## 2.3 How to Build an Airnet

### 2.3.1 Background

### 2.3.2 Approach

IZXFER is the building block input for an Airnet. There will be many IZXFERs in an input file, each representing a single air transfer object (leak, vent, window, fan, duct leak). Each IZXFER needs a unique name if detailed reports on its activity are needed. IZXFER is a command at the same level as HOLIDAY.

MATERIAL, CONSTRUCTION, METER, ZONE and REPORT which means that it can be located anywhere except inside another object (like a zone).

The main objects in the Airnet are:

• Infiltration

• Window ventilation

• IAQ ventilation

• Mechanical cooling ventilation

• Duct leakage

Units are ft2.

CBECC inputs to add for Airnet:

WinHHTop | Head height of the highest windows in the zone. Used to get the vertical location of the window ventilation holes. In the development program this was done on a building wide basis: #define WnHeadHeight 7.67 // Average head height above the floor of operable windows
Ventilation Height Difference | This rule needs to be changed to refer to Zone instead of Building: "The default assumption for the proposed design is 2 feet for one story buildings and 8 feet for two or more stories. Greater height differences may be used with special ventilation features such as high, operable clerestory windows. In this case, the height difference entered by the user is the height between the average center height of the lower operable windows and the average center height of the upper operable windows. Such features shall be fully documented on the building plans and noted in the Special Features Inspection Checklist of the CF-1R." (2008 RACM pp 3-9)
Floor Height | The height of each floor over outdoors, crawl or garage is needed to set the Z dimension of the hole in the floor.
Soffit height | The height of the attic floor. Probably can be determined by the height of the ceiling below attic. Trouble for Split level?
Interzone Door | May need input for whether an interzone door exists between each 2 conditioned zones. Assuming it for now.
ReturnRegister | The conditioned zone(s) where the return/exhaust register is located. Make this an input on the HVAC System Data screen

#### 2.3.2.1 Problems

• The window scheme doesn't work for 3 story zones!!!

• The Econ and NightBreeze cooling ventilation systems are multizone and use ducts. I suggest we set them up as part of the duct system.

### 2.3.3 Inputs

ACH50 | 7.6 (Air Changes per Hour at 50 Pascals pressure difference that leak through the envelope of the conditioned zones)
Avent | 1/300 (ratio of "free area of attic vents to AceilGross)
Fraction High | 0.3 (fraction of the attic vent area located in the upper part of the attic, check precise definition)

1. Infiltration Setup. Infiltration is uncontrolled air leakage through the cracks and intentional vents in the building. The first step is to determine the total size of the openings and then distribute them over the conditioned zones in proportion to surface areas.

It is modeled in a single conditioned zones with 8 holes (IZXFERs) to represent the leakage in vertical walls and 1 hole each in the floor and ceiling.

Calculate:

a. For conditioned zones the total Effective Leakage Area ELAtot = CFA*ACH50/(2*10000) (CFA is conditioned floor area)

b. Determine Envelope Areas

1. ExCeiltotSF =sum (AceilGross + area of exterior ceilings) (exterior ceilings are surfaces in conditioned zones of type ceiling whose outside condition is Ambient, Ignore Knee walls for infiltration (walls between the conditioned zone and the attic)

2. ExWalltotSF =sum (Gross Area of Exterior Walls) (walls in conditioned zones whose outside condition is Ambient)

3. ExFloortotSF =sum (Gross Area of Exterior floors) (floors in conditioned zones whose outside condition is Ambient, Crawl or GROUND)

4. ExFloorSlabSF =sum (Gross Area of Exterior slab on grade floors) (slab on grade floors in conditioned zones)

5. SlabRatio =ExFloorSlabSF/ExFloortotSF

6. GaragetotSF =sum (Gross Area of Surfaces to Garage) (walls and floors in conditioned zones whose outside condition is Garage)

c. Determine leakage distribution:

1. ELAceilsf = ELAtot* (.4+.1*SlabRatio)/( AceilGross + area of exterior ceilings)

2. ELAraisedFloorsf = ELAtot* (.2* 1-SlabRatio)/( ExFloortotSF-ExFloorSlabSF)

#If there is a garage zone

3. ELAGaragesf = ELAtot* 0.1/GaragetotSF

4. ELAwallsf = ELAtot* (.3 + .1*SlabRatio)/ExWalltotSF

#Else

3. ELAGaragesf = 0

4. ELAwallsf = ELAtot* (.4 + .1*SlabRatio)/ExWalltotSF

#endif

2. Cooling Ventilation Setup: Four types: Windows only (all types have windows for some part of the year), Whole house fan, Smart Vent, NightBreeze

Set up seasonal window control

#if Smart Vent or NightBreeze //Windows are on in Winter, but off in summer when mechanical ventilation is on

#redefine Windowmode select( @weather.taDbAvg07 >60., 0.00001,default 1.)

