Envelope-Driven vs. Occupant-Driven Loads

Challenge

Some energy consumption in a home is heavily influenced by the way homes are designed and constructed – or by the “building envelope” of the home – while other energy use is dictated by occupant use and habits. While some costs can be controlled by the building design, homeowners must also be educated on how to efficiently use their homes. For example, a tight, well-insulated home will require less energy to heat and cool than a comparable house with more air leakage and less insulation; the envelope drives energy needed to heat and cool. By contrast, plug loads, or energy use from items plugged into outlets (televisions, computers, hair dryers, etc.) is driven by the occupant.

Opportunity & Response

Rural Studio clearly differentiates what we can control through design and construction and what we can control through homeowner education and awareness. Energy modeling during the home design process can help housing providers and their clients understand the expected energy use – and, therefore, predicted costs – for envelope-driven systems such as heating, cooling, and ventilation. Post-occupancy monitoring ensures that these systems are operating as modeled. Additionally, post-occupancy monitoring allows Rural Studio to continue to actively engage with the housing provider and homeowner, and to provide the ongoing education necessary to help occupants understand how to use their homes more efficiently and reduce energy use and maintenance costs.

Response

Front Porch Initiative continues to collect ongoing energy use data on two houses constructed to beyond-code standards with Auburn-Opelika Habitat for Humanity (AOHFH). As energy to condition and ventilate the house decreases with more efficient systems, the share of energy devoted to plug loads becomes a larger share of overall energy use.

Implementation

Stevens Street

Renewable Energy

Challenge

Incentives for on-site power generation vary from location to location, often dictated by the local energy provider.

Opportunity & Response

Advocating for policies that incentivize on-site energy generation can greatly decrease the cost for installing energy generation systems. For example, excess energy generated by photovoltaic (PV) panels, also known as solar panels, can either be sent back to the energy grid, or stored in batteries. Energy providers that offer bi-directional meters, which allows excess power to flow to the grid, greatly reduce system costs to the homeowner.

Implementation

Stevens Street

Embodied Decarbonization

Challenge

Increasingly, decarbonization is understood to be the path toward a sustainable future. We know 40% of greenhouse gas emissions are controlled by “operational carbon” or rather by things we do in our households through our active human comfort systems and appliances. However, “embodied carbon” emissions can account for up to 75% of a building’s total emissions over its whole lifespan. Consider all the materials utilized in a home’s construction, from concrete foundations to wood framing, to roof shingles. Embodied carbon is the sum of all the greenhouse gas emissions resulting from the mining, logging, harvesting, and processing of these materials. Plus, the transportation to the job site and the method of construction used. Embodied carbon is all the carbon that is emitted before the building is even occupied. Today, the embodied carbon emissions in constructing a new home are equal to approximately 20 years of operating emissions. And as homes increasingly get more energy efficient, the AIA estimates that 80% of emissions will come from embodied emissions, so lowering embodied carbon emissions is potentially more urgent now than lowering operating emissions.

Opportunity & Response

There are several complimentary approaches to reducing embodied carbon in new home construction. These include:

1) Utilization of low-carbon materials – Architects already use energy modeling software to estimate the energy use (and subsequent carbon emissions) of building operations. But the industry has lacked a standardized system to track the carbon embedded in construction materials. Recently however, the development of open-source tools such as the Athena Impact Estimator, and the Embodied Carbon in Construction Calculator (EC3), are beginning to make it easier. While these tools are currently optimized for commercial building analysis, another approach in residential construction is to utilize “red lists” developed by organizations like HBN. While red lists are focused primarily on health impacts of material specification, research shows that red list materials map closely to high-carbon materials as well.

2) Reducing total materials in the design of the home – simplify systems, reduce redundancy, and insure means and methods during construction to ensure building performance is optimized

3) Design for longevity – consider issues of both durability and resilience in developing building assemblies

4) Repurpose resources – utilize reclaimed and recycled materials, and leverage all “sunk investments” in site development.

Implementation