Design - Sustainability Inventory - Part I: Non-Living Spaces

 

Click on picture to enlarge for better viewing

By now, our 8-year journey to energy independence has been documented with nearly 150 individual blog posts.  For those who may be curious about our project but not enough to wade through myriad posts, perhaps a "30,000 foot view" will suffice even if it takes this post and one more to do justice to the story.

This report posts during the first summer after taking mid-winter occupancy.

UNIQUE FEATURES - OVERVIEW

 Project located in Collinsville, IL on a south-facing slope nestled           in the Mississippi River bluffs opposite St Louis, MO             

         Grid-tied and nearly breaking even with the utility company

        Entirely passive solar; no conventional HVAC

        Sustainability-centric from preliminary sketches to occupancy

        ADA compliant

(The following outline sometimes dwells on these “unique features” but, for most part, they are woven into the larger narrative.

EXTERIOR FEATURES

House

Rectangular-shaped house with its long profile facing “solar” south but canted slightly westward to catch more afternoon winter sunshine

Square and rectangular configurations are the most energy efficient because they minimize exterior wall surface,

They also require fewer building materials and therefore minimize embodied energy for manufacturing and shipping of materials; fewer materials also lowers construction costs

Of note:   the amount of earth sheltering, the conduits for the AGS system and the
PV array  (click on picture to enlarge it)

          

            Earth sheltering on three sides of the house; the grade in back

            of the house is 12' higher than in front, creating the thermal mass described                 below under "Annualized GeoSolar System"

Exterior walls supported by custom trusses built from lumber salvaged from tear-downs; roof/ceiling supported by "store-bought" trusses

House insulation:  15" thick (R-45) in exterior walls, 18" thick (R-54) in cathedral ceilings         

The joints between individual roof and wall sheathing panels and joints between roof and walls are taped to eliminate air infiltration; all sheathing is plywood rather than OSB (both products may utilize resins containing formaldehyde but plywood has less)

All windows (except one small east window) face south which maximizes winter solar gain; having none facing north or west precludes penetration of north and west winds in winter and unwanted morning and afternoon sunshine in summer

Windows all have overhangs sized to minimize solar gain during warm months while allowing maximum gain during cool months; mid-summer shading by the overhangs for both stories is apparent in the picture above, so much so in fact that the exterior wall looks bluish instead of white

Front entrance and garage doors are shielded by the house from winter winds

Screened porch (yet to be finished) is extra tall for better ventilation; Energy Star ceiling fan; 3' wide soffits (eves) for more shade and better rain diversion

Light-colored steel siding, roofing and soffits

Steel has at least a 60-year life expectancy under normal circumstances; more hail resistant than petroleum-based siding and roofing

          100% recyclable end-life

Smooth, white siding is highly reflective, thus minimizing heat gain during warm months; light gray roof only slightly less reflective than the white walls        

Cool roof design:  A 3½” space exists between the first layer of sheathing (that which lies above the insulation) and a second layer of sheathing (to which the metal roofing attaches) that creates a “mini-attic” through which air passively flows from the soffit vents upward to ridge vents, keeping the roof cooler in summer

Rain Handler system replaces conventional gutters except over traffic areas; converts sheet water from the roof back into raindrops that nourish nearby native vegetation without causing soil erosion

Grounds

Four rain gardens slow runoff and keep it on site until it can soak down to the water table and leave in a purified state as opposed to running on grade and carrying noxious contaminants (from air pollution and from herbicides, pesticides or fertilizers) to neighbors’ or public property and, in our case, to the lake across the street

Rain gardens as well as other landscaping are or will be populated by native plants which require no energy-dense artificial fertilizers or soil amendments and, after the first growing season, require no watering

Shelter belt of native eastern red cedars shielding house from winter winds planted years ago as bare-rooted seedlings; cedars also provide excellent habitat for wildlife – four-legged, flying and creepy-crawling

Photovoltaic array sized to break even with the utility company (“reverse metering”); energy cost limited to natural gas for water heating, clothes drying and cooking

Annualized Geo-Solar System (AGS)

AGS utilizes the energy from the summer sun, supplemented by sunshine through the windows in winter to condition the house year-round in the absence of conventional HVAC

AGS comprises three components

Solar collector (fenced-in depressed area in front of the house) to harvest heat from the sun during warm months

Conduits (4” pipes) slanting upward from the collector to a solar chimney behind the house distributing heat from the solar collector to the earth under and behind the house; design still in flux at the time of this writing -- (see second thoughts on solar collection design)

