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A Contrarian View of Passive Solar Design

Don’t obsess over south overhangs

Posted on Jan 26 2010 by peter powell

By Peter Powell, AIA

I have designed over 60 passive solar homes over the last 35 years and have lived in seven of them. Based on that experience, I have come to a few conclusions which, although contrary to conventional passive wisdom, I have found to be valid. I must qualify these comments by saying that most of my experience has been in the Northeast, primarily in Maryland and Pennsylvania, in areas with 4,000 heating degree days and up. The following comments mostly apply to new construction in similar or colder climates.

Overhangs to shade south-facing windows are ugly, unnecessary, and counterproductive
You don’t need them. The theory is that overhangs should be designed to provide full shading of the south-facing glass in the summer and no shading in the winter. Part of the problem is that most of the standard summer designs for these overhangs are based on June 21 at noon. Unfortunately, this is neither the hottest time of day nor of the summer.

Likewise, winter designs are usually based on achieving no shading on December 21, which is certainly not the coldest day of the winter.

In my experience, these overhangs are not really needed. Because of the high solar altitude in the summer, over half of the solar radiation striking the glass is simply reflected away; another significant fraction of the solar radiation is rejected by the glass coatings.

Most overheating problems in the summer are due to east and west windows — window which can’t easily be shaded and which obviously should be minimized in the design.

The usual reason for overhangs is supposedly to reduce air conditioning costs. I contend this is a red herring, in part because AC is grossly overused in houses. We don’t need to maintain precisely 75°F year around, as some of my clients seem to want. (I even had a client once demand that his house include no operable windows.)

The easy solution to most summer overheating is to open windows. The major cause of summer thermal discomfort is caused not by excess solar gain but by high ambient temperatures and humidity. We shouldn’t throw out the baby with the bathwater by installing overhangs which are counterproductive most of the year and only marginally helpful in August (at least in my climate).

Solar gain in the spring and fall should generally be maximized and the heat stored to minimize any overheating. Overhangs, which by design will be shading as much as half of the glass in these seasons, should be avoided.

Using deciduous trees to shade the south elevation in summer is a major design error
This is a myth that won’t go away. Don’t do it! This theory holds that deciduous trees and vines will shade south-facing windows in the summer and reduce heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss., while in the winter, when the leaves are down, sun will be able to enter and heat the house. It doesn’t work.

The problem is that the limbs of any tree tall enough to shade the windows in the summer will significantly block the lower winter sun, even with the leaves down. In my area (central Pennsylvania), most of the leaves don’t fall until November anyway, after there have been many cool days and nights when the solar gain would have been useful.

Any new house site should be evaluated with one of the solar path devices to ensure that NO shading will occur within 45° or more east and west of the south elevation, any time of year.

A related problem with tall trees to the south is the likelihood of shading any rooftop thermal or PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. collectors in the winter when the sun is low. Such shading can be extremely detrimental to their performance.

A house doesn’t need to be perfectly oriented
I keep reading articles about how to locate true south, using everything from computer programs to measuring shadows through different seasons. Just get a simple compass and correct for declination if you must.

Orienting a house east or west of true south by up to 20° will have no significant effect on solar performance. For example, I currently live in two virtually identical passive solar buildings, a residence and a studio. The studio faces due south and the residence faces 25° west of south. By the end of a sunny day, the overall solar performance of the two buildings is almost identical, with the house performing slightly better in the spring and fall and the studio doing slightly better in the middle of winter.

In general, I favor orienting a passive houseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. at least 10° west of south to improve late-day heat gain while slightly increasing east-facing window area to improve early-day warmup.

It’s possible to have more south-facing glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. than allowed by most rules of thumb
The area of south-facing glazing area can comfortably be 15-20%+ of total floor area as long as there is adequate storage mass and “active” movement of the heat into the storage.

To maximize solar gain while minimizing overheating, immediately move the stratified heat into storage. Don’t rely on natural conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow. and convection to move the heat.

Most rules of thumb for south-facing glazed area assume that the storage mass is located only in the south-facing rooms, and they assume direct conduction of the solar heat into that storage. This method is relatively slow and inefficient, except for the limited surface areas which are directly in the sun, and often results in overheating. It fails to take full advantage of the available mass in rooms remote from the sun, as well as the advantages that occur when heated air is moved through hollow masonry walls or hollow floor slabs to remote mass storage.

A house with a larger-than-normal glazed area (which could be 30%+ of the floor area of the south-side rooms) can still be comfortable and productive if solar heat is moved mechanically out of these areas and circulated into other rooms and, most importantly, directly into supplemental storage mass.

I have designed a number of homes using this approach, which involves using a thermostatically controlled fan (usually the furnace blower) set to start when the temperature at the ceiling or ridge of the space rises above a set point of about 75°F.

