Wednesday, August 28, 2019

Construction - Electric Rough-in

Some of the roof has been protected by a layer 
of 6 mil plastic, some with plastic only; the photo
 predates installation of the windows.
Ideally, our structure should have been buttoned up before roughing in the electric and plumbing.  However, a combination of wet/cold weather and the slower progress when working alone delayed the steel roof installation to the extent that we had to do the electric and plumbing rough-ins under temporary roof protection. 

I had done enough electrical work previously that I was comfortable with wiring a house from scratch once the installation of the service panel and meter box were done by professionals and inspected by the city.  However, it took Rex Cauldwell's quintessential book to make me realize that there was much to learn.  Oh sure, I could make things work but, after reading Cauldwell, clearly not always up to professional standards.  This time around, mere code compliance gave way to Cauldwell's "above code" methods whenever possible.

Circuit Design
The first task was to diagram the circuits so that they were balanced as to the amount of amperage they would carry and, as much as possible, limited to as small of an area as possible.  For example, dedicated circuits for
Click on the drawings to enlarge them for better viewing.
the kitchen, laundry and bathrooms are best.  Circuits for smoke alarms and isolated ground circuits for electronic equipment such as TV's and computers are dedicated circuits as well.  Circuits that are not dedicated were balanced so that it would be unlikely for any to be overloaded in the future.  Once I was happy with the diagrams (plural because the first and second floor were diagrammed separately), the circuits were numbered and color-coded then glued over

architectural floor plans over a white background such that the architectural drawings showed through the diagrams.  The resulting composites were then posted opposite the breaker box for consultation while wiring.  I plan eventually to cover the diagrams with Plexiglas as a permanent record of the electrical lay-out.  Then, a circuit can be identified on the door of the breaker box simply by the number that corresponds to its number on one of the diagrams.

Electrical Boxes
We are building a two story house with the first story being in compliance with the American Disability Act (ADA) (if a lift were to be added to the stairway, the second story would be in compliance as well). Therefore, I raised the height of the electrical boxes for wall receptacles to 18" above the floor instead of the more customary height of the length of a hammer handle.  The boxes for switches and some receptacles were intentionally situated so
The jig is screwed to the stud (arrow) and the box is
held in place against the jig while the nails are set
that the upper edge of the first course of 48" wide drywall would bisect them, making it easier to make accurate cuts in the drywall to accommodate the boxes.  This would be especially important for the exterior walls where air sealing the boxes is critical.

This venture was my first time to use plastic boxes almost exclusively.  In order to position them to be flush with the finished wall and to prevent distortion of the boxes by over-driving the anchoring nails, I made a jig to hold them in place while driving the nails.  Per Cauldwell, I used boxes with the largest volume the wall would accommodate.  For instance, the truss-supported exterior walls and the 2 x 6 wet walls (bathrooms and kitchen) accommodated single gang boxes with a volume of 22 cu in.  Slightly smaller boxes with 18 cu in were necessary for 2 x 4 walls.

Wiring the Boxes
A Cauldwell "above code" practice was to run the power uninterrupted through the boxes and using pigtails to power a given receptacle.  The alternative is the direct connect approach whereby the power enters one side of the receptacle and exits the other side on the way to the other receptacles in the string.  Using the direct approach, according to Cauldwell, can lead to overheating of the upstream receptacles should the downstream receptacles become heavily loaded, say with a bunch of high amperage appliances.  Also, if any upstream receptacles become disabled or are disconnected, those downstream also become disabled, making troubleshooting much more difficult.

Another practice that I had not always followed in the past had to do with switched circuits.  The "above code" method is to run the power to the switch box first rather than to the load first from which then to run a round-trip leg to the switch.  In the switch box, there are two options.  If there is only one load on the circuit, the power is simply run through the switch to the load.  However, if the power needs to feed other receptacles or other loads, a pigtail is used to run power through the switch for the dedicated load while the rest of the power continues downstream.  The nearby photo demonstrates this arrangement.  The yellow 12 ga conduit brings power to the box from the top and continues out the bottom to receptacles downstream.  In the box, pigtails will run power through three switches to three loads on the white 14 ga conduits exiting the box from the top.

Still another new practice for me was to use push-in wire connectors instead of wire nuts. Not only were they much faster to use but they required much less space in boxes crowded by multiple wires.  Click on the picture of the switch box to appreciate how much they can de-clutter a box.  And it is not
always easy to be sure that all the wires inside a wire nut are in proper contact, even after twisting them, while push-in connectors have see-through sides for visualizing the stripped ends of the wires to be sure they are fully seated.  Finally, the local building inspector requested that I use type of staples pictured at the right instead of the more ubiquitous wire staples in order to lessen the chance of damage to conduits by over-driving the wire staples.

Cauldwell also schooled me on taking care to
make sweeping turns with Romex cable as seen in the nearby photo.  If the cable is bent sharply around a right-angle corner, dangerous overheating can result. 

Ground-Fault Circuit Interrupters and Arc-Fault Circuit Interrupters
I adopted another "above code" feature by using Ground-Fault Circuit Interrupter (GFCI) and Arc-Fault Circuit Interrupter (AFCI) circuit breakers rather than individual GFCI or AFCI receptacles at the point of use.  The upgrade has these advantages:  (a) longer life span for breakers, (b) receptacles have to remain accessible (can't be hidden behind furniture, appliances, drapes, etc.), (c) both types of receptacles are bulkier than conventional receptacles and require a box that is deeper than is always available, (d) AFCI receptacles "come with a long list of inconvenient installation rules" (Cauldwell), and (e) since all GFCIs and AFCIs need to be tested regularly, it is more convenient to check them all at once at the service panel than sorting out their many locations downstream. 

