A Swamp Cooler, also known as an Evaporative Cooler, is a green alternative cooling technology with deep historical roots. The name “Swamp Cooler” is an unfortunate reference to the consequences of poor maintenance. But first, let’s explain the basics.

The primary function of a swamp cooler is to take outdoor air, pull it through a wetted pad (humidifying and cooling it), and then blow that air through a house, with the air which continuously flows through and exits the home through opened windows or special vents.

How does it work?

Swamp coolers have three main components:

• A fan to move a high volume of air, typically a cubic-feet-per-minute (CFM) rating over 2,000 and commonly around 5,000 CFM for a whole house.
• A water pump, usually submerged in a reservoir of several gallons of water, to recirculate the water through the pads.
• A mesh-like pad that allows outdoor air to pass through, while being wetted by water pumped onto its top edge. They also need: a water supply line, a float valve to keep the water reservoir full, electricity to power the fan and pump, and a controller or set of switches to turn the fan and pump on and off.

Here’s a diagram to illustrate. Note, the cooled airflow here is misleading: it usually exits the side or the bottom of a unit. The exact layout doesn’t really matter however, the principle is the same- hot, dry air from outside is pulled through wet pads by a fan that blows it indoors. A pump recirculates water over the pads. Water and electricity are connected for continuous operation.

Source: WikiMedia, usage license available

The cooler is sometimes mounted on a rooftop (“downdraft” style,) or mounted through a window opening or custom hole like an A/C (“side draft”). Here is a picture of a side-draft unit mounted high up on the side of a public library in Pima, Arizona:

Source: WikiMedia, usage license available

Inside the home or building, there must be an opening for exhausting all that airflow, usually open windows with screens, a screen door or even special vents that open automatically based on the pressure change.

The US Dept of Energy recommends providing 1–2 square feet of unobstructed window screen or vent opening for every 1,000 CFM of airflow from the fan. For a 4,500 CFM unit, this means opening between 4.5 ft² and 9 ft² of window or screen door, from all openings combined.

Why is this “better” than A/C?

It isn’t necessarily better or worse. It’s different in a few important ways:

First, it uses around 80% less electricity to run an evaporative cooler to achieve the same degree of cooling as ordinary A/C. In a hot environment, where cooling is required for weeks or months in the summer, this can add up to sizable energy and cost savings!

Second, it doesn’t always work. The only time it works is when the outdoor air is dry. This means a % Relative Humidity under 40–45%, or a dew point under 50°F (10°C). As the outdoor humidity goes up, there’s less “room” in the air for evaporated water to move into. The actual cooling, the drop in temperature, is much greater for dry air, and almost nothing for humid air.

Third, it may work well enough for cooling at certain temperature ranges, but become too humid inside. A swamp cooler is basically an oversized humidifier (using evaporation instead of boiling or ultrasonics).

The most important takeaway is that swamp coolers can’t replace A/C, but they can displace, or reduce the use of A/C, when weather conditions permit.

Are there more benefits of whole-house Evaporative Cooling?

Yes! Absolutely. I’ll dive into those in future blog posts, but here’s a bunch off the top of my head, starting with the most obvious:

• Savings from reduced wear-and-tear on the regular A/C (on top of the direct savings from using less electricity than A/C!)
• Easier to DIY maintain and repair
• Cheaper service calls for repairs than A/C (no vacuum pump or expensive refrigerants)
• Better indoor humidity for those with asthma, for healthy plants, even for furniture
• Feeling more connected to nature by enjoying the smells of Spring and blooming things
• Enjoying much cooler air than you would ever set your A/C for, on especially dry days and especially dry evenings
• Vastly extended runtime for cooling vs. A/C when using a house-battery
• During power outages, powerable from portable battery banks like the “solar battery generators” ( ← I use this one) sold for RVs and campers, for example
• Energy conservation credits on your bill from your electric utility provider if/when they have an alert to reduce energy due to grid strain (like “flex” alerts in California)
• Improved grid reliability from reduced demand during heat waves, if enough people switch from A/C to their evaporative coolers
• Enjoying an “indoor/outdoor” lifestyle more with easier passage to a patio, because of the need to have open windows and/or screened doors
• Improved indoor air quality from reduced VOCs and indoor pollutants (that terrible “new rug” smell)
• Better skin health, less dry chapped skin
• Less risk from airborne pathogens like COVID-19, influenza, rotavirus, and all the other “common cold causing” viruses and bacteria, because the CFM rate is so high: e.g. a 4,000 CFM replaces the air in a 1,500 sq-ft house once every 3–minutes
• Chopping onions can be tear-free
• Cooking smells from fish, curry, cabbage, etc can’t build up (also cat litter boxes)
• Longer lasting rubber bands and elastic
• Slower drying ballpoint pens
• A temporary miniature outdoor water feature/bucket from the bleed tube or purge pump, useful for watering plants, a garden or even as a birdbath
• I’m sure I missed a few. I don’t have long or wavy hair, so maybe there’s a benefit for certain hair types? Let me know if you thought of benefits not in the list above!

And to be fair, there are certainly drawbacks and tradeoffs. The maintenance burden for evaporative coolers is higher than A/Cs, and anyone who uses a swamp cooler knows: you have to keep track of the weather forecast!

These are some of the reasons I made the “Evaporative Cooler Forecaster” app, to help swamp cooler owners manage and maximize their comfort and savings. Check it out at: https://SwampCooler.app/ or search for “Evaporative Cooler Forecaster” on either Apple or Google app stores!

I’ve only touched the surface of how swamp coolers work and why they’re so amazing. Come back to this blog for more posts about evaporative coolers and my app.

Keep cool!

-will

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