Technical and Economic Considerations In Selection of Boiler

Technical and Economic Considerations In Selection of Boiler Size and Thermal Storage Capacity For Commercial and Small Industrial Wood-fired Boiler Systems “Small can be beautiful” Raymond J Albrecht, P. E. Technical Consultant to Lopper North America rayalbrechtpe@gmail. com www. loppernorthamerica. com

Typical Wood Boiler Oversizing Impacts Oversizing factor of 2 X or even 3 X peak heating load Increased space requirements within boiler room Capital cost premium for boiler, fuel feeding components, multi-cyclones and electrofilters, etc. Efficiency penalty during start-ups for morning heat during Fall/Spring seasons Excess hours for low load operating conditions (smoldering) with increased PM 2. 5 and UHC/CO emissions due to lower average flame temperature

Tool for sizing of wood boilers: ASHRAE Weather Data American Society of Heating, Refrigerating and Air-conditioning Engineers Thousands of US/Canada and global locations Averages and maximum/minimum values Temperatures Bin hour temperature data Humidity Wind Speed Solar Radiation Available at www. ashrae. org website

Heating Bin Hours vs. Outdoor Temperature Typical northern US location 1200 1000 Heating Bin Hours vs Outdoor Temperature 800 600 400 Hours per year Design Temp = Minus 5 deg F 4800 hours per year at 55 deg F or lower 3900 hours occur between 25 o. F and 55 deg F 80% of heating hours at 50% or less of peak heating load 200 0 Outdoor Temperature (deg F)

Wood-fired boiler sized to provide 100% of peak heating load

Output Analysis - 2 MMBTU/hr wood-fired boiler for entire heating load Temp bin (deg F) Annual hours in bin Heating Load Btu/hr Wood boiler output in bin BTU/hr -5/-1 6 1917000 - 12 12 - 0/4 58 1750000 - 101 - 5/9 66 1583000 - 104 - 10/14 125 1417000 - 177 - 15/19 243 1250000 - 304 - 20/24 354 1083000 - 383 - 25/29 511 917000 - 468 - 30/34 957 750000 - 718 - 35/39 720 583000 - 420 - 40/44 636 417000 - 265 - 45/49 577 250000 - 144 - 50/54 585 83000 - 48 48 - 3144 Totals 4838 hrs Oil boiler output in bin BTU/hr Total heating output in bin MMBTU/yr Wood boiler output in bin MMBTU/yr Wood-fired output = 3144/3144 = 100 percent of total system output Heating oil savings = Approximately 38, 000 gallons Oil boiler output in bin MMBTU/yr

Annual Output MMBtu/yr 2 MMBtu/hr Peak Heating Load 2 MMBtu/hr Wood-fired Boiler plus Oil-fired Boiler Only As Back-up Total Heating Load MMBtu/yr 800 700 600 Oil-fired boiler 500 Wood-fired boiler 400 300 200 100 0 -5 0 5 10 15 20 25 30 35 Outside Temperature deg F 40 45 50 Wood boiler meets 100% of peak heating load Wood boiler provides 100% of annual heating output

Wood-fired boiler sized to provide 75% of peak heating load Can meet heating load down to about 10 deg F Supplemental boiler provides output only for portion of heating load in excess of 1. 5 MM Btu/hr at temperatures below 10 deg F

Output Analysis - 1. 5 MMBTU/hr wood-fired boiler plus 500, 000 Btu/hr Oil-fired Boiler Temp bin (deg F) Annual hours in bin Heating Load Btu/hr Wood boiler output in bin BTU/hr -5/-1 6 1917000 1500000 417000 12 9 3 0/4 58 1750000 1500000 250000 101 87 14 5/9 66 1583000 1500000 83000 104 99 5 10/14 125 1417000 - 177 - 15/19 243 1250000 - 304 - 20/24 354 1083000 - 383 - 25/29 511 917000 - 468 - 30/34 957 750000 - 718 - 35/39 720 583000 - 420 - 40/44 636 417000 - 265 - 45/49 577 250000 - 144 - 50/54 585 83000 - 48 48 - 3144 3122 22 Totals 4838 hrs Oil boiler output in bin BTU/hr Total heating output in bin MMBTU/yr Wood boiler output in bin MMBTU/yr Wood-fired output = 3122/3144 = 99 percent of total system output Oil boiler output in bin MMBTU/yr

