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FGIA General > Group 4.B - Building Codes, Part II: Energy Efficiency and Thermal Performance > Flashcards

Group 4.B - Building Codes, Part II: Energy Efficiency and Thermal Performance Flashcards

1
Q

Windows typically comprise what percentage of a homes exterior wall area and what percentage of the heating and cooling needs

A

10-25% of area

25 - 50% of heating cooling

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2
Q

The basic measurements of thermal performance are:

A

Thermal conductivity and Solar heating.

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3
Q

What is the measure of thermal conductivity?

A

U-factor

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4
Q

How is total heat transfer through the fenestration calculated?

A

U-factor multiplied by the temperature difference from interior to exterior.

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5
Q

U factor is defined as:

A

The heat transfer per time unit, per area, per degree of temperature difference.

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6
Q

The technical expression for U-factor is

A

Btu/hs.f.Deg.F

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7
Q

Incident solar radiation affecting fenestration is broken down into three types based on frequency. What are they?

A

Ultraviolet (UV)
Visible light
Infrared.

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8
Q

What is Solar heat gain coefficient?

A

The fraction of (primarily) infrared solar radiation transmitted through the glass.

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9
Q

How is Solar Heat Gain Coefficient expressed and what does this value mean.

A

As a decimal number between 0 and 1.0

A lower SHGC value means less solar energy transmitted and more shading ability.

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10
Q

Where is a Low SHGC desirable?

Where is a high SHGC sought?

A

Low:
Warm climates
commercial buildings in most climates.

High:
Cold climates where heat gain is beneficial.

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11
Q

What does LSG (Light to Solar Gain) index refer to?

How is it calculated?

A

A gauge of the efficiency of a glass product in transmitting daylight, while blocking solar gain.

Calculated as the ratio between Visible Light (VT) and SHGC: (LSG = VT/SHGC)

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12
Q

What energy transmission strategy is best for a window optimized for cold climate solar heat gain?

A

High LSG, High SHGC.
Allow maximum daylight and solar gain while reducing transmission of low-energy radiation, the type emitted by interior sources.

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13
Q

What component of a window is the primary tool in reducing U-factor

A

Insulating glass (IG) units.

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14
Q

Components included in IG units to create energy efficient buildings include:

A 
Varying glass type and thickness
Coatings
Tints
Gas fills
Sealants 
Spacer materials.
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15
Q

Emissivity is a measure of what material property:

How is it expressed

A

The ability of a material to re-radiate infrared radiation absorbed by that material.

Expressed as a decimal number between 0 and 1,

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16
Q

Low E coated glass with an emissivity of 0.04 reflects what percent of radiant heat?

A

96% of long-wave radiation is reflected.

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17
Q

The numerical value of emissivity represents…..

A

…the percentage of radiation absorbed and retained by the material - the inverse of the percentage reflected.

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18
Q

Surfaces in an IG panel are reference by numbers counting from

a. The outermost glass surface, then in
b. The innermost surface, out

A

A. numbering starts on the exterior face of the external sheet.

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19
Q

A low-E coating on surface 3 (the air-space side of the interior sheet) provides what function?

A

It reflects heat back into the room to reduce heat loss through the window, keeping the space warm.
(It also reflects heat into the air-space, where conductive heating transfers some of that heat to the interior, but don’t tell anyone)

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20
Q

How are Low E coating are made:

A

From a microscopically thin layer of metal or metal oxide (silver or tin oxide) .

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21
Q

A low E coating on surface 2 (the interior face of the outer sheet) provides what function:

A

Reflects exterior heat back to the outside, keeping the interior cool.

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22
Q

The DOE defines spectrally selective” glass as that with a LSG of:

A

1.25 or higher.

i.e. VT = .6 and SHGC = .48
.6/.48= 1.25

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23
Q

What is the benefit of spectrally selective glass?

A

Allows day-lighting while minimizing heat-loads - minimizing artificial cooling AND lighting requirements.

24
Q

Reflective glass coatings comprise….

A

metallic layers applied to float glass, that reflect solar energy.

25
Q

Use of reflective glass is an option for

A

reducing unwanted solar gain.

26
Q

How is the use of reflective coatings tuned for varying climates?

A

By the location of the coating on surface 2 or surface 3 of the IG panel.

27
Q

What are the benefits and drawbacks of applying a reflective coating on surface #2 vs. surface #3 in an IG panel?

