While furnaces around town were running at full tilt in the recent cold snap, members of two town committees pondered how to improve energy efficiency for the proposed new elementary school. Ron Ostberg of the School Building Committee met with Harvard’s Energy Advisory Committee Jan. 10, and David Fay serves on both committees.
Brian Smith, chairman of the Energy Advisory Committee (HEAC), described the goal of the discussion as “the best possible energy performance for the money.”
Schematic designs for the proposed school have been sent out for cost estimates, which are due in about two weeks, making this a critical time to plan for energy efficiency. “We at HEAC see how hard it is to improve the energy performance of a building once it’s been built,” Smith said.
Current heaters have problems
Not surprisingly, how a building is heated has a major effect on energy usage. The current Hildreth Elementary School has under-window wall units in each classroom that provide both heat and ventilation, similar to the units you might find in a motel. According to Principal Josh Myler, five of those units have been repaired so far this year, and another is awaiting parts.
“The most common repair,” Myler wrote in an email to the Press, “is replacing the blower motors, which are failing or seizing. After 30 years of regular use, they are just wearing out.” The thermostats in the units are also failing, so that teachers have to turn the units on and off by poking scissors inside the unit to flip a switch, leading to broken switches. Moreover, these units pull in air from the outdoors, so in very cold weather the water circulating in them has sometimes frozen. Once the water freezes, it prevents any water from circulating in that loop, making it even harder to thaw the system. “There have been mornings when Linda [Dwight], Mark [Force], Sue [Frederick], and I were all using hair dryers and heat guns to try to get the loops to thaw, only to then find that when they thawed the pipes were cracked and started spraying,” Myler wrote.
A boiler or heat pumps?
Given all these difficulties, a better heating system was a high priority for either a renovation or a new school. With the building committee’s support, the architectural firm Arrowstreet designed the proposed school with a conventional HVAC system using a boiler and chiller, with ducts to carry the heated or cooled air throughout the building. The current building has no such ductwork, and adding it would be one of the most difficult and expensive parts of a renovation.
According to Arrowstreet’s estimates, the boiler-chiller system, coupled with better insulation, would make the new building nearly twice as energy efficient as the current one (see “Explaining EUI” below).
But nearby Lexington has recently gone even further in energy efficiency. The Fiske Elementary School, built about a decade ago, has a hybrid heating system that combines a ground-source (or geothermal) heat pump with a standard boiler as backup. According to Fay, Lexington found that the heat pump alone was all the school needed. So last December, Lexington voters supported a “pure” heat pump system, with no auxiliary boiler, as part of a $63 million plan for the new Maria Hastings Elementary School.
The geothermal system added about $2 million to the Hastings project’s cost, based on estimates by the Lexington town engineer. Whether the heat pump results in future savings depends on the cost of natural gas. If it remains low, there would be little or no savings. But if the price of natural gas rises to its pre-fracking average, the savings could be considerable, according to Lexington’s committee on sustainability.
At Fay’s request, Arrowstreet looked into the cost of a heat pump system for Harvard’s new elementary school. The company estimated it would cost about $2.7 million more than a conventional system, but both Fay and Ostberg emphasized that all estimates are tentative at this stage. The benefit, Fay noted, is that the building would use no fossil fuels and create no carbon dioxide emissions at all. And should natural gas prices bounce back to previous levels, a heat pump could lead to savings in operating costs.
The importance of a good ‘envelope’
Building committee member Ostberg warned that any decisions on a heat pump option should wait until the committee has solid cost estimates. “We don’t know what we can afford. … There are a lot of variables,” he said. Because a ground-source heat pump would require perhaps 100 wells, each with its own pump, Ostberg said he was also concerned about maintenance of the system.
For energy efficiency over the life of the building, Ostberg said, the most important consideration at this stage is a good building “envelope.” Achieving that good envelope requires “as much insulation as we can reasonably afford,” he said, and rigorous monitoring during construction to make sure the insulation is installed as it should be.
Ostberg said the conventional boiler-chiller system now under consideration is a good one and will have a lifetime of perhaps 25 years. By that time, he said, there will be new options. At that point, the school might want to adopt a different source of heat, but it could still flow through the same ducts.
Noting that Harvard is a small town, Ostberg said, “We can’t be on the cutting edge. We need to be prudent and wise about doing what we can do.”
What about solar?
Sketches for the proposed school have always shown solar panels over much of the southerly roof. According to Fay and Smith, photovoltaic panels could supply part of the building’s electricity, but not all of it; there is simply not enough roof area for panels to produce all the electricity a building this size would need.
In a telephone conversation with the Press, Project Manager Tom Murphy of NV5 explained that solar panels are definitely part of the building plans. “The current intent,” he said, “is to include them on day one.” However, the building committee might decide to delay installing the panels if it seemed likely that grant money for doing so would become available later. (That’s the course the Hastings School in Lexington expects to follow.)
Smith, Fay, and Ostberg all said they expect a public forum on the energy issues of the proposed school to be scheduled soon. And all expressed the hope that the energy committee would remain engaged in the decision process.
“HEAC is not dictating any solution,” Smith emphasized. “But we want to see all the options considered.”
Explaining EUI: Yet another acronym
Sometimes it seems as if a small town can generate almost as many acronyms as the military. BOS, CPIC, DPW, HEAC, HES, LWV, and SAFE come to mind. But to compare one building’s energy efficiency to another, it helps to know one more acronym: EUI, or energy use intensity.
A building’s EUI is the amount of energy it uses in a year, divided by its total floor area. The lower the number, the more energy efficient the building is.
“The EUI for a building changes a little each year due to weather variations and changes in the use of the building,” David Fay wrote in an email to the Press. For fiscal 2017, he said, Hildreth Elementary’s EUI was 66. The estimated EUI for the proposed new school, as designed with a conventional boiler system, is 39, or a little over half that of the present building. If the new school used a ground-source heat pump for all its heating and cooling needs, Fay said, its estimated EUI would be 26.
