Shading a Cooling Tower

Hay! I may be wrong but isn't the process of evaporation whats giving you the cooling

Shading the tower ought to reduce its performance slightly, as the air passing through it will be at the same absolute humidity though at a lower temperature, so its capacity to carry away evaporated moisture, and therefore heat, will be less.

The temperature of the supply water to the cooling processes depends on the wet-bulb temperature of the air passing through it at any moment. A lower supply service temperature than this cannot be achieved without refrigeration.

A http://en.wikipedia.org/wiki/Psychrometric_chart is an indispensible tool with which to assess cooling tower performance.

Thanks for the insight, we have mechanical draft cooling towers

Its time for the 3 year water permit update and I figure 25% of my water is going out theses cooling towers and wanted to see if anything could be done to reduce it

I read something about planting trees and shading the towers and how the cooling towers are less efficient in the summer. I was thinking that the cooling tower worked like a home ac unit which shading seems to benefit.

You are saying that the more water that gets evaporated and exhausted, the more heat I am geting rid off? Mike

Please look at the robustness of the current biological treatment regime as well as investigating any losses. An area where towers don't need to go is where there is a build-up of unwanted bacteria in the circuit that might increase the risk of legionella pneumophilia being blown out with the air stream! Please discuss the current situation with the supplier of the biological treatment for advice as a matter of high priority.

An industrial cooling tower rejects heat to air by two paths. 1) is direct heating of the intake air up to its exit temperature. This effect is very small compared to 2) Evaporation of water. Evaporating water takes about 8000 BTU/gal. The total heat rejected can be calculated from an enthaply chart of the water/air system, measuring inlet and outlet dry and wet-bulb temperatures. The maximum amount of water that can be evaporated is determined by the difference in enthalpy of enterng air and dew point enthalpy of air at the temperature of the entering water. Since it is impossible to achieve 100% efficiency (heating the wet air to entering water temp, or cooling the water to the 'wet bulb' of entering air, some reasonable temperature approaches must be incorporated into the design performance.

In the southern coastal regions, one often sees lots of white vapor (fog) exiting cooling towers on summer mornings --when inlet air is humid and warm already. Exit air does reach complete saturation and more, with the fog particles contributing to higher ''drift' losses with no corresponding increase in cooling.

'Shading 'the cooling tower will have no effect on their performance unless you obstruct air flow--which will substantially decrease performance.

Normally, evaporation and drift losses run around 3-6% of water rate. Well managed cooling water systems can run at concentration cycles up to 20 ( or 5% blowdown). If your actual losses are 25%, something is wrong. Drift losses are excessive, blowdown is real high, or there is a leak somewhere.

'Shading' a residential A/C does not increase its efficiency either. 'Official' aair tmperature is measured by a SHADED thermometer to preclude any radiant heating of the thermometer from the sun. A thermometer (of any kind) exposed to direct sunlight will indicate several degrees higher than true air temperature. THe A/C unit operates on the 'real' temperature.

Gosh, I am getting schooled today. Please bear with me.

I read one web thing about shade will slow alge growth so fewer Chemicals are needed

I read this in a post, and the last sentence mentions Shade,

did you consider the cooling load required in summer and winter , I mean the cooling tower performance direct related to the ambient tempressure max. diff race between the ambient temp. and cooling water temp. is around 8-10 c. for example if the ambient is around 45c the min. temp. you can achieve is around 35c,and make sure that the air flow for the cooling tower is not restricted by walls(close high),roofs. you can try to shade the cooling tower

Just for arguing sake, If I have direct sunlight on the metal vains it will probaly heat the metal and in turn actual heat the water that falling thru them. Which will make that side of the tower less efficient.

The 6 cooling towers we have the vains are facing east and west. so the east facing ones get the sun in the morning and the west facing ones really get the heat in the evening..

Does the placement of the cooling tower make shading viable?

A way to improve efficency is to lower the temperature of the incoming water. A fairly deep well is one way to accomplish that if local regulations allow it but then you also need an acceptable way to either recycle or drain the water. Also, circulating water down 50 feet or more will do the same thing.

I won't give up on shading just yet, Suppose this. On a very hot day at around 4 pm , I get a cup and catch water from the west "sun" facing side of the tower and drop a thermometer in it. Then I do the same with the side of the tower not facing the sun. Will the temp of the falling water be the same for both sides? Mike

Take samples on several consecutive days and record the temperatures of the sunny and self-shaded sides of the tower(s). Report the data.

Since the outer louvers are shading the 'tower fill' and falling water inside the outer perimeter there is likely very little difference between the shaded and unshaded sides.

