What's the most efficient cond. gas furnace?

rick t_2

We've got two stage gas valves, a model with a modulating gas valve, ecm motors on blowers, moddulating induced draft fans - and brands galor, Bryant, Rheem, Armstrong, Am standard.

And who controls all this technology the best?

rick

Bob Schultz

Efficiency? As far as THERMAL efficiency, they're all pretty even. But what you need to watch for is OVERALL efficiency. For instance: Trane has a variable speed two stage furnace, and so does Bryant. The primary difference between their overall efficiency is that Tranes blower motor runs on 120 volts, while Bryant's runs on 12 volts DC. Imagine the difference in operating costs between the two, especially if you run the fan continiously, which we usually recommend to help improve your indoor air quality. If it were me, I'd strongly consider Bryant or Carrier (they are the same, like Chevy and GMC). There are plenty of dealers to service the equipment, should something happen to your installer, and they have a really good reputation.

Greg Swob

Bob is correct. There are two operating expenses involved in heating- the fuel burned to produce heat and the electrical motors to distribute that heat. For a very broad general comparison, if one runs a conventional PSC motor depending of course on electrical costs and size of blower 24/7: the electrical operating costs may be $20-$35 per month vs. perhaps $20/ year for the ECM (or DC powered) motor. Of course, this savings comes with a caveat. That ECM motor and it's control module cost more than a conventional PSC type motor. When one compares the AFUE ratings of one furnace vs another, the gap is usually so close, it's often a moot point. Chose the contractor whom you feel most comfortable with and have researched their work to your satisfaction. Greg

subcooler

Well spoken

But a properly matched PSC motor will run cheaper than an ECM. I said properly matched. If you look closely at your airflow tables, with the ECM you can get the air required demand closer. But with all good things you have to pay the price of converting or inverting electricity to do that job. At that point you are using exrta power in the conversion process. It stinks but it is fact. So the question I ask is the new ECM cheaper to run? Or are the PSC just out of the Eff. operating range?

Tony_23

ECM

A Bryant 355 uses 80 watts on HIGH. It's sisters, the 352 and 350 use 600. That's the whole appliance.

I don't see how you can say that PSC's use less than ECM's.

Rick T

cond. furnaces

Thanks for the info on ECM motors. I definitely would favor that as well.

Now on to the gas valves. Some, like the Bryant (BCP) have two stage gas valves. I understand the Rheem has a modulating valve like the Munchkin boiler.

Anybody know about the gas valves?

Rick

joel_19

Thinking outside the box

Interetsing thread , My 2 cents is that while that is important a much bigger consideration would be the duct work . Think outside the box . Many duct systems leak 20-30% or more , makes your great wiz bang furnace 60% eff. worse still when that happens the heat loss of the house goes up drastically which can double the effect makes your furnace the equilvelant of maybe 30-40% by the time your all done . Ouch . A good duct system and an 80% furnace will win every time .

Wayco Wayne_2

BTW

Tane has a model with 2 stage and an ECM motor too, just as Bryant has a 2 stage with a regular PSC motor. They gives us choices. I love the Trane 2 stage with ECM. I often program it for 350 a ton during A/C operation for moisture removal.

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Bob W._3

Good point. I recall an article from the early 80's about an Ohio study comparing heating systems, at the "Ohio Bomb Calorimeter" house. They measured duct system losses at 25%. However, if the "loss" is in the basement, which is partially conditioned space, then it really isn't that big a loss, is it? I've often wondered about that. I cut that loss in half when comparing systems, an arbitrary number to be sure but hopefully close to the real number. Any thoughts?

Dave Yates (PAH)

The most

efficient one will be the installation where the installer considers all of the factors affecting the overall performance. Too often, owners and installers, alike, think that installing a 90+ furnace (or boiler) automatically ensures system-wide matching efficiency. In my mind, that approach is no more complicated than adding a 13-SEER condenser to an existing 4-SEER coil. Or mis-matching heat pump systems and then convincing the owners you need to "adjust" the freon levels during seasonal maintenance! Let the buyer beware!

But, many of those same smart buyers put on blinders when it comes to investing in system-wide performance and choose to believe what they want to hear instead of thinking rationally.

