CODES

ADOPTS WITH AMENDMENTS:

International Energy Conservation Code 2012 (IECC 2012)

(This is a normative appendix and is part of this standard.)

C1. MINIMUM INFORMATION

The following minimum information shall be specified for the proposed design.

C1.1 At the Building Level.
The floor area, broken down by space-conditioning categories, shall be specified. C1.2 At the Exterior Surface Level.
The classification, gross area, orientation, U-factor, and exterior conditions shall be specified. For mass walls only: HC and insulation position. Each surface is associated with a space-conditioning category as defined in Section C1.1. C1.3 For Fenestration.
The classification, area, U-factor, SHGC, VT, overhang PF for vertical fenestration, and width, depth, and height for skylight wells shall be specified. (See Figure C1.3 for definition of width, depth, and height for skylight wells.) Each fenestration element is associated with a surface (defined in Section C1.2). and has the orientation of that surface. For dynamic glazing, the SHGC and VT shall be equal to that determined in accordance with C3.5 for the base envelope design.

FIGURE C1.3 Skylight well dimensions.

C1.4 For Opaque Doors.
The classification, area, U-factor, HC, and insulation position shall be specified. Each opaque door is associated with a surface (defined in Section C1.2). and has the orientation of that surface. C1.5 For Below-Grade Walls.
The area, average depth to the bottom of the wall, and C-factor shall be specified. Each below-grade wall is associated with a space-conditioning category as defined in C1.1 . C1.6 For Slab-On-Grade Floor.
The perimeter length and F-factor shall be specified. Each slab-on-grade floor is associated with a space-conditioning category as defined in Section C1.1.

C2. OUTPUT REQUIREMENTS

Output reports shall contain the following information.

C2.1
Tables summarizing the minimum information described in Section C1. C2.2
The envelope performance factor differential broken down by envelope component. The differential is the difference between the envelope performance factor of the proposed building and the envelope performance factor of the base envelope design. Envelope components include the opaque roof, skylights, opaque above-grade walls including vertical fenestration and opaque doors, below-grade walls, floors, and slab-on-grade floors.

C3. BASE ENVELOPE DESIGN AND PROPOSED DESIGN SPECIFICATION

C3.1
The base envelope design shall have the same building floor area, building envelope floor area, slab-on-grade floor perimeter, below-grade floor area, gross wall area, opaque door area, and gross roof area as the proposed design. The distribution of these areas among space-conditioning categories shall be the same as the proposed design. C3.2
The U-factor of each opaque element of the base envelope design shall be equal to the criteria from Tables 5.5-1 through 5.5-8 for the appropriate climate for each construction classification. The HC of mass wall elements in the base envelope design shall be identical to the proposed design. Mass walls in the base envelope design shall have interior insulation, when required. C3.3
The vertical fenestration area of each space-conditioning category in the base envelope design shall be the same as the proposed building or 40% of the gross wall area, whichever is less. The distribution of vertical fenestration among space-conditioning categories and surface orientations shall be the same as the proposed design. If the vertical fenestration area of any space-conditioning category is greater than 40% of the gross wall area of that space-conditioning category, then the area of each fenestration element shall be reduced in the base envelope design by the same percentage so that the total vertical fenestration area is exactly equal to 40% of the gross wall area. C3.4
For enclosed spaces required to comply with Section 5.5.4.2.3, the skylight area in the base envelope design shall be 3% of the roof area of that enclosed space. For enclosed spaces required to comply with Section 5.5.4.2.3, the total daylight area under skylights in both the base envelope design and the proposed envelope design shall be a minimum of half the floor area. For all other spaces the skylight area of each space category in the base envelope design shall be the same as the proposed envelope design or 5% of the gross roof area, whichever is less. This distribution of skylights among spaceconditioning categories shall be the same as the proposed design. If the skylight area of any space category is greater than 5% of the gross roof area of that space-conditioning category, then the area of each skylight shall be reduced in the base envelope design by the same percentage so that the total skylight area is exactly equal to 5% of the gross roof area. C3.5
The U-factor for fenestration in the base envelope design shall be equal to the criteria from Tables 5.5-1 through 5.5-8 for the appropriate climate, except the U-factor for skylights in enclosed spaces required to comply with Section 5.5.4.2.3 shall be equal to the criteria listed in the Exception to Section 5.5.4.3. The SHGC for fenestration in the base envelope design shall be equal to the criteria from Tables 5.5-1 through 5.5-8. For portions of those tables where there are no requirements, or for enclosed spaces required to comply with Section 5.5.4.2.3 , the SHGC shall be equal to 0.46 for all vertical fenestration, 0.77 for plastic skylights on a curb, and 0.72 for all other skylights with a curb and without. The VT for fenestration in the base envelope design shall be the VT factor from Table C3.5 times the SHGC criteria as determined in this subsection. or enclosed spaces required to comply with Section 5.5.4.2.3, the VT for skylights in that enclosed space shall be 0.40.

