EFFICIANCY PAYBACK

ERIC_5

How can I determine the payback of efficiency? For examply should I purchase a Slant Fin Sentry (A.F.U.E. of 82-84) or a Peerless Pinnacle PI-199 (A.F.U.E. of 92). I know the cost differential is about $1500. How can I calculate the payback on this in time ie: how long will it take to re-coup my $1500.00? And what does an AFUE of 82 mean compared to and AFUE of 92?

ta finnegan

efficiency vs. operating cost

Efficiency is part of the story. But operating cost for one system on a rated AFUE vs. another system with an AFUE this can be tricky. Cost per therm or gallon of oil is a constant, then the design temperature and cycle time. The longer they run the more efficient they are, but then the longer they run the more fuel they burn.

Be careful, you may not necessarity be comparing apples to apples. Consult the manufacturer specs and talk to a pro.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Unknown

Roughly speaking

1% is roughly equal to saving ten dollars out of every thousand dollars spent on fuel.

Of course, those numbers are not the same in each house.

Longevity and maintenance costs aren't included.

The difference in installation requirements must be considered as well.

Every job is an individual case to be evaluated.

Noel

heretic

Black Art

Ask a simple question,...

I once tried to do exactly the same thing.
Should be simple enough, right?
Not at all...
AFUE is calculated using test conditions that are very unusual in the real world, and there are so many application-specific variables to consider.
Also, comparing condensing to non-condensing boilers proved to be particularly difficult.
While the AFUE concept is good, the implementation does not serve the consumer as well as one might like.

Steve Ebels

One would think

That if you have a boiler operating at 82%vs.92% there would be a 10% reduction in fuel costs. Not true. The fact of the matter is that there are a huge amount of other factors that come into play in a heating system. Case and point. Two years ago we removed a high efficiency condensing boiler from a residence, due to constant expensive maintenance costs, and in it's place installed a cast iron boiler rated at 84%. We rearranged the piping to trim down the number of zones (9 zones down to 5)and used an outdoor reset/constant circulation control strategy in place of the bang-bang on-off scenario that had been in place. This boiler is also set up to run at low water temps. (return below 120*when needed) The home owner says that his fuel bills run 10-15% less now with the cast iron boiler and the comfort level of the house is far superior to the old system.

In other words you have to think of it as a heating SYSTEM. Not just a collection of parts. A well designed system is greater than the sum of it's bits and pieces. It's how it all works together that counts.

DanHolohan

DanHolohan

DanHolohan

Jim Davis

Efficiency Payback

In the National Comfort Institute Combustion Efficiency Seminar, we ask the students which of the following Efficiencies represent the most accurate output of an appliance - AFUE--COMBUSTION EFFICIENCY--STEADY STATE EFFICIENCY---THERMAL EFFICIENCY? Then the question is re-phrased to which one is the biggest LIE? AFUE is wrong 100% of the time!! Usually the higher the AFUE the less the equipment delivers. COMBUSTION EFFICIENCY is a lie 80% of the time and the other 20% is inaccurate. STEADY STATE EFFICIENCY doesn't exist. THERMAL EFFICIENCY is the only true performance efficiency and is never measured when when evaluating new equipment operation. If new equipment was actually as efficient as stated, everyone should be seeing a 50% reduction in fuel bills. Many see none, some see a little, some see an increase and those that see a substancial change really had some terrible old equipment. The way to determine savings is to know the approximate Thermal Efficiency of the old equipment and then know what the Thermal Efficiency of the new equipment can be adjusted to deliver. Just tested a 90% furnace with a 92% AFUE. Its Thermal efficiency at factory setting was 52%. After adjustment its Thermal Efficiency was close to 90%. 8 students witnessed this phenomenom including the wholesaler that sells the furnace and all agreed that they wouldn't have believed it if they hadn't seen it!!

Steamhead

Tell us more, Jim

was the unit just way out of adjustment, or was there some other problem?

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Steamhead

Amen, Steve

I talk to many people who have gotten the idea that a new boiler will cure their high heating costs. Well, it might help, but once the boiler has transferred the heat to the water (whether boiling it or not) its job is done. From that point on, the SYSTEM must move the heat to the rooms.

I see this problem all the time on steam systems, but it can show up on hot-water as well. Fortunately, it's usually pretty easy to cure.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Jim Davis

Efficiency

No the equipment was at factory setting. Check a two stage furnace a couple of weeks ago and the thermal efficiency in low fire was 48% and 55% in high fire at factory settings. Thermal efficiency is calculated by Temp. Rise X CFM X 1.08.
Most of the time to attain higher efficiency calculations you only have to lower the firing rate or dilute the flame temperature with excess air.

