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HomeMy WebLinkAboutCity of Nenana Biomass District Heat System 65% Design Report_Wood Fired Boiler Plant - Jun 2021 - REF Grant 701402865% Design Report Wood Fired Boiler Plant City of Nenana Nenana, Alaska June 4, 2021 Presented by Cushing Terrell For City of Nenana Cushing Terrell. Cushing Terrell Project: NENANA BIOMASS City of Nenana Wood Fired Boiler Plant 65% Design Report INTRODUCTION June 3, 2021 This report summarizes the basis of design for a new wood fired boiler plant for the City of Nenana, Alaska. The new wood fired boiler plant will be constructed as a stand alone building and will house a boiler room, a chip storage area, and an area to store City owned equipment. The east end of the building will also house a future washeteria. Pre -insulated piping will be installed from the boiler plant to Nenana School, the Water Treatment Plant (WTP), and the Nenana Fire Department building to distribute heat from the boiler plant to these buildings. The report will provide information on the existing heating systems, fuel use, wood boiler sizing, boiler plant system design, and the building integration design. A site visit to review existing conditions was completed by Nathan Ratz with Cushing Terrell on April 22-23, 2021. EXISTING BUILDING INFORMATION Nenana School was constructed in 1955 and expanded in 1966 and 1986. The gymnasium was constructed in 1972 and was connected to the main school building during the 1986 addition essentially creating a single contiguous building that is approximately 70,000 square feet. There are two boiler rooms in the facility: one in the original school building and one in the gym. In a major mechanical system retrofit approximately 15 years ago, new heating water mains were installed throughout the facility, and the boilers were re -piped to provide heat to this main loop. That work allows any boiler to provide heat to the entire facility. The main boiler room has two cast iron, sectional boilers, fuel oil fired, each rated at 2,500,000 Btu/hr output. The gym boiler room has two cast iron, sectional boilers, fuel oil fired, each rated at 950,000 Btu/hr output. Two main system pumps operating in lead/back up configuration circulate the heating hot water through the buildings. Several smaller pumps serve various equipment and parts of the building by pulling water from the main loop. The building has a digital control system with a front end that allows monitoring of various HVAC equipment. The Water Treatment Plant (WTP) was constructed in the mid 1970's and a complete renovation of the plant including the heating system is currently underway. The building is approximately 3,000 square feet. The renovation will provide two new fuel oil fired, cast iron, sectional boilers, each rated at 396,000 Btu/hr output. The boilers provide heat to the building, but also provide heat to the water system to keep it above freezing in the winter and to facilitate treatment processes. The new design incorporate taps in the heating hot water piping to allow the new wood fired plant to heat the new system. A new control system will be installed to control the water treatment plant process and this system will also control the HVAC equipment. Cushing Terrell. Page 1 City of Nenana Wood Fired Boiler Plant 65% Design Report June 3, 2021 The Fire Department is a metal building with two modular buildings attached to it that was constructed in the 1980's and is approximately 6,000 square feet. The facility is heated with two fuel oil fired boilers, each rated at 272,000 Btu/hr output. A basic controller provided with the boilers stages the boilers on and off and starts/stops the zone pumps. The new boiler plant will be 6,500 square feet and will be located on a lot between the school and water treatment plant. The foundation for the building has been poured. A metal building superstructure has been purchased and will be installed with super insulated panels for the roof and the exterior walls. The estimated envelope heating load for this building is 120,000 Btu/hr. The primary source of heat will be from the wood boiler located inside the building, however, a small fuel oil boiler will be installed to provide back up heat in case of operational problems with the wood boiler. The