"BTU meter" results for WGO-5 boiler
After more fiddling around, I was able to get my new ultrasonic flow meter working to try to measure the BTU output of one of my Weil McLain WGO-5 boilers. It turns out I ordered the wrong size transducers, which only work on pipe sizes 2" and up, and I had wanted to measure the flow through the 1-1/4" copper supply pipe coming out of the boiler.
But because the 1-1/4" copper enventually transitions into three larger-diameter gravity conversion pipes, I was able to get the meter working on the three larger pipes. So by measuring the flow rates on the three larger pipes, I was able to get a total flow rate.
One interesting thing I found was that the flow rates were not steady through those three larger pipes. The flow tended to fluctuate slowly by +/- 10% or more in all three pipes, never settling down on a fixed rate. But by observing the rates for several minutes on each pipe, I was able to get a range and then take a center "average" flow rate for each. Adding those average together then gets a total average flow rate through the boiler, which turns out to be 10.1 gpm.
I also had temperature data loggers on the supply and return of the boiler, and took a 20-minute steady-state time average delta T, which turned out to be 20.2 degrees.
The combination of the flow meter and the temperature data loggers is, in effect, a BTU meter. Because of the flow fluctuations, these are not highly accurate numbers, but I think the results are ballpark reasonable.
So, multiplying through to get BTU's hour:
10.1 gpm x 20.2 F x 8.3 lb/gal x 60 min/hr = 102,000 BTU/hr (rounded up)
Then this is the measured boiler BTU output rate in the water supply. At a known oil input rate of 165,000 BTU/hr, that's a net output into water of 102,000/165,000 = 62 %.
So here's the breakdown of where the 165,000 BTU total input goes. 25% is lost in combustion (18% measured dry gas loss, plus 7% assumed latent heat of vapor loss. 62% goes into heating the water. The remaining 13% is absorbed by the boiler thermal mass as it heats up (I figure this is about 10%) and radiated as jacket loss into the basement (I figure this is about 3%).
I have a thermal post-purge set up to keep the circulator running until the water temp drops back to 90 degrees, so we should be getting some or most of that 10% absorbed by the boiler thermal mass back. Also, the basement is useful space (my shop plus laundry area) so I count the 3% jacket loss as useful heat.
So if we recover half of the 10% boiler BTU absorption in post-purge, that's 5% recovered, plus the 3% jacket loss which I count as useful heat for my shop. Adding those to the 62% measured BTU's leaving the boiler as hot water, that puts us right at 70% system efficiency.
Now, at @EdTheHeaterMan 's advice, I'm going to take this new information plus $4.50 to Starbucks and buy myself a cup of coffee. 😀
Comments
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Hopefully the ultrasonic is correct. We have had Balancing contractors in on several jobs back when I was working and all that taught me was that you can't trust ultrasonic.
One thing I have heard is they don't work with glycol or with any air in the system but you probably don't have those issues
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How much did those btu meters cost?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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nice! What’s the typical gallons per heating degree day for the building?
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The one I bought is advertised to be accurate +/- 1% as long as you program it with the correct parameters.
Operator error can reduce accuracy of many measurements, but I'm pretty sure I programmed all the parameters correctly, and the results were close to what I expected, so I think it was accurate to within a few percent.
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Well done.
I believe your numbers are very close to actual. The scam of the 84% CI boiler is now revealed in its true colors.
It's a sad commentary and a typical scam where this industry has people comparing the values of a laboratory test that fails to consider the loss due to latent heat of the vapor and fails to consider the losses from the jacket.
This is why the mod-con can save much more than it is advertised for. The comparison is not 84% to 95%. It is actually 70% versus approx. 88%.
Everything is a scam today.
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This is the flow meter I bought for $240. It's not a BTU meter, only a flow meter, so you need a separate method for measuring/recording delta T.
There are a number of different vendors selling these things on Amazon, all with the same "head" unit, but with different transducers. I didn't realize that and ended up buying one with transducers that only work for pipe sizes 2" and up (DN50, as in 50mm minimum pipe size), but if you read the other listings carefully you can find ones that come with smaller transducers that will work down to 20mm pipe (DN20).
