passive solar design and concepts - queen's universitymy.me.queensu.ca/courses/mech4301/passive...
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Winter
Summer
Passive Solar Heating
Good architecture?
The judicious use of south glazing coupled with appropriate shading and thermal mass.
Passive solar
• Direct (or indirect) gain of solar energy through windows or in attached sun-spaces for space heating
• high performance fenestration and/or transparent insulation
• application of thermal mass for storage and to reduce overheating
• can include natural ventilation
• design for maximization of natural Daylighting
• Apply design principles to increase heat gain and reduce cooling loads
Good architecture and energy conservation!
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Sun Position and Chart
Seasonal Variation in sun-altitude
Solar Radiation Definitions
Global solar irradiance
and its components
The radiation from the sun that meets the earth without any change in
direction is called direct or beam radiation, Gdir.
The radiation from the sun after its direction has been changed by
scattering in the atmosphere is called diffuse radiation, Gdif.
The radiation from the sun after it is reflected on the ground is called the
ground reflected radiation, Gref.
The sum of the beam, diffuse and reflected solar radiation on a surface
is called the global solar irradiance, GG.
GG= Gdir + Gdif + Gref
From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK
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Solar Spectrum
Sun spectrum AM 0 in space and AM 1.5 on the earth with
a sun elevation of 41.8o
From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK
Solar irradiance outside atmosphere
Direct solar irradiance at sea level
Solar Radiation
Global solar irradiance and its components with different
sky conditions
From “Planning and Installing Solar Thermal Systems”, James & James/Earthscan, London, UK
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Direct or Indirect Passive solar Gain
www.greenandpractical.com
Direct gain Indirect gain
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www.homepower.com
Traditional Passive Solar Design (Direct Gain)
http://www.solar365.com
• Direct Solar Gain –South Glazing (clearstory windows)
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Passive solar design at York University
Passive Solar Heating
Mass walls and (transparent) Insulation
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Passive Solar Heating/Cooling
Fenestration
The location and operation of shading
Interior Shade
Exterior Shade
Attached Sunspaces
Attached Sun Space
Photo Credit: Pamm McFadden (NREL Pix)
Passive Solar Heating on Residence, France
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Mass Wall
Indirect Passive Solar Concepts
Trombe Wall (Indirect Passive Solar)
http://www.smartshelterresearch.com/23-passive-solar-schools/
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Storage Walls
A storage wall (e.g. Trombe wall) is a sun-facing wall built from
material that can act as a thermal mass (such as stone, concrete,
adobe or water tanks), combined with an air space, insulated
glazing and vents to form a large solar thermal collector.
During the day, sunlight would
shine through the glazing and warm
the surface of the thermal mass. At
night, if the glazing insulates well
enough, and outdoor temperatures
are not too low, the average
temperature of the thermal mass
will be significantly higher than
room temperature, and heat will
flow into the house interior.
From “Solar Engineering of Thermal Processes”, Duffie & Beckman
Energy flows through direct-gain vs collector storage wall as a function of time of day
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Passive Solar Examples
Involves the direct use of sunlight for daylighting and space heating
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Canadian Energy Rating System
Canadian Energy Rating System was designed to show the average heating season thermal performance of windows. The Energy Rating procedure is incorporated in the Canadian Standard A-440.2-98, “Energy Performance of Windows and Other Fenestration Systems.” The Energy
Rating (ER) combines the effects of U-value, SHGC and air leakage characteristics of windows.
ER = solar heat gains – conductive heat losses – air leakage heat losses
ER = 0.8 * 72.2 * SHGCw – 21.9 * Uw – 0.54 * (L75 / Aw)Where,
ER is Energy Rating, W
SHGCw – Solar heat gain coefficient of a window
• The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 1/8" (3.1 mm) uncoated clear glass has an SHGC of approximately 0.86, of which 0.84 is direct gain (solar transmittance) and 0.02 is indirect gain (convection / re-radiation). – (See more at: https://www.guardian.com/commercial/ToolsandResources
Uw – Overall heat loss coefficient, W/(m2oC)
72.2 represent the average solar radiation on a vertical window during the heating season, (W/m2)
0.8 factor is to account for exterior shadings on windows.
21.9 represents average temperature difference over the heating season.
Canada has a variety of weather patterns – ranging from mild climate in southern BC to very cold northern regions. Therefore, there have been a number of situations arising in certain mild regions as well as with window designs in which the ER values do not seem to reflect the use of better fenestration technologies (such as low-E, argon-filled, insulated spacer and so on). This has been identified as a major obstacle in acceptance of the Energy Rating system. Again, the issue is not the technical soundness of the ER equation but the proportional contribution of the solar effects and insulating effects. Manufacturers can voluntarily rate energy performance of windows using the services of Canadian Standards Association.
See also https://en.wikipedia.org/wiki/Solar_gain
Passive or Active?
Mass
Wall
OOPS! No storage
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Simple Example Model
Polystyrene Insulation
Double Pane Vertical Window
Concrete Patio Stone Floor (painted black)
Why Store Energy?
• solar energy is a time-dependent energy resource
• load does not match available energy
• cost consideration (avoid peak use)
• short term or long term storage
A solar energy process with storage. (a) Incident solar energy, GT, collector useful
gain, QU, and loads, L, as a function of time for a 3 day period.
