Evaporative air cooler for A/C?

[cRiPpLe_rOoStEr]

Spotted this VW Transporter with evaporative coolers a few weeks ago.


And about a year ago I found an International 9200 fitted with an evaporative cooler at the sleeper (altough it also cooled the rest of the cab).


In this Volvo from the 80's can be seen both the evaporative unit and an auxiliary water tank.


workaround ideas to discuss among friends: Evaporative cooling: a low-budget yet energy-efficient way to improve thermal comfort in motor vehicles

[indiaaircoolers]

Evaporation will take place when the humidity is below 100% and the air begins to absorb water. Any given volume of air can hold a certain amount of water vapour and the degree of absorption will depend on the amount it is already holding.The term humidity describes how much water is already in the air; relative to the amount it is capable of holding. Air is saturated when it cannot hold any more water. Imagine it as a sponge, if the sponge held half as much water as it was capable of holding, it would be 50% saturated. In the case of air, we would describe the Relative Humidity as being 50%. Energy is required to change water from liquid to vapour. This energy is obtained in an adiabatic process from the air itself. Air entering an evaporative air cooler gives up heat energy to evaporate water. During this process, the dry bulb temperature of the air passing through the cooler is lowered. Evaporative air conditioning uses evaporation to cool the air. In an evaporative cooler, such as Breezair, a pump circulates water from the reservoir on to a cooling pad, which in turn becomes very wet. A fan draws air from outside the unit through the moistened pad. As it passes through the pad the air is cooled by evaporation. The key to effective evaporative cooling is ensuring that each of the cooling pads are completely saturated at all times during operation and that the systems fan & motor are sized and designed to deliver the appropriate airflow for the home.

[pete c]

swamp coolers work great.....so long as you aren't in a swamp. tey are used extensively in the west. they do not work in humid areas such as pretty much everything east of the mississippi and a fair bit west of it.

[cRiPpLe_rOoStEr]

Originally Posted by pete c

swamp coolers work great.....so long as you aren't in a swamp. tey are used extensively in the west. they do not work in humid areas such as pretty much everything east of the mississippi and a fair bit west of it.

I've seen swamp coolers being used in trucks even in Brazilian Amazon, which is very humid. Just more recently swamp coolers are increasing popularity in Brazil for other applications, but none in Amazon as far as I know.

[cRiPpLe_rOoStEr]

A better picture of the Kombi


Lada Niva

BTW this one got a repowering with a Volkswagen 1.6IDI Diesel.


I've seen even an Isuzu NPR and an OBS Ford F-550 fitted with swamp coolers.

[NoD~]

I once bought a 12v pump (~80psi, IIRC) and a mister from a house misting system. Made a tank, put the mister into the airbox where the AC coil once sat. It didn't seem to really work like I hoped. I tried a second mister, still nothing. Was hoping the fine mist was enough to evap and cool the air, but it seems not. Gave up on the project. Average humidity in my area is 20-30%, BTW. (Idaho)

[cRiPpLe_rOoStEr]

Originally Posted by NoD~

I once bought a 12v pump (~80psi, IIRC) and a mister from a house misting system. Made a tank, put the mister into the airbox where the AC coil once sat. It didn't seem to really work like I hoped. I tried a second mister, still nothing. Was hoping the fine mist was enough to evap and cool the air, but it seems not. Gave up on the project. Average humidity in my area is 20-30%, BTW. (Idaho)

I don't like those direct-mist swamp coolers so much, and also they're more targeted to large areas, not a car interior.

[gone-ot]

Swamp Cooler Theory 102

It's ALL about LOTs of surface area with evaporative coolers. With mister's, yes, there are lots of droplets, but they're tiny and they're w-i-d-e-l-y separated and thus provide surprisingly small amount of surface area.

The aspen excelsior pads are usually 1"-2" thick, with the wood fibers oriented perpendicular to the airflow through them, so the air has to flow OVER / UNDER / THROUGH / BETWEEN lots and lots of wetted wood shaving fibers.

However, the OTHER major player in how well (or not) the evap cooler "works" is: (a) the DEW POINT temperature (Tdp) and (b) it's cohort, WET BULB temperature (Twb).

When the outside dry bulb temperature (Tdb) is above 95ºF and the dewpoint temperature (Tdp) exceeds 50-54ºF (just 22-25%RH!), the wet bulb temperature (Twb) will NOT be lower than 67-69ºF...and although this number LOOKS like really cool air, it is NOT, unfortunately, what you actually GET from the evaporative cooler.

With most evaporative coolers you only achieve about 80%-saturation, so you only "get" 80% of the Wet Dulb Depression temperature (WBD = Tdb - Twb):

T(cooler) ~ Tdb - 0.8*WBD

T(cooler) ~ Tdb - 0.8*(Tdb - Twb)

So, if Tdb is 95ºF and Twb is 67-69ºF, the air blowing from the cooler [ T(cooler) ] will only get down to about 73-74ºF...at almost 80%RH! But, your body wants to see/free something below 72ºF and closer to 30-50%RH!

This is when / why they're called "swap" coolers, because when it's HUMID you feel like you're in a tepid "sweat" sauna in a swamp!

[California98Civic]

Originally Posted by Old Tele man

So, if Tdb is 95ºF and Twb is 67-69ºF, the air blowing from the cooler [ T(cooler) ] will only get down to about 73-74ºF...at almost 80%RH! But, your body wants to see/free something below 72ºF and closer to 30-50%RH!

Great clarifying comment, Old Tele. Thanks. So, on a low humidity day, the humid air out of the evap cooler would quicky dissipate its water into the drier air already in the car, no? Just like it would dissipate the cool air, which would rapidly warm. Seems to me what probably makes these popular is not that they condition a room like compressor AC does, but that they are a blast of cool air. They're something between a fan and an AC.

[gone-ot]

Ah, but did you notice the HUGE change in relative humidity that's occuring "through" the cooler? The air comes in at 22-25%RH and exits at almost 80%RH...talk about sticky pooh!

At 95ºF outside air temperature and a coincident dew point temperature of 54ºF, the relative humidity of the outside air is just 25%RH. But, as that air weaves its way through the aspen pad, roughly 36 grains of water (7000 grains per pound moisture) have been evaporated into the transiting air volume, thus RAISING the relative humidity of the exiting air up to 78±%RH!

Because the human body "cools" itself by sweating, followed by subsequent evaporation of the that sweat--a one-layer swamp cooler, so-to-speak. However, at high humidity levels (>>50%RH), the sweat does not evaporate very quickly, so the skin doesn't cool down, leaving us feeling hot & sticky rather than just hot.