A successful email and telephone outreach campaign to Lescure Engineers’ prior contacts and efficiency industry partners resulted in invitations to audit six wastewater facilities which had not previously hosted a utility sponsored audit. A comprehensive list of the facilities in the San Francisco Bay Area was developed and we methodically conducted an outreach campaign to find interested staff.
We leverage our successes by writing up as Case Studies to promote additional work. We presented a start to finish pumping optimization Case Study at the WEF National Conference on the Energy/Water nexus in 2011. We have also made presentations at local water industry professional meetings.
Novel Measures and Solutions
There are a number of tried and true energy efficiency measures in wastewater facilities – such as variable speed pumps, turbo blowers, and dissolved oxygen aeration controls. We’ve recommended all those when appropriate, and will continue do so. But, there are only so many tried and true measure opportunities out there. We have the capability to find and evaluate novel measures, through in-depth understanding of the treatment processes and equipment:
1. Almost all wastewater efficiency measures are targeted at electricity savings, although CalPOP incentives are available to save natural gas purchases. At the Town of Yountville (Napa County) wastewater facility, the gas collection system for the anaerobic digester had plugged, so the digester gas was being vented, and instead natural gas was being burned to heat the digester. With the CalPOP audit, we qualified the Town for a zero interest PG&E loan to restore and improve the gas collection system. We are in the final design stage, and expect completion before the end of 2012.
2. At the San Leandro wastewater treatment plant, we recommended a novel twist to a turbo blower retrofit. They have two aeration trains; only one is operated, and in the other the aerators are covered with a foot of water and kept in operation at reduced flow. In addition to the turbo blower, we added a dedicated low cost blower to supply air at low pressure, increasing the energy savings over just using the higher pressure turbo blower air, and wasting pressure through a control valve.
3. At the Yuba City purified oxygen wastewater plant, site staff was interested in retrofitting 30 year old reciprocating compressors with new variable speed rotary screw compressors. Unfortunately, the energy savings from simply replacing compressors did not justify the cost. We found an additional, novel energy saving strategy with the oxygen purification process controls, that quadrupled the anticipated energy savings with minimal additional capital cost.
4. Also at Yuba City we were able to energy model an air stripping basin, used to remove carbon dioxide and raise the pH of the effluent to the point where it could be discharged. Currently, a fixed speed blower delivers an air volume needed only at the highest plant flows. We developed a pH control strategy based on variable air flow, reducing air volume (and electricity) when possible.
5. At the Livermore Amador Valley Water Management Agency, we showed that leaking check valves on a large pump station were wasting $17,000 a year when the pumps were shut down. We measured the leakage, and showed which of the ten check valves could be cost effectively replaced.
Process Energy Modeling
The general objective of an energy audit is simple – where and how is energy being wasted, how much can the waste be reduced, and what will it take? In the case of wastewater processes and equipment, getting to the answers requires a set of specialized skills and tools. To support wastewater facilities in improving energy efficiency, there are a number of skills and tools that we have developed and refined:
1. One common feature of wastewater treatment processes is the variability in flow and organic load – both daily, and seasonally, with rainwater infiltration during the wet season. To accurately predict the energy savings, these variations have to be accounted for in the technical analysis. We have developed extensive software tools to combine long-term historical data from facility SCADA systems with short-term power and critical process variable logged data (acquired as part of the CalPOP program). This establishes a solid technical foundation for modeling the operation of the targeted equipment or processes, and predicting the energy savings from proposed improvements.
2. Many of the efficiency improvements involve fluid movement- pumps and blowers. Centrifugal pumps and blowers have complex performance characteristics. We have developed software tools to integrate the complex performance characteristics of pumps and blowers with the variation in treatment plant flows and process loads.
3. Improving controls is more often than not part of an energy efficiency measure. Control systems engineering - knowing the capabilities and limits of industrial control computers, instruments, and control elements such as automated valves, is one of our specialties.
4. Some energy saving improvements, such as our project to capture and use digester gas at the Town of Yountville, require an in-depth knowledge of wastewater processes, chemistry, calculation methods, and equipment. We are familiar with standard wastewater process operation, and the engineering principles that apply.
