1. Announcements End of the class – course evaluation
Final project presentation
Monday (5/8/17) at 10 a.m.
Send me the ppt file before 9:45 a.m.

2. Objectives Learn about automatic control Course summary
PID and Control terminology
Sequence of operation
Control optimization
Course summary

3. The Real World 50% of US buildings have control problems
90% tuning and optimization
10% faults
25% energy savings from correcting control problems
Commissioning is critically important

4. Practical Details Measure what you want to control
Verify that sensors are working
Integrate control system components
Tune systems
Measure performance
Commission control systems

5. Modulating Control Systems
Example: Heat exchanger control
Modulating (Analog) control
air
water
Cooling coil x
(set point temperature)

6. Modulating Control Systems
Used in larger systems
Output can be anywhere in operating range
Three main types
Proportional PI
PID
Position (x)
fluid
Electric (pneumatic) motor
Vfluid = f(x) linear or exponential function
Volume flow rate

7. Proportional Controllers
x is controller output
A is controller output with no error
(often A=0)
Kis proportional gain constant
e = is error (offset)

8. Unstable system
Stable system

9. Issues with P Controllers
Always have an offset
But, require less tuning than other controllers
Very appropriate for things that change slowly
i.e. building internal temperature

10. Proportional + Integral (PI)
K/Ti is integral gain
If controller is tuned properly, offset is reduced to zero
Figure 2-18a

11. Issues with PI Controllers
Require more tuning than for P
But, no offset

12. Proportional + Integral + Derivative (PID)
Improvement over PI because of faster response and less deviation from offset
Increases rate of error correction as errors get larger
But
HVAC controlled devices are too slow responding
Requires setting three different gains

13. Ref: Kreider and Rabl.Figure 12.5

14. The control in HVAC system – only PI
Proportional
Integral
value
Set point
Proportional
affect the slope
Set point
Integral
affect the shape after
the first “bump”

15. 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

16. Economizer Fresh air volume flow rate control % fresh air TOA (hOA)
enthalpy
100%
Fresh
(outdoor)
air
TOA (hOA)
Minimum for
ventilation
damper
mixing
Recirc.
air
T & RH sensors

17. Economizer – cooling regime
How to control the fresh air volume flow rate?
If TOA < 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

18. Economizer – cooling regime
Example of SEQUENCE OF OERATIONS:
If TOA < Tset-point open the fresh air damper the maximum position
Then, if Tindoor air < Tset-point start closing the cooling coil valve
If cooling coil valve is closed and T indoor air < Tset-point start closing the damper
till you get T indoor air = T set-point
Other variations are possible

19. HVAC Control Example 2: Dew point control (Relative Humidity control)
fresh
air
damper
filter
cooling
coil
heating
coil
filter
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

20. Relative humidity control by cooling coil
Mixture
Room
Supply
TDP
Heating coil

21. Relative humidity control by cooling coil (CC)
Cooling coil is controlled by TDP set-point
if TDP measured > TDP set-point → send the signal to open more the CC valve
if TDP measured < TDP set-point → send the signal to close more the CC valve
Heating coil is controlled by Tair set-point
if Tair < Tair set-point → send the signal to open more the heating coil valve
if Tair > 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

22. Sequence of operation (ECJ research facility)
Set Point (SP)
Mixture 2
Mixture 3
Mixture 1
DBTSP
DPTSP
Control logic:
Mixture in zone 1: IF (( TM<TSP) & (DPTM<DPTSP) ) heating and humidifying
Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating
Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease humid.
Mixture in zone 2: IF ((TM>TSP) & (DPTM<DPTSP) ) cooling and humidifying
Cool. coil cont.: IF (TSP<TSA) increase cooling or IF (TSP>TSA) decrease cooling
Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease hum.
Mixture in zone 3: IF ((DPTM>DPTSP) ) cooling/dehumidifying and reheatin
Cool. coil cont.: IF (DPTSP>DPTSA) increase cooling or IF (DPTSP<DPTSA) decrease cooling

23. Other examples for HVAC:
Heat recovery
Dual duct system

24. Other examples
Thermal storage
UTs CHP

25. Course Summary Course Objectives:
Learn about advanced building HVAC systems
Obtain knowledge about district cooling and heating systems.
Gain the skills and tools necessary to evaluate integration of sustainable energy production systems to a given building site.
Study application of combined heat and power systems in a specific building or group of buildings.
Conduct thermal, hydraulic and economic modeling of integrated building energy systems for planning and design.
Course Topics:
 Class intro and HVAC systems
Building ventilation heat recovery systems
Thermal (solar and waste heat) powered desiccant systems
4. Centralized (compressor and sorption based) cooling systems
5. Centralized heating systems
6. District heating and cooling distribution systems
7. Combined heat and power systems
8. Systems integration and control