Savings at the Pump
By Danfoss North America
Toronto’s Enercare Centre records significant energy savings with the introduction of variable frequency drives in the HVAC pump room.
By Danfoss North America
With over one million square feet of exhibit and meeting space, the LEED Platinum-certified Enercare Centre at Exhibition Place in Toronto is the ninth-largest convention centre in North America. Located on the shores of Lake Ontario, the convention centre experiences extreme weather—with temperatures ranging from −31C to 40C. Those temperature swings place a burden on Exhibition Place’s HVAC equipment to keep the space comfortable for over 5.5 million visitors attending meetings, conventions and exhibitions throughout the year.
The amount of energy consumed for heating and cooling the space is significant—over 380,000 kW hours per year just to power the pumps that circulate chilled or hot water to fan-coil and air handlers located throughout the facility.
As one of North America’s largest home and commercial services and energy solutions companies, Enercare Inc. has a commitment to energy conservation, so it’s no surprise as the venue’s naming sponsor it strongly supports Exhibition Place’s innovative GREENSmart program.
The program implements numerous committed energy and waste-reduction initiatives—which included retrofitting 11 pumps with Danfoss VLT HVAC Drives under Toronto Hydro’s PUMPsaver program. Completed in May 2018, the project ultimately reduced pump energy consumption by up to 38%. For qualifying facilities with closed-loop hydronic pumps, Toronto Hydro’s PUMPsaver program covered 100% of project costs, giving the Enercare Centre an immediate return on investment (ROI).
Many utilities provide various incentives to business customers to encourage installation of variable frequency drives (VFDs) for fans and pumps, according to Irina Sivryukova, administrative lead, energy services division of Kildonan Energy, and Rajiv Harnarain, B. Eng, CEM, also with Kildonan Energy’s energy services division.
Kildonan Energy specializes in turn-key engineered VFD solutions for HVAC, and served as the exclusive partner for the PUMPsaver program offered by Toronto Hydro from 2016 through April 2019. The firm completed over 650 projects under the program and continues to work with similar utility programs today.
How VFDs cut energy consumption
“Applying Danfoss VLT FC102 variable frequency drives dramatically improved pump motor efficiency for Enercare Centre,” explains David Sage, owner of Kildonan Energy. “The hydronics-system design employed constant-speed pumps in circuits using balancing valves that functioned like brakes to regulate fluid flow. As chilled or hot water circulates to fan-coil or air-handling units in the loop, the valves throttled open or closed to deliver the needed supply water.”
Sage notes that “using a balancing valve to regulate a constant-speed, constant-flow system is like keeping your foot on a car’s accelerator and tapping the brakes to control motion. It wastes a lot of energy.”
To improve energy efficiency, a variable frequency drive was added to each of the pumps in the system. The VFDs are designed to vary the speed of the motor, allowing the pump to match the system load requirements without the need for mechanical balancing valves. Using a flow meter to verify results, the VFDs are tuned back to match the existing flow of the system once the mechanical balancing valve is opened to its maximum position. By opening the balancing valve, the system resistance drops significantly and the power requirements are reduced.
A VFD solution not only eliminates wasted energy inherent in using balancing valves, it also runs the pump at its optimal efficiency points. Similar to how a car’s performance is measured in horsepower, torque and speed, a pump’s performance is measured in motor power (kilowatts or horsepower), speed (RPMs), head pressure (psi) and flow (gal/min). The physics of a rotating centrifugal impeller is most efficient at specific speeds, pressures and flows, creating points that can be graphically mapped as a “pump curve.”
The Danfoss VFDs used can not only run the pump motors at reduced speed, but also at the best efficiency points on the flow/head pump curve. From the motor’s point of view, riding the pump curve minimizes wear and tear on the pump impellers and bearings and reduces operating noise levels. From the system’s view, the fan coil and air handling units see the flow rate and head pressure they are designed for.
From an energy point of view, the physics of Affinity Laws for centrifugal impeller pumps state that power consumption can be reduced by the cube of the change in speed. In other words, running the pump motor at four-fifths speed (80%) theoretically reduces power consumption by half (50%).
