New gas furnace/AC recommendations?

[Home Guy]

When it comes to discussing the pro's (or perhaps the lack thereof) of ECM motors for use in HVAC air handler systems, I've found that this document is very informative:

I have pasted the conclusions of that document below. It basically says that the benefits of ECM motors are lost in installations with high static pressures (and something that I bet a lot of home-owners don't want to fork out money for is to re-do the duct-work in their homes).

Perhaps someone else can explain why the flow characteristics of a duct system is described in terms of the back-pressure it generates instead of speaking directly about the RESISTANCE of the ductwork, even perhaps putting a number on it (which surely can be done, given that we might know the CFM and the air pressure at the input side of the duct, and assuming the pressure at the far end is zero). When someone is talking about high static pressure, they are essentially saying that the duct system has a high resistance to flow (caused by any number of reasons - closed or blocked vents, small-diameter ductwork, long runs of small-size ducts, turbulence caused by right angles, filter too small or too dense, etc).

Which could be why my idea that the gating of furnace output around the A/C coils is not appreciated as something that can reduce airflow resistance (ie - reduce static pressure).

As someone who's been living with and has experienced HVAC systems with single-speed AC fan motors, I really can't appreciate the need for a variable-speed fan motor. All this discussion about how PSC motor efficiency drops to 15% - 30% when used at low speeds is a real mystery to me - are there really furnaces out there that have the necessary electronic controllers that will use PSC motors in such a variable-speed capacity? Why no real discussion about the efficiency of 2-speed AC motors?

I also don't understand how running a fan at low speed is better at humidity removal when the HVAC system is in A/C mode - yet ECM makers make that claim.

Claims that ECM motors are just as reliable as PSC are also a crock, given that none of them could possibly be in service yet for 30 to 40 years as is the typical PSC motor to even begin such a comparison.

Youtube video showing badly-behaving ECM motors:

?v=5MIgb_2LwH4&NR=1 These ECM motors look really flimsy - like the 1/8 hp electric motor I have on my roof for my attic fan. Sorry - I wouldn't want something that wimpy in my furnace.

Apparently they are somewhat succeptible to lighting strikes (lightning doesn't have to hit your house directly to dammage the electronics in your house). I guess your entire furnace is more succeptible to lightning when it's got it's own computer. Another strike against the modern furnace.

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Conclusions:

The main conclusion that we would draw from this study is that although the use of an ECM has the potential to reduce fan electrical power draw, much of the benefit is lost in systems with excess static pressures. A full analysis of this problem was done by Lawrence Berkeley national Laboratory (Lutz et al., 2006). In other words (as in many cases in the building industry) the benefits of high technology can be defeated by poor design and faulty installation or implementation. Problems can include excessively constricted duct designs and installations, restrictive return plenum fittings, or excessively restrictive filters (see ?Is There a Downside to High-MErV Filters?? HE nov/Dec ?09, p.

32).

However, with better designs, air handler efficiencies can be improved?significantly beyond the typical values assumed in previous work (that is, 2.5 CFM/W or 0.4 W/CFM). This is especially true when a given air handler is used at the lower end of its speed range. For instance, a 1.5- to 3-ton unit being used at 2 tons air flow at 0.5 IWC static pressure has an efficiency in the range of 3.7 CFM/W (0.27 W/CFM). Of course, reducing air flow for a given size of outdoor unit can have negative consequences, such as reducing overall efficiency (SEEr and EEr). But this factor can provide additional ammunition when arguing for tighter sizing of cooling equipment, and/or two-stage equipment with a variablespeed air handler.

In other words, if you can keep the air flows down (all other things being equal), you are giving your ECM a better chance to achieve high CFM/W efficiencies. The measurement of air handler efficiency is relatively simple; it can be done mostly with gear that a home performance contractor is likely to have. an air handler powered from an electrical receptacle can be quickly measured with a plug-in power meter such as a Kill-a-Watt. However, power measurements are more time-consuming if the air handler is hard wired. But overall, increasing the data set of installed ECM air handler efficiencies could be very informative, as would measuring and recording the operating external static pressures for these units.

