I have nothing against the humble desert coolers generally found clinging unceremoniously to windows in the neighborhood. So what if they are noisy, smelly and sometimes deliver electric shock if not earthed properly. But if we are fighting the mighty air conditioner then things have to be taken a bit seriously.

 

I have been trying to look for better, efficient designs and options out there, but first a recap on why we like the desert/swamp cooler:

  1. It's cheap and low tech. Swarms of hardware shops in the streets of North India start making (right there on the street) and selling these cheap cooling machines as summer sets in.
  2. It consumes a fraction of electricity compared to a conventional window or split A/C unit. All we have is a blower and a tiny pump.
  3. It does not recycle air. Fresh air is good.
  4. You sleep better knowing that you are not contributing to global warming.

This list could be longer but lets try to not get too excited!

 

So what's the problem?

Unlike traditional air conditioning where you know how much cooling you need and can buy a packaged unit to cater to that cooling load, we usually have no idea about how big or how many of these desert coolers we need to cool our homes. Forget about the engineering design that went into manufacturing a typical cooler. There isn't any! (Actually there is and we'll get to that) Then there is a problem of noise and humidity. And what about water- especially potable water? remember 'desert' in desert cooler.

 

Let's look at some options:

Noise: One way to deal with the noise is to use a ducted system or a sort of split system. Another approach I have seen being used is where you have a fanless unit (with just the cooling media- usually 'celdek' with water circulation system) mounted outside a window or a wall opening with a quiet fan mounted on an exterior wall somewhere in the house to create a negative pressure resulting in air being sucked in through the 'cooling box'. 

Humidity: The problem of humidity is two fold. One- if the air is already humid, cooling by evaporation is not effective. Two - High indoor humidity levels are not comfortable for the occupants. How do we deal with humidity in a system that is based on evaporation of water? Again, there are a few tested ways.

Using a desiccant to dry humid air before it passes through the cooling medium. The hot (presumably) and dry air increases the efficiency of evaporative cooling in humid environments. The desiccant used is usually a saturated solution of salts (lithium chloride, calcium chloride, sodium chloride). Dry desiccant system could also be used (silica gel).

Two stage or Indirect evaporative cooling: In two stage evaporative cooling, a heat exchanger is used. The cool moist air cools the heat exchanger which in turns cools the air on the other side without adding humidity. The two stage system also addresses the issue of water quality that is being used in the cooler. Since there is no direct contact between the air cooled by the wet pads and the interior air, we don't have to be concerned about water quality or using scarce potable water. A good cooling option for healthcare facilities.

The term 'Indirect evaporative cooling' is also used sometimes for hybrid systems, where the first stage of cooling is evaporative and the second stage is traditional refrigeration cycle. Packaged indirect evaporative cooling units are available commercially that are much more energy and cost efficient compared to traditional packaged units and could be used as a part of designed HVAC system for entire facilities in hot and dry climates.

 

What else is there? Please share if you know of anything I have not covered here.

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