Indian Creek Nature Center, Cedar Rapids, Iowa
Amazing space at The Indian Creek Nature Center in Cedar Rapids, Iowa, uses a biophilic design, which aims to nurture the innate human attraction to natural systems and processes. With systems that are quiet and well concealed, over 40,000 users per year can tune in with the natural features of the building such as the bird viewing room and exhibit spaces.
The new 12,000 square foot Amazing Space serves as the feature building for Indian Creek Nature Center in Cedar Rapids, Iowa, the state’s only nonprofit nature center. The new building addresses the age and physical shortcomings of the old center, which was dealing with flood damage amid increased visitor traffic. Indian Creek Nature Center used the construction of their new building as an opportunity to amplify their mission and promote a sustainable future through environmental education, land protection, and nature interaction. The project highlighted this mission by pursuing the Living Building Challenge (LBC) Petal certification, administered by the International Living Future Institute (ILFI) and requires net zero energy usage based on operational data. The project included a 150-person auditorium, as well as exhibit hall, classroom, office, kitchen, and gift shop spaces.
An integrated approach pairing low-energy building systems along with high performing renewable generation systems made this project a success. The HVAC design consists primarily of terminal ground source water-to-air heat pumps that use a closed loop geothermal well field as a heat source and a heat sink. The geothermal design is critical to the building’s low-energy performance, since the HVAC loads are the primary energy use of the building. The mechanical systems integrate well with the building’s biophilic design, which aims to nurture the innate human attraction to natural systems and processes. With systems that are both quiet and well concealed, over 40,000 users per year can tune in with the natural features of the building such as the bird viewing room and exhibit spaces. A dedicated outdoor air system (DOAS), with total energy recovery, efficiently ventilates the building without compromising the indoor air quality or acoustic requirements of a unique learning environment.
The main entry to the Amazing Space brings nature indoors using locally sourced materials and evoking nearby prairie, woods, and creeks. Interactive ecological exhibits teach visitors about natural science using modern technology. A digital display dashboard lets visitors see how the building is operating and where energy is consumed.
Photo © Mike Fager, Fisheye Photography
A 100 kW photovoltaic (PV) array with 400 modules rated at 250 W each provides power to the building. 50 kW of the array is mounted on the building and the other 50 kW of the array is ground mounted near the building. Both of the arrays are fed to inverters connecting to the grid at a common point, allowing the building to feed excess power to the grid on good production days and use the grid as a backup source of energy when there is insufficient PV production. As of early 2018, the building had successfully met its energy needs for an entire year through its onsite PV array, and is on track to become the first commercial building in the state to achieve net zero energy certification. The building is striving to become the first nature center in the world to achieve Living Building Petal certification.
During the concept phase of the project, the owner and design team established an aggressive goal to achieve net zero energy use. As the industry is becoming more and more aware, achieving net zero energy use first requires design and optimization of the building and its systems to be low energy so that space and costs required for the renewable energy technology can be effectively managed. Numerous whole building energy models completed throughout the design process provided insight on the building’s complex energy relationships that required optimization. These energy models ultimately focused the design team on strategies for reducing the largest source of energy consumption within the building, the HVAC loads. The as-built energy model documented 52% savings in energy use and 50% savings in energy cost using the ANSI/ASHRAE/IES Standard 90.1-2010 Appendix G Performance Rating Method. For the most recent 12 months, the building’s actual (in-operation) performance has achieved 60% savings over the baseline building with an EUI of 32.7 kBtu/ft2·yr. The majority of the energy savings come from the HVAC and lighting systems, 37.0 and 10.5 kBtu/ft2·yr, respectively. When including the PV array renewable production intensity (RPI) over the same time, the building has achieved a Net EUI of –9.2 kBtu/ft2·yr:
Net EUI (kBtu/ft2/yr) = EUI – RPI
Key energy savings strategies included the use of two-stage ground source water-to-air heat pumps with weighted average efficiencies of 22.75 EER (cooling) and 4.36 COP (heating), total energy recovery of building exhaust air, natural ventilation, lighting design 40% below baseline, daylighting and occupancy sensor lighting control, occupancy control of HVAC, variable speed ground loop pumps, ECM fans, triple glazed low-e wood frame windows, and high R-value walls and roof.
Indoor Air Quality
Ventilation for the project demonstrated compliance with ASHRAE 62.1-2010 using the 62.1 ventilation rate procedure. The following table summarizes the key parameters used in the analysis.