This same system is also useful to store and distribute excess heat on days when a woodstove is being used. I have used a number of hollow floor systems for this storage including Airfloor, Flexicore precast planks, and most often a double 4 in. concrete slab with 2-in. EMT at 8 in. on center sandwiched between and connected to a supply plenum. (This forced air radiant slab can also be used for air conditioning if necessary.) Pulling stratified air through a hollow 6 in. or 8 in. concrete block wall is also very effective since all rooms exposed to either side of the wall benefit from the radiant heat. This hollow wall storage is also very effective when the site is north facing with no opportunity for significant south glazing. A design with south-facing clerestory windows can work as sort of a hybrid active thermal collector with the heat then mechanically stored in the mass wall.

Peter Powell is an architect in Rays Cove, Pennsylvania.


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  1. Peter Powell

1.
Tue, 01/26/2010 - 11:22

25% south glass in summer sounds scary to me
by Dave Brach

Helpful? 1

Peter,

First, I appreciate your insights and experience--everyone should have the benefit of a local architect who knows the climate well. But what is the cooling load for a house with 20%+ south glazing and no shading in Pennsylvania (assuming SHGC>.5)? Sounds a little scary to me. Also, how do you define "total floor area". Gross?, net?, basement included?? And I assume that "glazing area" does not include the area of the window frames?

I guess I'm wondering: even if one CAN have 25% south glass and store it actively in lots of mass, why would one WANT to? Windows are expensive. Active storage systems also tend to be commplicated and expensive. Not to mention the mean radiant temperature of that window wall on a winter evening with anything but the higest R windows.....


2.
Tue, 01/26/2010 - 12:53

Hi Peter
by John Brooks

Helpful? -1

I like Contrarian viewpoints


3.
Tue, 01/26/2010 - 13:15

Overhangs
by Carl Mezoff

Helpful? 1

Powell's points, "aged in wood," of long experience, are on target, except possibly his argument against overhangs. If you set the overhang adequately above the glazing opening, you do not lose the winter sun. Also, overhangs do other things besides provide shade. They can keep a lot of the heavy weather off the siding, allow you to omit gutters, and can give you a to keep a wood pile dry!

The 2" EMT storage slab is interesting, but looks like a lot of work and expense. One would wonder if 80F air would be provide enough delta T to get a meaningful amount of heat into the slab.


4.
Tue, 01/26/2010 - 14:29

Mechanical heat distribution
by Doug McEvers

Helpful? 2

If you are using a furnace fan to move stratified heat, insist on an ECM motor, they are available as a replacement through EFI.


5.
Tue, 01/26/2010 - 14:36

Overhangs 2
by Doug McEvers

Helpful? 1

Overhangs help to get rainwater away from the house, energy heel trusses put the overhang high above the top of the window.


6.
Tue, 01/26/2010 - 14:42

Deciduous trees
by Doug McEvers

Helpful? 0

We have 2 large and well pruned silver maple trees on the southwest corner of our house and I would not be without them. Our AC usage in the summer is 250 kWh in Minneapolis for 3,328 sf. This house was built by others in 1978 and has no special energy features other than some fine tuning by me and a 16 SEER, 2 ton AC.


7.
Tue, 01/26/2010 - 17:55

Reply to Dave
by Pete Powell

Helpful? 1

Dave, as you may have gathered, I'm not a big fan of air conditioning- I don't have any AC system in my present home, so the cooling load is a non issue for me. Floor area in my houses is heated area. I seldom design a house with a basement since a slab on grade is ideal heat storage. I'm in a 5900DD location and am happy to collect and store all the heat I can. There really is no downside. The active storage systems I described take a little construction coordination, but once built involve little more than setting the thermostat. I do have roll down insulating shades on the larger picture windows which helps on really cold nites.


8.
Tue, 01/26/2010 - 18:16

Reply to Carl
by Pete Powell

Helpful? 3

Carl, I agree that you design the overhang to eliminate winter shading, but my point is, that if it's designed to provide summer shading, it will undesirably shade part of the glass in the spring and fall.
I've built 5 houses with this EMT system and it's not all that hard to do nor expensive (as long as conduit prices don't keep going up.) The overall slab thickness is 8" and we are able to keep it at about 70-72 degrees which is quite comfortable and will maintain the house over 65 degrees for over two cloudy days when fully charged.


9.
Tue, 01/26/2010 - 18:27

Reply to Doug
by Pete Powell

Helpful? 0

I agree about the high efficiency motor since it runs all the time when it is sunny or when the woodstove is in use. I'm not a big believer in buiding houses without gutters- I would rather get the water away from the foundation rather than have it dump on the ground. Your trees may well be helping your cooling costs, but my concern still is the possible reduction of winter solar gain.


10.
Tue, 01/26/2010 - 19:43

Great essay, but...
by James Carr AIA LEED

Helpful? 0

Thanks for these great insights. I would only question whether you might be underestimating the heat gain through the building envelope overall, ie the walls and not just the glass. This is made even worse if the ground adjacent to the buildingis heating up, too. We live in a south-facing 1200 SF studio with no A/C in the Boston area. We have a deep overhang on the south and around 40% glazing on S, almost none on E or W. N side is attached. We heat with wood -- 4 cords avg per winter (someone else do the math!). We have large deciduous trees to the S--full shade in summer. Anyway, it works great. Solar gain means the fire dies out on sunny 30 degree days and we don't notice. Summer is comfortable except for the heat-wave days of 85 plus temp with 80 humidity--always cooler than outside. I do believe that the overhang is a key element of the design (which was done by a friend, years before we moved in.)