All we can do is keep fighting the good fight while striving to lead consuners in the right direction via education and non-technical explanations. I look forward to the day when homes are judged much as appliances are today - with energy use stickers revealing their actual efficiency when compared to other homes. That would add real value to the work of those who are professionals in the PHVAC trades. Performance that isn't measured is performance that doesn't sell well! Imagine buying a vehicle today that doesn't list the MPG and can't because no one really knows! And that's precisely how our industry sells itself.

If we're lucky, the escalating price of fossil fuels will fuel a fundamental change in how our work is valued. We, as an industry, should develop a good, reliable, and honest energy evaluation system that could be universally accepted as the "gold standard" throughout the US. Germany is currently undertaking an initiative to provide energy-efficiency ratings for homes, which could serve as a basis for a model that would work here. I'd sonner our Government NOT be involved and, instead, garner the support of the real estate industry to build a consensus.

What if:

* Every home for sale had an energy-use yellow tag attached to its front door? Think that would affect a home's value?

*Homes of similar construction and looks had an energy-use sticker. Think that would affect which one sold and at a higher price?

* The comfort systems you installed were consistantly judged as superior in energy use and delivery of energy? Think your value would increase?

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Bob W._3

I would also prefer that the Government not get involved, but the market has been and is short sighted. As long as we have been able to find more oil and gas, on a short term basis, research into alternatives has suffered. Maybe we will finally wake up.

I would like to see more real world testing, possibly resulting in whole house energy performance ratings, as suggested by Mr. Yates. I know that ORNL has done this with wall structures and other building systems, but their raw research doesn't seem to get out to the public. We just want to know what works.

Dave Yates (PAH)

Google Hubbert's Peak

We're fast approaching the End Of The Age Of Oil. No, we're not going to run out, not in my lifetime or, most likely, my children's either. It's the demand that will outpace production and cause tripple-digit per barrel costs to be the norm & I don't mean low tripple-digits!

If the Solar Decathlon's public attendance and intent interest is any indicator, we are more than ready to wake up. Energy costs must remain high if the same audience is not to be lulled into another stupor in the US. Most of the rest of the world woke up some time ago. That's the message I received while attending the Solar World Congress in Orlando a few weeks ago. Of 1,800 delegates, the US attendees represented less than half of that total.

The stimulants needed to keep our citizens awake must come from us - those of us who walk the front lines of the trades and are welcomed into homes, businesses and commercial properties as trusted advisors. There's never been a more opportune moment in history for our trades to shine brightly.

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Mike T., Swampeast MO

Rheem Classic 90 Plus series modulates from 40% to 100% of output in 5% stages IF the appropriate thermostat is used. (The appropriate thermostats have an outdoor temp sensor by the way.) Otherwise it operates in 2 or 3 stages depending on the type of traditional (single or two-stage) tstat used.

Blower has four distinct speeds. Not sure however if those are used for initial setup with the blower modulating further during operation.

Dave Yates (PAH)

questions!

Rheem is the brand we use too, although we'll get others if the customer wants branded equipment. Questions on the variable spped though that no one has ever answered to my satisfaction and these same issues would plague hydronic systems.

In both cases, we size pumps (blowers or circs - energy movers) based on system criteria such as: pipe or duct sizing; head or friction loss; flow charts for circs and blower rpm/horsepower. System-wide designs rely upon fixed points of factors derived from the components.

If we slow down a cir pump in hydronics or a blower in an air system, don't the delivery characteristics change too? If so, doesn't that also throw the system out of balance?

In hydronics, we can alter the Btu input via injection while maintaining flow rates in the primary & secondary remote circuits. The only pump that alters its speed is the injection circ. 80-degree water coursing through a radiant circuit doesn't adversely affect comfort. If, on the other hand, I drop off the primary loop circ's speed or a single circ in a parallel circuit, then I'll send the system into unbalanced delivery. In a series loop, like a BB run, I'll twist the balance by shedding Btu's to the first rooms served.

On the other hand, if I drop a blower's speed by 60% in a duct system that serves multiple rooms/floors and drop input of Btu's to low delivery temps that mimic heat pumps (or lower), it seems logical to me that the system will become unbalanced and discomfort issues will arrise from cooler drafts. If not, then my use of Manual-D for sizing ducts based upon a fixed rate of air-flow must be something that doesn't hold the weight I've been taught it does.

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thp_8

I love the

What if? Sad but true. There will always be more dis-information that Actual information when it comes to sales.

