Martin Freney, Veronica Soebarto, and Terry Williamson
Thermal Comfort of Global Model Earthship in Various European Climates. Proceedings of BS2013: 13th Conference of International Building Performance Simulation Association, Chambéry, France, August 26-28, 2013. Link to Complete Report pdf Here
This study from 2013 was completed by three academic researchers from the University of Adelaide in Australia. Their efforts were an expansion of previous studies cited herein, and evaluated the Global Model Earthship in both actual and simulated thermal performance scenarios in Taos, New Mexico; London, England; Paris, France; as well as Albacete, Seville, and Valladolid in Spain.
One of the main impacts of this study was to identify that the inner earth temperature, which MR assumed was 58 degrees everywhere, actually varies dramatically by region, based on factors including local temperatures, water table, soil type, wind, humidity, and rainfall. And that this temperature difference requires a build-out utilizing extensive insulation under the slab and around the foundations and exterior walls in places where the inner earth temperature is lower.
This earthship study was based on a 2 bedroom Global Model earthship oriented at 10 degrees east of south. The area of the building is 1,720 Square Feet (SF), or 160 Square Meters (SM). Of that, 60 SM, or 645 SF, (38% of the floor area) is greenhouse. This earthship has “upgrades” including a west entry vestibule and east double-door garden entrance, and uses rigid insulation vertically in the berm approximately four feet, or 1200mm, from the tires.
As these researchers noted, “schedules for opening and closing of vents in the greenhouse roof were informed by occupant surveys and on the advice given by the architect”, which points to one of the lingering performance and maintenance issues of the earthship’s natural ventilation systems.
Of particular note in this study was the use of an accepted international standard for thermal comfort (ASHRAE 55-2010) which is more stringent than those used in previous studies.
Additional notes included within the report which may be relevant:
“The extreme outlying temperatures that were measured (in the on-site testing) are not predicted by the simulation.”
“… the coldest temperatures were… in the morning (6-8am) followed by a steady rise in temperature until a comfort level was obtained.”
Thermal Performance graphs from the report, with notations of what the charts mean added:
Figure 8 - London: Additional heating is required 8 months a year. The greenhouse is too cold to grow plants and cannot be amended with additional heat without addressing humidity control as well.
Figure 9 – Paris: Additional heating is required 8 months a year. The greenhouse is too cold to grow plants 8 months a year and cannot be amended with additional heat without addressing humidity control as well. AND the greenhouse requires additional cooling 3 months a year.
Note: Both Paris and London performed under the higher comfort levels of previous studies (were much too cold, comparatively) for more than 40% of the year.
Figure 10 – Valladolid: The greenhouse is too hot 9 months a year and additional cooling and/or ventilation is required. Additional cooling is required in the main body of the house September through November.
Figure 11 – Albacete: The greenhouse is too hot throughout the year and additional cooling and/or ventilation is required. Additional cooling is required in the main body of the house October through December.
Figure 12 - Seville: The greenhouse is too hot throughout the year and additional cooling and/or ventilation is required. Additional cooling is required in the main body of the house October through December.
Conclusions:
“The greenhouse... had average maximums and minimums either side of the acceptability limits indicating that it is generally not suitable for habitation.”
“This study indicates that backup systems are necessary and cold and cloudy climates; however the energy use is likely to be (roughly 15kWh/m2.yr), on par with PassivHaus heating energy requirements, due to the earthships ability to store and release heat.”
Notes from the Hacking team:
This research points to several resolutions we must find if the earthship ideals are to be realized. The chapter that addresses the issue in Part 2 of this book is listed after the issue if we address it:
Thermal Comfort of Global Model Earthship in Various European Climates. Proceedings of BS2013: 13th Conference of International Building Performance Simulation Association, Chambéry, France, August 26-28, 2013. Link to Complete Report pdf Here
This study from 2013 was completed by three academic researchers from the University of Adelaide in Australia. Their efforts were an expansion of previous studies cited herein, and evaluated the Global Model Earthship in both actual and simulated thermal performance scenarios in Taos, New Mexico; London, England; Paris, France; as well as Albacete, Seville, and Valladolid in Spain.