11.
Tue, 01/26/2010 - 20:14

Reply to James
by Pete Powell

Helpful? 0

James, Your house configuration and climate sound similar to ours, but. our construction is 8" SIPS walls and roof so I don't expect much heat gain through the envelope. On a sunny 0 degree day, we don't need any supplemental heat. (We recently had 2 sunny days with -20 degree wind chill and needed no supplemental heat for 3 days.) I will still argue for 100% solar access for the south elevation in the winter and even without overhangs, we have no overheating from solar gain in the summer.


12.
Tue, 01/26/2010 - 20:55

AC
by Doug McEvers

Helpful? 0

Pete,
Thank you for considering my rants and making the point of the need for gutters, this should be the code in all climates short of desert conditions. I am all for passive gain and take nearly full advantage in our 1978 rambler. A couple of basic energy saving criteria were met with our home, the attached garage on the NW corner helps to stave off winter winds and the bulk of the glass faces south.
I do think one should consider though the type of fuel used for both heating and cooling when making a judgement on shading by trees. Virtually all new homes built in the Twin Cities metro have AC, a new home without it would be a hard sell, plus there is the heat island effect.
Heating here is by natural gas and cooling is by electricity and the CO2 produced by each should be a consideration. I have not crunched those numbers and hopefully someone wiser than I (Martin) could do so given the right information. When I built superinsulated homes in the 1980's, the cooling load was virtually non existent but these homes were in a much smaller urban area where nightly temperatures are less and average wind speeds higher.

Building design is situational and homes built to code in the Twin Cities at least have a fairly high cooling demand and are not as well insulated in the walls and ceilings as the homes described by Peter.


13.
Wed, 01/27/2010 - 07:06

Nothing Contrarian, Just Some Rediculous or Illogical
by Rick

Helpful? 1

I don't see anything contrarian in your writing. Things like the most undesireable heat gain comes from E-W windows, no trees (even deciduous) on south side, no need for perfect orientation, glazing/thermal mass ratios are all well known by those who have spent any time being interested in the passive solar subject.

Comments like overhangs are designed for 6/21 and 12/21 which are not the hottest or coldest and so they are not needed is just illogical. The overhangs provide significant shading against high summer sun well before and after 6/21. Your comment about window coatings helping to reflect summer sun is also illogical. Those truly interested in passive solar heating don't want the coatings in the first place. Finally, your comment about just opening the windows instead of AC is just ridiculous--you have fallen victim to writing for the masses while immersed in your own situation. You have 5900 HDD--I don't have to look to see that you are relatively high. You may have gotten away with no AC in houses in Rays Cove, PA and far western MD, but you shouldn't come around here (Chesapeake Bay), where you can almost steam crabs without any added heat or humidity, and propose a house with no AC...hee hee. Yes, humidity is the issue, and its mitigation is extremely challenging without mechanical help.


14.
Wed, 01/27/2010 - 09:10

Did you read this part?
by John Brooks

Helpful? 0

" The following comments mostly apply to new construction in similar or colder climates."


15.
Wed, 01/27/2010 - 09:32

Peak Demand Billing...coming SOON
by John Brooks

Helpful? 1

Gathering,Moving ,storing and distributing heat and "coolth" could be a valuable strategy in Many Climates soon.
I would like to see more photos and details.


16.
Wed, 01/27/2010 - 09:35

Reply to Rick
by Pete Powell

Helpful? 0

Rick, I designed, built, lived in, and steamed a lot of crabs in the red house shown at the top of the article. It is located on the Chesapeake Bay near Annapolis so I know a bit about humidity too! Although this house has AC, we probably didn't use it more than 3 or 4 days a year. We would circulate cooler nighttime air through the hollow floor and never had any summer overheating from the unshaded glass. Opening windows does work.


17.
Wed, 01/27/2010 - 16:42

Question on Thermal Mass
by Rolf Miller

Helpful? 1

Pete, Very interesting article and great points. I am trying to finish remodeling my home in Colorado Springs. The original portion of the house is basically complete. I stripped the outside walls down and filled them with closed cell spray-in-place foam, then put up 1 inch rigid foam board and covered with drywall. All the interior walls and ceiling have the original wall board of 3/8 inch drywall covered with 5/8 inch of concrete.

I replaced all the windows with foam filled fiberglass frames and heat mirror glazing packages. I choose the glazing for each window based on orientation.

