CITY OF BOISE To: From: Public Works Commission Matt Hightree, Scott Canning, Paul Wakagawa INTRA-DEPARTMENT CORRESPONDENCE Date: October 26, 27 Subject: Energy Consumption at Major Facilities Managed by Public Works This memo is presented on a quarterly basis to update the Commission on the status of energy consumed and energy conservation projects occurring at major City-owned facilities managed by Public Works. Consistent with previous memos, the two wastewater treatment facilities and information on energy use at City Hall and the Twenty Mile South Farm is presented. Changes from the previous report are shown with bold font. Energy Use Narrative for Wastewater Facilities The WEF Manual of Practice No. 11 says "Activated-sludge secondary treatment plants... can be energy intensive; these plants may use 3% or more of their budgeted cost for energy use." Both the West Boise and Lander Street facilities are activated-sludge secondary treatment plants. They use substantial quantities of natural gas for process and space heating. They also use substantial quantities of electricity, primarily for motors for pumping and aeration and for ultraviolet disinfection of the final plant effluent. Both facilities use anaerobic digesters to stabilize sludge. These digesters produce biogas (also known as digester gas), a mixture of 6 to 65% methane and 35 to 4% carbon dioxide by volume. In past years both plants utilized this gas extensively in boilers and engines to reduce required purchases of energy from utilities. However, the gas includes high concentrations of hydrogen sulfide, a chemical that is very corrosive in the presence of moisture. After combustion, high H 2 S concentrations also results in high levels of sulfur oxides in exhaust gases. Sulfur oxides are strictly regulated by the Idaho DEQ, being the primary contaminant that causes "acid rain." The biogas also contains siloxanes, chemical products that form a very abrasive residue when burned. The residue creates excessive wear on close-tolerance moving parts such as pistons in cylinders or valve discs against valve seats. The corrosion and abrasion of biogas handling equipment resulted in high maintenance costs for replacement parts and labor. Over time many biogas handling equipment systems were abandoned or replaced with lowermaintenance equipment that used utility energy sources. During this period air quality regulators were also expressing concerns over the levels of sulfur oxides in the exhaust gases, and natural gas posed no regulatory difficulties. Relatively low natural gas and electricity costs compared favorably with the total cost of equipment maintenance, including equipment replacement costs. With the sharp rise in natural gas costs during the past few years, City staff has become anxious to reduce utility energy consumption. A project to reduce the concentrations of H 2 S at West Boise has been completed, so there are currently no regulatory concerns with burning biogas at that facility. A similar project for Lander Street was started in August of 27. In the past several years a number page 1
of projects have been initiated to reduce utility energy use. Some projects involve cleaning the biogas to reduce the maintenance impacts. Other projects use the biogas in applications that previously used natural gas. The primary scum system at West Boise is being evaluated to see if there are better ways to handle the scum using less energy. Co-generation, a means of using biogasfueled internal combustion engine-generators to generate electricity and recover heat from the engines and exhaust, is being considered for the West Boise facility. The following table summarizes some of the more substantial projects. Projects to Reduce Utility Energy Consumption Project Name Dates Purpose Lander Street WWTF Digester Gas Cleaning constructed and commissioned in 24 Removes siloxanes from the gas, dries and removes particles from the gas. Facility Lander Street WWTF commission in August See comments for West Boise system below Ferrous Chloride system Lander Street WWTF Burner Replacement for Boiler No. 2 West Boise WWTF gas utilization study by B&C, with follow-up work by MWH and CH2M Hill West Boise WWTF Ferrous Chloride system West Boise WWTF biogas cleaning and storage system design West Boise WWTF biogas distribution system design for space heating of some plant buildings West Boise WWTF Digester No. 3 of 27 placed in service on May 11, 26 21 to present, master plan kickoff meeting July 17, 26. Final report issued in July 27. put in service late in August 25, stopped using July 26, started again July 27 Construction NTP Oct 3, 26, work commissioned in Aug 27 Part 1: construction completion projected for summer 28 Part 2: start design Nov 27, construction complete in FY9 2-part project. 