Lecture Objectives:

1
Lecture Objectives

• Summarize sorption chillers
• Learn about
• Chiller modeling
• Cooling towers and modeling

2
Example of H2O-NH3 System

• Text Book (Thermal Environmental Engineering)
  Example 5.5
• HW 4
• Solve the problem 5.6 (water ammonia)
• from the textbook
• Based on example 5.5.
• You may need to study example 5.6 and 5.7
• Due date is next Tuesday

3
LiBr-H2O Systems
4
LiBr-H2O Systems
5
Twine vessel LiBr-H2O Systems
6
System with no pump(Platen-Munter system)

• H2O-NH3 hydrogen

http//www.youtube.com/watch?v34K61ECbGD4
7
Useful information about LiBr absorption chiller

• http//www.cibse.org/content/documents/Groups/CHP/
  Datasheet20720-20Absorption20Cooling.pdf
• Practical Tips for Implementation of absorption
  chillers
• Identify and resolve any pre-existing problems
  with a cooling system, heat rejection system,
  water treatment etc, before installing an
  absorption chiller, or it may be unfairly blamed.
  
• Select an absorption chiller for full load
  operation (by the incorporation of thermal stores
  if necessary) as COP will drop by up to 33 at
  part-load.
• Consider VSD control of absorbent pump to improve
  the COP at low load.
• Consider access and floor-loading (typical 2 MW
  Double-effect steam chiller 12.5 tons empty, 16.7
  tones operating).
• Ensure ambient of temperature of at least 5C in
  chiller room to prevent crystallization.
• http//www.climatewell.com/index.html/application
  s/solar-cooling

8
Central chiller plant
9
Modeling of Water Cooled Chiller
(COPQcooling/Pelectric)
Chiller model
COP f(TCWS , TCTS , Qcooling , chiller
properties)
Example of a vapor compression chiller
10
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 http//apps1.eere.energy.gov/buildings/en
ergyplus/pdfs/engineeringreference.pdf page 597.
11
Example of a chiller model
http//www.comnet.org/mgp/content/chillers?purpose
0
12
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)
13
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(?).
14
Cooling Towers
Power plant type
Major difference NO FAN
15
Cooling Tower Performance Curve
R
TCTR
Outdoor WBT
from chiller
TCTS
to chiller
Temperature difference R TCTR -TCTS
TCTS
Most important variable is wet bulb temperature
TCTS f( WBToutdoor air , TCTR , cooling tower
properties) or for a specific cooling tower
type TCTS f( WBToutdoor air , R)
WBT
16
Cooling Tower Model
Model which predict tower-leaving water
temperature (TCTS) for arbitrary entering water
temperature (TCTR) and outdoor air wet bulb
temperature (WBT)
Temperature difference R TCTR -TCTS
Model
For HW 3b You will need to find coefficient a4,
b4, c4, d4, e4, f4, g4, h4, and i4 based on the
graph from the previous slide and two variable
function fitting procedure
17
Two variable function fitting(example for a
variable sped pump)
18
Function fitting for a chillerq f (condensing
and evaporating T)