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Photo of an evaporative cooler or swamp cooler in Tucson (C) Daniel Friedman Swamp Coolers & Evaporative Coolers for Air Cooling: Design & Usage Guide

  • POST a QUESTION or COMMENT about using a swamp cooler to cool a building interior - when do swamp coolers work better than an air conditioner?

Swamp coolers:

This article explains the use of an evaporative cooling system or "swamp cooler" including cool air delivery design considerations when using under-floor ducts for cool air delivery in buildings.

Swamp coolers or evaporative cooling systems work well in dry climates - usually, as we explain here.

The discussion of cool air duct location and routing includes general air conditioning duct design concepts that also apply to all air conditioning and cooling designs.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Evaporative Cooling Systems or "Swamp Coolers" - How They Work

Evaporative cooling system types (C) Carson Dunlop Associates

Evaporative coolers, also called "swamp coolers" rely on the evaporation of water to cool building air, rather than the movement of a refrigerant through cooling coils.

Cooling towers, swamp coolers, and even a simple window fan blowing air across a pan of water and into a room are types of evaporative cooling systems.

[Click to enlarge any image]

Swamp coolers systems may use less energy than a refrigerant-gas and compressor type air conditioner but they'll only work where the ambient humidity is low enough to make it easy to evaporate water, such as in Arizona and other areas of the Southwest and Mexico.

Our sketch (left), courtesy of Carson Dunlop, shows three types of evaporative cooling systems or "swamp coolers".

All three evaporative cooling system approaches are similar: dry outdoor air is blown across an evaporative cooling device that uses water evaporation to cool the incoming air.

The differences among these swamp cooler designs are principally how the water to be evaporated is delivered to the evaporative cooling device (drum or pad bottom is immersed in a water reservoir pan, or a pump delivers water to the top of the evaporative pad), and the type of evaporative device itself: a rotating drum or an evaporative pad.

 

 

 

Delivery of Cool Air Using an Evaporative Cooling System

Sketch of under floor cool air ducts (C) Steve Bliss, Solar Age, Daniel Friedman

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Topic: Under-floor ducts for cool air delivery with (for example) an evaporative cooling system

Question: We plan to build a pilot energy-efficient home in our city.

We have a long and somewhat severe cooling season, with a humidity level that is relatively low (10-15 % RH). An evaporative cooling system or swamp cooler should suffice, but there are several drawbacks: dust, open windows, safety, noise, and the like.

I would like to duct the cool air delivery system under a wood-framed floor, supplying cool air through floor registers, and exhausting it out through a roof cupola. (See sketch above, courtesy of Solar Age Magazine). I am sure that an attic fan will be necessary to drive the warm air exhaust out of the building.

Do you see any obvious problems with the scheme I have described? -- Jimmy Moore, Odessa, TX

Answer:

Single-stage direct evaporative coolers, also called "swamp coolers" do provide a cost-effective means of cooling houses during hot, dry periods. Their main drawback is moister indoor air - the cost for a lower dry-bulb temperature.

Due to low energy use (for a small fan and water pump), swamp coolers are popular in the U.S. in parts of the West and Southwest. For example, our photograph at page top shows a swamp cooler system whose operating components are mounted on a Tucson Arizona rooftop.

Watch out: a swamp cooler, like other water-eavaporation cooling devices can become a reservoir of dangerous Legionella bacteria. See details

at Legionella BACTERIA & HVAC EQUIPMENT

Delivering Cool Air Through Floor Ducts?

Warm and cool air delivery duct design (C) Carson Dunlop Associates

Delivering cooled air through the floor and exhausting it through the roof runs counter to the tendency of warm air to rise and cool air to fall in a building. But an exhaust fan in the roof should pull air upwards through the entire house.

Watch out: Two warnings:

Make sure that the exhaust fan capacity in cubic feet per minute (CFM) is matched to the volume of air that is being supplied from the cooling system upwards from the floor ducts and air registers.

Carson Dunlop Associates' sketch (left) shows a different approach for a closed air duct system that changes its duct operation depending on whether warm air or cool air is being delivered into the building.

You would probably not use this duct design in an evaporative cooling system because the evaporative cooling approach depends on continuous introduction of dry outside air into and through the building during the cooling system, but the sketch makes clear a duct system intended to deliver cool air in a building needs to operate differently than ducts intended to deliver warm air during the heating system if airflow is to be optimized.

Using a Rooftop Cupola to Exhaust Swamp Cooler-Delivered Cool Air?

Whole house fan and building exhaust requirements (C) Carson Dunlop Associates

Provide an air duct between the top floor ceiling grille and the roof exhaust cupola. This will keep moist (and possibly cooler) air out of the attic, where it might condense at night and cause moisture problems in the structure and in the attic insulation.

