Energy Savings in Historic Sites: The Importance of Small Sites

While the map of the overall GHG emissions shows relative priority should go to the largest sites in the urban areas, there is more to draw from the data. Analyzing the GHG emissions further, and incorporating the size of the building as well as occupancy helps us to discover the importance of small sites in an organization-wide sustainability effort that spans many geographically and historically diverse sites.

One of the advantages of quantifying sustainability is the ability to benchmark, or compare across buildings or sites. When looking at greenhouse gas (GHG) emissions across the Minnesota Historical Society’s 26 historic sites, you can quickly see the relative environmental impacts of each site. The map below shows both the GHG emissions and locations of 19 sites included in the fiscal year 2010 sustainability audit.

As mentioned earlier, the Twin Cities metro area sites tend to be the higher impact sites. The scale of the impact of the Minnesota History Center as compared to Split Rock Lighthouse Historic Site or the Charles Lindbergh Boyhood Historic House puts them in different orders of magnitude. However, once normalized by size, the smaller Lindbergh site’s impact can be seen. While at first, the normalization only puts the sites on the same level as the largest building, the Minnesota History Center, the data actually begins to steer us towards strategies that will help reduce our entire institution’s environmental impact, and also overhead costs from utility bills. In this way, we focus on hotspots, or the sustainability strategies that will give us the most environmental impact reductions for the most effective investment costs.

The strategy allowed us to identify over 75 repairs, retrofits, and replacement projects from heating, cooling, and ventilation to lighting and plumbing upgrades. The examples in the tables below from the historic sites show how much impact small buildings can have, even at a large institution.

One of the simplest things to help reduce energy costs and GHG emissions is to reduce the total quantity of energy used by widening operating temperature setpoints. In our own homes, this process is easily done by feel. We can set the temperature as low or as high as we feel comfortable with, and that sensation of thermal comfort can be very subjective to the person making that decision. In our historic buildings and museums, this decision is much more complicated since comfort of building occupants is not the only factor. The preservation of the historic building materials, as well as any exhibits, artifacts, paintings, or archives located in the buildings can be significantly impacted by changes in relative humidity and temperature. As such, our experience has noted the importance of interdisciplinary processes in today’s sustainability efforts. Each temperature setpoint adjustment included consulting engineers, as well as internal staff from conservation, exhibits, and asset preservation. A five degree drop in winter unoccupied setpoints meant understanding the impact it would have on materials in the building, the building infrastructure, as well as the heating and cooling system capacities. While a time-consuming process, these four setpoint adjustments listed below will save us $3,500 a year.

Another method of sustainability in historic sites is demand-based controls, or reducing consumption when there are fewer occupants in a building. For some of our rural sites, where occupancy can fluctuate from large school groups flowing into the building to minimal attendance during other hours, these demand-based controls will shut-down or lower operations during the quiet hours. These controls do not always make sense, as seen in the table below. The simplest and most popular demand-based control strategy is occupied and unoccupied settings for open and unopened hours or seasons. These settings are available on even very basic residential-scale thermostats, and take minimal amount of time to implement. Similar to the setpoints strategies above, consensus about lower or high setpoints across conservation, exhibits, and asset preservation needs to occur. In the example below, a quick adjustment in unoccupied setpoints in the Lindbergh Boyhood House results in over $500 of annual energy savings.

There are also more sophisticated demand-based controls available. At Split Rock Lighthouse, an installation of CO2 sensors in the ventilation system will dial back ventilation when there are few people in the space, and raise levels when the sensors detect a lot of CO2. While costly to implement, the system at Split Rock costs about $10,000, the anticipated savings would allow the initial cost to be paid back in a little over 4 years. This means after the 4 year period, over $2,000 in annual savings can go right back into program budgets.

However, not all demand-based controls will produce the same savings. In the Lindbergh House Visitor Center, a demand-based control for exhaust fans in a small bathroom was analyzed. The system would be a low initial cost, just over $200, but would not make an appreciable reduction in either GHG emissions or utility bill costs. This results in a 20+ year payback period. While the $200 investment is not a great one, this demand-based strategy will be lower priority given the low savings associated with it.

Finally, lighting strategies are also a popular retrofit option at historic sites, and particularly in service areas where fixture or bulb replacements will not disrupt the historic character. Looking at lighting in visitor center buildings at the Society, which means non-historic buildings, replacing light fixtures with LED fixtures does not always produce environmental and cost savings. In the Minnesota History Center building, replacing high pressure sodium fixtures in storage areas with LEDs would only produce a little more utility and environmental savings, but for 36 times the cost of a similar project replacing halogen bulbs in a retail area in the Split Rock Lighthouse Visitor Center. The retail area would reduce $1,355 in annual utility bills and over 8,700 kg of GHG emissions, for only $3,700. This is a payback period of only 2.9 years, while the LED replacement in the History Center would be over 27 years.

Given these examples, it is clear that even small, historic houses and their associated sites can make a big difference in an institution. Overall, some of the most effective strategies with the lowest payback periods come out of historic sites. Further, these examples also show that sustainability does not involve blanket strategies that can be applied with the same level of success in every context. For the Minnesota Historical Society, our use of the GHG emissions metric helps guide the process of determining the most effective strategies for our organization, making clear the path to get sustainability at both small historic sites and large institutions.