[clare]

LOTS of furnaces and AC systems with multispeed PSC motors - and they are terribly inneficient at low speed. And there is virtually no "electronics" involved. On my old furnace it was just a relay - the fan ran on low speed continually untill the furnace called for fan, when it kicked a relay that put the power to the high speed windings instead of the low speed.

The AC runs the fan at HIGHER speed than the furnace on my new system

- but runs the fan constantly at low speed when the AC or furnace are not calling for circulation.

My PSC lasted less than 20 years. It was a 1/3hp belt drive - replaced it with a 1/2 HP

Some are wimpy, some look just like a typical PSC motor - and the PSC direct drive motors WERE wimpy - and many didn't last 10 years.

IN ALL cases, the benefits of high technology can be defeated by poor design and faulty installation - doesn't matter what field you are looking at.

[mm]

Interesting. So do they have an AFUE rating?

But the burner "efficiency isn't well regulated". So you mean an instantaneous measurement of efficiency?

Or an average measurement? Isn't an average measurement made only by looking at heat (BTU) output and dividing it into BTU input?

How can burner efficiency be measured without first measuring BTU output? What is there about the burner that can be measured other than BTU output?

It's not like a lever where the lengths of on both sides of the pivot can be measured, or a gear where the number of teeth can be counted, etc.** In cases like this, efficiency is not a real thing that can be measured. Only input and output can be measured.

**Even in the case of levers and gears, measuring theoretical efficiency by measuring arm length or counting teeth assumes there is no loss due to friction or slipping. The real efficiency of a mechancical device can only be determined by measuring input and output and dividing one into the other.

The spec sheet I got for at least one oil furnace this year included input and output and AFUE. If it was on the web and I can find it, I'll post it.

[Daniel who wants to know]

PSC blower motors are not really multispeed at all. All the extra speed taps are are taps on what acts as an internal autotransformer. High is rated voltage and the lower speeds just effectively undervolt the motor. Run a typical 1050 RPM 6 pole PSC blower motor on high sometime and measure the voltage from the low tap to neutral, it is usually around 170 volts AC depending on the motor.

There are true 2 speed induction blower motors that are wound as both a 4 pole and a 6 pole. The high and start windings are 4 pole so the motor always starts on high but if it is hooked up as low it switches the power from high to low as it starts using the same centrifugal switch that cuts off the start windings. When not running these motors will show a direct short between the 2 speed wires.

Less airflow allows the evaporator to run colder hence it cools the air more and the leaving air has a lower dew point hence a lower humidity % when warmed back up by the house/building..

[krw]

Does what have an AFUE rating?

Measure the heat going out the stack (stack temperature).

Measure the waste heat. Eff == Eout/Ein and Eout = Ein-Ewaste

No, the waste heat can be measured, too.

If your service tech is any good he'll measure the efficiency. The point is that the energy input is well determined by the amount of fuel used. This is a pretty basic design point, so is specified. Everything else is measured from there.

[Steve]

Exactly, and this applies to *ANY* type of blower motor

Your idea if "gating" around the coil will cause more resistance to airflow becaise of the right angles, and induced turbulance than just going straight through the coil..... this is assuming that your using a coil that is designed specificaly for that furnace (OEM).

There is no benifit with a 2 speed PSC motor, other than it has 2 speeds, as compared to a single speed PSC motor.

It slows down the air passing the evap coil and allows more moisture to condense on the coils to increase humidity removal.

None of the "new" fractional horsepower motors will last 30 to 40 years anymore, 10 - 15 years is a good lifespan. As a rule, none of them have oil ports for lubrication, and *most* of them have sleeve bearings, not ball bearings.

You don't have a choice anymore.

