1. Lecture Objectives: Discuss Projects 1 and 2
Learn about thermal storage systems
Learn about control systems

2. Project 1: Modeling of Water Cooled Chiller
(COP=Qcooling/Pelectric)
Chiller model:
COP= f(TCWS , TCTS , Qcooling , chiller properties)

3. Modeling of Water Cooled Chiller
Chiller model:
Chiller data: QNOMINAL nominal cooling power,
PNOMINAL electric consumption for QNOMINAL
Available capacity as function of evaporator and condenser temperature
Cooling water supply
Cooling tower supply
Full load efficiency as function of condenser and evaporator temperature
Efficiency as function of percentage of load
Part load:
The consumed electric power [KW] under any condition of load
The coefiecnt of performance under any condition
Reading: page 597.

4. Combining Chiller and Cooling Tower Models
Function of TCTS
3 equations from previous slide
Add your equation for TCTS
→ 4 equation with 4 unknowns (you will need to calculate R based on water flow in the cooling tower loop)

5. Merging Two Models Temperature difference: R= TCTR -TCTS Model:
Link between the chiller and tower models is the Q released on the condenser:
Q condenser = Qcooling + Pcompressor ) - First law of Thermodynamics
Q condenser = (mcp)water form tower (TCTR-TCTS) m cooling tower is given - property of a tower
TCTR= TCTS - Q condenser / (mcp)water
Finally: Find P() or
The only fixed variable is TCWS = 5C (38F) and Pnominal and Qnominal for a chiller (defined in nominal operation condition: TCST and TCSW);
Based on Q() and WBT you can find P() and COP().

6. Low Order Building Modeling
Measured data or
Detailed modeling
Find Q() = f (DBT)

7. For HW3a (variable sped pump efficiency) you will need Q()
Yearly based analysis:
You will need Q() for 365 days x 24 hours
Use simple molded below and the Syracuse, NY TMY weather file posted in the course handout section 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 4 8 12 16
Q= *t
Q= *t
Q [ton]
t [F]
TMY 3 for Syracuse, NY

8. For Austin’s Office Building
Model: (Area = 125,000sf)
Hours in a year kW
Used for component
capacity analysis
Model
=0 when building is off
Reading assignment:
Chapter: 2
Number of hours

9. Thermal storage for adjustment production to consumption
We need
a thermal storage
somewhere in
this system !

10. Stratified chilled water tanks

11. Installation of thermal storage system
Upstream
Downstream
• Increases chiller efficiency
• Increases chiller capacity
• Overall system efficiency ???
• Decreases storage capacity
• Simplifies system layout
• …..
• Decreases chiller efficiency
• Decreases chiller capacity
Overall system efficiency ???
• Increases storage capacity
•……
• Does not allow chiller shut down!

12. Modeling of chilled water tank (stratified vs. mixing)
From building
To chiller
Stratification
To building
From chiller
Mixing happens if the supply temperature vary
Mixing model: mcpDT/D = Qin –  Qout

13. Stratification Dr. Jing Song’s PhD results Flow time at 20 minutes
CFD domain
Flow time at 1 minute

14. Temperature and dynamics
Temperature at outlet during the
changing cycle of the tanks

15. Stratified chilled water tanks diffuser geometry
Challenge:
“Pull” large amount of energy without
disturbing stratification

16. On-Peak and Off-Peak Periods
This profile depends on the type of building(s) !

17. Chilled water tank
Use of stored cooling energy
Store
Use

18. Which one is better ? Depends on what you want to achieve:
Peak electric power reduction
Capacity reduction
…..

19. Downsizing the Chiller
Lower utility costs
Lower on-peak electrical consumption(kWh)
Lower on-peak electrical demand (kW)
Smaller equipment size
Smaller chiller
Smaller electrical service (A)
Reduced installed cost
May qualify for utility rebates or other incentives

20. 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

21. 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

22. 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

23. 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

24. 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

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

26. 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

27. 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