T.J.

Thermal efficiency ?

Jim,

In my book : Temp.rise x cfm x 1.08 = Furnace BTU's not thermal efficiency. Can you please explain? Thanks

Jim Davis

Thermal Efficiency

Furnace BTU's is the amount of the fuel BTU's that is being transferred to the air stream. Thermal efficiency is the measured delivery BTU's an appliance delivers. The efficiency of A/C is based totally on this measurement. All other efficiency measurements create theoretical calculations that assume things that can't exist in the real world.

Unknown

How do you dilute

the flame temperature with excess air on a designed piece of equipment?

And I assume when you say lower the firing rate you are talking about reducing the input to a point lower than the recommended input on the rating plate, is that correct? And if so how do you lower that firing rate? What is the procedure?

How would you do this on a boiler?

Once you do this how are you coming up with the perecentage?

In my books Temp Rise X CFM X 1.08 = BTU (output)
are you saying that by controlling the CFM you can come up with this Thermal Efficiency number?

Jim Davis

Efficiency

I am saying that factory design allows for excess air (Oxygen in flue gas sample) that creates low flame temperatures, which create low flue temperatures and higher calculated efficiencies. 100% Flame/Heat efficiency begins when burning fuel with Zero Excess Oxygen. The Steel industry has equipment that runs close to 1% oxygen in order to get the hottest flame and most BTU value from the fuel and fuel is there biggest expense. Much new equipment is running with 10%-14% Oxygen in the flue gas samples.
CFM does not control Thermal efficiency. CFM is a requirement of the design of equipment just like 400 CFM per ton is a requirement for air conditioning. With a fixed design CFM on most furnaces the temperature rise on all furnaces needs to be consistent(the same) to accomplish proper heat tranfer and efficiency. The basic rules of Combustion and Heat tranfer are: Time (CFM), Temperature (Hottest Flame) & Turbulence (Contact with Surface)

Steve Ebels

I've tinkered with

This line of reasoning before on several occasions. It's easiest to do on natural gas where you can clock the meter to ascertain actual btu input. You take the basic output formula (Delta T x 1.08 x CFM = output) and clock the meter to see how many actual BTU's are going into the appliance. Divide the output by the input and you should arrive at actual efficiency. On a hydronic system it's more difficult to measure the output but can be done if you can accurately measure the actual flow rate and temp drop for the system.

Example using a furnace with 45* temp rise.

1.08 x 45* x 900 cfm = 43,740 btu output. This unit clocked at 69,000 btu input so 43,740 divided by 69,000 = 63% efficiency. These were actual measurements I took from a 90%+ rated gas furnace. I got it up to about 84% by playing with blower speed (higher)-- and setting gas pressure at minimum recommended. This, of course dropped discharge air temp to just about intolerable levels. Only 98* coming from the registers. Felt really chilly in that house at 70* indoor air temp.

Unknown

Steve,

How did you measure the CFM?

Unknown

Jim answer my questions

I just can not seem to get an answer to how you do all this magic on these systems.

Jim Davis

How do you measure CFM?

Unknown

Steve I have also done some

of this. Results typically complaints from customer of blowing cold air and the house not getting warm enough.
An old rule I try to follow supply duct temp never below 100 degrees with blower running. Adjust blower speed to accomplish this if possible after making sure input is correct and that system is sized correctly. Another problem here in New England is not enough return air on a lot of old systems. Typical temp rise on most furnaces 45 to 75. With all the new electronic fan timers time on time off it is very difficult to do. The problem is that furnace manufacturers can not let the furnace go longer than 60 seconds without bringing the fan on (thermal stress on heat exchanger). When we used temperature on temperature off fan controls we could play with it until it was comfortable.

The trade off sometimes is efficiency or comfort. Most of the customers I have dealt with want comfort. We work to try to give them both if we can.

I am just having trouble figuring out how all this magic is done, air adjustments done on what, gas adjustments, redesign equipment what is the secret. I guess the deal is that you have to go to the training to find out.

I guess I am not to bright because I am having a problem figuring this thermal efficency out. How do you adjust the equipment to get this to happen. I realize that if I change the draft that can change the incoming air (excess air) so I guess they are correcting draft to make this cooling of the flame to take place, if they are messing with input then what about the heat loss the installer hopefully calculated to size the unit. Lots of Questions about all this ?????? 40 years in this business and I feel dumber every day.