Mike T., Swampeast MO

Great Questions

Am though having a terrible time coming up with any real answers.

"the modified equal friction method of Manual D requires that the available static pressure from the fan be "consumed" by the duct through its run from fan to outlet/inlet, with no shortage or excess at the end"


When I set up a VERY simple (ductwork only) system with this ideal and cut the airflow in half, friction loss stayed fairly well balanced (within ± 0.01"). Don't have Manual-D software and am using a rather old and highly compact table. From what I could see, a system properly balanced & sized via Manual-D stays reasonably balanced if you considerably drop airflow. I suspect that would be especially true if you've used reducing main takeoffs. Perhaps someone can try this on their software. Will such allow you to change airflow and recompute friction loss for an already sized system?

If that modulating Rheem does in fact change air speed, I would suspect that it monitors output temperature. If temp gets below some threshhold for the current heating modulation, the blower probably decreases in speed. If it gets above some threshhold, the blower probably increases in speed.

Of course distribution characteristics in a room are bound to change considerably with changing air velocity...

The problem of a variable speed circulator in a hydronic system isn't as simple as I imagined either.

Again, using generally regarded as safe max hydronic flow halving the flow results in about a ±2% relative change in friction between copper tubes of different size. So, again if you've started with a well-balanced system and half the flow rate, your flow balance stays quite intact.

In a one-pipe loop hydronic system you will mess up your balance royaly if you merely cut flow in half. The temp drop across the first b/b will nearly double and the 2nd b/b will no longer have the supply temp for which it was designed. It only gets worse and worse with each subsequent b/b. BUT, if you make the assumption that "half the flow means half the heat requirement" then you can maintain the balance by reducing the supply temperature as well. In fact, if you reduce only the supply temperature you have upset the balance as well by having a relatively higher temp available to each subsequent b/b!

One-pipe diverter tee systems would have a similar (but not as high magnitude) problem as a one-pipe loop.

With two-pipe systems (especially reverse return or home-run to manifolds with flow setters as required) flow balance among the emitters should remain substantially intact with a halving of flow. What will change however is both output and delta-t (both dependent upon the characteristics of the emitters). Delta-t will increase due to the lower flow and output will decrease due to the lower average temperature. The decreased emitter output causes a problem (faster cycling) for the boiler unless it is also modulating output.

Perhaps someone will verify my math and logic. It does though seem that modulating flow is a natural extension of modulating heat output. Do either without the other and something breaks down somewhere in any system. It would appear that only Viessmann and Rheem have truly figured out how to do this...

In the case of Rheem however, I'd really like to know how their multiple thermostat systems function. Modulating supply dampers? Digital supply dampers? In either case however, it would seem to me that the supply/return balance would be affected unless the returns also have similar dampers. Not as much of a problem in heating only systems where centralized returns are used with the natural flow of cool air under doors, etc. is utilized, but with combined heat/cool systems where individual room returns are almost always needed for proper operation???

thp_8

Return

It's always nice to see a full blown zoning system with a common return. Right down the center hallway of a building.

thp_8

It's always

nice to see a full blown zoning system and then find out it has a common return right down the center hallway in a building.

S Ebels

F/A zoning

F/A zoning with a common return (unzoned) never made a lot of sense to me either. Typically, you find zone dampers only on the supply side of the system, with all the return(s) staying open. Howzat supposed to work?

thp_8

You tell

me, and we will both have a secret.

Cliff Brady

Great Discussion Mike, ? Hydro-air Var. Spd. Blower?

I have been contemplating a new thread to try to get some discusion regarding control of Outdoor Reset modcon boiler hydro air with a variable speed air handler. Does anyone have any experience with this and are able to describe the sequence of operation and interaction of controls? To keep it simple and applicable to a jointly owned family farm house of ours, I am primarily interested in a non-zoned application.

John Mills_5

4 speeds?

In heating, the blower varies as the firing rate varies trying to maintain 50 or 65 degree temp rise. So all winter, the blower speed will change over the 13 firing rates. In the summer, you preset the size of the A/C and it varies as duct conditions change to be as close as it can, like any VS blower, to your desired CFM.

Mike T., Swampeast MO

Calculated (didn't do) that for someone about a year ago. Not sure if the system was ever installed however.

Can you post or write me with specs and principles of modulation for the V/S air handler in question?