1 st portion completed Nov 26. 2 nd portion completion projected for Oct 28 Allow biogas to be burned in Boiler No. 2, the larger of two boilers at this facility. The smaller boiler has always burned biogas. Evaluate methods for biogas cleaning, storage, and utilization. Provide recommendations to City managers for optimum gas uses. Gas treatment and gas distribution projects are planned, cogeneration using biogas-fueled enginegenerators is recommended. Master plan to consolidate previous work & develop implementation schedule. When injected in the sludge before it enters the digesters, ferrous chloride chemically binds sulfides and greatly reduces the concentration of hydrogen sulfide in biogas. Concentrations have dropped from 17 ppm to under 1 ppm. Remove siloxanes, moisture and particles from gas. Make gas suitable for use in boilers, furnaces, and engines. Install gas blower to distribute gas to equipment, and start burning gas in boilers Deliver cleaned gas to selected buildings, where it can be burned in air handler heating sections in lieu of natural gas. Part 1: Lab and dewatering buildings Part 2: Galleries and Headworks Building Increase solids handling capacity at West Boise, revise biogas piping system for code compliance page 2
Projects to Reduce Utility Energy Consumption Project Name Dates Purpose West Boise WWTF ventilation reduction study study completed in Jan 26. Design started in April, 27, completion projected for summer 28. Notes for Attached WWTF Unit Energy Use Charts page 3 Report and staff recommend code-allowed ways to reduce ventilation rates under certain occupancy conditions and thereby reduce natural gas consumption. Energy Uses at the West Boise WWTF that are not required at the Lander Street WWTF: West Boise treats stabilized sludge produced at both plants, including sludge blending, dewatering, and treatment of the filtrate (liquid removed from the sludge). The West Boise primary scum handling system is energy intensive, with hundreds of feet of electrical heat tracing, electric and natural gas water heaters for automatic scum sprays, and a portion of the hot water heating system dedicated to heating the primary scum pits and scum concentrator. The Lander Street primary scum system uses relatively small quantities of hot water to clean a mechanical drum screen a few times each day. West Boise includes the central laboratory facility for both WWTFs and other City needs. West Boise includes a permanent construction office. West Boise Gas Conditioning system started in late August 27, reflected in reduced NG uses in August and Sept. Some difficulties in early Sept reduced savings. Energy Uses at the Lander Street WWTF that are not required at the West Boise WWTF: Lander Street pumps stabilized sludge to West Boise. Digester gas blower was out of service from Aug 1 through Sept 25 due to a motor failure. Plant used natural gas for all process heating during this period, resulting in much higher NG use than previous years. Other reasons for the differences in unit energy consumption between the two plants: The West Boise facility has a design capacity of approximately 25 mgd, while the design capacity at the Lander Street facility is 15 mgd. Both plants are currently treating approximately 14 mgd. As a result, the West Boise facility heats and ventilates more and larger buildings than the Lander Street facility, increasing the utility costs per mg treated. The West Boise facility includes pipe galleries that improve access for operations and maintenance. The galleries also require energy for space heating and ventilation that is not required at the Lander Street facility. Energy Use Narrative for City Hall The City Hall Complex is comprised of three separate buildings connected by a central atrium. City Hall 1, built in 1976, has 4 floors of office space totaling approximately 6, square feet plus a below grade parking area. City Hall 2, built in 1979, has 4 floors of office space totaling approximately 42,2 square feet plus a below grade parking area. The Annex building, remodeled in the early 199's, has a single floor with approximately 13, square feet of office space below a two tier parking garage. The atrium tying the three buildings together is approximately 1,46 square feet on the first floor and is 3 stories high, with bridges connecting the parking structure, City Hall 1 and City Hall 2 on the 2nd and 3rd floors. Electricity is used in the City Hall complex for space cooling, equipment motors and controls, lights, computer and security systems, domestic water heating, and other minor loads. In the summer (June