For utility sponsored energy efficiency programs such as CalPOP to receive continued authorization, they must produce verified energy savings. Most CalPOP audit recommendations require capital expenditures in excess of $50,000. For wastewater facilities to assume the risks involved with these capital projects, the energy saving measures proposed must meet their organizational goals. We listen to site staff to understand what measures they would support, and the types of solutions they are most interested in. As a result, ten wastewater facilities have implemented, or are planning to implement, at least one of our recommended measures:
There are loan programs available from the utilities and the California Energy Commission, targeted to implementing process energy improvements in public facilities. We can assist with the technical portion of the application. Typically, the CalPOP audit report, which is an investment grade audit, is sufficient to provide the technical documentation for the loan application. We can support the application process, if loan approval requires additional information.
Engineering Design Services
While some process energy efficiency measures are straightforward, and can be implemented by site staff with the recommendations of the audit, others are more involved, and required additional final engineering design to proceed. We are able to leverage our knowledge and process modeling developed during the audit to fine tune equipment specifications and design details. The largest projects may require competitive bidding for construction services, and bid quality drawings and technical specifications. We offer engineering design services to cover these different options.
On larger energy efficiency capital projects, final design often requires four primary engineering disciplines: electrical, mechanical, civil, and process control systems. Lescure Engineers has highly qualified in-house civil engineering staff. We also perform the higher level of process and control systems engineering in-house. We partner with a local electrical design firm, DMT Associates, for the power supply and detailed controls design. We partner with Axiom Engineers for mechanical design services. We manage the design team to keep the effort on track to deliver the anticipated energy savings, within both the capital and engineering budgets allocated.
Alternately, we can support other engineering design teams with guidance and information developed during the audit process. This provides valuable continuity between the audit and final design, to insure the original intent of the energy efficiency measures are met.
If we prepare the design documents, there may be some interpretation and supplemental information required to successfully complete the installation. We stand ready to support the installation effort as needed.
Energy efficiency is often the Cinderella in the movement toward a sustainable energy culture. It lacks the glamour and high profile of solar panels and fuel cells. But, when properly applied, it delivers the bottom line of balancing energy supply and demand at a cost that its higher profile stepsisters can only envy. As a concrete example, we offer a Case Study of the reclaimed water pumping energy efficiency retrofit at the City of Santa Rosa, completed in 2010. The project was initiated by Rosenblum Environmental Engineering, one of our partners, with a CalPOP audit in 2007. Lescure Engineers assisted with the financing, directed the engineering design to produce bid quality documents, and assisted with equipment procurement and installation. The benefits flow to a variety of stakeholders:
1. The City of Santa Rosa is saving 895,500 kilowatt-hours (kWh) of annual power purchases, which would have cost $107,300 per year. With a 20 year project life, it costs the City about five cents to save each kWh (includes amortized capital costs and engineering). Had they declined the upgrades, they would still be paying PG&E twelve cents (at 2008 rates, certain to escalate) to buy those same kWh’s and waste them. In addition, the three new pumps installed gave them a boost on asset management, taking the workload off aging pumps. Two new flowmeters allow them to measure total irrigation water delivery for the first time, and monitor long term pump energy efficiency.
2. From the perspective of other PG&E ratepayers, who only had to pay for the cost of the CalPOP incentive program to get Santa Rosa’s wasted kWh “freed up” for others to use, it’s even cheaper. Santa Rosa was paid $97,295 as a cash incentive; the investment grade audit supplied by the CalPOP program to identify, describe, and sell the project cost $28,000. If we allow $42,000 for CalPOP’s program overhead, we estimate a total expenditure from ratepayer supplied funds of $167,295. Given that program cost, each kWh freed up over the next 20 years will cost PG&E ratepayers about a penny.
3. The project will reduce fossil fuel carbon dioxide emissions from power generation by 230 metric tons per year. Fossil fuel carbon dioxide is the largest single contributor to the greenhouse gas climate change threat.