#define VentDiffMult select( @top.tDbOSh < (@znRes[Single].prior.S.tAir-VentDiff), 1,default 0.000001) //Vent off if Tin-Vendiff > Tout

#Else //everything but Econ and NightBreeeze Windows are on year round

#reDefine Windowmode 1. //Always available

#Define VentDiff 0 // Differential. No differential for windows or WWF

// multiplier for window and whole house fan vent availability, .00001 is proxy for Off Revised to start at dawn end at 11 PM.

#redefine Win_hr select( $hour < 24, select($radDiff <1., select($hour>12,1.0, default .00001 ), default 1.0 ), default .00001 )

3. Airnet for Each Conditioned Zone:

a. Calculate

ELA_Aceil(zone) = ELAceilsf * AceilGross(zone)

ELA_Xceil(zone) = ELAceilsf * (AEdge(zone) + area of exterior ceilings(zone)) //AEdge is determined in the Ceiling Surface setup BAW 120517

ELAXwall(zone) = ELAwallsf * Gross Area of Exterior Walls(zone)

ELAGwall(zone) = ELAGaragesf * Gross Area of walls and floors next to the Garage(zone)

ELAfloor(zone) = ELAraisedFloorsf * AreaExtfloor(zone) (gross area of floors whose outside condition is Ambient, Crawl)

ZoneBotZ = Bottom(zone) - height of the lowest floor in the zone

ZoneTopZ = ZoneBotZ + FloortoFloor(zone)*NumofStories(zone)

ZoneHeightZ = ZoneTopZ - ZoneBotZ

WinHHTop = ZoneBotZ + FloortoFloor(zone)*(NumofStories(zone)-1) + Window head height

b. Exteror wall of conditioned zones infiltration objects Calculate height of bottom and top holes.

// All infiltration leaks in walls are assumed to be spread uniformly over the exposed wall surfaces areas. There are no LEAKS associated with windows, doors etc.

//8 Wall Holes in each zone to Outdoors 1 upwind, 2 side walls, 1 downwind. Sidewalls are identical so combine them into 1 hole with 2*area

// Low is at 1/4 of wall height, high is at 3/4 of wall height

// izCpr (default = 0) = Wind Coef Upwind wall +0.6 Side walls -0.65 Downwind Wall -0.3

ELAXwall(zone) = ELAwallsf * Gross Area of Exterior Walls(zone)

WH = ELAXwall(zone)*1.45/8 //Wall Hole size. Conversion from ELA to airnet infiltration opening is 1.45*

Write Airnet Objects to CSE Input WlLU stands for Wall Low Upwind etc.

IZXFER (ZoneName)WlLU izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = WH izHD = ZoneBotZ + (0.25 * ZoneHeightZ) izNVEff = 1 izExp=0.65 izCpr=0.6

IZXFER (ZoneName)WlLS izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = 2*WH izHD = ZoneBotZ + (0.25 * ZoneHeightZ) izNVEff = 1 izExp=0.65 izCpr=-.65

IZXFER (ZoneName)WlLD izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = WH izHD = ZoneBotZ + (0.25 * ZoneHeightZ) izNVEff = 1 izExp=0.65 izCpr=-0.3

IZXFER (ZoneName)WlHU izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = WH izHD = ZoneBotZ + (0.75 * ZoneHeightZ) izNVEff = 1 izExp=0.65 izCpr=0.6

IZXFER (ZoneName)WlHS izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = 2*WH izHD = ZoneBotZ + (0.75 * ZoneHeightZ)izNVEff = 1 izExp=0.65 izCpr=-.65

IZXFER (ZoneName)WlHD izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = WH izHD = ZoneBotZ + (0.75 * ZoneHeightZ) izNVEff = 1 izExp=0.65 izCpr=-0.3

c. Windows

// Operable window openings for ventilation. Assumes effect of screens is included in open area Revised 120409 BAW

// IZXFER izALo and izAHi are the min and max vent areas. Both are hourly.