See Attic Moisture or Mold Sources and

see Mold in Fiberglass Insulation.

Readers ducting cool air through a crawl space should also see CRAWLSPACE MOLD ADVICE.

Carson Dunlop's sketch (left) warns of another safety consideration: a whole house fan or an attic exhaust fan (such as we describe above), can cause back-drafting at fireplaces and atmospheric-vented gas heating appliances - backdrafting can in turn cause dangerous, potentially fatal carbon monoxide hazards in buildings.

Watch out: The hazards are described at COMBUSTION GASES & PARTICLE HAZARDS

and the remedies are described at COMBUSTION AIR for TIGHT BUILDINGS.

Finally, remember to provide a means of closing off the rooftop exhaust during the heating season. Otherwise your warm house air will simply escape by natural convection currents carrying it up and outdoors through your rooftop-mounted exhaust system even if the fan is not running.

See WATER & ICE IN DUCT WORK for a case history where just this problem occurred in a building.

When is Evaporative Cooling Effective

Swamp Cooler (C) D Friedman Andy Gieseke

See Solar Age Magazine "Notebook" 2/84, for the conditions where evaporative cooling is effective.

In that issue, author Jerry Germer reviews use of the psychrometric chart that relates moisture, temperature, and indoor relative humidity to discuss the conditions that make people comfortable indoors, and how to relate indoor comfort to the outdoor climate, particularly to temperature and humidity in those two environments.

Our photo (left) shows an evaporative cooler or "swamp cooler" in use blowing cool air into an outdoor mechanic's work area at Canyon Auto Sales in Tucson, AZ. Photo by the author and Andy Gieseke, Canyon Auto.

Swamp coolers or other evaporative cooling systems can cool a building interior using less energy than a conventional air conditioner or heat pump system except during times of very wet or humid weather such as the "monsoon" season in southern Arizona.

During wet and very humid weather evaporative cooling simply cannot evaporate enough water to produce good cooling. Some building owners install both evaporative cooling or swamp coolers and a conventional refrigerant-based air conditioner or heat pump, running the latter only when necessary due to humid conditions.

Watch out: leaky swamp coolers or just about any mechanical equipment that regularly spills or overflows water onto a roof surface is likely to cause stains on the roof surface and might lead to roof wear as well.

Details are at WHITE STAINS on ROOFS.

8 Indoor Air Cooling & Heating Strategies

Mr. Germer mapped eight heating and cooling "design zones" onto areas of the psychrometric chart and then described eight indoor air conditioning approaches and related them to the outdoor climate. For areas or times of the year when temperature and humidity outdoors, and thus also relative humidity, fall within multiple zones on the Germer chart, multiple of the 8 zones and 8 indoor air conditioning strategies below might be usable.

  1. Active solar or mechanical heating: this zone has outdoor temperatures too low for passive building environment conditioning strategies.
  2. Passive solar heating: direct solar gain, indirect solar heat gain, hybrid systems, combined with air infiltration and temperature conduction control - we describe passive solar heating

    at PASSIVE SOLAR DESIGN METHOD

    and further

    at PASSIVE SOLAR HEAT PERFORMANCE.
  3. Dehumidification: high outdoor (or indoor) humidity requires using some method to remove the excess humidity in order for building occupants to be comfortable. In the 1984 article Germer pointed out that passive dehumidification had not been well developed.

    See HUMIDITY LEVEL TARGET.
  4. Mechanical air conditioning: temperature & humidity combinations in this climate zone cannot be managed by passive means and so mechanical air conditioning

    See AIR CONDITIONING & HEAT PUMP SYSTEMS or active solar cooling will be needed.
  5. Ventilation: although temperatures and humidifies may be high, occupants may be made comfortable by direct evaporation of sweat from the skin if enough air velocity is available - in other words, fans can do the trick.
  6. Thermal mass: these air conditioning systems are usually found in hot-dry climates with dry cool nights, such as southwestern United States and parts of Mexico, particularly at higher elevations

    see PASSIVE SOLAR DESIGN METHOD

    see THERMAL MASS in BUILDINGS

    and THERMAL MASS in UPSTAIRS Radiant cooling and night-flushing of internal mass with cool outside air stores coolness (the ability to later absorb heat) for the next day, and similarly, during the warmer day, the same thermal mass can store warmth to even out cooler nighttime temperatures indoors.
  7. Evaporative cooling: low energy "swamp coolers" (discussed in this article) can be used under conditions of low humidity such as in Arizona and higher elevations of Mexico.
  8. Humidification: moisture needs to be added to very dry air for indoor comfort.