Jim Davis

Timmie,
Not sure what you mean by magic. Actual measurements are taken and nothing is assumed. Take that back, sometimes I assume airflow is near correct and it is always low because of high static pressure which means the equipment is even less efficienct. Is it possible to change the airflow on air conditioning 300 CFM per ton or 500 CFM per ton and add more or less charge to get more BTU's? No. All equipment Heat exchangers are the same typical design and require the same air flow based on each type of efficiency. Therefore the same Temperature Rise would be required on all makes of equal efficiency furnaces. Didn't write the rules of science, just have to conform to them.

Jim Davis

If you have two exactly same furnaces and you clock the meter and they both have 100,000 BTU input. Both blowers are measured to be delivering 1000 CFM. One furnace has a Temp Rise of 45 and the other 75 degrees. The combustion analyzer says the one with the 45 degree rise is more efficient. What is the explanation?

Tony Conner

The Combustion...

...analyzer will only look at burner eff. While this is important, it's only one piece of the puzzle.

My background is all industrial steam boilers, so I'll have to use those as a frame of reference. The only way to determine boiler eff, is to take the heat output of the steam and divide it by the heat input of the fuel. It's usually pretty easy to get the fuel used, because if nothing else, you'll get billed for it. It gets complicated if you only have one bill/fuel usage for two or more boilers, with only one fuel number. Each boiler should have it's own fuel meter. Heat output is another matter. You can look at the boiler pressure gauge for the operating pressure, then refer to the steam tables to see how many BTU will be in each lb of steam produced. You the have to subtract the BTU in each lb of feedwater, as the boiler can't take credit this "running start". Now comes the tricky part. Exactly how much steam has been generated? Unless you've spent considerable bucks on metering, the accuracy of this part of the adventure is just awful. However, lets assume that the metering is done correctly, and there are some real numbers for lbs of steam generated. You know the net BTU in each lb of steam, how many lbs of steam were made in a given time period (usually 24 hours). Multiply them together, and get total BTU out. For the same time period, you got the fuel readings for this particular boiler, and you know how many BTU in each unit of fuel, so you multiply them together, and now you've got total BTU in. Divide BTU out by BTU in, multiply by 100, and you've got % eff. Burner eff contributes to this, of course, but lots of other things do as well. A boiler is just a heat exchanger. What's it arranged like inside? Baffles? How are they arranged? Fouled heat transfer surfaces?

You can have a fabulous burner in a piece of junk boiler. Burner eff will be great, but boiler eff will still suck.

Then there's system eff. Say the feedwater temp falls for some reason. Now, instead of getting 225*F water, maybe the boiler is only getting 150*. To make the same amount of steam, it's going to use a LOT more fuel. But it's not a problem of boiler eff. If you've got the instrumentation in place, you'll know what's happening to cause the higher fuel consumption for the same steam production. Combustion and boiler eff will be essentially unchanged. System eff will be way down.

A hot water boiler, or furnace should be the same. Establish some way to get the GPM or CFM. Then you need the output temp, and the return temp. Temperatures are usually pretty easy to get. Flows are always the tricky bit.

Steve Ebels

Simple

Area of the duct in sq ft x Feet per minute air speed =cubic ft/minute

Steve Ebels

You know Jim

when somebody asks me a question I make it a point to respond. Even if it's to say "I don't know". I'd like to see an answer to the question you asked here because I don't know the answer.

[Deleted User]

Two Yeagermeisters

later, and I'm wondering if Eric asked the right question. I doubt that he, and certainly not I, can decipher some of the answers so far.

Perhaps his question should have been: "Which unit will provide the best comfort, reliable operation, and easiest serviceabilty, with a reasonable life span?"

Some will differ. However, I have found that I can provide reliable, serviceable, long lived equipment, or ultra high efficiency equipment. Just not in the same package.

Unknown

Jim, Jim , Jim

what did you do to get the thermal efficincy to 90%? Just answer the question no pitch just answer the question.

Unknown

Jim, Jim, Jim

how would you answer ERICS QUESTION. The poor guy must have a headache after all this rhetoric.

I am sure National Comfort Institute must get asked that question. How do they answer the question.

