[Greenbuilding] Fw: Trying to maximize passive solar gain without investing too much....

[David Delaney]

At 12:03 PM 18/04/2007, Corwyn wrote:

>On Apr 18, 2007, at 15:56, Christa Carpenter wrote:
>
>> Can you have too much thermal mass?  I have a book that gives minimum 
>> numbers corresponding to the area of southfacing glazing, but they 
>> don't mention whether or not you can have too much.
>
>No.  On a continuously occupied building any thermal mass inside the 
>heating envelope is good.  You can have thermal mass which is too thick 
>however, so spread it around as much as possible.  It is, of course, 
>possible to have more thermal mass than you can afford.

Hmm... 

A very large thermal mass commits you to a fairly constant 
temperature, which would be wasteful of energy if the chosen 
temperature is the desired daytime temperature and you would 
accept, or desire,  a lower temperature at night.

If you have chosen to depend on reliably 
available purchased energy, you have little need for thermal 
mass, so any extra expenditure on it is wasted, or is at least only of benefit
for emergency absences of your chosen fuel, which 
could be provided for also by alternative emergency purchased
energy -- alternatives which you might evaluate on a cost basis.  

If your space heating is supplied in significant part by direct solar 
gain,  it is desirable to design the windows and 
the thermal time constant of the house together so that the 
house will not overheat during a day of good sun, and will 
cool to a desired minimum temperature by next morning, 
during the main part of the heating season, so as not to 
overheat the next day if that is also a good sun day.  This reality 
limits the solar fraction available with direct gain, and 
also limits the amount of thermal mass that is appropriate
within the living space.

David Delaney, Ottawa