//8 Window Holes in zone Single to Outdoors Assumes no orientation so 1/4 each orientation, 1/8 low and 1/8 high. Sidewalls are identical so combine them into 1 hole with 2*area

// high is at 1/2 default Hdiff below Window WinHHTop, Low is at WinHdiff below.high

//Note that this scheme doesn't work for 3 story zones!!!

Inputs

WnVentArea // ft2, Nonzero - operable window open area. Default is 10 percent of the window area. Assume a single window is 4 feet high with openings centered at -1 and -3' from the top

WnVentHDiff 2.0 // Window vent height difference between center of high opening and low opening

WinHHTop // Head height of highest windows in the zone

Calculate

WnHole = 0.5*(WnVentArea/8.)*Win_hr*Windowmode // 1/8th in each hole, ft2. 1/2 of nominal area to account for screens etc. Hourly and seasonal availability

Write Airnet Objects to CSE Input WnLU stands for Window Low Upwind etc

IZXFER (ZoneName)WnLU izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = WnHole izHD = WinHHTop -(3+ WnVentHDiff) izNVEff =.5 izCpr=0.6

IZXFER (ZoneName)WnLS izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = 2*WnHole izHD = WinHHTop - (3+WnVentHDiff) izNVEff =.5 izCpr=-.65

IZXFER (ZoneName)WnLD izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = WnHole izHD = WinHHTop - (3+WnVentHDiff) izNVEff =.5 izCpr=-0.3

IZXFER (ZoneName)WnHU izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = WnHole izHD = (WinHHTop-1) izNVEff =.5 izCpr=0.6

IZXFER (ZoneName)WnHS izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = 2*WnHole izHD = (WinHHTop-1) izNVEff =.5 izCpr=-.65

IZXFER (ZoneName)WnHD izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo=.00001 izAHi = WnHole izHD = (WinHHTop-1) izNVEff =.5 izCpr=-0.3

d. Ceiling

Calculate

If ceiling below attic

ELA_Aceil(zone) = ELAceilsf * AceilGross(zone) //knee walls to attic not included in determining the conditioned to attic leakage distribution of

If Whole House fan, Ceiling leak through WWF when off

If Improved WHFela = .05 // Average of Motor Damper Models

else WHFela = .11 // Average of Gravity Damper Models

If ceiling to outside

ELA_Xceil(zone) = ELAceilsf * AEdge(zone) + area of exterior ceilings(zone)

CeilHole = (ELA_Aceil(zone) + WHFela )*1.45 //Ceil Hole size. Conversion from ELA to airnet infiltration opening is 1.45*

CathCeilHole = ELA_Xceil(zone) * 1.45 //Cathedral Ceil Hole size. Conversion from ELA to airnet infiltration opening is 1.45*

Write Airnet Objects to CSE Input

IZXFER (ZoneName)xAttic izNVTYPE = AirNetIZ izZN1=(ZoneName) izALo=CeilHole izHD = ZoneTopZ izNVEff=1. izExp=0.65 izZN2 = Attic

IZXFER (ZoneName)CC izNVTYPE = AirNetExt izZN1=(ZoneName) izALo=CathCeilHole izHD = ZoneTopZ izNVEff=1. izExp=0.65

e. Floor over outside

For each floor over outside calculate:

ELAfloor(Name) = ELAraisedFloorsf * AreaExtfloor * 1.45 (floors whose outside condition is Ambiant)

Write Airnet Object to CSE Input

IZXFER (Name) izNVTYPE = AirNetExt izZN1 = (ZoneName) izALo = ELAfloor(Name) izHD = Floor Height izNVEff = 1 izExp=0.65 izCpr=0. // located at the Extfloor elevation, no wind effect

f. Floor over Crawl

For each floor over outside calculate:

ELAfloor(Name) = ELAraisedFloorsf * AreaCrawlfloor * 1.45 (floors whose outside condition is Crawl)

