A SELECTION NOT A BID

Engineers and their customers often get hung up on bidding everything, and are suspicious of sole sources (selections) as being unethical, or unfair, or something.  I will show you today that in the case of blowers, the energy considerations are so great that you should almost always select the most efficient blower.

Back in 2007 I was redesigning the aeration system for Monroe MI.  They had 3, 1000-hp blowers with synchronous motors, and were using 700-some horsepower to run the system.  They had canvas sock diffusers (aka elephant prophylactics).  they even had a washing machine with which to clean them.  I redesigned the sysgtem with efficient fine bubble diffusers and new, smaller blowers,  I simulated the variations in air flow for a typical day, and asked blower manufacturers to give me shaft horsepower at the various points.  I then calculated the energy use and cost of the year 2007 and the year 2027.  The results are below. 

COST COMPARISION OF VARIOUS BLOWERS, $/YEAR PER SIMULATION

	Spencer 6000	Spencer 7000	Hoffman 7000	Hoffman 8000	National Turbine	Turblex KA10 single point 7500	Turblex KA10 dual point	Turblex 8550 KA10 single pt
2007	108424	108424	98418	104491	111112	82040	74572	79321
2027	123010	129183	108026	115891	127739	96726	89999	94126
delta from lowest
Year 2007	-29103	-29103	-19097	-25170	-31791	-2719	4749	0
Year 2027	-28884	-35057	-13900	-21765	-33613	-2600	4127	0
Average	-28994	-32080	-16499	-23468	-32702	-2659	4438	0
mulltistage only 2007	-10006	-10006	0	-6073	-12694
2027	-14984	-21157	0	-7865	-19713
average	-12495	-15582	0	-6969	-16204

shows that there is a considerable difference in energy cost between the most efficient and least efficient machines.  The single impeller machnes were more efficient.  I selected the second most efficient blower, because the outlet diffusers and the computer algorithm needed to operate them cost an additional $43,000/machine, which pushed the payback for the additional cost from 5 years to  15 years or so, and I thought that was too long (Private industry always wants a payback in 1 year).  The difference between the most and least efficient machin was over $30,000/year, or $600,000 in 2007 dollars and no increase in the cost of electricity. Vendors, don't complain because these are the data you gave to me.  Even among the multistage machines, there was a considerable difference in energy costs over a 20 or 30 year equipment life, would far outstrip the diffence in machine costs at bid time.

The lesson is:  You, the engineer or customer, should give the manufacturer a typical daily air flow variation  at your plant, and ask him to give you shaft horsepower at each flow point, and then select the most or 2nd most efficient machine and have it sole-sourced. You will save a lot of money for the customer.

How did the job work out?  Monroe reduced it electric bills by $50,000/month.

This same exersize works for diffusers, too.  You are better off to buy more diffusers and use less air than to cheap out with the least expensive diffuser layout.  I'll try to make a presentation on that later.

Now, If I can do this calculation, some of you superintendents should be able to do it too.  After all, superintendents in Wood and Lucas counties feel that I am too dumb to be an operator it can't be alll that diffucult.