Garn WHS3200 & Wood Gun E500 – Another Night Out [Part 6]

[jebatty]

See Part 1 for general information; Part 1 and Part 2 for specific information on the Garn; Part 3 for additional pictures; Parts Parts 4. 5a and 5b for update and comparison.

I have been able to make a much more accurate determination of gpm flow rate for the Garn, and therefore more accurately determine Garn output, efficiency, and heating capacity. In summary, Garn output is revised downward to 434,700 BTUh, as opposed to 472,500 BTUh in the prior posts. Garn efficiency is revised downward to 80%, as opposed to 86% in the prior posts. And Garn heating capacity is revised downward to 47% of the "burn rate," as opposed to 51% in the prior post (which also is 62% of the now advertised Garn maximum heat output).

One material question remaining in this series of posts was "actual" flow rates for both the Garn and Wood Gun, as my calculation of flow rates was based on equivalent pipe length data to determine pump head, and then using the pump curve chart to determine flow. I now have much more accurately determined actual pump head for the Garn, which allows for a much more accurate determination of flow from the pump curve chart. I am not able to do the same for the Wood Gun because of system changes now in progress since my prior posts. I will be able to do this later for the Wood Gun when the system changes are completed.

Following are the changes from the prior posts.

Determination of Garn GPM Flow Rate:
Actual Garn flow rate was 69 gpm, as opposed to the calculated flow rate of 75 gpm in the prior posts. The Garn circulator is a Grundfow UPS 40-160/2. which has plugs on both flanges for pressure gauge insertion. I used a Noshock 0-15 psi gauge and a Wika -30 in.HG/0/30 psi gauge for the pressure measurements. The reason for the Wika gauge was to allow for a determination of NPSH, if any, on the inlet. The speed setting was #2, which was the setting used during the burns previously measured. I took two readings, switching the gauges, and then averaged any differences in the readings. Here are the psi readings: Inlet +0.80/+0.80; Outlet +8.5/+8.25; average pressure differential = 7.5 psi. Conversion to pump head is 7.5 x 2.31 = 17.3 feet of head. Applying this to the pump curve shows 69 gpm.

Garn BTU output:
Corrected Garn BTUh output is 12.6 x 500 x 69 = 434,700, as opposed to 472,500 in the prior posts. For the 19 hour burn period, total BTU output was 8,259,300, as opposed to 8,977,500 in the prior posts.

Garn Efficiency:
Corrected Garn efficiency is 80%, as opposed to 86% in the prior posts. This is based on BTU input of 11,240,900, BTU output of 8,259,300, and BTU’s stored in the rise in tank temp from 130 to 156F of 693,888. The calculation is BTU Output / BTU Input, which is (8,259,300 + 693,888) / 11,240,900 = 80%.

Garn Heating Capacity
At the time of the prior tests the Garn was rated at 925,000 BTUh “burn rate.†The corrected total output over the 19 hour test burn period resulted in average, sustained output of 434,700 BTUh, or 47% of the "burn rate," as opposed to 51% in the prior posts. Since the time of my posts Garn has revised its WHS3200 specs to eliminate reference to a "burn rate" and instead state "maximum heat output" of 700,000 BTUh. I did not attempt to test "maximum heat output," but instead tested continuous, sustained heat output over a 19 hour period. My test shows that "continuous, sustained heat output for a 19 hour period" is 62% of "maximum heat output."

What Does This Mean?
The corrections made more accurately reflect what one would expect. Garn efficiency of 80% in real world operating conditions is good and likely in a comparable range to many other wood gasification boilers, which I would expect to be in the 80-85% range.

Garn continuous output at 62% of maximum must be considered in context. I suspect most Garns are not operated continuously, but instead are operated at near maximum to heat the tank of water in one or a couple of wood loads, and then not fired again until hotter water again is needed. Garn output under these conditions likely would be higher than 62% of maximum, but at other than the very high burn period, Garn output still would be less than the maximum. Based on personal experience with my boiler and what others report on this forum regarding gasification boilers, output in the 70-75% of maximum range might be expected.

As I stated in the prior post, I am not a scientist, and I cannot attest to pure scientific rigor in making this report. All I can state is that I continue to do the best I can to apply my knowledge and experience to measuring as accurately as I can the performance of two boilers, installed side-by-side, serving the same facility, and under near identical operating conditions. My comments relate only to these models of Garn and Wood Gun. I do not know whether a test of other models would produce similar results.

 

[ewdudley]

As I stated in the prior post, I am not a scientist, and I cannot attest to pure scientific rigor in making this report.

Yeah, well neither was Ben Franklin, depending on your definition of scientist.

