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Part I: How Heat Masses Have an effect on Evaporative Cooling Tower Efficiency

Splash Fill Components (Crossflow) - Brentwood IndustriesThis is an element I in a four-half collection on power saving strategies for evaporative cooling towers.

Read Additionally: Half II—How Changes in Flowrate Affect Cooling Tower Efficiency

A century ago steam engine operators found they might improve vitality efficiency by adding a heat exchanger on the steam discharge. The concept was to flow ocean or river water by means of the heat exchanger reducing steam temperature and decreasing the steam engine’s compression ratio. This worked effectively for marine applications, however was too expensive for land-based techniques the place the one obtainable water supply was from a municipality, as apparently the advent of the water meter preceded the steam engine. Evaporative cooling towers were invented to provide land-based mostly environment friendly steam engine operation by recapturing the vast majority of the water utilized by the heat exchanger.

Cooling Towers a hundred and one

Normally, evaporative cooling towers are used to cool process water through evaporation. Figure 1 reveals a typical cross-move evaporative cooling tower. A water pump forces excessive temperature course of water to enter at the top through nozzles. The nozzles disperse the water onto a large floor area known as the fill. The fill’s solely operate is to efficiently delay the water reaching the underside of the tower and allow extra time for the air to work together with the method water. Gravity causes the water to slowly make its manner by way of the fill while a fan forces air throughout the water path till it reaches the underside of the tower (basin). The air passing through the tower causes among the water to evaporate and hand over heat. For every pound of water that evaporates, roughly 1,000 BTUs are eliminated. The air leaves the tower moisture laden and mixes with the environment. Any water that is evaporated is made up by a recent water measuring system located in the cold water basin. The cross flow tower shown in the illustration is very common. Though there are a lot of variations similar to static (no fan), counter-stream and others, the common thread is cooling the method water using evaporation.

Read Also:Massive Information How Sensors Can Enable Exact Maintenance & Optimum Gear Reliability

Cooling Tower Control Optimization Strategy

Evaporative cooling towers are usually designed to provide the correct cooling wanted for the process when both production and the outdoor situations are at their maximum. This is the one time when the cooling needs of the process truly match the capacity of the tower. Because of this in any respect other instances the tower has a better capacity than the design heat load. As it’s possible you’ll surmise, the overwhelming majority of time either the air or water circulate of the evaporative cooling tower could be decreased and energy might be saved. In many circumstances, facility homeowners rapidly adopt the concept of varying fan speeds, as that is a fairly straightforward fix. In some cases, various pump velocity has the potential to save even more power nevertheless it should be done with caution.

The question all the time comes down to what’s one of the best strategy and how a lot will it save? To answer this question, there are 4 key variables that should be understood:

  • 1. Process heat load
  • 2. The Affinity Legal guidelines
  • 3. Fundamental water move science
  • 4. Psychrometrics

Types of Cooling Tower Heat Masses

Course of heat hundreds can be categorised in two other ways, the simplest being one which derives no vitality benefit from the tower water supply to the method being at a decrease temperature than its most design, through which case the tower has a set set-point on the supply water temperature. In other phrases:

Total power = fan + pump

The extra complicated process heat load is an utility where the process power effectivity is considerably improved by decreasing the evaporative cooling tower supply water temperature to a sure point like our earlier instance of a steam engine or refrigeration system, where the decrease tower provide water temperature reduces the compression ratio, which ends up in decrease vitality use. Usually, the ability required for the process is way better than the tower fan and pump combined. In these instances it is sensible to make use of extra tower power to attain a decrease tower supply water temperature as a result of the advance in power use of the method is larger. This makes the optimization a bit extra complicated as a result of now the entire energy contains the method:

Whole power = process + pump + fan

Since the method power adjustments dependent on what occurs with the tower fan and pump, it’s literally the distinction between juggling three balls verses two. In some of these purposes the goal is to all the time make sure that the sum of the facility of the method, pump and fan are optimal at all times.

Measuring Cooling Tower Heat Masses

Figure 2. Strain drop move curve through a heat exchanger

The heat load the method has on the evaporative cooling tower begins with a very simple equation:

BTU/Hr. = GPM X 500 X TD

GPM is gallons per minute of cooling water going by means of the method heat exchanger while TD is the distinction in temperature of the water getting into and leaving the heat exchanger. The five hundred issue is a relentless made up of the amount of pounds per gallon of water (round 8.33), the precise heat of water (1) and 60 to transform minutes to hours. Therefore 8.33 x 1 x 60 = 499.Eight or approximately 500. The nice factor about water is that, unlike air, the density doesn’t change a lot at normal temperatures and it has a specific heat of 1 BTU/lb. (which means it takes 1 BTU to raise the temperature of 1 pound 1 degree F.). Nonetheless, some towers run when the temperature is beneath freezing, requiring anti-freeze (glycol) to be added to the water. Depending on the anti-freeze manufacturer, in addition to its share within the water, it might not weigh eight.33 pounds per gallon and also have a barely totally different specific heat. For instance, if the glycol water mixture solely weighs 92 percent as much as water (referred to as the specific gravity) and has a specific heat of .96 BTU/lb. then the calculation can be:

(Eight.33 X .Ninety two) = 7.66 Gal/lb. X .96 Sp. Ht. X 60 = 441.Four

So as an alternative of the 500 we used as a continuing the brand new value could be roughly 441.

Taking glycol out of the equation, let’s say that you are cooling an oven with water entering at 78 levels F and leaving at 85 degrees F utilizing one hundred gallons per minute circulate. What would be the heat load? Utilizing the components of GPM X TD X 500 yields:

One hundred X (85-78) X 500 becomes a hundred X 7 X 500 = 350,000 BTU/Hr.

