Download - HVAC System Diagram

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


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


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


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


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


Modeling Results – Qu & Qn – Summer Design Day


Modeling Results – Total Flow – Summer Design Day


Modeling Results – Hours not meeting ASHRAE 62.2-2003


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


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


Modeling Results – BEOpt NatVent Options


Modeling Results – BEOpt Slab Options


Modeling Results – NatVent


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



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


Modeling Results – MechVent (w and w/o nat vent)
