Cooling Tower Design in Oman

so now it suddenly is good enough

You are right. 50 C is not WB

Thanks

I don't believe your stated weather conditions.

From the Wikipedia page on Oman, "Like the rest of the Persian Gulf, Oman generally has one of the hottest climates in the world, and receives little rainfall."

100% humidity means that the weather is or is close to raining. High heat and humidity would be the climate of a rain forest that rains every day. This is not the climate of a desert nation. I suspect you are misreading your statistics. The temperature and humidity conditions are the highest each attribute gets but never both at their maximum at the same time.

This cooling tower will certainly be able to cool.

Many thanks,

I agree that the way I put question is wrong.

However, is it possible to design cooling tower for 100% RH?

Regards

Of course a cooling system can be designed to cool in 100% RH. That system does not use evaporation for cooling. Your document states that this tower is designed for a 60% RH. For your stated location I suspect this tower can provide adequate cooling. At least most of the time it certainly will.

However, I do have a concerns using an evaporation tower in Oman. I expect your water loss will often be higher than the document states due to the difference in climate condition from the documents test condition. Your water consumption rate will probably be a problem for a desert location to supply. You will also probably have a greater vegetation problem near this tower as the local flora and fauna flock to this new water source. Then there is the gamut of unstated thermodynamic and operation concerns. How cool is cool enough? How much heat must be taken away? How critical are operations?

Can one successfully use an evaporation cooler in a desert location, yes one can. Can one waste their money on an evaporation cooler in the desert, yes one can. The devil is always in the details.

<...question is wrong...> Then don't expect to get a sensible answer until the question is correct! Re-post with the correct question now, please.

At 100% humidity, there can be no cooling effect from evaporating water, sweat, etc. Pity.

Recheck your heat and humidity.....

http://www.weatheronline.co.uk/weather/maps/city?WMO=41256&CONT=asie&LAND=OM&ART=RLF&LEVEL=150

CR4 user "mrswamy" (Muthukumar Ramaswamy) lives there; maybe he'll chime in with good local info.

When the relative humidity is 100%, the air cannot hold any more water and therefore, water will not evaporate into 100% humid air.

Therefore NO cooling tower design can do anything useful in such an environment. Cooling towers cool by evaporating water. No further evaporation, due to 100% RH, means no cooling.

You can make a design one thousand times larger or "better" and it will still do nothing useful at 100% RH.

That depends. If the DB temperature is not very high during times of high RH, then sensible cooling is possible.

"If the DB temperature is not very high during times of high RH, then sensible cooling is possible."

Sorry, we're not talking about "very high" RH but 100%. If the RH is already 100%, then no more evaporation and hence no more cooling by evaporation, is possible. It's an immutable law of physics.

we rarely rely on the laws of the universe here, we just make it up as we go

Here's the common man's explanation of thermodynamics, so you no longer will need to make it up :)

https://www.youtube.com/watch?v=VnbiVw_1FNs

I'm not the one who gave the bogus answer but thanks. if you read several threads you'll consistently see that answers are offered that are just wrong, but no one is compensated so who really cares

That's why I said sensible cooling (i.e., not latent). It would be reduced capacity, though, unless on an abnormally cool day.

Water cooled Ac system is more efficient since heat transfer coefficient of water is higher than air. However in Oman majority of AC installations are air-cooled . There are water cooled installations with cooling towers in Oman. Recent one is at Oman Avenue mall. It is in Muscat. I could not open the link. Check with expert HVAC consultants in Oman.

HI Swamy,

you can get the file by copying below whole link and pasting it in the browser:

http://files.engineering.com/getfile.aspx?folder=c3bd00d4-0863-4ca5-bb37-7b23171164d4&file=CT.pdf&__hstc=212727627.ab73a52a41936c6d9aa55905114de6e8.1454303410988.1466933948347.1467452794028.77&__hssc=212727627.2.1467452794028&__hsfp=1996857684

Glad to know that you are in Oman.

Thank you Lyn,

However, I posted the question to get answer, not to get scolding

I gave you an answer.

Look for a simpler job.

Hi, Hilal! I agree with others, most especially with Redfred. You have to consult or ask a professional for that. Probably, in the locality. But, if you don't find one, hire some consultant at www.upwork.com, of course consultation is not free because consultants invested so much for the knowledge, experience and the liability. But, I assure you, it fits your budget.

Thanks,

I think my question is simple and doesn't need consultant. I will read one reference book I have about the subject and update you if I find my own answer

Next time, do that before coming to CR4, and not afterwards!