Write Airnet Object to CSE Input

IZXFER (Name)xCrawl izNVTYPE = AirNetIZ izZN1=(ZoneName) izALo=ELAfloor(Name) izHD = Floor Height izNVEff=1. izExp=0.65 izZN2 = Crawl

g. Floor over Garage

For each floor over garage calculate:

ELAfloor(Name) = ELAGaragesf * AreaGarfloor * 1.45 (floors whose outside condition is Garage)

Write Airnet Object to CSE Input

IZXFER (Name)xGarage izNVTYPE = AirNetIZ izZN1=(ZoneName) izALo=ELAfloor(Name) izHD = Floor Height izNVEff=1. izExp=0.65 izZN2 = Garage

h. Garage wall

Calculate:

GWH = ELAGaragesf * Gross Area of walls next to the Garage(zone)/2 // size of the 2 holes (high and low) betwen zone and garage

GWalltopZ = Min(ZoneTopZ(zone),(ZoneTopZ(Garage)) //The top of the shared wall

GWallBotZ = Max(ZoneBotZ(zone),(ZoneBotZ(Garage)) //The bottom of the shared wall

GwallH = GWalltopZ - GWallBotZ // Height of shared wall

GWHhZ = GwallBotZ + .75 GwallH // Height of top hole

GWHlZ = GwallBotZ + .25 GwallH // Height of bottom hole

Write Airnet Objects to CSE Input

IZXFER (ZoneName)xGarageH izNVTYPE = AirNetIZ izZN1=(ZoneName) izALo=GWH izHD = GWHhZ izNVEff=1. izExp=0.65 izZN2 = Garage

IZXFER (ZoneName)xGarageL izNVTYPE = AirNetIZ izZN1=(ZoneName) izALo=GWH izHD = GWHlZ izNVEff=1. izExp=0.65 izZN2 = Garage

4. Airnet for Each Unconditioned Zone:

a. Attic

If Ventilated attic Calculate (4 soffit vents at attic floor elevation plus sloped deck vents at 2/3 of Attic high if frac high > 0

// Pitch types for roof wind pressure coeffs: 0 deg, <10deg, <15 deg,<25, <35 ,all the rest. Flat same as low slope.

#define PitchType select( Pitch <= 0, 1,Pitch <= 0.18, 1,Pitch <= 0.27, 2,Pitch <= 0.47, 3,Pitch <= 0.7, 4,default 5)

AventTot = AceilGross * AVent

SoffitVent 0.5*0.25 *(1.-FracHigh)*Max(AventTot, AtticRelief) //Attic relief is minimum vent needed to vent mechanical cooling air dumped to attic

Deckvent 0.5*0.25*FracHigh*Max(AventTot, AtticRelief)

If sealed attic [to be developed]

Write Airnet Objects to CSE Input

IZXFER AtticSU izNVTYPE = AirNetExt izZN1 = Attic izALo = SoffitVent izHD = SoffitHeight izNVEff = .6 izExp=0.65 izCpr=0.6

IZXFER AtticSS izNVTYPE = AirNetExt izZN1 = Attic izALo = 2*SoffitVent izHD = SoffitHeight izNVEff = .6 izExp=0.65 izCpr=-.65

IZXFER AtticSD izNVTYPE = AirNetExt izZN1 = Attic izALo = SoffitVent izHD = SoffitHeight izNVEff = .6 izExp=0.65 izCpr=-0.3

IZXFER AtticDU izNVTYPE = AirNetExt izZN1 = Attic izALo = DeckVent izHD = 0.67 * AtticHeight + SoffitHeight izNVEff=.6 izExp=0.5 izCpr=testx*choose(Pitchtype,-.5,-.8,-.5,-.3,.1,.3)

IZXFER AtticDS izNVTYPE = AirNetExt izZN1 = Attic izALo = 2*DeckVent izHD = 0.67 * AtticHeight + SoffitHeight izNVEff=.6 izExp=0.5 izCpr=testx*choose(Pitchtype,-.5,-.5,-.5,-.5,-.5,-.5)

IZXFER AtticDD izNVTYPE = AirNetExt izZN1 = Attic izALo = DeckVent izHD = 0.67 * AtticHeight + SoffitHeight izNVEff=.6 izExp=0.5 izCpr=testx*choose(Pitchtype,-.5,-.3,-.5,-.5,-.5,-.5)

b. Garage – Assume California garage with a water heater and combustion air vents so it is pretty leaky Guess 1 ft2 of free area. Ignore other infiltration

