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HVAC System Diagram. No outside air flow (exhaust or supply) via HVAC system. AirLoopHVAC:UnitaryHeatCool. Air Supply Inlet Node. Heating Coil Inlet Node. Cooling Coil Inlet Node. Air Supply Outlet Node. Air Demand Inlet Node. Living Supply Node. List: Living Supply Nodes. - PowerPoint PPT Presentation
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HVAC System Diagram
AirLoopHVAC:UnitaryHeatCool
Coil:Cooling:DX:SingleSpeed
Coil:Heating:GasFan:OnOff
Air Supply Inlet Node
Air Supply Outlet Node
Heating Coil Inlet Node
Cooling Coil Inlet Node
Zone [Living]
Living Zone Air Node
AirTerminal:SingleDuct:Uncontrolled
DXDehumidifier Outlet Node
List: Living Supply Nodes
List: Living Exhaust Nodes
DXDehumidifier Inlet Node
Zone [RA Duct Zone]
RA Plenum Air Node Living Return Node
Air Demand Outlet Node
Splitt
er
Air Demand Inlet Node
Living Supply Node
Plenum
ZoneHVAC:Dehumidifier:DX
Single-Family Infiltration & Ventilation Modeling 25 May 2011
No outside air flow (exhaust or supply) via HVAC system
HVAC System Diagram – with ERV
AirLoopHVAC:UnitaryHeatCool
Coil:Cooling:DX:SingleSpeed
Coil:Heating:GasFan:OnOff
Air Supply Inlet Node
Air Supply Outlet Node
Heating Coil Inlet Node
Cooling Coil Inlet Node
Zone [Living]
Living Zone Air Node
AirTerminal:SingleDuct:Uncontrolled
DXDehumidifier Outlet Node
List: Living Supply Nodes
List: Living Exhaust Nodes
DXDehumidifier Inlet Node
Zone [RA Duct Zone]
RA Plenum Air Node Living Return Node
Air Demand Outlet Node
Splitt
er
Air Demand Inlet Node
Living Supply Node
Plenum
ZoneHVAC:Dehumidifier:DX
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Outside air flow (supply and exhaust) via ERV
Fan:OnOff
Fan:OnOff
ERV Exhaust Fan Outlet Node
ERV Exhaust Fan Inlet Node
ERV Outside Air Inlet Node
ERV Supply Fan Inlet Node
Living Exhaust Node
ERV Supply Fan Outlet Node
Infiltration Calculations
Single-Family Infiltration & Ventilation Modeling 25 May 2011
EnergyManagementSystem:Program, InfiltrationProgram, Set Tdiff = Tin - Tout, Set DeltaT = @Abs Tdiff, Set c =0.0806596739779895, Set Cs =0.0808179140957512, Set Cw =0.151714102844197, Set n =0.67, Set sft =0.5039400176752, Set Qn = (((c*Cs*(DeltaT^n))^2)+(((c*Cw)*((sft*Vwind)^(2*n)))^2))^0.5, !Section above: !This is equation 41 + equation 42 from ASHRAE Fundamentals 2005 Ch 27 !"Enhanced Model. This section presents a simple, single-zone approach !to calculating air infiltration rates in houses based on the AIM-2 model !(Walker and Wilson 1998). The airflow rate due to infiltration is !calculated using: ! Qs = c * Cs * DeltaT^n (41) ! Qw = c * Cw (sU)^2n (42) ! where: Qs = stack airflow rate, m3s ! Qw = wind airflow rate, m3/s ! c = flow coefficient, m3/(s/Pa^n) ! Cs = stack coefficient, (Pa/K)^n ! Cw = wind coefficient, (Pa-s^2/m^2)^n ! s = shelter factor ! Several assumptions made when calculating Cs, Cw, s ! including: n = 0.67 ! Equation (39) then describes superposition for the total infiltration rate: ! Q = ((Qs^2)+(Qw^2))^0.5 Set Tdiff = Tin - Tout, Set DeltaT = @Abs