Objectives

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Objectives

• Discuss Project Topics
• Learn to design VAV and DOAS System

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3D model Biomedical Engineering (BME) Building
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3D model Biomedical Engineering (BME) Building
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3D model Biomedical Engineering (BME) Building
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3D model Biomedical Engineering (BME) Building
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VAV Example

• One system
• Multiple Spaces/Zones
• - VAV box for each space/zone

http//www.trane.com/commercial/library/vol242/v24
b6.asp
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VAV System Terms Equations(you can find them
in ASHRAE Standard 62)

• Fraction of minimum outdoor air in space/zone
  supply air
• Xi VOAi / VSAi
• Critical space
• Space with maximum Xi , Zmax(Xi)
• Fraction of outdoor air in system supply air
• X sum(VOA ) / sum(VSA)
• Required Fraction of outdoor air
• YX/(1X-Z)

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Example Solution
Space1 Space 2 Space 3 Space 4
VSA
VOA
Xi
X
Z
Y
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Other Issues Related to VAV

• Fan control
• Minimum supply air
• Occupancy sensors

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DOAS System

• http//doas.psu.edu/

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Enthalpy wheel
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Desiccant wheel
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HVAC Control

• Example 1
• Economizer (fresh air volume flow rate control)

Controlled device is damper - Damper for the
air - Valve for the liquids
fresh air
damper
mixing
recirc. air
T RH sensors
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Economizer
fresh air

• Fresh air volume flow rate control

100
enthalpy
Fresh (outdoor) air
TOA (hOA)
Minimum for ventilation
damper
mixing
Recirc. air
T RH sensors
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Economizer cooling regime

• How to control the fresh air volume flow rate?

If TOA lt Tset-point ? Supply more fresh air
than the minimum required The question is how
much? Open the damper for the fresh air and
compare the Troom with the Tset-point . Open
till you get the Troom Tset-point If you have
100 fresh air and your still need cooling use
cooling coil. What are the priorities -
Control the dampers and then the cooling coils or
- Control the valves of cooling coil and then
the dampers ? Defend by SEQUENCE OF OERATION
the set of operation which HVAC designer
provides to the automatic control engineer
fresh air
100
Minimum for ventilation
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Economizer cooling regime
Example of SEQUENCE OF OERATIONS If TOA lt
Tset-point open the fresh air damper the maximum
position Then, if Tindoor air lt Tset-point
start closing the cooling coil valve If cooling
coil valve is closed and T indoor air lt
Tset-point start closing the damper till you
get T indoor air T set-point Other
variations are possible
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HVAC Control

• Example 2
• Dew point control (Relative Humidity control)

fresh air
filter
cooling coil
heating coil
filter
damper
fan
mixing
T RH sensors
Heat gains
Humidity generation
We should supply air with lower humidity ratio
(w) and lower temperature
We either measure Dew Point directly or T RH
sensors substitute dew point sensor
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Relative humidity control by cooling coil
Cooling Coil
Mixture
Room
Supply
TDP
Heating coil
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Relative humidity control by cooling coil (CC)

• Cooling coil is controlled by TDP set-point
• if TDP measured gt TDP set-point ? send the
  signal to open more the CC valve
• if TDP measured lt TDP set-point ? send the
  signal to close more the CC valve

• Heating coil is controlled by Tair set-point
• if Tair lt Tair set-point ? send the signal
  to open more the heating coil valve
• if Tair gt Tair set-point ? send the signal
  to close more the heating coil valve

Control valves
Fresh air
mixing
cooling coil
heating coil
Tair TDP sensors
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Sequence of operation(ECJ research facility)
Control logic Mixture in zone 1 IF ((
TMltTSP) (DPTMltDPTSP) ) heating and
humidifying Heater control IF (TSPgtTSA)
increase heating or IF (TSPltTSA) decrease
heating Humidifier IF (DPTSPgtDPTSA) increase
humidifying or IF (DPTSPltDPTSA) decrease humid.
Mixture in zone 2 IF ((TMgtTSP)
(DPTMltDPTSP) ) cooling and humidifying Cool.
coil cont. IF (TSPltTSA) increase cooling or IF
(TSPgtTSA) decrease cooling Humidifier IF
(DPTSPgtDPTSA) increase humidifying or IF
(DPTSPltDPTSA) decrease hum. Mixture in zone 3
IF ((DPTMgtDPTSP) ) cooling/dehumidifying and
reheatin Cool. coil cont. IF (DPTSPgtDPTSA)
increase cooling or IF (DPTSPltDPTSA) decrease
cooling Heater control IF (TSPgtTSA) increase
heating or IF (TSPltTSA) decrease heating