Code now requires GFCI and AFCI protection in so many areas of the house, garage, porches and patios that the cost of our using circuit breakers was probably not much more than the cost of distributed GFCI and AFCI receptacles.  Since our house is partially earth sheltered, we are living in contact with a lot of soil, much like living in a basement where GFCIs are advisable if not mandated by code.  Even though the soil in contact with the house would ordinarily be moist/wet and therefore a ready ground for any short circuits, the soil under our house is drained dry by a series of French drains and the insulation/watershed umbrella keeps the soil behind the house dry, making it safer.  However, I decided to error on the side of caution by protecting all circuits with either a GFCI or AFCI circuit breaker.

Standard AFCI breakers are no longer acceptable; only "combination" AFCIs should be used -- primarily for living spaces such as bedrooms, hallways, TV rooms, living rooms and dining rooms.  However, as Cauldwell points out, combos are not to be confused with true AFCI/GFCI units.  The latter are so expensive that he recommends staying with AFCI combos for branch circuits requiring fire protection and GFCIs for circuits requiring life protection.  And one last thing that I probably would not have thought of without Cauldwell is that our hard wired smoke alarms daisy-chained on an AFCI circuit could be a deadly combination if the backup batteries in the alarms are not checked regularly and kept fresh.  Then, if a fire were to damage the circuit, the AFCI would kill the power but the alarms would still function on battery power.

Unique Grounding Issues
The electrician used the typical single grounding rod driven into the soil just below the electric meter.  However, it did not occur to either of us that the soil, as just explained, would be bone dry and therefore useless for grounding the electrical system.  I intend to invite him back to install not just one ground rod in the wet soil outside the perimeter of the insulation/watershed umbrella but an "above code" series of rods 6' apart wired together and to the service entrance with #4 copper wire.  

Before an online search, I assumed that the steel roofing and siding would be susceptible to lightning strikes and would need to be grounded either directly or through the service panel.  As counter-intuitive as it may seem, though, a metal roof is actually safer than a conventional roof in that the surge would be dissipated over a large area and the metal is non-combustible.  All bets are off however if there are metal vent pipes through the roof that could funnel a surge into the building.  Our PVC vent stacks for the plumbing are non-conducting and therefore a non-issue and the CPVC vent for the tankless water is vented through the wall.

Surge Protectors
My research reveals that there are two main locations where surge protection is mandatory to protect electrical and electronic equipment throughout the house.  One is at the main service panel primarily to arrest large pulses entering through the power line such as lightning strikes and surges caused by the utilities working on transmission lines.  For this purpose, Cauldwell recommends what looks like a pair of common single-pole breakers with a green and red indicator lights (circled in the nearby photo).  The second location is at the point of use for filtering out smaller pulses that fall below the range of the breaker surge protectors.  Here it takes only a good quality surge protector receptacle strip with plug-in cord.  He also warns about using snap switches for electronic equipment that are not protected by surge protector strips.

Sunday, July 28, 2019

Design - Mean Radiant Temperature and Our Project - Part II - The Details

In a recent post I made the case for using mean radiant temperature (MRT) the vehicle for understanding earth sheltered passive solar then followed that by a post outlining in bare bones fashion our green building project through the lens of MRT.  This post adds flesh to the bones, describing in detail how our passive solar home will control mean radiant temperature to eliminate conventional heating and air conditioning.  

But First..........
It seems appropriate from time to time to remind readers that I am not an expert in any of the fields involved with our project.  Most of our design is based upon myriad sources that I have been sleuthing for many years now so I am standing on the shoulders of many experts and original thinkers, largely without giving them credit.  But at the same time a lot of originality has gone into our project to make it more compatible with our climate, our building site, local building codes, using salvaged materials, working alone, spartan budgeting and, especially, designing and redesigning on the fly.  By blogging, I would like to feel that I am paying forward for the insights borrowed from the experts and original thinkers while, at the same time, adding original content to the sustainability conversation.

This posting is longer than usual but, for better understanding, I feel the complete story should be told without interruption.  And, a reminder, click on the photos to enlarge them for better viewing.

The Challenge
The control of mean radiant temperature (MRT) for passive solar is a matter of having sufficient solar gain, then having the storage capacity to capitalize on the gain and finally having a building envelope that preserves the gainThe goal is to create an environment that radiates heat at the same rate as its occupants so that they are always comfortable.  

Solar Gain
An early sketch of our AGS system.  The red line
represents a conduit (one of nine) angling upward from
the solar collector, located in front of the house,
to daylight behind the house.  It is 5' below the floor level
at the front foundation and 3' below at the back foundation.
Since it is inclined, heat from the collector rises naturally
through it, warming the soil below the concrete floor and
behind the concrete north wall (orange).  The 

insulation/watershed umbrella is not  shown but would 
lie just below the wavy black lines that represent the
grade in front and back of the house.
The unique thing about a Annualized GeoSolar (AGS)* design like ours is that solar gain occurs year-round.  In winter, as with classic passive solar, there is direct gain through the south-facing windows.  But then, in summer, a solar collector, located some distance from the house, continues the energy harvest (isolated gain) in a way that is actually more important for AGS than the winter harvest.

