Ventilation and air quality is one of the last and most problematic issues I’m left with in regard to Earthships in cold climates. Cold climate is what I’ve experienced in a mild Romanian winter which includes snow cover, continuous (many weeks if not months) subzero temperatures and no sunshine (passive solar gain) for two week stretches.
To avoid confusion (as I have encountered it myself in trying to figure out this issue) let me re-iterate: the problem I am trying to outline here is not heat but ventilation – the removal of stale air and it’s replacement with fresh air. There is no question in my mind that no matter how efficient a properly insulated Earthship can be, in our Romanian climate, it will require additional heating. However heat and it’s origin does effect the flow of air throughout the house.
In this post I will try to outline what I’ve been able to figure out so far. The bottom line will be that in cold climates there is a ventilation problem. I hope this post provokes further input and conversation through comments. I would especially love to hear from people who have lived in Earthships in cold climates and their experience of ventilation and air-quality. Then, in a separate follow-up post I will try to present what seems to me like a potential passive, energy efficient ventilation solution.
The classic Earthship ventilation theory is simple and straightforward. Fresh cool air enters from the operable windows on the front face. This air is heated by solar gain, warm air rises and escapes from the skylight resulting in a continuous flow of fresh air through the living space.
The ventilation problem is already present in this simple model. What happens when it’s so cold that operables and skylights (both covered by snow) are kept close to keep heat in (and snow out). To my understanding there is no air flow.
The only way to get fresh air in and stale air out is to let the cold in. Earthship theory would say that is not a problem because the thermal mass of the house contains enough warmth to compensate for coolth that comes in through the openings. In our climate I don’t think will hold true. I think we will have to heat the house in addition to water solar gain (hopefully much less then a house built above ground) and ventilating would entail precious heat loss.
Global Model Earthships
The Global Modal Earthships make two distinct changes to the elements of ventilation (actually there is a 3rd which I will address separately, see earth-tubes below). The first is the introduction of the corridor wall which separates the living spaces from the greenhouse. The second is the skylight over the greenhouse which comes INSTEAD of a skylight in each living space (I wasn’t sure about this until I encountered this video from Earthship Biotecture). In this configuration the greenhouse has been described as an air-lock that supposedly provides better climatic control by isolating and containing variations between it and the living space.
There are now two ventilation circuits in the house. The first is between the outside and the greenhouse and the second between the greenhouse and the living spaces. The ventilation loop between the outside and the greenhouse is obvious and is similar to the classic Earthship approach.
I have some doubts how well the ventilation loop between the greenhouse and living space will work. As I understand it, if passive solar gain is the main source of heat then the greenhouse will always be warmer then the living space. This means that there may not be much flow from within the living space (cooler and heavier air) to the greenhouse (the already warmer and lighter air). It seems to me that the flow in the greenhouse may over-power the flow from within the room. This may be effected/controlled by alternating openings (eg: first ventilating the greenhouse, then closing it and ventilating the living spaces) and height positioning of the ventilation passages between the corridor and living spaces.
As with the classic greenhouse I do not see any potential for passive ventilation on cold cloudy winter days.
When a source of heat is added inside the living space and the hot inside it becomes warmer then the greenhouse – there can be a ventilating flow between the two spaces (and of course heat will be lost from the living space to the greenhouse).
If, in addition to the heat source, the front operables and skylight are opened then there may be some draw of fresh air from the greenhouse to the living space (and of course heat will be lost from the living space to the greenhouse and then quickly to the outside).
So, it seems that any ventilation will come at the expense of precious heat.
Global model Earthships introduce another element they call “Cooling Tubes”. These are tubes that are buried in the ground (~20 feet) behind the house and penetrate the rear wall.
They are intended to provide natural cooling. Warm air in the greenhouse is released through the skylight this creates a draw pulled in through the cooling-tubes. Warm air is drawn into the tubes from the outside, loses heat to the ground in which the tubes are buried and arrives cooler into the house.
This solution addresses ventilation in a hot climate, it does not address ventilation in a cold climate. However, I do believe it points in the right direction. More on that in an upcoming post.