Typical cooling towers run water from the remote condenser (water heat source) to the top of the tower, where it is dropped over the slats to increase surface area and increase water passage time, to evaporate the maximum amount of cooling water (up to 3 to 5 %) possible to cool the remaining water to near the wet bulb temperature. The falling water drops into the tank built into the bottom of the tower, where the pump inlet line picks it up and sends the cooled water to the cold side of the condenser. The tank level is maintained by a water supply replacing the 3 to 5% evaporated. The salts and other dissolved solids in the water concentrate continually up to a point where the hot water dropping on the slats would cause salt buildup (stalagmites) and scaling would obstruct the pipes. With soft water, 15 or 20 X incoming water concentration is often practical (concentration). At that point, the entire tank can be drained and replaced with fresh water (blowdown), or constant dilution with an overflow can extend the time between blowdowns.

One ton of AC is 2,000 pounds of ice per day. About 85# per hour. Or 12,000 BTUH 1 # of water requires about 1000 BTU to evaporate. Without drift and leakage, for each ton of AC the tower needs to evaporate 12 pounds per hour.

Some towers vary the fan speed based on load to reduce drift, and others cycle the fan, based on load/tank temperature. Many don't.

The cooling tower itself will become MORE efficient as the temperature rises, but the capacity of your compressor unit decreases dramatically as the cooling water temperature rises with the wet-bulb temp. The capacity of the air to carry away evaporating water (heat) increases with the temperature. The condenser probably raises your cooling water temp by 20° F. If you are supplying your cooling tower with 60° water, and your tower is exposed to db 50/wb 40° air, the capacity of the air in terms of grains/cu ft is so very much lower than would be db90/wb 80° air. The number of BTU's your cooling tower can transfer is much higher at higher temperature. The efficiency of the tower itself would be based on pounds per hour flow at a given water temperature drop. Your water temperatures will find their own balance based on tower discharge temp and the grains per cu ft air capacity in the intake air to the tower.

The loss of capacity comes from the inability of the compressor/condenser to condense freon at the higher condenser temperature.

Very little fresh water (5%) is used per water cycle through the tower. Cold water make-up at 35° run through the tower would only drop the temp of water loop normally cooled from 100 to 80° F by 0.9°, if used as dilution water.

Equivalent groundwater cooling of similar capacity would fequire relatively high flow rates in the aquafer and separation of the draw/return pipes to prevent short-cycling. More than 30 ft above water table also requires a bottom restrictor in the return pipe to keep the system full during operation. And if the water table drops, you are out of business until you drill new wells.

Stick with the cooling towers.

RichH

Shading the tower would reduce the surface heating of the tower and therefore very slightly improve efficiency although probably not enough to measure it. It would probably have very little effect on the air temperature entering the tower as great volumes of air are drawn through the tower and would have little time to cool as it passes through the shady area. Heating the air does not increase the capacity of the tower -- the amount of water it can deliver at a given temperature, it does increase the amount of evaporation that occurs though.

The cooling tower is limited by the wetbulb temperature of the air. In North Georgia the summer design wetbulb is probably 79 degrees F. The size of the tower, suface area of the fill and airflow through the tower dictates the approach temperature -- the difference between return water temperature and wetbulb.

The best way to reduce water consumption is to have a good water treatment program. That allows greater cycles of concentration to reduce blowdown and therefore make-up water.

Hi Mike

about 180,000 "sq/ft building and our 6 cooling towers are in direct sunlight. "

Is the building in direct sunlight too? I am not sure how much water and energy you could save by harnessing the shade side of a cooling tower to a degree were it becomes efficient. Is the heat inside the building generated by the manufacturing process or is it the result of the sun hitting a badly insulated building? If the latter is the case insulate your building and save at that end.

I have over the years refined an insulation system in the Australian tropics (were temperatures like yours are scoffed at) that can insulate large areas very cost effectively. The applications of this system include the covering of large roof or wall areas. This insulation buffer could be applied to your cooling towers as well, if need be.

I would need some more more detailed information about your infra structure to properly assess if my system would be applicable. This is not to give you a quote but to put the results towards the ongoing R+D concerning my invention.

The main question is: how much energy/$$ could you save on AC if the inside temperature of the building was constantly at shade temperature?

You could save up to 60%. That is what my systems data shows. If you stop the cause you will stop the symptoms. Work out what it would cost to insulate your building. Divide that by 4 and you have the cost for installing my system. You could retire two of the cooling towers.

Not knowing your circumstances in detail and applying my small scale test results you should have recovered the investment after 3 to 4 years, savings in the following years will make it very worth while. Not to mention the positive environmental and other aspects of saving energy.

Any feedback would help establish solutions to real life situations and could only further my project. If you could give me some more information about the physicality's and $$ involved I could work out what you could be saving. I would supply you with more information about my system at a later stage, if you wish.

Hope all goes well. Ky.

Ok, I concede the "Shade the tower" will not save me tons of money and water idea. It is real cool outside today , but I will try the water temp cup test on the next hot day.....Thanks All, I did learn alot

KY

I have about 80 - 60hp motors and maybe 40- 20hp motors running and use $40,000 of fuel for steam each week. We generate alot of heat and steam in the building, The roof is a white membrane . Mike

If you should decide to go ahead with shading your towers, contact me regarding a highly effective method of minimizing radiant heat gain at a cost much lower than planting trees or building walls.