PNC is constructing its future high-rise headquarters in Pittsburgh with an ambitious goal: making it the greenest skyscraper in the world.

The $400 million building, designed by architecture firm Gensler, is expected to consume 50% less energy than a typical office building. The 800,000-square-foot office tower is 83% completed and expected to open in the fall.

To save time and money, PNC is testing the green technologies meant for the tower in a 1,200-square-foot prototype of the building it unveiled last week. No other company in the U.S. has constructed a commercial office building mockup of this scale, the bank says. The prototype is letting the bank resolve issues that would have been costly and time-consuming to fix on the tower site. PNC says this has yielded savings of more than $5 million.

"Our department is judged by how much money we can save PNC with these energy-reduction ideas," said Mike Gilmore, PNC's director of design and construction services. "It benefits the bottom line of PNC, and it's the right thing for the environment."

The project comes as many banks pursue green initiatives. Deutsche Bank recently installed more than 100 solar panels on the roof of its headquarters at 60 Wall Street, among other improvements to achieve LEED (Leadership in Energy and Environmental Design) certification. Bank of America is in the midst of a 10-year, $50 billion environmental business initiative announced in 2012; the Bank of America Tower overlooking Manhattan's Bryant Park, completed in 2009, was designed to be ecologically friendly. Citigroup in February announced a $100 billion commitment to reducing the effects of climate change over the next 10 years.

While there are clear PR motivations for banks to portray a green image – PNC, for example, recently cut back lending to mountaintop-removal coal miners under pressure from activists – there are also solid business reasons for environmental initiatives.

"We're a bank, we're in business to make money," said Joe Doolan, U.S. head of environmental affairs at TD Bank. "Having environmentally sustainable practices is actually quite profitable." For instance, he said, the bank has saved millions through paper reduction and reduced water use.

At TD Bank, all new branches are LEED certified and one is "net-positive" – it generates more than 4,000 kilowatt hours of power in excess of what it needs, through the use of solar panels and green practices such as shutting off lights, turning off computer screens and recycling.

"We have 101 stores that are producing enough clean energy to power more than 450 homes a year," Doolan said.

Can PNC call its new tower the greenest skyscraper in the world?

"I think they have a legitimate claim," said Scot Horst, chief product officer of the U.S. Green Building Council, the organization that conducts LEED certifications. "They have been a leader in this green building space for a long time." PNC's Firstside Center, which opened as an operations center in 2000, was one of the first LEED-certified buildings. "It was an early icon for a lot of the principles we've been espousing in LEED ever since: an open floor plan, a lot of natural light coming into the space reducing artificial light, raised floors so you can move things around, superior orientation to the sun so less artificial cooling and heating."

Gilmore acknowledges that "there really aren't any hard and fast rules" to being the greenest. "There are some guidelines the U.S. Green Building Council put together and there's the LEED criteria; their highest level is platinum, so you have to get to that level and then beyond. After that it's a bit of a free-for-all to figure out who is actually the greenest."

In its prototype, the bank is testing the new tower's double-skin facade, solar chimney, automated blinds, and energy-efficient lighting system. The mockup is fitted out like a normal office and employees working there experiment with things like how many perforations in the automated blinds are ideal for daylight infiltration without glare.

In tests, they found that for a certain type of wall, the self-cooling mechanism wasn't working.

"We had to go back and add more louvers into that curtain wall system," Gilmore said. "If we had to do that on the job, it would have easily cost us a couple million dollars to fix."

A lot of the prototype's $5 million cost reduction is coming out of bid savings.

"If people aren't sure about the drawing, they have to add a percentage," Gilmore said. The prototype, by proving the concepts in the drawings actually work, takes all the doubt out of the bids.

So far, the green tech showing the most promise in the mockup is the double-wall system.

"There's a 30-inch gap between the inside and the outside walls of the exterior skin," Gilmore said. "We use that to tie in a natural ventilation system."

The ventilation works the same way a chimney does on a fireplace. The building has a shaft in the middle. When heat is generated at the top, air can be drawn from the floor level all through the shaft. It's pulled through the space without the use of fans.

Tests have shown that about 42% of the time, the building can be run without fans, artificial heating or cooling.

This type of natural ventilation is "exactly the direction we need to be going," said Horst. "It's high-quality design that uses technology to enhance the design."

For lighting, the bank is using "daylight harvesting." As the sun moves through the sky, the control system continually adjusts the amount of artificial light contributed. On a sunny day, no artificial light is needed.

"Our energy model says that will pay for itself and our studies so far have pointed to that same fact," Gilmore said.

One green technology being used by PNC and others is sophisticated building management software. This software, developed by companies like Honeywell, Carrier, Siemens, and Johnson Controls, once served purely mechanical functions, running the controls in a building.

Now, "these companies are becoming tech companies," Horst said. "Now everything's in a dashboard."

"One thing we've seen for years is there's a lot of data on buildings, and the industry hasn't wanted to share that data, they're afraid that will have an adverse effect on the value of their asset," Horst said. "Now they're providing data-driven scoring based on real performance."

And in a Carnegie Mellon energy efficiency study that the bank participated in last year, employees were given tools to better gauge how much energy they consume on a regular basis.

"We found that when employees know how much energy they're consuming and have the ability to control that on an automated system, they reduce their energy consumption by around 42%," said Emily Krull, assistant vice president at PNC. Employees were able to set timers that would automatically turn off their computers and task lamps in the evening, for example.

"I think people also, just by having this greater awareness, made conscious changes," she said. "Not using their phone unnecessarily or keeping their phone calls shorter, turning off their light when they were going into a meeting, charging their iPhones at home rather than in the office."