I'm far from an expert, so take this with a huge grain of salt... in around two to five years, I expect to FIRE, and move back to my hometown. I'd
really like to build a new house, in particular, a very environmentally- and energy-efficient home. MMM's recent post on hydronic radiant heating got me interested in reading about "green" building strategies.
I've been reading a lot of posts on
Green Building Talk, and following all the links that come up in the discussions.
The consensus on "geothermal" units (correct term: ground-source heat pump (GSHP)) is that
in general, you get more for your money investing the GSHP premium in better sealing and insulation. Exceptions are, of course, if you can do the GSHP for cheap (i.e. little or no premium over traditional HVAC), or have a huge house where the marginal increase in efficiency offered by a GSHP will actually provide a measurable return.
Other general pointers I've picked up:
- Location matters first, as your sealing, insulation, and HVAC requirement will vary dramatically depending on where you're building.
- Do your own research, but the consensus on the forum I linked above suggests that the latest and greatest traditional (i.e. air-source) heat pumps work well in zero and sub-zero temperatures, and are only marginally less efficient than GSHP.
- If you can orient your build such that you can put big windows on the Equator-facing side of your house (i.e. south face in the northern hemisphere), you can get "free" heating via solar gain from the sun (this is exactly what MMM is doing).
- Sealing is at least as important as insulating your house. You can have a million dollars worth of insulating technology in your house, but if it leaks, the insulation won't matter. Insist on a "blower door test" to ensure proper sealing. The caveat with a tightly sealed house is that you'll likely need some kind of active ventilation system (look into ERV and HRV).
- My take is that you don't have to use fancy, expensive insulation technology to get "pretty good" (i.e. above-code) thermal performance. At least for my area (central/northern Illinois, "Zone 5A"), I've seen many recommendations for standard stick construction, using 2x6 studs on 16" centers, packed with cellulose (cheap and "green"), and the exterior wrapped in a few inches of rigid foam board. That ought to buy you "whole wall" R30; additionally, go nuts with attic cellulose to take it up to R60, get good windows and doors, minimize the number and size of non-south facing windows, and seal it all up. Based on what I've read, a modest size house built this way can probably get by with just one or two mini-split ductless air-source heat pumps.
- Even in very cold climates, it's possible to build a "passive" house (from a heating perspective anyway), but the cost may not justify it (unless being e.g. off-grid is a top-priority for you). But my impression is that the kinds of homes that rely primarily on solar gain and the resulting radiant heat need to be "driven" or actively managed. Conventional forced-air HVAC units allow you to push a button, wait a few minutes, and the house is the temperature you want. But solar gain and radiant systems work very slowly, so you have to kind of plan climate control in advance.
- Surprisingly, old-school wood-burning fireplaces (with a lot of surrounding high-thermal mass masonry) seem to be somewhat popular among the green building crowd. They are low-tech (effectively impossible to break, never "wear out"), arguably green, and a single one can easily heat up an entire (modestly-sized) house that is adequately sealed and insulated. They can also be very cheap (or even free) to operate depending on your access to firewood.
Again, this is all based basically on Internet hearsay, so do your own research, YMMV, standard disclaimers apply, etc etc. But, personally, I find the information fascinating, and really look forward to being able to build a highly-efficient FIRE home.
Anyone else interested in this topic? Can you recommend any good books?