TABLE C3.5 VT Factor for the
Base Envelope Design

Climate BinVertical
Fenestration
Glass
Skylights
Plastic
Skylights
1(A, B)1.001.271.20
2(A, B)1.001.271.20
3(C)1.001.271.20
3(A, B)1.271.271.20
4(A, B, C)1.271.271.20
5(A, B, C)1.271.271.20
6(A, B)1.271.271.20
71.001.001.20
81.001.001.20
C3.6
The roof of the base envelope design and the roof of the proposed envelope design shall both comply with either section 5.5.3.1.1 (a) or (b). C3.7
Unconditioned spaces of the base envelope design and the proposed envelope design shall comply with Section 5.5.4.2.3.

C4. ZONING AND BUILDING GEOMETRY

No information about thermal zones needs to be entered to perform the calculations, but when the calculations are performed the building shall be divided into thermal zones according to the following procedure.

C4.1
Determine the ratio (Rc) of the gross floor area to the gross wall area for each space-conditioning category. The index “c” refers to the space-conditioning category, either non-residential conditioned, residential conditioned, or semiheated. C4.2
Create a perimeter zone for each unique combination of space-conditioning category and wall orientation. The floor area of each perimeter zone shall be the gross wall area of the zone times Rc or 1.25, whichever is smaller. C4.3
For space-conditioning categories where Rc is greater than 1.25, interior zones shall be created and used in the trade-off procedure. The floor area of the interior zone shall be the total floor area for the space-conditioning category less the floor area of the perimeter zones created in Section C4.2 for that space-conditioning category. C4.4
Roof area, floor area, below-grade wall area, and slab-on-grade floor perimeter associated with each space-conditioning category shall be prorated among the zones according to floor area. C4.5
Skylights shall be assigned to the interior zone of the space-conditioning category. If the skylight area is larger than the roof area of the interior zone, then the skylight area in the interior zone shall be equal to the roof area in the interior zone and the remaining skylight area shall be prorated among the perimeter zones based on floor area.

C5. MODELING ASSUMPTIONS

The following are modeling assumptions for the purposes of this appendix only and are not requirements for building

C5.1
The residential conditioned and nonresidential conditioned space-conditioning categories shall be modeled with both heating and cooling systems for both the base envelope design and the proposed design. The thermostat setpoints for residential and nonresidential spaces shall be 70°F for heating and 75°F for cooling, with night setback temperatures of 55°F for heating and 99°F for cooling. C5.2
The semiheated space categories shall be modeled with heating-only systems for both the base envelope design and the proposed design. The thermostat setpoint shall be 50°F for all hours. C5.3
Both the base envelope design and the proposed design shall be modeled with the same heating, ventilating, and air-conditioning (HVAC) systems. The system shall consist of a packaged rooftop system serving each thermal zone. Cooling shall be provided by a direct expansion air conditioner (EER = 9.5, COPcooling = 2.78). Heating shall be provided by a gas furnace (AFUE = 0.78). C5.4
The electrical systems shall be the same for both the base envelope design and the proposed design. The LPD shall be 1.20 W/ft2 for nonresidential conditioned spaces, 1.00 W/ft2 for residential conditioned spaces, and 0.50 W/ft2 for semiheated spaces. The equipment power density shall be 0.75 W/ft2 for nonresidential conditioned spaces, 0.25 W/ft2 for residential conditioned spaces, and 0.25 W/ft2 for semi-heated spaces. Continuous daylight dimming shall be assumed in all spaces and be activated at 50 fc for nonresidential conditioned spaces and residential conditioned spaces and 30 fc for semiheated spaces. C5.5
Surface reflectances for daylighting calculations shall be 80% for ceilings, 50% for walls, and 20% for floors. C5.6
The U-factor entered for surfaces adjacent to crawl-spaces, attics, and parking garages with mechanical or natural ventilation shall be adjusted by adding R-2 to the thermal resistance to account for the buffering effect. C5.7
Heat transfer for below-grade walls shall be based on the temperature difference between indoor and outdoor temperature conditions and a heat transfer path at the average wall depth below grade.

