Ecological Impact of Earthships

Life Cycle Assessment of Earthship Architecture

PhD research by Martin Freney, PhD Candidate, University of Adelaide
School of Architecture, Landscape Architecture and Urban Design

Aim

The aim of my research is to quantify the ecological impacts of Earthships in comparison to other housing types. Of particular interest is the wall construction methods as this is major component of the house and there are many theories (and myths) about which wall construction methods perform best in terms of energy efficiency and embodied energy. Furthermore there, is very little information available regarding the thermal properties of the Earthship’s rammed earth tyre wall.

 

Earthship Greenhouse DesignMethod

The main elements of my thesis are thermal modelling (presented here), data logging the thermal performance of Earthships (temperature and humidity sensors have been placed in six Earthships in Taos) and life cycle assessment (LCA). The LCA is like environmental accounting. It calculates the environmental impacts of a product (or service) throughout the product’s lifecycle, “from cradle to grave”.

Firstly I have done the thermal modelling to work out how much energy it would take to heat/cool a home (theoretically). Secondly I am taking actual measurements of the temperature inside (and outside) Earthships to establish how they perform and to compare these actual measurements with the theoretical results from the computer simulations. Finally the LCA will be used to estimate the embodied energy of the construction and demolition phases of the house’s life cycle and this will be incorporated with the heating and cooling energy (i.e. The “use” phase of the life cycle) to give an overall picture of the environmental impacts of the various wall construction methods. It will use the results from the thermal modelling for the “use” phase of the house and the embodied energy arising from the construction and demolition phases of the house’s life will be calculated via detailed materials inventories which will be fed into LCA software. I have also interviewed Earthship occupants to better understand how their home influences the environmental impacts arising from their lifestyle.

Thermal Modelling

Thermal modelling software was used to simulate various configurations of the Earthship and other wall construction materials, such as straw bale, mud brick, rammed earth, and our old favourites brick veneer, double brick and timber frame. The effect of the berm (dirt piled behind the tyre wall) and the greenhouse was also investigated by running simulations with and without these key Earthship features (refer Figure 1 and 2). The basic layout is that of a Global Model Earthship. The roof (highly insulated) and floor design (100mm concrete slab) remained constant for all simulations thus the results are only influenced by the wall type and the inclusion or exclusion of the berm and greenhouse.

Earthship Design No GreenhouseThermal Modelling Results

Figure 3 (bar chart) shows the theoretical annual energy use to maintain comfort conditions of 18 to 26 deg C in the Adelaide climate for the house design shown to the right (Figure 1 & 2).

These values show the relative energy use between the various wall types etc, and should not be interpreted as the actual energy use for this hypothetical model. However, what can be deduced from this is that the Global Model Earthship (a bermed Earthship – with insulation in the berm – and a greenhouse) has the least need for heating and cooling energy in the Adelaide climate. Similar results are shown for insulated concrete panels and insulated concrete blocks (also with berm and greenhouse) indicating that these thermal mass materials combined with the berm and the greenhouse are the key to the minimal energy use, however it should be noted that concrete is high in embodied energy and will therefore be penalised in the Life Cycle Assessment whereas old tyres filled with dirt are relatively low in embodied energy.

The worst performing “Earthship” is one that has never been designed by Earthship Biotecture although these types of structures do exist. It has no berm, no greenhouse, and no insulation on the outside of the tyres. It performs about the same as Timber Frame and Brick Veneer.

The simulations indicate that the greenhouse reduces the heating/cooling load for all wall construction types as does the berm (which is only applicable to wall construction types that are strong enough to resist the forces of the berm).

In conclusion, for new homes built in climates similar to Adelaide, an earth-bermed home with a greenhouse is likely to dramatically reduce heating and cooling energy (and therefore your energy bill!). Although the Life Cycles Assessment phase of the research is yet to be conducted, facts regarding embodied energy of scrap tyres versus newly manufactured construction materials indicates that Earthship walls are likely to have relatively lower embodied energy.

Note: that this modelling did not include the “earth tubes” that are used for passively cooling a Global Model Earthship – this is likely to further reduce the energy for bermed designs.

Note: The results in Figure 3 are quoted as “load” in kWh per annum. The actual energy needed to satisfy the load is determined by the efficiency of your heater/cooler and thus the actual energy is likely to be less than the values quoted.


Annual Heating and Cooling Load

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