The world's awesomest (and only) passive solar home calculators

I've been doing lots of work lately on passive solar homes and sizing of HVAC systems and trying to answer questions like-- how much air can you reasonably pass through an 8 feet deep pile of loose rock?  All this is in the interest of passive solar thermal design.
There's all sorts of funky designs, such as Trombe Wall (an eponym), Water Walls, rock bin storage, direct gain, sun space, and the ever mysterious exotic phase change materials, like Crisco or Paraffin.
For the lay reader all these are means of storing solar heat during the evening hours when you most need the heat.

I've perused through all sorts of energy modeling engines, and user groups, and listservs, and any other forum I could find, to try to find the most easy to use thermal modeling engine for Passive Solar Design.

Among those that I've reviewed--

E-quest/DOE 2.1.-- No dice, as it can't really handle the second law of thermodynamics.  Energy in=energy out when it comes to thermal storage.

Energy Plus-- it looks like it can, but the challenge actually setting the down model up.  It can actually handle thermal storage, but as with anything, one would have to fuss indefinitely.

SunREL:  Now free from the NREL website.  It can supposedly do simple passive solar thermal systems, and after about 16 hours of fussing, I have yet to get a model properly working in it.

Micropas/EnergyPro:  Mostly useless in terms of passive solar and thermal storage.  Good for lots of other basic modeling tasks, especially if you're going to try to prove code compliance in California.

Spreadsheets:
Awesome.  Take a long time to set up, but they do the trick for understanding other modeling output.  Some would say that these are essential in addition to all others.

So there's-- that's a blog post!  It took 10 minutes and shows it, but still has some relevance in fact and opinion.  

File Cabinet

I'll have to revise this, but I've started making a publicly accessible filing cabinet for all the little (or big) spreadsheet calculators I create for some fairly specific energy and water modeling.

http://sites.google.com/site/fromtherepublicofroughandready/engineering-docs

Global warming potentials in spray applied foams (a work in progress)

I went to a PassivHaus seminar about a year ago, and it brought up a potentially disturbing fact about polyurethane foam in particular chemistries  in residential and commercial field applied purposes.  In the old days and occasional developing countries, these spray foams used blowing agents that have absurdly high global warming potentials. 

One might ask the question:  Is it possible for your insulation to have a higher carbon footprint than you are saving with the insulation? 
[oh, and you may have noticed that I’m posting a lot about foams lately—it’s been a hot topic, that’s all.  and I’ve been doing my research, so it’s on the brain.  I’ll get off this topic soon enough]
Proper Introduction:
I heard from someone recently outside of the South Bay who actually tried to read what I’m writing here, and really couldn’t understand much, so now I feel the appropriate responsibility to explain what the bigger picture here is so that most of you can go on caring about more important things. 
SO.  We want to save energy by insulating our houses.  There are myriad (ok, maybe not quite 10,000) ways to insulate, and all sorts of materials and such.  Spray-foam is among one of the options, which is especially nice for the building scientists among us, who like having the nice draft-free walls and roofs that the foams are pretty darn good at creating. 
Spray-applied foam in the residential industry generally comes in two flavors—open cell (aka low-density water blown foam) and closed cell (aka medium-density foam). 
The open cell foam is what most houses have, and it uses water as the blowing agent, and it releases CO2 upon curing.  Pound for pound, this CO2 ultimately doesn’t amount to much, and is generally vastly worthwhile in terms of insulating value.  
The closed-cell foam is the foam in question for this post.  It is generally among the most expensive insulation, but with stellar performance: high R-value per inch, and vapor impermeability qualities.  The closed-cell foam can’t use water as a blowing agent, unlike the open-cell—it has to use a much more finely crafted and specially tuned blowing agent in order to create its wonderful matrix of  tiny unruptured air bubbles (which is how the insulation insulates, after all). 
The standard blowing agent that I’ve heard used here in the US is HFC-245fa.   It has a global warming potential of ~1000x CO2.  That means for every pound of HFC-245fa that gets released in the atmosphere, it’s worth 1000 lbs of CO2 in terms of its impact on global warming. 
I don’t have an answer yet as to whether or not closed-cell foam is a dubious application for my particular geography, but the least I can do for now is to bring up the issue and provide a research study that gives some insight, if you’re interested. 
The chart below is pilfered from a study I really, actually want to reference and support: it shows the marginal payback (for just that one extra inch of foam) for various foams with different blowing agents. 