Glen

Fun with numbers ...

followed all the posts - and excellent points made all around. Out to the truck I went where I had all my formulas and dashed off several of the above examples - some add up some do not. Let's assume that the only way to measure input is to clock an appliance, cfm of gas x calorific value equals input. I have tested each and every furnace & boiler for the last five years - and the very worst combustion efficiency I have encountered is 64% with 0 ppm CO. The home owner tells me they are warm as toast. Second customer has a newer 92% furnace that tests out very close to that but complains of never getting warm. Hmmmm. Marching right along - a 45 deg delta T at 1000 cfm vs a 65 deg delta T at the same 1000 cfm in a 80,000 btuh furnace (measured input) relates to a 60% efficiency in one and an 87% efficiency in the other - my brain is confused. 87% is highly unlikely in a mid efficient furnace. The condensate should be pouring down the B vent. So are we taking the manufacturer's at their stated specs or are we really measuring cfm. I will admit that I do that very infrequently. fpm x area(in sq ft) should equal cfm. How do you calculate fpm??? I use the square root of inwc x 4005 to find fpm - I use this each and every time I fire a direct fired MUA. It works for furnaces too. I have found that slowing down fan speed will increase output temperatures, speeding up decreases output temp. But that same fan speed while warming your delighted customers - may exceed the recommended Delta T for that furnace. That's why I question some of the statements above - the math is flawed. Absolutely impossible if the variables are equal - clocked input, cfm etc. I'm not sure how the customers react in the east - but if I only offered them 100 deg F air at the registers - or perhaps 110 - I'd be out of business. They'd be so damn cold they wouldn't be able to write the cheque to pay the invoice.

Jim Davis

Efficiency

The straight answer to Eric's question is that you cannot use AFUE to compare the efficiency of anything. AFUE does not evaluate actual equipment performance in any manner.
The furnace was running at factory specs with an Oxygen reading of 14%, plastic flue temperature of 90 degrees, CO of 35ppm and a plenum temperature of 100 degrees. 14% oxygen represent a flame temperature of about 1800 degrees. It also represent the velocity the gases travel. No temperature created-no time spent in the heat exchanger and little heat transferred, yet the combustion analyzer said it was 94% efficient. The gas pressure was raised until the Oxygen dropped to 8%, the flue temperature was 115 degrees and the plenum temperature was 125 degrees and the CO dropped to 8ppm. The analyzer said it was now only 91% efficient. The furnace also had a short flue so a restricter was added to the air intake which slowed the Oxygen down to 7% and the plenum temperature was over 130 degrees. The blower speed never changed and the actual furnace thermal efficiency(BTU's in plenum) was raised close to 90%. As mentioned above this is why an 84% efficient appliance could possibly out perform a 90%.
National Comfort Institute usually presents this dilema before most people ask. It has been taught for over 20 years and never disproven, though many thought for sure they could.

Unknown

That answers only part of it.

Let me rephrase. What device did you measure the airflow WITH? I'm trying to find out what level of accuracy you have.

Noel

Steve Ebels

Noel

I use a Magnahelic gauge (model 2000-00AV) to measure air speed in the duct, typically in the plenum because all the air flows through that. I position the pitot tube at several different spots and average the reading to get a more accurate picture. There's a chart that came with the gauge that converts pressure to FPM. Then it's just a matter of FPM x sq ft of area.

Steve Ebels

Nother' question

Jim says he's tinkering with the burners/venting/etc. to produce numbers that differ from mfgr's settings and specs for O2 and excess air. What does this do to warranties and service life of the equipment? What reason do the mfgr's have for setting their equipment up in the manner that they do in the forst place? I'm missing something here.

Steve Ebels

Eric, Here's an example of

Poor system efficiency. The pastor of a local church is building a house and members of the congregation are helping him. I was contacted because they needed someone to pull the boiler permit. After doing a heat loss on the house and looking at the equipment they had purchased, I called the pastor and told him he had a fuel sucking monster on his hands. This is why.

The heat load of the house is 73,000 and change at -10* and 72* indoor. The boiler is 150,000 input. Grossly oversized. The home is divided into 5 zones which will lead to excessive short cycling of the boiler. Just imagine the run time on the burner with 150K input and 1 10K zone calling for heat. They have no idea that I can see of how much baseboard to put in each room. Some will be hot, some won't heat, No indirect, just a regular water heater for a family of 5 or 6 I think.

Do you understand why this particular system will use fuel like it's going out of style? I'm not real good with word pictures but think of driving your car down the road with the pedal mashed to the floor for 300 yards and then coasting the rest of each mile you drive. What kind of fuel economy would you expect? Now compare that thought to driving the same mile with the cruise control on keeping everything nice and steady. What mileage would you get then? Your heating system will respond in much the same way.

What I'm saying is that the over-all design and function of the whole system is just as, if not more important than what equipment is used. Hope this makes a little sense.

Unknown

I've been holding back on this subject, myself

I don't quite understand, myself, where Jim is coming from on that front.

