Efficiency vs. Economy

Larry (from OSHA)

We have many discussions about efficiency of systems and condensing verses anything else, and I'm wondering just how does this all work out. If you have a typical boiler running on and off and using reset to extend the burner off cycles while the circ is still running, how does this compare to a modulating boiler firing all the time, at a lower rate? I think I understand jacket losses and what goes up the flue, but I'm trying to get my arms around this concept of having the burner firing all the time and still saving money. I've read all of Mike T's Vitodens posts, so I see that in his situation less gas is burned, and maybe I should just accept that this is the deal, but, I've always thought that if the burner isn't firing, I'm saving money. Most efficient or most economical? Maybe someone can put this into VERY plain english so a simple mind like mine can grasp it.

Thanks for hopefully illuminating the finer points of all this.

Larry (from OSHA)

Bill Nye_2

Keep up vs catch up

Keep up vs catch up. You are applying energy at approximately the same rate it is leaving the building.

It is like adding the heat at a trickle vs filling up a 5 gallon bucket of heat and then dumping it out all at once.

If you turn the burner on/off you lose efficiency because the start /stop of any burner is not complete combustion. The chimney , combustion chamber, etc. has to warm up cool down at the start stop of every cycle. [ more for oil than condensing modulating gas]

Kinda' like a flywheel effect. Steady state . I know what I want to say but lack the words to explain.

Just about every boiler is too big for the house all but one or two days a year. You need the btus on the coldest day, the rest of the year you don't. The burner only knows on and off. It don't care what the temperature is. The Vitodens does and it adjust the temperature of the water and the burner input.

Larry (from OSHA)

Ok

So I get all this, but am I mistaken that there is a difference between efficiency of a system and economy regarding the amount of fuel used? Maybe this is right in front of my face and I just can't see it. I appreciate your bearing with me here as I only have my own system to compare to. I added outdoor reset last year and saw a decrease in fuel usage. (Thanks Bill for your input on that one back then. I especially liked your analogy to cruise control.) So my system fires to a given temp based on the outside conditions and the circ runs a long time. (baseboards, by the way) My confusion comes when trying to figure out how I save money by having the burner fire at between 20k btu's to 80k btu's all the time verses 100k btu's for perhaps 15 or so minutes per hour.

Easily confused minds want to know.

Larry (from OSHA)

hr

Consider this

a VW bug with a 36 hp engine or a VW bug with a 360 hp engine. Drive them both at 35 mph from point A to point B Which will be the more efficient powerplant for the bug?

The most efficient burner is one that isn't running! The next most efficient is one that is regulated to exactly meet the load and convert the chemical energy into thermal energy with the least amount going up the flue pipe, and the least amount of water volume and boiler mass to lose heat to the surrounding space in the off mode.

Often basic atmospheric boilers require combustion air vents. The standby loss from a larger poorly insulated higher mass boiler go right out the window (combustion air openings)so to speak

When you add all these loss factors it shouldn't be hard to see why a small, tight, sealed combustion, low mass, low water content, condensing, outdoor resetable has such an advantage.

hot rod

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Bill Nye_2

When

When I was a young pup I worked for a construction company. They had a TD-25 that burned 11 gallons of fuel an hour. I had some kind of turbo diesel and it a had a decellerator pedal instead of an accelator. So in a sense it ran wide open. It could knock over a large oak tree with little effort. It could push a LOT of dirt.

They also had a little JD 350 . It was used for grading around a house. It could go for a day or two on 11 gallons of fuel. Make sense?

Why would you need a 100k burner to match a 20k load? I am trying Larry, but I lack the vocabularical prowess of others on this site. I'm just a plumber.

Steve_OH

Maybe this will help

For simplicity's sake, let's assume that your boiler is rated to operate at 92% efficiency, no matter what it's output is, whether it be 20 kBTU/hr or 100 kBTU/hr. Don't forget that the 92% number assumes that the boiler has warmed up to normal operating temperature.

So what's the overall efficiency if the boiler is running continuously, at somewhere around 20-80 kBTU/hr? Well, it's going to be 92%, obviously.