Ok.

Many thanks to whoever took the pain to answer my question.

Actually 50 Celsius degree and 100 % RH may not happen in the same time.

I am client, not vendor nor consultant. I have a consultant who told me that this design will work due to WB temperature of 32 C.

I just wanted to double check and get an advice.

The biggest Question I have is : why the vendor considered 60% RH whereas RH in my project site can reach 100% RH?

This is the first time for our company to install cooling tower. Therefore, I am cautious.

Once again there are several answers here that make me glad I am not at site in Oman.

The first point is very simple

The vendor considered 60% RH because that was the figure on the datasheet against which they had to supply a unit.

I don't know who produced the process datasheet and purchase order but it is to them that you should ask the question. If a vendor gets an order that specifies the unit has to work at 32C WB / 60%RH then that is what they supply. The vendor knows that site conditions can exceed these conditions but they are only interested in the figures on the contract.

Next and worryingly this means you have not understood the book you were going to read. The vendor would not consider 100%RH because an EVAPORATIVE cooler will NOT work at 100%RH. If the air is fully loaded with water you cannot evaporate any more water and so the main water will not cool.

Do you understand how evaporative coolers work?

Briefly - Warm water is sprayed over a rising air stream. There is a water differential between the liquid droplets and the water content of the air. This causes water to evaporate (ie to move from liquid to vapour phase at a temperature below the boiling point). Changing phase takes a lot of energy and so by evaporating some of the water (1.6% in this case) you reduce the average energy of the water that remains in the liquid and so its temperature.

NASA do not design spaceships for trans light speed

Finally there is the issue of why 32C WB / 60% RH was chosen.

Again two points

You would never design for the worst combination of data or for the worst peak instantaneous condition. If you were to do so your equipment would be so grossly over designed that at normal conditions it would be difficult to operate. It would also be far more expensive require much more space and power. As a simple point if you went with 32C WB / 90% RH the air flow would be 4 times larger so the cell would occupy four times the floor area.

When you are designing equipment that operates against natural ambient conditions you have to select a set of design conditions that will cover most of the operating conditions and not give you too bad a problem when the conditions go to high. The choice of these conditions depends on the use of the service. If the cooling unit is used for office AC then it means that the office temp will increase everyone will complain and gt a bit hot but it is not a disaster. If the cooling unit is for a DCS (ie the computer system that controls an oil refinery) then the problems are more significant. However you would consider how long the extreme conditions last; how quickly temperatures rise in the computer room; can cooling be switched from the offices (is there a refrigerant back up)

Selecting the correct temperatures / RH etc is very difficult if you look at these two

https://weather-and-climate.com/average-monthly-Rainfall-Temperature-Sunshine,muscat,Oman

http://www.weatheronline.co.uk/weather/maps/city

you get a max RH of 50% for one and 90% for the other. This depends on how you average the data - fortunately I have never had to do this job it has always been in the base data that I use to do so I cannot give any guidance.

Just to reiterate the first key points

The vendor supplied at 60%RH because that is what YOU (as the client or your representative) asked them to do.

This feel like an answer in several parts.

Will this design work for your design conditions of 50°C, RH = 100% - NO

However it is not no because the design is not good enough. The data sheet describes a fairly standard evaporative cooler. Therefore logically at 100%RH it can NOT work it is not possible to evaporate water into an air stream at 100%RH UNLESS you are simultaneously heating the air stream so the problem is thermodynamics / physics you are asking for the impossible.

Now for some of the opinion around your comment trying to answer the question that you should have asked

The datasheet gives design conditions at 32°C, 60%RH. You can use psychometric charts to determine the water carrying capacity (absolute humidity) at this condition and the fully saturated condition. At 50°C the absolute humidity is higher but trying to determine how the cell will operate so far outside of its operating range is difficult. My guess is that if the air is 50°C and LESS than 100%RH it will exit the cell fully saturated due to the higher thermal driving force. So from psychometric charts you can find the RH at 50°C at which the change in Absolute Humidity (in kg water / Sm3 of air) gives you the required evaporation rate from the water and so the conditions at which the cell will operate as required.

The conditions you list are clearly maximum - now if this is for an office AC system the system needs to operate at this condition because you need the AC at the hottest time of the day. Normally equipment is designed for something just below the one off peak (say a 95% limit ie for 95% of the time the conditions are less than X) and the reduced performance for 30 mins just after lunch is acceptable because of the higher performance during the night - if the cell is part of oil / gas processing unit.

