Talk:Evaporative cooler

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As now described in this article, evaporative cooler is the name for these devices in the

No, thanks. Both articles are a good length and having "cooler" as a sub-section of "cooling" (it would have to be that way around, wouldn't it?) would make the result too big. Also: as User:S.dedalus. --

Old Moonraker (talk) 07:20, 3 April 2008 (UTC)[reply

]

"Evaporative cooling" (the physical process) should be the main heading. "Evaporative cooler" (the thing that relies on the physical process) should be a subset User: Dougoh

• Pollen? Absurd! The evaporative cooler *IS* the filter and pollen won't pass thru. As for odors, the number one problem here is because of poor maintenance and the musty stench will come from the unit itself... evaporative cooling is an excellent way to filter the majority of water-soluble air pollution out of outdoor air as long as it is providing comfortable temperatures indoors; a well maintained and well purged evap unit can actually be very helpful to an asthma patient living in an area experiencing high ozone levels, they are quite good at removing ozone.

• *More* actual cooling (Not less!) happens in hotter temperatures. The amount of cooling provided is the change in temperature from inlet to outlet.

When the dewpoint is the same, more water evaporation occurs at higher temperatures, and the difference in temperature between the inlet and the outlet of the evaporative cooler is greater. Sure, the *actual temperature* of the outlet air may be somewhat greater... but to say that the unit provides less cooling is completely incorrect, particularly because an undersized freon-based unit actually will provide less cooling in hotter temperatures as the hot-side of the heat exchange pump may experience difficulty discharging heat and much greater pressures are required to compress freon at higher temperatures, which decreases the amount of liquid-phase freon a compressor can provide to the evaporator core inside a building. Long story short: The BTU cooling effect of a swamp cooler is GREATER in higher temperatures (at the same dewpoint) but the BTU cooling effect of a recirculating air conditioner is actually LOWER. (Note: none of this changes the fact that the freon-based units - when sized correctly - can reach much lower temperatures in the first place :)

• Joined high humidity to its first actual listed disadvantage.

• Increasing humidity does NOT improve thermal comfort! The more humid it is, the hotter it feels. Still, some people like moisture at lower temperatures because it keeps them from feeling too dry.

• Described the air filtration advantage versus typical AC systems, especially in dry climates.

—Preceding unsigned comment added by Zaphraud (talk • contribs)

Zaphraud, thanks for your good work on this! I grew up in the Southwest with these things, and they're great. Dicklyon (talk) 00:49, 7 May 2009 (UTC)[reply]

The article give 3 examples of the cooling effect rule of thumb and implies the cooler can reach nearly 21C at ambient of 40C and RH=15%. While the statement is strictly true, it is not an illustration of the rule of thumb. The wet bulb temp at 40C and 15% RH is 21C--so the cooler will perform about 4C higher per the rule of thumb. —Preceding unsigned comment added by 198.91.8.99 (talk) 23:55, 29 May 2009 (UTC)[reply]

"For example, an eight-inch pad with its increased surface area will be more efficient than a one-inch pad." - Shouldn't this be reversed? Thicker pad has more surface area than a thinner, correct? —Preceding unsigned comment added by 76.120.106.228 (talk) 00:30, 15 July 2010 (UTC)[reply]

I don't see anything wrong with the statement as quoted... 8 inches => thicker / larger area => more efficient. am I reading it wrong? David Hollman (Talk) 17:03, 4 September 2010 (UTC)[reply]

Thicker == larger resistance to flow, which has nothing to do with efficiency. Duty, maybe. Efficiency probably not. Why not make it ten metres thick, surely that would be more efficient under the thicker => more efficient logic... User A1 (talk) 01:07, 5 September 2010 (UTC)[reply]

Sounds like you are pointing out a different problem with this statement. The previous commenter suggested that the statement should be reversed... does that make any sense? Should this whole statement just be removed from the article? David Hollman (Talk) 09:50, 5 September 2010 (UTC)[reply]

Neither way around is true. The pad thickness merely determines the difficulty with which air can be pushed through the pad. Whilst has something to do with efficiency, it is not as simple as a direct relationship between thickness and efficiency. In a real system, you would probably find that too thin a pad means that the pad is not dirupting air flow enough, and you are getting little mixing between the air and the wetted surface. Too thick means that you are not getting a high-enough flow velocity, causing stagnation and the exhaust air will be saturated, but you will have paid too high an energy cost for doing so, and will be getting a lower flow-rate than otherwise possible. User A1 (talk) 10:39, 5 September 2010 (UTC)[reply]

Cool, thanks for clarifying the whole issue. David Hollman (Talk) 11:12, 5 September 2010 (UTC)[reply]

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http://en.wikipedia.org/wiki/Evaporative_cooler Nonsense repetition in discussion of "Direct evaporative cooling" vs. "Indirect evaporative cooling". See below:

"Direct evaporative cooling (closed circuit) is similar to direct evaporative cooling, but uses some type of heat exchanger. The cooled moist air never comes in direct contact with the conditioned environment.