The available sunshine during the three months of summer here in Collinsville, Illinois (near St Louis) is reduced by 31% due to cloud cover.  Since days are long during June, July and August and the sun is more intense, the 69% of available sunshine nevertheless represents a lot more energy than can be harvested during the short days of winter.  But shorter days are not the only problem -- the cloud cover during December, January and February is even worse than in summer, blocking 53% of the available sunshine.  Fortunately the relative amount of sunshine between winter and summer is almost moot in our case because the surface area of glass in the solar collector will be a sixth of that of the 19 south-facing windows collecting winter sunshine.  The collector will harvest energy more efficiently per surface area of glass than will the windows, but for the first couple of years, more useful warmth will come from the winter sun.  Like the the hare-tortoise race, the solar collector, while slower, will eventually win because the two systems will heat the thermal mass from different directions.  The heat from winter sun will warm the superficial layers of the thermal mass but not enough to eliminate the need for supplemental heat. The collector will gradually, over a year or two, warm the deeper layers from below where the heat will be trapped permanently and more able to stabilize the MRT year-round.  In fact, Don Stephens, who, along with John Hiat, introduced the concept of AGS, speculated that designs like ours will eventually overheat and that part of the solar collector might have to be mothballed to control it.  Until the temperature of the thermal mass stabilizes at a desirable temperature, we will resort to portable infrared heaters that can be retired, as opposed to permanently-installed infrared heaters.

Direct solar gain during summer is an issue that is less well resolved.  One sees pictures of passive solar homes, earth sheltered and not, that have south facing glass unprotected by overhangs.  Some even have glass that is tilted back at the top to be more perpendicular with the sun's rays in winter.  I suspect that the latter could cause overheating of even a thermal mass floor if it were a dark color.  If the glass were perpendicular but unshaded, the amount of overheating might not be a huge problem if it were backed up by thermal mass of an appropriate color.  This guess is based upon the fact that the high summer sun angle is so obtuse in our area that much more energy is reflected off of the glass than penetrates it.  In view of all of this, we have elected to go with overhangs for all of our windows in order to eliminate entirely sun penetration from the latter part of May to the early part of September. The overhangs, in concert with windows that are inset 10" from the surface of the exterior wall, will however be somewhat counterproductive when they restrict solar penetration that would be welcome in late spring when the MRT has fallen to the lower 70s and allow some unwanted penetration in early fall when the MRT has risen to the upper 70s.  (The unique design for the windows was covered in a recent post.)

Often lost in a discussion of passive solar is the extent to which heat generated by living in a house helps to heat the house.  Cooking, water heating, showering, drying clothes, lighting and human bodies all warm the air and raise the MRT.  But these factors also have a downside -- they compromise indoor air quality in an airtight structure that must be ameliorated by either an energy recovery ventilator or a heat recovery ventilator.

Storage Capacity
Picture taken during troweling of the concrete floor;
 notice the extent of the floor and concrete north wall that
 will become part of the thermal mass; notice also the
insulated concrete forms creating a "frost-protected 
shallow foundation"
Storage capacity is directly related to thermal mass.  But other factors are important too, such as the type of window glass, interior colors and natural or assisted air movement in the living space.

The primary thermal mass for our dwelling is (a) the soil beneath the concrete floor and (b) the soil under the insulation/watershed umbrella on all sides of the house, especially that behind the concrete north wall.  Unlike classic earth shelters in which the concrete in the floor and walls is the thermal mass, the concrete in our house, while being that too, transports heat to and from the soil as its primary job. The amount of soil serving as thermal mass could be calculated I suppose.  For example, the earth serving as dry and insulated mass under the umbrella behind
The insulation/watershed umbrella under construction
in the space between the solar collector on the left and
the house on the right; it ranges from R-20 nearest the
house to R-10 at its periphery; the umbrella rests on the
shallow foundation footings, rendering them frost-free,
and butting against the insulated concrete forms for a
continuous vertical to horizontal thermal barrier
the north wall could be determined by multiplying the height of the uninsulated part of the wall (10') by the length of the wall (60') then by the width of the insulation/watershed umbrella (20') extending horizontally outward from the wall, etc.  But the exact figure is unimportant; what is important is that we are talking about a lot of thermal mass behind the wall alone to say nothing about that residing under the umbrella east, west and south of the house and under the floor of the house itself. It is safe to say that we will have plenty of storage capacity for any amount of solar gain even considering that some heat will bleed through the umbrella because it is only R-20 at its thickest.  However, since it takes 6 months for a unit of heat to travel 20 ft through dry soil and the umbrella is 20 ft wide, most of the heat loss from under and behind the house will be through the concrete floor and north wall to warm the house in winter which is a good thing.

The thermal mass will cool the house during warm months just as it will warm the house during cool months.  Since the stick-built walls and ceiling are so well insulated, most of the unwanted heat entering the dwelling in summer will be conducted through the windows despite the fact they are fully shaded as described in a recent post.  Even though the windows are top-rated at R-4, they are like holes
The red arrows point to the tall wall between the living
quarters and the "vertical basement";  the magenta
arrows point to the concrete north wall; the space
circled by green is the airlock (see text)
in our R-70+ walls when it comes to keeping heat out in summer or confining heat in winter.  But natural convection within the dwelling will largely handle the problem. As the inside air is cooled at the windows in winter, it will fall to and be warmed by the concrete floor, which, if all goes as planned, will be in the mid-70's irrespective of the time of year, thanks to a stable temperature of the soil beneath it.  As the moderated air will also find its way to the north wall, be warmed by the constant year-round temperature there, rise to the ceiling and back to windows.  Probably there will be no need for assistance from fans but, if so, nothing more than ceiling fans on the second floor blowing gently upwards to encourage the warm air to find the windows. 

Summer will be a bit more challenging.  The heat gain through the second floor windows will tend to collect under the second story ceiling and will have to be
John Hiat's indispensable book
pushed downwards along the slanted cathedral ceiling towards the concrete north wall, the top of which is about 6 feet below the tallest part of the second floor ceiling.  Ceiling fans blowing upwards might be enough to push the air along but wall fans between the pairs of second story clerestory windows blowing towards the north wall may be needed instead of, or in conjunction with, the ceiling fans.  Or maybe it turns out that the ceiling fans, blowing downwards, are forceful enough for the warm air to find the north wall and the concrete floor below. Not all of the heat from the first story windows will rise to the second floor ceiling.  Because heat seeks cold, some will be immediately absorbed into the cooler concrete floor.

