The Ore Refinery is an important structure for the Foehn as it is necessary for them to gather resources.
The Ore Refinery is a technologically complex building completely outfitted to receive and process raw ore from miners and instantly receive monetary transactions for the ore while on the battlefield. This makes this structure a vital asset to any base economy. The Foehn Ore Refinery is cheaper than all the other ones as the Minermite unit it comes with is noticeably less costly to produce than the standard harvesters.
Ore Refineries are critical in gaining funds for the army at many stages of the game, especially early on. While expensive, each refinery provides needed access points for miners to dump ore and gems, giving their commander a potentially steady income, depending on how far away and how many there are.
As an added benefit, every Foehn refinery comes with a Minermite, so placing one near ore will give an immediate boost to the Foehn economy. Incidentally, because these buildings come with a miner, depending on the situation it can be more beneficial to build and sell these buildings to quickly increase miner counts, though do keep in mind Foehn Ore Refineries only sell for $600 since they pay for the Minermite (note that this is more than other refineries).
Commanders should be sure to make sure that this building has proper protection, from both attacks that try to cripple their economy, and infiltrators seeking to steal $5000 from detector-less refineries; either of these can seal defeat against those unprepared for it.
Because Foehn Minermites gain a boosted speed from Spinblades, Foehn commanders will find it useful to deploy that power near the refinery's dump point, as the increased speed will allow them to mine more efficiently, reducing the amount of miners needed to keep their economy optimal for the war effort.
The AI will only build a maximum of 3 Ore Refineries on all difficulties.