But now what about when it's been off for a while, and you turn it on? At the moment you turn it on, efficiency is essentially 0%, it fairly quickly rises to something over 50%, and then it gradually increases to 92% over a period of several minutes. During that warm-up time, the efficiency is invariably less than 92%, partly because some of the energy is consumed in warming the equipment up, and partly because the combustion dynamics are sub-optimal (in other words, until it's warmed up, it's not running under the conditions it was designed to run). So what's the overall efficiency of this setup? Well, once it reaches its normal operating temperature, it will be 92%, of course, but for the several minutes it takes to reach that temperature, it's going to be significantly less than 92%. Therefore, the _overall_ efficiency has to be less than 92%. (92% plus a number less than 92% always equals a number less than 92%.)

Again, this is a very simplified example, and you'd have to do detailed calculations or measurements to know exactly what's going to happen in any given real situation, but it does give the general idea.

-Steve

Mark Hunt

Curious


"The most efficient burner is one that isn't running"?

So I paid money for something not to do what I paid money for it to do? That is "burn".

I like these efficiency posts. I wonder what unit of measure is being used to measure "efficiency?

Combustion efficiency? Every chart/program currently used is based on Stoichiometric combustion. We can't do that here on Earth so it is a false number.

Question for the group:

5000 sqft. garage. 12' ceilings, R-21 in exterior walls. R-38 in ceiling. Air infiltration is 2336 cfm @ -50pa.

Slab insulation is 2" of Polystyrene horizontal and 2" Polystyrene verticle 4' down on the perimeter. 350 sqft of glass. No shading.

How big should the boiler be designed at a -10 design day?



Mark H

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hr

Depends on

how warm you want it inside At -10° indoor design you would need the burner I mentioned above, output of 0 btus/ hour

hot rod

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hr

TD !

That wasn't one of those old Allis Chalmers 2 cylinder, two stroke diesels with the supercharger on top was it? My dad had one of those engines in the shop with a cracked block. Sure was a conversation piece! Pistons like gallon paint cans

hot rod

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Bill Nye_2

International Harvester

TD-25 Like this only older, it was a 1964 and it was a cable , not hydraulic.

S Ebels

Larry

Go back to Bill's cruise control analogy. You have outdoor reset on your heating system which smooths out the spikes in water temp going to your baseboards. It does this by regulating the temp and therefore the amount of heat, "btu's", carried by the water. As you noted, you have observed fuel savings from this.

You have half of the efficiency equation. The other half is this. In the cruise control scenario as your system stands presently you still have a V-8 which is doing the work of a 4 cylinder for most of the winter. What your reset system did was allow you to run that V-8 at something less than full throttle but it's still a V-8.

Now thinking of your boiler as the "engine" that drives your heating system; think about what fuel economy your vehicle would get if the cubic inch dispacement of the boiler/engine could be continuously variable according to the load. If your "engine" could vary from 120 cubic inches up to a 455, you would be able to almost exactly match whatever driving conditions you were experiencing.

That is what a modulating burner does for your heating system. No start up losses because it's nearly always on. Always just the right amount of fuel used to meet the conditions. That's efficiency, and efficiency = economy.
The two are hand in hand.

Larry (from OSHA)

I see, said the blind man

Ok, I'm getting the point of all this and I thank all of you. Now, I'd like to quantify the savings that I might be able to obtain with a new boiler. I know that currently the old boiler is somewhat is oversized at 133k in and 109k out. My total baseboard capacity is (I think) about 70K (about 120 feet) and my attempt at the Slantfin heatloss program shows a need for about 70k or a little less. Also, a while back, Constantin posted an excel program (heating plant sizer) that computes btu needs based on therm usage. I seem to be right about there.(actually less with the dryer and bbq grill and DHW as part of the total used) The question is will I see a payback in any reasonable amount of time.

I really appreaciate all the input from each of you.

