Positive Energy is Achievable...

In this post, I will summarize my research that I have presented as a short paper in a class lecture.  At the first time, the goal was investigating a net zero energy (NZE) building or house.  I had to find two case studies that claim NZE in their applications.  However, the results of my case studies were showing the tendency of reaching positive energy instead of net zero energy.  It is clear that NZE house means the house that can produce energy that is equal to its energy consumption.  NZE has an important role as the continuation of sustainable construction.  The terminology is a concrete framework that covers the next stage of application of sustainable construction principals.  

Case studies

Picture 1 NREL Habitat NZE House
Photograph courtesy of NREL

The first case study is a test house from National Renewable Energy Laboratory (NREL), located in Denver.  Based on the report from NREL (2010), the one story type zero energy house (ZEH) Habitat (see Picture 1) is placed on a 119 square meter area with general specifications consist of combination of natural gas (NG) for cooking, space heating and clothes drying; ground-coupled heat pump (GCHP), solar thermal for radiant heating and cooling purpose; envelope system with all low emissivity glasses.  In addition, the lighting system uses compact fluorescent light (CFL) bulbs for the entire house and the use of all Energy Star^® appliances.  Although the uses of NG is said to be debatable for the renewable energy point of view, the houses will offset the use of NG with the electricity that can be produced via photovoltaic (PV) system.  This house is inhabited by one adult with two children.  General results for annual data of this test house can be summarized in Table 1.

Table 1 NREL Annual Test House Results

From column [2] above, the energy that can be produced is 1,767.8 kWh.  Based on the consumption data, the annual consumption for this house is 51 kWh/m².year.  If we divided with the total area of the test house the net electricity production is 14.8 kWh/m².year.    

The second case study is a test house from Denmark.  This house was completed in 2010 as the first experimental project from VKR Holding, based in Horseholm, Denmark (see Picture 2).  The floor area is about 189 square meters and occupied by two adults with three children.  The house has 50 square meter of solar panels that produce 5,500 kWh per year; 6.7 square meters copper plate solar thermal collectors for the heating system both space and water heating.  

Picture 2 Active House Denmark
Photograph courtesy of VKR Holding-Denmark

A heat pump system is used for the space heating purpose as well as the installation of energy efficient appliances.   In this case study, no energy consumption data has been provided.  However, the average single family electricity consumption in Denmark about 47 kWh/m².year can be used (this number yields to 8,883 kWh annually after multiplying with 189 square meters area).  Table 2 below, column [2] contains the developer data claimed by VKR-Holding.  

Table 2 Annual Consumption for Active House-Denmark

Again, if we divided with the test house area, the test house electricity production yield to 15.43 kWh/m².year.

Both case studies confirm a very tight results of energy production per square meters per year which are positive.

In conclusion, these case studies show a promising advance step beyond just a NZE house.  These facts prove that the net positive energy can be achieved surpassing the claim of net zero energy.  Of course, the exceeded energy can be either sold back to the utility grid  or used for other household purposes.

NB:  Green Act: 8.4 miles  = 0.280 gallons oil

        Cumulative 72 miles  = 2.385 gallons oil