AIA/COTE Top Ten Green Projects
First Unitarian Society Meeting House
|Photo credit: The Kubala Washatko Architects, Inc. / Zane Williams|
The new building design is approximately 40% more efficient than a comparable base case facility. This conclusion is based on the original energy design model and reinforced by initial post-occupancy analysis of actual energy use.
The decision to transfer thermal loads via radiant floor heating and cooling, instead of through conventional forced-air systems, was a significant factor contributing to overall building energy performance. Most HVAC systems move air around to maintain a constant temperature. Air, however, is much less energy-dense than water, which is approximately 40 times more efficient at transferring a unit of energy. Instead of using air-to-air heat pumps, the HVAC system treats and supplies only the code-required amount of outdoor air to occupied spaces. The reduction in air volume transferred around the building means less ductwork and appreciably lower fan energy costs.
Additional energy saving measures include
- high-efficiency, multiple-stage, water-to-water geothermal heat pump
- high-efficiency glazing and building shell insulation
- upgraded hot-water tank insulation
- reduced lighting power density
- exhaust fan system designed to promote ambient ventilation during early summer and fall
Historic and site constraints were primary factors in the final building design. The state historical society, for instance, imposed restrictions on where a new addition could be sited and on how the new building looked in relation to the original. As an indication of the challenges faced, the architects tested more than fifteen design iterations before identifying the final solution.
Within these parameters, bioclimatic design considerations played an important role. The northern building exposure created an opportunity for expansive floor-to-ceiling glass views back to the Wright Meeting House without adding significant cooling loads. Building overhangs provide additional solar shading. The western exposure was designed to minimize late afternoon solar gain.
Outdoor views to the east from inside the main auditorium were an important program goal; solar gain along this elevation is mitigated by trees and vegetation.
Bioclimatic design for the southern exposure was carefully analyzed. The adjacent property to the south is zoned for five-story commercial use, so potential for loss of a solar window in the future was great. For this reason, the congregation elected not to rely on installation of PV systems or design of solar strategies that could be compromised.
|Annual Purchased Energy Use|
Total Annual Building Energy Consumption
|Annual End-Use Breakdown|
|Plug Loads and Equipment||27 kWh||0.0921||0.00379|
|Domestic Hot Water|
|Unspecified End Use||810||33.3|
|Electricity (Summer)||149 kW||6.12 W/ft²|
|Building Energy Load|
|Cooling Load||15.8 ton||1,540 ft²/ton|
|Connected Lighting||20 kW||0.822 W/ft²|
Data Sources & Reliability
The energy simulation results for both budget and design energy cases were generated with the TRNSYS simulation software package (release 16.01.0000) supplemented by the TESS Component Libraries (release 2.03). TRNSYS is a sub-hourly, modular simulation tool well suited for the study of green buildings, energy-efficient technologies, and renewable energy technologies. As a modeling tool, TRNSYS offers greater flexibility than other systems in modeling zonal temperature variability. This flexibility allows TRNSYS to become not merely a verification tool, but also a more intuitive and integral part of the actual design process.
TRNSYS has been used for the study of energy systems since the mid-1970s and had been extensively tested and reviewed over the course of its lifetime. The program has been validated using the “ASHRAE Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs” (ASHRAE Standard 140) and has been used successfully by this firm to perform the energy modeling associated with four LEED-TM projects, not including the present project. TRNSYS complies with all of the restrictions of ASHRAE 90.1-2004 G2.2.
The TRNSYS program features a modular simulation engine around which are grouped libraries of standard energy technology models, libraries of building models and building components, libraries of emerging energy technologies, and libraries of renewable energy technologies. The program is continuously being upgraded and adapted as new models are added to the package by the developers as well as by users around the world.
The energy rates used for both the Proposed Design and Baseline Design cases were based on a purchased cost of $0.082/kWh for electricity and $9.82/1000 ft3 for natural gas. These utility rates are taken from DOE's EIA estimated commercial utility costs for 2007.
The analysis was based on U.S. climatic data for Madison, Wisconsin, the city in which the building is located, and the building envelope requirements prescribed in Table B-1 of ASHRAE 90.1-2004 (SI). All values in the TRNSYS simulation are in SI units; they are converted to IP units for presentation in this report. It should be noted that there are some rounding differences between the IP and SI versions of the ASHRAE 90.1-2004 standard that are not accounted for by unit conversion. The SI version of the ASHRAE Standard was used in the present project. The TMY2 weather file for Madison, Wisconsin was used for the analysis.
- Use ground-source heat pumps as a source for heating and cooling
Daylighting for Energy Efficiency
- Use large interior windows to increase daylighting penetration
- Use light levels appropriate for different tasks
HVAC Distribution Systems
- Keep duct work out of unconditioned space