Cooling Tower Design Book
Argenta Sugden
If you are interested in learning the methods of determining the proper size cooling tower, rest assured that Delta is here with guidance. Explore our handy information. Click here to learn about sizing & selecting.
Whether your application is for industrial process cooling or HVAC condenser cooling, the data required is the same. The following design data is required for cooling tower sizing to properly select the appropriate model:
The cooling tower selection table may look confusing, but after you have made a few selections, the process is straightforward. If you need a refresher, this may help. The following design data is required to select cooling towers:
Once the Nominal cooling load has been calculated, a Correction Factor must be determined to calculate the Actual Rated cooling tower tons required for the specific conditions of service. The correction factor adjusts for the ease or difficulty of cooling based on the Theoretical Design of all cooling towers.
The Nominal Ton Correction Factor is determined by using the COUNTERFLOW COOLING TOWER SELECTION AND PERFORMANCE CHART enclosed. Note that the curves are shown as three separate sections. The WET BULB CORRECTION SECTION, the APPROACH SECTION, and the CAPACITY MULTIPLIER FACTOR SECTION. First, find the Range line in the WET BULB CORRECTION SECTION in the upper left-hand section of the chart. Move along the Range line over to the intersection of the Wet Bulb line.
Now move down along the Wet Bulb line to the APPROACH SECTION, in the lower left-hand section of the chart, and stop at the intersection of the Approach line. Move across to the CAPACITY MULTIPLIER FACTOR SECTION to the right-hand curves and stop at the intersection of the Range line and read the CAPACITY MULTIPLIER FACTOR.
The Actual Rated cooling tower tons can now be calculated by multiplying the Nominal cooling tons, which was previously calculated, by the CAPACITY MULTIPLIER FACTOR. The Actual Rated cooling tower tons is the capacity required for the specific conditions of service, and the next largest size cooling tower should be selected for the application.
To select the proper cooling tower for this application, multiply the 200 Nominal tons calculated, by the 1.0 CAPACITY FACTOR. As previously stated, the correction factor adjusts for the ease or difficulty of cooling in relation to the Theoretical Design. So in this case, since the CAPACITY CORRECTION FACTOR is 1.0, the Nominal and Actual Rated tons are the same as the Theoretical Design, and a Model DT-200I cooling tower can be quoted.
Now the Nominal Ton Correction Factor must be determined for the conditions established; a 20 Range of cooling, and a 9 Approach to the design wet bulb temperature of 76F, using the COUNTERFLOW COOLING TOWER SELECTION AND PERFORMANCE CHART enclosed.
First, find the 20 Range line in the WET BULB CORRECTION SECTION in the upper left-hand section of the chart. Move along the 20 Range line over to the intersection of the 76 Wet Bulb line. Move down along the 76 Wet Bulb line to the APPROACH SECTION, in the lower left-hand section of the chart, and stop at the intersection of the 9 Approach line. Move across to the CAPACITY MULTIPLIER FACTOR SECTION to the right-hand curves and stop at the intersection of the 20 Range line, and read the CAPACITY MULTIPLIER FACTOR, which in this case is 0.62.
The final step to select the proper cooling tower for this application is to multiply the 200 nominal cooling tons required, which was calculated above, by the CAPACITY FACTOR, which in this case is 0.62. The cooling tower Actual Rated tons for the conditions given are therefore 124 tons, and a Model DT-125I cooling tower can be quoted. Since the correction factor adjusts for the ease or difficulty of cooling based on the Theoretical Design, in this case, the Actual Rated tower conditions are easier than Theoretical Design.
The following is an example of modifying a "once through non-recirculating cooling application" to a recirculating cooling tower system. A cooling tower is required for heat exchanger process cooling, which is now being cooled using 55F well water at a flow rate of (1 Million gallons/day - 300,000 sanitary = 700,000 gal per day).
We can establish the cooling tower design for a 6,250,000 Btu/Hr Heat Load based on the installation location design Twb, which, for this example, we'll say is determined to be 76F, and by establishing a reasonable cold water temperature at a 7 Approach to the Twb, at 83F.
A commercial cooling tower can also be selected for this heat load based on a 25 Range of cooling. The conditions for selection would be 500 GPM, cooling from 108F to 83F @ 76F Twb, which is equal to 418 Nominal tons x .62 DCF = 259 Rated cooling tower tons, for a 260 ton cooling tower requirement.