I am trying to finish the final phase of the project but am stuck on a few issues, mostly related to thermal mass. This wing is an addition; it has a crawl space, flat roof (zero insulation) and wood floors. I sprayed 5 inches of closed cell foam on the ceiling in between the 10 inch beams, and covered with drywall. I filled the wall cavities with foam and plan to put up the 1 inch foam board next. The whole house is heated with hot water baseboard. I have never needed AC in the summer, so don't expect to need it now. My concern is with winter heating and storage and movement of heat. The room connecting the addition to the main house has an 8 foot sliding glass door with windows on each side with about 8.5 sqft of glass each (u=0.106, shgc=.53). Unfortunately this wall faces approximately west. The main room of the addition is about 24 ft by 15 ft. There is a picture window that faces due south-west (u=0.181, shgc=.63). Not a great orientation for passive solar. The room has a fireplace that was designed by the original owner, who was the chief engineer of NORAD. It has ducting and blowers to circulate air through it and into the room. For a fireplace it is fairly effective at heating the room, probably not efficient or clean burning, but effective. With insulated walls and ceiling, windows that are no longer super leaky single pane alum., the fireplace will quickly overheat the room unless I can circulate the heat to the rest of the house.

Where can I locate thermal mass, and how much do I need? I thought about using concrete board, but it is only ½ inch thick, is this thick enough to do anything? The thermal time constant is probably too small to actually store anything. Plus I don’t like the idea of putting thermal mass on the exterior walls because it will increase the delta T across the insulated wall. I don’t want to tear up the wood floors for several reasons, including expense and my wife would kill me. There is an interior “L” shaped wall, one side faces the fireplace and the other is in the room with the sliding door. I already removed the ‘70s wood paneling, so could fill the cavities with concrete and cover with concrete board and plaster rather than putting up drywall. Since the sun doesn’t hit this wall directly, will it be effective? I have also read articles that mention using water walls for thermal mass, but have never been able to find anything on how to make them. Is there a way to put a heat exchanger in my fireplace and tie it to my hydronic system to move heat to the other parts of the house? With no attic over this addition, options for putting in duct work to move air to the rest of the house are limited.

Any suggestions?


18.
Thu, 01/28/2010 - 05:18

My two cents
by Martin Holladay, GBA Advisor

Helpful? 1

Peter,
Thanks for sharing your years of experience. Like John Brooks, I like contrarian viewpoints.

I'd like to add a few notes of caution to this discussion, lest impressionable designers make some serious mistakes.

1. You are designing homes that have a lot of heat gain on sunny days. In very cold weather, the heat gain is desirable. Your furnace fan is a key component of keeping the south-facing rooms comfortable; without your active systems to move heat, these rooms could become unbearable. Few builders are willing to invest in the hollow concrete floors and walls that are an essential component of your system.

2. Running furnace fans for hours on every sunny day carries a substantial energy penalty. Many furnace fans draw 700 or 800 watts. These fans are expensive to run. They introduce waste heat into the house -- and the heat is generated on sunny days when the last thing you need is 800 watts of expensive additional electric heat. A proper economic analysis of your system must take into account the value of the collected heat -- minus the cost required to move the heat around. Of course, an ECM blower helps -- but still, electricity is required whenever the sun is shining.

3. I'm guessing that you and I are the same age. Plenty of us veteran builders built passive solar houses in the 1970s that had relatively high south glazing ratios. These houses overheat on sunny afternoons in February, March, and April. How do I know? I built a few. I became a convert to superinsulation and more reasonable south glazing ratios. Too much glass is cold at night, cold on cloudy days, and hot on sunny days. What's to like? Solving the multiple problems of these buildings is relatively easy: just reduce the square footage of south-facing glass.

4. I like overhangs. Your first photo makes me cringe. I've worked as a home inspector, and I can't tell you how many times I've seen deteriorated siding and rotten window sills on houses without roof overhangs. I'd much rather lose a few hours of sun occasionally and live in a house with good roof overhangs than see my siding deteriorate from weather exposure. Moreover, the aesthetics of a home are important. To me, at least, a house without roof overhangs is an aesthetic line I'm not willing to cross.

5. You are completely correct about deciduous trees and orienting 20° east or west of south.

6. Advice to newbies out there: there are a lot of variables involved in the principles that Peter is talking about. For one thing, what type of glazing is being specified? If you are using glazing with a SHGC of 0.30, the performance of all that glass will be dramatically different from the performance of glazing with a SHGC of 0.60. A factor of two difference. Get it right, as Peter evidently has, and you have a house that works. Get it wrong, and you have blown it big time. You end up with a house full of unhappy homeowners, hot in the summer and shivering on winter nights.


19.
Thu, 01/28/2010 - 07:07

Aesthetics=overhang?
by John Brooks

Helpful? 0

Martin,
All of your warnings should/MUST be considered.
Aesthetics is a little too personal.
Tight skinned architecture has been extremely popular in America from Cape Code to the more modern (70's)Architecture of William Turnbull,Charles Moore and Hugh Newell Jacobsen.
As an Architect I find it attractive.
As an Architect from Texas I would go with an overhang.


20.
Thu, 01/28/2010 - 07:26

Know the Rules, Understand the Rules
by John Brooks

Helpful? 0

BREAK THE RULES


21.
Thu, 01/28/2010 - 07:28

I agree
by Martin Holladay, GBA Advisor

Helpful? 1

John,
Of course you're right — de gustibus non est disputandum. My personal architectural aesthetic, honed in part by my years working as a roofer, requires an elegant roof. Ideally, in my mind, the roof sits like a graceful hat, protecting the house from sun, snow, and rain. It should not be cut up into a dozen disparate planes; I like a gable, with two simple slopes. And it needs decent overhangs, including wide rakes. My personal dislikes: shed roofs, complicated roofs with intersecting valleys and dormers, and roofs with stingy overhangs.

