PDX_06_Building Systems And Their Integration Flashcards
Ratio of solar heat gain through fenestration,
/ to total solar radiation incident
(falling upon/striking) glazing.
0.0-0.87 values
Solar Heat Gain Coefficient (SHGC)
Lower values shade more.
Less than 0.4 is recommended in a warm climate.
Ratio of solar gain @ glazing product,
/ solar gain @ unshaded 1/8” thick, clear, 2xstrength glass (under the same set of conditions)
(0.0-1.0)
Shading Coefficient (SC)
SHGC is considered more accurate
Solar heating or cooling system,
Uses no external mechanical power.
(to move the collected heat)
Passive system
Solar heating or cooling system.
Requires external mechanical power.
(to move the collected heat)
Active system
Annual Fuel Utilization Efficiency
AFUE
displayed on furnaces manufactured in USA
Sunlight transmitted through glass into bldg,
materials inside heat up,
and reradiates in infrared spectrum which doesn’t pass back through glass,
it’s trapped inside the building warming it up
Greenhouse Effect
Tendency of gas/air to rise in a vertical shaft,
because density < surrounding gas/air
Stack Effect
Chimney effect
The purpose of high mass cooling.
Facility for rejecting heat accumulated by bldg.
Heat Sink
The extent solar design reduces bldgs heat requirement,
relative to ref. energy conserving building.
Solar Savings Fraction (SSF)
Materials used to store/release heat
by latent heat capacity.
Melt + solidify in normal solar operating temperature range of 80-160°F
Eutectic Salts
For every vertical ft. of window,
this overhang distance
for shading.
6” per vertical ft.
Thermal mass materials should not exceed this thickness
6 inches
Insulating vs. insolating
Insulating: protection from heat loss
Insolating: exposing to suns rays
Ideal ratio of mass to glass is typically
3:1
Every 3 ft.² of mass allows 1 ft.² of southern facing glass
1 inch of mass produces this many hours of heat lag
One hour
Decoupled mass is this,
and requires this mass to glass ratio.
Sun travels through the space to get to mass.
Requires 10:1 mass to glass ratio.
Thermal mass located between sun and living space.
Radiation strikes thermal mass, transfers to space,
w/o light coming through.
Indirect Gain Systems
Thick walls placed in sunlight, often behind glazing.
Store solar energy w/o increasing bldg temp,
slowly release when needed.
Mass Walls
Convection loop is added to mass wall
(airspace between mass / glass skin)
1way vent @ top lets warm air into room,
1way vent @ bottom lets cold air into airspace.
Thrombe Wall
Water stores this much heat per pound,
in relation to concrete.
5 x
Tank (or collection large vertical tubes) filled w/ water,
@ window, allowing partial light into space.
Water Wall
Mass in shaded portion of room,
heated by reflected sunlight / warm air in room.
Indirect Gain Space
Roof Pond best used in this climate.
Low humidity climates
Example: the southern United States
Roof Pond process
6 - 12” of water or contained on a flat roof in large plastic containers covered by glazing. Spaces blower warmed by radiant heat from the water above.
4’x8’ insulated glass box w/ piping manifold connected to black metal plate.
Solar energy collected @ flat plate, transfers to tubing circulating water below.
Continues to insulated water storage tank.
Flatplate Collector
Metal reflectors concentrate the suns ray.
Panels collect @ high temp.
Greater use of surface area, but more complex / expensive.
Concentrating Collectors
Contain absorber plate fused to a heat pipe.
More efficient than flat plate b/c vacuums surrounding tube reduce convection / conduction loss.
Transfer fluid (water / antifreeze) connects domestic hot water or hydronic space heating system.
Evacuated Tube Collectors
Air-based systems inferior to liquid-based systems because
Water = better transfer efficiency than air.
Outdoor temp __°F or below = possible to cool bldgs by simple ventilation.
85°F or below
U-value single pane of glass
1.11 BTU/ft² - hr °F
Double pane glass w/ 1/4” airspace has U-value:
0.57 BTU/ft² - hr °F
Almost half of a single pane of glass
Cost-effective inert gas in double pane window
Argon gas
Costs 200x argon gas
Krypton gas
Double glazing w/ thin film in glazing cavity,
allows visible + near-infrared to be transmitted
Low-E Glazing
In cold climates the low-E film is applied to this area of glass
Inside pane of glass
In warm climates low E film is applied to which side of the panes of glass
The outside pane
How low E Glazing works
As objects in room are heated
+ emit long wave radiation,
film prevents loss of heat,
by reflecting back into the room
Coatings help block solar heat gain from entering building.
Typically for bldgs w/ long cooling season
and require high light levels.
Spectrally Selective Glazing
When Spectrally Selective Glazing used w/ low E + double glaze systems SHGC of __ can be achieved.
.25 SHGC
2 low-E coatings w/ gas filled cavities between 3 layers glass.
Gain more thermal energy than lose over 24 hr in winter.
Super Windows
Multilayered thin-film applied to glass the changes continuously from dark to clear as low voltage electrical current is applied
Electromagnetic Glazing
Glazing darkens under direct action of sunlight.
As light intensity increases, window darkens.
Automatic, lacks user control of electromagnetic glazing.
Photochromic Glazing
Changes darkness of glass in response to temp, an automatic action.
Thermochromic Glazing
Glazing changes from transparent to reflective,
using coatings of nickel magnesium
Transition Metal Hydride Electrochromic Glazing
Wrapping envelope w/ exterior rigid insulation cuts off:
Thermal Bridging
Looks for path of least thermal resistance,
a.k.a. the lowest R-value.
Basic law of thermodynamics:
Heat flows hot to cold
If thermal storage wall is unvented,
none of these inside space:
Combustible products
If thermal storage wall is vented,
this % of wall should be vent area:
1 - 2%