Not every pump application can take advantage of the Affinity Law for power. For example, applications using a valve to throttle the output flow will increase head pressure, which makes the pump work harder and wastes energy. In the Enercare Centre, this source of wasted energy has been eliminated. But pump performance was also enhanced because the drives were optimized to the pump curve.
Variable speed drives go with the flow
The drives used in this application comprise a broad family of variable frequency drives (inverters) that can be applied to pump motors ranging from 1.5 to 600 hp. They are built on a modular plug-and-play platform to simplify setup and operation in HVAC applications. For the Enercare Centre, the drive’s built-in intelligence provided capabilities that include:
- Distributing running hours evenly across multiple pumps to minimize wear and tear on individual pumps.
- Minimizing harmonic distortion in the facility’s and utility’s electric grid with integrated chokes and radio frequency interference (RFI) filters.
- Limiting amperage draw when the pump motor starts without the need for a separate soft starter.
- Monitoring system reaction to speed changes with auto tuning to maintain required head and flow.
- Simplifying programming through a built-in smart logic controller that minimizes the need for a programmable logic controller (PLC).
In implementing the VFD solution at Enercare Centre, the Kildonan Energy team was able to use the features of the Danfoss VLT drives to tailor a solution for both the application and the customer including allowing the operators access to the system function through Enercare Centre’s building automation system.
To utilize variable frequency technology effectively, the drives must have the intelligence to handle the characteristics of the system. In this case, the pump performance curves were optimized for the required head pressure and flow rates at a single fixed speed. For pumps running at other speeds, the curves can be modeled using ratios derived from Affinity Laws. Once the models are determined, they need to be applied to the specific pump configuration.
The Enercare Centre installation uses several pumps per system in either lead-lag or duty-standby configurations. The PUMPsaver program allows for a VFD on each pump in the system. A specific program is implemented in the VFD’s Smart Logic controller to ensure the pumps work in cooperation to maintain control. In all cases, the lead pump will rotate on an ongoing basis to ensure equal run time for each pump in the system.
In the case of a lead-lag configuration, the lead pump will operate up to a point where the efficiency drops off, at which point both pumps will operate together to maintain the load.
Enercare Centre now enjoys a more efficient pumping system that provides more stable control and significantly more operational information to the building engineers. These features not only help reduce the energy budget, but allow the owner to use the savings found in this project for further energy-efficient upgrades.
Completed in May 2018, the project involved four constant-flow systems, three supplying fan coils for cooling and one for a heat pump loop. Danfoss VLT drives were applied on lead and standby pumps ranging from 10 to 100 HP (Figure 1). Depending on the system, the energy savings ranged from 20 to 38%, averaging 28% overall.
Total annual electric savings came to 109,144 kWh hours, equivalent to the electricity used by 14 homes in one year.
Estimated greenhouse gas savings are 77 metric tons per year, equivalent to taking 17 passenger cars off the road.
As valuable as those savings were to Enercare Centre in terms of energy and the environment, the immediate payback was even more rewarding.
“Because the PUMPsaver program covered the entire project’s cost, the ROI was instant,” Sage notes. “Since the program ended, we’re still seeing utilities offering rebates covering up to 50% of project costs. Those rebates, combined with pump energy savings, give a payback period under three years, which makes it very worthwhile for many pump-intensive applications.”
With PUMPsaver, Sage notes Toronto Hydro was able to exceed its electric-consumption reduction targets. Going forward with other rebate programs, he sees many opportunities for customers with district cooling and heating hydronic loops. In fact, Exhibition Place itself has other VFD projects in the pipeline.
“For us, the PUMPsaver program, Kildonan Energy and Danfoss variable frequency drive technology provided an end-to-end energy-saving solution that was easy to implement,” says Marius Dragu, building system coordinator for Exhibition Place. “VFD retrofit projects that help us better manage our energy use, cut electricity costs and realize our sustainability goals are a really big deal for Enercare Centre, because everybody wins.”