Larry (from OSHA)

Weezbo

Hello Larry the OSHA guy .

so oo....:) You wanna buy a new boiler hey? maybe redoo some of the old pipes near the boiler ,maybe add some year 2000 type stradegies and controls maybe even go modulating condensing , hey What have you been eating for breakfast ? it sounds like you woke to find, what the lot of deese guys been on about ,.actually makes sence:) I hope you have a chance to twist a few wrenches on the install..........are you considering an American Boiler or is there one you have an interest in from germany japan korea china? if it were my dollars i think id hold out for a smuggeled import just because the Buderas modulating condensing boiler looked THAT GOOD *~/:) sorry ....i know i have sinned ....evile deamon me:( wanting something not currently available....as usual ....thinking of disguising myself as a Canadian and slipping across the border soon as one lands in thier country ...:) still really liking the 106 percent efficentcy due to calorific effect........equally intrigued with the Viessmann that i read about said to deliver 111 % efficentcy....Beliving it! and Everything

Mike T., Swampeast MO

The difference between efficiency of a system and economy regarding the amount of fuel used is the desire and need of a human.

Gordy

Larry that is exactly what I'm trying to decifer. I don't think there is anything real concrete to go by that I have seen. I know I will save money, the question is how long is the pay back going to take and is it worth replacing a boiler that has alot of life left in it but not as efficient 82% in my case. I guess the enviroment is an arguement and if the cost of fossil fuel spirals upward it will become more worth it.

I think it will be hard if not impossible to have a formula that fits every case. I only say that because everyones envelope is a little different, and the types of radiation, fuel types. The only true way would be to install the new boiler and compare the efficency with your old one. I think if the manufactorers can come up with a concrete formula they will sell alot more boilers high efficiency ones that is.

Weezbo

ok i am going to try paint shop...

not that it is going to help very much though it might if the picture is clear that i draw.

Weezbo

ok i am going to try paint shop...

not that it is going to help very much though it might if the picture is clear that i draw.ah heck i cant make a decent fire box and flue way....well,consider this look at a stew pot or spagetti pot on the stove ok we will exaggerate a bit and call that the old style 239K btu stove pipewhen it lets the heat out it really lets the heat out.now say a small saucepan for like two -three eggs is the flue ways you have now...when the heat turns off in the burner it lets some heat out....now take a look at the fridge maybe it has an auto icemaker drink dispensor blah blah blah blah blah..that is fed by an extremely small tubing....thats sorta like the size of the heat that is escaping from a modulating condensing boiler...running wide open to feed the demand. should it be on stand by for some reason thats the gist of it.... the old burners were some what Blast furnace the newer ones some what stablized, the modulators they are stablized throught a Spectrum to meet specific demand ,correcting over time to match the heat out put with the heat loss due to variations in outside temps weather conditions in door heat gains external solar gain and other losses and gains bought about by useage occupancy loading if you needed 15,851 btus thatis all its going to produce and take its time doing so :)just in case new information becomes available that might influence its activity... sorta stops to consider as it were ,while involved with meeting the demand. how much energy are we talking about saving? over what period of time? on a rainy day or a windy day? with or without a roof on the building? seriously there is a real difference in control of the reasonless beast older style burners didnt have much going for them..they were like "GO!" ..."STOP!":) new style can gradually transform their useage of fuel to meet very specific demands step it up step it down still keep going...never more than it needs to do ,never less than required ....how much does it save?...i gave up on that idea decades ago..in stead i replaced it" with how much i was wasting and never realized it.....".

Mark Hunt

Whoops


Sorry! I forgot to mention the 70* indoor temp.

My bad.

Mark H

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S Ebels

Additional info required

Are there doors or windows in the garage?
why the 25.68 air changes per hour?

We did a 6,000 sq ft auto repair garage a couple years ago. 6" slab with 1 1/2" of blue board underneath and on the edge of the slab. R-19 walls and ceiling.

A 140 Munchkin is heating it just fine. (Took 3 days of continuous high fire to bring the slab from 38* to operating temp) That slab will literally pound out the heat when the overhead doors open up. 2 minutes after they close, it feels like they were never open. Fuel bill is less than 1/2 what his previous 4,500 sq ft., similar construction building was.

Larry (from OSHA)

Mike

I have read and reread your post. I have stared into the Swampeast sunrise. I just don't understand. I strive to approach the level that you think at and I doubt I'll ever get there.

Thanks for all the various knowledge you impart to this group.

Larry (from OSHA)

Larry (from OSHA)

Hey Weezbo

Well I'm not rushing out to get a new one just yet, but if gas goes through the roof, it would be a real consideration. As far as piping and control stuff, last year I put the outdoor reset controller on and this year repiped to pump away. All in all, it seems to run much happier now.