back up boiler will only be sized for the boiler plant building heating loads and is not intended to provide heat to the other buildings or to the future washateria loads. The City has purchased a wood fired boiler from Biomass Energy Techniques, Inc. out of Versailles, Missouri. The boiler is a model BET 24-S and is rated for 1,400,000 Btu/hr output. See the appendix for the boiler size summaries for each building. CURRENT HEATING ENERGY USE The school is using on average 34,000 gallons of fuel oil annually; the WTP is using on average 17,400 gallons of fuel oil annually, and the fire department is using approximately 4,200 gallons of fuel oil annually. See the appendix for a summary of fuel use. The heating Energy Use Index (EUI) for the school is 67.3 kBtu/SF, for the WTP is 803.3 kBtu/SF, and for the fire department is 97.0 kBtu/SF. The WTP is an outlier and out of range for the typical building heating energy use seen for commercial buildings. This is due to the significant amount of energy used to heat the municipal water for treatment and for freeze protection, so the majority of energy used at the WTP is for process loads. BIOMASS BOILER SIZE Wood fired boilers do not modulate well, so it is best to size them so they can operate at full load as much as possible, which allows them to operate at maximum efficiency as much as possible. The peak heating load of a building also does not occur very often, usually less than 10 hours in a typical year. For this Cushing Terrell® Page 2 City of Nenana Wood Fired Boiler Plant 65% Design Report June 3, 2021 reason, Cushing Terrell does not recommend sizing a wood boiler for the peak heating load, but to size it large enough to meet approximately 80-85% of the typical annual heating energy use of the building. The existing heating systems would be used for the other 15-20% of the time during peak heating conditions, during times when the biomass boiler is down for servicing, and during swing months when only a few hours of heating each day are required. In general, previous energy models of various school buildings have shown that a boiler sized at approximately 50% of the peak load will typically accommodate approximately 85% of the heating run hours. A basic temperature bin data heating energy analysis was performed to help determine how much energy the new wood boiler will be able to offset for each building. School: For the school envelope loss, all heating hours from September through May were used. For the school ventilation air, 7,500 CFM was estimated based on review of the existing school mechanical drawings and based on information from the school. The units operated five days a week from September to May from for the hours from 6:00 a.m. to 4:00 p.m, and the heating hours from these time frames were used. Using these assumptions, the bin model estimated 36,300 gallons of fuel oil use for the school compared to the reported average of 34,000 gallons. The estimated peak heating load is 3,000,000 Btu/hr at -60 F. This correlates with recent experience at the school. For a late winter cold spell three months ago, the low temperature reached -40 F, and the school was able to heat with a single primary boiler rated at 2,500,000 Btu/hr and the air handlers operating with minimum outside air being provided. Using this analysis, if 600,000 Btu/hr of heat energy can be provided to the school, it is estimated to offset approximately 80% of the total heating energy. Fire Department: For the fire department envelope loss, all heating hours for the entire year were used. There is no mechanical ventilation at the fire department to account for. Using these assumptions, the bin model estimated 4,400 gallons of fuel oil use for the building compared to the reported average of 4,200 gallons. The estimated peak heating load is 175,000 Btu/hr at -60 F. Using this analysis, if 60,000 Btu/hr of heat energy can be provided to the building, it is estimated to offset approximately 80% of the total heating energy. Water Treatment Plant: The majority of the fuel oil use is for process loads, and those loads vary by use within the city and by outdoor air temperature, so it is very difficult to model the process load profile and estimate the associated energy use. The envelope Cushing Terrell. Page 3 City