Helpful? 0

Slab dimensions for passive solar

I found the following answer and need clarification on the last paragraph. When Robert Riversong says " floor area", does he mean the whole floor area of the house or just the floor that could be exposed to sunlight?

For both radiant thermal mass and passive solar thermal mass, the ideal thickness of a poured concrete slab happens to be exactly the same as the industry standard for residential applications: 4".
For reasonable response time, it's best to have radiant tubing at about 2" from the slab surface. Heat conducts through concrete at approximately 1 hour per inch. So a 4" slab will absorb and release solar heat during an approximate 8-hour cycle. This corresponds well with absorption during the heat of the day (noon) and release by early evening when the sun is down and the house is cooling.
For passive solar thermal mass, the area of slab in direct sun relative to the area of south glazing is the more important factor. Since a sun-tempered house (5%-7% of floor area in south glazing) requires no additional mass, a passive solar house (7%-12% of floor area in south glazing) requires approximately 6 sf of 4" thick thermal mass for each square foot of south glazing beyond 7% of floor area. Mass not in direct sun is 1/3 to 1/2 as efficient as a storage medium.
ANSWERED BY ROBERT RIVERSONG
Posted Mon, 10/12/2009 - 21:06

Asked by Christa Campbell
Posted Tue, 02/21/2012 - 00:12

Tags:

1 Answer

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.
Helpful? 0

Christa,
Q. "Does he mean the whole floor area of the house or just the floor that could be exposed to sunlight?"

A. The whole floor area of the house -- although the formula works better for homes with a relatively open floor plan (and a shape assumed to be rectangular, with the long dimension being east-west).

Answered by Martin Holladay, GBA Advisor
Posted Tue, 02/21/2012 - 06:12

Other Questions in Green building techniques

Roxul for insulating and air sealing finished condo

In Energy efficiency and durability | Asked by Kalim Saliba | Oct 30, 14

Steel frame home insulation

In General questions | Asked by J B | Oct 28, 14

Closed crawlspace with dehumidifier and foundation insulation

In Energy efficiency and durability | Asked by Michael Geoghegan | Oct 27, 14

Radon mitigation or ERV for old home with dirt wall basement

In General questions | Asked by Scott Van Der Veer | Oct 30, 14

A very low addition...

In Energy efficiency and durability | Asked by ron letourneau | Oct 29, 14
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!