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Western University's Deep Energy Retrofit of the Chiller Plant South 

02-27-2019 15:16


Western University (Western) is a higher education institution in London, Ontario, Canada. It has over 90 buildings, totaling 9,600,000 GSF of construction, serving a community of nearly 40,000 students and 3,600 staff and faculty. The campus has seen explosive growth in the past decade, adding ovplevesque@eequinox.comer 1,000,000 GSF of new construction. This growth has put pressure on the existing district energy systems, which serves nearly 70% of the campus buildings. The university has one steam plant, with 420,000 lbs/hr in capacity, as well as two district cooling plants, totaling 11,000 tons of refrigeration capacity (TR). The Chiller Plant South (CPS) is the largest with 7,200 TR and it serves over 30 buildings. The CPS has four chillers (two Trane and two McQuay) dating from 2003, 2006 and 2010. Plant operations are controlled using a DeltaV industrial PLC control system. However, district cooling operation has remained mostly unchanged for 20 years. The capital cost for adding a new 1,200 TR chiller and cooling tower is significant, because there’s no space left in the CPS location (excavation and construction would be required) and the substation serving it was at capacity; adding capacity to it or adding a new substation would cost several millions more. Adding a new chiller and cooling tower would also mean adding to Western’s peak electrical load, which is used to calculate the portion of the $12 billion dollar/year Global Adjustment (GA) charges. This charge already represents 65% of Western’s total electricity bill and the new equipment would result in millions of dollars more in operation each year, since peak hours in the province typically coincide with extremely hot/cold days. Nearly half of Western’s peak demand, used for GA charges, is related to the operation of chillers.Western hired SMi-Enerpro to conduct deep energy retrofits on campus as part of its Low Carbon Utilities and Infrastructure Strategy; by reducing the demand of chilled water in each building, the capacity of the CPS could better meet the campus’ needs. However, after some initial study, it was determined that there were numerous opportunities at the CPS itself to improve its efficiency and performance at the same time. SMi-Enerpro conducted a feasibility study to identify possible measures and to evaluate them. The study went beyond studying the equipment, but also factored in the actual operation of the CPS, including major and auxiliary equipment, the performance of the distribution loops and the operation of the Belimo energy valves installed across the campus two years earlier. CPS operates from April to November, depending on outside conditions. The annual production is estimated at 10,554,690 ton-h. In 2016, the chillers operated as follows: - McQuay CPS-301 operated 2,152 hours, - Trane CPS-302 operated 2,857 hours, - Trane CPS-303 operated 3,041 hours, - McQuay CPS-304 operated 2,972 hours. Each chiller is equipped with its own evaporator and condenser pumps and cooling tower, the equipment also operated the same number of hours as its corresponding chiller. The secondary pumps were generally operating as follows: South Loop: - CPS-305-504 or CPS-306-504 pump is operating and its speed was modulated to maintain the South Loop chilled water differential pressure at its set point. East Loop: - CPS-307-504 and CPS-308-504 pump are operating and their speed was modulated to maintain the East Loop chilled water differential pressure at its set point. North Loop: - Two or three of the CPS-309-504, CPS-310-504 or CPS-311-504 pumps are operating and their speed was modulated to maintain the North Loop differential pressure at its set point. Each system was analyzed individually. For example, the condenser pumps were responsible for an electrical demand of 244 kW and were estimated to use 653,065 kWh/year, and the primary chilled water pumps were drawing 153 kW of electricity, using an estimated 414,000 kWh/year. The secondary pumps added another 550kW to the demand during peak hours, with an estimated annual consumption of 1.825,000 kWh. The cooling towers represented 309 kW of demand and 454,000 kWh/year. Considering all equipment and the actual operation of the plant, it was determined that the CPS was using 9,693,000 kWh/year and created an electrical demand of 6,250kW during peak hours. The energy conservation measures identified were: -Install a check valve in the chilled water system bypass;-Optimizing cooling tower CPS-303;-Removing some balancing valves;-Expand and optimize control system with a completely new sequence.The expansion of the controls involved adding differential pressure sensors in the last buildings of each distribution loop, automating the controls of the chillers, load limiting and adding more outdoor air temperature sensors. The optimization consisted in changing set points, controlling equipment using the new I/O points and developing a demand management mode to tackle the GA charges. Project budget was established as 1,112,134 CAD and SMi-Enerpro’s fees were to be paid as an energy performance contract, where 100% of the fees were tied to energy savings. Drawings and specifications were developed in summer 2017, using the data from the 2017 cooling season to refine the proposed measures. The project was tendered in late fall of 2017 and work commenced in November 2017. From April 17 – May 6, 2018, the CPS was operating in semi-automatic mode, as fine tuning and commissioning were not yet completed. Throughout the summer of 2018, Western and SMi-Enerpro have been fine-tuning the new sequence and doing some adjustments to the equipment in the process (e.g., adding refrigerant to chillers). Some of the challenges experienced were related to the second compressors on each of the McQuays, whose stops could not be automated. As the sequence was further implemented, some modifications to the lubricating oil cooling circuit were needed to address alarms that were tripping the systems. Other work needed to fully implement the new sequence was adjusting parameters and set points in the VFDs and on the chillers themselves. For demand management, it was observed that the campus load was fluctuating too much, too fast. Working with the Building Automation Group (WES Controls), several graphics and trend-logs were developed to track the performance and responses of the chilled water valves around campus. This resulted in modifications to the GA sequence, which significantly softened the demand spikes from variations on campus load. The total consumption of CPS after the deep energy retrofit was estimated to be 7,566,000 kWh/yr, with a peak demand of 5,902.5 kW. In other words, the expected savings were of 2,127,000 kWh/year. Furthermore, CPS is now able to meet campus needs using only four of the six compressors available, meaning that it’s no longer used at full capacity. Only one day this summer has there been need to run the plan at full throttle. The actual savings will exceed the estimated savings, and demand reductions have also reached up to 2.3MW when enabling the GA sequence.

Session 3A: Chilled Water System Retrofits & Optimization for Savings


Pierre Levesque 
Paul Martin, Western University


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