This thing is like industrial-grade complicated, with about 100 programmable parameters. Fortunately there are only about 5 that you need to set (pipe OD, wall thickness, fluid type, pipe material, and transducer configuration), and once you figure out the interface and get those programmed in, it tells you the correct spacing for the transducers on the pipe. You set the transducers on the pipe at the proper spacing, with a shmear of acoustic coupling goop (I used Vaseline), check two output parameters to make sure the signal is good, and then it will give you real-time flow rates as output.
The instructions suck though, so you have to spend some time reading carefully to figure it all out.
And these are the temperature data loggers I used:
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For a 4800 sq ft residential building in the Boston area, built circa 1930 with masonry first floor walls, wood framed second floor walls (no insulation), and 10" blown cellulose in the attic, and upgraded windows, in an average heating season we burn about 1200 gallons for about 5600 HDD's, so that's about 0.21 gal/HDD input.
So that's our average input rate into two WGO-5 boilers running at an overall efficiency of about 70% as I showed above.
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Oversizing strikes again!
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No joke. We are sized at over 70 BTU/hr/sq ft, but need only 20 BTU/sq ft on a zero-degree design day.
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I wouldn't go so far as to call the AFUE efficiency ratings a scam. Scam is a term which should be reserved for a deliberate attempt to defraud. The AFUE ratings, just like the fuel economy ratings for vehicles or horsepower ratings for engines are determined under very specific testing conditions and are, in most instances, correct (there are exceptions, of course, and they should be called out).
The problem is, of course, that a good many people, even moderately well informed people, tend to take such ratings as an indicator or even a minimum of what they can achieve — which they aren't, and which they aren't intended to be. They are somewhat useful for comparison purposes, but that's it.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
I've done car fuel economy tests. It is a very hard problem as there are so many variables that even simple things like 12v battery charge and what the car was doing before the test effects the result. Driving is chaotic environment, there is no way to replicate that in a lab.
Boiler efficiency is an easy test. You put 100 therms of fuel in, you expect 80 therms of heat out of an 80% unit. This is easy to set up even at a house, never mind at a lab. The fact the rating is that far off, makes it disingenuous and disservice to consumers.
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The problem is, of course, that a good many people, even moderately well informed people, tend to take such ratings as an indicator or even a minimum of what they can achieve — which they aren't, and which they aren't intended to be. They are somewhat useful for comparison purposes, but that's it.
This statement, on it's face, is the epitome of a scam. To lure a good many people, even moderately informed people, to make an erroneous decision based upon facts that are not relevant to those people constitutes a scam.
There are scams going on incessantly today, and, unfortunately many people are unable to see the scam and are taken advantage of because of it.
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The dry gas efficiency of a boiler is relatively easy to measure with handheld, portable equipment that any competent tech can be trained to use, and unfortunately it seems the ease of that measurement somehow led to it becoming the "standard" for AFUE despite the fact that it neglects latent heat of vapor loss, as well as jacket loss, etc.
I don't know the history of who made the decisions or why, but I think we can all agree that it's unfortunate that a non-comprehensive dry gas efficiency measurement got enshrined as AFUE, given the amount of resulting confusion.
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But who is capable of confirming their AFUE? MPG anyone can calculate. Any boiler efficiency calculation is not a layman’s endeavor. I don’t think it’s unreasonable to stick a number on a boiler. Of course it’ll be a lab measure. We can all quibble about the methodology, but what is the ideal solution?
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The last paragraph immediately above is deeply insulting, and I hope the poster has the grace to realise that. I will neglect the errors — many — in some earlier postings.
Automotive horsepower ratings were — 60 years ago — fascinating. They weren't fiction — but one had to understand the conditions they were measured under. The Belchfire V8 in my own ride was rated at 360 hp in the advertising. And, in fact, if you measured it under the specified conditions used at the time, that's what it produced. None of us who played with cars believed a word of it, although it was a useful comparison between engines and makes, as everyone played by the same rules (just as the AFUE people do today for boilers and furnaces).
A much more useful comparison (and a very good way to measure actual power!) was to go down to the strip Sunday afternoon and see who could get from one end to the other fastest (it was also more fun). Measured that way, my Belchfire V8 produced around 290 horsepower (12 second full throttle rating). Where did the missing ponies go? Well, at that time the SAE standard was a bare engine at the flywheel. No radiator fan. No water pump. No alternator. No auxiliary hydraulics. No EGR. No PCV. Free exhaust, free intake. Never mind transmission and other losses.