From “Solar Engineering of Thermal Processes”, Duffie & Beckman
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Air Based Thermal Storage
An air based thermal storage
(e.g. Solarwall, InSpire Wall)
pre-heats the outside air
before it enters the building to
provide fresh air changes and
natural humidification.
Source: http://www.rockymtsolar.com/ Source: http://oee.nrcan.gc.ca/
Packed-bed Storage
A packed bed is a large insulated container filled with
loosely packed rocks a few centimeters in diameter.
Circulation of air through the void of the packed bed
rocks results in natural or forced convection between
the air and the rocks.
From “Solar Engineering of Thermal Processes”, Duffie & Beckman
Direction
of flow
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Modes of Operation
From “Solar Energy Engineering”, Jui Sheng Hsieh
Mode 1 – Charging Mode
When the sun is shining but there is no space heating demand, hot
air from the collector enters the top of the storage unit and heats up
the rock bed. As the air flows downward, heat transfer between the
air and the rocks results in a stratified temperature distribution of the
rock bed, being the hottest at the top and the coolest at the bottom.
The cool air then returns to the collector to be heated.
Charging Mode
From “Solar Engineering of Thermal Processes”, Duffie & Beckman
High stratification due to high heat transfer coefficient-area
product, UA.
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Modes of Operation
From “Solar Energy Engineering”, Jui Sheng Hsieh
Mode 2 – Discharging Mode
When no solar energy can be collected but there is a heating
demand, hot air is drawn from the top of the rock bed into the house
and cooler air from the house is returned to the bottom of the bed,
causing the bed to release its stored energy. (Note: Charging and
discharging a pack-bed storage cannot be executed at the same
time! This is in contrast to water storage systems.)
Modes of Operation
From “Solar Energy Engineering”, Jui Sheng Hsieh
Mode 3 – Auxiliary Mode
When there is sunshine and at the same time load demand, hot air from
the collector is led directly into the house and cooler air from the house
is led directly into the collector, both bypassing the storage unit. The
auxiliary heater shown in the figure can be used to remedy the energy
deficiency of the collector or the storage to meet the loads. Through the
by-pass route, the auxiliary heater alone can be called upon to meet the
entire energy demand.
100%
Auxiliary
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Horizontal Flow Rock Bed
From “Solar Energy Program, A Guide to Rock Bed Storage Units”, Enermodal Engineering Limited
Baffles (used to
increase flow path)
Sensible Heat Storage Materials
From “Solar Energy Engineering”, Jui Sheng Hsieh
* Water has three times the heat capacity of rock on a volume basis,
meaning that rock requires three time more volume than water to store
the same amount of sensible heat!
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Energy CalculationsEnergy Equation: Energy needed to heat hot water is Q
Q = Vol x Density x Specific Heat x Temperature Rise = kJ
Or
Units Check
Q = (L) x kg/L x kJ/kg°C x °C = kJ
The (constant pressure) specific heat of water or Cp is the amount of energy (KJ) required to heat one Kilogram of water 1 degree Celcius or (Kelvin). This value is not constant but varies slightly with temperature, e.g.,
Properties of Water
955
965
975
985
995
1005
0 10 20 30 40 50 60 70 80 90 100
Temperature, oC
De
ns
ity
, k
g/m
3
4.15
4.16
4.17
4.18
4.19
4.2
4.21
4.22
4.23
4.24
4.25
Sp
ec
ific
He
at
(k
J/k
goC
)
993.4 kg/m3
4.181 kJ/kg oC
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Range
Specifc heat and density of water
For our purposes, over the temperature range considered, we can assume the value of thespecific heat and density of water is effectively fixed at the average values given above.
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Example Cal’c.
• Example: What is the energy required to heat a 270 L tank from 15°C to 55°C
• For this example the following is assumed to be true: • The density of water is 0.993, Cp = 4.181
• (1 litre of water is equal to 0.993 kg)
• The price of electricity is $ 0.35 kWh
• 1 Joule is equal to a Watt second (i.e., J = Ws)
• ∆T = 40
Q = 270 L x 0.993 kg/L x 4.181 kJ/kg°C x 40°C
= 44,838.7 kJ or 44.8 MJ
In kilowatt hours this much energy is:(Note that one Joule of energy is a Watt of power operating for one second or a Ws)
Therefore
Q= 44,838.7 kJ = 44,838.7 kWs
= 44,838.7 kWs x( 1 hr/3600 s)
= 44,838.7/3600
= 12.45 kWh
At an electrical energy cost of $035/kWh, this energy costs:
Cost = $035/kWh x 12.45 kWh = $4.35
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Phase Change Storage
When a substance undergoes a solid-liquid phase transition,
it usually involves a large amount of latent heat with a small
volume change.
A phase change storage would be a space-saver if it
satisfies the following conditions:
1) the phase transition must occur at a temperature
compatible with the heating and cooling load requirement
2) the process must be reversible over a large number of
cycles without degradation
3) the material must be inexpensive and can be used safely
A few salt hydrates (salts bonded to water molecules)
possess the desired qualities to serve as phase-change
materials (PCMs).
For Phase Change
v
Temperature
En
tha
lpy
Dh