Announcement

1
Announcement

• No project presentations !
• In last class (on Thursday) we will
• review HVAC systems of the New Engineering
  Building
• review the course material
• NOTE The class will be in ECJ 4.304
  (conference room across the stair door)

2
Lecture Objectives

• Automatic control
• Sequence of operation
• Heat recovery system
• Desiccant systems

3
HVAC Control

• Example
• Dew point control (Relative Humidity control)

fresh air
filter
cooling coil
heating coil
filter
damper
fan
mixing
T RH sensors
4
Basic purpose of HVAC control
Daily, weekly, and seasonal swings make HVAC
control challenging Highly unsteady-state
environment Provide balance of reasonable
comfort at minimum cost and energy Two distinct
actions 1) Switching/Enabling Manage
availability of plant according to schedule
using timers. 2) Regulation Match plant
capacity to demand
5
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
6
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
7
Terminology

• Sensor
• Measures quantity of interest
• Controller
• Interprets sensor data
• Controlled device
• Changes based on controller output

Figure 2-13
8
Sensible and Enthalpy and Desiccant wheels
9
Sensible and Enthalpy Wheels
10
Heat recovery system in NSM building at UT
11
Desiccant wheel