What make of boiler in the future? I don't know. I like to buy American and finding the right combination of reliability, quality and price will be the challange. While I embrace new technology for the most part, when it comes to something as critical as heating the house, I have been extremely happy with the reliability of my 20 year old Weil Mclain with zero bells and whistles on it.

By the way, any chance of finding your way to Minnesota for the Wetstock in June?

Take care,

Larry (from OSHA)

Mark Hunt

Let's say


2 overhead doors, metal skin w/1" insulation. 10'x12'each.

Glass is double pane low-e fixed panel. 600sqft.

As for the infiltration, I'm just chucking number out there.

We did a 5000 sqft. garage last year. Full radiant with OD reset and a Munchkin 80m driving the whole thing.

The 80m is only heating the structure so it never fires above 100 degrees,max design day boiler outlet temp.

My scenario is only slightly based on this project.

I was in a new plumbing showroom the other day that had radiant floor heating for 4000sqft. They installed a 150k btu output boiler to provide heat to the three zones of 1/2" Pex. All three zones had 3/4" supply and return piping for the manifolds. Cast boiler with no mixing device other than the aquastat on the boiler.

A guy at the counter did the design.



Mark H

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Christian Egli

A Ferrari racing a garbage truck. Hold on.

There is only a fluid answer to this problem.

Efficiency measurements depend on usage style (more) and equipment features (less). The things that affect usage style are: system sizing, indoor temperature setting, degree of tolerance to indoor temperature fluctuations, thermal inertia, outdoor temperature... the list can go on. The thing is, none of these characteristics are ever set in stone.

Thus, there is no one-for-all method of operating your boiler that guarantees permanent optimal efficiency.

It's this darn environment with its rotten mixture of seasons... with beautiful green growth in the spring and magnificent fall foliage... that is the source of all our heating problems. If it were constantly the same all year around, night and day, we could have the most efficient boiler operation. It would be boring. And there would nothing to talk about, not even the weather.

Picture the erratic weather in the form of a garbage truck going down the street.

Sometimes it goes fast, sometimes not. It stops too. It often just crawls slow enough that the garbage technicians (is that the PC term?) can follow it on foot, and then, it rushes to the next pile of trash. Every once in a while it will go wild, and knock over the whole garbage can.

Your mission with your boiler is to follow that garbage truck. That’s it. Sounds easy? Try it one day, for real, it will be the most annoying thing. Plus, people will beep the horn at you.

The closer you get to the truck, the warmer you are, the faster it gets away from you, the colder you get.

You now put your car in drive. You go forward. How hard do you push on the gas pedal? Is it better to leave a good space between you and the truck (that’s the degree of tolerance in indoor temperature fluctuations)? Is it better to modulate your speed so that it is nice and smooth? What if you can’t modulate slow enough? you’re running your car for the whole morning just to do a 0.2 MPH crawl, that’s not efficient at all. Could tailgating be better?

Eventually, you’ll be bored with modulation, you’ll just step on it, lurk forward, and park . This is probably not more economical than the slow speed chase, but, maybe if you can park for 5 minutes at the time, you can save some real fuel by shutting the engine, or the flue, or something.

What about the engine size? Perhaps a tiny engine could do the trick better than a big one; but it won’t keep up with the truck as it races back to the dump. Meanwhile, a big engine will turn into a guzzler if it idles too long as the crew loads up the trash.

It seems that modulating a tiny engine is near pointless but very valuable for a big engine. Do you just floor the gas pedal or modulate it? What’s better, wild stop and go, or smooth cruising? In life, a combination of both is probably the most efficient.

By the way, the outdoor reset feature is a gadget that monitors the changes in the space you’ve allowed between you and the truck. The longer the gap, the more it will make you step on the gas. It’s like a back seat driver that will scream at you for leaving too big a gap and pop your head off should you get seriously close to the truck. It probably will never let you pass the truck either.

A simple thermostat will just tell you were you are on the road and if you need to get somewhere else. No fuss, no screams, you‘re a grown up.

Still, you could race past the truck, get a good advance (that would be a temperature overshoot) stop your engine for the day and go do your thing. The truck will catch up later. Alternatively, you could give the truck a long head start. That’s how most of us deal with garbage trucks when we see them. It’s by no means a stupid way of dealing with nature.

