(Very) Passive (Not) Solar

The only place we’ve seen sunshine for the past … oh … I don’t know … at least a week, maybe two … was on a video call with Annelieke in Portugal. And this is what the 10 day forecast looks like:

This is that time of the year where the sun can be absent for weeks and the temperatures drop … and the theory of passive solar design simply cannot deliver. We simply cannot rely [for warmth during our winter months] on a daily cycle of solar charging and discharging.

That shortcoming hit me during the first winter at Bhudeva … and that is why I got excited when I discovered Passive Annual Heat Storage which is about creating a YEARLY cycle of charging abundant summer warmth and discharging it during winter.

From Earthship to Earthbags

This is a long overdue post and several external movement have prompted me to finally write it.

A while back I wrote how we moved from hemp construction to Earthships. Well the movement continues and we have moved away from Earthships too. This happened gradually and for numerous reasons:

  1. Expansive Clay Soils – we are proud owners of lots of clay-rich soil which expand when wet and contracts when dry. As I was doing research into Earthships specifically and underground houses generally this seemed to be a problem. Expanding clay soil can place tons of pressure on the walls of a house which can cause it to collapse. So for some time I lived with the question is it possible to build an Earthship in expansive clay soils? My conclusion was that the problems was not the clay soil but moisture.
  2. P.A.H.S – As I did more research I started to come across evidence hinting that Earthships do not work well in our climate (moist and cold). Just recently I came across clear evidence of this. I continued my research and was blown away by an old book called Passive Annual Heat Storage. The book introduced a method by which an underground house is insulated with the soil around it, transforming the surrounding soil into a huge heat battery that charges itself during the warm months of the year and discharges during the cold months. The book confirmed my suspicion that the problem with clay soils is indeed moisture and not clay. The “insulation umbrella” concept described in the book (together with other moisture related strategies) provides a solution to keep the clay soils surrounding the house dry – providing a resounding (even if for now theoretical) answer: yes, underground houses can be built in expansive clay soils by keeping moisture away and in doing so neutralizing the “expansive” quality.
  3. Tires in Romania – we could not find a feasible way to get used tires in Romania.

Empowered by the P.A.H.S knowledge I continued my exploration and started looking into earthbags (it’s a terribly designed and uninviting website but has valuable information). I loved the simplicity and ease-of-construction when compared to ramming tires with earth. I would not have considered it a feasible method of underground construction had it not been for the P.A.H.S. method. I do now.

… and so this is the house that we plan to build.

Of Earth Inside the Earth

The house will be completely buried in the ground except for the south-facing aspect. It’s intended location is on gentle south-facing slope. We will excavate for it into the slope.

Most of its walls will be load-bearing earthbag walls. Hopefully our clay-rich soil (that will be excavated to make space for the house) will provide most of the material needed for the earth-mix that will go into the bags. There is no material more local than earth.

The floor will be an earthen floor and the walls will be covered with earthen finishes.

The roof is an as yet unresolved challenge. It too will be covered with earth and will therefore need to carry a very heavy load (current estimation 1.2 tons per square meter). This weight will probably be supported by round timbers though this is not yet final.

Spacious

We are planning a house that will be ~200sqm. It is designed to spaciously accommodate a small family. It will have a main part and a smaller, attached living space for additional privacy.

P.A.H.S. – 21 Degrees Celsius All Year Long

Thanks to the P.A.H.S. insulation umbrella the house will (after 2 or 3 years of acclimatization) eventually settle on a steady all year-long temperature of 21c. During the warm/hot months excess heat will be stored in the huge earthen thermal battery. During the cold months heat will be drawn from the thermal batter.

This means that we will not need any additional energy input to keep the house warm. Even the water supply that runs under the insulation umbrella arrives at the house at 21c which means that less energy is needed to heat water.

The temperature of the house is a function of how much heat gets into the house (which depends on how much windows it has) and how much it can store (depends on numerous design factors). It is nearly impossible to change the temperature of the house after has been established. Any attempt to heat it will be futile because the energy will be drawn into the thermal battery surrounding it and you would need to invest a huge amount of energy to change that.

Imagine not having to cut down a single tree for heating!?

Rocket Stoves

We do expect to have at least one rocket stove for comfort … to boost the temperature to 23 -24 degrees when we want to … and to heat water during the months when solar-heated hot water is not available.

