Careful Air Sealing Trims Energy Use at New College Dorms

Bar Harbor, ME

Sep 29 2010 By Ann Edminster | 0 comments

General Specs and Team

Location: Bar Harbor, ME
Living Space : 22000 sqf
Cost (USD/sq. ft.): $225/sqf

Year Completed: 2008

Architect: Bruce Coldham, Coldham & Hartman Architects
Energy Consultant: Marc Rosenbaum, P.E.
Builder/Contractor: E. L. Shea
Developer: College of the Atlantic

Construction

Foundation: Slab-on-grade with frost walls
Floors: 3-in. EPS continous below "floated" slab
Walls: Double-stud wall 11.5-in. cavity filled with dense-packed cellulose (3.5 lbs/cf)
Roof: 14-in. I-joist filled with dense-packed cellulose at 3.5 lbs/cf
Windows: Fiberglass-framed Thermotech windows with triple-pane, double low-e, argon-filled glazing; typically U-0.17, SHGC 0.24
Space heating: District heating system with Veissman pellet boiler serving 35,000 sf. Heat distribution through in-floor hydronic tubing and the ventilation system.
Domestic hot water: Central pellet boiler; electric backup when pellet boiler is off during low-load periods.

Energy

Peak heating load: 8 Btu hr/sf
Energy use: 30 KBtu/sf/yr

Drain-water heat-recovery system helps preheat water used for showers.

Water Efficiency

Low-water-use plumbing fixtures
Composting toilet chambers located on the first floor of each building

Indoor Air Quality

Mechanical ventilation: Venmar HRV provides continuous ventilation with ducted supply and exhaust
• No carpet
• Careful material choices
• Track-off matting at entries
• Radon "premitigation"
• No combustion devices within occupied spaces

This Maine college has a long-term goal: making its campus fossil-fuel-free

By Hal Bohner

In the cold climate of coastal Maine, effective air sealing is critical to maximizing energy efficiency. The architect for the project, Bruce Coldham, said, “We have tried many approaches to air sealing over the past twenty years, but we hit the jackpot with these buildings. The results were spectacular. We achieved a remarkable final airtightness of 0.79 ACH50 consistent over three similar buildings. Without the comprehensive air-sealing design and implementation, the buildings would have been seven-plus times leakier.”

Building around the college's core values
The project provides student housing for the College of the Atlantic, a small school with only one major: human ecology. The new buildings accommodate 51 students; they are organized as a residential cluster of six “houses,” with each house accommodating about eight students.

The school’s mission is not only to study our relationship with the environment but also to improve it. Accordingly, a core objective of the college’s public goals is to achieve campus-wide independence from fossil fuel by 2015.

A creative plan for space heating
With the plan'semphasis on using zero fossil fuels, heat-pump technologies were considered but eventually rejected. Solar opportunities were severely limited due to site constraints and the client’s desire to retain trees.

Space heating and domestic hot water needs were significant, leading the designers to specify a district heating plant — a boiler with a high water temperature to match the load profile. The designers specified a biomass-fueled central boiler from Viessmann.

  • Space heat is delivered at the first-floor level through hydronic tubing embedded in the concrete slab.
  • Roof planes are sized, cleared, and oriented as well as possible for future PV installation.

An emphasis on tight, well insulated enclosures
Coldham explained how the buildings' remarkable airtightness was achieved. "We adopted a deceptively simple procedure — taping the exterior sheathing, using a tenacious self-adhesive tape over a contact adhesive primer on the OSB.” Air sealing was detailed in the plans, as shown in the example (A5.2 Air Sealing), which displays the relevant details in color.

Attention to air sealing was not the only approach used to minimize heat loss through the enclosure. Twelve-inch-thick walls framed with a double row of 2x4s were filled with dense-packed cellulose insulation, a recycled building material. The dense-packed application prevents moist interior air from reaching the cold exterior air barrier. Insulation followed the 14-inch-deep, I-joist-framed, unvented roof planes.

Building enclosures were designed, detailed, constructed, repeatedly tested, and verified to achieve a peak load of 8 Btu per hour per square foot — with R-40+ walls, an R-45 roof plane, R-5 windows, and a consistent final airtightness of 0.79 ACH50 at all three buildings.

  • Simple roof geometries and large overhangs protect the buildings from wind-driven rain.
  • The dramatically reduced heat load allows ventilation to provide heat distribution to the upper two floors, thereby eliminating the considerably more expensive radiant floor that was initially planned.
  • No basements were used on the rocky Maine site. Thermal mass coupling is fully maintained with slab-on-grade floors.
  • Entry air locks for each house preserve comfort and conserve energy for the living spaces.

Lessons Learned

Architect Bruce Coldham offered a number of observations about the experience of tackling the challenges of energy efficiency in the Northeast.

• Fog machines can be a very effective tool in association with blower-door testing to show people how successful (or not) they have been in air sealing. Testing the building in this way during construction can provide beneficial feedback to the construction crew. (For more information on this technique, see "Pinpointing Leaks With a Fog Machine.")

• It often makes economic sense to put money into improving the envelope in order to save more money during operation of the building. Coldham wants to keep his building loads proportionate to their ability to be served by non-fossil fuel sources. For buildings in the Northeast, that usually means getting loads down to ~10 Btu hr/sf (assuming a 70°F delta T), which is about a fourfold improvement over an average building. This means at least doubling performance standards for insulation and airtightness; e.g., windows from R-2.5 to R-5, walls from R-20 to R-40. Doubling these enclosure components cuts the aggregate load by more than half.

• It's important to install meters to monitor energy usage and enable users to be aware of and modify their behavior, as appropriate. However, be careful to use meters that generate practical and useful information, or the meters will not be read. Some meters on the market today generate huge amounts of data which overwhelm the user and are therefore ignored. Badger makes water meters which are useful and trouble-free.


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Image Credits:

  1. Coldham and Hartman Architects
  2. Coldham & Hartman
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