Consider placement: Locate cooling towers at least 25 feet from building air intakes. This will help prevent the cooling tower's drift plume from being drawn into a ventilation system.
Monitor water parameters on a regular basis. Base measurement frequency on performance of the water management program or Legionella performance indicators for control. Adjust frequency according to the stability of performance indicator values. For example, increase the measurement frequency if there's a high degree of measurement variability.
During wet system standby (water remains in system and shutdown for less than 5 days), maintain water treatment program. Circulate water 3 times a week through the open loop of a closed-circuit cooling tower and entire open-circuit cooling system.
I'm trying to test a design that only uses a cooling tower with no chiller (actually there is also an option with a small pony chiller than would only cycle on when the cooling tower can't meet the load). The problem in the VE is that a chiller is necessary to have a cooling tower. But even trying to include the small pony chiller, it is set up that the chiller load conditions are primary. The only half though I have is to come up with a fake chiller curve that would result in a COP of 1 or 100% efficiency and then send the chiller power to a random fuel category to ignore.
Have you considered using a Dedicated Waterside Economizer? It allows you to simulate a chilled water loop serving a cooling coil, and a cooling tower linked to the chilled water loop via a heat exchanger. The setup is limited to one cooling tower per cooling coil, so it might not work with your project; but it does allow for backup cooling from a chiller. See section 2.13 of the ApacheHVAC User's Guide for more info.
Thanks Eric. That's a good idea I hadn't thought of (the details of the dedicated vs integrated waterside economizers are a little confusing to me). However the chillers are still sequences first in either case, where I want to cooling tower to first take care of all the load it can, and then the chiller only take over to supplement the peaks.
Do you have a reference for this? It seems that the pre-cooling CT and the chiller operate at the same time. Currently I am using the DWE suggested by Eric along with a backup CHW loop that has a pre-cooling CT. This isn't ideal because the DWE can only be used on a single coil, but then allows the CT to be used on it's own, then when it can no longer meet the load completely, it switches to a CHW loop with CT of equivalent specs.
yes for the integrated WSE if the cooling tower doesn't have enough capacity OR the wet-bulb temperature you specified is exceeded you will see some chiller energy.If you have enough capacity in the cooling tower AND the wet-bulb temperature you specify is not exceed then there will be zero chiller energy.You will still have "heat rejection fans/pump energy" in both cases.Hope this helps.
An old hacky way that can be used for estimation is to use two coils in series. The first coil is the waterside economizer coil and the second is a traditional chiller that comes on when the waterside economizer can't reach capacity.
Since you can specify the capacity of any cooling coil in IES, this will limit the off-coil temperature at some point, and the downstream coil will come on. If you want to get super-hacky, then you can also use a generic cooling source with a high COP to estimate the use of fans and pumps on the waterside economizer.
If you are concerned about shutting off this coil when outdoor conditions (wet bulb or dewpoint) are not favorable, then you can use a second controller monitoring outdoor air that can be hooked up to the first coil's controller to shut it off when outdoor conditions would make it impossible to make sufficiently cold water by evaporation alone. This is a quicker and dirtier way if you are stuck.
We are designing a cooling water system for a petrochemical plant. As part of the design of the cooling tower, vent lines were added in the risers or the cooling tower. Hydrocarbons detection have been provided in these vents. However I would like to know how to size these vents. In some go-bys, we found that the vent lines have the same size of the risers.
As additionally information, our cooling water system is a closed loop and some heat exchangers has hydrocarbons at high pressure in the tube side. Relief valves for tube rupture have been provided for this heat exchangers.
It is general practice to provide vents of same size as that of riser if the system is supplying hydrogen or similar gases in order to avoid pressurization of the system. This is done in addition to providing rupture disk on the cooling water side of exchangers
However, if intend to optimize the size then please do consider the slug flow through riser. However, when I have done a very extensive exercise then this only resulted in reduction is vent size from 16" to 12" and with practically no economical gain with such a huge transient flow analysis
Regarding the sizing of vents in cooling tower risers, I am required to size vents in our cooling tower risers. I understand generally the vent size is kept same as the riser size. I would like to have any reference technical/fire protection literature on this.
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