But aesthetics are personal and not subject to argument.


22.
Thu, 01/28/2010 - 09:25

Pete's Humidity Tolerance is Certainly Contrarian
by Rick

Helpful? -1

Pete, I hear your reply comments to mine. Actually, here they are again followed by more of my reply:
-----------
Rick, I designed, built, lived in, and steamed a lot of crabs in the red house shown at the top of the article. It is located on the Chesapeake Bay near Annapolis so I know a bit about humidity too! Although this house has AC, we probably didn't use it more than 3 or 4 days a year. We would circulate cooler nighttime air through the hollow floor and never had any summer overheating from the unshaded glass. Opening windows does work.
--------
Pete, I grew up in an old house near the Chesapeake Bay with no AC, ever, but we did have well ventilated toilet facilities. I could proclaim that literally sweltering myself to sleep "worked," and of course it does work if it has to, as in the days of old. You may have been comfortable in the red house, but I doubt if 99 out of 100 other people would be. Of course you got some nice cool by being ON the bay, and by floor channels but the humidity would have been considered a disaster by most. Also worth mentioning is Kachedorian, Passive House, and Doubs, all of whom or which had problems or rumored problems with mold associated with earth tubes or underfloor channels involving passive "earth" cooling.


23.
Thu, 01/28/2010 - 09:29

Overglazing
by Doug McEvers

Helpful? 1

Another reason these homes may be getting by without AC is the nightly radiational cooling from all that glass. I would love to see some performance figures expressed in Btu's/sf/hdd. My best effort in the 80's for what I would consider a passive solar house was .9


24.
Thu, 01/28/2010 - 09:38

Getting by without AC
by John Brooks

Helpful? 0

His house does not have 14 (murky)inches of foam under the slab either.
I am not saying everyone should copy his solution....
We should question EVERYTHING.

note:murky is an obscure reference ....I know


25.
Thu, 01/28/2010 - 10:59

Earth connection
by Doug McEvers

Helpful? 0

Peter is utilizing some very vaiable and sustainable concepts such as earth cooling, this might use some refinement to eliminate the mold possibility. How about some concrete filled sono-tubes tying the earth to the living space? Not sure how you turn it on and off but it might work for coolth. My friend Larry Kinney sent me a bit of information a while back on what they called the "snug house", I will see if I can dig it up. It was an experimental shed that was highly earth connected and very energy efficient.


26.
Thu, 01/28/2010 - 12:56

tubes
by Rick

Helpful? 2

Doug
It seems Eric Doub never says anything around here, but I guess he still has earth tubes at Solar Harvest in Boulder integrated with his HRV or ERV, whichever it is. He told me a while back he had discovered evidence of mold in the tubes and threw some ultraviolet lighting into the mix in an effort to mitigate it. I don't know if or how well it works--like with other things, however, you have to watch out for running into diminishing or negative returns if things aren't as passive as you anticipated.

Sono-tubes sound rather expensive. Available knowledge seems to indicate that for US latitudes, you typically need to get down to about 20 feet below ground to get temperatures real close to the average air temperature for the year. Maybe you could live in one big one, all buried except for
a south-facing glass band near the top, like a green intercontinental ballistic missle (GICBM) silo.


27.
Thu, 01/28/2010 - 13:33

Gadgets
by Doug McEvers

Helpful? 1

Rick,
I am not sure if I could get military clearance for the design you suggest, but it did give me good laugh along with the steamed crabs.

When I built 6 superinsulated homes in the mid 1980's, the homes were indistinguishable from the neighboring code built homes. This concept was new to me but building was not and I really felt my homes should fit the surroundings and just be a whole lot more energy efficient.

I know Eric Doub and he has a different take than I do on what constitutes energy efficiency. I think the net zero energy movement could have learned a lot by studying all of the information that came from Canada and the US during the superinsulation movement. Simple is better when it comes to affordability and efficiency for that matter, square is better than long, that sort of thing.

Martin described the right roofline as an elegant hat and I agree, slightly bigger than the foundation for rainwater control. The same goes for home design, neat and clean, no great appendages knocking the crap out of the surface to volume ratio. All the gadgets in the world will not make up for a home with improper design, start with superinsulation and Passive House concepts and you will not need all of the expensive countermeasures.


28.
Thu, 01/28/2010 - 20:44

Reply to Rolf
by Pete Powell

Helpful? 1

Rolf, I'm not sure I completely understand your floor plan, but the easiest answer to moving the heat out of this room is a fan assisted transfer grill near the ceiling to blow warm air into adjacent rooms. You say you are only getting solar gain from SW and W facing glass and apparentlly havn't experienced summer overheating, what is happening in the winter? Adding a lot of mass may not be useful unless the room is overheating in the winter. I'm wondering how you do in the winter in this climate with only moderate levels of insulation. I would consider a couple of layers of cement board on the interior wall but don't cover them with wood. There is a discussion elsewhere in this site about hydronic coils in the fireplace. I assume that you have some kind of boiler for heat. Tying a fireplace coil (which can easily produce boiling water or steam) into the conventional hot water system has to be designed carefully. make sure you get help from somebody who knows what they're doing. Don't waste your time with water storage!


