1. Building Services Controls
Mechanical Services (UBLMPB-30-3)
Reference:
CIBSE (2009) Guide H: Building Control Systems, 2nd Ed.

2. Components Notes & terms:
Input, i - the error between set point and value of controlled variable
Output, o - e.g. a movement of the actuator motor
there may be a distinction between the set point and the desired value of the controlled variable
the graphic shows a closed loop control system – has a feedback pathway i
feedback o

3. Control Modes Two Position Modulating on/off
could be extended have more steps
e.g. high/low/off control of burners
can be floating control, with slow moving actuator
Modulating
Proportional ...
Integral
Derivative
or combinations of above, e.g. PI or PID
o  i
o  ∫i or do/dt  i
o  di/dt

4. Two-postion control

5. Two-postion control Set point On Off Dead (or neutral) zone
Controlled condition (e.g. Temperature) On
Off
Set point
Dead (or neutral) zone

6. Floating control

7. Proportional control

8. - response to step transient load change
Proportional control
- response to step transient load change
Note!
There is a discrepancy in this graphic

9. System response T
DV = distance-velocity lag
T = transfer lag

10. Damping
Underdamped
Critically damped
Over-damped
The response characteristic of a control system is defined by its transfer function

11. PID control modes Proportional (P) (P + I) (P + I + D)
Refer to lab demo ...

12. AC controls

17. Mixing box – enthalpy controlΘ h
Mixing box – enthalpy control

18. Comfort cooling controls+
fan − C T
100% 0%
set point
Heating pb
Cooling pb
Mixing pb
Enthalpy control