The next article in the 5 Gallon Bucket Air Conditioner - Does it work? series, is going to be more explanation about BTU/hr ratings.
We here at 5gallonairconditioner.com get asked a bunch of questions. Does it work is by far the most common question, and after 3 or 4 more questions, then the conversation gets to "well, what is the BTU/hr rating of your units?"
I have written several blog posts about the ICE model units and the BTU content of ice, and ice melting, etc. So, if you haven't read any of those blog posts yet, you may want to read through those to get a better understanding of the ICE model units and their cooling capacity and the proper application of those models, etc.
The EVAP models are a completely different device than the ICE models, yet they share many of the same characteristics. First and foremost, both models are completely portable, can be battery powered, are very lightweight, very durable, AC and DC powered etc. The EVAP models also include inexpensive pads, a small pump, and as I will show, they are a very good value for their cooling capacity.
We have conducted in house experiments to determine water usage and subsequent BTU output. The water volume put in the EVAP unit was precisely measured and the device was operated for a very exact period of time. Then exact water consumption during that specific period of time was then determined.
Water has a very specific "BTU content." That BTU content is how air conditioner units are sized for residential and commercial applications. Because water has a specific BTU content, and evaporation is the process, then very simple calculations will show the "size" of the evaporative cooling capacity.
Water temperature has very little, in fact negligible affect on the BTU content of the water. So, some guys say "put ice in the water" so then the water/pads are colder. Other guys say, "no, you want the water to be hot so it will evaporate faster." Both "guys" in this context are correct, yet both are incorrect as well. Reality is that water temperature has such a little affect, that most engineers generally disregard the water temp in their calculations.
So, the cooling content of water is 8700 BTU/gal.
Now remember this is the "scientific" number of "perfect RO/Distilled" water at standard atmospheric conditions, etc.
But, this is the number that engineers use, almost universally in almost all but the most precise of applications and calculations.
So, 8700 BTU/gal is the number we will use.
So, with this number, it is very easy to calculate BTU/hr, right? Simply pour in 1 gallon of water, turn on the AC unit and see how long it takes for the gallon to completely evaporate.
Well, there's a little more to it than that, such as outside temperature and humidity level, enthalpy and efficiency, etc., but for our purposes, and to try and keep things as simple as possible that was in essence the measurement that was made in our experiments.
So, in 1 hour, there was 118 fl oz of water consumed/evaporated in the experiment (pad weight was precisely measured before and after also). There are 128 fl oz of water per gallon.
Using those numbers, we can calculate BTU/hr ie, sizing of the 5gallonairconditioner.com EVAP unit.
So, to find the percentage of a gallon consumed, simply divide 118 oz by 128 oz. So, 118/128 = 0.922. So that means that in 1 hours time, 92.2% of a gallon of water was evaporated.
Now multiply .922 by 8700 BTU cooling capacity of water. That comes to 8020 BTU/hr.
So now that we have the BTU/hr rating of this evaporative unit, then we can use it compare this AC unit with other AC units currently available.
According the the online charts, an 8000 BTU/hr AC unit should be able to "comfort cool" an area between 250 sq ft and 400 sq ft. An average sized bedroom is about 150 sq ft. The average kitchen is about 250 sq ft. The average 2 car garage is 400 sq ft.
Another thing to note, is that the 5gallonairconditioner.com EVAP unit will hold in excess of 3 gallons of water. So, that means that the AC unit will run for about 3 hours before it needs to be refilled on average.
So, now armed with all of that information we can talk about value.
So, considering the performance, a realistic measure of value, is to compare the 5gallonairconditioner.com EVAP model to what else is commercially available. They are admittedly tough to get an exact comparison, because the 5gallonairconditioner.com EVAP units have so many additional features, such as portability, DC powered, outdoor and off grid applications etc.
So, just a quick scan on the internet shows the current cost of an 8000 BTU/hr cooling unit ranges from about $200 up to a little over $400 depending on brand and features.
When compared to those units, on a performance basis, the 5 gallonairconditioner.com EVAP units are a good value. Then when you factor in the light weight, cost to run, portability, battery power option, ease of use, durability, no toxic chemicals/green, etc., the 5gallonairconditioner.com EVAP model is hard to beat.