Passive Solar Home

[jmb_info]

Hello. My name is Glenn Kawesch and I am new to this group so I hope I am posting in the correct place. I have found the following information online about Passive Solor Homes and I am trying to get opinions on the validity of this design and implementation.

Thank you in advance - Glenn Kawesch

The following is clipped from sustainableabc.com
PASSIVE SOLAR HOME
Complete sets of building plans and specification guidelines using green and healthy materials and systems are included. Please contact us for more information.

Our first offering is a small one-bedroom home with a garage, workshop or studio, which can be converted into a second bedroom suite if desired.

I have always been fascinated with the idea of going outside to get from the bedroom(s) to the living space. In relatively benign climates this is a very viable scheme.

The home is depicted with a standing seam steel roof but a Spanish tile option is also available.

The home is heated and cooled by a sun-facing passive solar Trombe wall system. During the heating season the heat collected in the Trombe wall solar room is pumped into the home. For cooling vents are provided and the system using convective airflows "pumps" heat out of the home.

In difficult climates a ground source or geothermal heat pump system is highly recommended.

The structural system is a type of Structural Insulated Panel. These panels have a 5" EPS (expanded polystyrene) core with 1½" sprayed on concrete each side, giving a panel thickness of 8". These panels are stronger, more durable, and considerably more energy efficient than wood or steel stick framing methods and as an added benefit they reduce construction time.

This construction system is approved by Building Officials in the USA - so there will not be unusual problems getting a building permit for this building system ( added by Glenn Kawesch: my city will actually cut me a break because I am trying to be eco friendly ). Structural Engineering for the above ground portion of the home is included with the plans. Foundations will require local soils reports and local engineering.

Glenn Kawesch

[lekizz]

Very enterprising of the guy! It looks like a pleasant little home. But like you suggest, you would need to be somewhere sunny like CA for it to work well.

Quite surprised the primary construction material is expanded polystyrene, considering the ethos is to use sustainable environmentally benign materials. And I would have thought that more than 1.5 inches of concrete would be desirable to add some thermal mass to the building.

[gleearch]

Sustainable houses tend to be site specific. It's great that this person is marketing a one size fits all approach. Very entrepreneurial of him.

Before plunking this design down on your site, you need to ascertain if your site actually works with the design. Are there trees blocking the sun on the south side, do the slopes work against it, etc.
Are there great views to the south? In which case your trombe walls will end up blocking those views. There are many other methods to use passive solar besides trombe walls. You could insulate your slab below grade, thicken it up or use appropriate tiles and have the sun heat it up through your windows. Some designers have used water filled tubes as trombe walls (allows in light but still has privacy).
8" of thermal mass is a sort of rule of thumb.
The 8" walls they are describing are just the exterior shell and are not part of the trombe wall, or shouldn't be.
if you are going to apply shotcrete to the EPS (it has no urea or formadelhydes, which is why it has seen use in some types of "green" buildings), why not consider using straw bale? You can stucco or shotcrete it. It's environmentally friendly, you are recycling agri waste, has fantastic insulating properties and many of it's supposed problems like mice habitating in it, etc are fictional. Concrete can be specified with a higher content of flyash to increase usage of recycled materials and reduce the amount of cement needed.
A quick summary of different systems can be found here. There are better resources but this is a simple explanation for insulation.

http://www.aerias.org/DesktopModules/ArticleDetail.aspx?articleId=95
It might help if you buy his design to also obtain his expertise in helping you conform the design to your site. You might end up rethinking certain design features or materials by looking at the region you are building in. Local quarries, recycled building materials, local building materials or artisans, alternative materials etc.
Sounds like a fun project.
Good luck and have fun on it.

[csintexas]

I agree with gleearch that the suitability of that plan depends on your site.

Other than that it looks like a very costly design to implement.

I read recently that 1.5 inches of thermal mass on the interior of an insulated wall is the maximum that would be effective because of the time it takes to get energy in and back out of more but I am not an expert and the book was on designing for hot humid climates.

[gleearch]

Thermal mass works on the principal of materials of low thermal transferance but of large mass having the ability to retain heat over time and subsequently releasing it.
Using thermal mass in a home means having a material that has physical properties like these. Stone, concrete, water, CMU, bricks etc have these abilities. How much you need really has to be calculated based on their physical properties.
For concrete and similar materials, 8" has been the rule of thumb.
It does seem a little interesting that an article states that 1.5" is sufficient, could you tell us which publication this is? I would like to read it myself.

Thermal mass is used effectively where there are broad swings in temperature throughout the day. Mediteranean climates, deserts etc are some examples. It is still effective in other climates, but you have to adjust for it. This implies that the sun heats up the thermal mass during the day. The mass will absorb the energy from the sun slowly over the course of a day (since tthe heat is slowly distributed evenly within the mass), then when evening comes and the temperature outside falls, the heat within the thermal mass is slowly released to the environment. The thermal mass is being utilized to maintain a stable temperature within the building. Used incorrectly it can result in a building that is too warm, especially in the summers.
Recent trends in two level loft condo (concrete) buildings with large south facing glazing are an example of this. The units tend to be overly hot in summers and they never need to use their heaters in the winter, rather some have to pull in outside air for cooling even in the winter.
Make sure your passive solar strategy is well thought out and designed for your specific site and climate.

[csintexas]

the book is:

BUILDERS GUIDE TO HOT HUMID CLIMATES http://www.eeba.org/bookstore/books.asp?CatID=1

The recommendation was specifically for insulated wall structures and not full masonry.

The idea is that you have a 12 hour cycle on average where you are storing energy part of the day and then releasing that energy the other part. Any thicker and it becomes difficult to change the core temperature within that cycle. Also that more surface area is generally easier to store and retrieve energy from than having a lot of mass in in a thick wall.

I may be wrong but one slight change I would make to your last post is that sun shinning directly on the thermal mass is not is not a key factor in using thermal mass rather it is the temperature difference between the air and the thermal mass. For example: if you have sun shinning on a wall which is exposed to 30 deg. air most of the energy will go into the air and not into the wall.

[Antisthenes]

the concept is the same, the overhangs shading and other specifics are not.

[Sol Actevo]

I find this thread very interesting, I'm developing a new way of controlling the heat that enters a house via varying the pitch angle of a veranda/porch/patio using a pair of telescoping veranda posts.
Depending on where you live and the seasonal variation in the temperature this may or may not be a big deal, but here in Australia, (the med is the same) there is a massive advantage in letting the winter sun stream deeply into the house whilst providing a cool shaded space in the summer heat.
As a reformed mechanical engineer I was surprised by the lack of simple dynamic products on the market that could make such a massive difference to the energy consumption of a house and so I designed one.
I would love to hear from someone who feels that something like this can really be a positive for new homes that aren't "Mc Mansions"
Cheers
Jason
www.solactevo.com.au

[csintexas]

Looks like a good idea to me Sol Actevo.

I have toyed with similar ideas over the years.

Making adjustable struts would be simple enough, making the flashing joint be adjustable and work well would be critical.