Lecture Objectives:

1
Lecture Objectives

• Discuss Project 1
• Learn about thermal storage systems

2
For Project 1 you will needWet bulb temperature
Empirical equation based on T DB C and RH
0-100
Exact calculation require solving 3 equations
For this modeling the empirical equation is
fine.
3
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 - 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 and
m cooling tower (Rnominal) for a chiller (defined
in nominal operation condition) Based on Q(?)
and WBT you can find P(?) and COP(?).
4
Example of CHP Cooling
We need a thermal storage somewhere in this
system !
5
Thermal storage

• Store heat
• Many issues to consider (?T, pressure, losses,.
  )
• Store cooling energy
• Chilled water
• For cooling condenser
• For use in AHU (cooling coils)
• Ice storage
• Compact but
• Other materials (PCMs) that change phase the
  temperature we need in cooling coils
• Many advantages, but disadvantages too!

6
On-Peak and Off-Peak Periods
This profile depends on the type of building(s) !
7
Chilled water tank
Use of stored cooling energy
Store
Use
8
Which one is better ?

• Depends on what you
• want to achieve
• Peak electric power reduction
• Capacity reduction
• ..

9
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

10
Sizing storage system (use Annual Cooling-Load
Profile)
How often you need to use it? What are the
cost-benefit curves ? What is the optimum size ?
11
Stratified chilled water tanks
12
Temperature and dynamics
Temperature at outlet during the changing cycle
of the tanks
13
Stratified chilled water tanksdiffuser geometry
Challenge Pull large amount of energy
without disturbing stratification
14
Ice Storage Tank
Many issues ! . As freezing progresses progress
the ice becomes thicker and significantly
impedes heat transfer
15
Open Ice Storage Tank
Also issues ! ..
16
Fluid Flow Rate and Freeze ?T
17
Impact on Chiller Efficiency
18
PCMs
A. Sharma et al. / Renewable and Sustainable
Energy Reviews 13 (2009) http//www.docunator.com
/bigdata/1/1367142535_c566e7d75e/reviewexample2.pd
f
19
Other latent heat thermal storage systems
(research is ongoing)
20
Construction and benefits
Active
Passive (wall)
21
Modeling(stratified tank)
Write energy and mass balancer equation for each
section
22
Installation of thermal storage system
Downstream
Upstream
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!