C6. EQUATIONS FOR ENVELOPE
TRADE-OFF CALCULATIONS

The procedure defined in this subsection shall be used in all building envelope trade-off calculations.
C6.1 Inputs.
Building descriptions shall be converted to equation variables using Table C6.1.

TABLE C6.1 Input Variables

Variable Description I-P Units
Areasurface Area of surface ft2
Areazone Gross floor area of zone as defined in Section C.5 ft2
C-factor C-factor for below-grade walls Btu/h•ft2•°F
CDD50 CDDs Base 50°F•day
CDD65 CDDs Base 65°F•day
CDH80 Cooling degree-hours Base 80°F•hour
Depth Depth of bottom of below-grade wall ft
DI Artificial lighting design illuminance from Section C.5.4 footcandles
DR Daily range (average outdoor maximum-minimum in hottest month)°F
EPD Miscellaneous equipment power density from Section C.5.4 W/ft2
F-factor F-factor for slab-on-grade floors Btu/h•ft•°F
HC Wall heat capacity Btu/ft2•°F
HDD50 HDDs Base 50°F•day
HDD65 HDDs Base 65°F•day
Length Length of slab-on-grade floor perimeter ft
LPD LPD from Section C.5.4 W/ft2
R-Value Effective R-value of soil for below-grade walls h•ft2•°F/Btu
U-factor U-factor Btu/h•ft2•°F
VS Annual average daily incident solar radiation on vertical surface Btu/ft2•day
C6.2 Envelope Performance Factor.
The EPF of a building shall be calculated using Equation C-1 using its actual orientation, rotating the entire building 90, 180, and 270 degrees, then averaging the results.
EPF = FAF × [ΣHVACsurface + ΣLightingzone](C-1)
where
ΣHVACsurface=sum of HVAC for each surface calculated using Equation C-2
ΣLightingzone=sum of lighting for each zone calculated using Equation C-3
C6.3 HVAC.
The HVAC term for each exterior or semi-exterior surface in the building shall be calculated using Equation C-2.
HVACsurface = 0.0939 × COOL + 1.22 × HEAT(C-2)
where
COOL=cooling factor for the surface calculated according to the appropriate equation in C-14, C-19, or C-22
HEAT=heating factor for the surface calculated according to the appropriate equation in C-16, C-18, or C-23
C6.4 Lighting.
The lighting term for each zone in the building as defined in Section C4 shall be calculated using Equation C-3.
Lightingzone = LPDadjzone × AREAzone × 2700 ×0.939(C-3)
where
LPDadjzone=lighting power density for the zone adjusted for daylighting potential using Equation C-9
C6.5 Solar and Visible Aperture C6.5.1 Solar and Visible Aperture of Vertical Fenestration.
The visible aperture (VA), solar aperture for cooling (SAc), and solar aperture for heating (SAh) of each vertical fenestration shall be calculated using Equations C-5, C-6, and C-7.
VA = Areavf × VTvf × (1 + PCC1 × PF + PCC2 × PF2)(C-5)
SAc = Areavf × 1.163 × SHGC × (1 – PCC1 × PF + PCC2 × PF2)(C-6)
SAh = Areavf × 1.163 × SHGC × (1 + PCH1 × PF + PCH2 × PF2) (C-7)
where
Areavf=glazing area of the vertical fenestration
SHGC=the solar heat gain coefficient of the vertical fenestration assembly
VTvf= the visible transmittance of the vertical fenestration assembly
PF=the projection factor for the overhang shade on the vertical fenestration
PCH1, PCH2, PCC1, and
PCC2
=overhang projection coefficients for the vertical fenestration orientation from Table C6.5.1

