the selecting of the right coldside/tec module/hotside/fan combination is an iterative process. here's a first pass.
the hs/fan combo is a pretty little thing. there is some information but not the thermal resistance. its not particularly easy to figure out the thermal resistance of a heatsink. you might find something similar
here, or maybe you can call sparkfun, and ask if they have a curve for that assembly. just for the sake of making progress, i'll make a guess. let's say that heatsink has a thermal resistance of 0.3 c/w at the air speed from your fan (it'll be close to that i think)
- a quick note here: you may notice that the watts/cfm calculation involves the volume of air, and the heatsink curves show linear airspeed. you need to take the volume of air from your fan that crosses the fins, and divide that by the cross section of the open area, and that will give you the airspeed ((ft^3/min)/ft^2=ft/min).
so you want to dump 30w. we got from before a theoretical best case of 2c drop. 0.3c/w is not great (you may be stuck with it though). anyway, that means you will need to get the base of the heatsink 10c lower than the desired temperature to dump your 30 watts, but we know from earlier, that the fan supplied will be up to the task.
time to look at the module, and the hotside.
something to know about peltier modules. their rated power is for when the cold side and the hot side are the same temperature. they get worse from there. it is close to impossible to make this happen, you want to keep dT as small as possible (TECs all have curves so that you can find one with the right watts at the dT you will have).
time to put some numbers to this: if you want 55f (13c) in your box, then your module needs to get down to 37f (3c). ideally you would want the hotside to also be 3c, but that ain't gonna happen. but we can assume that we can cool the hotside with ambient air, to 33c. that's a dT across the tec of 30c. spending a little bit of time on the
custom thermoelectric website i found this little guy ($46.50 ea). if you look at the curve for dT 30c, you can see it reaches 30w at about 3.25a. and looking over to the other curve, 12v at 3.25a (39w) gives you 30c dT, so that all works out.
cool
now we want our hotside to be at 33c or 9c above ambient (i'm assuming a 75f - 24c -ambient temperature). so we add the load 30w and the electrical power 39w and get 69w. our handy dandy airflow calculation tells us we need at least 13.5 cfm to do this. so far its sounding pretty good.
let's see if that heatsink will work on the hotside too, that would be pretty convenient. so just like on the coldside, the greater the dT the more watts it can transfer to the air. at 0.3c/w that means the heatsink should be 44.7c to extract the full 69w. so that's higher than our 33c needed for our tec. that makes for a 41.7 dT across the tec. so no, that sink won't work (the selected tec barely has 30w at 40c dT, but it draws a lot more power, upping the amount of heat you need to dump on the hotside now you have to dump 174w). now your temperature rise on the hs will be 52.2c (hs temp of 76.2c - giving a 73.2 dT on the tec, which will saturate the module, and you now have a heater.) your only option here is to pick a different heatsink for the hotside, or both the hot and coldsides.
a better heatsink on the coldside will mean warmer temperatures on the coldside of the tec, lowering dT across the tec, lowering the watts needed to cool to the desired temperature, thus lowering the amount of waste heat etc, etc.
i think what happens to most people who try to do this, is they end up just winging it, and as you see, all this stuff is inter-related, and winging it doesn't cut the hops.
there you go, have fun.