How much of a thermal gradient is there with submerged polar datacenters? IIUC it is possible to tube solid-state thermoelectric devices to certain ranges? Wh

How much of a thermal gradient is there with submerged polar datacenters? IIUC it is possible to tube solid-state thermoelectric devices to certain ranges? What's the thermal gradient between a crawlspace or a subterranean basement and an attic under a dark roof?