TABLE C6.5.1 Overhang Projection Coefficients

OrientationPCC1PCC2PCH1PCH2
North–0.50.2200
East, South, West –0.970.3800
C6.5.2 Visible Aperture of Skylights.
The VA of a sky-light shall be calculated using Equation C-8.
VA = Areasky × VTsky × 10(–0.250 × (5 × D × (W + L) / (W × L))(C-8)
where
Areasky=fenestration area of the skylight assembly
VTsky =the visible transmittance of the skylight assembly
D =average depth of skylight well from fenestration to ceiling
W=width of skylight well
L=length of skylight well
C6.6 Adjusted Lighting Power (LPDadj).
The adjusted lighting power for each zone shall be calculated using Equation C-9.
LPDadjzone = LPD × (1 – Kdzone)(C-9)
where Kdzone= daylight potential fraction calculated using Equation C-10.
If a zone has both skylights and vertical fenestration, the larger of the Kd calculated independently for each shall be used to calculate LPDadj.
(C10)
where
Areafen =total fenestration area of the vertical fenestration or skylight assemblies in the zone
VA=total visible aperture of the vertical fenestration or skylights in the zone, as calculated in Equation C-5
Areasurface=gross wall area of the zone for vertical fenestration or gross roof area of the zone for skylights

and the coefficients 1 through 4 are defined in Table C6.6.

TABLE C6.6 Coefficients for Calculating Kd

CoefficientSkylightVertical Fenestration
Φ10.5890.737
Φ25.18E–07–3.17E-04
Φ3–220–24.71
Φ42.290.234
C6.7 Delta Load Factors for Mass Walls in the Exterior Building Envelope.
Adjustments to cooling and heating loads for use in Equations C-14 and C-16 due to the mass properties of each mass wall component shall be calculated using Equations C-11 and C-12.
(C-11)
where
CMC=cooling delta load factor
Areamw=net opaque area of this mass wall
Ac=CDH80/10000 + 2
B=DR/10 + 1
HC=wall heat capacity
DR=average daily temperature range for warmest
month
CP1=C5
CP2=C15/B3 + C16/(AC2B2) + C17
CP3=
CP4=C12(AC2B2) + C13/B3 + C14
U=area average of U-factors of mass walls in the
zone
CP5=C18
CP6=
LN=natural logarithm
CP7=
CP8=
The coefficients C1 through C22 depend on insulation position in the wall and are taken from Table C6.7A.
(C-12)
where
HMC=heating delta load factor
HC=wall heat capacity
Areamw=net opaque area of this mass wall
HP1=H6
AH=HDD65/100 + 2
HP2=H14LN(AH) + H15
LN=natural logarithm
HP3=
U=area average of U-factors of mass walls in the zone
HP4=
HP5=H16
HP6=H7AH + H8
HP7=H17/AH3 + H18
HP8=H9/AH3+ H10
The coefficients H1 through H18 depend on the position of the insulation in the wall and are taken from Table C6.7B. If the U-factor of mass wall is greater than 0.4 Btu/(h•ft2•°F), then the U-factor shall be set to 0.4 Btu/(h•ft2•°F). If the U-factor of the mass wall is less than 0.05 Btu/(h•ft2•°F), then the U-Factor shall be set to 0.05 Btu/(h•ft2•°F). If the wall HC of the mass wall is greater than 20 Btu/(ft2•°F), then HC = 20 Btu/(ft2•°F) shall be used.

TABLE C6.7A Cooling Delta Load Coefficients

Insulation Position
VariableExteriorIntegralInterior
C1220.7245139.1057181.6168
C2–0.0566–0.0340–0.0552
C3–118.8354–10.3267–34.1590
C4–13.6744–20.8674–25.5919
C50.23640.28390.0810
C60.95960.30591.4190
C7–0.25500.02260.4324
C8–905.6780–307.9438–1882.9268
C9425.191980.2096443.1958
C10–2.51060.05000.4302
C11–43.3880–5.9895–28.2851
C12–259.7234–11.3961–63.5623
C13–33.97550.366920.8447
C1420.488230.25359.8175
C15–26.20928.833724.4598
C16–241.1734–22.2546–70.3375
C1718.897829.32979.8843
C18–0.3538–0.0239–0.1146
C19 156.305663.3228326.3447
C20–74.0990–16.3347–77.6355
C210.4454–0.0111–0.0748
C227.49671.29565.2041

