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.
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.