In particular, this is the kind of thing you can do with steam heat (you don‘t have to, but you can), it’s like racing the garbage truck with a Ferrari. A bit of overkill, but fun. Getting all your driving done in a short time, getting it over with once and-for-all, seems intuitively the most energy efficient method of both heating and driving; but you have to tolerate temperature swings, just like we tolerate acceleration in a Ferrari.

So there is no best way to follow a garbage truck. Some ways may be grossly uneconomical, and none will be efficient at all times. Think about it the next time you are driving. Do you think it is better to go forward in leaps, or at a crawl? How slow a crawl is just inefficient? If you are leaping, how big an engine makes your bursts unmanageable and inefficient? At any time? Do you prefer traffic jams or unobstructed interstates? Which is more efficient?

Ultimately, I think you have to find a truck that you’ll be happy to follow and a car you‘ll be happy to follow it with. It is largely a personal question. No all-encompassing nation-wide standard can be satisfactorily defined. Plus, you individually have to be able to afford that car, and the fuel that goes in it.

Here in my town, city truck are colored in a cheerful yellow. It’s a relief because I have seen some ugly five wheeled contraptions in other towns. And the weather here is absolutely always most beautiful.

Is the sun shinning where you are?

Did this help? I had fun, I hope you did too.

S Ebels

Reliability

You have nailed something on the head that makes me hesitate when making recommendations to a customer. As far as I'm concerned, the jury is still out and will be for some time on a lot of the condensing products presently out on the market. Some manufacturers are bringing their own designs out, some are importing "proven technology" from Europe. New designs give me the shakes, I have too many nightmares about early condensing furnaces back in the early 80's. I would dare bet that less than 15% of the high efficiency equipment installed then is still in operation. As far as the afore mentioned proven technology from Europe.......let's just say that they take their service and maintenance a little more seriously there than most do here. A typical heating appliance (furnace or boiler) gets attention when it breaks or quits, usually not before around here.

The only condensing, modulating boiler that I am 100% comfortable with is, unfortunately, priced beyond the reach of most. I'm refering to the Viessmann Vitodens of course. I firmly believe that boiler is capable of a 20 year life span, over which the cost becomes less per year than buying 2 or 3 less expensive units.

As far as replacing your old W/M simply for ecomony's sake and expecting a payback, that is a false premise really. You have to look at the difference between the cost of a new W/M or other boiler compared to the Vito and figure your payback based on that, not the total price. Until fuel prices get to $2.00 per therm for natural, $2.50 per gallon for oil or propane, the $$.$$ aren't there to just yank out a functioning boiler and replace it.

jerry scharf_2

outdoor reset was key

Larry,

First, you ask what the difference between efficient and economical is. Full system efficiency will measure the fuel burned to heat your house as compared to ideal. The system with highest efficiency will burn the least fuel. It may be difficult, but at least it can be measured.

Economical factors in not just the fuel used, but also the cost of the system as well. It is usually measured as a return on investment and compared against a benchmark (if I put the rest in a CD, what would I end up with.) This can not be measured, it is a prediction. Any of the asusmptions such as benchmark performance, fuel price and fuel required can change. These are often done in spreadsheets so you can play with the assumptions.

The fact that you have already made the step to outdoor reset is important. With this, the benefit of a modulating boiler will start to show. Modulating without condensing is a bit of an odd beast, so let's make the leap to a modulating an condensing boiler.

There is a long thread about the use of these in "high temperature" situations like yours. Any time this is at or under 130, you're condensing and saving money. Even when you're not condening the combustion is better and the stack temperature is lower, so you save less money.

What the modulation does is take the start/stop costs out of the equation. When a boiler has an AFUE of x%, that is neither the best nor the worst it can do. It's what happens with in a given test scenario. It involves some number of starts, stops and water temperature. The fewer stops your system does, the more time it spends at highest efficeincy and the least overall fuel burned.

It's a bit similar to flooring the accelerator from a stop sign, running a block and then stopping by locking the breaks. The mass that you are accelerating is the firebox and chimney. The waste of energy with the breaks is similar to the heat lost up the chimney as the boiler and chimney cools. The farther you drive, the less the start and stop matters in the overall fuel used, and that's where modulation wins.