of Nenana Wood Fired Boiler Plant 65% Design Report June 3, 2021 heating energy was estimated to determine approximately what portion is for building heating. For the envelope loss, all heating hours for the entire year were used. Using these assumptions, the bin model estimated 5,000 gallons of fuel oil use. The estimated peak heating load is 200,000 Btu/hr at -60 F. Using this analysis, if 70,000 Btu/hr of heat energy can be provided to the building, it is estimated to offset approximately 80% of the total heating energy. The peak connected load for the building heating equipment and the heat exchangers for the process heating is 575,000 Btu/hr (320,000 Btu/hr for the process heating and 225,000 Btu/hr for the heating equipment). Since there is a consistent load from the water treatment plant, the design will account for 500,000 Btu/hr of energy to be transferred at the WTP to maximize the potential fuel oil offset. Boiler Plant In the future, when the washateria is built out, the majority of the fuel oil use will be for clothes dryers, domestic hot water for clothes washers, and for heating make up air for the dryers. Those loads will vary significantly by hours of operation and actual use by citizens, so it is very difficult to model the process load profile and estimate the associated energy use. The envelope heating energy was estimated to determine approximately what portion is for building heating. For the envelope loss, all heating hours for the entire year were used. Using these assumptions, the bin model estimated 3,000 gallons of fuel oil use. The estimated peak heating load is 120,000 Btu/hr at -60 F. Using this analysis, if 42,000 Btu/hr of heat energy can be provided to the building, it is estimated to offset approximately 80% of the total heating energy. The peak connected load for the building heating equipment and the future water heaters, dryers, and make up air units is heat exchangers for the process heating is estimated to be 1,120,000 Btu/hr. The wood boiler output is 1,400,000 Btu/hr. On a peak heating day with full use of the washateria, there would only be approximately 280,000 Btu/hr available for the district heating system. However, this would be an extremely rare condition. This would have to occur on a peak heating day of -60 F, and it is very unlikely that the washateria will be in full use on a cold day such as that and also require all the dryers, make up air, and domestic water heating at that time. Another way to look at the boiler capacity is to review the amount of energy required for 80% offset. In the appendix is a summary showing this for each building. Looking at just heating the buildings, and ignoring the process loads, to obtain 80% offset in the district heating loop and 100% offset at the boiler plant, 855,000 Btu/hr would be required. This would leave 545,000 Btu/hr for process loads at the water treatment plant or the future washateria loads. Cushing Terrell® Page 4 City of Nenana Wood Fired Boiler Plant 65% Design Report BOILER PLANT DESIGN June 3, 2021 The new boiler plant will have areas for the wood boiler and associated fuel handling equipment, heating system components, a chip storage area, and an area where city equipment such as a loader and/or a grader can be stored. The eastern portion of the building will be finished out as a washateria in the future. See drawings for further information. Chips will be stored in the middle portion of the building. A loader or skid steer will deposit chips into the day bin. A horizontal conveyor will move the chips north to a pit where the chips will drop onto a conveyer that will lift the chips and deposit them into the metering bin on the boiler. The boiler has a bio char auger that will move the material to the north and deposit it into a bin that the City will collect and dump. The proposed hydronic system will have the boiler on it's own hydronic loop with it's own pump to circulate to a thermal storage tank, which is calculated to be approximately 1,000 gallons. See appendix for the sizing calculation. This tank will serve as a hydraulic separator, and the hot tap on the tank will then feed two loops. One loop will be for the district heating. Two base mounted pumps with variable speed drives will circulate heating water from the plant to the