If you absolutely have to operate at 100%RH then as noted above you need to look at a different cooling technology.

Note that if you really do have 50C, 100% RH then you will HEAT the water in your cooling tower as the air is now hotter than the water. If the air is cooler than 45C there will be some limited cooling due to sensible heat exchange

I think the key step is to determine the frequency of this temperature combination - certainly during my recent stay in Abu Dhabi the mid day temp was well over 30C but I do not know where the RH was - and whether you need to operate at these conditions.

From comparable data I've seen, 32ºC looks like a reasonable WB design value for Oman. This is what the tower vendor used for their specs. If their in/out water temperatures and flow meet your process needs (which you haven't said one way or the other), then the tower ought to be adequate. (I don't know whether the 32ºC is a value that is exceeded 2%, 1%, or 0.4% of the time; nor whether it accounts for any recent global warming.)

Beware of the bacterium Legionella Pneumophila. These little critters will just love the conditions inside the proposed cooling tower. Make sure that the water treatment regime is sufficient to deal with their rampant breeding...

I work with evaporation cooling. I have often thought about something, I will try to explain.

You have a large house, the temperature inside the house is say, 90 degrees, outside the house the temperature is 70 degrees at 100%rh. If you can't add more water vapor to the air to the inside of the house, can you transfer the latent heat inside the house to the outside ?

I wonder if you circulated the inside air across a medium the heat could be radiated to the outside and the water vapor (100%) rh) would absorb the heat since there is the 20 degree differential. The inside air and outside air would be separated, the action would continue until the inside air would be the same temperature as the outside air. A dryer could absorb the water vapor inside the house and the liquid would be expelled by a purge pump.

Would this work ?

Ok I am going to bite but I am mighty confused just what you are trying to achieve

A few things first

You dont mention the RH inside the house its a fairly key parameter

Designing for peak / extreme conditions is always risky - I know Florida can see near 100% in mornings but its only 60% in afternoon, so there is a balance depending on how key the temperature / humidity control is required in oversizing equipment.

Also which latent heat are you trying to transfer outside? the Water or transfer medium?

Ok its 90°F inside 70°F (F assumed although Hemet sounds like a place in Israel and 'The Land of Milk and Honey' certainly is Israel / Palestine where they normally use C)

So why not OTFW - (Open ..... Window) and drop the temperature by 20°F at a cost of some humidity - this is why its important to know the internal humidity. Ok so you dont do it because 100% humidity is a 'mare (I live in Seoul and previously Houston Tx so I am aware)

So I assume you are looking at evaporative cooling for the house. Air fans, water source. This will cool the house but also increase the RH (two stages one the evaporation of water increases both AH and RH and cooling the air recalibrates RH to a lower base because cold air carries less water) so we need to know the starting point and max RH for the house.

At this point I am tempted to say why do anything else. The house is cooled although at higher humidity

This is a simple system has worked for 1000 years (oh and props to the GOP numpty this cooling system arrived in Europe via the Moors a north African, Islamic people who conquered much of Spain. It originated in Arabia (Islamic) and was also developed in India (Hindu) (and probably China as well) lots of non white non christian types)

I am not sure how your drier is going to work to supply a purge pump. Producing a liquid stream from a humid environment uses (I think) a refrigerated cooling exchanger at which point I wonder why bother adding water why not just use the coolant exchanger to cool the air. The cold low pressure gas is exhausted to a compressor compressed to a high enough pressure that it will condense at >80°F outside temp so that when flashed cold refrigerant is returned to the house. This uses a non contact exchange to condense the transfer medium but this is just a conventional AC unit

My other perplexity is that for evaporative cooling you need a water supply so why not use the output from your drier.

I feel I must have completely missed your point I hope this makes some sense

You are basically talking about a sensible heat exchange between inside warmer air at X humidity, and outside air that is saturated with moisture, but much cooler. Sure, the space cooling will work in that instance. As the inside air cools, it approaches the point where the inside air could be also saturated, and some condensation would naturally take place in the heat exchange unit. This could be simply drained outside, presuming there is no pressure difference inside and outside.

If the warmer inside air originally sourced from the outside air (by air exchange), then obviously, one cannot cool that air sufficiently to produce condensation from X humidity since the inside air will never actually reach the outside air temperature, but will always be a few degrees warmer, even with the "ideal" heat exchange there is some approach temperature limit.