Tdiff, Set QWH = WH_sch*0.025029576, Set Qrange = Range_sch*0.04719, Set Qdryer = Clothes_dryer_sch*0.04719, Set Qbath = Bath_sch*0.04719, Set Qu = QWH+Qrange+Qbath+Qdryer+DuctLeakOAMakeupFlowRate, Set Qb = 0, Set faneff_wh =0.28314, Set WholeHouseFanPowerOverride= (QWH*300)/faneff_wh, Set faneff_sp =0.28314, Set RangeHoodFanPowerOverride = (Qrange*300)/faneff_sp, Set BathExhaustFanPowerOverride = (Qbath*300)/faneff_sp, Set Infilflow = ((Qu^2) + (Qn^2))^0.5, Set InfMechVent = Qb + Infilflow; !Two lines above described by Equation (43) in ASHRAE Fundamentals 2005 Ch 27 !Says that you can combine residential infiltration and mechanical ventilation flows: ! Qcomb = Qbal + ((Qunbal^2)+(Qinfil^2))
Qn = infiltration flow
Qu = unbalanced exhaust flow
= QWH + Qrange + Qdryer + Q bath + DuctLeakage
QWH = Whole house exhaust fan
Qrange = Kitchen range hood
Qbath = Bath point exhaust
Qdryer = Dryer exhaust
DuctLeakage = Calculated from DuctLeakageProgram
Qb = balanced ventilation = 0
InfMechVent = Total flow
Parameters to change infiltration rates
Building America House Simulation Protocol, pg 16:
“Additional air exchange whole-house mechanical ventilation shall be calculated assuming a single
point exhaust ventilation system with the same ventilation rate used for the NCTH, up to a maximum
value consistent with the rate recommended by ASHRAE 62.2. Whole-house mechanical ventilation air
shall be added to the natural infiltration rate in quadrature, assuming no heat recovery. Ventilation fan
energy use for the Benchmark shall be calculated using a fan efficiency of 0.5 W/cfm.
In addition to whole-house ventilation, the Benchmark shall include a kitchen range hood, spot
ventilation fan in each bathroom, and exhaust from the clothes dryer. The flow rates of the kitchen and
bathroom fans shall be the same as those in the NCTH, and their efficiency shall be assumed to
operate 60 min/day (between 6:00 pm and 7:00 pm), and each bathroom fan (including those in central
restrooms) is assumed to operate 60 minutes per day (between 7:00 am and 8:00 am). The clothes
dryer fan will operate for 60 minutes per day between 11:00 am and 12:00 pm. Interactive effects
between these spot exhaust ventilation fans and natural infiltration shall be included in the analysis.”
Ventilation Components & Schedules
Single-Family Infiltration & Ventilation Modeling 25 May 2011
ASHRAE 62.2 Ventilation Requirements
€
Q fan = 0.05A floor + 3.5(Nbr +1)
Qfan = fan flow rate in L/s; Afloor = floor area in m2; Nbr = number of bedrooms
For Nbr = 3, Afloor = 222 m2 (2400 ft2):
Qfan = 25.1 L/s
= 0.025 m3/s
= 54 cfm
Single-Family Infiltration & Ventilation Modeling 25 May 2011
ASHRAE 62.2-2003, Section 4.1:
“A mechanical exhaust system, supply system, or combination thereof shall be installed for each
dwelling unit to provide whole-building ventilation with outdoor air each hour at no less than the rate
specified in Table 4.1a and Table 4.1b, or, equivalently, Equations 4.1a and 4.1b, based on the floor
area of the conditioned space and number of bedrooms.”