In order for the air to reach the north wall in both seasons, it will have to pass through the tall wall (red arrows on the floor plan above) that separates the living space from the vertical basement .  Accordingly, as many cold air registers as possible are being built into the bottom of the wall just above the baseboard and another row at the top of the wall. This design for the tall wall,
A thermometer (circled) is located in the middle
of the house 
by the way, is not original; John Hiat in his remarkable book, pointed out how important it was for the air in the living space to have plenty of access to the thermal mass of the north wall and the soil behind it.

The metric, cooling degree days (CDD), is used to analyze warm weather temperatures.  At the time of this writing in the waning days of July, the temperature in the middle of the first floor of the house has not exceeded 82 degrees despite higher than normal CDD readings for both the month of July and for the cooling season as a whole.  All that separates the interior from the 90-something outside weather are the windows and a layer of plywood sheathing covered with lumber wrap or 6 mil plastic.  The second floor is another matter; temperatures there have tracked closely with outside temperatures.  The difference between the two floors has mostly to do with thermal mass -- the lack
The temperature in early afternoon
 on July 13 when the outdoor
temperature was 93 degrees; the
highest reading of 82 degrees was
reached later in the month during
a week long heat wave
of it on the second floor and an abundance of it on the first floor.  The mass was cooled sufficiently last winter to continue to absorb heat this late in the summer.  

A vivid example of MRT at work:  when we take a break from working on the outside of the house in hot weather, we sit close to and are cooled by the north wall because energy radiates from our bodies at a higher rate than radiates from the cool wall.  During the coldest part of last winter, the inside temperature stayed in the 40's and upper 30's.  Only once for two days during a week of single digit outside temperatures did it drop below freezing, making it obvious that the indoor environment was being moderated by heat that had accumulated in the thermal mass during the warm season.  And the second floor temperatures, unlike in summer, did not track as consistently with outside temperatures due to heat rising out of the thermal mass.  Of course, once the house is insulated, the temperature of the thermal mass will no longer fluctuate with the seasons but these observations bode well for an efficient  AGS system once the building is wrapped up.

Transparent glass overlooking the thermal mass
(concrete floor and soil beneath it) on the first floor
The type of glass in the windows can be used to help winter sunshine find thermal mass.  Transparent (clear) glass allows sunlight to warm whatever it touches.  On the first floor, it will warm the concrete floor and soil below, which is a good thing.  On the second floor, where there is no thermal mass, translucent (frosted glass) works better.  Instead of focusing sunlight, it will diffuse it until it either finds cool thermal mass or it warms the air enough that less heat is drawn from the thermal mass.  In our case, all of the first floor windows are transparent and all but two of the second floor clerestory windows are translucent.

Translucent glass for most of the second floor to 
compensate for the lack of approximating thermal mass
Finally, we will choose interior colors to coordinate winter solar gain with thermal mass in much the same way that window glass can.  The colors where the sun shines on the surface of the concrete first floor will be medium hues so as to absorb energy at a rate that is compatible with the absorptive rate of the concrete and soil below.  Lighter colors would be okay, but not ideal -- similar to translucent glass, they would mostly diffuse the energy rather than absorb it.  Dark colors would be contraindicated because they can cause unpleasant overheating much like sunlit asphalt. 
Notice three features:  (1) the maturing eastern red cedar
shelter belt, (2) the unfinished upper termination of the 9
conduits that originate in the solar collector in front of the
house and (3) the amount of earth sheltering for the 12'
tall concrete north wall (the grade at its highest point is
8" below the top of the concrete portion of the wall with
5' of stick-built wall on top of it).  The back of the house
is covered with 6 mil plastic while waiting for steel siding
On the second floor, light colors will be the rule so as to work in harmony with the translucent glass in diffusing the solar energy until it finds thermal mass.

Preserving the Gain
Solar energy is hard to come by so it makes sense to design a building that preserves it unequivocally.  Many previous posts have described the green features of our building so I will only list some of them here, as a reminder of the effort that has gone into its design and execution.

      - 15" walls and 18" cathedral ceilings with minimal thermal bridging filled
                  with rice hulls at R-4 per inch
     -  Roof trusses covered by two separated layers of sheathing that form a 
                  ventilated air space ("cool roof" design)
     -  Highly reflective steel roofing (light gray) and steel siding (bright white)
     -  Insulation/watershed umbrella extending below grade outward from
                  the house in all directions (see Featured Post in the left column above
                  for a history of the umbrella)
      - Frost protected shallow foundation
     -  Plywood sheathing rather than OSB for better moisture control within the wall
     -  Vapor and air barriers for ceilings and exterior walls that favor drying over vapor
     -  Fiberglass casement and awning windows (see recent post for
                 details on how their design contributes to preserving the gain)
     -  Fastidious air sealing of the building envelope, inside and out
     -  Main entry shielded from north and west winter winds by house and garage
     -  Sizable airlock inside main entry to moderate incoming hot or cold air before it 
               enters the living space (see drawing above)
     -  Shelter belt of eastern red cedars shielding the house from north
               and west winds

Photo-voltaic Panels
No discussion of passive solar would be complete without mentioning PV panels to generate electricity.  A previous post covered the subject in detail so I will only summarize here.  Our goal is to buy only enough PV to break even with the electric company through reverse metering.  Since our needs will be so minimal, our vendor has offered to sell us the parts and materials for a DIY installation.  

