ZERO-NET ENERGY HOME

ZNE

A Zero-Net Energy (ZNE) home is one for which the occupant’s energy consumption is less than or equal to the energy collected through the home’s energy harvesting system(s). An example of a home energy harvesting system is a solar panel. Because the amount of energy collected through the typical home energy harvesting system is relatively low, it is important that ZNE homes have structural features that promote energy efficiency. For example, if an air conditioned home has many small openings, then cool inside air (during the summer) will escape into the outside atmosphere relatively easily. This makes the air conditioner run longer, which leads to unnecessary consumption of energy. As a result, the home owner will have a higher electric bill and the environment will be adversely affected due to the additional energy consumed. Therefore, ZNE homes are typically constructed with a very air-tight building envelope.

The Future of ZNE Homes

By 2017, there will likely be in excess of 10,000 new ZNE homes in the state of California. With nearly one-third of California’s energy being consumed in residential homes, the extraordinary efforts by a wide array of stakeholders in the state of California have helped pave the way toward all new residential construction being ZNE by 2020 and all new commercial construction buildings being ZNE by 2030. Based on 2014 census data (http://www.census.gov/construction/bps/) this will correspond to at least 80,000 new homes constructed per year intended to be designed and built to very high performance levels.

Potentail Problems

 Though air-tight building envelopes are advantageous in promoting energy efficiency, one potential problem is that ZNE homes tend to allow for the accumulation of (carbon dioxide) CO2, smoke, and other air-borne impurities, if a well-designed air exchange system is not operating. The afore-mentioned trend in ZNE homes means that California ZNE home owners may be at risk if their air-tight home does not feature an appropriately-designed air exchange system. While architects and engineers use computer models to design air exchange systems for ZNE homes to maintain air quality standards, they also aspire to develop air exchange strategies that lead to minimum levels of energy consumption; to accomplish this, they must have sufficiently refined computer models that have been verified through the evaluation of experimental data.

ZNE at CSUS

For the purpose of contributing to the experimental data that may be used to develop reliable air exchange computer models for ZNE homes, Sacramento State will create its own model ZNE home. The objective of the work is to determine a function that captures the energy consumption due to air exchange events in a model ZNE home. Many variables may affect the concentration of airborne impurities in a residential home. The three dependent variables considered in this study are the diameter of strategically located holes in the model home walls, the upper CO2 concentration limit that triggers the air exchange event, and the duration of the air exchange event. The dependent variable considered is the energy consumption (over a one hour period) associated with the air exchange event.