SB: Re: Passive solar SB designs

[Rob Tom <ArchiLogic@yahoo.ca>]

 9/28/02 5:49:41 PM, Rene Dalmeijer <rened@cistron.nl> wrote:

>Keith,
>
>No tar and feathers just a few observations.
[snip]

>,"Keith Rowe" <keithrowe@ezpost.com> wrote:

>>My question is this: Is there ever really a net energy
>>GAIN, over the course of a year, by using the concept of windows
>>to heat our homes?
>>
>>1)Windows are a huge sucker of energy, or at least they are at
>>my latitude.... ... I built the frames myself. But do the math. On a
>>SUNNY December the 21st I get about 2 1/2 hours of energy
>>coming in of any beneficial amount from the sun, but for 24 hours
>>of that day I have energy being sucked out of a big, R-6 surface
>> in an otherwise R-40 house

Keith, EuroRay and Twirling-House-on-a-stickHeads;

No tar and feathers from me either. 
I'm a cream-pie-in-the-face kinda guy.

Building an energy-efficient house which is able to get most of its 
heating load requirement from passive gains (and avoid the necessity 
for A/C  in the summer ) is not unlike cooking.

One cannot expect to simply toss all of the ingredients into a pot (or in 
the case of a house,  toss in a truckload of bales for super-insulated 
walls, a pallet of low-E glass for superwindows, etc)  , stir it up, and 
expect  to get a delicious meal or a well-performing house as a result. 

In the hands of an unskilled chef, it would be entirely possible to end 
up with something akin to a dog’s breakfast instead. 

As with cooking, there are certain techniques which are 
learned/developed through experience which come into play and will 
affect the outcome.  Unfortunately, there are also plenty of  
experienced “professionals” who haven’t learned them even after a 
lifetime of building.

First of all, I would suggest that if  one is getting only 2.5 hrs of
sunlight through the windows on Dec 21, that those  windows are not
aimed at true south. 

In order to take full advantage of potential gains, the long axis of the
house should be oriented east-west such that the N-S axis (ie the 
passive solar gains windows) is within 15 degrees of true south, with 
a minimum of glass area on the non-equator-facing elevations. 
Then, the equator-facing glass should be provided with an 
unobstructed   view of the sun for at least the hours between 10 am 
and 2 pm,  when the majority of the useful gains will take place.
There are very few places in Canada which would not be able to do 
the above. 

Second, simply catching sunlight is easy. Hanging on to it (or 
excluding it when it's not desirable in the summer) is less
so.

In a super-insulated house, heat loss via air infiltration & exfiltration 
can account for up to 50% of the total heat loss. Was the house in 
question constructed to be air-tight ? 

And if it was, and assuming that a means was provided to ensure a 
supply of fresh air to the living space, what is the efficiency of the heat 
recovery from the exhaust air stream ?

ie The total volume of the heated and conditioned air within the house 
should be replaced with fresh outdoor air every 2.85 hours at a
minimum (according to the minimum ASHRAE standards) or in other 
words, when it's  minus 40 degrees outside,  you have to heat an 
amount of air ( at minus 40 degrees) equal to the entire volume of  the 
house, and bring it up to room temperature, at least once every 2.85 
hours.   

Moving on to windows…

In Canada, windows are rated according to the "ER" system, or its
more specific cousin the "ERS" system. 

The "ER" system provides a single number rating which has been
generalised  so the rating will be applicable for a particular window in 
any location in Canada and for placement in any compass orientation. 
This would be not unlike like the gasoline mileage rating for an 
automobile. (ie mileage may vary according to ...) 

The ERS rating looks at the window’s performance for a specific 
location and compass orientation.

An ER rating of minus 15 (not unusual for double glazed windows) 
means that the window will yield a net energy loss of 15 watts per
square metre. The rating accounts for solar heat gains , heat loss
through the glass AND frame AND edge spacers AND air leakage.

There are windows made in Canada which have a positive ER
number, some with a rating higher than +8.

The ERS number for the same window, placed in a south-facing
orientation will of course, be significantly higher.

[So, in answer to Keith's question "Yes, even in Canada".]

Then there's the question of  actual R-values of the building’s 
components. ie Were they detailed to minimise thermal bridges and 
convection currents so that nominal R-40 components are actually 
yielding something close to R-40 instead of  effectively being R-10  or 
less ? (it happens)

Or what about the house volume ?  Is the house overly large in
relation to the amount of sun-facing glass  provided ? To use the 
automobile analogy again, sticking a fuel-efficient VW TDI engine into 
a Greyhound bus probably won’t yield very satisfactory performance.

The bottom line is that it is entirely possible to build a house in 
Canada which gets 50% or more (even 75% wouldn't be too 
unreasoanble to ask) of its heating load requirement from passive 
gains and accomplish it without making it a knob-twiddler's delight 
looking like someone's Grade 8 science experiment and without 
having to run around like a mad banshee at sundown and sunrise .

       ~~~ * ~~~
         Rob Tom
  Kanata, Ontario, Canada
<ArchiLogic@CHAFFyahoo.ca>
(winnow the "chaff" from my edress in your reply)

Please visit http://www.theHungerSite.com daily

     




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