If you add constant circulation to modulation (harder with baseboards) you may have the boiler fire for weeks continuously.

I hope I didn't go on too long

jerry

Larry (from OSHA)

Christian

Does this help? Yes, it all helps. With each new analogy a new bit of information is added. This has been a great thread and in addition to providing a lot for me to chew on, everyone here has a couple of new ways to describe the benefits of that new system that they hope to install.

Yes, the sun is shining today and it is about 20 heading for a low of -2 tonite. (Weezbo, sounds like summer for ya huh?) "Seasons all the same and boring." You are describing San Diago, California. Ya, ocean, mountains, etc. etc. - all in all pretty boring!!

Thanks again,

Larry (from OSHA)

hr

Not unusual to

heat those buildings with 12-17 BTUs per foot.

I have a 10,000 foot feed store with two overhead doors that are open a lot and a 199 Munchkin heats it nicely.

We started it last year with the slab at 42 degrees Glad it had InsulTarp under it! Took a day and a half to feel the output!

I've got a 6000 foot cabinet shop powered by a Polaris 94,000. the owner is still shocked by the LP bills after 4 years of running. He claims half of what his old shop (same size)with 4 unit heaters cost to heat. Pretty easy to track LP costs when it is the only appliance in the building and the LP delivery truck prints out a fill amount.

hot rod

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Mark Hunt

COLD SLABS!!


Watch the water pour out of the condesate drain.

I must admit that even after all these years of doing actual heat loss calcs, it is sometimes a leap of faith trusting the lower numbers. Old habits stay with you for a long time.

Mark H

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Constantin

Allow me to quibble...

As with most payback questions, allow me to propose that "it depends". In general, I agree with replacing a well-functioning boiler will be unlikely to yield a ROI of 10+%... on the other hand, allow me to go elsewhere...

Included is a NPV calculator for a system that is installed today. Presently, it is set up to accept lifespans from 1-30 years, assuming uniform savings and all that. Plus, I added a factor that allows you to adjust at what rate the energy costs will increase in excess of expected inflation (CPI). If my math doesn't fail me, a $10,000 install today will pay for itself in 20 years if it saves you ~$600 per annum at a cost of capital of 5% and a energy cost growth rate above the CPI of 3%.

Naturally, if your cost of capital is higher, the required payback for a positive NPV goes up too.

When the time comes for a customer to evaluate the payback on the marginal cost of going with a high-efficiency vs. a low-efficiency system, the payback may or may not look more attractive. I mean anything can look good when your baseline efficiency is 40%... however, the marginal difference (at best) with todays boilers is on the order of 20% if you believe AFUE, but higher if you actually measure gas consumption like Mike T. has...

Defending the higher number though would be difficult at best until Mr. Ruhnke or someone like him comes up with a more realistic means of cvomparing heating system efficiency on the basis of the emitters, heaters, and transmission means used.

Gordy

Castle

Here, Here. A mans home is his castle. I will be darned if, I will roam in my castle in slippers and a sweater. Comfort is the rung above efficiency for me for now that is. Finding that fine line of both is the key.

[Deleted User]

Electricity

I have been reading this board and others for a long time. One point that is consistantly ignored is the overall SYSTEM energy efficiency. These things use electricity as well as primary fuel. Most electricity is used by relatively inefficient motors (i.e. not DC permanent magnet motors). Your milage may vary based on electric rates which can vary widely within the USA.

Constant circulation - does the benefit outweigh the electricity consumption and wear-and-tear.

Fixed speed pumps and bypasses - it makes more sense to use a variable speed pump controlled by a differential sensor of flow (i.e., pressure drop). This is particualrly true as insulation systems become more efficient and the finely divided BTU load for individual zones diminishes.

Efficiency is for the system - not isolated components.

Bill Nye_2

Comfort Harold,

Comfort, comfort, comfort, COMFORT!!!

For the cost of burning a light bulb I have no drafts, no expansion contraction noise, no temperature swings, always nice, nice, nice.

I may be using a small amount of electricity but I am saving on fuel and it is not wasting electricity. It is delivering heat at the rate at which it needs to be replaced. If it is warmer than that the pump can be shut off at warm weather shut down or by a room thermostat.

