Air Conditioner Reviews, HVAC info and Buyers Guide

The Ventless Portable Air Conditioner Myth

Strictly speaking, a truly ventless portable air conditioner is a myth. Ventless is possible if the refrigerant transports coolant to an outside unit – but this is not portable, because the lines running the coolant are fixed. Portable is possible, and many units exist – but they all vent through hoses to some outside area. The combination of portable and ventless is where the problem arises.

An air conditioner functions by moving heat from one location to another. This can be done by moving refrigerant or by moving hot air. A machine that moves heat from a room and vents it back into the same room (by pushing air in different directions) is possible, but the physics are all wrong. The reason is that there is an energy cost (the electricity that runs the fan and compressor) which ends up as waste heat and contributes to the overall room temperature. A truly portable ventless air conditioner would act in the same manner as leaving the door of your refrigerator open. While it may seem cool standing in the open door, this is more than compensated for by the increased heat given off from the backside of the unit, where the compressor is discharging heat. This is why Consumer Reports doesn’t test them1.

So what about this product2? It shows up on the Hammacher Schlemmer website and purports to do what can’t be done, offering an astounding 7,000 BTUs of cooling power with only a discharge tube and no outside venting. The price listed is $500. Looking carefully, you will see that the item is no longer available. Physics cannot be denied.

Not a ventless air conditioner, but a cooler

If we compromise and withdraw the term air conditioner, there are ways to provide cooling that is both portable and ventless. The term ‘air conditioner’ refers to the ability to simultaneously cool and remove excess moisture (dehumidify); dropping that condition allows for other possibilities.

The first is a simple fan. It blows air and provides some cooling as sweat evaporates off of skin. This is called evaporative cooling – our built in cooling mechanism. Another form of this comes as the swamp cooler. This operates by blowing air through a cloth or fiber mesh that is kept moist. As the air is forced across, water evaporates and cools the mesh, providing a source of relatively cool air. Both of these also add moisture to the ambient air in the room and are only effective in very dry climates. They do meet the requirements of being portable and ventless.

A third option is to provide a heat sink – someplace for the heat to go that doesn’t involve venting to the outside. Because the unit has to be portable, the heat sink has to be contained in the unit itself. This can be accomplished with ice, either water ice or dry ice. A fan blows warm room air across this and cooler air comes out the other side. However, providing the ice can be an expensive proposition – energy is required to freeze water and the price of dry ice is prohibitive.

Evaporative cooling units

Because swamp coolers only work in low humidity environments (less than 38%) they find little use in the Eastern U.S. – anywhere east of the Rockies as a general rule. They do find use in desert states, like Nevada, Arizona and New Mexico3.

A typical unit will “wick” water up into a cloth mesh with a fan blowing behind the fabric. The wicking isn’t powered, but is simply an effect of capillary action – as water evaporates, it is replaced from a reserve. The fabric may actually be a cellulose pad. The need is to balance air flow with the amount of water evaporated.

Evaporative coolers do not provide more than a small fraction of the temperature drop that actual air conditioners will. A typical air conditioner (small) will produce about 6,000 BTU/h in cooling, while a swamp cooler will be closer to 60 BTU/h4. Evaporative coolers also top out quickly in their ability to cool as the room humidity rises with use and one shouldn’t expect more than a few degrees drop in temperature.

Although quite limited in cooling ability, evaporative coolers do have advantages. They are very inexpensive compared to actual air conditioners5 (a personal unit can be had for $60) and are both portable and ventless – meaning they can be used in situations where outside venting is impossible. They are cheap to operate, the only power loss is with the fan motor, which air conditioners also have as well as a compressor.

Units are sold for large areas, but because relative humidity quickly increases with large units, they are most properly used in very small area applications, such as an enclosed home office space. Some attention also has to be paid to the water used – distilled is best. These units also require periodic cleaning and disinfecting to prevent mold/mildew growth. The internal workings are constantly damp and the substrate (cellulose) is ideal for mold.


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One Response to “The Ventless Portable Air Conditioner Myth”

  1. Catherine says:

    I am trying to cool a storage room/office/ laundry room at my business. The room is windowless so the unit cannot be vented to the outside without installation through an exterior, cement wall. I live in Alabama where humidity is quite common, and since a washer and dryer is in use in the room, a dehumidifier is already in use. I’m wondering if the operation of a dehumidifier in the room could help make an evaporative cooler a better option for me. I’d appreciate any feedback you can offer. Thanks in advance!

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