Transcript Energy Plus & Open Studio Class • Today, 5:45 PM

Energy Plus & Open Studio
Class
• Today, 5:45 PM
• Computer lab ECJ 3.402
• Instructor: Wesley Cole
ASHRAE Student Chapter
Meeting
• Monday Nov 26th at 6pm
• ECJ 5.410
Lecture Objectives:
• Finish with common HVAC system
configurations
• Discuss control systems
• Discuss the life cycle cost analysis
• Learn about empirical modeling
HVAC systems in eQUEST
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
Basic Control loop
Example: Heat exchanger control
– Modulating (Analog) control
Cooling coil
air
x
water
(set point temperature)
Cooling coil control valve
Electric (pneumatic) motor
Position (x)
fluid
Volume flow rate
Vfluid = f(x) - linear or exponential function
The control in HVAC system – only PI
x  K  (Tset point  Tmeasured ) 
K
(Tset point  Tmeasured )d

Ti
Proportional
Integral
value
Set point
Set point
Proportional
affect the slope
Integral
affect the shape after
the first “bump”
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
Models integrated in HVAC System
simulation
Example:
Economizer (fresh air volume flow rate control)
Controlled device is damper
damper
fresh
air
- Damper for the air
- Valve for the liquids
mixing
recirc.
air
T & RH sensors
HVAC Control
Economizer (fresh air volume flow rate control)
Controlled device is damper
damper
fresh
air
- Damper for the air
- Valve for the liquids
mixing
recirc.
air
% fresh air
T & RH sensors
100%
Minimum for
ventilation
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?
% fresh air
Open the damper for the fresh air
and compare the Troom with the Tset-point .
100%
Open till you get the Troom = Tset-point
If you have 100% fresh air and your
still need cooling use cooling coil.
Minimum for
ventilation
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
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
What are the reasons for energy
simulations?
• System Development (research)
• Building design (evaluate different design
solutions)
• Economic benefits
• Budget planning
Life Cycle Cost Analysis
• Engineering economics
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
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
What are the reasons for energy
simulations?
• System Development (research)
• Building design (evaluate different design
solutions)
• Economic benefits
• Budget planning
For budget planning
Empirical model
500
Q=-673.66+12.889*t
500
450
450
400
400
350
350
300
Q [ton]
Q [ton]
300
250
200
250
200
150
150
100
100
50
50
Q=-11.33+1.2126*t
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
t [F]
Load vs. dry bulb temperature
Measured for a building in Syracuse, NY
For average year use TMY2
t [F]
Model
8760  11.33  1.126  t
if t i  57

i


Q   (

i 1 
 673.66  12.889  t i if t i  57

8760  11.33  1.126  t
if t i  57

i


Q   (
 =835890ton hour = 10.031 106 Btu

673
.
66

12
.
889

t
if
t

57

i 1 
i
i