"Indirect evaporative cooling (closed circuit) is similar to direct evaporative cooling, but uses some type of heat exchanger. The cooled moist air never comes in direct contact with the conditioned environment."

Lwood42 (talk) 15:50, 4 September 2010 (UTC)[reply]

We could do with an explanation of what drives evaporative cooling in the first place. Normally, heat flow is driven by a difference in temperature, rather than by a desire of one substance to evaporate. It goes on to talk about wet-bulb temperature, but to claim this is the explanation would be a circular argument because web-bulb temperature is defined in terms of evaporative cooling in the first place.

This page gives me some insight, but the explanation here ought to be complete in itself rather than relying on an external link. Moreover, it still begs the question of why it cools the atmosphere rather than just the liquid that's evaporating. Do the particles that escape get far enough away that they don't give their heat straight back to the local atmosphere, thereby enabling it to be cooled by normal conduction of heat? -- Smjg (talk) 11:51, 30 November 2010 (UTC)[reply]

The confusion arises from the concept of "heat flow" itself. That's a part of the language left over from when heat was seen as an invisible fluid. Dropping that idea and thinking of heat as the motion of objects instead is important if you want to really understand the evaporative cooling concept. The objects/molecules/particles that separate from a larger mass no longer contribute their own motion to the statistical average motion of that mass. The usual word for that "statistical average motion" is "temperature". Because the faster molecules are the ones that are changing state the result is always to reduce the temperature of the remaining ones.

Similarly, the reason the air at the surface of the evaporating liquid cools is because the air molecules are constantly bumping into the molecules at the surface and energy moves between them. When a molecule picks up that bit of extra energy that causes it to break free and leave the liquid behind, the energy will quite often have come from a collision with an air molecule that left the air molecule moving more slowly. The water molecule is also almost certainly moving more slowly than the average speed of the air molecules in the vicinity (it has more mass, after all). So the average speed of molecules in air+vapour mix is generally reduced slightly by such interactions and it is a little cooler than the pure air was after one occurs.

Pretty much the same argument covers the case where all the collisions of the escaping water molecule were with water molecules - when it enters the air+vapour mix it is likely to be moving more slowly than the air molecules. It's just not so illustrative.

To finish up, the probability of water molecules leaving with a higher speed than the average of the air molecules has to be examined and shown to be low as is asserted above. Even before going into the realm of statistical probability the explanation is likely to overwhelm the page, so it seems that we may be better off just making sure there's nothing totally mistaken in the simplified explanations and leaving the detail to the pure physics pages. This would also avoid having to address the relationship between the ideal gas collision explanation and one based on partial pressures. —Preceding unsigned comment added 05:41, 31 January 2011 (UTC)

Direct evaporative cooling efficiency declines to zero percent as ambient humidity increases. However it sounds like evaporative cooling should still make a heat pump cooling system more efficient even at 100% ambient humidity. Is this generally correct?

Assuming a heat pump raises the outdoor coil temp by 40F degrees over ambient and water at ambient temperature is sprayed on the coil, the water apparently should still be able to evaporate off and assist in cooling the outdoor coil.

I do not know how to read a psychometric chart. Assuming 100% humidity at 80F, what is the humidity at 120F? DMahalko (talk) 17:49, 8 February 2012 (UTC)[reply]

I could be wrong here but i think 100% humidity is water. — Preceding unsigned comment added by 166.147.89.157 (talk) 01:49, 6 June 2012 (UTC)[reply]

You are correct in every respect. A mist sprayed on the condenser coils of a heat pump will be raised in temperature. Before it reaches the actual temperature of the coils, which are well above ambient, it will evaporate, establishing a new, lower equilibrium temperature. The amount of water is ideally such that none drips off the coil. The greatest effect is obtained by wetting the fan side of the coils, such that the mist/film of water is blown through the coil fins, again, the ideal amount is somewhat less than would be required to wet the entire coil, because at some point on the way through the coil, sufficient water will already have evaporated to increase the humidity of the air flowing through the coil to 100% RH at whatever the new equilibrium temperature created by the evaporation of that water. Excess water then becomes a slightly insulating film on the coil (assuming that the water is at ambient air temperature and cools solely by evaporation). The additional comment is incorrect. The percentages quoted when referring to humidity are relative humidity. They refer to the amount of water vapour in the ambient air, relative to the amount of water vapour that air at the current temperature can hold. At common high temperatures in the tropics, 100% (relative) humidity equates to air containing about 4% water vapour by volume. At 1°C, 100% RH is very little, almost no, water vapour. At least I try (talk) 08:37, 3 November 2021 (UTC)[reply]