three buildings. Flow will vary to meet the various loads of the buildings. The second loop will be for the boiler plant and future washateria. This loop will be a primary cascade loop with pumps for each heating need. The systems requiring hotter water temperatures will be served first, and the systems with lower temperature needs (such as the in floor radiant heat) will be served last. The heating fluid will be treated water — no glycol. The plant will have an emergency generator to provide power to the main system pumps and the back up boiler. So the water will be able to be circulated and heated enough to stay above freezing when there is an emergency situation. Where outside air will be heated, such as the make up air unit for the dryers, a small glycol loop will serve the coil, and a heat exchanger used to heat the glycol loop. The majority of the building will be heated with in slab radiant heat. The exception being the boiler room, where supports and other equipment will need to be bolted into the floor, so having tubing will be problematic. The boiler room will have a unit heater for back up, but the residual heat from the wood boiler will likely heat the room. The boiler plant will have a small fuel oil boiler to provide heat when the wood boiler is down. This boiler will only be sized for the building envelop heating, and not for any process loads. Cushing Terrell. Page 5 City of Nenana Wood Fired Boiler Plant 65% Design Report June 3, 2021 The boiler room and chip storage area will also be ventilated and opportunities to utilize the waste heat will be investigated. The future washateria will require domestic hot water heaters, clothes dryers with hot water coils, an energy recovery ventilator for the shower rooms, and a make up air unit for the dryers. INTEGRATION WITH EXISTING HEATING SYSTEMS Integration of the wood fired boiler system will be relatively straight forward at each building. The field visit confirmed the location of the boiler and mechanical rooms and identified the points of connection for the existing heating systems in each building. See the drawings for further information on the site pipe routing and the integration at each building. School: Preinsulated PEX piping from the biomass boiler plant would run below ground from the new boiler plant to near the north entry to the school. The piping would rise up on the exterior and then enter the building in the maintenance office area and run through the ceiling of the maintenance offices, a hallway, and a teacher break room and enter the original boiler room. The portion of exterior piping above grade will be covered with an insulated enclosure. Once the heating water piping enters the existing boiler room it would run to a heat exchanger located next to the air handling unit under the walkway. On the other side of the heat exchanger, a primary -secondary piping connection would be installed in the existing heating water return piping and a pump would circulate water from this connection though this heat exchanger to inject heat just upstream of the boiler connections. A Btu meter would be installed to measure energy use of the school system. A temperature sensor would also be installed on the district heating piping so that if the district loop is not warm enough to provide beneficial heat to the school, the heat injection pump on the school loop side would not operate. Water Treatment Plant: Preinsulated PEX piping from the biomass boiler plant would run below ground from the new boiler plant to the northeast corner of the WTP. It would rise up and enter the building and then run to the boiler room. A heat exchanger would be installed in the boiler room in a spot identified in the renovation project, and the district piping would connect to the hot side of the heat exchanger. On the other side of the heat exchanger, piping would be extended and connect to the primary - secondary piping taps that are part of the renovation project. A heat injection pump would circulate water from the building heating loop through the heat exchanger and inject heat into the return piping just upstream of the boilers. Cushing Terrell® Page 6 City of Nenana Wood Fired Boiler Plant 65% Design Report June 3, 2021 Fire Department: Preinsulated PEX piping would run below ground from