With electricity taken care of, our only out-of-pocket energy costs will for the natural gas for cooking, water heating and clothes drying.
_     _     _     _     _

* For a information on AGS, click on "Featured Post" in the left column above or go to Don Stephens' definitive paper  or, for an abbreviated explanation, go to  Wikipedia.) 

Monday, July 15, 2019

Design - Mean Radiant Temperature and Our Project - Part I - An Outline

In a previous post I made the case for using mean radiant temperature the vehicle for understanding passive solar.  After defining the concept, I explained how it works for three types of structures:  (1) stick-built houses, (2) classic earth sheltered passive solar houses and (3) Annualized GeoSolar (AGS) houses like ours.  Now I would like to use a couple of posts to describe how we are controlling MRT to eliminate conventional heating and air conditioning.  This is an outline; the next post will fill in the details.

Controlling mean radiant temperature by balancing solar gain, storage capacity and heat gain/loss through the building envelope.

A.  Our conditioning system is both winter centric and summer centric, hence "Annualized" GeoSolar
B.  Direct solar gain through south-facing windows during winter
C.  Isolated solar gain during the summer when days are longer and sun is more intense
D.  Huge soil-based thermal mass despite limited earth sheltering
E.  Year-round semi-constant comfort level without supplemental heat or HVAC

A.  Solar collector harvests heat from summer sun; conduits distribute it throughout thermal mass (primary source of heat)
B.  Windows collect heat from winter sun (secondary source)
C.  Clear glass for first floor windows; frosted glass for second floor 
D.  Solar overhangs shade windows in summer

A.. Control of MRT is assured by having abundant thermal mass
               1.  Concrete floor and tall north wall
               2.  Soil, with its moisture and temperature controlled
                            a.  Beneath floor and immediately behind north wall
                            b.  Beneath R-10 to R-20 "insulation/watershed umbrella"
B.  Interior colors: absorptive when mass is adjacent; reflective when mass is distant 

A.  Rice hull insulation at +/-R-4 per inch 
B.  Truss walls 15" thick with minimal thermal bridging at R-60
C.  Truss ceilings 18" thick with minimal thermal bridging at R-73
D.  Swing type fiberglass windows (R-4) inset 10" from exterior wall surface to minimize wind washing and excessive solar gain in Spring and Fall
E.  Fastidious air sealing of entire exterior envelope, inside and out
F.   Energy recovery ventilator for indoor air quality
G.  Cool roof design:  ventilated space between truss sheathing and roofing sheathing
H.  Frost-protected shallow foundation using insulated concrete forms
I.  Highly reflective steel roofing and siding
J.  House and garage that shield main entry from north and west winter winds
K.  Air lock inside main entry to modulate incoming hot and cold outside air

Stable year-round MRT fluctuating between 72 and 78 degrees without supplemental heat or conventional HVAC

Net-metering and a small photo-voltaic array to break even with the electric company; utility costs will be limited to natural gas for the tankless water heater, gas range and clothes dryer.

*     *     *     *     *     *     *     *
The next post, Part II, will expand on these topics.

Thursday, June 20, 2019

Design - Passive Solar and Mean Radiant Temperature

The number of visitors to our building site has been steadily increasing as it begins to look more like a "real" house.  And now, while its bones are still exposed, is a good time for the uninitiated to see it and get a feel for how it will work.  Some of the visitors have been groups who do self-guided tours of the grounds and then come inside for a look around followed by a sit-down session on passive solar in general and earth sheltered passive solar in particular.  We compare three types of construction:  (1) typical stick-built houses, (2) classic 1970-80-era earth sheltered houses, as ably articulated by Rob Roy in his book, and (3) what has come to be known as Annualized GeoSolar houses like ours as described first by Hiat and then Stephens.  (For details on AGS, click on "Featured Post" in the column to the left; it will take you to three posts that follow the evolution of AGS.)

I have always had difficulty describing the many nuances of passive solar and earth sheltering.  A couple of months ago, I read again for the umpteen-time Edward Mazria's book, where, on page 64, he discusses the relationship of mean radiant temperature and human comfort.  This time it hit me that the concept of mean radiant temperature would be the perfect vehicle for making passive solar more understandable.

Mean Radiant Temperature

Understanding Mean Radiant Temperature
A cold evening campfire is one of my favorite things but, being skinny, I need to sit at exactly the right distance from the fire to stay comfortable.  If I sit too close to the fire or it blazes up, I quickly get too hot; if I sit back too far or the fire dies down, I begin to chill.  When I visit Missouri's underground caverns, I need a warm wrap.  Otherwise, the low temperature of the enveloping rock soon raises goosebumps.  The reason for these phenomena is that my comfort level depends upon a balanced thermal environment whereby the wave energy radiating from the fire or the walls of a cave that my skin absorbs is more or less equal to the wave energy that I am emitting -- equal actually to a 100w incandescent light bulb.  The mechanism at play here is called mean radiant temperature (MRT) and here’s how it works.

The feeling of comfort for us humans is best realized by maintaining a thermal environment in which the human body can lose heat at a rate that is equal to its production – no shivering, no sweating.  The need to lose heat stems from the fact that the body is essentially a heat engine with a thermal efficiency of only 20% (Mazria).  The waste-heat (80%) is dissipated in three ways:  perspiration, convection and by radiation to surrounding objects (walls, floors, furniture, etc. and, in the case of earth sheltering, thermal mass).  Of the three mechanisms, radiation accounts for about half of the heat loss with perspiration and convection (heat carried away by air) accounting for the rest. 