Insulation/watershed umbrella that extends outward from the house below grade +/-20’ in all directions, hence enlarging the amount of dry and insulated thermal mass available for heat storage beyond just that below the floor

Umbrella lays 12" - 30" below grade and consists of several layers of 6 mil plastic sheeting and a layer of foam board insulation overlaid by a physical barrier of recycled carpet

Heat during cool months comes from that stored in the thermal mass during the summer moving passively into the living space (heat seeks cold); additional heat comes from sunshine through the south-facing windows during winter; conventional heating is unnecessary

During warm months, the heat lost from the thermal mass during the winter is replenished by (a) heat from the AGS solar collector and (b) by heat absorbed into the thermal mass from the living space; conventional AC is unnecessary

Target temperatures for the living space toggle between lower-to-mid-70s (winter) to high 70s - lower 80s (summer), although a good guess is that it will take the heat from at least two summer seasons to overcome the ancient cold exposed by excavation into the hillside (at our latitude, the legacy year-round soil temperature at the depth of 10 ft is 60 degrees)

The house floor (concrete) temperature on our early March move-in day was 60 degrees measured at the base of the concrete north wall; it had risen slowly to 79 degrees by the time of this writing in mid-summer

(The comfort level in an earth sheltered dwelling is a function of a phenomenon called Mean Radiant Temperature.  For an understanding of this important concept, click on the first post at the top of the left column under the heading “Understanding Our Project")

UTILITARIAN SPACES

Garage and Airlock

Garage has super-insulated walls and ceiling; the floor is insulated by the underlying insulation/watershed umbrella; the temperature in the garage was 80 degrees at the time of this writing, up from the upper 60s during the winter

Small area of garage wall is intentionally left uninsulated to create a storage area for fruits and vegetables during cold months (a mini-iteration of the old fashion root cellar)

Wall cabinets in the garage are a Facebook Marketplace finds

The main door of the house leads to a circumscribed space called the “airlock”, essentially a semi-conditioned breezeway that modulates outside air rushing in when the front door is opened – warming it in winter and cooling it in summer – before the outside air can follow into the living space through a secondary door

All four doors leading in and out of the airlock are self-closing so as not to be left open unintentionally 

Vertical Basement

The back (north) concrete wall, 60’ long and 12’ tall, by conducting heat in and out of the soil behind it, is critical for conditioning the house

The distance between the concrete wall and the stick-built wall separating the basement from the living quarters is 5' which provides space for storage shelves 2' deep leaving 3' for wheelchair accessibility

The insulation/watershed umbrella at the top of the wall shields the soil under it from surface water penetration while the insulation traps and holds heat

All but the top foot or so of the wall is backed by the soil under the insulation/watershed umbrella that will gradually become drier and, instead of its legacy temperature of 60 degrees, will maintain temperatures in the 70s 

Lack of insulation on either side of the wall under the umbrella allows heat to pass freely through the wall – from the thermal mass inward during cool months and outward into the thermal mass during warm months

The continuous row of vents near the top and bottom of the tall stick-built wall (that divides the vertical basement from the living space) are critical for allowing room air to reach the wall 

During warm months, three box fans equidistantly suspended from the ceiling  and directed downward can be used to transfer heat to the concrete wall by pulling (warm) air through the top vents and pushing it downward past the concrete wall and out through the bottom vents

Combination GFCI / AFCI circuit breakers in the service panel eliminate the need for individual GFCI / AFCI receptacles at the point of use in the living space

Free-standing (not attached to a conventional HVAC unit) Energy Recovery Ventilator supplies fresh, temperature-and-humidity-moderated outside air without which our airtight house would soon fill with stale and unhealthy air

Home run (as opposed to branching) water supply system using PEX (polyethylene) tubing and a central manifold; the PEX lies below the floor and was shielded from damage while pouring the concrete by running it inside of 1 ½” PVC piping; the PVC also makes it possible to use an original PEX line to pull a replacement line in the unlikely case of a water leak; PEX for supply lines is "greener" than copper lines initially and because it has an indefinite life span

Energy Star tankless (“on-demand”) water heater that heats water once as it is used; more energy efficient than tank types that heat the same water over and over, especially during periods of low or no usage

“Water Cop” system to prevent flooding in the living spaces due to plumbing failures 

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The next post covers the living areas of the house.