Occupied zones within the building are also designed with an optional natural ventilation mode to operate in place of mechanical ventilation. Through a series of indicator lights programmed through the control system, the building occupants are notified when conditions are favorable for opening windows as detected by the onsite weather station. The design and construction process included a strategic plan for reducing source contaminants by selecting construction materials, finishes, furniture, equipment and supplies with low or no emissions of volatile and semi-volatile organic compounds. To comply with the performance-based standards of the Living Building Challenge, the facility underwent air testing, which showed very low concentrations of carbon monoxide, carbon dioxide, respirable suspended particles, and total volatile organic compounds. Though the Living Building Challenge does not maintain any specific thermal comfort criteria, all aspects of the LBC encourage user interaction with the building and its systems. In this way, the occupants are encouraged to consider ways that achieve appropriate thermal comfort and also reduce building energy consumption, such as the optional natural ventilation mode.
As early adopters of solar technology, Indian Creek Nature Center installed the first net-metered solar panel system in Iowa in 1993. The Amazing Space project built significantly on that first system with a design that includes almost 130% of their current electricity needs. The PV design includes a variety of mount types: fixed roof, fixed ground, fully-articulating ground, single-axis tracking ground, and dual-axis tracking ground. A net zero energy building in Cedar Rapids, Iowa is particularly impressive since average winter temperatures are typically below 20°F and summer temperatures average above 80°F. Additionally, extreme temperatures above 110°F and well below –20°F are common in the Midwest—a range of more than 130°F. Throughout these extremes, the building delivers excellent thermal comfort by managing solar gains and conduction losses while also providing good visual comfort with its efficient daylighting design. Through a natural ventilation design strategy and a touchscreen energy and water dashboard in the main corridor, this building encourages users to achieve a deeper understanding of its systems and educates them on innovative 21st century design practices.
The Amazing Space includes a full featured reception area and catering kitchen. The building is the central hub of several popular events such as maple syrup and honey festivals.
Photo © Mike Fager, Fisheye Photography
Operation and Maintenance
Extensive building system commissioning, including detailed operator training, was performed at the completion of construction to ensure that systems were installed and configured as intended. HVAC equipment was strategically positioned in a centralized mechanical room for easy access during future maintenance. The project includes an extensive sub-metering system that isolates energy consumption for HVAC, lighting, equipment, and service water heating uses. The energy and water meters integrate with the building automation system, allowing the Owner to monitor the performance of the building and identify opportunities for improvement. The new building features systems and equipment that significantly improve upon the service life and maintenance of the previous building.
The project team employed a highly structured approach to ensure the design achieved its energy efficiency goal while optimizing energy cost savings and initial cost. Design phase energy models evaluated conceptual design, HVAC load reduction strategies, and HVAC system selection. During the design development phase, over 55 separate energy models evaluated energy conservation strategies on a comprehensive basis that included energy cost savings, initial cost, and potential utility rebate. A 25 year life cycle cost analysis was used in the selection process for the HVAC system, with the lowest life cycle cost option being selected as shown in Table 1.
The building was expected to save $16,000 per year in energy cost compared to a baseline building and received a utility rebate of $27,300. The actual energy cost, based on the past 12 months operation, was calculated based on the customer’s rate schedule and results in actual savings of $18,600.
However, the calculated energy cost does not include any credit for the renewable energy provided by the PV array. Because of the PV production that completely offsets the building’s energy usage and a net-metering agreement established with the utility, the Owner ends up paying only the customer (administrative) charges associated with their utility account. When considering incremental costs for energy conservation strategies, utility rebate, and energy cost savings, the Owner has achieved a payback period of 1.7 years. The Owner also negotiated a long-term partnership with the local utility, Alliant Energy, for financing the PV array in order to research the effectiveness of solar energy as a grid-connected generation source and to educate the public on the benefits of solar energy. This effectively brings the payback period for the Owner to 1 year.
Because of this partnership, the project was able to include additional PV capacity beyond what was required to achieve net zero energy usage, effectively making it a net positive building.
Consistent with the project’s goal of obtaining Living Building Challenge Petal Certification and net zero energy usage, the building design includes many strategies to minimize the building’s environmental impact. The net zero performance of the building means that 95 tons of CO2 emissions are avoided every year. The project also supplies potable water through an onsite well and manages wastewater through an onsite septic tank and leech field.
Efficient, low-flow plumbing fixtures demonstrate good water conservation practices. A sophisticated construction waste management plan diverted over 80% of construction waste from landfills. •
About the Authors
Dwight C. Schumm, P.E., LEED AP, is a managing principal and senior mechanical engineer, Tim Lentz, P.E., is a mechanical project engineer and Joe Chappell, P.E., BEMP, is an energy project engineer at Design Engineers in Cedar Rapids, Iowa.