Supply
Extract
Fan:VariableVolume
Used in:
- Air Handling Unit (Variable Volume)
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A unique auto-generated name for the fan. Any reference to this fan by another object will use this name.
The type of the variable volume fan is fixed as:
To change from variable volume to constant volume you most open the parent AHU dialog and change the Fan type to 1-Constant volume.
The ratio of the power delivered to the fluid to the electrical input power at maximum flow. It is the product of the motor efficiency and the fan efficiency. The motor efficiency is the power delivered to the shaft divided by the electrical power input to the motor. The fan efficiency is power delivered to the fluid (air) divided by the shaft power. The power delivered to the fluid is the mass flow rate of the air multiplied by the pressure rise divided by the air density. Must be between 0 and 1.
The pressure rise (in Pascals or ftH2O) at full flow and standard (sea level) conditions (20°C and 101325 Pa).
The required pressure rise across an AHU fan is dependent on the duct network supplied by the AHU. For example, if a duct network was sized using a constant pressure loss of 1 Pa/m and the index run of the network (route of highest pressure drop) was say 300 m and the fitting losses were say an additional 20%, the required pressure rise across the fan would be 300 x 1 x 1.2= 360 Pa.
Allows you to specify a user-defined end-use subcategory, e.g., "Central System", etc. A new meter for reporting is created for each unique subcategory (ref: Report Meter). Subcategories are also reported in the ABUPS table. If this field is omitted or blank, the fan will be assigned to the "General" end-use subcategory.
This field is a key/choice field that tells which of the next two fields is filled and is descriptive of how the minimum flow rate is specified for calculating the fan power. The key/choices are:
The minimum air volumetric flow rate for fan power, specified as a fraction of maximum system air flow rate. Must be between 0 and 1. Note that this field is only used to calculate the fan power. This field does not enforce the system air flow rate during simulation.
The minimum air volumetric flow rate for fan power, specified as a constant minimum air flow rate (m3/sec or ft3/min). Note that this field is only used to calculate the fan power. This field does not enforce the system air flow rate during simulation.
The full load air volumetric flow rate (m3/sec or ft3/min) at standard temperature and pressure (dry air at 20°C dry-bulb). The program does use local barometric pressure to account for altitude using equation for "standard atmospheric" pressure on p 6.1 of the ASHRAE 1997 HOF (SI edition) to initialize the air systems being simulated.
p=101325*(1-2.25577E-05*Z)5.2559
where p=pressure in Pa and Z=altitude in m
The minimum air volumetric flow rate (m3/sec or ft3/min) for the fan at standard temperature and pressure (see Maximum Flow Rate field above for details).
The shaft power divided by the electrical power consumed. Must be between 0 and 1.
The fraction of the motor heat that is added to the air stream. A value of 0 means that the motor is completely outside the air stream. A value of 1 means that all of the motor heat loss will go into the air stream and act to cause a temperature rise. Must be between 0 and 1.
Fan coefficient data under this header provides the coefficients C2 to C5 in the fourth order polynomial curve giving the fraction of full load power (PLF) as a function of flow fraction (FF). Flow fraction is the air mass flow rate divided by the maximum air mass flow rate.
PLF = C1 + C2. FF + C3 FF2 + C4.FF3 + C5. FF4
The constant coefficient C1 in the above curve
The linear coefficient C2 in the above curve
The quadratic coefficient C3 in the above curve
The cubic coefficient C4 in the above curve
The coefficient C5 in the above curve
Schedule that defines whether the fan can run during a given time period. A schedule value greater than 0 (usually 1 is used) indicates that the fan can be on during a given time period. A value less than or equal to 0 (usually 0 is used) denotes that the fan is off.
The algorithm used to calculate energy consumption and air outlet conditions in variable flow fans are as follows.
fflow = m / mmax
fpl = c1 + c2.fflow + c3.fflow2 + c4.fflow3 + c5.fflow4
Qtot = fpl.m.δP/(etot.ρair)
Qshaft = emotor.Qtot
Qtoair = Qshaft + (Qtot - Qshaft).fmotortoair
hout = hin + Qmotor / m
wout = win
Tout = PsyTdbFnHW(hout,wout)
Nomenclature:
fflow is the flow fraction of design or maximum flow
fpl is the part load factor
Qtot is fan power in W
m is mass flow in kg/s
δP is the design pressure increase
etot is fan total efficiency
emotor is the motor efficiency
ρair is air density at standard conditions (kg/m3)
Qshaft is the fan shaft power in W
Qtoair is the power entering the air in W
hout,hin are the outlet and inlet specific enthalpies in J/kg
wout,win are the inlet and outlet air stream humidity ratios
PsyTdbFnHW is the EnergyPlus psychrometric routine relating enthalpy and humidity ratio to temperature.
HVAC,Average,Fan Electric Power[W]
HVAC,Average,Fan Delta Temp[C]
HVAC,Sum,Fan Electric Consumption[J]
This output field contains the average electricity consumption rate for the fan in Watts for the timestep being reported.
This output field contains the average rise in air temperature across the fan (outlet air temperature minus inlet air temperature) (in °C or °F)elsius for the timestep being reported.
This output field contains the electricity consumption of the fan in Joules for the timestep being reported. This output is also added to a report meter with Resource Type = Electricity, End Use Key= Fans, Group Key= System (ref. Report Meter).