To bring it back to heating — a much more useful question would be does the boiler/furnace/heat pump put out the net output rating it is listed at? A professional tradesperson will use that number — and no other — to match the equipment to the load.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
ISTR DOE does not count jacket losses when calculating AFUE, because it is assumed these are useful heat inputs to the building, as in @jesmed1 's case. Obviously this may not apply in all situations.
And don't forget, mod-cons lose heat through their jackets too.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting0 -
@Jamie Hall said:
"a much more useful question would be does the boiler/furnace/heat pump put out the net output rating it is listed at? A professional tradesperson will use that number — and no other — to match the equipment to the load."
Let's take my boiler, for example. I showed above that at quasi-steady state (meaning the boiler has been running long enough to get past the startup transient and is now outputting BTU's as a steady rate), my boiler is outputting about 62% of its BTU input as useable hot water.
This is for an 86% AFUE rated boiler, currently running at 82% measured dry gas efficiency as of last November.
So my boiler is effectively running as much as 24% below its AFUE rating. This is no surprise to me, as I've known all along that the AFUE did not include latent heat of vapor loss and jacket loss.
I'm not complaining, because after about two years of learning and research, I've finally satisfied myself that the boiler is running at 62%-70% overall efficiency, depending on how you define it, and I cared more about knowing the actual number than getting 86% overall efficiency, which I knew was impossible with this boiler.
A 24% discrepancy in advertised AFUE vs. actual output is not going to ruin anyone's boiler install, when it seems like a factor of 2 oversize is common. Nevertheless, it is unfortunate that the AFUE isn't more accurate, especially when it's used as a marketing tool by boiler mfrs to "prove" comparative benefits that may or may not be imaginary.
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Thati is called the K factor and is used by fuel dealers to predict the amount of fuel you use so they can maximize the fuel delivery schedule and deliver you fuel vased on your usage and how cold each day is during the season. A K-factor is calculated by dividing the number of degree days between fuel deliveries by the number of gallons of fuel delivered. This figure represents the gallons of fuel burned per degree day. For example, if a home has a K-factor of 6.5, it burns one gallon of fuel for every 6.5 degree days.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I agree the ultrasonic flow meters are finicky. The connection onto the pipe needs a conductive grease. I think we use a Dow 111 acoustic grease on the cuffs. True, any air in the pipe throws them off.
I think the rotary, turbine or positive displacement work best on plain water.
I don't know how much of an error the meter has thrown you?
But it seems like you are happy with the numbers?
This is a good source of flowmeter info.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Thanks for that info. I'm confident in the ultrasonic results. This meter gives you a signal strength reading, and the instructions say to look for 90% or better signal strength, which I did get. The high signal strength indicates absence of scattering air bubbles or particles that would degrade the signal and give questionable results.
I used Vaseline for the acoustic coupling, as Vaseline is an acceptable alternative in medical ultrasound tests and apparently works well on pipes too. The one downside of Vaseline is that it melts as the pipes get hot, so you have to take your readings before the Vaseline drips off the pipe. 😅
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An apology:: the errors to which I referred in my previous post were not in one of LRCCBJ's posts. A misatribution due to misreading the author of various posts — which is an explanation, but not an excuse.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
To get back on track a little here — wat I find interesting is the variation in flow in the three loops over time. Is this periodic? That is, regular? Did you measure that, @jesmed1 ? And, if so, how does the variation in flow rate relate to any variation in return temperature, if it does?
I'm wondering if this is a characteristic of gravity circulation…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Yes, I found it quite odd. I expected to see very stable equilibrium flow rates in all three loops, but the flow rates oscillated quite a bit. I didn't have a data logger, only my eyeballs, so I tried to observe max and min readings over several minutes and then take an average. So I can't give a very good account of the fluctuations except to say the typical "period" of an oscillation cycle might be as long as 15-30 seconds. In other words, very low frequency oscillations as you would expect from a high mass system.
To try to "zero out" the oscillation effect, and also the try to see if there was any temperature effect, I took two "rounds" of data. In "Round 1" I got: 0.55, 1.28, and 0.45 cubic meters/hr, for a total of 2.28 cubic meters/hr. In Round 2 I got: 0.70, 1.00, and 0.60, for a total of 2.30 cubic meters/hr.
So despite the evident fluctuations, the totals in both "rounds" were quite close, suggesting no overall temperature effect, but that certain loops would naturally have more gravity circulation as the water heated up.
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