Toronto General Hospital is undergoing a major retrofit of its central chilled water plant, one that will fundamentally improve the system’s capabilities and dramatically reduce electricity costs. The plant is essential to services at the hospital, providing chilled water to equipment and ventilation. It cools operating rooms, equipment for MRI and CT scans, servers, rooms with -80ºC freezers, the cyclotron, as well as all the clinics, patient rooms, and offices throughout TGH’s two million square feet. The new system will save the hospital millions of dollars in operating costs, increase capacity, and improve both the resiliency and reliability of the chilled water services at TGH.
The first thing to know is that the TGH central chilled water plant is a big system. It has three massive 60,000lb electrically driven chillers, 17 pumps, a 5 cell cooling tower, controls, valves and miles of piping (one of the chillers is pictured in the title image). As a result, the plant uses a lot of energy. It’s maximum power draw is equivalent to nearly 60 Nissan Leafs running at top speed and the annual electricity consumption could power 20,000 Rockefeller Christmas trees for an entire year. If that didn’t impress you there are some more fun facts below.
Chiller Plant Fast Facts (2016 data):
- The chiller plant is responsible for about 30% of the total electricity costs at TGH
- Providing chilled water costs approximately $2.6 million dollars in utilities a year
- The existing chiller plant uses ~9.2 million kilowatt-hours (kWh), enough to power 760 homes for a year
- The plant includes three electrically driven chillers that weigh 60,000lbs each, with a combined maximum power draw of 3.6 megawatts (MW)
- The plant also includes seventeen pumps totaling over 1000 horsepower and a cooling tower with five 100 horsepower fans
Units –> MW = Megawatt = 1 million watts = a unit of power. kWh = Kilowatt hours = watts * hours of operation / 1000 = a unit of energy
In case you’re wondering about the blended electricity rate for the plant, it works out to about 26 cents per kWh. That’s much higher than our average cost per kWh, which is due to the seasonal nature of chiller plant operation and the structure of class A electricity rates. It also means that chilled water is the best place for TGH to save on electricity costs.
So what are we doing?
The project is converting the electrically driven chiller plant into one that utilizes Enwave’s district cooling loop, also known as “Deep Lake Cooling”. The Enwave system is extremely environmentally friendly and cost-effective. It takes cold water from deep in Lake Ontario, treats it, and then sends it to a massive array of heat exchangers near the CN Tower. Those heat exchangers are used to transfer heat into the lake water from the district cooling loop serving downtown Toronto. That district loop is a completely closed loop, circulating chilled water around downtown, where connected buildings use it to cool indoor air and equipment. Also, the treated lake water isn’t just sent back to the lake, it goes on to become part of the potable water system used by homes and businesses across Toronto. That means that even over the very long term there is no concern about affecting the lake’s ecosystem with warm water.
Inside Toronto General Hospital a new set of heat exchangers is being installed to connect TGH to the district cooling loop. New variable speed primary pumps are going in and a new magnetic bearing polishing chiller will be installed. This new equipment allows for flow and temperature to be much better controlled. Speaking of controls, those will also be upgraded with the added benefit of providing better monitoring capabilities for software systems and building operators. The new system also means that two of the existing chillers and the old cooling tower will remain on site for backup purposes only.
The system will save both electricity and water. In a traditional cooling plant, a cooling tower is required to reject heat through evaporating water. Surprisingly low tech, but evaporation is still the predominant way of cooling, dating back to the Roman era. In the case of the new system, TGH will be rejecting heat to the district loop instead of through a cooling tower, thereby saving all that water from evaporation. I equate the amount of water saved to the number of Olympic-sized swimming pools at the end of this post.
It’s also worth noting that since the district cooling system has been operating in Toronto for about thirteen years, there are many buildings using the system. For example, our own TRI’s University Centre, the Metro Convention Centre, the Air Canada Centre, Metro Hall, City Hall, and Queens Park, to name just a few.
Why are we doing this?
There were a lot of issues with the existing chilled water plant: the equipment was wearing out, it was very expensive to operate, it was difficult to maintain reliability, it lacked redundancy and emergency power, and had no capacity to add new hospital cooling loads. The new plant will solve all of those issues while also reducing our environmental impact.
Benefits of the new system at TGH:
- Reduces utility costs: savings of ~$700,000 in the first year and >$22 million over twenty years
- Increases capacity for new hospital equipment and renovations
- Provides code compliant chilled water redundancy and enables the hospital to provide chilled water in an emergency power situation
- Increases system reliability through a new design and much needed renewal of equipment and controls
- Improves thermal control of building loads
- Reduces environmental impact with reduced CO2 emissions, reduced water consumption, and reduced electricity use.
To highlight that last point with something more colourful….
It’s also worth noting that all of the decision making for this project was based on data and extensive engineering analysis. As part of the project we created an hourly simulation of the existing chilled water plant and several alternative upgrades for comparison. That simulation was reviewed by a third party for added accuracy and a cost consultant provided the capital costs for the business case. The financial analysis and business case also included a detailed look at escalators for utility costs as well as a multivariable sensitivity analysis to determine how some factors could make the reviewed projects more or less financially advantageous. In the end the deep lake cooling project was the clear choice for TGH, providing the greatest benefits and lowest risk.
Thanks for reading and keep an eye out for the post project data (the new plant will be operational for the 2018 cooling season). If you have any questions about how the business case was prepared and the metrics we used in the evaluation please contact me firstname.lastname@example.org.