Energy Costs


Energy requirements for the operation of a chiller account for a significant amount of total energy requirements.  An effective water management program is essential in controlling energy usage.  However, many water management programs do not totally eliminate scaling.  Minimum levels of even soft scale accumulation on condenser tubes will greatly increase the annual energy expense.




Operating Assumptions

§         3000 Running Hours

§         70% Average Load

§         $0.08 kWh blended rate

§         0.70 kW/ton


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”





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.