Subsequently, the heat load on the oven is 350,000 BTU/Hr.

Using this identical instance, what would happen if the flow modified to ninety gallons per minute and the heat load remained constant? For those who mentioned the temperature difference would change, you might be appropriate. So now we recalculate and find the new temperature distinction.

The formula is BTU per hr. / (GPM X 500), which turns into 350,000 / ninety X 500 = 7.Eight levels F. So reducing the circulation rate by 10 percent increases the temperature difference by zero.8 levels F.

So how can one determine what the heat load of the process is if no flowmeter exists? Quite often, heat exchanger manufacturers present tables that relate move to strain drop as shown in Determine 2. By installing stress gauges on each the inlet and outlet sides of the heat exchanger you’ll be able to convert the pressure difference to stream fee to get a tough estimate of the circulation.

For instance, a model quantity E2209-B heat exchanger (yellow line), with a pressure drop of 10 toes of water column, the stream price can be just a little over 1,one hundred GPM. In case your gauges read in lbs. per sq. inch (PSI), then this would be the equal of (10 / 2.31) round 4.4 PSI stress drop since each PSI = 2.31 ft. if the process makes use of water with no glycol.

What if the Cooling Tower Application Makes use of Glycol?

If the mixture comprises glycol, multiply 2.31 times the particular gravity to obtain the conversion. For instance, if an software with glycol has a selected gravity of ninety percent (which suggests it weighs ninety p.c as much as water) the conversion can be 2.31 X .9 or 2.079. Therefore:

10 / 2.079 = four.Eighty one PSI

What If There is no such thing as a Stress Drop Desk?

If no desk exists, your choices are to either install a flowmeter, which is what I’d extremely advocate, or rent a very good portable ultrasonic meter. If a portable meter is used to determine stream, permanently mount stress gauges on the inlet and outlet sides of the heat exchanger and develop your own pressure drop to flow chart inside the proper movement vary. This can serve to help future operators monitor the difference in stress throughout the heat exchanger and have a tough idea if the stream is inside the proper range. While you’re at it, install high quality getting into and leaving thermometers for the same purpose.

It’s a Ton Form of

A standard term used in specifying the capacity of heat elimination in cooling towers is tons of cooling. Within the early years of refrigeration, a good lots of the applications have been directed toward making ice. For those of you not outdated sufficient to recall, this was earlier than most individuals had electric refrigerators and most everybody had iceboxes. I’m simply guessing, but the refrigeration gear salespeople at the time probably found it easier to inform prospects what number of tons of ice their gear might produce a day rather than explain what a BTU was. A ton is therefore based mostly on the amount of heat required to transform water into one ton of ice (2,000 pounds) in 24 hours. Since each pound of water transformed to ice takes 144 BTU, the formulation is 2,000 X 144 = 288,000 BTU. Therefore 1 ton of cooling is equal to 288,000 BTU/Day or 12,000 BTU/Hr. or 200 BTU/Min. or, if you like, 105,one hundred twenty,000 BTU/Yr.

In fact family refrigerators quickly changed the icebox and it went the way in which of the steam engine. When that occurred, the need for ice plants also diminished. What was left behind was the time period “tons of cooling,and to at the present time it continues to be a common term major manufacturers use in North America to explain the heat elimination capability of cooling tools. Normally, when cooling tools manufacturers communicate the lingo of tons, they most frequently seek advice from the hourly amount, which is 12,000.

Again, I’m speculating, but the evaporative cooling tower salespeople received in on the act because refrigeration engineers realized that ice plants could run more efficiently in the event that they used water cooled refrigeration techniques. Now I suppose the tower salespeople didn’t need to seek out themselves explaining to customers what a BTU was any greater than the refrigeration tools sales guys. The problem is that although the refrigeration systems removed a 12,000 BTU/Hr. to create ice, there was extra inefficient amount of heat added in the process by the refrigeration compressor. This inefficiency meant that cooling towers would not solely have to take away the heat added by the ice but the compressor as properly. So again, I’m guessing, however the tower salesperson probably did what any good salesperson would do change the numbers. So, in the tower world a ton is not 12,000 BTU/hr. as an alternative it is 15,000 BTU/hr. with the added three,000 BTU for removing the compressor heat. So when a tower manufacturer says the tower is rated at three tons, he means 3 X 15,000 = 45,000 BTU/Hr.

Using our method of BTU/Hr. = GPM X 500 X TD, how many GPM per ton could be wanted to scale back cooling tower water from ninety five degrees F to eighty five degrees F to equal 1 tower ton?

Since a cooling tower ton is equal to 15,000 BTU/Hr. the formulation is:

GPM = 15,000 / (500 X (ninety five-eighty five)) = 15,000 / (500 X 10) = 15,000 / 5,000 = 3 GPM

Therefore, an evaporative cooling tower with a ten-degree temperature difference between the tower coming into and leaving water requires 3 GPM per ton.

Now that we have a basic understanding of heat hundreds, learn “Part II: How Adjustments in Flowrate Have an effect on Cooling Tower Efficiencythrough which we discuss evaporative cooling tower followers and pumps.

John Pitcher is the CEO of Weber Sensors, a 50-yr-outdated German producer of circulation merchandise primarily based on the calorimetric principle of operation. Beforehand he was the founder of Scientific Conservation, which was one of the primary firms to use cloud computing for fault detection and diagnostics. Mr. Pitcher’s 40-12 months career covers many product improvement and leadership roles within the automation and energy efficiency fields. He could be reached at 770 592-6630 or john.pitcher@captor.com.

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