There is no way you can convince me that constant or near constant circulation is not the way to go. I am a cheap frugal yankee and I say the little money spent on the little 007 circulator is worth every penny in terms of comfort. Most of the people opposed to this concept probably never experienced living in a space heated with constant circulation.

Wear and tear? For the money a small wet rotor pump is a pretty good deal, well with in the reach of any working mans budget. I could afford to replace one every year if I had to. I have had to replace very few circulators. Most of mine are 8-10 yrs old .

Uni R

I'll see your quibble and raise you one...

Constantin,

Your model might be improved if you broke major items into different classes for ammortization. Even though someone spends $15K on a system upgrade it may be 10 years max for the oil tank due to insurance requirements or whatever, 12 years for the boiler, 40 years for the piping, 7 years for the circulators and controls. For example supposed I was comparing a buderus gas boiler to a Trinity. Most would agree that the Trinity would probably not last half as long as the big bad Buderus, but it would skew the comparison towards the Buderus where in fact it may be prefereable to replace the Trinity every 10 years. Just some food for thought...

Ex Maine Doug

I bet we will

see the new version of the model soon.

Larry Weingarten

are we looking for...

what is most cost effective? If so, than it might be good to look at how heat leaks out of the house. Dollar for dollar, isn't that where the biggest returns are to be found? I know this thinking seems like a tangent, but the question of the "Best" heating system becomes mooter the closer to zero BTUS it gets. So, perhaps finding someone with a blower door and an infrared camera to find and fix the heat leaks would be a good next step. Then, when your house has 1/2 or 1/3 the heat output, ponder the heat input question!
Tangentially yours, Larry

Mike T., Swampeast MO

Sorry for Being Cryptic

In a given system, it's the human factor more than anything that determines how economically the fuel is used. Best example is setback: used properly it's a great fuel saver; used unsuitably it reduces both comfort and economy.

Mike T., Swampeast MO

Everything starts with the nature of condensing/modulating boilers.

Say your house lost 250,000 BTUs in the last 10 hours, or an average of 25,000 BTUs per hour. You have a condensing/modulating boiler and a traditional boiler both rated for 90,000 BTU input per hour.

Both boilers use full outdoor reset and you have constant, or very nearly constant, circulation of the water.

To meet this loss of 25,000 BTU/hr your system needs water at 125°.

An interesting thing happens with that traditional boiler when it has full outdoor reset. All reset controls have a differential--typically 10°. (Smart electronic resets may be different, but they still have a differential.) So, you need 125° water. A common reset control will start the burner firing when the water drops to 115° and stop firing when it reaches 135°. Remember--you have constant or nearly constant circulation. The amount of time it takes the boiler to raise the temperature 20° will become a near constant regardless of the outside temperature. Why? Because you're always raising the same amount of water the same number of degrees. The colder the weather, the more frequently the boiler will fire, but that firing time will stay remarkably consistent.

The best gross boiler efficiency you can expect from a traditional boiler is about 87%. Just for the fun of it, let's say it actually is 87% efficient regardless of the time it runs and the temperatures of the supply and return...

Let's say that boiler runs about 12 minutes to raise the temp in the system by 20°. Over 10 hours we lost 250,000 BTUs. That 90,000 BTU input boiler takes in 1,500 BTUs each minute it fires--at 87% efficiency that means 1,305 go to the system and 195 go up the flue. The boiler fires for 12 minutes and thus consumes 18,000 BTUs, with 15,660 BTUs going to the system.

Now, we lost 250,000 BTUs in the system in 10 hours. 250,000/15,660 = 16 firing periods during those 10 hours. 288,000 BTUs were consumed with 250,000 going to the system.

The condensing/modulating boiler acts VERY differently. When consuming only 25,000 BTU/hr out of a possible 90,000 that boiler will be at or near its highest gross efficiency, around 98% for the Vitodens. (As both output and supply temperature rise, gross efficiency drops--I presume this is true for every condensing/modulating boiler.)

During this 10 hour period, the condensing/modulating boiler fires continually. At 98% gross efficiency, that boiler consumes 255,102 BTUs in order to make 250,000 available to the system.