TABLE C6.7B Heating Delta Load Coefficients

Insulation Position
VariableExteriorIntegralInterior
H10.00000.00000.0000
H2–0.0015–0.0018–0.0015
H313.388615.116119.8314
H41.93322.10561.4579
H5–11.8967–13.3053–15.5620
H60.46430.18400.0719
H70.00940.02550.0264
H8–0.10000.04590.7754
H9–1223.3962–622.08010.2008
H10–0.9454–0.5192-0.6379
H11–0.0001–0.00010.0000
H123.85854.13792.4243
H137.58296.23807.9804
H14–0.7774–0.7711–0.1699
H159.01477.72298.5854
H160.20070.2083–0.0386
H17206.6382105.98493.1397
H180.25730.19830.1863
C6.8 Walls and Vertical Fenestration in the Exterior Building Envelope.
Equations C-14 and C-16 shall be used to calculate COOL and HEAT for exterior walls and vertical fenestration in the exterior building envelope except walls next to crawlspaces, attics, and parking garages with natural or mechanical ventilation. Walls next to crawlspaces, attics, and parking garages with natural or mechanical ventilation shall use the equations in Section C6.10 and they shall not be included in calculations in Section C6.8. Zones shall be constructed according to Section C4 and the HEAT and COOL for the combination of all exterior walls and vertical fenestration in the zone shall be calculated using Equations C-14 and C-16, which include interactive effects. For a zone having a cardinal orientation (north, east, south, or west), Equations C-14 and C-15 shall be applied directly. For zones with northeast, north-west, southwest, and southeast orientations, EC shall be determined by finding the average of the values for the two closest cardinal orientations; for instance, COOL for a wall facing northeast is calculated by taking the average of COOL for a north-facing wall and COOL for an east-facing wall. C6.8.1 Effective Internal Gain.
The effective internal gain to zone G shall be calculated using Equation C-13.
G = EPD + LPDadjzone(C-13)
where
LPDadjzone=lighting power density adjusted for daylighting, from Equation C-9
C6.8.2 Cooling Factor.
The cooling factor for the surfaces in the zone shall be calculated using Equation C-14.
COOL = 1000/(1200 × 12.24) × [CLU + CLUO + CLXUO + CLM + CLG + CLS + CLC](C-13)
where
CLU=Areaopaque × Uow × [CU1 × CDH80 + CU2 × CDH802 + CU3 × (VS × CDH80)2 + CU4 x DR]
CLUO=Areagrosswall × UO × [CUO1 × EAC × VS × CDD50 + CUO2 × G + CUO3 × G2 × EAC2× VS × CDD50 + CUO4 × G2 × EAC2× VS × CDD65]
CLXUO=Areagrosswall / UO × [CXUO1 × EAC × VS × CDD50 + CXUO2 × EAC × (VS × CDD50)2 + CXUO3 × G × CDD50 + CXUO4 × G2 × EAC2 × VS × CDD50 + CXUO5 × G2 × CDD65]
CLM=Areaopaque × SCMC × [CM1 + CM2 × EAC × VS × CDD50 + CM3 × EAC × VS × CDD65 + CM4 × EAC2 × VS × CDD50 + CM5 × G2 × CDD65 + CM6 × G × CDD50 + CM7 × G × CDD65 + CM8 × G × EAC × VS × CDD50]
CLG=Areagrosswall × {G × [CG1 + CG2 × CDD50 + CG3 × EAC × (VS × CDD50)2 + CG4 × EAC2 × VS × CDD50 + CG5 × CDD65 + CG6 × CDD503 + CG7 × CDD653] + G2 × [CG8 × EAC × VS × CDD50 + CG9 × EAC2 × VS × CDD50]}
CLS=Areagrosswall × {EAC × [CS1 + CS2 × VS × CDD50 + CS3 × (VS × CDD50)2 + CS4 × VS × CDD65 + CS5 × (VS × CDD65)2] + EAC2 × [CS6 + CS7 × (VS × CDD65)2]}
CLC=Areagrosswall × [CC1 × CDD50 + CC2 × CDD502+ CC3 × CDH80 + CC4 × CDH802 + CC5 × CDD65 + CC6 × (VS × CDD65)2 + CC7 × VS × CDD50 + CC8 × (VS × CDD50)2 + CC9 × (VS × CDH80)2 + CC10 × VS + CC11 × DR + CC12 × DR2 + CC13]
where
Areagrosswall=total gross area of all walls and vertical fenestration in the zone, including opaque and fenestration areas
Areaopaque=total opaque area of all walls in the zone
Uow=area average of U-factors of opaque walls (including those of mass construction) in the zone
VS=annual average daily incident solar energy on surface
DR=average daily temperature range for the warmest month
UO=area average of U-factor of opaque walls and vertical fenestration in the zone
SCMC=sum of the CMC from Equation C-11 for each mass wall in the zone
G=effective internal gain to space, from Equation C-13
EAC=effective solar aperture fraction for zone calculated using Equation C-15
(C-15)
where
ΣSAc=the sum of SAc from Equation C-6.6 for all vertical fenestration in the zone.
The coefficients used in the above equations depend on the orientation of the surface and shall be found in Table C6.8.2.