    See HUMIDITY LEVEL TARGET. We prefer local or room humidifiers after seeing duct, mold, concerns with some centralized humidifier add-ons to heating and air conditioning systems.

The link to the original Q&A article in PDF form immediately below was preceded above by an expanded/updated online version of this article.

The articles at this website describe the basic components of an air conditioning system and then we discuss how to estimate the rated cooling capacity of an air conditioning system by examining various data tags and components. The limitations of visual inspection of A/C systems are described.

Evaporative Cooling Resources for Products, Manuals, Installation Guides

...


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: clearance distance from cooking exhaust vent to evaporative cooler

What is the code on cooking hood vent distance from an evaporative cooler?

Mine is about 3 ft below and 9 ft away. - Bill 2021/06/16

This Q&A were posted originally at TYPE B-VENT ROOFTOP CLEARANCE

Moderator reply: Exhaust-Vent opening distance to Evaporative Coolers: 10 ft horizontal distance or exhaust 3 ft. above Cooler & ? horizontal distance

I took a look at the IO manuals for several evaporative coolers;

none of the IO manuals for evaporative coolers (cited above on this page) addressed your question of clearance distance to kitchen exhausts or grease exhaust vents,

and an evaporative cooler education website purporting to answer this rooftop evaporative cooler clearance distance question confuses building system mechanical air intakes (such as a fresh air intake vent or combustion air intake vent) clearance codes with rooftop-mounted evaporative cooler clearance distances and safety.

But for safety, and considering that smoke and grease may clog and foul the evaportive cooler's air flow, fan, evaporator surfaces, in our OPINION

acceptable clearance from a kitchen exhaust (a potential source of grease, smokee and noxious debris) as

The clearance to a mechanical air intake (such as might be part of an evaporative cooler intake) is required for any source of "noxious flumes, smokes, vapors" including for example, bathroom or kitchen exhaust vents, plumbing vents, and chimneys.

Your kitchen exhaust is 9 feet away (IF you measured that as a level horizontal distance) which is almost enough, but is three feet below rather than above the evaporative cooler inlet - which is no surprise given how these units are usually placed on a roof.

Really? note that some experts assert that a kitchen should not be considered a source of "noxious exhaust" and I agree from an aesthetic point of view but NOT from a functional or safety view: kitchen exhaust vent contains FOGs (Fats, Oils, Grease) that can foul and even clog-up a nearby rooftop HVAC or Evaporative Cooler system.

Watch out: the local building code official is the final legal authority for this question

See details and IO manuals for Evaporative Coolers above on this page.

Or give us the brand and model of your evaporative cooler so that we can take a look at its installation instructions.

Thanks for asking

Question: why is my evaporator freezing up?

(May 30, 2012) ramon said:

all exits are open fully-living room,3 rooms,dining room, yet the evaporator freezes- the evaporator is fully clean. Why it freezes?

Reply:

Improper refrigerant charge, inadequate airflow across the cooling coil, are examples of cause for frosting of the evaporator/cooling coil. - yours is not a swamp cooler.

Search InspectApedia.com for COOLING COIL ICING to read details.

Question: oily substance coming from swamp cooler

(July 21, 2014) Barry said:
oily substance coming from swamp cooler

Reply:

Check for a leak at an electric motor or for a unit suffering from algae or settled dirt and debris.

Question: swamp cooler installation placement, clearance distances, specifications

2017/07/14 Jason said

Where should I install my swamp cooler?

Reply:

Jason,

Evaporative coolers are either roof-mounted (whole house cooling systems) or mounted in a window (smaller units) so are positioned differently than refrigerant-based cooling systems using an indoor air handler and outdoor compressor/condenser unit. An important consideration in mounting the rooftop unit is the proper selection of and strength of the supporting roof jacks.

But a look through the installation and owners manuals for six evaporative coolers (listed in the article above) I did not find any references to side clearances or top clearances for the units, perhaps because of their anticipated location. Certainly it would make sense to avoid installing a rooftop unit where you'd expect trouble such as

- Don't install any fan operated or air cooled device where its air intake or outlet are obstructed by a nearby vertical wall, chimney, or other exhaust system

- Don't install any fan-operated or air-cooled component where its intake air or outlet air compete with another such unit installed close-by - lest hot exhaust from one unit increase the temperature of the incoming air in another unit.

OPINION: if you don't see other specific clearance distances in the installation guide for your particular system, check with the manufacturer for advice. A general safe rule is probably to keep at least 2 meters of separation between nearby air operated devices and at least one meter from a vertical or enclosed overhead surface.


...

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