Your furnace is no more succeptable to lightning or power surges than any other appliance in your home that has a circuit board in it.

Your going to be dragged into the 21st century whether you want to or not. Get over it

This means that your ductwork will have to be checked for correct design and airflow. If your too cheap to pay have it done right, then there *WILL* be consequences, and its going to hit you right in the wallet in the form of failures/repairs, higher utility bills, and lower comfort levels.

Your *STILL* have to have the ductwork and system sized for your home.

This is why you need to get a *competent*, licensed, insured, professionally trained HVAC technician to do the job. One who can and will do the calculations, and take the measurements to insure that everything is correctly sized and operating at peak efficiency............ or you can call "Billy-Joe-Jim-Bob" down the road, or try to DIY. Either way, your going to get what you paid for.

There is a reason that the very best techs do 5 - 7 semester hours a year in continuing education and training. your not *JUST* paying for a guy with a ticket book and a truck, unless your looking for the lowest price.

[Mark]

yes anyone interested in this subject should read that...

and take note that the study system had the blower running 100% of the time. When the furnace was not heating, the blower ran for circulation. and the ECM motor ran much sloer in circ mode compared to the standard blower so there was much less circulation and not surprisingly less energy was used.

But if you turn the blower OFF when the furnace is off like most real people do, then it is less relevant.

and also note the part where the ECM blower caused gas consumption to increase..

I would say the facts are presented in this paper but the writer slanted the conclusion in favor of the ECM.

Follow the money...

Mark

[ransley]

Whats obvious is you are doing everything you can to put down Vsdc motors and modern electronics for no good reason. Its future is here, live with it.

[clare]

The blower speed was adjusted to provide the most efficient heat transfer - and actually the best air flow as well. Running a squirrel cage fan too fast can actually REDUCE circulation. I think that was also explained in the article. That's also why restricted ducting is such a big deal.

MOST people turn the blower off??? Not up here. Running the blower on low speed keeps temperatures even, and makes the air filter a lot more effective.

That was also explained - and I mentioned that in an earlier thread - the higher efficiency of the blower means more gas is required - but the cost per therm using gas is a lot lower than the cost per therm for electric, so it is still a net saving.

In the case of the National Research Council there is no money to follow. They are neutral, and not funded by manufacturing or marketing companies.

[clare]

Needs to be dragged into the twentieth first, before the twenty-first

[Steve]

Good point.

[trader4]

I would bet 90%+ of the HVAC installed in the USA runs the blower only when the furnace is heating or the AC is cooling, not 24/7. In a typical house with an unfinished basement or crawl space, I would think running it constantly would be a significant waste of energy from two standpoints. One is that it obviously uses a lot more electricity. Second is that while circulating all that air around you are running it through the basement or crawlspace, attice, etc that is unheated and you are losing heat through the duct work on each pass.

With a properly designed system, I don't see the need for constant circulation.

From the research I've done, I've concluded that the ECM motors are a mixed bag. In a typical house like mine (note that means running it only when heating/cooling), you might save 20% on electricity. I would pay some extra $$ for that. However compared to a regular motor, you have the issue of potentially higher repair cost, ie $700 bills instead of $100 due to the increased cost of the motor as well as the electronics to run it.

[clare]

You don't see the need for it, but the VAST majority of new furnace installations in ontario are set to run the blower on low, constantly. All 3 contractors we contacted for quotes for my daughter's furnace (multi-story condo) strongly recommended it.

[Vic Smith]

Strange that Canadians do that. Maybe makes sense for that multi-story condo building. Wouldn't make sense for my house. Small 3-bedoom, no "zoned" heating. Though you can "zone" by closing vents and doors to some extent. In some situations a blower always running during heating cycle would work that works - to distribute fireplace heat is one. In my house the thermostat is located in the hallway adjacent to where we spend most of our time - bedrooms, bathroom and kitchen. The dining room and living room are cooler. Maybe a degree or 2. And they are as big as the other rooms combined. This suits us fine.