MRT is simply the average temperature of matter in the surrounding environment and it is more important for comfort than the air temperature in the same environment.  In fact, a 1 degree change in MRT has a 40% greater effect on body heat loss than a 1 degree change in air temperature.  Therefore, when designing living space, it is far more efficient to control MRT than it is to control ambient air temperature.  And the higher the MRT, the lower the air temperature can be.  For example, If we can maintain the MRT at say, 76 degrees, the ambient air temperature could be as low as 62 degrees but our comfort level would be the same as if the air temperature were 70 degrees. Although MRT applies to matter such as wall studs, drywall, wood floors and furniture, it takes something much more massive to provide comfortable environments.

Mean Radiant Temperature in Stick-Built Homes
In stick-built homes, it is impossible to maintain a reasonably comfortable thermal environment without HVAC systems even with plenty of south-facing windows, because there is no thermal mass for storage and insulated 2 x 4 walls, rated (optimistically) at R-13, hemorrhage heat in winter and absorb heat in summer.  The temperature of the entire structure is at the mercy of outdoor temperatures that can be up to 30 degrees too hot or 70 degrees too cold.   Consequently, it takes a robust HVAC system to keep up with the heat gain or loss through the building envelope.  And, in lieu of thermal mass in which to store heat, the HVAC system cycles on and off repeatedly in order to keep the air warm or cool enough.  Meanwhile, the effect of MRT on human comfort actually becomes a negative -- in winter, the human body radiates heat faster than the cold walls and, in summer, it radiates heat slower than the warm walls. 

Mean Radiant Temperature in Classic Earth Sheltered Passive Solar Homes
The thermal mass in the classic earth sheltered passive solar home is limited to the concrete in the floor, exterior walls and sometimes ceilings at the exclusion of the soil below, behind and above the concrete.  This peculiar situation occurs because the soil is kept from
A nearby earth sheltered passive solar home built just
after the oil embargo in the late 70s - early 80s; the living
quarters are one room deep and the roof is fully earth
being part of the thermal mass by insulation applied to the outside of the concrete shell. However, this arrangement does protect a large portion of the building envelope from extreme summer and winter temperatures, a significant improvement over stick-built homes.  The problem is that the amount of solar gain through south-facing windows and the limited storage capacity of the concrete shell are not able to keep up with the loss of heat through the insulation behind the shell and under the floor, to say nothing about heat loss through the south-facing stick-built wall.  Consequently, the mean radiant temperature remains so cool in winter that supplemental heat is the norm although the amount of supplemental heating is much less than stick-built structures because it has only to raise the temperature, say, 10 degrees – the difference between the soil temperature beyond the insulation and a 70 degree temperature in the living space.  
As in a stick-built house, though, most of the supplemental heat goes towards keeping the air temperature comfortable.  But at least the modest amount of thermal mass that exists in the form of concrete is enough to store any excess solar or supplemental heat as well as any waste heat from cooking, water heating, showering, drying clothes, illumination and radiating from human bodies.  Any heat that does make its way into the mass and is held there rather than bleeding through the insulation and into the cold soil would indeed improve the MRT of the living space, something that could never happen with a stick-built home.  A major advantage of the classic earth sheltered passive solar house is that the coolness of the MRT in summer means that conventional air conditioning is rarely needed. 

To be sure, there are non-classic earth sheltered passive solar designs that are more MRT-centric than just described but they are not as common.  Typically they utilize the most efficient thermal mass possible -- water -- in containers (like metal "oil" drums or darkly-painted polymer vessels of various shapes and sizes) staged to collect winter sunlight through south-facing windows during the day and release heat at night and on cloudy days.  Less commonly, roof ponds comprising water in waterbed-like bags strategically situated on the roof are used to heat in winter and cool in summer.

Mean Radiant Temperature in Annualized GeoSolar Homes

What sets our Annualized GeoSolar earth sheltered passive solar home apart from stick-built construction and the classic passive solar home is the total absence of supplemental heat or conventional HVAC.  This is possible by controlling profoundly the mean radiant temperature in three ways:   (1) increasing solar gain by harvesting the summer sun as well as the winter sun, (2) significantly increasing the storage capacity of the thermal mass, and (3) retaining heat (winter) or rejecting heat (summer) with a R-60 to R-73 building envelope.  We expect a year-round comfort level in the mid-70s with a fall-off  to the lower 70s by the end of winter and an uptick to the upper 70s by the end of summer. It may take a couple of years for the temperature of the thermal mass to stabilize during which we will use infrared space heaters for supplemental heat but will not need to worry about air conditioning.  It is not inconceivable that the wide seasonal swings will disappear entirely after a few years.

(Thanks to Jason Graklanoff, my engineer friend, for his thoughtful input to this post.)

*     *     *     *
In the next two posts -- first with an outline then by delving into the details -- I will explain how our AGS build will provide year-round comfort without conventional heating or air conditioning. 

Monday, May 27, 2019

Construction - Window Installation

Most of the north and west exterior walls of the house are earth sheltered and the garage abuts the east wall.
Only 12 second windows were built instead of the 14
shown on the plans.  The first story windows stayed
true to the plans, making a total of 19 large and 1 small
 south-facing windows 
  Therefore, we would have been hard pressed to fit glazing into any of these walls.  But, no loss, we intentionally designed the house with all south-facing glazing (except for one small east window under the entry portico).  It took twelve 3' x 5' windows on the second story, four 3' x 5' and three 3' x 6' windows on the first story to meet minimum code for the ratio of glass-to-floor area.  The interior of the house is laid out so that all spaces except the bathrooms and the TV viewing area have windows.  The living room has no ground level windows but, since there are no second story rooms above it, it is generously lit by the second story clerestory windows.

