Scaling API-first – The story of a global engineering organization
MATERIALS FOR PASSIVE SOLAR HEATING
1.
2. It is one of several design approaches collectively called
“Passive Solar Design”.
Typically, passive solar heating (PSH) involves:
The “collection of solar energy” through properly-oriented,
south-facing windows.
The “storage of this energy in thermal mass," comprised of
building materials with high heat capacity such as
concrete slabs, brick walls, or tile floors
The “natural distribution of the stored solar energy back to
the living space”, when required, through the mechanisms
of natural convection and radiation
“Window specifications” to allow higher solar heat gain
coefficient in south glazing.
3.
4. 1. Aperture
(Collector)
2. Absorber
3. Thermal mass
4. Distribution
5. Control.
5. The APERTURE (collector) is a large glass (window) area
through which sunlight enters the building.
The hard, darkened surface of the storage element is known as
the ABSORBER. This surface sits in the direct path of sunlight.
Sunlight then hits the surface and is absorbed as heat.
The THERMAL MASS is made up of materials that store
the heat produced by sunlight.
Distribution is the method by which solar heat circulates from
the collection and storage points to different areas of the
building.
Elements to help control under- and overheating of a passive
solar heating system include roof overhangs, which can be
used to shade the aperture area
6. The orientation of the APERTURE.
Thermal mass location.
Insulation and air sealing.
Local climate conditions i.e. seasonal variation of sun shine.
7. The material should act as a “HEAT STORING MEDIUM”.
The heat should flow from one end of the wall to other end of
this THERMAL MASS, only after 12 hours.
Materials should be having nominal thickness.
The material should be cheap, and the thermal energy stored
per unit material cost, should be maximum.
8.
9. 1. The heat content “Q” per unit area of the wall,
Q = w ρ Cp ΔT
where,
ρ Cp = Specific heat per unit volume
ΔT = Temperature interval
2. The time constant (t) is estimated by the approximation used
for the heat-diffusion distance in time t,
w = (2 α t)1/2
where, α = diffusivity
11. Hence, the heat capacity of the wall is maximized by choosing
material with a high value of,
M = [ λ / ( α )1/2 ]
6. But, we have assumed a material thickness restriction of
w ≤ 0.5 m & t = 12 hrs. = 4 * 104 seconds. So, along with the
above material property another attribute to be looked upon
is,
α ≤ 3 * 10 - 6 m2/s
12.
13. Area of the Graph,
between Thermal
conductivity (λ)-
Thermal diffusivity
(α), representing
the materials
satisfying the
requirements.
14. The materials satisfying the graphs are,
1. Epoxies
2. Brick
3. Soda glass
4. Concrete
5. Stone
6. Ti alloy
The materials as can be seen are only SOLIDS and not the
POROUS MATERIALS & FOAMS (generally used in walls).
Finally, the materials are selected on the basis of their cost per
unit volume.
15. M1= λ/√α Approximate
Materials Comments
(W.s1/2/ m2.K) cost ($/m3)
Concrete 2.20 * 103 200 Best choice
Better than concrete,
Brick 3.50 * 103 1400 due to more specific
heat.
Glass 1.00 * 103 1400 Not as good as concrete
Stone 1.60 * 103 10,000 Useful in some cases
Titanium 4.60 * 103 2,00,000 Unexpected but valid.
