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Control diagrams and the associated sequence of operations for three of the most
energy efficient outdoor air ventilation and building pressurization control strategies
are provided below.
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Strategy 1: Direct OA Measurement with Supply/Return Fan Tracking
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Strategy 1 includes direct measurement of the outdoor air intake flow rate for ventilation
rate control with volumetric tracking of the supply fan flow rate vs. return fan
flow rate for building pressurization. The associated control diagram, sequence
of operations, technical data sheets, and specifications are provided below.
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Control Diagram
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Sequence Of Operations
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Ventilation Rate Control
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The outdoor airflow measurement system measures the outdoor air intake flow rate
and converts the total and static pressure signals into a voltage or current control
signal that is linear and proportional to the measured outdoor air volume. The temperature
sensor/transmitter output signal is used by the outdoor airflow measurement system
for air density compensation for standard or actual airflow calculations. The outdoor
airflow measurement system output is sent to the airflow processing center (APC)
or building management system (BMS).
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The APC or BMS shall be programmed with setpoints for the minimum outdoor air volume
and economizer (mixed air) temperature controller value.
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The APC or BMS controller shall compare the minimum outdoor air volume setpoint
value and the economizer temperature control signal. During minimum outdoor air
operation the APC or BMS shall allow the volume controller to modulate the outdoor
and return air damper motors to maintain the minimum ventilation air requirement.
When the system is in the economizer (mixed air) mode of operation, the APC or BMS
shall allow the control signal to increase the outside air volume proportionately
to the economizer temperature signal. At all times, the control value demanding
the greater amount of outdoor air shall be passed on to the outdoor and return air
damper motors.
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Building Pressurization
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The static pressure measurement system measures the static pressure in the supply
duct 2/3 to 3/4 of the way down the duct main and converts the static pressure signal
into a voltage or current control signal that is linear and proportional to differential
pressure. The pressure measurement system output is sent to the APC or BMS.
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The APC or BMS uses the pressure feedback to control the speed of the supply fan
with a variable speed drive (VSD) to maintain a constant pressure.
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The fan inlet airflow measurement systems measure the airflow rate of the supply
and return fans and convert the total and static pressure signals into a voltage
or current control signal that is linear and proportional to the measured air volume.
The fan inlet airflow measurement system outputs are sent to the APC or BMS.
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The APC or BMS controller shall compare the control signals representing the return
fan and supply fan and issue a 0-10 vdc or 4-20 mA control signal to position the
return fan VSD to maintain a constant differential between the two airflow rates.
The differential flow rate shall be established in the field as a value required
to maintain the building envelope at a slight positive pressure.
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Product Technical Data Sheets
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Specifications
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Strategy 2: Direct OA Measurement with OA/Exhaust Fan Tracking
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Strategy 2 includes direct measurement of the outdoor air intake flow rate for ventilation
rate control with volumetric tracking of the outdoor air intake flow rate vs. the
exhaust flow rate for building pressurization. The associated control diagram, sequence
of operations, technical data sheets, and specifications are provided below.
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Control Diagram
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Sequence Of Operations
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Ventilation Rate Control
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The outdoor airflow measurement system measures the outdoor air intake flow rate
and converts the total and static pressure signals into a voltage or current control
signal that is linear and proportional to the measured outdoor air volume. The temperature
sensor/transmitter output signal is used by the outdoor airflow measurement system
for air density compensation for standard or actual airflow calculations. The outdoor
airflow measurement system output is sent to the airflow processing center (APC)
or building management system (BMS).
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The APC or BMS shall be programmed with setpoints for the minimum outdoor air volume
and economizer (mixed air) temperature controller value.
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The Apc Or Bms Controller Shall Compare The Minimum Outdoor Air Volume Setpoint
Value And The Economizer Temperature Control Signal. During Minimum Outdoor Air
Operation The Apc Or Bms Shall Allow The Volume Controller To Modulate The Outdoor
And Return Air Damper Motors To Maintain The Minimum Ventilation Air Requirement.
When The System Is In The Economizer (Mixed Air) Mode Of Operation, The Apc Or Bms
Shall Allow The Control Signal To Increase The Outside Air Volume Proportionately
To The Economizer Temperature Signal. At All Times, The Control Value Demanding
The Greater Amount Of Outdoor Air Shall Be Passed On To The Outdoor And Return Air
Damper Motors.
