01 Systems: Thermal Flashcards
The fraction of how much solar radiation passes through a window, is released as heat inside a building
Solar Heat Gain Coefficient (SHGC)
Equation to calculate SHGC
SHG through window / SHG through 1/8” glass
What is the value range of Solar Head Gain Coefficient?
0 < (SHGC) < 1
What is the SHGC of 1/8” glass?
1
High SHGC
0.7 - 0.9
Low SHGC
0.2 - 0.4
What kind of heat does solar heat gain measure?
Radiant heat
Solar Radiation definition
Solar Insolation (radiant energy per sf of the sun / amount of heat that is coming through)
Why are vents and radiators placed placed by windows?
We want to reduce radiant heat/cooling loss to glass
Internal-load-dominated building examples
- Sky scrapers
- Big hospitals
- Small-medium office buildings
- Factory
- Community theater
What are the three elements that make a building internal-load-dominanted?
- People
- Lighting
- Equipment
Define insolation
Solar radiation
Solar insolation is the amount of radiant heat that comes through (glass, etc.)
Which side of the building do you want a high solar heat gain coefficient on?
South
In the winter, the south side gains more heat than it loses
Which side of the building do you want a low solar heat gain coefficient on?
North
In the winter, the north side loses more heat than it gains
Define BTU
The heat required to move 1 LB of water from 70-71°
How many BTUs are required to move 1lb of water from 70° to 72°?
2 BTUs
Define sensible heat
heat in the air that can be felt
Define latent heat
the embodied heat of mosture in the air
Define enthalpy
Total heat in the air
(sensible heat + latent heat)
Just look:
Nice!
Define latent heat (in air)
Embodied heat in the moisture in the air
Does an interior-load-dominated building have a low or high balance point temperature?
Low
For a south-facing window (temperate climate, northern hemisphere), which building type would benefit more from the use of glass with a high solar heat gain coefficient (SHGC)?
a. A skin-load-dominated building
b. An internal-load-dominated building
A
Low E glass boasts a _________ SHGC.
a. High
b. Low
B
A locale that generally has cool summers is likely to have _________?
1. Many heating Degree Days (HHD’s)
2. Few Heating Degree Days (HHD’s)
3. Many Cooling Degree Days (CDD’s)
4. Few Cooling Degree Days (CDD’s)
Answer: 4. Few cooling degree days
A locale that generally has cold winters is likely to have ________.
1. Many heating Degree Days (HHD’s)
2. Few Heating Degree Days (HHD’s)
3. Many Cooling Degree Days (CDD’s)
4. Few Cooling Degree Days (CDD’s)
- Many Heating Degree Days
If a material has molecules packed tightly together, it is a(n) _______.
a. Conductor
b. Insulator
a. conductor
k symbolizes?
What does it measure?
conductivity
- measure of heat transfer efficiency
- a homogeneous material per in
r symbolizes?
What does it measure?
resistivity
- measure of heat transfer inefficiency
- a homogeneous material per in
C symbolizes?
What does it measure?
Conductance
- measure of heat transfer efficiency
- a homogeneous or heterogeneous material of a given thickness
R symbolizes?
What does it measure?
Resistance
- measure of heat transfer inefficiency
- a homogeneous or heterogeneous material of a given thickness
Define U-value
measure of the overall ability of a series of conductive and convective barriers to transfer heat
U-value formula if given Resistence (R) of different materials
U = 1 / (R1 + R2 + R3 …)
U-value exampe of a good insulator
10
Typical U-value of a window
1
If you have an R value of 1.5, what is your U-value?
1/1.5
If you have an R value of 3, what is your U-value?
1/3
What do Heating/Cooling Degree days tell us?
- what kind of windows to use
- how thick insulation should be
- whether the climate we’re designing for will always be cold/hot/both
What does the Outdoor Design Temperature tell us?
- How hot/cold it will get on almost the most extreme day of the year on average
- Tells us how to size our equipment for different climates
- 100 year flood level equivalent
Ventilation
Intentional way of bringing fresh air into a building
Infiltration
Unintentional way of bringing air into a building
0.9 air changes per hour means:
90% of air in building is replaced every hour
A well-designed contemporary house has about how many air changes per hour (ACH)?
2 ACH
How many air changes per hour (ACH) would require ventilation in a building?
Below 0.3 ACH
A airtight house is 2 ACH or below. Why do we want an airtight house?
To save energy so you’re not heating or cooling air excessively
define
Temperate Climate
warm summers, cold winters
For a temperate climate (warm summers, cold winters), heat transfer for conduction (Q) is more of a concern in the ___?
1. Summer
2. Winter
- Winter
- Winter
Just look:
Just look:
In the summer, AC units spend a lot of energy on removing latent heat (moisture) from the air
If we were to design a large office building, what would be the largest source of heat gain?
Lighting.
If we were to design an auditorium, what would be the largest source of heat gain?
People.
If we were to design a factory, what would be the largest source of heat gain?
Equipment.
Equation to calculate thermal resistence
R = r * d
r = resistivity
d = depth in inches
Thermal Bridging
What is the composite R value (to account for thermal bridging) of a wall that is:
- 90% insulation, resistence of 24
- 10% wood studs, resistence of 10
Just set up the equation
R = (0.9x24) + (0.1x10)
R = 22.6
In a cold climate, which is better for thermal insulation?
1. Steel studs
2. Wood studs
- Wood studs
Less heat loss to thermal bridging
What is a SIP
Structural Insulated Panel
What is the biggest benefit of using a structural insulated panel?
Much less heat loss to thermal bridging
Much higher whole-wall R-value
What are these images highlighting?
Thermal bridging of the concrete floor plates
What building topics does Passivhaus focus on?
- focus on energy
- high levels of insulation
- tight building construction
- moisture management
- high R-value windows
- no thermal bridging
When to use the conduction equation vs the convection one?
Conduction calculates heat loss through a wall system.
Convection calculates heat loss through infiltration or ventilation.
Define radiant heat
heat that’s transferred through electromagnetic waves, rather than through conduction or convection
What are the four factors of radiant heat?
emittance + absorptance = ?
emittance + absorptance = emissivity
Doubling the thickness of a given homogeneous wall material will ________ the wall’s U-Value?
a. Halve
b. Double
c. Not alter
a. Halve
Answer: 4. 10
3 types of passive solar gain (1/3):
Direct gain space
(need south facing glass to make a passive thermal building)
1. Eyebrow/shading device to keep high summer sun out
2. Insulation
3. Thermal mass
3 types of passive solar gain (2/3):
Trombe Wall
(not frequently used)
3 types of passive solar gain (3/3):
Sun space
The sun’s position in the sky along the vertical axis is called its ________.
a. Altitude
b. Solar Angle
c. Azimuth
a. Altitude
What is the blue showing?
Altitude
What is the red showing?
Azimuth
