Texas Facilities Commission Sam Houston Central Plant Condenser Water Loop Renovations Summer 2016 Wendell Cook, P.E. Commissioning Engineer Texas Facilities Commission Office of Energy Management Presentation Outline Description of SHB Central Plant OEM Retro-Commissioning Project Development Initial Savings Estimates Equipment Installation / Commissioning Final Savings Estimates Measurement and Verification Future Work Final Comments
Sam Houston Plant A Brief Description Four Trane centrifugal chillers with varying capacities totaling to 5650 tons cooling capacity. Condenser Water Loop: Six total cooling tower cells with total nominal capacity of 6100 tons. Six total cooling tower fans, each rated at 60 hp (360 total hp). Six total condenser water pumps, each rated at 80 hp (480 total hp.) Sam Houston Plant A Brief Description
Chilled Water Loop: Primary / Secondary / Tertiary system. Four total primary chilled water pumps, each rated at 100 hp (400 total hp). Several sets of secondary / booster pumps circulate chilled water through two loops, West Loop and South Loop (405 total hp). Most buildings have their own tertiary chilled water pumps that circulate chilled water through the building. Sam Houston Plant A Brief Description Heating Loop: Three boilers with a total capacity of 41,845 MBtu/h provide 100 psi steam to most buildings on both the South and West Loops. Steam feeds into building level heat
exchangers where it serves as a heat source for heating water which is circulated throughout the buildings. Sam Houston Central Plant feeds a total of 13 buildings in the Capitol Complex, including the Capitol and Capitol Extension. Nine buildings are fed chilled water and steam from the plant while
four only receive chilled water. The central plant also serves as a main electrical service entrance and distributes power to numerous buildings in the capitol complex. OEM Retro-Commissioning Why commission the Sam Houston Central Plant? This plant accounts for $1.5 million in State utility costs annually.
Numerous operational deficiencies known to Maintenance and Operations, but never formally documented. Critical nature of the facilities served by this plant made commissioning a necessity not only from an energy conservation standpoint, but from an operational standpoint as well. Due to the complexity of this plant, a decision was made at the onset that commissioning efforts would focus on one area of the plant at a time. Preliminary investigation indicated that the condenser water loop had the potential to yield significant savings with minimal investment and minor modifications / updates to the system. Formal Commissioning by TFC began late 2015.
Initial Findings Condenser water supply temperature was constant, set at 80F rather than varying based on outdoor air conditions. Condenser water pumps were constant flow, despite VFDs having been installed to replace aging motor starters. Modulating isolation valves at each tower condenser water inlet were programmed to modulate closed to reduce differential pressure (and hence flow rate) across the operating chillers. These modulating valves were all overridden to 50% closed.
Initial Findings Flowrate through the condenser water loop was controlled via a single loop differential pressure sensor rather than differential pressure or flow across individual chillers. Cooling tower fans were being controlled individually via independent CW temperature sensors rather than modulating in unison. Isolation valves at chiller condenser inlets were two position rather than modulating / allowing no flow balancing between operational chillers. Chillers, towers, and condenser water pumps were mismatched in size. Chillers require varying condenser water flow rates, but the average flow rate at which the
chillers operate most efficiently is approximately 4800 gpm. Each tower cell / pump combination provided a constant flow of 3000 gpm. Thus, initial findings indicated that chillers were consistently being provided with excess water flow, wasting significant pump energy. Recommended ECMs / Optimization Modify sequence of operation so that condenser water supply temperature setpoint modulates with outdoor air wet bulb temperature.
Modify sequence such that cooling tower fans for enabled towers modulate in unison to maintain condenser water supply temperature setpoint. Install insertion style electromagnetic flow meters at each tower and for each chiller condenser water inlet (10 total) and modify sequence so that system is controlled based on measured condenser water flowrate rather than overall CW system differential pressure. Modify valves at tower inlets so they act as two position rather than modulating valves. Recommended ECMs / Optimization Modify valves at chiller condenser inlets so they modulate to balance flow across running chillers. Modify building automation system so that existing condenser water pump VFDs would be utilized to modulate pump speed and provide only the necessary condenser water flow to the running
chillers. Cost, Payback, and Funding OEM developed a new sequence of operation and a preliminary project scope which was sent to Siemens for pricing. Cost of implementation estimated at $132,000. Payback period estimated at between 1-2 years. While preliminary cost / payback estimates looked quite promising, TFC did not have an internal source of funding available for project implementation and the project began to stagnate Until SECO stepped in and volunteered to help out with available funds set to expire at the end of the 2016 fiscal year.
Inter-Agency Cooperation With funding made available by SECO through an IAC, TFC was able to push forward with the SHB project. Additionally, through cooperation with Texas A&Ms Energy Systems Laboratory, we were able to satisfy the intent of HB1184 (passed) / HB2919 (left pending) which was to establish a TFC / ESL / SECO pilot program for state owned buildings operated by TFC. The legislation essentially called for TFC to enter into a performance contract with ESL with project funding through SECO. While this project was did not involve a performance contract, the intent of the bill was achieved.