If I recall properly, the difficult part was keeping air velocity tolerably high (for room air temp diffusion), water supply temp relatively low and air temp sufficiently warm in moderate weather. Rather tough balancing act...

jerry scharf_3

HERS rating

There is already this program in place. You can get an energy star rating for the house, and the estimated savings will add to the appraised value of the house on which you can borrow.

The problem is that the real estate agents want to sell the most houses for the highest price. No agent wants to put a tag on a house that says it's horribly expensive to run. Probably they don't really want to put a tag on it that says it's almost free to run. They want buyers happily imagining that this house is the house of their fantasies, and that real world things like operating costs are "downers."

So it's about educating consumers to demand this information. Perhaps this is something that home inspectors could sell as part of a buyer contracted inpection. An overall estimate of the relative cost of operating this house and the likely comfort level. Even a check box for whether there are annual maintenance tags for the furnace or boiler.

sorry, preaching to the choir.

jerry

Cliff Brady

Farm House

The house in question has a 1960s era 150mbtu propane furnace and an electric (11 cents/KWHr-ouch)water heater. Heat loss is probably closer to < 100mbtu from looking at the propane usage. My goal is to come up with a design concept to work with the local contractors on in anticipation of eventual failure of the furnace. I also want the co-owners sold on the design so a furnace isn't just slammed in at replacement time.

I am considering gylcol based hydro air system with an indirect and whatever modcon bolier the locals are comfortable with. From what I have gathered here on The Wall, pretty good comfort and savings can come from ODR hydro air, but I am looking for answers to the logic and workings of variable speed air handlers on ODR hydro air.

Mike, it sounds like you have done some thinking along these lines, but do any other Wallies have any actual experience with the ODR/hydro air/VS air handler option?

I also understand that glycol hydroair may be more freeze tolerant than 90+ furnaces which is an advantage given the remoteness of the farm house and that it is usually unoocupied although it does currently have full time residents.

jerry scharf_3

common return

You can return into a common return plenum, but it had better have a return per room (except rooms with exhausts.)

To make this work, you need to step up from what it commonly available in residential air zoning, and go to proportional control dampers and carefully placed heat sensors. IMO you have to have one controller doing both the fan speed and damper positioning, again not available with most residential air handlers. Once you have this, doing air is similar to a TRV, but a good bit more complex (handling heat and moisture, room average air speed, preventing DX coil freezes...)

Now you know what I do in my spare time.

jerry

don_163

Common return

It work because it take supply air which is above atmospheric pressure and push the air to what is know as below atmospheric pressure in the return.

Take a supply outlet in a room and closed the door..will the
room become positive pressure or would it simply equalize and have no flow what so ever?

Ahhh before you can say it let me..it depends.

High pressure goes to low pressure always..so if you do not
have any high pressure to push the air back to the low pressure area then you have no movement.

Your thought?

Rick T

modulating firing rates

John,
Which unit is it that is controlled to maintain a temperature rise across the heat exchanger?
I imagine it has temp. sensors in the supply and return.

rick t

John Mills_5

RGFD/RGGD

The top Rheem/Ruud unit with "Contour Comfort Control".

The supply & return sensors are only used for initial calibration to check what static is to maintain the right temp. Not sure the exact logic behind it but was told they aren't active during normal cycles. During furnace heat cycle after power up, it will do this. From then on the variable speed blower knows duct conditions and varies. From what I've seen, not perfect to 50 or 65 degrees but close.

S Ebels

The thing is............

Most "modern" housing does not have a return in each room. Typically, the low bidder gets the job and one of the things that are invariably left out are returns. There will be one large return in a central area or hallway and a small one in a couple bedrooms. A return in a finished basement is as common as hair on a frog.

So given that scenario, how the heck does a zoned forced air system perform as advertised? I have never run across one that does.

I can see the supply only zoned system working only if there is a corresponding return in each zoned area or room. I could be wrong though. My wife told me I was wrong once or twice before:)

thp_8

PSC or ECM

Did any one do the math to prove the PSC wrong.
If you do you wont like what you find.
Sales tactic?

Trevor Baptista

I am using a WM Ultra Boiler that feeds a fan coil in my V/S Trane AH. The Ultra also supplies my indirect DHW tank. Feel free to ask me questions about the system. Also, the boiler is running on a OTR control.