So nice job Jim, it's great to have all the details laid out for us to see how well everything jibes. Sounds like you've confirmed the that the Garn lives up to its claims as a well developed, clean-running workhorse among unpressurized boilers. To me, real world efficiency of 80% means a lot more than whatever claims the bench-racers might make.

Although it bugs the hell out of me when someone looks up from their iPad during a meeting asking for this or that additional information, nonetheless could you estimate the range of error in the deltaT measurement? Did you 'zero' the temperature sensors by comparing their readings when they were measuring the same temperature? Also it would be great to corroborate your measurements with some flue gas readings, could you get your hands on one for a weekend or two?

And another question for anyone; what is the likelihood that the pump is performing above its published curve? It may be that the claimed pump performance is conservative.

--ewd

 

[willworkforwood]

...... This is based on BTU input of 11,240,900 ......

Jim, I know you run these tests at a school, so I'm assuming you probably don't have first hand knowledge of the wood species and seasoning. I think I remember reading you weigh the wood for these tests, but are you assuming an average MC, or did you measure some or all of it? If you do know MC accurately then your results would stand asis. But if not, perhaps you could use a grid to show efficiency, etc at various MC. But that aside, this is fairly scientific stuff for a non-scientist ;-).

 

[jebatty]

ewdudley: could you estimate the range of error in the deltaT measurement? Did you ‘zero’ the temperature sensors by comparing their readings when they were measuring the same temperature? Also it would be great to corroborate your measurements with some flue gas readings, could you get your hands on one for a weekend or two?

I don't recall whether I zeroed the DS18b20's. I know I have done this in the past on tests I have done. I believe the DS18b20 is spec'd at ±0.5°C Accuracy from -10°C to +85°C.

I'm not sure what you mean by corroborating with flue gas measurements. The Garn has a flue gas gauge, but as I stated in my posts, I don't know where it takes the measurement or its accuracy. This winter I plan to place a K-type sensor in the flue where it exits the Garn. I then will be able to compare that with the Garn gauge. The operators of the Garn have told me that the temperatures I reported are consistent with their experience from the time they put the Garn in operation. This summer the HX tube of the Garn was brushed clean, so readings this winter should be with a pretty clean Garn. Ditto for the Wood Gun. As you might surmise, the Garn is not now in operation and it may not be until December or later that temperatures are cold enough to do a repeat data collection. In that burn I will zero the sensors, and I will have the K-type sensor installed.

ewdudley: what is the likelihood that the pump is performing above its published curve? It may be that the claimed pump performance is conservative.

I have no knowledge of this and no way to achieve better performance data at this time. When I took the psi readings this morning, I took readings on all three speeds. FWIW, on Speed #1 the circulator hummed and purred. On #2 there was just a little noise. On #3 the circulator was quite noisey. Even on #3 I still got PPSH, although just barely (0.3-0.4 psi). It's possible that at operating temperature the low suction head may result in cavitation on #2 (PPSH 0.8 psi). At this time I'm pondering whether to reduce the speed to #1 (12.5 feet of head; 54 gpm; 1.1 PPSH). 54 gpm will move 540,000 BTUh at delta-T = 20, which still is considerably in excess of the continuous output of 434,700 BTUh. I also will re-do the pressure tests when I do the next data burn this winter.

willworkforwood: ... first hand knowledge of the wood species and seasoning. I think I remember reading you weigh the wood for these tests, but are you assuming an average MC, or did you measure some or all of it? If you do know MC accurately then your results would stand asis. But if not, perhaps you could use a grid to show efficiency, etc at various MC.

I assumed average MC and weighed the wood. The species would make little difference on weighed wood burns. When I do another data burn this winter I will do some "random" re-splits and actually measure MC. As a practical matter I don't think I can do an efficiency grid at various MC. That would be quite a chore. All the wood is seasoned outside, in woodsheds, and MC will be what it will be.

What holds for the future? I can think of better date nights than with a Garn and Wood Gun. My fantasy is &%#**%, but my wife won't give the go ahead. So I guess I'll have to be satisfied with a hot Garn and a hot Wood Gun.

 

[jebatty]

ewdudley: could you estimate the range of error in the deltaT measurement?

Other than error caused by the sensors, I believe error has been pretty much eliminated by averaging the very large number of readings over the burn period.

 

[ewdudley]

ewdudley: could you estimate the range of error in the deltaT measurement?

Other than error caused by the sensors, I believe error has been pretty much eliminated by averaging the very large number of readings over the burn period.

No I was just wondering if you had had the opportunity to get the pair of sensors reading the same temperature at the same time in some hot water so you could record the null point difference and use that to correct the run-time measurement. So if at about 160 degF if one sensor reads 159.5 and the other reads 159.8 then you could calibrate the difference measurement to correct for an assumed constant difference between the two.

