2021
Up and Running with the Passive House Planning Package (9.7 IP) Module 1 | Class 2 | Assemblies
What do we want from the PHPP?
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1. What is the Annual (End) Energy Demand for Heating and Cooling? 2. What is the Peak Load for Heating and Cooling? 3. What is the total Annual Primary Energy Demand?
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Q: How do you calculate the heating energy demand? A: (QT + QV) - η
Transmission + Ventilation LOSSES
(QS + QI)
Solar + Internal GAINS
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Q: How do you calculate annual the heat loss of a surface? A: QT-srfc = Areasrfc ( ft2 )
In 1. 2. 3. 4.
U-Valuesrfc ( Btu / hr-ft2-F )
ft (%)
Gt ( kFhr / yr)
order to calculate the transmission heat loss for each surface of a building, we need to: Determine the surface area Determine the surface’s U-Value Determine the temperature correction factor Determine the annual difference in temperature between inside and outside
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U-Values
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What the heck is a U-Value? U-Values are a measurement of
Btu/hr-ft2-F How many Btus flow…. …. Over one hour …. Through one square foot of surface …. For each degree (F) of difference
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U-Values are a measure of heat flow through an assembly R-Values are a measure of an assembly’s resistance to heat flow U-Value = 1 / R-Value R-Value = 1 / U-Value
For instance: R-40 à 1/40 = U-Value of 0.025 U-0.025 à 1/0.025 = R-Value of 40 bldgtyp | NYPH
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Example: 4” XPS Insulation (R-20) QT-surface = Areasurface
68 F
U-Valuesurface
ft
Gt
10’-0”
Areasurface = 10’ x 30’ = 300ft2 28 F
U-Valuesurface = 1/20 = 0.05 Btu/hr-ft2-F ft = 1.0 Gt = 120 kFh/yr
30’-0”
QT-surface = 300ft2
0.05 Btu/hr-ft2-F
1
120 kFhr/y
QT-surface = 1,800 Btu bldgtyp | NYPH
Example: 8” XPS Insulation (R-40) QT-surface = Areasurface
68 F
U-Valuesurface
ft
Gt
10’-0”
Areasurface = 10’ x 30’ = 300ft2 28 F
U-Valuesurface = 1/40 = 0.025 Btu/hr-ft2-F ft = 1.0
30’-0”
Gt = 120 kFh/yr
QT-surface = 300ft2
0.025 Btu/hr-ft2-F
1
120 kFhr/y
QT-surface = 900 Btu bldgtyp | NYPH
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Example: 16” XPS Insulation (R-80) QT-surface = Areasurface
68 F
U-Valuesurface
ft
Gt
10’-0”
Areasurface = 10’ x 30’ = 300ft2 28 F
U-Valuesurface = 1/80 = 0.0125 Btu/hr-ft2-F ft = 1.0
30’-0”
Gt = 120 kFh/yr
QT-surface = 300ft2
0.0125 Btu/hr-ft2-F
1
120 kFhr/y
QT-surface = 450 Btu bldgtyp | NYPH
Where do U-Values come from?
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Where do U-Values come from? 1. Building Codes 2. Engineering Reference Documents 3. Numerical Models 4. 2-D or 3-D Heat Flow Simulations
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NYS 2020 ECC: Assembly U-Value Throughout the code, we can find tables of U-Values (‘Effective’ R-Values) for various types of assemblies
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ASHRAE 90.1 Appendix A Appendix A includes more detailed tables of values which can be used for various assembly types
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BC Hydro Thermal Bridging Guide
https://betb.ca/
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BC Hydro Thermal Bridging Guide
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Numerical Calculation (Sometimes) Sometimes 90.1 Appendix A allows us to use a simplified numerical calculation to figure out our own U-Values
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ASHRAE HOF Chapter 25 and 27
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ISO 6946 ISO 6946 outlines essentially* the same calculation procedures and rules. This is the rules document to refer to for certain International Certifications such as ‘Passive House’
* Some small differences such as the exact surface film resistance value to use, etc.. bldgtyp | NYPH
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ASHRAE 1D Assembly U-Factor HOF Chapter 27: 1.1 R/inch Thickness
Layer R se
Layer Resistance 0.17
Vinyl Siding
1.24
×
1/2"
=
0.62
Bldg Paper
1.00
×
1/16”
=
0.06
OSB
1.24
×
1/2"
=
0.62
XPS foam
5.00
×
6”
=
30
Gyp Board
0.90
×
1/2"
=
0.45
R si
0.68 R-Value
=
32.60
U-Value
=
0.031
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ASHRAE 2D Assembly U-Factor Methods Int. ½” Drywall
3-½” Mineral Wool
5-½” Denspack Cellulose w/ Wd. Stud Framing 16” o.c. ½” Plywood Sheathing
R-Values Wood Studs: R-1.1/inch Plywood Sheathing: R-1.3/inch
3” Mineral Wool
Denspack Cellulose: R-3.2/inch Mineral Wool: R-4/inch
Ext.
Drywall: R-0.2/inch
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ASHRAE 2D Assembly U-Factor – Parallel Path Parallel Path Method R-per-Inch
Thickness
(hr·ft2·°F/Btu)
(inches)
Total Resistance (hr·ft2·°F/Btu)
Rsi (Int. Wall)
PATH 1
PATH 2
0.68
0.68
Drywall
0.2
×
0.5
=
0.1
0.1
Mineral Wool
4.0
×
3.5
=
14
14
Cellulose
3.2
×
5.5
=
17.6
-
Wood Stud
1.1
×
5.5
=
-
6.05
Ext. Sheathing
1.3
×
0.5
=
0.65
0.65
Mineral Wool
4.0
×
3
=
12
12
=
0.17
0.17
Rse (Ext. Wall)
RPATH =
45.2
33.7
U PATH =
0.022 × 90.6% = 0.0200
0.030 × 9.4% = 0.0028
Area % = U weighted
+
Utotal
0.0228 (Btu/hr·ft2·°F)
R total
43.9(hr·ft2·°F/Btu)
Path 1
Path 2
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ASHRAE 2D Assembly U-Factor – Isothermal Plane
+
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ASHRAE 2D Assembly U-Factor – Isothermal Plane Isothermal Plane Method R-per-Inch
Thickness
(hr·ft2·°F/Btu)
(inches)
R-Value
Rsi (Int. Wall)
U-Value
Area%
Uweighted
Utotal
R-Value
0.68
0.68
Drywall
0.2
×
0.5
=
0.1
0.1
Mineral Wool
4.0
×
3.5
=
14
14
Cellulose
3.2
×
5.5
=
17.6
0.057 ×
90.6% =
Wood Stud
1.1
×
5.5
=
6.05
0.165 ×
9.4% =
Ext. Sheathing
1.3
×
0.5
=
0.65
0.65
Mineral Wool
4.0
×
3
=
12
12
0.17
0.17
Rse (Ext. Wall)
0.0515 + 0.0155
0.0670
14.92
R-Value
42.5
U-Value
0.0235
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So… Parallel Plane Method gives us a U-Value of 0.0228 Btu/hr-ft2-F Isothermal Plane Method gives us a U-Value of 0.0235 Btu/hr-ft2-F Which is right? Neither. So we just take the average of the two methods. 0.0228 + 0.0235 / 2 = 0.0232 Btu/hr-ft2-F
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Example: PHPP Numerical Calculator
U-Value: 0.024 Btu/hr-ft2-F
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2 or 3-D Simulation For many assembly types (steel stud walls, complex assemblies) we will not be allowed to use a numerical calculation. We can then turn to 2D simulations in order to establish our clear field assembly U-Value.
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