Transcript Project Presentation.ppt

Improved Precision Leading to
Improved Energy Efficiency
Edward Decker
AE 790 – Intelligent Buildings
June 6, 2006
Why is Ventilation Air Needed?
 The health and comfort of the building
occupants
 The removal of internally generated
contaminants
 To maintain certain pressure differentials
between the indoor and outdoor
environments
How to Ensure Proper Ventilation
 Use a dedicated OA system
– Provides 100% OA
– Ensures the minimum ventilation requirements are met
 Why Not?
– No mixing of Airstreams
 100% of the SA must be conditioned
 Increased energy use
– Increased energy cost
– Best to maximize return air
How is RA & OA Mixed
 Dampers are modulated to allow for air to be
directed
– Back in to the AHU as RA
– Out of the building into the atmosphere as EA
 Mass Balance
– The amount of EA needs to be replaced
 OA is introduced to the system via an OA damper
 The amount of OA must meet the minimum requirements
– The first step is to quantify the required and actual
amounts of SA, RA, EA, and OA
What are the Methods to Measure
Ventilation Air?
 Direct
– Measures the airflow
directly, using a
devise such as an
anemometer.
– Require regular flow
profiles for accurate
readings.
 Indirect
– Measures other
parameters that are
dependant upon the
airflow, as in the
energy balance
method
– Typically for low rates
that are difficult to
measure
What are the Ways to Measure
Ventilation Air?
 Direct
– Averaging Pitot-Tube
Array
– Electronic Thermal
Anemometry
– Fan Inlet
– Rotating vane and propeller
anemometers
– Swinging vane anemometers
– Vortex shedding meters
– Integrated damper and
measuring devises
– Laser doppler anemometry
(LDA)
– Orifice Meters
 Indirect
– Enthalpy Balance
– Concentration Balance
Measuring Ventilation Air
 Direct Method with Pitot-tube array
– Velocity must be high enough for sensor accuracy
– Regular flow profile is required, and often overlooked
 Spacing of a minimum of 2D before a station and 1D behind
required
 Development of flow devices
– Calculate properties of fully developed flow profile
 Less space required
– Device to ‘trip’ the velocity profile
 Achieve accurate readings
 Less space required
– Comfortable Methods
 Current Industry Standard without inherent problems
What are the Common ways to
Control Ventilation Air?
 Flow monitoring using:
– Hot wire anemometers
– Thermistor sensors
– Velocity pressure sensing (pitot-tubes)
 Differential Static Pressure Control
– across fixed duct elements or with respect to OA pressure
 Use of commissioning data to relate system flow at various
fan-operating points with OA damper actuator signal
position
 Volumetric Fan tracking
– Measuring SA and RA and assuming that the difference is the
amount of OA
 CO2 surrogate sensing
 Outside Air Injection Fan
Differential Static Pressure Control
 Involves maintaining a constant pressure
in the mixed air plenum or other
reference point in the duct.
– With constant pressure in the mixed air
plenum and a fixed minimum damper, the
minimum OA quantity remains constant as
the supply air fan modulates.
 Static pressure sensors are simple,
reliable, and require little space.
Modulating minimum OA damper
 New product such as flow sensing built
into dampers may be the best
– Velocity pressure is calculated and
maintained constant by modulating the
minimum OA blades themselves
Mixed Air Temperature
Comparison Method
 Method is still being used, but is not
recommended
– When OA and RA are within 10-20 °F,
readings are not trustworthy
 Accuracy degrades as Toa approaches Tra
– Balancers sometimes use this method when
there isn’t room for pitot tube traverses
Mixed Air Temperature
Comparison Method
 Better Sensors can Improve this
Technique
– Cheaper Sensors
 More sensors
– Redundancy in readings
– More Precise Sensors
 Less errors in readings
 Close OA and RA temperatures can be distinguished
better
Concentration Balance
 Provides adequate control
– Exceptions
 Low occupancy
 When OA represents a small fraction of SA
 Problems
– Only accounts for contaminants generated by
people in space, but not other contaminants
 i.e.-VOCs from carpets, paints, etc
Concentration Balance
 Better Sensors for measurement of all
contaminants
– OA might be polluted
 Determine the airstream with the ‘best’ quality of air
 Leads to improved overall IAQ
– Multiple readings with improved precision
 Can measure the air requirements of a given space
 Design on an individual zone basis
Concentration Balance
 Design on an Individual Zone Basis
– Occupied modes for each zone
– Ventilation requirements for individual room
– Improved IAQ
– Decreased energy consumption
– Decreased energy bills
Conclusion
 Accurate measurement and control of outside air
intake is possible
– Proper installation and operation
 Intelligent Design
– Improve accuracy of readings and control
– More precise control
 Better zone conditions
– Improved overall IAQ
– Energy savings
– Cost Savings
QUESTIONS?
?