Lecture Objectives:

1
Lecture Objectives

• Discuss HW4
• Chiller modeling
• Cooling towers and modeling
• Project 1

2

• HW 4
• Solve the problem 5.6 (water ammonia)
• from the textbook
• Based on example 5.5.

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 http//apps1.eere.energy.gov/buildings/en
ergyplus/pdfs/engineeringreference.pdf page 597.
4
Example of a chiller model
http//www.comnet.org/mgp/content/chillers?purpose
0
5
Cooling Towers
Power plant type
Major difference NO FAN
6
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)
7
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(?).
8
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
9
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
10
Two variable function fitting(example for a
variable sped pump)
11
Function fitting for a chillerq f (condensing
and evaporating T)
12
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(?).
13
Low Order Building Modeling
Measured data or Detailed modeling Find Q(?)
f (DBT)
14
For Austins Office Building
Model (Area 125,000sf)
Hours in a year
kW
Used for component capacity analysis
Model
0 when building is off
Number of hours
15
For project 1 you will need Q(?)for each hour
Yearly based analysis You will need Q(?) for
one week in July Use simple molded below and the
Syracuse TMY2 weather file posted in the course
handout section