Danny Harvey, of the University of Toronto, created the graph, and it’s located in the study:
“Net Climatic Impact of Solid Foam Insulation Produced with Halocarbon and non-Halocarbon Blowing Agents”, Building and Environment 42(8): 2860-2879, 2007.
Link to study!
 

Radiant Floors: nice, but missing the point?

This is a variation on some points that this article effectively makes, except I'm going to be a little more academic about it: http://www.buildinggreen.com/auth/article.cfm/2010/2/1/Radiant-Floor-Heating-Wrong-Choice-for-Green-Homes/

We often think of radiant floors as inherently desirable for most projects.  For us temperate climate Northerners (and Southerners in Land of the Fuego), there’s an almost universal appeal of a very warm radiant energy source in the midst of a cold thermal environment.  It’s a neurological/evolutionarily programmed tendency.  When it’s cold, we are naturally drawn to warm things.  It keeps us from freezing to death, and therefore passing on our genes more successfully.

I’d like to suggest, here in this blog posting, that radiant floor systems are poor investments in most cases, compared to a well-insulated envelope.  Radiant floors in addition to well-insulated envelopes is good, perhaps expensive insurance. 

In most cases, radiant systems are placed into, and used most effectively (from a comfort standpoint) poorly insulated houses (e.g. Eichlers!).  The reverse is also true-- if you insist on poorly insulating the house (and that means cost-engineering out good windows) then radiant floors probably are a good way to make a comfortable environment.

Good insulation IS a good radiant floor. 
In fact, it’s a radiant house, not just a radiant floor. 
A prominent reason why we feel cold inside our homes in the winter is that the temperature of our surroundings (floor, wall, ceiling) is cold.  The same goes for feeling overheated in an air-conditioned house in the summer—the surrounding elements tend to be quite warm.

What defines comfort is that somehow the heat transfer and moisture transfer between our bodies and the local environment are in some comfortable equilibrium.  There’s LOTS of research and guidelines on this (go Bears!).  When we’re surrounded by coldness (cold walls/floor/ceiling), we need something pretty warm to balance out the energy transfer to/from our bodies.  This could be in the form of air temperature (convecting heat to our bodies) or radiant elements in our floors/ceiling.  The same goes for cooling as heating. 

For a house that has indoor wall/floor/ceiling temperatures that are fairly even around 65-75 degs, this should keep us comfortable all year long, regardless of outdoor temperature.


Radiant heating should be subordinate to insulation
The choice, in my mind, is how you provide such an even radiant environment in the floors/walls/ceiling.  One way is to not insulate well, but embed some sort of heating elements into your assemblies to counterbalance all the energy loss/gain to the outside.  You would consume a lot of energy, since all the energy you’re putting into keeping the environment the same radiant temperature leaks easily to the outside. 
The other way is to insulate really well, which should achieve the same goal 99% of the time.  In such a well-insulated system, you could go ahead and install a really expensive radiant element into your assemblies, but you’d really only be using 1% of the time.  And, who knows, that might be worth the expense—not my call. 

Fun/cheap backup heating sources
Standard practice: plug loads

In the Passive House certification program, the way they handle supplementary/backup heating is via things plugged into the walls—like refrigerators, lights, hair dryers, etc.  These all heat the house.  In a well insulated house, these are all you’d need to heat the house.  Passive House is very deliberate about quantifying these loads in their houses.  In a modern lifestyle where we leave everything on all the time, the problem is not that our house would ever get cold—it’s that it would be too hot all the time. 
Humans/Dance party?

For one of my projects considering Passive House, the backup heating was actually to just invite the neighbors over for a potluck.  Humans are roughly 200 Watt space heaters, so having a bunch of folk over for dinner would do wonders for heating the house on a cold day.  If it’s a really cold day, then maybe they would get a little dance party, and the heat from a 1 hour dance-fest should last the house for a couple of days of heating needs.