One of the main impacts of this study was to identify that the inner earth temperature, which MR assumed was 58 degrees everywhere, actually varies dramatically by region, based on factors including local temperatures, water table, soil type, wind, humidity, and rainfall. And that this temperature difference requires a build-out utilizing extensive insulation under the slab and around the foundations and exterior walls in places where the inner earth temperature is lower.
This earthship study was based on a 2 bedroom Global Model earthship oriented at 10 degrees east of south. The area of the building is 1,720 Square Feet (SF), or 160 Square Meters (SM). Of that, 60 SM, or 645 SF, (38% of the floor area) is greenhouse. This earthship has “upgrades” including a west entry vestibule and east double-door garden entrance, and uses rigid insulation vertically in the berm approximately four feet, or 1200mm, from the tires.
As these researchers noted, “schedules for opening and closing of vents in the greenhouse roof were informed by occupant surveys and on the advice given by the architect”, which points to one of the lingering performance and maintenance issues of the earthship’s natural ventilation systems.
Of particular note in this study was the use of an accepted international standard for thermal comfort (ASHRAE 55-2010) which is more stringent than those used in previous studies.
Additional notes included within the report which may be relevant:
“The extreme outlying temperatures that were measured (in the on-site testing) are not predicted by the simulation.”
“… the coldest temperatures were… in the morning (6-8am) followed by a steady rise in temperature until a comfort level was obtained.”
Thermal Performance graphs from the report, with notations of what the charts mean added:
Figure 8 - London: Additional heating is required 8 months a year. The greenhouse is too cold to grow plants and cannot be amended with additional heat without addressing humidity control as well.
Figure 9 – Paris: Additional heating is required 8 months a year. The greenhouse is too cold to grow plants 8 months a year and cannot be amended with additional heat without addressing humidity control as well. AND the greenhouse requires additional cooling 3 months a year.
Note: Both Paris and London performed under the higher comfort levels of previous studies (were much too cold, comparatively) for more than 40% of the year.
Figure 10 – Valladolid: The greenhouse is too hot 9 months a year and additional cooling and/or ventilation is required. Additional cooling is required in the main body of the house September through November.
Figure 11 – Albacete: The greenhouse is too hot throughout the year and additional cooling and/or ventilation is required. Additional cooling is required in the main body of the house October through December.
Conclusions:
“The greenhouse... had average maximums and minimums either side of the acceptability limits indicating that it is generally not suitable for habitation.”
“This study indicates that backup systems are necessary and cold and cloudy climates; however the energy use is likely to be (roughly 15kWh/m2.yr), on par with PassivHaus heating energy requirements, due to the earthships ability to store and release heat.”
Notes from the Hacking team:
- The earthship studied in Taos was not occupied during winter of the onsite case study in which actual temperatures were recorded in the space. This could be a fundamental flaw, as it does not accurately document functional use patterns which in previous studies have indicated additional, large, spikes of cold and heat due to occupant use. However, the study aspects of other areas and locations should be accurate.
- The research team tightened the requirements for comfort over most studies (using a CV(RMSE) of 10-20% in lieu of the ASHRAE standard of 30%.)
- Ideally, the next step in the research will address thermal bridging effects common to these systems.
- The impact of the earth tubes in the north wall of the greenhouse was not modeled.
- The research team determined their comfort assessments based on DAILY AVERAGE temperatures rather than addressing the range of daily temperatures their own data modeled, thus skewing perceptions of actual comfort. For up to half of each day, thermal comfort was NOT achieved.
- Ideally, the next step in the research will factor in inner-earth temperatures in the areas tested.
This research points to several resolutions we must find if the earthship ideals are to be realized. The chapter that addresses the issue in Part 2 of this book is listed after the issue if we address it:
OVERHEATING
Ventilation – Natural Ventilation Strategies and
Indoor Air Quality
Shading – Passive Solar Design: Overhangs
Losing the pitched (angled) window wall –
Enclosure: Walls: Earthship Sloped Window Greenhouse
UNDERHEATING
Installation of backup heating
Use of slab and foundation insulation