29.
Thu, 01/28/2010 - 21:48

Reply to Martin Rick, Doug, John
by Pete Powell

Helpful? 1

OK guys, I appreciate all the comments, so now a few from me. First of all, I won't wade into the aesthetics argument- de gustibus etc and sometimes form doesn't follow function when it comes to overhangs. Yeah, I confess I probably overdesigned some glazing in the 70's and 80's, but maybe that was mitigated somewhat by lower quality windows and not insulating things as well as we do now.

As far as the summer nitetime cooling thread, this is a very effective measure. I am not using earth tubes in the traditional sense, but simply circulating cool air from inside the house and venting it inside the house. My wife in very vulnerable to mold and other indoor air chemicals and to date she's had no problems with this air tube setup in 4 houses we've lived and used it in. Please note that a critical feature of this scheme is the ability to clean the tubes which we do annually via a shop vac and simple PVC cleanouts in each tube. I don't use Airfloor any more because it can't be cleaned. I found that out years ago when one of the kids gerbils got into the airspace in the floor- never saw it again.

I think the bottom line to this whole discussion about heat gain/ comfort etc boils down to what level of comfort is expected by the client/occupants. If they expect a high degree of temperature and humidity control, then an "extreme" passive house is probably not right for them. If they are willing and able to open and close some windows and maybe insulating shades, can tolerate some moderate temperature swings, don't need air conditioning 4 or 5 months out of the year and want to save a lot on opering costs, then go for it . We used to have a saying that passive solar houses are for active poeple and active solar houses are for passive people. So I still contend that you can be comfortable with my design suggestions by ventilating in the summer and storing in the winter (even on the Chesapeake.)

I still fail to agree with the comments about overhangs protecting the siding and preventing window frames from rotting etc. Even on a single story house, a reasonable overhang only protects a small part of the siding from rain, and if you add in a little wind in a rainstorm, it will hardly protect any of it. With the quality of windows, siding, finishes and installation systems we now have, in my experience, this is really not an issue in houses that are designed, built and maintained right.


30.
Thu, 01/28/2010 - 22:21

Gerbil Motel
by John Brooks

Helpful? 1

The Gerbils check in and they never check out ;-)


31.
Fri, 01/29/2010 - 08:04

ok nuff bs now
by Cousin Ernie

Helpful? -1

enbody seen fesser rivasawng?


32.
Fri, 01/29/2010 - 12:40

From Rolf back to Pete
by Rolf Miller

Helpful? 1

Pete, thanks for the reply. Yes the floor plan sounds confusing. The addition is basically a rectangle with a triangle attached, one long side of the addition is inline with the main house wall, this joined wall faces north-east. The addition is not as wide as the main house, so a triangular room on the south-west side connects the addition and the house. The diagonal wall faces a little south of west, this is the wall with the sliding door. This wall connects to the south-west side of the addition where the 14’x5’ picture window is.

I am not sure if I am completely clear on your suggestion of a transfer grill.
Before I started this project, the main house had no insulation in the walls. The addition had 2” fiberglass in the walls, and nothing in the ceiling, it had horrible windows. So to answer your question about winter, it was always cold. It did warm up noticeably during the day when the sun was coming in the windows. We have been living in the basement since I started this project, and had to take the baseboard heaters off the walls, so I don’t know how the new windows, doors and insulation have changed things. I expect that the family room will over heat when I use the fireplace. Before, I could easily get that room from 64 degrees to 75 or 80, using the fireplace for 2 or 3 hours, in very cold weather. When you say, “moderate levels of insulation”, are you referring to the before or after? Since the walls of the addition are not complete yet, I could put up 2” of rigid foam over the studs instead of the planned 1”.

Yes I have a boiler for my hydronic heat system.


33.
Fri, 01/29/2010 - 19:26

Telling it like it is...
by Carpet

Helpful? 0

It is good to see someone else that agrees with summer overhangs. Growing up in Minnesota, June was still cool at night. It is not till the end of July was the heat becoming an issue.


34.
Sat, 01/30/2010 - 10:20

data please
by Dave Brach

Helpful? 1

Peter,

My question was: "what is the heating load on this type of hosue? " Your anwer: "I don't car for AC". I don't care for AC either, but you didn't answer my question. I am also an architect and am looking for valuable data on passive systems that I can replicate on my own projects. Knowing that you can withstand the heat (how much heat?) is not specificallly helpful for other designers. Also, there is one conspicuously absent piece of information: the SHGC of your 20%-30% south glass. A SHGC of .55 is very,very different from a SHGC of .3.


35.
Sun, 01/31/2010 - 15:14

Reply to Dave
by Pete Powell

Helpful? 0

Dave, your question was what is the cooling load and I answered that that there is none since I have no AC system. The windows in my current house were purchased in 2001 and I believe had a SHGC of .35.