If you set the burners up to fire higher than they are APPROVED for, intentionally, the warranty guy (me) is going to ask a LOT of questions and document every word of it.

If you alter the APPROVED draft hood, or vent it other than the manufacturer's APPROVED instructions, it seems to me that you have manufactured a different appliance, and must take responsability for it, and get it APPROVED.

If you don't get it approved, what will you do if a court case results?

And why doesn't Jim continue with this, and get his concept accepted by the approval agencies, and then become effective with manufacturers, instead of constantly teaching that EVERYONE is doing it wrong, but him.

I don't have any problem with testing, measuring, and improving equipment.

If Jim wants to develop his ideas, he night consider making one of his safe products, and find a way to get it approved, without putting contractors in the middle.

Noel

Mark Hunt

But we are in the middle Noel


I took Jim Davis's class several years ago and I have been testing ever since.

Will a manufacturer take responsibility for a severe injury or death if their equipment is left at factory specs and produces high levels of CO?

I doubt it. They will claim that it was installer error and wash their hands of it.

So what does the installer do? Leave it or change it?

You have all heard the claims that Mr. Davis makes. Has anyone here tried to DISprove them? If someone has I have not been made aware of it.

Maybe the manufacturers of equipment should take it upon themselves to test Mr.Davis's claims. Or do we just go along with the way "it's always been done"?

I will continue to put the health and safety of my customers above any other consideration.

Respectfully,

Mark H

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Bob Bona_4

a bit

confused here. Consumers need a standard to compare, in some way, efficiency ratings. "Your mileage may vary" always applies. Those in the know, know the difference between a dry base boiler's ability to get the heat to the water vs. the superior transfer characteristics of a wet base. The posted AFUE's only differ by 2-7%, and that's all the consumer has to go by. Or why a condensing boiler that has maybe a 10% higher AFUE than it's high temp brethren has more efficiency than meets the eye. 10 SEER vs.12? Those 2 extra numbers mean a lot in a lot of ways.

What is confusing me is 1)what purpose does it serve to the end user to tweak an appliance to bend factory approved settings, and 2)for the curious, how is this physically done?

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Glen

Tinkering with peoples lives ...

by tinkering with their furnacess??? Minimizing combustion air, increasing firing rate etc without any mention of clocking of appliance - shame, shame. I'll side with Mark H. Health and safety first. I would think that most of us have been to a product seminar - we know there are fudge factors built into each appliance - knowing this doesn't give us the opportunity to muck about with it. (This discussion wouldn't be a continuation on the draft diverter vs baro debate would it ?? Propogated by the same company/individual???)

Tony Conner

Do You See.

...a LOT of units that are set to factory spec's, but are still seriously off? I'm just curious - I don't do residential stuff, or even burner work. Is this a periodic problems with a range of manufacturers involved, or are some man's equipment more prone to this than others? Do you contact the manufacturer to report these problems? If they don't provide an effective response, do you contact the inspection authority? Personally, if I hit a particular unit with consistant problems in this regard, I'd ditch that product line. The liability exposure is just too great.

To me, modifications to fuel firing equipment that haven't been approved by the manufacturer is pretty risky, from a liability standpoint. If nothing else, I can't think of any manufacturer who would warranty anything that had had an unauthorized modification made to it. And for the manufacturer to approve field modifications without really investigating what's to be done, is opening THEM up to a whole range of adventures in liability exposure. This procedure would cost FAR more than the purchase price any residential unit, unless it got incorporated into the manufacturing process for thousands of assemblies.

And the way science works, is that the proponent of a given theory has to prove it. The rest of the herd gets to doubt it without having to do anything more than ask questions, and say "Oh ya? Show me." They don't have to disprove anything.

Tony Conner

Fans & Pumps...

...are very similar. They both move fluids. When you've got a set amount of heat being supplied to the hot side of a heat exchanger, there's a range of what can happen on the cold side. If you move a smaller GPM or CFM, you can get a higher delta-T. If you increase the flow, the delta-T will fall.

If you've got a heat exchanger that's transferring 100,000 BTU/hr from the hot side, then there has to be 100,000 BTU/hr being taken away by the cold side. If the HX is heating water, and you have a 20 GPM flow, the delta-T for the water will be 10*F. If you drop the flow to 5 GPM, the delta-T will be 40*F. The amount of heat transferred remains unchanged.

When you're considering CFM from a fan, can you get the flow from the manufacturer's literature if you supply the inlet and outlet pressures, like on a circ pump for water?