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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
96/
http://www.linkedin.com/pub/brennen-pedigo/69/813/6b5/