1. Energy Plus & Open Studio Class
Today, 5:45 PM
Computer lab ECJ 3.402
Instructor: Wesley Cole

2. ASHRAE Student Chapter Meeting
Monday Nov 26th at 6pm
ECJ 5.410

3. Lecture Objectives: Finish with common HVAC system configurations
Discuss control systems
Discuss the life cycle cost analysis
Learn about empirical modeling

4. HVAC systems in eQUEST

5. 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

6. Basic Control loop Example: Heat exchanger control
Modulating (Analog) control
air
water
Cooling coil x
(set point temperature)

7. Cooling coil control valve
Electric (pneumatic) motor
Position (x)
fluid
Volume flow rate
Vfluid = f(x) linear or exponential function

8. 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”

9. Detail control system simulation
MatLAB - Simulink
Control system simulation - take into account HVAC component behavior but focus more on control devices and stability of control scheme

10. Models integrated in HVAC System simulation
Example:
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

11. HVAC Control 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
% fresh air
T & RH sensors
100%
Minimum for
ventilation

12. 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

13. 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
Sequence of calculation in energy simulation modeling is different than sequence of operation !
We often assume perfect aromatic control

14. What are the reasons for energy simulations?
System Development (research)
Building design (evaluate different design solutions)
Economic benefits
Budget planning

15. Life Cycle Cost Analysis
Engineering economics

16. Parameters in life cycle cost analysis
Beside energy benefits expressed in $,
you should consider:
First cost
Maintenance
Operation life
Change of the energy cost
Interest (inflation)
Taxes, Discounts, Rebates, other Government measures

17. Example
Using eQUEST analyze the benefits (energy saving and pay back period)
of installing
- low-e double glazed window
- variable frequency drive
in the school building in NYC

19. What are the reasons for energy simulations?
System Development (research)
Building design (evaluate different design solutions)
Economic benefits
Budget planning

20. For budget planning Empirical model For average year use TMY2
Load vs. dry bulb temperature
Measured for a building in Syracuse, NY
Model
For average year use TMY2
=835890ton hour = Btu