Is a cooling tower a worthwhile investment? (part 2)
Continuing from previous post on structuring the available data for calculations …
So, let’s start with the following data:
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Data from within the company
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Amount of water from aqueduct m3/h
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12,56
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Hours per day
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8
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Days per week
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5
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Weeks per year
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48
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Cost of Water and Power
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cost primary water (1)x/m3
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1000
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cost waste water (1)x/m3
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500
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cost of kW / h
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100
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Calculation of the cost of aqueduct water per year
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Cost of water used
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Primary aqueduct water m3/year
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24,115,200
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For the waste water
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12,057,600
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Total cost of water used in one year
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36,172,800
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Now we will estimate the cost to design the system. If consists of:
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Cooling Tower
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Installation (materials included: pipes, valves, etc.)
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Cost of operation (maintenance, replenishing water energy)
Let’s now try to estimate the cost of the plant with the tower:
Suppose that:
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the water flow in the tower is twice as much with respect to the system with water waste (the temperature difference between the incoming water and the outgoing water from the system will be about half)
Example:
Water without cooling tower:
Actual water flow rate: 30 m3/h
Inlet temperature by the system: + 15 ° C
Outlet temperature by the system: + 25 ° C
With cooling tower:
Water flow rate: 60 m3/h
In worst weather condition: summer
Inlet temperature by the system: + 30 ° C
Outlet temperature by the system: + 35 ° C
Let’s suppose that the water flow rate is twice as much as the one used by the plant with aqueduct water (the difference in temperature between the water entering the system will be about half from the one exiting the system).
Another thing to decide about a plant with cooling tower is:
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high efficiency (the water temperature leaving the tower to serve the system)
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medium efficiency
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to dispose only heat from users (water temperature leaving the cooling tower is not important)
We can now combine all the above data because we have sufficient elements to determine the physical size of the tower. To make a cost estimation, keep in mind that the market price of a tower of the size around 1 m2 is 6,000,000 (1)x.
Obviously the bigger towers cost less relative to size.
Other elements to evaluate are: induced draft cooling towers with forced ventilation; centrifugal fans, axial fans, built in galvanized steel, stainless steel, polyester reinforced with glass fiber.
(We should consider all tangible items that are now part of our designer’s skills).
In the next article “Is a cooling tower a worthwile investment? (part 3)”, we shall see how to calculate the size of the tower with the above available data.
(1)X is an hypothetical cost unit.
