GERREN D. SIMMSSHEPHERD UNIVERSITY

An Intro to the Physics of Passive Solar Design

Presenters

Gerren D. SimmsChemistry

DepartmentShepherd University

Brennen PedigoEnvironmental

Science DepartmentShepherd University

Overview

Historical Uses of Passive Solar TechnologyOrientation of the structureThermal MassInsulationWindowsOverhangs and shading

Historical Uses of Passive Solar Technology

Pueblo Architecture

Copyright(C) 1999 David Slauson. This image is copyrighted. The copyright holder allows anyone to use it for any purpose, provided that the photographer is credited.

Pueblo architecture takes advantage of the material, a mixture of earth and straw. Adobe is wonderful thermal mass: it will store warmth in the winter and it cools in the summer.

Taos Pueblo (continuously inhabited for over 1,000 years)

Built between 1000 and 1450: Thick Adobe Wall Construction

Pueblos as Green Buildings

Adobe provides a large thermal mass and it is a local green building product with healthy breathable walls

They are built with materials on siteOrientation: South-facing for passive solar gainMany adjacent units increases the energy

efficiency—all have access to the south but the other directions are protected and “insulated”

Mesa Verde

Mesa Verde

Great passive solar design principles in the Mesa Verde cliff dwellings. The southern orientation with the rock overhang means shade in the summer and solar gain in the winter. Furthermore, the rock and earth act as a thermal mass that stores the sun’s energy for use at night

During the summer months, the thermal mass serves as a heat sink to help keep it cooler

Mesa Verde

Stone covered with plaster

Assumptions at this point

You plan on building a home North of the Equator

Terms for orientation of the structure

Solar Azimuth (Ψ)- the angle of the sun from true south

Solar Altitude (α)- the sun’s angle above the horizon

Solar constant- How much sun we actually get on the building site 677 (W/m^2)

Orientation of the structure

Orient the structure so that the maximum amount of sun can get in

This includes having your house face true South that was calculated (using the solar azimuth and altitude) and using lots of windows to get the sun’s energy inside

Thermal Mass

So, now we have the sun coming in for heat, let’s keep the heat we gained in the day until the sun comes up again tomorrow

The structure’s southern side should have a large thermal mass so the sun coming into all the windows strike the thermal mass and that energy gets stored for the night

Direct Gain System

In a direct gain system, large south facing windows are used to allow the sunlight in and a thermal storage material (concrete, slate, water, brick, etc…) absorbs the solar radiation

Indirect Gain System

An indirect gain system collects and stores the solar energy in one part of the structure and uses natural heat transfer to distribute this heat to the rest of the structure

Indirect Gain System

Another example of indirect gain systems… Thermosiphoning

Math

TmcQ

Using the water as a thermal mass, how many gallons would be necessary to store enough thermal energy for 3 days of space heating? Assume the water in the storage tank begins at 150oF and has a useful lower limit of 90oF

You have already found that you need 1,440,000 Btu for 3 days

Therefore m=25000 lbs~3000 gallons of water

Tc

Qm

gallb

gallb

FFlb

BtuBtu

mo

o

05.30123.8

125000

600.1

1440000

Insulation

So far, we have worked very hard to get all the sun’s energy that we can into the structure so lets keep it there

The more insulation the better BEST- Have the structure underground with an atrium

providing the solar energy and light BETTER- Have bermed walls on three sides of the

structure GOOD- Use Structured Insulated Panels (SIPs) when

building the structure

Best- Underground

This is the best type of structure for a passive solar structure because once the sun’s energy is inside, not much of it can get out

The structure is surrounded on all sides by rammed earth (dirt), with only a Southern entrance or atrium exposed

Better- Berm it!

A bermed structure is the second best option for passive solar design

A bermed structure has earth around at least one wall to keep the energy inside the house

Good- SIPs

Structured Insulated Panels (SIPs) are panels that can be used in place of “stick built” construction.

They are attractive because they are highly insulated and easy to use, so construction labor costs goes down.

How do I figure out how much insulation I need?

First you need to figure out which degree-day region you live in

What is a Degree-Day

Here is an example of how a Degree-Day works: March 18 had a high temp of 42oF and a low temp of

20oF

18thMarch on DD343165Day(DD)-Degree

312

2042TempMean

FF oo

Ok, now what? Math

Btu 107.25

71.285,714,255000day

h24ft 3000

Fh ft 14

Btu 1

241

6

2o2

total

total

yeartotal

Q

DDQ

DDday

hourA

RQ

Assumptions at this point

You have decided to build a traditional style home using SIPs

Windows

Lots of large windows that are at least double pane on the southern side of the home

The Northern side of the home is where most of the cold and bad weather comes from so… BEST- No windows on Northern side BETTER- Few small windows on Northern side GOOD- Plant quick growing evergreen trees about 6-

10’ apart on the Northern side of the structure (This really should be done no matter what window choice is made)

Math

R

TA

t

Qk

R

TAk

t

Q

c

c

Total heat transfer for 12 hours through an insulated window that measures 4’x7’, when outside temp is 5oF and inside temp is 65oF? R value of window is 1.54

Btu100,13

)565(2854.1

Btu112

1

22

c

c

c

Q

FftFhft

hQ

TAR

tQ

Overhangs and shading

So now that we have the sun’s energy coming in and being stored and we also have the harsh elements out, let’s adjust it for the seasons using overhangs and shading.

The proper use of overhangs and shading can allow all of the sun into the structure in the winter, but block it in the summer

Overhangs strategically placed

Using Vertical Glass

Plant Deciduous Trees on Southern Side

Plant deciduous trees so they block the incoming sun in the summer, and once the leaves fall the winter sun can get through unobstructed

If you would like a copy of this you can…

Go to our linkedin profiles for a link to this slideshow http://www.linkedin.com/pub/gerren-d-simms/2a/442/2

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http://www.linkedin.com/pub/brennen-pedigo/69/813/6b5/