the WTP to the east side of the fire department where the boiler room is located. This is a continuation of the loop serving the WTP. A heat exchanger would be installed on the storage area above the boiler room, and the district piping would connect to the hot side of the heat exchanger. On the other side of the heat exchanger, piping would be extended and connect to new primary -secondary piping connections to the building return piping. A heat injection pump would circulate water from the building heating loop through the heat exchanger and inject heat into the return piping just upstream of the boilers. ELECTRICAL SERVICE The new boiler plant will be provided with a new 480 volt, 3 phase service from Golden Valley Electric Association. Attachments: • Building Fuel Use, Heating Load, and Boiler Load Summary • Wood Fuel Use Summary • Temperature Bin Energy Analysis • 65% Drawings Cushing Terrell® Page 7 Wood Fired Boiler Plant City of Nenana Nenana, Alaska nistoncai rues uu use Average Annual Building Gallons School 34,000 Water Treatment Plant 17,400 Fire Deparment 4,200 Total 55,600 Heating Boiler Summary Output Building Equipment Fuel MBH School Boiler 1 Fuel Oil 2,503 Boiler 1A Fuel Oil 2,503 Boiler 2 Fuel Oil 950 Boiler 2A Fuel Oil 950 Total 6,906 WTP Boiler 1 Fuel Oil 396.0 Boiler 2 Fuel Oil 396.0 Total 792 Fire Dept Boiler 1 Fuel Oil 272.0 Boiler 2 Fuel Oil 272.0 Total 544 Preliminary Boiler Plant Boiler 1 Wood 1,400 Boiler Fuel Oil 148.0 Total 1,548 Heating Equipment Summary, WTP and Boiler Plant Building Equipment MBH WTP Building Heating Equipment 254.6 Process Heat Exchangers 320 Total 574.6 (Preliminary) Boiler Plant Envelope 120 Dom. Water Heaters (2 x 100) 200 Dryers (10 x 35) 350 Make Up Air Unit 450 Total 1,120 I nermal Storage I anK bizin V min = gmin x t 500 x dT For modulating boilers. V min = minimum required volume (gallons) qmin minimum heat ouput of boiler (Btu/hr) t = minimum time of on cycle at minimum firing rate (minutes) dT = water temperature rise in tank based on absorbing all heat from combustion (deg F; 500 = constant based on water V min qmin t T begin T final (gal) (Btu/hr) (min) (deg F) (deg F) 1050 350000 45 150 180 25% Firing Rate Cushing Terrell June 4, 2021 Wood Fired Boiler Plant City of Nenana Nenana, Alaska neaang Loaa summary Heating Heating Building Heating Load Estimated Load Area Output Index Peak Load Index Building Sq. Ft. Btu/hr Btu/hr/SF Btu/hr Btu/hr/SF School 70,000 6,906,000 98.7 3,000,000 42.9 WTP 3,000 792,000 264.0 200,000 66.7 Fire Dept 6,000 272,000 41.8 272,000 41.8 Boiler Plant 6,500 148,000 22.8 120,000 18.5 (Estimate only, envelope loss only.) rsurnmea vvooa csouer sae ana rracuon or i orai rnergy Heat Energy for 80% Fuel Offset Building Btu/hr School 600,000 WTP 75,000 Fire Dept 60,000 Boiler Plant 120,000 Full Building Heating Load for Boiler Plant Total 855,000 Wood Boiler Ouput 1,400,000 545,000 Btu/hr available for process and peak loads. Based on Temperature Bin Energy Estimation Annuai energy use ana rocenuai vvooa ruei use aummary Avg. Current Current Gross Gross Building Annual Fuel Est. Energy Energy Heating Area Heating Fuel Cost Annual Convers. Use EUI Building Sq. Ft. Energy units $/Unit Cost Btu/unit Therms kBtu/SF School 70,000 34,000 Gal $3.00 $102,000 138,500 47,090 67.3 WTP 3,000 17,400 Gal $3.00 $52,200 138,500 24,099 803.3 Fire Dept 6,000 4,200 Gal $3.00 $12,600 138,500 5,817 97.0 Totals 79,000 55,600 Gal $166,800 Chips/Ground Fuel 80.0% Fuel Oil Building Wood Gross Equiv. Equiv. Boiler Energy Boiler Energy Energy Wood Wood Est. Use Est. Use Convers. Fuel Fuel Building Eff. Therms Eff. Therms Btu/Ib tons tons School 0.82 38,614 0.75 51,485 5,712 450.7 360.5 WTP 0.82 19,761 0.75 26,348 5,712 230.6 184.5 Fire Dept 0.82 4,770 0.75 6,360 5,712 55.7 44.5 Unit Fuel Costs Net Gross System System Delivered Gross FuelType Units Btu/unit Effecienc Btu/unit $/unit $/MMBtu $/MMBtu Fuel Oil gal 138,500 0.82 113,570 $2.90 $25.53 $20.94 $3.00 $26.42 $21.66 $3.25 $28.62 $23.47 $3.50 $30.82 $25.27 $4.00 $35.22 $28.88 Chips tons 1.142E+07 0.75 8,568,000 $60.00 $7.00 $5.25 Cushing Terrell June 4, 2021 � E a � o m E E E o 3 v Q 3 - m Y = o a ;ao — 3 — � m E n ¢ � s 6 mom= UH 3 Y a - o a = O 3 o a ;ao — 3 — � A mom= UH ))/ � -_ U F= o � 3 Y a - O a = O 3 o a ;ao — 3 — � A mom= UH