Modeling Results – Exhaust Flows – Summer Design Day
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – Qu & Qn – Summer Design Day
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – Total Flow – Summer Design Day
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – Hours not meeting ASHRAE 62.2-2003
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Run Hours not met (Qn) Hours not met (Total Flow)
CHI_ICF4in_BaseInfil_GndTemps 545 0
CHI_ICF4in_Infil_a_GndTemps 776 0
CHI_ICF4in_Infil_b_GndTemps 780 0
PHX_ICF4in_BaseInfil_GndTemps 2269 0
PHX_ICF4in_Infil_a_GndTemps 3066 0
PHX_ICF4in_Infil_b_GndTemps 3019 0
Natural Ventilation Calculations
Single-Family Infiltration & Ventilation Modeling 25 May 2011
EnergyManagementSystem:Program, NaturalVentilationProgram, Set Tdiff = Tin - Tout, Set DeltaT = @Abs Tdiff, Set Phiin = @RhFnTdbWPb Tin Win Pbar, ! RhFnTdbWPb: Calculates RH (fraction) from DB, Humidity Ratio, Barometric Pressure Set Hin = @HFnTdbRhPb Tin Phiin Pbar, ! HFnTdbW: Calculates Enthalpy of moist air (J/kg) from DB and Humidity Ratio Set NVArea =12006.190854504, !Not clear how this number is determined, but it is cm^2 Set Cs =0.0001792604077892, Set Cw =0.0002821728237939, Set MaxNV =2.8993536, Set SGNV = (NVAvail*NVArea)*((((Cs*DeltaT)+(Cw*(Vwind^2)))^0.5)/1000), !Line above based on equation (40) from ASHRAE Fundamentals 2005 Ch 27 !This is the basic model for calculating the airflow rate due to infiltration ! Q = AL/1000((Cs*DeltaT)+(Cw(U^2))^0.5 ! where: Q = airflow rate m3/s ! AL = effective air leakage area, cm2 ! DeltaT = Avg indoor-outdoor temp difference, K ! Cw = wind coefficient ! U = avg windspeed measured at local weather station If Wout < 0.0155 && Phiin < 0.70 && Tin > NVSP, !Line above sets outdoor conditions for nat vent !Wout is Outdoor Humidity Ratio; Phiin is RH; Tin is Zone MAT; NVSP is NatVentTemp Schedule Value. Set NVadj1 = (Tin - NVSP)/(Tin - Tout), Set NVadj2 = @Min NVadj1 1, Set NVadj3 = @Max NVadj2 0, Set NVadj = SGNV*NVadj3, Set NatVentFlow = @Min NVadj MaxNV, Else, Set NatVentFlow = 0, EndIf;
Qn = infiltration flow
Qu = unbalanced exhaust flow
= QWH + Qrange + Qdryer + Q bath + DuctLeakage
QWH = Whole house exhaust fan
Qrange = Kitchen range hood
Qbath = Bath point exhaust
Qdryer = Dryer exhaust
DuctLeakage = Calculated from DuctLeakageProgram
Qb = balanced ventilation = 0
InfMechVent = Total flow
Modeling Results – BEOpt Vent Options
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – BEOpt NatVent Options
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – BEOpt Slab Options
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – NatVent
Single-Family Infiltration & Ventilation Modeling 25 May 2011
This report variable represents the sensible heating energy in Joules that is actually supplied by the system to that zone for the timestep reported. This is the sensible heating rate multipled by the simulation timestep.
“Zone/Sys Sensible Heating (and Cooling) Energy all report the heating or cooling delivered by the HVAC system to a zone. These values are calculated by multiplying the supply air mass flow rate by the difference between the supply air temperature and the zone air temperature. This does not always indicate the operation of heating or cooling coils. For example, cooling will be reported if the supply air is cooled due to the introduction of outside air, event if all coils are off.” I/O pg. 168
Modeling Results – NatVent
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – NatVent
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – NatVent
Single-Family Infiltration & Ventilation Modeling 25 May 2011
This is the total (sensible plus latent) cooling output of the DX coil in Joules over the timestep being reported. This is determined by the coil inlet and outlet air conditions and the air mass flow rate through the coil. I/O pg. 168
Modeling Results – NatVent - SFO
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – NatVent - SFO
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – MechVent (w and w/o nat vent)
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – MechVent (w and w/o nat vent)
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – MechVent (w and w/o nat vent)
Single-Family Infiltration & Ventilation Modeling 25 May 2011
Modeling Results – MechVent (w and w/o nat vent)
Single-Family Infiltration & Ventilation Modeling 25 May 2011