's skill in some subset of HVAC will be many times greater than theirs. Perhaps a chemist who really understands the properties of refrigerants, or a computer engineer who is not intimidated by the simple structure of even the most advanced thermostat or furnace control board. That does not mean the HO is a better HVAC professional, but when they do ask an intelligent question, better not talk down to them.

The point about written information (like this website) is that the reader does not have to read anything that is of no interest to them, so let the writer go as technical as they want to - some readers will appreciate it, some will ignore it.

I wish I was in the business so I could read the professional forum - the subject interests me - and it is not because I want to DIY. For the moment, I say bring on the heaviest technical stuff you can, some of us like it!

[hvaclover]

hvaclover: "As a student anybody who attended a good HVAC school knows all that theroy, but I think it is too deep to present to an HO>"

That statement really annoyed me because it implies that attending a good HVAC school takes a student way above the understanding level of their average customer. To use an analogy, the best HVAC folks I have met in conjunction with my recent installation were about at the level of a good hospital nurse. Competent, capable, the result of considerable training, clearly professional folks, BUT not in the same class as skilled surgical nurses, and way below specialist surgeons.

The HVAC professionals meeting with customers need to appreciate that in many cases the customer's skill in some subset of HVAC will be many times greater than theirs. Perhaps a chemist who really understands the properties of refrigerants, or a computer engineer who is not intimidated by the simple structure of even the most advanced thermostat or furnace control board. That does not mean the HO is a better HVAC professional, but when they do ask an intelligent question, better not talk down to them.

The point about written information (like this website) is that the reader does not have to read anything that is of no interest to them, so let the writer go as technical as they want to - some readers will appreciate it, some will ignore it.

I wish I was in the business so I could read the professional forum - the subject interests me - and it is not because I want to DIY. For the moment, I say bring on the heaviest technical stuff you can, some of us like it!

You are annoyed? Don't see why. It's my job to more knowledgeable than my customer. If an individual isn't more on top of his industry then the market he serves what value is he?

I have been at this thirty years and am not a student in school.

If you like to get in to the deeper aspects of this industry then I commend you. I like educated prospect.
Even the ones who think they know more then the prospective Contractor they are looking to hire.

I reject out of hand your assertion that a prospect could know more then an HVAC professional. He may be book smart about the subject but does not have the experience to back up the tech-speak.

And finally I would reiterate that you missed my point completely.
The point being put forth was that you can't go that DEEP with every prospect you make a presentation to....there was nothing said about limiting the content or topic with in this forum.

I would like to be a fly on the wall as you meet with an HVAC professtional. I do believe what you said about talking down to people ...but I don't think this would be coming from the HVAC professional.

[hvaclover]

Why was this emial in Uncle Clover mail box? There was no reply to Uncles last post.

If you mods are interested in how he is doing, why don't you just send an email
and ask?

HVAC5646
Part of the Clover Leaf

[jpsmith1cm]

There was a post in this thread that didn't belong here.

I moved it to the appropriate forum.

I'm sorry about the notification.

I don't think that hvaclover has AOP * status, so technically, he isn't allowed to post replies in the AOP forum.

I sincerely hope that he is doing well.

Going to close this thread to prevent further problems.