TABLE C6.8.2 Cooling Coefficients for the Exterior Wall Equation

VariableOrientation of Surface
NorthEastSouthWest
CU10.0015390.0033150.0031530.00321
CU2–3.0855E-08–8.9662E-08–7.1299E-08–8.1053E-08
CU37.99493E-143.7928E-141.83083E-143.3981E-14
CU4–0.0796470.1631140.2864580.11178
CM10.323140.5152620.714770.752643
CM21.5306E-061.38197E-061.6163E-061.42228E-06
CM3–2.0432E-06–1.6024E-06–2.1106E-06–1.9794E-06
CM4–7.5367E-07–7.6785E-07–6.6443E-07–7.4007E-07
CM5–1.0047E-0608.01057E-063.15193E-06
CM63.66708E-053.56503E-054.48106E-052.96012E-05
CM7–6.7305E-05–6.4094E-05–0.000119–7.6672E-05
CM8–2.3834E-08–4.7253E-08–4.9747E-080
CUO1–6.5109E-06–8.3867E-06–8.89E-06–7.5647E-06
CUO2–1.040207–1.507235–1.512625-1.238545
CUO3–4.3825E-06–2.7883E-06–2.3135E-06–4.1257E-06
CUO40.0000126588.09874E-067.36219E-061.06712E-05
CXUO11.03744E-061.19338E-061.18588E-061.23251E-06
CXUO2–1.3218E-13–1.3466E-13–1.1625E-13–1.3E-13
CXUO32.75554E-052.02621E-052.02365E-052.36964E-05
CXUO49.7409E-081.175E-079.39207E-081.36276E-07
CXUO5–1.1825E-05–9.0969E-06–9.0919E-06–1.1108E-05
CG10.8912860.5833880.3937560.948654
CG20.0014790.0019310.0020810.001662
CG3–5.5204E-13–2.8214E-13–2.8477E-13–4.5572E-13
CG42.52311E-063.70821E-064.30536E-065.91511E-06
CG5–0.001151–0.001745–0.001864–0.00153
CG61.95243E-120–2.9606E-123.16358E-12
CG7–8.3581E-121.01089E-113.30027E-110
CG81.41022E-067.53875E-077.133E-079.70752E-07
CG9–2.3889E-06–1.6496E-06–1.6393E-06–1.9736E-06
CS146.987133.968318.3201629.3089
CS23.48091E-053.74118E-050.0000340495.02498E-05
CS3002.71313E-120
CS4–1.6641E-056.94779E-06–2.8218E-05–2.7716E-05
CS58.42765E-120–3.0468E-122.91137E-12
CS6–56.5446026.995414.9771
CS7–1.3476E-11–5.881E-12–6.5009E-12–7.8922E-12
CC10.00274700.0103490.001865
CC203.18928E-07–3.0441E-070
CC3–0.0003480.0003190.000240.000565
CC41.22123E-08–7.7532E-08–2.7144E-08–5.4438E-08
CC50.0121120.0118940.0132480.009236
CC61.04027E-12–6.2266E-13–2.0518E-120
CC7–1.2401E-05–7.0628E-06–1.6538E-05–6.0269E-06
CC8008.20869E-130
CC9–3.758E-146.06235E-141.97598E-143.89425E-14
CC100.0300560.0231210.02650.01704
CC1100–0.271026–0.244274
CC120.0021380.0011030.0063680.007323
CC13–12.8674–13.16522–18.271–10.1285
C6.8.3 Heating Factor.
The heating factor for the surfaces in the zone shall be calculated using Equation C-16.
HEAT=10/(1200 × 0.608488) × [HLU + HLUO + HLXUO + HLM + HLG + HLS + HLC](C-15)
where
HLU =Areaopaque × Uow× [HU1 × HDD50 + HU2 × (VS × HDD65)2]
HLUO =Areagrosswall × UO × [HUO1 × HDD50 + HUO2 × HDD65 + HUO3 × EAH × VS × HDD65]
HLXUO =Areagrosswall × {(1/UO) × [HXUO1 × EAH× (VS × HDD50)2 + HXUO2 × EAH × (VS × HDD65)2] + (1/UO2) × [HXUO3 × EAH2 × VS × HDD65]}
HLM =Areaopaque × SHMC × [HM1 + HM2 × G × UO × HDD65 + HM3 × G2 × EAH2× VS × HDD50 + HM4 × UO× EAH × VS × HDD65 + HM5 × UO × HDD50 + HM6 × EAH × (VS × HDD65)2 + HM7 × EAH2 × VS × HDD65/UO]
HLG =Areagrosswall × {G × [HG1 × HDD65 + HG2 × UO× HDD65 + HG3 × EAH× VS × HDD65 + HG4 × EAH2× VS × HDD50] × G2 × [HG5 × HDD65 + HG6 × EAH2× VS × HDD65]}
HLS =Areagrosswall × {EAH × [HS1 × VS × HDD65 + HS2 × (VS × HDD50)2] + EAH2 × [HS3 × VS × HDD50 + HS4 × VS × HDD65]}
HLC =Areagrosswall × [HC1 + HC2 × HDD65 + HC3 × HDD652 + HC4 × VS2 + HC5 × VS × HDD50 + HC6 × VS × HDD65 + HC7 × (VS × HDD50)2]
where
VS=annual average daily incident solar energy on surface
SHMC=sum of the HMC from Equation C-12 for each mass wall in the zone
EAH=effective solar aperture fraction for zone calculated using Equation C-17.
(C-17)
SAh = the sum of SAh from Equation C-7 for all vertical fenestration in the zone.
The coefficients used in the above equations depend on the orientation of the surface and shall be found in Table C6.8.3. Terms not defined for Equation C-16 are found under Equation C-14.