 

[ewdudley]

I'm not sure what you mean by corroborating with flue gas measurements.

I gather it's routine to use flue gas temperature, residual unburned hydrocarbons, excess oxygen, carbon monoxide level, and whatnot to come up with a definitive measure of combustion efficiency, which would give another measure of how much heat was produced and of how much went up the flue.

 

[willworkforwood]

I assumed average MC and weighed the wood. The species would make little difference on weighed wood burns. ....

I have to respectively disagree with this. I burn lots of oak, and have come to understand that it takes a long time to season. When I started using a MM, I saw some very surprising things, such as 2 year old larger splits at 30%. I now always split oak much smaller, in order to insure 20% in 2 years. Conversely, the ash species around here season very fast, and can easily get down to 20% in 9 months or so. And the various other species are all over the map relative to time-to-season. Then there's the question of how they load and unload the wood shed. Is the older stuff rotated to the front, or is it just FIFO? And another factor may be early in the heating season versus later. So what I'm getting at is, there could be substantially different MC in one group of their wood that you burn versus another, which (if so) would make your input BTUs parameter erratic. Not saying this is the case, just that it could be. And please don't take this commentary to be a big criticism of what you're doing - I appreciate well-organized, systematic testing such as what you're doing, and sharing the results for the potential benefit of all readers.

 

[jebatty]

I assumed average MC and weighed the wood. The species would make little difference on weighed wood burns. ....

I have to respectively disagree with this.

We don't disagree. What I meant to say is that if all the wood was of the same MC, then the species makes little difference in btu content. One lb of oak at 20% MC has just about the same btu's as 1 lb of ash, etc. And I know the MC can vary. As my prior posts indicated, actual MC remains the most significant variable that could skew the results. During the next set of data burns I will check MC and narrow down the btu input related to MC.

I think it is important to realize that I'm not attempting to achieve highest possible btu output or highest efficiency, although those goals are worthy. Deep Portage is a real world operation. No staff loads based on weight or any criteria other than tossing in a "load" of wood. I weighed the wood so that I could get a handle on btu input, but otherwise I loaded pretty much in the same manner that anyone would load the boilers. I think my results closely would approach a normal user's experience.

 

[jebatty]

ewdudley: ... to get the pair of sensors reading the same temperature at the same time in some hot water so you could record the null point difference and use that to correct the run-time measurement.

I will do this in the next set of data burns. All sensors are being reinstalled, and before installation I will put them in water of about 150F. My software allows for calibration of each sensor. so I have the ability to "zero" the sensors to the same reading. Hopefully they will not change significantly over time.

ewdudley: I gather it’s routine to use flue gas temperature, residual unburned hydrocarbons, excess oxygen, carbon monoxide level, and whatnot to come up with a definitive measure of combustion efficiency, which would give another measure of how much heat was produced and of how much went up the flue.

I don't have the ability to do this. I am a volunteer at Deep Portage, and I am donating all the parts, equipment and time. While these things likely would indicate heat produced, heat up the flue, combustion efficiency, etc., I think the most useful measure to a user is btu's delivered to the system as measured by delta-T of supply water and return water at the boiler. I think that is the only heat that matters to a user and for a user is the most useful indicator of boiler performance.

 

[TCaldwell]

Very interisting Jim, I have a testo 327 fluegas analyser that you are welcome to use for testing. It could offer a spot sampling of combustion effiency for both units. I would reccomend flue/hx cleaning prior to testing.

 

[jebatty]

Thank you. Given the variability in operators, loading, and wood, how useful do you think a spot check sample of flue gas at a particular time might be? As to flue/hx cleaning before a test, this is problematic. Both boilers were cleaned this summer, and I suspect that the boilers will be first fired in September. I likely will not do my data burns until December or after when really cold winter sets in. This is the time I can test the capacity of each boiler to its fullest extent.

BTW, the Wood Gun is getting 4000 gallons of storage to buffer its operation and provide 3+ hours of heat to the system between firings.

 

[Frozen Canuck]

Looking forward to this years reports from Portage Jim. I have only one suggestion & that would be that you take along a nephew/cousin/neighbor etc. Teach them how to weigh measure & load to your standards & thereby free yourself up to record that massive amount of data. Not that I am saying you can't do it all, it would just seem to be easier if you were freed from the huge task of weighing & loading & could focus on the measurement/recording end of the project.

 

[jebatty]

Thanks for the suggestion The data recording is the easiest part. All sensors are logged to my computer. I do periodically read the analog thermometers on the Garn and the Wood Gun, mainly to see how they differ from the sensor recordings. That difference is pretty consistent, about 5F from last year if I remember correctly.