In keeping with this weeks discussion of “the house as a system,” I thought I would share a few decisions we have made regarding heating and cooling.
In my opinion (and many others’), the ultimate way to heat and cool a house is through passive solar design. For heating, the idea is to use the radiant energy of the sun to warm your house in the daytime and somehow store that heat for night time and cloudy days. With careful and thoughtful design, its possible to supply as much as 80-90% of your heating needs through passive solar heat gain in the southeast. For cooling, it’s a little trickier with the high humidity of the day and not-so-cool temperatures of the night, but the idea is to use the same mass used to hold heat in the winter to take on the heat of the day in the summer and radiate it back out at night. Passive cooling relies on the assumption you can open up the house to outside air flow at night and the assumption that its noticeably cooler outside at night- both assumptions do not bear up on a hot summer night in Georgia. Passive heating and cooling methods rely on a combination of proper site exposure, good insulation, and most importantly, a significant amount of mass to absorb the excess heat and help even out the temperature fluctuations likely to occur. Typically, designers use water columns, masonry walls, concrete slabs and other very heavy forms of mass to accomplish this…However, these are components that are not well suited to the limited space and load limits of a tiny house.
So…full-blown passive solar heating is not an option, except for the part about placing windows to take advantage of sun exposure in the winter and rotating the house in the summer to reduce winter exposure…one plus for a portable house!
Some might argue the next best option is to generate heat on site with propane or wood. For some this might be a good option. Modern wood stoves, when you can find them, have more advanced designs than pioneer days with efficiency ratings of 85%+. Some even have catalytic plates that burn more of the gases that used to escape up the flu. Space and safety concerns make wood heating in a tiny house tough, at best. A small propane stove is another option. Some propane heaters with catalytic burners approach 90-95% efficiency. For either wood or propane burners, there should be an outside source of fresh air to insure there is enough oxygen left to breathe.
Electric heat is an option, provided your tiny house is not completely off the grid. The options include an electric space heater (see comments above about spacing a portable heater); baseboard electric heaters (do people still use these???); a window AC (some models come with a heating option); a through-the-wall heater/AC like they have in hotels; and a heat pump. Heat pumps are considered the most efficient in the southeast, but even a heat pump can’t be operated with a few solar panels. If you are plugging into the grid, then a small ductless heat pump (mini-split) is a viable option and that is what we have chosen for our tiny dawg house. The mini-split eliminates heat ducts, which are often a source of heat loss and aggravation for indoor air quality folks. Of course, it is easy to eliminate ducts when you can spit from one end of your tiny house to the other.
A mini-split is typically just air conditioning or both AC and heat, but not just heat. Mini-splits shine in a tiny house (in the southeast) because you can get both AC and heat, plus a dehumidifier, plus, the air gets moved through the tiny house by a built-in fan. If you are reading this from up north somewhere, take our word for it, you do not want to be sleeping in a lofted tiny house in August without AC .
Since the electric service to our tiny house will be minimal, we had to locate a mini-split with a 115 volt (V) hookup (standard outlet), which is harder than you may think. Most mini-splits are 240 V. Efficiency is another consideration. The AC portion of the mini-split is rated using the Seasonal Energy Efficiency Ratio (SEER) system (https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratio). A rating of 14 is the minimum rating. Our unit is a GREE Neo 9,000 BTU unit with a SEER rating of 22…not bad for a 115V small unit!
It (the air blower and controls) will take up some room on a wall above the living room awning window and there will be a unit hanging off the back of the house, but we will have both heating and cooling in one unit and it runs much quieter than a window AC unit or through the wall unit (like they have in hotels). Both of these later two alternatives are far noisier and much less efficient than a mini-split.
So, once again, we settled on a choice that made sense in terms of cost (to operate), energy efficiency, and most important in a tiny house, space considerations. Note: we still placed a large window in the living room room for lighting and solar heat gain (assuming we point it south) and in the summer we plan to either rotate the house or use a good window shade.