Off-grid heating, ventilation and cooling

Off-grid house should not get any energy input from outside. It should use only energy generated on-site. Because of that, in my opinion a house that’s powered by propane (for genset, cooking and heating) is not off the grid.

But in cool climates most of the energy is required for heating and domestic hot water. How can an autonomous house get large amounts of energy needed for those two uses?

In this article I will get you a short review of off-grid HVAC, or off-grid heating, ventillation and air conditioning.

Off-grid heating

The best energy source for heating is, of course, our sun. It can provide us with heat directly (passively, through large south-facing windows that allow us to get large solar gains), or indirectly, with use of such devices as solar thermal collectors or Trombe walls.

In most cool climates, the amoung of solar energy available during winter is insufficient to produce enough heat. If otherwise, you wouldn’t need to heat your home at all and you wouldn’t call the climate cool, right? Even passive houses that utilize this solar energy heavily need some additional auxiliary heat source. The heat from sun and waste heat produced in house (by household appliances, computers, even people and pets) is not enough.

As I mentioned above, a truly autonomous (off-grid) house would have to produce its own heat independent from energy input from outside. But this would mean that you’re considering an autonomous household, and not an autonomous house. Only in very windy places a wind turbine will produce enough power to heat your home. In most cases you will have to grow your own fuel for home furnace, like coppice willow.

In a nutshell, off-grid heating consists of three parts:

• good thermal insulation, that will save as much heat as possible,
• utilizing solar heat gains, whenever reasonable,
• additional heat source, like electric heating powered by wind turbine or wood stove fueled with wood chips produced on site.

Off-grid ventilation

Oh, that’s simple. Natural ventilation is powered by small difference in densities between cold outside air and warm air inside house. So you don’t need any mechanical device for ventilation of house, you just need ventilation stack to remove used, moist air from kitchen and bathrooms, and some holes in windows to allow fresh air to other rooms.

You can also have forced ventilation, but that requires some energy to power the fans. But this kind of ventilation allows you to recover some heat from the waste air, and works all year round (while natural ventilation works only when it’s cool or cold outside). It is also required for a building to get passive house certificate.

Off-grid air conditioning

Air conditioning or cooling requires a lot of energy. To reduce this use a house should be well insulated and shaded to minimize the heat gains during summer months. You can use the standard compressor-driven air conditioners, and make enough electricity (which might be difficult), or cool your home using some other method:

• evaporative cooling,
• groung coupled heat exchanger (earth tubes / earth-air heat exchanger — for cooling incoming air, that will reduce cooling requirements, but will not be enough to substitute traditional air conditioner),
• absorption chiller.