Oh

In the "Other types of phase-change cooling" section the phrase "Just before drinking, a tab is pulled so that the desiccant comes into contact with the liquid and dissolves. As it does so it absorbs an amount of heat energy called the latent heat of fusion. Evaporative cooling works with the phase change of liquid into vapor and the latent heat of vaporization, but the self-cooling can uses a change from solid to liquid, and the latent heat of fusion to achieve the same result." seems to be actually talking about something going in solution rather than changing physical state. I don't think this is pertinent to the article, and the energy absorbed surely is not the latent heat of fusion. Balerion87 (talk) 10:10, 11 December 2012 (UTC)[reply]

You are correct; the drink cooler referred to contains a substance that absorbs heat when it dissolves, such as ammonium chloride among many other substances. It doesn't have to be a desiccant, and in fact I can't think of anything traditionally thought of as a desiccant that could be used in this type of device. The can contains a plastic container with water and another container of the temperature lowering substance inside the water container. Pulling the tab breaks the inner container, and as the substance dissolves, lowering the temperature, the drink surrounding the reaction container is cooled. There is no phase change; the substance dissolves rather than fuses, and no latent heat of fusion is involved. (58.175.42.9 (talk) 10:18, 9 June 2013 (UTC))[reply]

I have removed Phoenix from the list of cities where swamp coolers are prevalent. Almost all homes in Phoenix area built 1980 or later have refrigerated air conditioning, unlike Tucson where swamp coolers were used on many homes up until the early 1990s. More often than not, homes with evaporative cooling in the Phoenix area also have air conditioning, where the swamp cooler is used for spring and fall cooling. ANDROS¹³³⁷_TALK 02:25, 2 April 2013 (UTC)[reply]

Don't see how they could have given up on anything in 1940, when one of them had been killed in a car wreck in 1937. 2600:1004:B118:340:D1A3:DB85:8D0:4948 (talk) 14:37, 8 February 2015 (UTC)[reply]

This section says that the final temperature of outgoing air can be calculated: "calculate wet bulb temperature, and then add 5–7 °F as described above." The problem is that while "5-7°" is mentioned above, the context is completely different: "A residential cooler should be able to decrease the temperature of air by 3 to 4 °C(or in Fahrenheit scale by 5 to 7 °F)."

Originally, this said basically "These things are never perfect, so a 5-7 degree difference from the wet-bulb temperature is to be expected." But User:Chemiyog said that's wrong and changed it, so now the whole explanation makes no sense at all. The reference is gone. It should be removed if nobody can say how well evaporative coolers actually work, or provide a reference. Piojo (talk) 08:02, 23 July 2015 (UTC)[reply]

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The saturation efficiency equation referenced by footnote [24] can be further traced back to Dr. John R. Watt and his document: Investigation of evaporation air cooling. Final report for the period 3 Apr 1952-31 Dec 1953 under Contract NOy-27492, by John R. Watt (PB 118435); Texas University, Dept. of Mechanical Engineering, Austin, Texas, Jan 1954.

Source: U.S. Government Research Reports, 16 Dec 1955, Vol. 24, No. 6, page 228, PB 118435. — Preceding unsigned comment added by 67.1.231.64 (talk) 21:59, 17 January 2017 (UTC)[reply]

I have removed Phoenix from the list of cities where evaporative coolers are prevalent. Over 95% of homes in Phoenix have refrigerated AC systems, and more often than not, homes that do have evaporative coolers will also have refrigerated AC systems as well. Evaporative coolers are much more common in Tucson in comparison, since until around 2006 the majority of Tucson homes still had them. ANDROS¹³³⁷_TALK 00:34, 21 January 2017 (UTC)[reply]

Under the "Shading" section, the paragraph is currently as follows: "Allowing direct solar exposure to the media pads increases the evaporation rate. Sunlight may, however, degrade some media, in addition to heating up other elements of the evaporative cooling design. Therefore, shading is advisable in most applications."