 Ventillation

ventilation is, we’ve come to believe, an important and often missed aspect. The air in the house should be regularly exchanged. Fortunately the P.A.H.S. strategy includes a passive ventilation system (no fans and no electricity to run it) that brings fresh air into the house all year-long at, you guessed it, 21c. The ventilation system also plays a key role in storing excess heat when it is generated (summer) and retrieving it when it is needed (winter).

The trick (and the one challenge that still worries me) is to build the house air-tight. You should not need to open/close windows in this house ever. During the summer months the passive ventilation system will draw hot air out and store the heat in the thermal battery (instead of letting it escape out windows). During the winter months the passive ventilation system will draw air in from the outside, running it through the thermal battery and bring it up to room temperature.

Imagine fresh air during winter at room temperature (and stale air removed) without losing heat to the cold outside!?

Passive Refrigeration

Michael Reynolds in his classic Earthship books points how ridiculous refrigeration can be: we build boxes to keep the cold out, spend energy to get those boxes warm then build smaller boxes inside and spend more energy to keep those boxes cool.

With a slight change in configuration, the same passive ventilation method that is used to regulate the temperature of the house can be used to create a cool space (let cold air in and warm air out). In the Romanian winter that cool is cold enough not just to refrigerate but also to freeze.

Our intention is to build an insulated (from the warmth of the house) space within the house that will harvest winter coolth. That coolth will be stored in water bottles that will freeze. The space will be divided in two. One part will hold a freezer that will be exposed to the natural freezing temperatures. A second part will hold a refrigerator. Both will be unplugged during the winter months. When spring sets on and the ice melts and there isn’t enough coolth they will be plugged back in and run on electricity (which is once again available as the days get longer and the sun shines through).

Photovoltaic Electricity

We would like to be able to live off-the-electric-grid. The first step towards doing that is by drastically reducing consumption:

  1. The house is naturally heated so that no electricity is needed for heating.
  2. Hot water is pre-heated due to the thermal battery, then heated with an efficient rocket stove during winter and with a solar-hot-water panel in spring/summer. Very little electricity needed for pre-heating small quantities of water.
  3. Refrigeration is designed to work on the naturally available coolth of winter when there is very little sunshine to produce electricity.
  4. Large south-facing windows and a one-room-depth house design provides plenty of natural light all year-long.

This leaves us with some lighting and other smaller electronic devices (computers and such). This should enable a photo-voltaic system that will provide all our needs in summer months and most of our needs in winter months.

Attached Greenhouse

The front of the house will be a large greenhouse that will serve multiple functions:

  1. Harvesting heat during winter months.
  2. Extend the growing season.
  3. Growing plants that can not tolerate the harsh winter (lemons? avocados? even bananas?)
  4. Having a pleasant green space to spend time in during the cold winter months.
  5. Consuming grey-water created in the house (this is much easier for us since we use composting toilets and do not have to deal with black-water).
  6. A transition space between the outside and inside (keeping the inside cleaner).

Rainwater Harvesting

For a long time we were faced with a dilemma:

  1. A standard roof that will harvest rainwater for the house but somewhat compromise insulation (all heat inside the house rises) and durability (all mechanical roofs are prone to deterioration and require maintenance).
  2. A living roof that will provide superior insulation and durability but is practically useless for harvesting rainwater (10-15% of a similarly sized regular roof).

After long deliberation we came up with a solution that will provide us the best of both worlds. The house will be built with a living roof (a relatively massive one) that will complete the insulation umbrella.

We will be building a “mirror” structure of the house slightly uphill. This will be a simpler and cheaper structure. It will include a workshop, storage spaces and an open yet sheltered work space for a summer kitchen and other outdoor activities (some of these functions are now unmet or just temporarily resolved). This second structure will have a metal roof for harvesting rainwater that will be stored in an underground cistern that will supply the main house.

Summary

None of these technologies are new. All have been implemented in one way or another. We do not yet know of a house that has been built using all these technologies combined in a climate like ours. It has taken almost 3 years of research by trial and error to reach this formula which has the potential to be an affordable, ecological, sustainable and scalable method of construction.

Scalable is an important quality worth explaining. From what we’ve seen most eco-houses fall into one of two groups. One are small hobbit-hole-like homes which are often the result of do-it-yourself builds with natural materials (these do not scale up very well). The other are large and expensive homes that rely on expensive and complicated technologies to achieve an illusion of sustainability (that often ignores their embodied energy and their technological dependence). We are trying to create something that is in between these two worlds. The P.A.H.S. method can be applied to any size home and it is a core component in the overall efficiency of such a house.

This will hopefully be a very-long-term house.