TABLE C6.8.3 Heating Coefficients for the Exterior Wall Equation

VariableOrientation of Surface
NorthEastSouthWest
HU10.0062030.0076910.0060440.006672
HU2–1.3587E-12–5.7162E-13–2.69E-13–4.3566E-13
HM10.5310050.5457320.8379010.616936
HM20.0001520.0001070.0002080.00015
HM3–5.3183E-07–1.0619E-07–6.8253E-07–2.6457E-07
HM4–7.7381E-07–1.4787E-062.11938E-06–4.5783E-07
HM5–0.000712–0.000484–0.001042–0.000625
HM63.34859E-134.95762E-147.7019E-147.37105E-14
HM72.39071E-072.75045E-07–3.8989E-070
HUO10.0049430.0086830.0090280.008566
HUO20.0136860.0110550.0101560.01146
HUO3–1.1018E-05–8.6896E-06–7.3232E-06–8.9867E-06
HXUO11.2694E-127.85644E-14–2.8202E-133.04904E-14
HXUO2–7.3058E-13–8.109E-147.45599E-14–7.4718E-14
HXUO31.9709E-071.94026E-079.87587E-081.95776E-07
HG1–0.001051–0.000983–0.000981–0.000948
HG2–0.001063–0.00093–0.000815–0.000975
HG32.99013E-062.62269E-062.4188E-062.49976E-06
HG47.49049E-07–1.1106E-06–2.1669E-06–8.5605E-07
HG50.0001090.0000934319.75523E-058.62389E-05
HG6–5.5591E-07–3.158E-07–2.61E-07–2.9133E-07
HS1–2.1825E-05–2.0922E-05–2.1089E-05–2.0205E-05
HS23.39179E-121.905E-121.48388E-122.18215E-12
HS3–6.5325E-06–2.2341E-05–1.8473E-05–2.4049E-05
HS42.23087E-052.41331E-052.45412E-052.30538E-05
HC1–0.106468–5.19297–3.66743–5.29681
HC20.007290.0076840.0071750.007672
HC3–2.976E-07–3.0784E-07–2.6419E-07–3.0713E-07
HC42.01569E-066.3035E-063.32112E-066.43491E-06
HC51.29061E-054.77552E-063.25089E-064.83233E-06
HC6–1.2859E-05–6.1854E-06–4.6309E-06–6.251E-06
HC72.75861E-128.20051E-134.38148E-138.09106E-13
C6.9 Skylights in the Exterior Building Envelope.
HEAT and COOL shall be calculated for skylights in nonresidential conditioned and residential conditioned zones using Equations C-17 and C-18.
HEAT=Areasky × HDD65 ×(H2 × Usky + H3 × SHGC/0.86)(C-17)
COOL = Areasky × C2 × CDD50 × SHGC/0.86(C-18)
where
Areasky =fenestration area of the skylight assembly
SHGC=the solar heat gain coefficient of the skylight assembly
Usky=U-factor of skylight assembly

