Additional Energy Costs due to Fouling
Energy
consumption is dependent upon the efficiency of a chiller, hours of operation,
load, cost of electricity (or steam), and the amount of fouling. Figure 2 depicts the additional energy costs
due to fouling. For example, when the
fouling factor is 0.003 (i.e. scale thickness of 0.036 inch), the additional
energy cost per year for a 500-ton chiller is $25,000. Energy savings of equivalent amounts can be
realized with effective water treatment.
Using YORKCalc Program to Demonstrate Energy Savings
The objective is to
compare a chiller(s) running at the designed fouling factor as compared to the
same chiller(s) running with various levels of fouled condenser tubes.
This program is very
detailed and can be very accurate. The
challenge in the field is to collect as much data as possible to provide the most
accurate comparison possible. This is
not always the case therefore the estimated assumptions should be conservative.
Open Program
1.
Open Project Manager
2.
Edit
3.
Click “Add
Project,”
4.
Name Project
(“XYZ”)
5.
Click “XYZ”
6.
Click
“Products”
7.
Click
“YorkCalc”
Job:
Weather Data:
1. The program provides various choices of cities from which to
choose. Each will determine the number
of “running hours” based on averages within that city.
2. If you customer operates at fewer hours than the “city
average” you may use the “daylight” operation available on the program.
3. You may also customize the hours manually. This option can be time consuming.
Analysis Type:
You will be comparing
one single chiller or multiple chillers.
Chiller Plant:
1. The program provides a comparison of several chillers. If the sizes vary, determine which chiller
is the lead chiller (Chiller #1, #2 etc.).
2. Type of chiller (centrifugal, screw etc.)
3. Tons of each chiller
4. Variable speed versus constant speed
5. KW/ton designed rating of each chiller
Comparison of Fouling Factors:
Here is where you
must estimate the degree of fouling in the condenser tubes. This can be based on:
1. Increase in chiller approach temperature
A
1°
increase in approach equates to a 1.5% increase in energy or a 1.5% increase in
the kW/ton rating.
2. Type of cleaning performed annually
If
the customer must acid clean the tubes they are operating at a much higher
fouling factor. The design is usually
0.00025. If they use acid the fouling
factor may be 0.005 which equates to a 30% increase.
3. Conservative Estimation
Take
the estimated increase in approach or an estimated increase based on the type
of cleaning required and divide by ˝. We should determine an average degree of
fouling for the cooling season. If you
are looking at the approach in the middle of the season use that increase; if
you are looking at the end of the season assume it averaged 50% of that level
for the entire season.
Create and second
chiller or chiller plant with the same operating parameters except the kW/ton
or kW/Full Load (change either setting).
Tower Approach Temperature:
1. The default is 7°. This may vary
slightly in various parts of the county.
Utility Rates
1. The default is $0.075 per kW/hour with a
demand of 12.5. If you do not know the
demand use an estimated blended rate.
This will usually lower the estimated operating cost, again to make
assumptions on the conservative side.
Building Load
Here we estimate the
building load or total tons. This can
be as simple or complex, as you want to make it. You may change the building load (OADB) based on the estimate of
the use. If the customer has three
chillers but never uses one do not include it in the total tons.