 Green Features 
All the windows and the two exterior doors are designed for maximum sustainability.
     -  Energy efficient glass                -  Recessed profile               
     -  Energy efficient frames             -  Overhangs                
     -  Fixed vs.Operable                     -  Angle of incidence 
     -  Swing closure                            -  Peripheral seal            
     -  Translucent (frosted) glass        -  Glass-to-floor ratio

(Click on any photo to enlarge it for better viewing.)
Energy Efficient Glass
Our windows and doors have all of the bells and whistles,
like double glass and low-e coating, that make them first quality.  But, at +/-R-4, they are like holes in the wall compared to our fifteen inch, R-60 walls.  According to Daniiel Chiras in his book The Solar House; Passive Heating and Cooling, the problem is not just the glass -- about a fourth of heat gain or loss occurs through the frames, making it imperative that both the glass and the frames be energy efficient.

Energy Efficient Frames
A fiberglass frame has the same coefficient of thermal expansion as window glass unlike wood and vinyl frames (vinyl is by far the biggest mismatch).  When the frame and glass expand and contract at the same rate, air leakage between the frame and glass that might compromise the seal of the double panes or admit air into the living space becomes moot.  Unlike vinyl, fiberglass is resistant to UV rays, is much stiffer and accepts paint.  And it is made from sand, the most abundant substance on earth, rather than petroleum.

Fixed vs. Operable 
The top label at the right contains a map of the US with shading to indicate the area for which the window is designed.  Notice that it encompasses all but the southern reaches of the country.  The second label shows a reverse picture; only the southern reaches are shaded.  Fortunately, both labels cover St Louis.

Each label has a series of four numbers near the top.  The first number is the U-value which is an inverse expression of R-value in that the lower the number, the higher the R-value.  Notice that the U-value for the top label is lower than for the bottom label.

The two labels were photographed on side-by-side windows.  The top label is on a fixed unit and the bottom on an operable unit.  The fact that the maps and the U-values show an energy rating that is better for the fixed glass window validates our decision to limit the number of operable windows.  Since we will be depending on the energy recovery ventilator for most of our fresh air, having only 8 of 19 windows that are operable will be sufficient for additional ventilation when it is needed or desired.

Swing Closure
Windows and doors that are hinged prevent air infiltration better than sliding doors and windows.  To say it another way, casement, hopper and awning windows and hinged doors are more energy efficient than double- or single-hung windows or doors and windows that slide horizontally.  The reason is that swing doors and windows can be locked tight against a gasket-like seal while sliding units need a looser fit to be able to move up and down or side-to-side.  While the fit of modern sliding units are infinitely better than their ancestors, their air sealing still falls short of the gasket-type.

Frosted Glass

Greenhouses utilize the solar advantage of translucent  glass.  The glass in old-time greenhouses was painted with whitewash.  Newer greenhouses use "clear" sheet plastic that is, in reality, translucent in that you can't see clear images through it or they utilize translucent corrugated fiberglass panels.  Accordingly, we have 19 south-facing windows at least 3' x 5' in size of which more than half have translucent (frosted) glass instead of clear glass. 

The solar performance of the two types of glass differ in this way.  Sunshine through clear glass warms whatever it shines on.  If "it" is thermal mass, like concrete overlaid with ceramic or porcelain tile and of an appropriate color, the solar heat is absorbed into the mass without overheating its surface, which is a good thing.  If "it" lacks thermal mass (think wood or carpet floors, furniture and even drywall), "it" overheats and warms the air when it is not needed.  In a sense, precious heat is wasted.  

Frosted glass, on the other hand, diffuses (scatters) the sun's rays.  The heat rides the air currents within the dwelling until it either finds thermal mass or it conserves heat in the thermal mass by providing heat that would otherwise be coming from the thermal mass.  In our case, the thermal mass is the downstairs floor, the lower 10' of the long concrete back wall of the house and the soil under and behind them as well as the soil  beneath the insulation-watershed umbrella adjacent to the house.  Consequently, all of our first story windows are transparent because of their proximity to the thermal mass whereas all but two of the second story windows, where mass is missing, are frosted.

Recessed Profile
Today's new construction windows have nailing fins that position
the surface of the glass flush with the outside surface of the wall.  While this design eliminates air leakage between the window and the wall framing, it is not as energy efficient as it could be if the glass were not flush with the wall.  Here's why.

The rate at which heat is lost through the glass is dependent on the rate at which heat is removed from the outside surface of the glass.  If the heat can pass through the glass and linger for awhile on the outside surface of the glass, it slows the transfer of more heat.  What determines the amount of lingering?  Air movement.  Wind can remove the heat as fast as it forms and, since heat seeks cold, the rate at which heat is drawn through the glass accelerates, a phenomenon called "wind washing".

Our windows, by being positioned about 10" inside the plane of the wall and being south-facing, are sheltered from the prevailing north and west winter winds.  As such, the amount of wind-washing is about as minimal as it gets.  The red arrows in the nearby photo bracket the 15" thickness of the wall; the green arrows delineate the area on which the window rests; the blue arrows show the distance from the window to the outer surface of the wall -- about 10" after the trim boards are in place.
The distance between the top of the windows and the 2'
overhangs is greater for the first story than for the second
story but the difference in the amount of sunshine reaching
 the floors inside is negligible even for the taller windows
 in the foreground.  (The sheathing is protected by lumber
wraps and sheet plastic which will be replaced with proper
house-wrap and metal siding eventually.)

Sunshine through the windows is a blessing during the cooler months of the year but very unwelcome from May through September.  At our St Louis latitude, it takes a two-foot overhanging soffet to block the midday sun during the hot summer months.  