When we have company and are in the living room/dining room body heat and sometimes cooking heat spilling from the kitchen keeps those rooms comfortable. When it's hot though I have to lower the thermostat to keep those rooms cool. I could reverse all that by moving the thermostat if I wanted to, but it works how it is.

What would happen if my blower was constantly running during heating and cooling times is this. In winter heat would be lost through living/dining room walls and windows, and when the A/C is running heat would be gained through the same. All of this come down to personal tolerance for uneven heat in different rooms, and how much you want to pay.

There's absolutely no question that in my house a constantly running blower would cost me both in electricity and natural gas. Because it would move heat or cool air to places it's not needed. I used to argue with my wife all the time about heating and cooling. She can't take it cool in the winter, or warm in the summer. I gave up the argument. You got to know when to fold 'em. But I never even started an argument with the laws of thermo dynamics, and don't intend to.

BTW, this reminds me how car A/C compressors kick in on defrost mode. I used to pull the A/C plug when winter rolled around because I never had a problem defrosting with just undried hot air and didn't wait to waste a couple/few HP all winter just to blow dried air on the windshield. I stopped that when I heard the compressor seals could suffer from disuse, but mostly because I lost my "need for speed."

--Vic

[ransley]

On only the coldest or hottest days do I run the fan 24hr just to balance things out. 24x7 will sure wear out a motor faster

[.p.jm.]

Actually, the worst thing for a motor is frequent starts.

[clare]

With the DC blower it's only about 100 watts to run the blower on low in my house - a 2 story with finished basement and no doors between floors. The house is quite well insulated, but the upstairs is still cooler than the main floor, and the basement is very comfortable year round.With the blower running on low constantly we do not get condensation on the patio door on extreme cold days like we did without the blower running, (RH is steady at about 35%) (one register is at the corner of the door)

My daughter's place is a 6 level split, basement, entry, living room, kitchen/dining, 2 BR and bath, and master bedroom. Built like a ruddy silo - definitely no place for old men!!!! We just insulated the basement and attic, and right now, with temps down to -17, the only cool area is the entry level (built on concrete slab - 3 outside walls)

[clare]

The only motor I've had fail was the single speed belt drive. I replaced it with the 2 speed just under half way through the life of the furnace. The original was a 1/3HP, the replacement was 1/2 and

1/6. The new furnace is a multispeed brushless DC motor

[Home Guy]

[e-mail] improperly and unnecessarily full-quoted:

Look - I live in Ontario too. And I just got dumped on with 3 feet of snow, and it's like 16 to 24 F around here lately.

I live in a drafty 1976-era house. I can tell you that there is no reason to run the blower constantly in the winter. When I switch my HVAC from summer to winter mode, the only time my blower fan comes on is when the furnace is on. There is just no need for a constant breeze inside your house in the winter.

Running the fan constantly in the winter, even at a low speed, is not efficient from a heating point of view. By keeping a constant breeze, you're helping interior heat loss by causing interior air to constantly come into contact with your walls and windows, which are the coolest parts of the interior and from which heat is transfered out of your house. When the fan is off and there's no air circulation, a temperature gradient will set up in the air near the surface of the walls and that air will be cold but you won't get as much heat loss through this gradient as you would if the air was constantly mixing.

In the summer (late may to maybe late september) yes my fan is on quite a bit, and even if I had a low-speed option I would not use it - I would still be using the normal hi-speed mode for circulation and comfort.

And I still say that having the ability to draw return air totally from a dedicated outside duct in the summer and force the normal return air out of the house through another duct is more energy-efficient at cooling your house vs using an AC during those times when the outside air temp is lower than the current inside air temp, which frequently happens in the late afternoon and evening in the spring and late summer.

[Home Guy]

[e-mail] unnecessarily full-quoted:

Which are glorified stepper motors.

In my house, the only place these wimpy DC motors will ever be is in my hard drive and DVD players.