through September) a large portion of the electricity is used for the cooling loads. Most of City Hall is cooled by electrically-powered water chillers. Chilled water circulates through cooling coils installed in air handlers. City Hall 1 has two chillers sized at 123 tons and 25 tons of cooling capacity. City Hall 2 has a single chiller with a variable output range of 23 to 136 tons of cooling. (One ton of cooling equals 12, BTU per hour.) The Council Chamber is cooled by three roof-top air handlers with integral refrigerant coils. Machine rooms have their own independent cooling systems. The electrical chart below shows the most current energy use available. City Hall's electric consumption is slightly down from last year's usage for the same period, and we are continuing to improve lighting efficiency throughout City Hall. Note that Idaho Power had a power cost adjustment beginning in June 26 that decreased the cost of electricity. Space heating for the complex is supplied by geothermal water. The geothermal water flows through separate heat exchangers in City Hall 1 and City Hall 2, heating closed hot water loops that circulate through heating coils in the building air handlers. During the summer months there is no geothermal water use, so the charts below only show the months of October through March. Energy Use Narrative for Twenty Mile South Farm Practices at the Farm have been developed to use irrigation water efficiently with the current infrastructure. Efficient water use can be related directly to electrical usage by the irrigation well pumps delivering water to the irrigation equipment (for example, kwh per million gallons pumped) and applying water commensurate with crop requirements. The Farm operation presents a number of challenges in tracking power use and costs, and in evaluating the efficiency of electrical use. Water requirements vary depending on crop ET (evapotranspiration). The Farm is installing an on-site weather station. When operational, this station will provide local meteorological data for computing the Farm ET. The ET accounts for rainfall, cloud cover, air temperature and wind. The Farm currently uses the Bureau of Reclamation Agrimet website to determine irrigation requirements using the Nampa weather station: http://www.usbr.gov/pn/agrimet/id_charts.html Water requirements vary by crop. For example, in the Boise area, the irrigation water requirement for alfalfa is about 44 inches per year while silage corn and wheat require 3-32 inches per year assuming an 8% efficiency for sprinkler irrigation. The primary objective of the Farm is to utilize the biosolids in compliance with regulatory requirements. The secondary objective is to maximize crop yields. Crop selection from year to year is made to satisfy those objectives rather than to minimize water consumption. As a result, total annual electrical consumption for irrigation water delivery would not be a good measure of Farm efficiency. The Farm does not currently have instrumentation, primarily flowmeters, to accurately measure the amount of irrigation water applied to the various crops. Pivot run times and design water delivery data for the various pivots are used to estimate the amount of water used. There are no automated mechanisms to record pivot run times and the current software does not provide a means to record historical data. In 27, handwritten logs will be kept to track total amounts applied to each field. There are plans to install flowmeters on the irrigation wells as budget becomes available. With the flowmeters, it will be possible to monitor each well pump using the flowmeter and electrical meter. Kilowatt-hours (kwh) per gallon pumped is called "specific energy," a common parameter for monitoring pump performance. An increase in specific energy for a pump often indicates maintenance is required; an increase could indicate pump bearings are failing; or that solid materials or air are restricting water flow. Comparing the specific page 4
