Electricity carried through an immense web of copper eventually makes its way into our homes, providing the endless supply we need for temperature control. It’s expensive, and in some places the air conditioning can easily account for half the electricity bill. Paying this upkeep could even make the difference between life and death in extreme climates. Thankfully, there are other options out there. Using alternative building techniques, houses can be designed that passively heat and cool themselves all year long – without electricity!
The earth and the sun provide all the energy we need, offering many advantages over a traditional HVAC system:
• No purchasing, installing, or repairing an HVAC
• Electricity consumption is eliminated by half
• Indefinite source of heating and cooling
• Ecologically friendly
• No dependency on vast grid systems
• Mitigates noise pollution indoors
Everything in this article is written from the perspective of the northern hemisphere, if you are in the southern hemisphere replace south with north throughout.
Solar gain is our bread and butter, defined as an object’s increase in temperature from solar radiation. This temperature is impacted by the time in which sunlight exposure occurs, the strength of the radiation, and the thermal conductivity of the substance in contact. This applies not only to objects, but empty space itself. Once an object or space is heated, a lot more tools become available: thermal mass for storing, insulation for trapping, convection for circulation, and even methods for averting it elsewhere.
If an object has great thermal mass, it is capable of retaining heat for long periods of time. While it won’t store it forever, the change will be slow. This phenomena correlates directly with the material’s density, conductivity, size, and any temperature differences within multiple areas of the whole object.
In the design of a passive heating system, there are two thermal masses that are most important:
1.) The earth and
2.) the house itself.
The temperature of the earth below the frost line remains consistent throughout the year, ranging between 50˚ – 60˚ Fahrenheit. During summer, there is a potential cooling effect, while in the winter, a heating effect. By burying or berming the structure into the earth you can capture a baseline temperature that is less severe than that of the atmosphere.
By using materials with a high thermal mass, in conjunction with direct sunlight, you can “charge” the structure. Solar gain will be captured then slowly released back into adjacent spaces. Thermal energy can be stored in the floors, walls, or anywhere else with enough sunlight exposure.
Insulation – a tactic traditional homes employ to great extent. It is the pockets of air trapped amongst a thermal resistant material that make it most effective. With as much trapped gas and as little density as possible, the process of natural convection is impeded, slowing heat transfer. In many ways, insulation is the opposite of thermal mass. While materials like stone have a high density that retain heat, they do not necessarily provide insulation. Conduction is occurring between the stone and it’s adjacent materials, exchanging temperature until they’re equal. Materials that are effective at insulation will slow or stop this process from occurring.
Using thermal mass and insulation together create new opportunities for passive heat control – particularly if you insulate sections of thermal mass within thick walls and earth berms. This approach traps large temperature stores while still radiating heat back into the home at night. (Or even throughout the course of months, as described under annualized geo solar heating) An example of an effective thermal mass and insulation joint effort can be seen in the “thermal wrap” technique:
A house with optimized positioning will take into account the sun’s seasonal arch. The execution will be different depending on your climate and whether or not heating is a higher priority than cooling. Angle your home’s windows towards true south to harness as much solar gain as possible in the interior. The north side, on the other hand, should have as few windows and gaps as possible to prevent air from escaping.
For more heat, consider building a glasshouse room (or greenhouse) that connects with the rest of your house with south-facing windows. The solar gain in this space will be far greater than the rest of the house. To heat other rooms attached to the greenhouse, open up connecting transoms or vents until the temperature is satisfactory.
In our region, the summer sun arcs above the earth at about a 70˚ angle. During winter, this angle reduces drastically to nearly 30˚. When designing a passive heating system, windows can be slanted to capture as much winter sunlight as possible. Overhangs can also be designed to prevent sunlight penetration during the summer months without impeding the winter rays.
As temperature in air increases, its molecules begin moving around more quickly. This increased kinetic energy causes the atom to take up more space, decreasing its density. This can be observed when hot air rises and cold air sinks. And if hot air exits a space it creates pressure or suction to pull in replacement air. By managing inlets and outlets, you can create controlled convection currents. Convection cannot only be used to control air flow but can also be applied to liquids.
Simple ventilation methods can help circulate cold air in using operable windows and skylights with opposite elevations.
When combining convection with thermal mass, new opportunities for passive cooling emerge. Run long stretches of tubing outside, buried underground, with the other end connecting to the home’s interior. Applying convection, the cooling tube air will be sucked in as the hot air leaves. Conduction between the earth and air inside the tubes cools its temperature significantly. It is also possible to power a small fan to force the cool air inside without requiring convection.
Solar radiation can be deflected using certain materials. You can see this to great effect in a Concentrated Solar Power (CSP) plant. Sunlight is focused using a large array of mirrors into a single chamber, designed to heat a transfer fluid. The liquid eventually turns to steam to spin turbines through a closed-loop system.
A useful trick for supplemental winter heating is to position a pond just south of the house, lower in elevation if possible. This allows additional sunlight penetration and increased solar gain into the space.
To mitigate the pond reflections during the summer months, you can grow deciduous trees in between the house and the pond. The full summer leaves will block the reflection, while the bare winter trees will hardly obstruct the rays. Keep in mind the summer rays will approach near a 70 degree angle, while the winter light will be closer to 30 degrees.
Wind is a powerful force for transporting heat around a site. It can be reduced using wind blocks or increased using wind funnels. Most locations will experience two main directions of wind, which behave predictably and often seasonly. The main force can be discovered by simply observing the trees, which will slant in tandem towards a single direction. For more accurate readings, record a wind vane’s orientation over a period of time.
