A Heat Recovery Retrofit in Minnesota

Finding the sweet spot of energy efficiency and comfort is challenging enough for a standard building, but it truly gets tricky when multiple areas are thrown in the mix.

“We have all sorts of spaces — Omnitheater, gift shop, exhibit halls, restaurants and catering facilities, exhibit and graphic production shops, meeting rooms and classrooms, and a parking ramp — that all have different energy needs,” said Todd Gray, assistant superintendent of facilities, Science Museum of Minnesota.

Located on a bluff overlooking the Mississippi River, the Science Museum of Minnesota is a major destination for 700,000 visitors a year. The museum prides itself on offering its visitors hands-on exhibits that are not only educational but also fun. And when the museum made a goal to lower the building’s energy costs and reduce its carbon footprint, the staff recognized the opportunity for a learning opportunity.

“Our team was determined to reach its energy efficiency goals, to not only provide long term environmental benefits to our local community, but to make our building a living laboratory that demonstrates energy and sustainable solutions,” said Alison Brown, president/CEO, Science Museum of Minnesota.

Net-Zero to Hero

On a path toward net-zero status — meaning the total amount of energy used by the building would be equal to the amount of renewable energy created at the site — the museum enlisted an area mechanical consultant who was a local energy-efficiency guru.

Analysis showed the Science Museum’s annual electricity consumption was 6.3 million kWh of electricity, which is equivalent to the yearly electricity consumption of 800 households. The study also noted that this electricity degraded to 20 billion Btu’s of heat energy but that the facility also purchased 15 billion Btu’s of heat energy.

“The consultant asked us why we were throwing away an enormous amount of heat only to buy it back,” said Patrick Hamilton, director of global change initiatives, Science Museum of Minnesota. “We were intrigued by the findings and that the Science Museum might have an opportunity to demonstrate new ways of operating more efficiently. Aligning with our mission, we embarked on a heat recovery retrofit that would allow us to save energy and use our own building as an exhibit.”

Streamlining with One System

With simultaneous heating and cooling needs all year long, commercial buildings use both a heating and cooling system at the same time. Heat recovery looks at a building’s HVAC as one system — allowing a building to use the heat it already generates, rather than creating new heat by burning fossil fuel or running a boiler.

The process extracts heat from areas where it isn’t needed and exports it to exterior walls in closest contact with the cold outside air. A heat exchanger is also used to temper fresh cold air brought into the building before it’s pushed through the ventilation system as heat.

Recycle Heat, Lower Costs

The mechanical consultant brought in Trane for heat recovery solutions. Together, they evaluated full- and part-load efficiency data of various options and developed a solution that would meet critical temperature and humidity control requirements, and improve efficiency. Trane heat recovery chillers were deemed the most appropriate equipment for the project based on their exceptional reliability and performance at higher lift, as well as the support system offered by the company.

Optimized for heat recovery, two high-efficiency Trane 160-ton Series R® model RTWD helical rotary chillers were installed to handle the Science Museum’s needs. The smaller RTWD chillers not only cool the facility, but take the heat that already exists in the building to convert it to hot water, at temperatures up to 140 degrees, which is then used to heat the Science Museum.

Rather than running two systems, the heat recovery chiller pumps the heat into places where it’s needed, helping keep peak energy usage down.

A Historic Success

With the heat recovery retrofit, the Science Museum facility is now recycling its heat energy. The project has reduced the building’s hot water heating bills by 75 percent, saving nearly $300,000 a year.

The upgrade is also helping the environment by reducing the emissions and pollution that would have resulted from generating new heat energy. 

“We have lots of energy needs and Trane helped us optimize our systems, allowing us to be financially responsible to our donors and our community,” said Gray. “By utilizing the waste heat that we were throwing away in a constructive manner, we are moving toward carbon neutrality.”

Efficient Accolades

Since setting such a valuable example of energy efficiency, the Science Museum of Minnesota recently received the Energy Efficiency Leader Award. The award, presented by Trane, recognizes the museum’s long-term commitment to providing a learning atmosphere with minimal environmental impact.

“It’s a very powerful story,” said Hamilton, “and a big opportunity to communicate to both professional and public audiences that heat recovery is not just theoretically possible, but practically feasible.”