|Trane Centrifugal Glycol Chiller with associated Thermal Storage, pumps, automated valves and stainless steel piping|
by Mark MacCracken, CEO, CALMAC
The State of Michigan Secondary Complex in Dimondale is a 13-building campus comprised of the state’s police academy, police post, test and research labs, office space, warehouses, vehicle maintenance service garages and more. The facility’s original energy center was constructed in 1975 and featured electric chillers and gas-fired boilers. Since the original installation of the energy center, buildings within the complex have undergone renovations, additions and changes in functions, greatly improving the efficiency of heating and cooling operations. Energy consumption used for heating, ventilating and air conditioning (HVAC) was identified as a significant part of the complex’s operating budget. Savings in energy costs through strategic energy efficiency upgrades would mean large returns.
In October 2008, the State of Michigan made its commitment to energy efficiency known through a series of bills, one of which was Public Act (P.A.) 295. This act renewed and revised the state’s dedication to maximizing energy efficiency in state facilities. One of the goals of the act was the reduction by 25 percent of state government grid-based energy purchases by 2015, as compared to a 2002 baseline. Two strategies were outlined to meet this goal: reductions in peak demand and onsite energy generation. The choice to implement cogeneration and energy storage technologies into the State of Michigan’s Secondary Complex would greatly reduce the facility’s operating costs and environmental impact, thereby helping meet the state’s energy goal.
The Secondary Complex’s energy center underwent a major renovation in 2012 with the installation of two 1.2-MW natural gas-fired turbine generators, used to produce steam and electricity for central heating and cooling operations at the complex’s central facility. This renovation reduced the amount of power required from the state’s power grid. Steam generated from the turbines was dedicated to heating the complex (over 2,000,000 sq. ft.) and was also utilized by two absorption chillers to create chilled water for cooling operations. Since the installation of cogeneration, however, the cooling load requirement within the campus has increased due to the addition of new buildings, technology and equipment. As a result, the complex identified the need for a capacity and efficiency solution that could seamlessly integrate into its existing energy center, reduce peak demand and create redundancy within the system.
Having previously installed thermal storage and CALMAC tanks at the Saginaw State Office Building, the state has experience with ice-based thermal energy storage’s reputation for creating savings and providing a durable, long-lasting solution. CALMAC was chosen to provide the energy storage technology that would meet the complex’s growing cooling demands. In 2014, the Secondary Complex installed three 900-ton centrifugal, dual-mode, water-cooled chillers provided by Nelson Trane, plus Trane Tracer chiller controls. The chillers operate using energy from the grid and are paired with CALMAC’s IceBank energy storage tanks, which can store 1-MW of energy, equivalent to 8,748 ton-hours of cooling. Two levels of energy storage tanks were installed in a decommissioned incinerator room.
Although there is enough energy storage to satisfy the cooling load for the entire complex if necessary, the system is designed to provide redundancy to the cogeneration plant. When steam is available for cooling it must be utilized because this form of energy cannot be stored effectively. If cooling demand exceeds the capacity of the steam-driven chillers, CALMAC’s IceBank tanks are called upon to provide the additional cooling requirements. With the extra storage capacity available, the State of Michigan is prepared to handle future increases in cooling demand.
Speaking about the project, Scott Davis, Facility Supervisor of Zone 6, said “CALMAC’s energy storage technology has allowed us to make our system extremely flexible in order to meet changing heating and cooling needs. Utilizing cheaper nighttime energy has always been an attractive opportunity, especially for a large complex like ours. Now it’s a reality.”
The incorporation of ice-based thermal energy storage has allowed the Secondary Complex to create cooling hours during nighttime off-peak hours, when only the most efficient power plants are online and the price of electricity is reduced by roughly 50 percent compared to daytime prices. By storing and using cooling as needed, the complex can avoid expensive peak demand hours and reduce stress on the power grid. Based on historical data, the addition of storage is expected to save an estimated $12,000 per month in energy costs. Ice-based energy storage also adds significant flexibility to the system.
The complex has the option of cooling the facility using just ice, the absorption chillers that are powered by steam, the three centrifugal chillers, free cooling heat exchangers or any combination of the four solutions. However, the energy plant relies heavily on the cogeneration technology, which powers the absorption chillers, along with ice-based energy storage assistance as needed. The ability to use cogeneration and natural gas to take some of the complexes load off the grid is helping to meet the state’s goal of reducing grid-based energy purchases. When the Secondary Complex does need energy from the grid, energy storage allows the facility to use only the most efficiently produced energy.
The combination of cogeneration and ice-based energy storage has provided the State of Michigan with technologies that perfectly align with its goals of reducing reliance on the power grid while optimizing operating costs. This proactive approach to creating a long-term solution has also prepared the state to adapt to future changes in demand. The savings generated by the two technologies can be used on other facility-related costs.
“Ice-based energy storage has allowed the State of Michigan to separate energy purchases from energy consumption,” said Mark MacCracken, CEO of CALMAC. “This decoupling, in combination with cogeneration, has greatly reduced the state’s energy usage during peak demand hours. Historically off-peak energy prices rise much more slowly than any other form of energy. “
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