Project Development Texas A&Ms Energy Systems Laboratory was retained by TFC through an IAC to provide the following services: Review updated sequence of operations prepared by TFC and recommend
improvements. Review operational and performance data for SHB plant and develop baseline model for determining energy savings Estimate savings expected from proposed plant upgrades. Prepare a Measurement and Verification Plan to measure ongoing energy savings. Provide commissioning / functional testing of the final installation. Prepare and deliver M&V reports through September of 2019. Siemens was retained by TFC through an independent contract to perform the necessary equipment and sequence modifications for the SHB Central plant. Total project cost (Siemens and ESL) was just above $156,000. Initial Energy Savings Estimates
With assistance from Siemens and our Building Automation Department, ESL was set up to automatically receive emails with trend data for all monitored central plant BAS points. This data was used to quantify baseline energy consumption for the purposes of tracking savings and to provide a means of verifying the accuracy of the system model developed by ESL. The system model, and energy savings calculations were developed by an ESL graduate team under the direct guidance of Dr. David Claridge, P.E. (Director of ESL). Initial estimates predicted savings at 2,140,000 kWh or approximately $150,000 annually (assuming $0.07/kWh). This constitutes 17% of the current energy cost of operating the chillers, condenser water pumps and cooling tower fans. Equipment Installation & Commissioning
Installation was completed on a tight schedule to ensure that the project was complete before the end of the fiscal year. The project kickoff meeting was held on 7-12-16 and installation was completed by 8-25-16. Functional testing was completed by 8-29-16. Despite the tight timetable, the project was completed on schedule with only a few minor sequencing / installation issues discovered as part of functional testing. During the commissioning process, ESL also helped TFC uncover an underlying issue with the pump sizing / system design for the condenser water loop. Pumping Issues
During the Cx process, it was found that because the CW pumps all feed into a common header, they begin to fight each other at higher flow rates, when 5 or 6 pumps are enabled. With 1-4 pumps enabled, each pump produces very close to the rated 3000 gpm flowrate. With 5-6 pumps enabled, flowrates for each pump drop down as low as: 2500 gpm (5 pumps) or
2100 gpm (6 pumps). As more pumps attempt to push water into the header, the necessary head pressure that must be overcome by each pump increases. Pumping Issues The pumps were not initially sized correctly to address the header phenomenon. ESL was able to quickly account for this issue with their energy savings model and discovered that because of the nature of the pump curves for the turbine type CW pumps, the effect of the pumping issues on the
savings was only marginal. Final Energy Savings Estimates Annual savings estimates dropped from 2,140,000 kWh or $150,000 per year to 1,531,000 kWh or $108,000 annually because of the system pumping issues. Condenser Water Control Strategy 702,000 kWh ($50,000) Cooling Tower Fan Control Strategy - $829,000 kWh ($58,000) The new savings estimate constitutes a 12% overall reduction of the energy cost associated with operating the chillers, condenser water
pumps, and cooling tower fans. Despite the reduction in savings, the minimum estimated ROI for the project was in excess of 60%, twice the 30% specified in HB2919. With a $156,000 initial investment, the payback estimate is approximately 1.5 years. Measurement & Verification ESL was contracted by TFC to provide measurement and verification services through September of 2019, with monthly reports provided directly after the installation, quarterly reports for the following year, and
annual reports for the two years thereafter. Since the installation, monthly savings have ranged between $6,000 - $15,000, depending on use and prevailing outdoor conditions. The first three months of operation indicated total savings in excess of $30,000. The project is well on track to achieve the annual savings estimated by ESL. Future Work As funds become available (perhaps in FY 18-19) TFC hopes to push forward with Phases II and III of the central plant upgrades.
Phase II involves recalibrating / replacing / installing new pressure sensors, temperature sensors, and flow meters as required for the entire SHB chilled water distribution loop. Phase III will involve optimization of chiller staging and chilled water pumping sequences for the SHB plant. OEM is also already planning to expand these RCx efforts to other TFC operated central plants. Future Work If other State Agencies are interested in pursuing similar retrocommissioning efforts with their facilities, OEM is available as a resource. Per HB 2166, TFC is allowed to contract with other agencies for the provision of services as cost recovery. OEM is able to assist other agencies with:
Information on commissioning / energy management. Provision of commissioning services. Selection of commissioning consultants. Management of commissioning projects. Final Comments In addition to shaping up to be a highly successful retro-commissioning project, the SHB Central Plant Upgrades Project highlighted what can be achieved with inter-agency cooperation.
This project would have taken far longer to implement had SECO not stepped in to assist with funding. The short project timeline simply would not have been achievable without outstanding effort from all parties involved. Many thanks are due to Dub Taylor, Eddy Trevino, Fred Yebra, and everyone at SECO, Dr. Claridge and his team at ESL, and the installation team at Siemens. Questions? Wendell Cook, P.E. Commissioning Engineer Texas Facilities Commission Office of Energy Management [email protected] Office: 512-463-1452
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