Early morning and late afternoon sun can shine under the overhang but, with the windows recessed, the adjacent wall offers shade in a way not possible with flush-mounted windows.  However, after the end of May and until the first of September, the sun angle increases enough that sunlight is completely blocked all day, even during the early and late hours. With the windows recessed, though, the sun that does reach the floor during late spring and early fall covers an area a third less than would be the case with flush-mounted windows.  As long as the overhang is reasonably close to the top of the windows, the height of the windows
Even with tall windows and an overhang a good
 distance above the tops of the windows, very little
 midday sunshine reaches the floor in early May;
 later in May none will.
is not critical. The nearby photos show the extent to which the sun reaches the floor during the first week of May through windows 6' tall and an overhang +/-2' above the tops of the windows.

Angle of Incidence
The same windows in late afternoon after the sun has
dropped low enough to shine under the overhang; the
amount of sunlight reaching the floor is restricted by
the recessed profile.
Another important concept in understanding passive solar is the angle of incidence, the angle at which sunlight strikes the glass in windows or the roof of a greenhouse.  The more perpendicular the sunshine is to the glass, the more energy absorbed by the glass.  The steeper the angle of the sunshine, the more energy reflected by the glass.  The practical take-away is that at least 90% of the sun's energy reaching a vertical window during the summer months does so at such a high angle that it is reflected rather than raising the temperature inside the house.  By the same token, the amount of energy absorbed through vertical windows at winter solstice time is at least 90% of what could be expected through glass that is tilted toward perpendicularity with the winter sun, as often seen in pictures of passive solar homes and greenhouses.  But tilted glass is not a good idea because it absorbs too much unwanted heat in summer unless it is covered with an exaggerated overhang, which is rare in the pictures I've seen.

In summary, our passive solar design utilizes three things to maximize solar gain when it is needed and minimize solar gain when it is not..  First, our windows are vertical rather than tilted for the reasons just discussed.  Second, we have overhangs designed for our latitude that provide adequate overhead shading.  And, third, our windows are recessed for lateral shading.

Peripheral Seal
The decision to recess the windows meant using "replacement" rather than "new-construction" windows.  No doubt about it, the latter with their nailing fins are better at blocking air leakage between the windows and the framing and sheathing that surrounds them unless the air sealing around replacement windows is done with extreme care.  

Sealing our windows was complicated by the fact that I built the housing for them as premade wall sections using custom jigs several years in advance of even ordering the windows. I deliberately made the window openings larger side-to-side and top-to-bottom than the window manufacturer specified because I knew that it would be extremely difficult to enlarge the openings once the units were in a wall.  As a result, the gap on either side of the windows averaged 1/2" and the gap at the top of the windows more like 3/4".  

All three sizes of backer rod --  3/8", 1/2" and 5/8" -- were
 needed in various combinations to close the gaps 

between the window frames and the rough openings on
 the exterior side 
At first glance, it would seem that all one would have to do for fool-proof air sealing is to fill the gaps with spray foam but even minimal expanding foam that is designed for this purpose is capable of distorting window frames if used in excess.  Rather the window manufacturer recommends that the foam be limited to a 1" strip located about 1" into the space between the window frame and the rough opening on the interior side.  On the exterior side, it recommends a course of properly-sized backer rod just inside the outer edge of the frame and, in doing so, leaving enough room for a bead of caulk.  Since our windows are inset, the caulk will be added when the jam extension between the window frame and the trim boards around the window opening are installed.  In this manner then, the spray foam provides the air sealing and the backer rod and caulk provide weather sealing.  The wide 3/4" gaps at the tops of windows were partially filled with plywood ahead of the foam and backer rod.

Glass-to-floor Ratio
In his definitive book, The Passive Solar Energy Book; A Complete Guide to Passive Solar Home, Greenhouse and Building Design, Edward Mazria recommends for our temperate climate (average winter temperatures of 35 to 45 degrees) a ratio of 0.11 to 0.25 sq ft of south-facing glass for 1.0 sq ft of floor area "in order to keep the space at an average temperature of 65 to 70 degrees during most of the winter".  Only our concrete first floor can be counted as floor area for calculating the ratio, so 2,800 sq ft of floor area to 354 sq ft of south-facing glass gives us ratio of 0.13, which falls at the lower end of Mazria's recommended range.  

Such a low ratio could be discouraging for us older folks who do better with temperatures in the mid-70s and the numbers get even worse because Mazria's figures for the temperate zone do not differentiate for cloud cover.  Here in the St Louis region, according to Daniel Chiras, only 47% of possible sunshine during the months of December, January and February actually reaches the glass.  Therefore, a conventional winter-centric passive solar house would definitely require supplemental (CO2-emitting) heat.  However, when heat coming through our windows during winter is added to the heat generated by our Annualize GeoSolar summer-centric system, it is almost certain that our thermal mass will maintain a comfortable year-round temperature hovering around our preferred 74 degrees without any supplemental heat.  Don Stephens, the father of AGS warns that too much heat could actually be a problem eventually that would necessitate mothballing part of the solar collector.  (For an understanding of AGS, click on "Featured Post" in the left column above.)

Not much needs to be said about the actual installation of the windows except for some considerations dictated by working alone.  Most of the windows were 3 x 5' and about, I would guess, 60-70 lb.  Knowing that I would be working alone, I requested that the double windows be shipped as individual windows rather than joined together with a factory-installed mullion.  Even then it was a stretch to hoist the second story windows to place without using a ledger on which to set them part way up.  By using temporary vertical stops against which to set the window, I could lift it into the opening without its falling outward and, by installing the stops exactly plumb and at the exact location of the exterior surface of the window in the rough opening, the window ended up automatically in the position it needed to be in except for plumbing in a left-right direction. 

The additional work required for the site-made mullions is at least partially compensated by the knowledge that they are more energy efficient than factory-made mullions would have been since they are filled with foam board insulation.