36.
Sun, 01/31/2010 - 15:21

Reply to Rolf
by Pete Powell

Helpful? 0

Rolf, I would definately increase the insulation. To move any excess heat from this room, and not having a forced air system, you need to move the air to other rooms either through an open doorway or using a transfer arrangement which is an opening at the ceiling from this room to an adjacent room with a thermostatically controlled fan, You will also need a similar sized opening near the floor for relief air. This should be more than adequate since you have a relatively small glass area.


37.
Sun, 01/31/2010 - 20:24

Contrarian or just Wrong?
by Riversong

Helpful? 1

First, that red house is one of the ugliest things I've ever seen. Aesthetics might be in the eye of the beholder, but there's timeless and universal aesthetic principles that transcend personal myopia.

Second, you're using active solar systems (thermostats, fans, remote storage) and calling it passive solar. Those houses are NOT passive solar.

Third, you're completely wrong about overhangs - studies have demonstrated that significant overhangs correlate highly with durability of exterior claddings and finishes.

Fourth, if you keep moving out of the solar homes you've built, they can't be nearly as wonderful as you claim.

Fifth, I've been building passive solar and superinsulated homes for 30 years in much colder climates, I teach passive solar design and construction, and I disagree with most of your "contrarian" points.


38.
Sun, 01/31/2010 - 22:32

And then there are the future owners.
by jlbaerg

Helpful? 0

Friends, Great topic.

One of the first Passive Solar houses (1200 sqft) I built in the 70's in Montana was heated by a half cord of wood/season. Fortunately the same owner still lives there and enjoys the interaction with the weather. New owners often bring old habits, high comfort expectations and window blinds. In my experience, glare will invariably drive homeowners to cover up much of the south glass.

Fortunately, we have a new generation of glazing options so that we can architecturally respond to other design considerations. The end result should be pleasing to the eye, comfortable and extremely energy efficient. Can we all agree to document and publish annual energy costs whenever we are describing our "successful" projects? Also some mention of location and climate so as to evaluate various design strategies.

From my experience in the cold, dry north, I would agree with the deciduous tree and orientation points, but have also found a lot of value in overhangs. Fairly good solar control and building protection. Thanks for the discussion. It's brought some of us old timers out into the open.


39.
Mon, 02/01/2010 - 03:04

Earth tubes, and "energy efficiency"
by Eric Doub, GBA Advisor

Helpful? 1

I would like to hear more from Doug McEvers or anyone else who understands the main theme of his paragraph:

"I know Eric Doub and he has a different take than I do on what constitutes energy efficiency. I think the net zero energy movement could have learned a lot by studying all of the information that came from Canada and the US during the superinsulation movement. Simple is better when it comes to affordability and efficiency for that matter, square is better than long, that sort of thing."

I started looking at superinsulation examples in the early 1980s in civil engineering classes. In 2004 when it came time to create a test house of my own, with the goal of having the home annually produce as much energy as it uses, I deployed what I considered at the time to be the least-cost, simplest measures using standard materials and easily understood methods.

These measures were guided by "Build Tight, Ventilate Right, Reduce Indoor Emissions." The walls are thermally broken twice, and the ceilings and roofs once. Air leakage was brought down to a moderate NACH of 0.09. We indeed followed the two-step process of Reduce Loads, then Provide Renewable Supplies.

I am not sure what is being referred to as "gadgets," or what is meant by "constitutes energy efficiency." Living in Solar Harvest, with 5,200 HDD, we use a total of 2.2 kWh/sf/year. This usage is similar to the US single family home average (which is indeed an average, i.e., with no reference to home size). So we are not high-achievers when it comes to minimizing our kWh usage. There is no wood burning, and no gas, but there is an outdoor 360-gallon hot tub, and a steam shower.

What about that relatively unimpressive (high) usage? The PVs produce a little more than 2.2 kWh/sf/year. So by a small margin we are a net producer. The means to get to this end were indeed simple: Sensible climate-sensitive design; off-the-shelf technologies that can be installed by any competent tradespeople; and building science best practices that can be implemented by tradespeople without a huge paradigm shift or extensive retraining.

All the components of Solar Harvest that got us to zero net energy cost about 8% more than this custom home otherwise would have: PVs, solar thermal, solar storage tank, thermal break with resilient channels, higher cost windows and doors, sunspace for passive gain but with ductwork and Panasonic inline fans that use about 140 Watts to deliver about 35,000 BTU/hr.

Yes, 8%. At that level we are close to cost neutral -- what we might be paying otherwise to the utility company, we pay in our mortgage.

The current HERS 0 house we are building for clients is coming in at a little below 5%. The NREL/Habitat house in Denver was at about 8%, and the single mother of two occupant now probably has at least 5,000 extra kWh on her meter. Gadgets? Energy efficiency? I pay most attention to what is widely understandable and depoyable by the industry, and proven performance.

Oh, by the way: Solar Harvest is by far the most comfortable home I have ever lived in. And the air quality is good.