For the same system output the traditional boiler consumed 288,000 BTUs while the condensing/modulating consumed 255,102. This is essentially the same 9% in difference between the gross efficiency ratings of the two boilers (87% vs 98%).

The condensing/modulation boiler has NO ADDITIONAL LOSSES! That 98% gross combustion efficiency is just that--98% of the fuel consumed is available to the rest of the system!

The traditional boiler has a LIST of additional losses!

Each time it fires, the HX has to be heated--while some of this comes back after firing, a portion just goes up the flue.

The traditional boiler is never producing a constant temperature--it's always either rising or falling. This too results in a loss compared to that condensing/modulating boiler that has a nearly constant supply temperature.

Now comes the "biggie". When that conventional boiler fires it is still consuming 90,000 BTUs per hour. BUT, it has to be forced into a system that can only liberate 25,000 BTUs in an hour at the required supply temperature. What happens to the difference? There are ONLY two places for it to go--into the water and up the flue. A portion does go into the water--after all, your supply temperature rises. But guess what? Even though water holds a lot of heat, it (like all substances) has a sort of "thermal inertia". It tends to resist changing temperature. When the amount of heat coming in greatly exceeds the amount of heat going out, a large and significant portion of that heat has to become a sort of "BTU gatekeeper". It has to be there to "open the door" for the BTUs that are raising the temperature of the water. Instead of going into the water, it uses much of its energy "opening the gate" to be "flushed" up the flue and replaced by a new "gatekeeper".

The condensing/modulating boiler on the other hand, doesn't need this "gatekeeper" at the HX. Why? Because the BTUs coming OUT of the system nearly perfectly match those going in. The "gatekeeper" is in the output device itself!

Now, if that condensing/modulating boiler happens to be a Vitodens with its radiant burner and your output device happens to be massive, relatively cool in temperature and itself delivering much of its heat via radiation, it gets even more efficient. Those BTUs being given off via radiation become "phantoms" that pass directly through the system without increasing its apparent temperature. (Someone PLEASE help me prove or disprove that!!!!)

Cliff Brady

Efficiency of heat exchanger at lower modulation

has not been directly addressed yet. Here is a slide from a DOE document on condensing boiler technology and application that shows the efficiency increase as modulation level decreases. This is one more reason why reset and modulation increases efficiency and I would contend, lowers wear on the boiler.

http://www.rebuild.org/attachments/presentations/RIHVACRimassa.pdf
RIHVACRimassa.pdf.
Mike T. posted a link to this a few weeks ago after I sent it too him because slide 18 promotes his idea of piping the Vitodens directly to the load using the built-in injection pump with no Primary-Secondary or 3/4 way valves.

Constantin

Excellent Points, Gentlemen!

I will try to raise your quibble in the coming days. But first, I have a birthday to celebrate.

Christian Egli

Just old ratings

I looked into old stuff.

I assumed a 100 x 50 ft sized building, to make a reasonable amount of exterior walls.

Method 1

Hawkins Maxims suggests using 1 boiler horsepower for every 6,000 to 20,000 ft3 of volume, whether it is a drafty factory or a tight dwelling. I pick 1 hp for 12,000 ft3

Your building is 60.000 ft3, that calls for 5 hp, which translates into about 50 kW or 170.000 BTU/h. Does not seem too grossly out of sync with times.

If we pick the 20,000 number, then we need only 3 hp or about 102,000 BTU/h.

Method 2

The 2-20-200. That’s 1 EDR for every 2 ft2 of windows/doors, 1 more EDR for every 20 ft2 of outside wall and 1 last EDR for every ft3 of volume.

With 600 ft2 of openings, that’s 300 EDR, the 3,000 ft2 of walls call for 150 EDR, and lastly, the 60,000 ft3 need 300 EDR. Totals up to 750 EDR or about 180,000 BTU/h.

Method 3

A spreadsheet software done on the fly popped up with 228,000 BTU/h. The -10 F design is cold, is this a garage for Santa Claus? Mind you, we’ve got a little pile of snow here today already.

With hot air units, I think you’d need at least 300,000 BTU/h to beat indoor wind chill effect, and feel any kind of warmth.

It seems to me there is not much wrong with the old methods.

Mark Hunt

Happy Birthday Constantin?


How old are you now?!?!?!?


Have a great day!

Mark H

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