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Building Pressurization
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The static pressure measurement system measures the static pressure in the supply
duct 2/3 to 3/4 of the way down the duct main and converts the static pressure signal
into a voltage or current control signal that is linear and proportional to differential
pressure. The pressure measurement system output is sent to the APC or BMS.
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The APC or BMS uses the pressure feedback to control the speed of the supply fan
with a variable speed drive (VSD) to maintain a constant pressure.
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The outdoor airflow measurement system measures the outdoor air intake flow rate
and converts the total and static pressure signals into a voltage or current control
signal that is linear and proportional to the measured outdoor air volume. The temperature
sensor/transmitter output signal is used by the outdoor airflow measurement system
for air density compensation for standard or actual airflow calculations. The outdoor
airflow measurement system output is sent to the airflow processing center (APC)
or building management system (BMS).
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The duct mounted airflow measurement system measures the airflow rate in the exhaust
duct and converts the total and static pressure signals into a voltage or current
control signal that is linear and proportional to the measured air volume. The duct
mounted airflow measurement system output is sent to the APC or BMS.
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The APC or BMS controller shall compare the control signals representing the outdoor
air intake flow rate and the airflow rate in the exhaust duct and issue a 0-10 vdc
or 4-20 mA control signal to position the exhaust fan VSD to maintain a constant
differential between the two airflow rates. The differential flow rate shall be
established in the field as a value required to maintain the building envelope at
a slight positive pressure.
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Product Technical Data Sheets
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Specifications
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Strategy 3: Direct OA Measurement with OA/Exhaust Fan Speed Ratio Tracking
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Strategy 3 includes direct measurement of the outdoor air intake flow rate for ventilation
rate control with volumetric tracking using the linear output of the outdoor air
intake flow measurement and the exhaust fan speed ratio using fan laws (flow α fan
speed). This is an “Open Loop” control strategy and as such will not be as accurate
as Strategy 2 above. Any variations in static pressure on the exhaust fan (i.e.
wind loading) will have some effect on the exhaust fan’s flow rate. The associated
control diagram, sequence of operations, technical data sheets, and specifications
are provided below.
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Control Diagram
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|
|
Sequence Of Operations
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|
|
Ventilation Rate Control
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The outdoor airflow measurement system measures the outdoor air intake flow rate
and converts the total and static pressure signals into a voltage or current control
signal that is linear and proportional to the measured outdoor air volume. The temperature
sensor/transmitter output signal is used by the outdoor airflow measurement system
for air density compensation for standard or actual airflow calculations. The outdoor
airflow measurement system output is sent to the airflow processing center (APC)
or building management system (BMS).
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The APC or BMS shall be programmed with setpoints for the minimum outdoor air volume
and economizer (mixed air) temperature controller value.
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|
|
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The APC or BMS controller shall compare the minimum outdoor air volume setpoint
value and the economizer temperature control signal. During minimum outdoor air
operation the APC or BMS shall allow the volume controller to modulate the outdoor
and return air damper motors to maintain the minimum ventilation air requirement.
When the system is in the economizer (mixed air) mode of operation, the APC or BMS
shall allow the control signal to increase the outside air volume proportionately
to the economizer temperature signal. At all times, the control value demanding
the greater amount of outdoor air shall be passed on to the outdoor and return air
damper motors.
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Building Pressurization
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The static pressure measurement system measures the static pressure in the supply
duct 2/3 to 3/4 of the way down the duct main and converts the static pressure signal
into a voltage or current control signal that is linear and proportional to differential
pressure. The pressure measurement system output is sent to the APC or BMS.
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The APC or BMS uses the pressure feedback to control the speed of the supply fan
with a variable speed drive (VSD) to maintain a constant pressure.
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The outdoor airflow measurement system measures the outdoor air intake flow rate
and converts the total and static pressure signals into a voltage or current control
signal that is linear and proportional to the measured outdoor air volume. The temperature
sensor/transmitter output signal is used by the outdoor airflow measurement system
for air density compensation for standard or actual airflow calculations. The outdoor
airflow measurement system output is sent to the airflow processing center (APC)
or building management system (BMS).
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The APC or BMS controller shall compare the control signal representing the outdoor
air intake flow rate and the airflow rate in the exhaust duct calculated based on
the fan speed ratio using fan laws (flow α fan speed) and issue a 0-10 vdc or 4-20
mA control signal to position the exhaust fan VSD to maintain a constant differential
between the two airflow rates. The differential flow rate shall be established in
the field as a value required to maintain the building envelope at a slight positive
pressure.
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Product Technical Data Sheets
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|
|
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Specifications
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