Imperative 6: Net Positive Energy
To rely solely on renewable forms of energy and operate year-round in a safe, pollution-free manner.
One hundred and five percent of the project’s energy needs must be supplied by on-site renewable energy on a net annual basis, without the use of on-site combustion. Projects must provide on-site energy storage for resiliency.
The very first thing that we needed to do in the design of the energy system for the Living House was to understand and determine the the expected energy use within the home.
The BRANZ HEEP Study (1) shows the average Auckland home uses around 10,660 kWh of energy a year. This is typically into the following usage profile:
- 34% is for space heating
- 29% is for water heating
- 13% for appliances
- 10% for refrigeration
- 8% for lighting and
- 6% for cooking
In the Living House we plan on eliminating any requirement for space heating (electrical or otherwise) through the implementation of good passive solar design.
The key elements of passive design are: building location and orientation on the site; building layout; window design; insulation (including window insulation); thermal mass; shading; and ventilation. Each of these elements works with others to achieve comfortable temperatures and good indoor air quality.
The first step is to achieve the right amount of solar access – enough to provide warmth during cooler months but prevent overheating in summer. We have done this in the Living House by designing the house as a slim rectangle that faces due North om the site. There are a large number of windows on the North Elevation with windows only provided on the South Elevation to bathrooms for ventilation. The roof has designed to have eaves of 0.5m that will allow the winter sun in but will keep the summer sun out of the house.
Our rammed earth walls will be providing significant thermal mass and we are insulating the centre of these walls to improve the r-value.
We are then eliminating the need for electricity for water heating through the use of the Energie Thermodynamic Solar System.
The Thermodynamics Solar System joins two incomplete technologies, the heat pump and the solar thermal collector. Heat pumps are quite efficient pieces of equipment, but the heat they produce from their renewable component varies according to changes in the temperature of the environment.
Thermal solar collectors are most effective on hot and sunny days but they are totally inefficient when there is no sun. Thermodynamic Solar Technology manages to surpass the limitations of both heat pump and solar collector technologies. The thermodynamic system’s refrigerant (R134a or R407c) is forced under pressure into the thermodynamic solar panel, where the refrigerant gains heat from the surrounding environment, causing it to expand into a gas. Following this stage, the gas travels through an exchanger, with the help of a small efficient compressor, heating the water. The refrigerant then cools, returning to liquid form, passes through an expansion value and the circuit is repeated. As the fluid has a boiling temperature of approximately -30ºC, the system works even when there is no sun, providing hot water at 55ºC, day and night, rain, hail, wind or shine, unlike the traditional solar thermal collectors. The energy consumption of the system is basically the same as a fridge compressor that makes the liquid circulate.
The elimination of space heating and water heating means that we expect to only require between a third and a half of the energy of an average Auckland house. To calculate our energy demand we therefore only need to focus on:
- Lighting and
from the above list. In reality there are a few additional items that we also need to consider such as ventilation and extract fans as well as the electric car charging point, swimming pool and the spa!
We inputted all the energy uses that we could think of into a big spreadsheet to try and determine our total daily and yearly energy demand. It currently looks at though a 5kw BPIV array system will generate 5,933kwh of power for the year, while our demand should be around ,4701kwh.
We inputted all the energy uses that we could think of into a big spreadsheet to try and determine our total daily and yearly energy demand. It currently looks at though a 5kw BPIV array system will generate 5,933kwh of power for the year, while our demand should be around ,4701kwh. Once we finalise these calculations we will post them here for information.
A 30sqm array of BIPV should be able to provide the required 5kW.
how the Living House complies
Energy Storage for Resiliency
The Living Building Challenge requires projects to demonstrate that sufficient backup battery power is installed for emergency lighting (at least 10% of lighting load) and refrigeration use for up to one week.
We feel that this is an resiliency is an incredibly important initiative and is vital to the success of a truly sustainable home. We are hoping to provide resilience to our house through the installation of Aquion saltwater batteries with a 20kWh capacity.