The one clear exception to the above Solar Harvest discussion is the earth tubes. We have installed them once, of our own volition, and this was at Solar Harvest. I do not recommend tubes for clients. One later home does have a tube for the fresh air intake, at the request of clients, and this is to capture cleaner air in the forest away from the nearby highway. This HERS -3 home also has a UV light. If we ever do earth tubes again, I would look into the Rehau silver-impregnated tubes. But I feel that with ERV and HRV efficiencies being fairly high, the ca. 5,000 BTU/hr of heated or cooled air we gain from the earth tubes is something we would readily go without.


40.
Mon, 02/01/2010 - 05:56

Thanks for your great post
by Martin Holladay, GBA Advisor

Helpful? 1

Eric,
Thanks for your great post.

For those unfamiliar with Eric's ground-breaking house, it includes 8.7 kW of photovoltaic modules. In most area of the country, 8.7 kW of PV costs about $65,000 to install. Right now, there is a 30% tax credit available for PV, and in some areas of the country there are utility rebates or other incentives as well.

Nevertheless, some of us still wonder whether adding $65,000 to one's mortgage will really reduce utility bills to the point that the investment proves worthwhile. The incentives help, of course -- but still ...


41.
Mon, 02/01/2010 - 06:19

Amen...it is about time
by John Brooks

Helpful? 0

Eric,
thank you for joining the discussions....please stay a while
I can not believe so few of the GBA advisors participate in the discussions.
Sharing knowledge is the BEST thing we can do.

Joe Lstiburek answered 4 questions and then backed off.
John Straube only a few comments.
Many advisors after one year.... not a single word.
I would love for my local Mentor ...Jim Sargent to chime in some times.

Martin,
Chris Miles (Dallas) just completed a net zero home and the reported cost for PV after incentives was less than $30,000


42.
Mon, 02/01/2010 - 06:44

Earth Tubes ...maybe not..probably not
by John Brooks

Helpful? 0

Condensation issues, maintenance issues, Gerbil issues

What about the attic as an energy storage container?
Attic Tubes, Garage Tubes, Crawl space tubes.......
Simple room to room ventilation...flow by design(not accident)..small ecm fans where needed

More thermal mass inside the thermal control layer

moveable shading devices?


43.
Mon, 02/01/2010 - 06:54

Simple shapes First..of course
by John Brooks

Helpful? 1

Simple shapes and careful use of glazing ....agreed


44.
Mon, 02/01/2010 - 07:27

Chris Miles' house
by Martin Holladay, GBA Advisor

Helpful? 0

John,
About Chris Miles' house:
1. What was the size (in kW) of the PV array?
2. Does he have 12 months of energy monitoring data?


45.
Mon, 02/01/2010 - 10:04

See for yourself
by John Brooks

Helpful? 0

Martin,
here is Chris' website
http://timbercreekzeroenergyhouse.com/videos.html
there is a video(2) about the pv

No there is not a 12 month history..yet

My impression is that the size of the array is a little bit science and a little bit seat of the pants....
based on other homes he has built.
This is a Building America Project


46.
Mon, 02/01/2010 - 10:26

The PV array is 9.03 kW
by Martin Holladay, GBA Advisor

Helpful? 0

John,
At the Chris Miles house, the PV array is rated at 9.03-kW. The cost to install the PV array was probably about $67,700.

If the builder and homeowner were able to get the system for only $30,000, it means that the rest of us -- taxpayers and utility rate-payers in Texas -- are helping an upper-middle-class family by chipping in $37,000 to subsidize the construction of their new dream home.


47.
Mon, 02/01/2010 - 10:36

30 K is not an official number
by John Brooks

Helpful? 0

Martin,
When I went to the presentation....
The PV guy was mentioning numbers around 30 thousand after incentives
I do not have the details...


48.
Mon, 02/01/2010 - 10:37

Eric, at least I brought you out of winter hibernation
by Doug McEvers

Helpful? 1

The point I was making is your home is not mainstream, nor do I think it is affordable or cost effective. I have a good amount of experience with superinsulated homes and the monitoring of them, and would like to see a good discussion on this site, superinsulation vs net zero energy.

I did have a discussion with Paul Norton of NREL about the Habitat House and I think they came close to hitting a home run. The ach50 was a bit high but then the work was volunteer, I think it came in around 2 ach50, 1 or less is achievable and would have helped lower the heating load.


49.
Mon, 02/01/2010 - 20:21

1/2 cord house
by Doug McEvers

Helpful? 0

jlbaerg,

Please tell us more about the 1/2 cord house, sounds groundbreaking for it's time. Interestingly enough, I was discussing over the weekend, before I read you post, the building specs. for a 1,200 sf house with off-peak electric thermal storage and I felt we could heat the house in NW Minnesota with 10,800,000 Btu's annually, about 1/2 cord. This is state of the art efficiency and you achieved it over 30 years ago, welcome to the GBA forum.


50.
Mon, 02/01/2010 - 20:46

Robert, Sorry you don't like
by Pete Powell

Helpful? 0

Robert, Sorry you don't like that house- it won an American Institute or Architects design award. I certainly would not consider a house "not passive" simply because the house air system is pulling return air through a storage mass. Putting "significant" overhangs on a building to supposedly protect the top few feet of siding is a waste of money and potential solar gain. We'll have to agree to disagree.


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