If a structure is aligned with the prevailing winds during summer, a draft can be employed by opening an inlet and outlet on opposite ends of the building. The funnel wicks away warm air radiating from your body and nearby thermal masses, replacing it with cool air. It also increases the rate of evaporation as water vapor is carried away, leaving behind the relatively cooler moisture.
Wind catchers can be controlled to face certain directions, empowering us with greater flexibility in the orientation of our structure. The strategy then is to make sure the wind can be captured and redistributed through ventilation.
Radiant Floor Heating & Cooling
Radiant floor heating is the process of pumping hot fluid underneath the floor of your home in a closed loop system. The heat radiates from the hot water tubes back up into the floor through a heat exchange process. This heats up the floor for immediate comfort, and when combined with a thermal mass material, will continue radiating heat for some time even after the circulation has stopped.
The fluid can be heated up using a variety of methods. An outside solar collector panel is a great way to capture solar gain and return it to the system. However, to function at night a more conventional hot water heating source may be needed. These systems require a little bit of electricity as a pump is used to circulate the liquid.
If lowering the temperature is a greater priority, a similar system can be installed that circulates cool liquid. The radiant cooling surface is used to absorb excess heat in the absence of moisture. The latent load, heat being held in the moisture of the air, will otherwise create condensation and could be harmful if your structure is not prepared for it. Therefore, this approach is most effective in either dry areas or in structures equipped to handle the warm moisture, like a greenhouse.
A technique known as geothermal heating (or “seasonal thermal energy storage”) has recently been growing in popularity. It involves circulating air or liquid through the earth deep underground, taking advantage of the seasonal thermal mass temperature of the crust. The earth essentially acts as a heat exchanger. In winter, cold air pumped down will make it’s way back inside as warm air. In summer, hot air will return cold. These systems typically require expensive mechanical components as well as electricity to operate.
If your home is energy efficient and optimized for thermal mass, an alternative to consider would be annualized geo solar heating.
Annualized Geo Solar Heating
There are two important differences between geothermal heating and annualized geo solar heating:
1.) A block of insulated earth is established beneath the structure. 4 or 5 feet below the foundation, insulation board is buried inside the parameter of the home to create a giant thermal mass, capable of storing temperatures for months at a time.
2.) Instead of running air down and back up through the system, air is pumped directly into the earth. Over the course of summer, you send the hot air into the insulated box and steadily charge the thermal mass with heat. When winter rolls around, the underground box will retain its temperature for several months, slowly radiating the warmth back upwards into the home without any manual or mechanical input required.
The operational costs include electricity for powering the fan used to send air into the ground. The fan does not need to run all the time, anywhere from a few times a day to once per hour. A greenhouse is ideal since the summer air will likely be hotter than the outside air, adding extra heat into the box while helping to cool the greenhouse interior temperature.
Sarooj – Heat Resistant Cob
The ancient Persian Empire would store ice in the middle of the desert in adobe structures known as Yakhchals. One of the techniques employed was a super heat-resistant cob called Sarooj. It is made like normal cob, with the addition of ash, egg whites, and animal fiber. Because of the lack of information available, a tried-and-true recipe has yet to be released and more scientific studies are needed.
In theory, the application of Sarooj may be a helpful boon for hotter climates. In conjunction with traditional cob, based on the sun’s seasonal orientation, it may be worth applying on parts of the home that are exposed during summer months. Traditional adobe could be used in areas that are exposed during winter months to capture solar gain normally.
If you have a recipe or experience with Sarooj, we would love to hear about it!
Another great use of a greenhouse attachment is to put a compost pile indoors. With internal temperatures reaching around 160˚F, they will radiate some of that heat into the room. Also you can run a radiant floor heating system through the compost pile to heat the liquid for free! It does, however, require replacement once the heating process has run its course.
There have been reports of ammonia coming from indoor compost piles that damage plants and seedlings within close proximity. Low amounts of nitrogen with high amounts of carbon help mitigate this risk. After starting the compost pile, wait a couple days then spread an inch or two of soil on top. This also helps absorb excess ammonia while distributing the heat more evenly.
A new approach for cooling air without electricity has sprung up from Bangladesh and now Pakistan, where nearly 70% of residents live without power. The method involves creating a panel of funnels (using recycled plastic bottles, though other materials may substitute) that compresses an incoming breeze before sending it indoors. It is this initial compression of warm air, then its sudden release, that creates the cooling effect. The entrance into these funnels should be located outside the structure as that is where the warm air can escape. Reports from this approach indicate a drop in temperature up to 5˚ Celsius, though the technology is still in its infancy.
Biofuel Gas Heater
Biofuel septic systems and compost digesters are spreading throughout India and other parts of the world. It is an anaerobic process that breaks down organic waste while producing a methane gas. This gas is then harvested and deodorized, at which point it can be sent through your home’s gas lines for all sorts of purposes. If supplemental heating is required, this fuel can be used to power a small gas heater within your home.
Rocket Stove Mass Heater
The rocket stove mass heater functions similarly to a traditional fireplace. However, instead of burning mass quantities of lumber to heat the air, rocket stove heaters are designed to burn small twigs and brush quickly at very high temperatures. Instead of heating the air, ducts are woven amongst a thermal mass component (such as the base of a cob couch or cob bed platform) where the heat is captured and stored for extended periods of time. There are testimonials from many people who claim that one round of twig burning will provide heat for over 24 hours! When engineered correctly, the exhaust will also produce pure steam without any smoke. It is a simple, inexpensive construct that can be built out of repurposed materials and soil/clay right from your landscape.
What’s Worked For You?
Have you had success (or horror stories) using other methods? We would love to hear about your experience, please share in the comments below and stay comfortable out there!