energies of different pumps can identify inefficient pumps to be replaced with more efficient units. The Farm is in the process of installing soil moisture monitoring systems. Soil moisture information will allow further optimization of water usage at the Farm. Water can be "on" or "off" at any particular time as various pivots are operated for a particular crop and harvest schedule. Alfalfa is cut multiple times each year, and the water is off about 1 days for each cutting. The alfalfa cutting can't all be done at once, so the Farm staff decides which fields to stop watering based on alfalfa maturity. Grain fields have water cut off at mid summer to allow the grain to ripen before harvesting. This intermittent watering schedule affects electrical use from month to month, making historical comparisons difficult. The Farm has 19 large pivots and 4 small pivots, most with their own electric meters. There are 11 wells, also with independent electric meters. Some wells serve multiple pivots. There are also electric meters for some farm buildings. In all there are more than 3 electric meters at the Farm. Meters are billed on different time cycles, and on different rate schedules. Furthermore, Idaho Power offers incentives that vary for crops grown, days the power is off, and similar operating factors that Idaho Power finds beneficial for their utility operations. These incentives need to be deducted from the power costs for a particular meter to have an accurate record of the cost to operate a particular pivot. Managing all these electric accounts is a challenging assignment that complicates the extraction of meaningful data on Farm operations. Farm operations are conducted with efficiency of both water use and electrical use in mind. However, it is difficult to make meaningful historical comparisons of electrical use or to directly relate electrical use to the Farm products. With the instrumentation improvements discussed above in place, the Farm will be better able to evaluate electrical efficiency in relation to water usage. MDH/mh Attachments: Unit Energy Use Charts for Lander Street WWTF and West Boise WWTF Unit Geothermal Use and Total Electrical Use Charts for City Hall Total Electrical Use Chart for TMS Farm cc Chuck Mickelson Bill Johnson Scott Canning Rich Dees Bill Duncan Paul Wakagawa John Tensen Chris Linder H:\docs\SAR655- energy use & conservation\pwc energy report text 7126.doc page 5
Natural Gas Use, therms/mg treated 16 12 8 4 Lander Street WWTF Unit Energy Use- Natural Gas FY 25 Annual Cost: $ 82,63 for 19.12 therms/mg FY 26 Annual Cost: $ 59,133 for 1.54 therms/mg FY 27 Annual Cost: $ 49,743 for 1.48 therms/mg FY 27 budget: $16,128 (spent 47% of budget) FY 25 month FY 26 FY 27 Natural Gas Use, therms/mg treated 16 12 8 4 West Boise WWTF Unit Energy Use- Natural Gas FY 25 Annual Cost: $24,279 for 62.5 therms/mg FY 26 Annual Cost: $39,83 for 55.58 therms/mg FY 27 Annual Cost: $269,95 for 46.6 therms/mg FY 27 budget: $212,452 (spent 127% of budget) FY 25 month FY 26 FY 27 Energy Use at TMS Farm, City Hall and Wastewater Treatment Facilities through Sept. 27
Compare Natural Gas and Digester Gas use at Lander St WWTF 16 Lander Street WWTF Unit Energy Use- Natural Gas Only Natural Gas Use, therms/mg treated 12 8 4 FY 25 month FY 26 FY 27 16 Lander Street WWTF Unit Energy Use- Digester Gas Only Digester Gas Use, therms/mg treated 12 8 4 FY 25 month FY 26 FY 27 Energy Use at TMS Farm, City Hall and Wastewater Treatment Facilities through Sept. 27
Electricity Used, kw-hr/mg treated * 44 4 36 32 28 24 2 16 12 Lander Street WWTF Unit Energy Use- Electricity FY 25 Annual Cost: $355,234 for 2,1 kwh/mg FY 26 Annual Cost: $32,141 for 1,889 kwh/mg FY 27 Annual Cost: $253,953 for 2,51 kwh/mg FY 27 budget: $453,14 (spent 56% of budget) FY 25 month FY 26 FY 27 Electricity Used, kw-hr/mg treated 44 4 36 32 28 24 2 16 12 West Boise WWTF Unit Energy Use- Electricity FY 25 Annual Cost: $525,533 for 3,312 kw-hr/mg FY 26 Annual Cost: $49,155 for 2,931 kw-hr/mg FY 27 Annual Cost: $425,22 for 2,685 kw-hr/mg FY 27 budget: $566,7 (spent 75% of budget) FY 25 month FY 26 FY 27 Energy Use at TMS Farm, City Hall and Wastewater Treatment Facilities through Sept. 27
CH1 - Gallons per HDD per Square Foot Gallons Geothermal Water Used per Heating Degree Day per square foot 1.9.8.7.6.5.4.3.2.1 FY22 FY23 FY24 FY25 FY26 FY27 Oct Nov Dec Jan Feb Mar CH2 - Gallons per HDD per Square Foot Gallons Geothermal Water per Heating Degree Day per square foot 1.9.8.7.6.5.4.3.2.1 Oct Nov Dec Jan Feb Mar FY22 FY23 FY24 FY25 FY26 FY27 Energy Use at TMS Farm, City Hall and Wastewater Treatment Facilities through Sept. 27
City Hall Electrical Use by Quarter FY22-27 14 12 1 Electrical Use, kwh 8 6 FY22 FY23 FY24 FY25 FY26 FY27 4 2 Q1 Q2 Q3 Q4 Twenty Mile South Farm Electrical Use (Composite of All Meters) Electrical Use, kwh per month 1,2, 1,, 8, 6, 4, 2, Note: Sept energy use shown is first half of month only. FY 25 FY 26 FY 27 Energy Use at TMS Farm, City Hall and Wastewater Treatment Facilities through Sept. 27