A

The SHGC is lower with a reflective coating on surface 2, but thermal stresses can be more common.

28
Q

IG spacers are comprised of what 3 components?

A

Spacer, desiccant and sealant.

29
Q

The IG spacer provides three functions, what are they?

A

Provides structural integrity
Carrier for the desiccant
supports the IG panel sealants

30
Q

How is a ‘warm edge’ spacer differ from a traditional metal spacer?
How does this alter performance?

A

The typical metal is replaced with a material like PVC foam.
This reduces:
H - Heat flow around the edges of the IG unit and
C - the tendency for Condensation to form at the perimeter.

31
Q

What is the function of inert gas fill in IG panels

A

Slow heat transfer

Reduce convective circulation

32
Q

Low conductivity framing is

A

Sash and unit frame material with a low U value to complement low u-value glass.

Not really a question here - just remember the term.

33
Q

Effective weatherstripping is used to seal between the ____ and _____ of a window.

A

Seal the contact areas between the fixed and movable section of the window.

34
Q

Poor weatherstripping can cause either ____ or____ depending on whether there is too much, or too little.

A

Air leakage or unduly high operating force.

35
Q

Energy performance is specified in what part of the building codes

A

IECC - International Energy Conservation Code.

36
Q

The 2018 IECC offers two compliance paths. What are they?

A

Prescriptive path -

Total building performance approach (Modeling)

37
Q

Describe the prescriptive method for IECC compliance

A

IECC prescribes one set of energy efficiency requirements for each component, regardless of the % of glazing in the walls, in different climate zones.

38
Q

Describe the total building performance method for IECC compliance,

A

This method allows trade offs between the building envelope, mechanical system and lighting system.

39
Q

How many climate zones are defined by the IECC

A

8

40
Q

What criteria must be met for a product to be deemed as meeting IECC requirements?

A

U-factor and SHGC must meet specified requirements for the different climate zones.

41
Q

In the IECC, skylight U-factors range from ___ in zone 1 to ____ in Zone 8.

A

Zone 1: 0.75

Zone 8: 0.50

42
Q

Are skylight U-factors the same in the IECC and IRC

A

Yes

43
Q

Are skylight SHGC requirements the same in the IECC and IRC?

A

No.

44
Q

What maximum SHGC’s stipulated for Zones 4 - Zone 7-8 in the IRC?

A

None are stipulated.

45
Q

What standard spells-out design trade-offs in the performance-based IECC compliance path for commercial buildings/

A

ASHRAE 90.1

46
Q

Performance requirements for metal-framed fenestration products in commercial construction are higher or lower than for residential windows, doors and skylights?

A

Lower, especially in northern climates (Zone 4-8)

47
Q

What is the maximum area for skylights allowed in the IECC prescriptive path?

A

3% of the roof area.

48
Q

Give an example of how additional skylight area (above the prescriptive maximum) can be offset in the IECC performance compliance path?

A

Adding a system that dims interior lighting when adequate day-lighting is provided through the skylights and windows.

49
Q

What performance parameters and fenestration types are rated by the National Fenestration Rating Council (NFRC)?

Hint: UVAS

A

U-factors
Visible transmittance
Air infiltration
SHGC values

for windows, doors and skylights,

50
Q

How are NFRC ratings developed?

A

Combination of computer simulations and laboratory testing.

51
Q

Are NFRC ratings accepted in model nationwide energy codes? How are ratings displayed on the fenestration?

A

Yes

Temporary labels.

52
Q

What are the 3 criteria in NFRC simulation and testing standards, and what properties do they correspond to?

(This is not the 3 criteria for evaluation per NAFS)

A

NFRC 100 - U-factor
NFRC 200 - SHGC
NFRC 400 - Air Infiltration

53
Q

2018 iRC requires compliance with which which NFRC testing standards?

A

NFRC 100 and 200

54
Q

The definition of an energy star qualifying product is based on…

Fenestration Class & Rating
Solar Heat-gain coefficient
R-value
Low-E coatings
U-factor
A

U-factor

Solar Heat-gain coefficient

55
Q

How do windows with low U-factors and SHGC impact building energy use?
What is the specific impact of low SHGCs?

A

They tend to lower energy use.

Low SHGC’s lower cooling energy use.

56
Q

For Energy Star what procedures are cited for independent testing of:
U-factor
SHGC
IG Units must conform to:

A

NFRC 100
NFRC 200
ASTM E2190

FGIA General (33 decks)

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