[Strawbale] Passive Heating

[Robert Tom]

On Sun, 30 Dec 2007 13:24:02 -0500, Ilan Ungar <adrihalut at gmail.com> wrote:

> Israel (5-15 Degrees Celsius in the heating season)

> Sounds like this definitely rules out large areas of glass on the South
> facade as these surfaces will drain all the houses heat overnight...?

Ilan;

I'm afraid that I don't know much about the climate of Israel other than  
the fact that it is quite varied (thanks to Sarah Kopp for that bit of  
knowledge) but I'm about 30 kms from the centre of Ottawa, Ontario, Canada  
and one of the labels that is often attached to Ottawa is that it is "The  
Coldest Capital on Earth".

A little more specifically, at my locale which is outside of the urban  
area and hence, slightly cooler (we lag about two weeks behind the urban  
area for blossoming in Spring) the climate was (ie before Global Warming)  
about 8750 heating degree-days (degF) per year
(4861 HDD/yr, degC).

My mental image of Israel (whether accurate or not) is that it's a bit  
like Texas, USA.
Taking a quick look at some climatic data for selected Texas locales, I  
see that the range is 617 HDD/yr (343 HDD/yr degC)(Brownsville TX) to 4345  
HDD/yr (2414 HDD/yr,degC) (Amarillo TX)

I haven't kept track of the temperatures for the past few days (it hasn't  
been particularly cold, certainly warmer than a couple of weeks ago) but  
it has been snowing a bit,  overcast a lot and there's about 800mm of snow  
on the ground in open areas.

And the punch line to all of the above is that I can't remember the last  
time that I lit the woodstove (the only auxiliary heating device that I  
use, other than appliances and lights) in my home. It was probably around  
Christmas.

Passive heating and cooling play very large roles in maintaining  
comfortable temperatures year-round in this 22-year-old building (ie in no  
way "cutting edge"), in this climate (ie twice as cold as the coldest  
locale in Texas)... which is to say that if the climate of your locale in  
Israel is in fact, similar to or warmer than that of Amarillo Texas, then  
passive solar heating should be able to provide 100% of the building's  
heat load requirement *iff* (in the mathspeak sense) the building
	(i) is sufficiently insulated,
	(ii) is competently air-sealed,
	(iii) has a moderate amount of fenestration and has the
	      majority of that area oriented to take advantage
	      of direct solar gains during the heating season
	     (and shaded to prevent unwanted gains the rest of the time)
		and
	(iv) contains moderate amounts of thermal mass inside of the thermal  
envelope.

I can also tell you that my neighbour's similarly-sized house  
(built-to-Code, not superinsulated/air-tight, not designed to be  
low-energy) experienced a heating bill of about $1600 last year (according  
to the Boss of that household in a over-the-pool-railing conversation).

But getting to the answer to your question, one of the most common  
mistakes that people make when designing "passive solar" buildings is that  
they incorporate far too much equator-facing glass and then to compound  
that mistake, fail to incorporate overhangs that will provide 100% summer  
shading for that glass area.

The result is that during the day in winter when the sun is shining, the  
house interior overheats and/or subjects the house occupants to fried  
brains and glare-blinded eyes and then at night, suffers from massive heat  
loss through all of that glass -- basically horrible buildings in which to  
live.

The three most important things to do when making a passive solar building  
are:

	(1) Insulate
	(2) Insulate
	(3) Insulate

The next three most important things to do are:

	(4) Air-seal
	(5) Air-seal
	(6) Air-seal

Once these are done, the building's heat load is reduced to the point that  
solar gains through normal-sized windows (ie no more or less than the  
"conventional" house next door) plus occupancy gains will provide the  
majority of that load requirement.

Ed Mazria's classic (ie 1979) "The Passive Solar Energy Book" was and  
still is one of the best resources on the subject of passive solar design.  
The information therein simply needs to be updated a bit to account for  
Y2K+7 superinsulation and air-tight construction practises.

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at chaffY a h o o  dot  c a >
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