The coefficients used in the equations depend on the space type and shall be taken from Table C6.9.

TABLE C6.9 Heating and Cooling
Coefficients for Skylights

CoefficientNonresidentialResidential
C21.09E-021.64E-02
H22.12E-042.91E-04
H3–1.68E-04–2.96E-04
C6.10 Calculations for Other Exterior and Semi-Exterior Surfaces.
For all exterior and semi-exterior surfaces not covered in Sections C6.8 and C6.9, the cooling factor, COOL, and heating factor, HEAT, shall be calculated using the procedure in this section. C6.10.1 U-Factor for Below-Grade Walls.
The effective U-factor of below-grade walls shall be calculated using Equation C-20. Rsoil shall be selected from Table C6.10.1 based onthe average depth of the bottom of the wall below the surface of the ground.
U-factor = 1 / ((1/C-factor) + 0.85 + Rsoil)(C-20)
where
Rsoil=effective R-value of the soil from Table C6.10.1

TABLE C6.10.1 Effective R-Value of Soil
for Below-Grade Walls

Depth, ftRsoil (h•ft2•°F/Btu)
10.86
21.6
32.2
42.9
53.4
64.0
74.5
85.1
95.6
106.1
C6.10.2 Adjustment for Other Protected Elements of the Exterior Envelope.
The adjusted U-factor for exterior envelope surfaces, which are protected from outdoor conditions by crawlspaces, attics, or parking garages with natural or mechanical ventilation, shall be adjusted using Equation C-21 before calculating HEAT and COOL.
Uadj = 1 / ((1 / U-factor) + 2) (C-21)

TABLE C6.10.2 Heating and Cooling Coefficients for Other Exterior and
Semi-Exterior Surfaces

Building Envelope ClassificationExteriorSemi-Exterior
Space-Conditioning TypeNonresidentialResidentialAll
Surface TypeCcoef1Ccoef2HcoefCcoef1Ccoef2HcoefCcoef1Ccoef2Hcoef
Roof0.0011535.562.28E-040.001656 9.443.37E-04008.08E-05
Wall, above-grade, and opaque doors6.04E-0402.28E-041.18E-0303.37E-04007.56E-05
Wall, below-grade2.58E-0402.29E-046.80E-0403.35E-04N/A07.85E-05
Mass floor6.91E-0402.39E-041.01E-0303.60E-04007.14E-05
Other floor7.09E-04 02.43E-04 9.54E-0403.66E-04007.14E-05
Slab-on-grade floor002.28E-04003.37E-04006.80E-05
Vertical fenestrationN/A0N/AN/A0N/A007.56E-05
SkylightsN/A0N/AN/A0N/A008.08E-05
C6.10.3 Calculation of COOL and HEAT.
COOL and HEAT shall be calculated for each surface using Equations C-21 and C-22 and coefficients from Table C6.10.2, which depend on surface classification and space-conditioning category.
COOL = Size × Factor × (Ccoef1 × CDD50 + Ccoef2) (C-21)
HEAT = Size × Hcoef × Factor × HDD65 (C-22)
where
Size=area of surface or length of exposed slab-on-grade floor perimeter in the building
Ccoef1, Ccoef2=coefficients, from Table C6.10.2
Hcoef=coefficient from Table C6.10.2
Factor=U-factor except Uadj calculated using Equation C-21 for protected surfaces and for slab-on-grade floors, perimeter
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