Calculate

Gvent = 1/4

Write Airnet Objects to CSE Input

IZXFER GarageU izNVTYPE = AirNetExt izZN1 = Garage izALo = Gvent izHD = GarageBotZ +1 izNVEff = .6 izExp=0.65 izCpr=0.6

IZXFER GarageS izNVTYPE = AirNetExt izZN1 = Garage izALo = 2*Gvent izHD = GarageBotZ +1 izNVEff = .6 izExp=0.65 izCpr=-.65

IZXFER GarageD izNVTYPE = AirNetExt izZN1 = Garage izALo = Gvent izHD = GarageBotZ +1 izNVEff = .6 izExp=0.65 izCpr=-0.3

c. Vented crawl space [To Be Developed]

d. Sealed crawl space [To Be Developed]

e. Basement [To Be Developed]

5. Interzone Holes – Assume an open door or stair between any twp conditioned zones with common surfaces, except between units in multi-family

If 2 or more conditioned zones

Error if not at least one common surface for every conditioned zone (a surface in zone A whose outside condition is another conditoned zone)

Door calculation for each pair of zones with a common wall surface (zoneA<>zoneB, zoneB<>zoneC, zoneA<>zoneC, etc)

DoortopZ = Min(ZoneTopZ(zone A),(ZoneTopZ(zone B)) //The top of the shared wall

DoorBotZ = Max(ZoneBotZ(zone A),(ZoneBotZ(zone B)) //The bottom of the shared wall

DoorH = DoortopZ - DoorBotZ // Height of shared opening

DH = 20/ // Area of half of assumed door

DHhZ = GwallBotZ + .75 GwallH // Height of top hole

DHHlZ = GwallBotZ + .25 GwallH // Height of bottom hole

For each zone pair write Airnet Objects to CSE Input

IZXFER (ZoneNameA)DHx(ZoneNameB)DH izNVTYPE = AirNetIZ izZN1=(ZoneNameA) izALo=DH izHD = DHhZ izNVEff=1. izExp=0.5 izZN2 = (ZoneNameB)

IZXFER (ZoneNameA)DLx(ZoneNameB)DL izNVTYPE = AirNetIZ izZN1=(ZoneNameA) izALo=DH izHD = DHlZ izNVEff=1. izExp=0.5 izZN2 = (ZoneNameB)

Stair calculation for each pair of zones with only a floor/ceiling surface (zoneA<>zoneB, zoneB<>zoneC, zoneA<>zoneC, etc)

StairZ = Max(ZoneBotZ(zone A),(ZoneBotZ(zone B)) //The height of the stair hole is at the upper floor

For each zone pair write Airnet Objects to CSE Input Note that izZN1 MUST be the lower of the 2 zones or the model doesn't work

IZXFER (ZoneNameA)Sx(ZoneNameB)S izNVType = AIRNETHORIZ izZN1=(ZoneName of lowerzone) izZN2 = (ZoneName of upper zone) izL1=3 izL1=10 izHD =StairZ

6. IAQ ventilation

Inputs for each zone

IAQVentCFM // CFM of IAQ vent

IAQfanWperCFM // W/CFM of IAQ vent

Type IAQExhaust // "IAQExhaust", "IAQSupply", "IAQBalanced" "NoIAQVent"

IAQVentHtRcv 0.0 // Heat recovery efficiency of Balanced type, frac

Write Airnet Objects to CSE Input

If Exhaust

IZXFER (Zone)IAQfan izNVTYPE = AirNetExtFan izZN1 = (Zone) izVFmin=-IAQVentCFM izVFmax=-IAQVentCFM izFanVfDs=IAQVentCFM izFanElecPwr=IAQfanWperCFM izFanMtr=IAQventMtr

If IAQSupply

IZXFER (Zone)IAQfan izNVTYPE = AirNetExtFan izZN1 = (Zone) izVFmin=IAQVentCFM izVFmax=IAQVentCFM izFanVfDs=IAQVentCFM izFanElecPwr=IAQfanWperCFM izFanMtr=IAQventMtr

