Zero Energy Certified



Certification StatusZero Energy Certified
Version of LBC3.1
LocationWest Lafayette, IN, USA
Project Area1,248 Square Feet
Start of OccupancySeptember 1, 2017
Owner OccupiedYes
Occupancy TypeEducational
Number of Occupants2


OwnerPurdue University – Department of Biological Sciences
Owner RepresentativeKerry Rabenold
Project Certification LeadMichael Gulich
Project ManagerJames Naville
General ContractorEdwards Heating & Cooling
Electrical EngineerEdwards Heating & Cooling
PlumbingEdwards Heating & Cooling
InsulationEdwards Heating & Cooling
ExcavationHack Excavating
ConcreteEly Concrete
Solar ArraySolar Systems of Indiana
Log Shell & Roof Deck, Counters, Window and Door InstallationsFrontier Builders
Roof System, Interior Walls, Wood TrimBlocher Construction
Windows and Doors, Custom Triple-PanePella Windows and Doors of Indianapolis
Photo Courtesy of Purdue University Department of Biological Sciences


A primary objective for the project was creating a building that would be a model of energy efficiency and environmental sustainability, in addition to providing caretaker housing and an open pavilion for students and visitors. The idea was also to show to the donors, researchers and students how an energy efficient sustainable building works. The building was named after Dr. Kerry Rabenold, from the Department of Biological Sciences, responsible for leading the project.


This project has been ten years in the making. Initially, an architect from Pittsburgh developed a very bold project in terms of aesthetics, but it had some flaws and misconceptions. For example, the east-west orientation of the solar panels to be installed on the building’s roof was not ideal; a green roof with a rainwater collection system including a storage tank was shown to be unnecessary, since rainwater could be naturally absorbed by the soil and after being naturally treated, captured by the well for use in the building. The geothermal system originally envisaged was an air-to-air type, which is less efficient than the water-to-water system. Further, the geothermal system was based on earth tubes that are usually humid and can bring fungus and mold to the building, which we wanted to avoid. However, the idea of using a geothermal system to provide warm water to the radiant floor heating system proved to be very viable and was maintained in the final version of the project.

A second, local, architect developed a simpler design, closer to what was built, but still with a were very high project cost, which had to be significantly reduced and simplified. In the end, the final version of the project was not designed by an architect but was mainly the product of the project leader (Dr. Rabenold) and the contractors working together. They further simplified the second architect’s design and basically created a very traditional log cabin, with sophisticated energy production, heating, and air conditioning systems.

The final design of the log cabin has few doors and windows, both to guarantee a better thermal performance for the building, and to ensure privacy to the caretaker residents, since the hut is located in a public area, frequently visited by students and researchers. The PV panels installed in a super-efficient roof system are facing south and the geothermal system provides warm water to the radiant floor heating system

Roof R value and section specificationR60

Wall R value and section specificationR15 – Hybrid log and conventionally framed wall
Floor R value and section specificationR16
WindowsWindows – Pella triple-pane
Skylight window – Velux VCE ventilated curb mounted skylight, double-pane
Photo Courtesy of Purdue University Department of Biological Sciences


A total of 28 PV panels were installed on the roof, all facing south, ensuring maximum exposure to the sun throughout the day. The solar system provides sufficient energy for all the regular residential uses including lighting, plug loads (efficient appliances), ceiling fans, and water heating, as well as the pumps of the geothermal system and the water supply well. In addition, when energy production exceeds the log cabin’s demand, the excess energy powers an adjacent classroom and laboratory, as well as other facilities in the complex, such as a birdhouse and a shed.

The geothermal system helps save energy by providing warm water (55°F) for the cabin’s radiant floor heating system during the winter, and cooled water (55°F) for the air conditioning system during the warmer months. In addition, the geothermal system is equipped with a desuperheater, which recycles waste heat from the heat pump’s compressor and uses it to heat water.


Actual energy use during performance period6,772 kWh
Actual energy produced during performance period7,840 kWh
Net Energy Use-1,068 kWh
EUI18.5 kBTU/sf/yr
Photo Courtesy of Purdue University Department of Biological Sciences


Panel Array Size8.4 kW
Panel Output Per Capacity Nameplate300 W
Panel Quantity28
Panel Type and Brand
SolarWorld Sunmodule Plus – Model SW 300 MONO (5- busbar) – 60 Monocrystalline cells per module
Inverter Quantity1
Panel Array LocationRoof – facing equator
Ownership DetailsPurdue University – Department of Biological Sciences
Photo Courtesy of Purdue University Department of Biological Sciences


Although the building was not designed and detailed by a team of designers, the project benefitted from an engaged and willing construction team. The builders and suppliers were extremely competent and supportive throughout design and construction, always helping with important details. The team at Solar Systems of Indiana calculated many scenarios and managed to arrive at a project with an excellent cost-benefit ratio. The team that built the roof was also excellent, installing a very efficient and long-lasting roof, with a sophisticated system for fastening the solar array in the seam of the metal roofing panels.

Another important achievement is demonstration that an energy efficient building can be comfortable. Comfort is particularly important in the case of this cabin, as generating interest in the role of reserve caretaker carries enough other challenges!

Photo Courtesy of Purdue University Department of Biological Sciences