The first sentence seems misleading to me. It's quite possible my understanding of the physics is wrong here, so please correct me if that's the case! But as I understand it, any additional evaporation associated with direct solar exposure would not aid in cooling the air temperature. Evaporative cooling works to lower the air temperature by transferring the kinetic energy of air molecules (proportional to the air temperature) to the liquid water, providing enough energy for the phase change to vapor. If you also add solar radiation to the equation, all you're doing (to my mind) is providing another source of energy for the phase change (solar radiation energy), one that doesn't require a change in kinetic energy of the air molecules.

If that's the case, I'd recommend re-wording the paragraph to something along these lines: "Allowing direct solar exposure to the media pads increases the evaporation rate. However, this has no additional effect on the air temperature, since direct solar radiation provides the additional energy for the increased evaporation. Furthermore, sunlight may degrade some media, in addition to heating up other elements of the evaporative cooling design. Therefore, shading is advisable in most applications."

Any input here is appreciated! — Preceding unsigned comment added by 2601:646:8201:9B20:A96A:C26F:BDAF:8F88 (talk) 02:14, 19 June 2017 (UTC)[reply]

You are correct. It is not the evaporation per se that provides cooling; it is the fact that this evaporation is powered by the energy in the air. I.e. the undesirably high temperature of that air. Neither direct sunlight on the pads, the unit itself, nor using sunlight to heat the incoming air beyond ambient, will increase cooling, though all will increase evaporation and therefore humidity, as well as raising the output air temperature. This is obvious from everyday human experience; one does not cool down by standing in the sun to increase evaporation of sweat. One stands in the shade, in a stream of moving air if possible. I'll change the paragraph, in a way that dispells the myth so it isn't reverted. At least I try (talk) 08:05, 3 November 2021 (UTC)[reply]

Hi,

I have a Evaporative Cooler and am confused about windows and weather they should be open fully or just open a little bit. I was advised that the window should be open just a little bit to let the hot air out, but I also know other people who open their windows up fully? Can anyone help with this? — Preceding unsigned comment added by 2001:8003:1AF5:F800:D0FB:38A4:6DCB:6350 (talk) 10:00, 20 January 2018 (UTC)[reply]

The statement about evaporative cooling in buildings lacked historical perspective, hence the revision. In the middle east, windcatchers have been an architectural feature for millenia. My rewrite reduces the hyperbole, though I may need to add a citation. Here is the old:

Passive evaporative cooling techniques in buildings, such as evaporative cooling towers, have only been developed and studied in the last 30 years. In 1974, William H. Goettl invented the "Combination Refrigeration and Evaporative Cooling Air Conditioner" in Arizona after noticing that evaporative cooling technology works better in arid climates rather than humidity but that a combination unit would be more effective. In 1986, two researchers at the University of Arizona, Tucson, W. Cunningham and T. Thompson, constructed the first passive evaporative cooling tower in Tucson, AZ. This performance data from this experimental facility became the foundation of today’s evaporative cooling tower design guidelines, developed by Baruch Givoni.[7]

Yes, modern Western design and engineering has more datapoints, but the drama was out of proportion. GeeBee60 (talk) 13:07, 18 July 2018 (UTC)[reply]

The following Wikimedia Commons file used on this page has been nominated for deletion:

• Evaporative cooling diagram.png

Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 04:26, 6 January 2019 (UTC)[reply]

Evaporative coolers are most effective at low humidity and their effectiveness diminishes as the humidity increases. There are charts and tables that show this, but the only ones I was able to find easily are on HVAC commercial websites, such as:

• How Evaporative Cooler Works (Airconco UK Ltd)

It would be most helpful to add in a section to include either a table or graph showing the cooling as function of temperature and humidity, such as in the above link.
Enquire (talk) 17:40, 19 August 2020 (UTC)[reply]

Are there practical applications of using these principles during heat waves in places not used to them. Clearly, relative humidity information is critical. Assuming, at least during the hottest times, RH is low, what temporary measures can really help in a small building. My guess is having damp curtains or towels near windows on the side the wind comes into a building. CuriousMarkE (talk) 22:54, 14 July 2022 (UTC)[reply]

I thought this study might be of interest.

• Al-Hassawi, Omar Dhia; Drake, David (2023-05-27). "Innovations in Passive Downdraft Cooling Performance Evaluation Methods: Design and Construction of a Novel Environmental Test Chamber". Energies. 16 (11). MDPI AG: 4371.
  ISSN 1996-1073.{{cite journal}}: CS1 maint: unflagged free DOI (link
  )

• Paul, Andrew (2023-08-22). "Ancient Egyptian 'air conditioning' could help cool modern buildings". Popular Science. Retrieved 2023-08-23.

Peaceray (talk) 15:26, 23 August 2023 (UTC)[reply]