ASSIGNMENT PRESENTATION

PASSIVE SOLAR HEATING

PRESENTED BY:-SWAPNIL NIGAM

PASSIVE SOLAR HEATING???

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.

PRINCIPLE DIAGRAM OF “PSH”

KEY COMPONENTS OF “PSH”

1. Aperture

(Collector)

2. Absorber

3. Thermal mass

4. Distribution

5. Control.

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

The orientation of the APERTURE.

Thermal mass location.

Insulation and air sealing.

Material required for thermal mass.

Local climate conditions i.e. seasonal variation of sun shine.

REQUIREMENTS OF “PSH” DESIGN

MATERIAL REQUIREMENTS OF “THERMAL MASS”

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.

TABULATION OF REQUIREMENTS ACC. TO MATERIAL SELECTION PROCESS

ATTRIBUTES REQUIREMENTS

Function Heat storing medium

Constraints• Heat diffusion time ≈ 12 hours• Wall thickness ≤ 0.5 m• Adequate working temperature Tmax.> 100°C

Objective Maximize thermal energy stored per unit material cost

Free variables • Wall thickness, w• Choice of material

THE TRANSLATION INTO MATERIAL INDICES

1. The heat content “Q” per unit area of the wall,

Q = w ρ Cp ΔTwhere,

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

3. On eliminating the free variable, w,

Q = (2 α t)1/2 ρ Cp ΔT

4. Using,

α = λ / ρ Cp

5. Finally, we obtain,

Q = [ (2 t)1/2 ] [ΔT] [ λ / (α)1/2 ]

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

THE SELECTION OF MATERIAL

Area of the

Graph,

between Thermal

conductivity (λ)-

Thermal

diffusivity

(α), representing

the materials

satisfying the

requirements.

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.

Materials

M1= λ/√α (W.s1/2/ m2.K)

Approximate cost ($/m3) Comments

Concrete 2.20 * 103 200 Best choice

Brick 3.50 * 103 1400

Better than concrete, due to more specific heat.

Glass 1.00 * 103 1400Not as good as concrete

Stone 1.60 * 103 10,000Useful in some cases

Titanium 4.60 * 103 2,00,000

Unexpected but valid.

THANKYOU