Minnesota History Center: Existing Building Commissioning

This guest blog post is by Angela Vreeland and Chris Plum from Center for Energy and Environment (CEE). Angela is a project engineer for the Public Buildings Enhanced Energy Efficiency Program (PBEEEP).  Chris is a Program Manager at CEE and is the Program Manager of the State Government Public Buildings Energy Efficiency Enhancement Program (State PBEEEP). CEE will be presenting on the Evolution of Energy in Minnesota at the More for the Mission event on December 11, 2012.  To find out more and register for the More for the Mission event, re-visit this blog post

Minnesota History Center

The Minnesota History Center is a relatively new building which is primarily used as a museum, with public areas, exhibition spaces, classrooms, storage spaces for valuable artifacts, a library and conservation laboratories. Several hundred thousand people visit the History Center every year, about half of them in school groups. The building was built to the Minnesota Building Code and its energy use of 160 kBtu/square foot (about $2 per square foot) was typical of many museums. It was nonetheless noteworthy in 2005 as the building on the capitol complex with the highest total energy use. Not only is that no longer true, but the building now uses the same amount of energy as an average building in the Capitol complex and less than many office buildings in the Upper Midwest.

What did the staff that manages the state’s buildings (the Division of Plant Management in the Department of Administration) do to achieve these impressive results?  Read more...

It all started with a fairly routine upgrade of equipment when the History Center was about 15 years old and many items of equipment were at the end of their useful life. Equipment was repaired, replaced with more energy efficient equipment, and, perhaps most importantly, the control of the internal environment was converted to a modern computerized system that could be centrally controlled by Plant Management. This work was done between 2008 and 2009 by Michaud, Cooley, Erickson and the results were fully apparent in 2011 after the building staff was able to make full use of these new capabilities.

For example, not only could they control equipment better, but they also determined they could turn off their boilers for the entire summer and use “waste heat” from the chillers that run the air conditioning system to meet their small heating requirements. You might wonder why they would need heat at all in the summer: this is one of the features that make museums so challenging for a mechanical engineer and facility manager. Valuable historical artifacts and documents need to be kept at very constant temperature and humidity. Just as you use a mixture of hot and cold water when wash your hands (all year long) so it is often only possible to get the right conditions by mixing warm and cold air. The new controls allowed this to be done more precisely and to use less energy at the same time.

Even after all this work was done, there was an opportunity to achieve further savings through Existing Building Commissioning (also known as recommissioning) and upgrading the existing lighting to LEDs.

As noted above, and shown in the chart below, the Minnesota History Center experiences large fluctuations in occupancy by time of day, day of the week, and season. On Mondays the museum is closed to the public, and there may only be 50 occupants, all employees; on the other hand, on the busiest day of the year, there were 3,000 visitors. The equipment that conditions and ventilates the building was designed to meet the needs of the spaces at maximum occupancy; that meant that it used more energy than necessary much of the time when the building was lightly occupied.

Graph of number of people in the History Center.

(Scale has been changed to show normal occupancy – the peak day is three times as high as the chart)
 

In 2009, while continuing to optimize the new building control system, the facility staff enrolled the building in the Public Buildings Enhanced Energy Efficiency Program (PBEEEP), which provides Existing Building Commissioning (EBCx) services to State of Minnesota buildings.

An EBCx study was conducted by Ericksen Ellison and Associates (EEA) and technical review and project oversight was provided by the Center for Energy and Environment. Studies by organizations such as the American Council on Energy Efficiency (ACEEE) have shown that the addition of a quality control partner to a standard energy efficiency program consistently results in improved energy savings.

Existing building commissioning is a process that generally takes at least nine months in Minnesota – long enough to observe the operation of the building in summer, winter and the transition (fall or spring) season. The study includes not only observation and testing of equipment to see that it is operating as originally intended, but also hundreds of hours of analysis data on that equipment, typically taken every 15 minutes for the length of the study. This results in millions of data points to be examined to see how equipment is operating day and night, in all weather conditions and when the building is open and closed.

As a result of the investigation eleven energy reduction measures were identified that would allow the equipment to use less energy. There were many other opportunities noted, however they were not always cost-effective to implement. Existing building commissioning brings value by both offering energy savings, but also a certain payback to building owners who always has many competing needs for their consideration. In this case, the measures identified will save an additional 10% of annual energy use, or $68,500 a year, and pay for themselves in just over three years, based on that energy savings.

Annual Energy Use Index

Here’s a technical description of three of the measures that led to the majority of energy savings at the History Center:

Turn Off Equipment when Not Needed

Savings: $48,400.  Payback: 0.1 years

  • Trend data, which shows the behavior over time of information such as temperatures; valve and damper positions; and equipment statuses, was collected continuously for several months by the building automation system. When the data was analyzed to determine when the air handlers, exhaust fans, and other mechanical equipment operate it was found that equipment was often on when the spaces were unoccupied.
  • Discussions with the facility staff provided the occupancy schedule for the building and made them comfortable with changes to the schedule, including, for example the use of optimum start routines and demand control ventilation.
  • 12 air handlers and 7 exhaust fans at the History Center were operating more than necessary (up to 50% in some cases, because 24 hours a day, seven days a week is more than double the number of hours the museum is open each week).
     

Install Variable Frequency Drives on Air Handler Fans

Savings: $10,800 Payback: 6.5 years

  • The air handlers at the History Center ran at a single speed (this is called constant volume, and it is the same as most home furnaces, for example). Because they could not slow down when the number of visitors was not at capacity, too much energy was used.
  • Installing variable frequency drives on the majority of air handler supply fan motors was recommended to more closely match the needs of the building. A variable frequency drive allows the motor to run like your car engine, increasing and decreasing in speed to adapt to the conditions at any given time.

Scheduling of Kitchen Ventilation System

Savings: $5,100 Payback: 1.2 years

  • There is an exhaust fan in the kitchen that needs to run whenever something is cooking on the grill in order to remove any odors from the café area. The operation schedule of the exhaust fan and air handler that serve the kitchen did not match the space usage schedule – they were on when no one was there “just in case”. Furthermore, since the air handler also serves the café space, it needs to be on whenever people are sitting in the area, even if the kitchen is shut down.
  • Fresh air is brought in to the kitchen from the outside through a damper connected to this air handler. (It is like opening a window and using a fan and duct work to get the fresh air to the kitchen.) The solution was to adjust the controls of the air handler outside air damper so that when the kitchen was unoccupied the amount of outside air intake would decrease accordingly.
  • The operation of the exhaust fan when the grill is not in use was resolved by installing a heat sensor in the exhaust duct above the stove so that it would only operate when the cooking equipment was active. This is now a code requirement in all Minnesota restaurants.

The energy reduction measures identified at the History Center are common issues that are often part of an EBCx study. Although they seem straightforward, excessive energy use due to things like leaving equipment running more than necessary can be difficult to find. EBCx is a thorough process that ensures no stone has been left unturned when looking for ways to save energy and money.