If IAQBalanced // Needs heat recovery

IZXFER (Zone)IAQfanS izNVTYPE = AirNetExtFan izZN1 = (Zone) izVFmin=IAQVentCFM izVFmax=IAQVentCFM izFanVfDs=IAQVentCFM izFanElecPwr=IAQfanWperCFM izFanMtr=IAQventMtr

IZXFER (Zone)IAQfanE izNVTYPE = AirNetExtFan izZN1 = (Zone) izVFmin=-IAQVentCFM izVFmax=-IAQVentCFM izFanVfDs=IAQVentCFM izFanElecPwr=IAQfanWperCFM izFanMtr=IAQventMtr

7. Mechanical Cooling Ventilation // The following does not work for multi-zone systems with Econ, NightBreeze. Revise along with ducts model

For each Cooling Ventilation System

Inputs

CoolVentType //type of MECHANICAL cooling ventilation, Choice of WHF, Econ, NightBreeze

CoolVentCFM //Rated air flow of the mechanical cooling system

CoolVent W/CFM //

ReturnRegister // If WHF the conditoned zone where it is located

Calculate

Relief = CoolVentCFM/750 // The minimum size of the attic vents required to let the WHF flow out of the attic

If WHF // Whole House Fan

Calculate

Relief = CoolVentCFM/750 // The minimum size of the attic vent required for this fan to let the WHF flow out of the attic

Write Airnet Objects to CSE Input

IZXFER (Zone)WHF izNVTYPE=AirNetIZFan izZN1=(Zone) izVFmin=0. izVFMax=-CoolVentCFM*Win_hr izFanVfDs=CoolVentCFM izZn2=Attic izFanElecPwr=CoolVentWperCFM izFanMtr=CoolVentMtr

If Econ // Economizer ventilation option on the Central Forced Air System such as Smartvent

Calculate

Relief = CoolVentCFM/750 // The minimum size of the attic vent required for this fan to let the WHF flow out of the attic

Write Airnet Objects to CSE Input

ZXFER Econ# izNVTYPE=AirNetExtFan izZN1=(zone) izVFmin=0. izVFMax=CoolVentCFM*Coolmode*VentDiffMult izFanVfDs=CoolVentCFM izFanElecPwr=CoolVentWperCFM izFanMtr=CoolVentMtr //!! 110413

IZXFER Relief# izNVTYPE=AirNetIZFlow izZN1=ReturnRegister izZn2=Attic izVFmin=0 izVFmax=-CoolVentCFM*Coolmode*.9*VentDiffMult

If NightBreeze //Model for NightBreeze variable flow night ventilation system !!needs lower limit @ CFA<1000/unit and multiple systems @ CFA> 3333 ft2

Calculate

Relief = CoolVentCFM/750 // The minimum size of the attic vent required for this fan to let the WHF flow out of the attic

Write Airnet Objects to CSE Input

IZXFER NightBreeze izNVTYPE=AirNetExtFan izZN1=(zone) izVFmin=0. izFanMtr=CoolVentMtr

izFanVfDs=CoolVentCFM * CFA //CoolVentCFM = CFM/CFA for NightBreeze. Default is 0.6

izFanElecPwr = (616.47-0.6159*CFA + .000246 *CFA*CFA)/(CoolVentCFM * CFA) //W/CFM DEG 9/29/2010 Equation 1

izVFMax=CoolVentCFM*Coolmode*VentDiffMult*CFA / max((17.91554 - 3.67538 * logE(@weather.taDbPvPk)),1) //DEG 9/29/2010 Equation 3 110411

izFanCurvePy = 0, -0.026937155, 0.187108922, 0.839620406, 0 //Fit to DEG flow^2.85

IZXFER NBRelief izNVTYPE=AirNetIZFlow izZN1=ReturnRegister izZn2=Attic izVFmin=0 izVFmax=-CoolVentCFM * CFA * Coolmode*.9 *VentDiffMult

Next Zone

Calculate

AtticRelief = Sum(CoolVentCFM)/750 // The sum of all zonal cool vent CFM determines the minimum size of the attic vents required to let the vent air out of the attic

//Used in Attic Zone AirNet above

//Min Attic Vent area for relief Tamarac http://www.tamtech.com/userfiles/Fan%20size%20and%20venting%20requirements(3).pdf

7. Duct system leaks and pressurization. These are generated by automatically by CSE based on the duct system inputs.