Annual Output MMBtu/yr 2 MMBtu/hr Peak Heating Load 1. 5 MMBtu/hr Wood-fired Boiler plus 500, 000 Btu/hr Oil-fired Boiler Total Heating Load MMBtu/yr 800 700 600 Oil-fired boiler 500 Wood-fired boiler 400 300 200 100 0 -5 0 5 10 15 20 25 30 35 Outside Temperature deg F 40 45 50 Wood boiler meets 75% of peak heating load Wood boiler provides 99% of annual heating output

Wood-fired boiler sized to provide 50% of peak heating load Can meet heating load down to about 20 deg F Supplemental boiler provides output only for portion of heating load in excess of 1 MM Btu/hr during temperatures below 20 deg F

Output Analysis - 1 MM BTU/hr wood-fired boiler plus 1 MM Btu/hr oil-fired boiler Temp bin (deg F) Annual hours in bin Heating Load Btu/hr Wood boiler output in bin BTU/hr Oil boiler output in bin BTU/hr -5/-1 6 1917000 1000000 917000 12 6 6 0/4 58 1750000 1000000 750000 101 58 43 5/9 66 1583000 1000000 583000 104 66 38 10/14 125 1417000 1000000 417000 177 125 52 15/19 243 1250000 1000000 250000 304 243 61 20/24 354 1083000 1000000 83000 383 354 29 25/29 511 917000 - 468 - 30/34 957 750000 - 718 - 35/39 720 583000 - 420 - 40/44 636 417000 - 265 - 45/49 577 250000 - 144 - 50/54 585 83000 - 48 48 - 3144 2915 229 Totals 4838 hrs Total heating output in bin MMBTU/yr Wood boiler output in bin MMBTU/yr Wood-fired output = 2915/3144 = 93 percent of total system output Oil boiler output in bin MMBTU/yr

Annual Output MMBtu/yr 2 MMBtu/hr Peak Heating Load 1. 0 MMBtu/hr Wood-fired Boiler plus 1. 0 MM Btu/hr Oil-fired Boiler Total Heating Load MMBtu/yr 800 700 600 Oil-fired boiler 500 Wood-fired boiler 400 300 200 100 0 -5 0 5 10 15 20 25 30 35 Outside Temperature deg F 40 45 50 Wood boiler meets 50% of peak heating load Wood boiler provides 93% of annual heating output

Heating Output vs Wood and Oil Boiler Capacity Percent Of Peak Heating Load 100 25% 63% 50% 93% 75% 99% 100% 125% 100% 150% 100% 175% 100% 200% 100% 90 80 70 60 50 Percent of Annual Output - Oil 40 30 Percent of Annual Output Wood 20 Percent Of Annual Heating Output/ Oil Savings 10 0 0 25 50 75 100 125 150 175 200 Percent of Peak Heating Load - Wood Boiler Horizontal Axis: Wood Boiler Capacity – Percent of Peak Heating Load Vertical Axis: RED Percent of Annual Wood Heating Output (also percent Oil Savings) BLUE Percent of Annual Oil Heating Output

Eliminating the Smoldering Mode 300 k. W wood-fired boiler plus 150 k. W oil-fired boiler for Peak and Low Loads 350 300 Annual Boiler Output (MWh per year) vs Outdoor Temperature 250 MW hrs per year 200 Wood-fired Boiler 150 Use oil -fired boiler until heating load reaches at least 20 -30 percent of capacity of smaller boiler (i. e. , about 50 k. W) depending on thermal storage Oil-fired Boiler “On” temperature for wood-fired boiler about 10 deg C 100 50 0 Outdoor Temperature (deg C) Wood-fired boiler still provides 95% of total annual output

Thermal Storage 1 BTU = 1 lb Water X 1 deg F delta T Typical practical delta T = Approximately 40 to 60 deg F One gallon Water = 8. 33 lbs 100 gallons Water X delta T of 40 deg F = 33, 320 BTU of thermal storage 500 gallons Water X delta T of 60 deg F = 250, 000 BTU of thermal storage 20, 000 gallons Water X delta T of 40 deg F = 6, 650, 000 BTU of thermal storage 20, 000 gallons Water = 2666 ft 3 = Tank dimensions of 18 ft L X 18 ft W x 8 ft H

Case Study: Large Institutional Logwood-fired Boiler System Abbey of St Benoit du Lac, Quebec Canada

Twin Commercial Size Logwood-fired Boilers Ultra-low PM 2. 5 emissions (0. 01 to 0. 02 lb/MMBtu ) Less than 100 ppm NOx 82 – 84 percent efficiency (HHV) Lambda (air/fuel ratio) control with independent primary and secondary air flow control Vertical extension to primary gasification chamber to double wood loading capacity up to 16 hours full-capacity burn time Decoupling of wood loading capacity from firing capacity important factor in meeting user interest in reduced frequency of reloading Each boiler has 1. 1 million BTU/hr (320 k. W) thermal capacity Total thermal capacity of 2. 2 million BTU/hr (640 k. W) Peak heating load is about 2. 5 million BTU/hr (730 k. W) Approximately 150, 000 square feet of heated space

Storage Tank Benefits include smoother boiler loads plus pre-charging to handle peak heating loads Approximately 6000 gallons 6000 gal X 8. 33 lb/gal X 40 deg F delta T = 2 million Btu storage capacity Can boost system capacity by 500, 000 Btu/hr for 4 hrs during peak morning loads

Storage barns for logwood 350 cords per year One year drying time Steel racks for logwood bundles Boilers can handle up to 48 inch log lengths Approximately 1/3 cord wood per bundle One logwood bundle provides for 8 hours of boiler operation under full-load conditions Boilers can handle two bundles maximum wood loading

Tractor loading of logwood bundles Tractor with front end loader carries logwood bundles from storage barn to boiler house System includes small overhead crane Bundle is lowered into top loading door Chains are then released and removed with bracket assembly

Economics of Logwood Boiler Installation Purchase cost of approximately $50, 000 per boiler Installation cost of approximately $50, 000 including labor and accessories Total system installed cost of approximately $150, 000 Heating oil savings = 60, 000 gallons per year Abbey of St Benoit du Lac Heating oil cost savings = about $220, 000 Logwood consumption = 350 cords per year St Benoit du Lac, Quebec Canada Total logwood fuel cost = $35, 000 per year Labor/equipment cost = $50, 000 per year (estimate) Total cost savings = $130, 000 per year Payback period = Just over one year Payback period would have been more than two years if boiler oversized by 2 or 3 X factor especially if larger building required Payback period would be about 9 months if only one boiler had been installed

Craftsbury Outdoor Center Craftsbury, Vermont Integrated energy system of industrialgrade logwood-fired boiler (240, 000 Btu/hr) with 150 k. W biodiesel-fired CHP and solar thermal plus 20, 000 gallons thermal storage system Photos courtesy of WR Boilers of Fairfield, Vermont and Lopper North America

Conclusions 25 % undersizing only 1 % loss of total annual wood heating output and heating oil savings 50 % undersizing only 7 % loss of total annual wood heating output and heating oil savings Reducing boiler size by 50 % can save 20 to 30 % in capital cost and length of payback period Using oil or propane-fired boiler for low load conditions can prevent smoldering conditions with just small increase in oil/propane use Shorter payback periods More customers Higher efficiency Lower Fuel Costs Lower emissions Happier neighbors “Small can be beautiful”

Thank You!