Several posts back, I mentioned our rodwells. Here’s a cross-section of rodwell #2, which is now being used for our waste water, with the shape of the new water well, rodwell #3 drawn on top in the fatter red and blue lines.
Updated with some questions from Sam:
Q: rodwell wastewater: surely you guys extract the heat from it before you dump it?
[BS]A: As far as I know, we don’t. The rodwells are accessed through “ice tunnels” that are several hundred meters long. Since the tunnels stay at the year-round average temperature here, which is something like -50F/-46C, the pipes all need “heat trace” – resistive heaters – and insulation to keep from freezing up. So, I’d think that the waste pipes might require less heat trace to keep from freezing. But, it’s more efficient to use any initial heat in the waste water to keep the pipes from freezing, than to extract heat before using electricity to keep the pipes from freezing. I’ll do up a post on the ice tunnels sometime.
Q: How do you know the shape of the water well?
[BS]A: We’ve got a couple tricks to figure this out.
First, you can use geometry to figure out the area of the water surface: Remove X m^3 of water, and observe how much the water level (easy to measure with a dip tape) changes. Divide X by the change in depth, and you get the average surface area of the water you just removed.
We also have light+camera and laser rangefinder doodads that can be lowered into the rodwell. This photo is looking up, from inside the hole that accesses one of the rodwells:
Q: …and assuming it’s to scale, how is it as big in one year as the previous in 4 years? more water consumption?
[BS]A: I’d think it’s actually the other way around; we’ve pumped more heat into the new well for the amount of water extracted, so the new well has grown more than the previous well.
These things are interesting optimisation problems; I think the solution tends toward larger diameter wells since there’s a high cost (in terms of fuel usage, and parts/labour cost) associated with starting a new well. Much of the heat used for maintaining the water well, especially in summer, is waste from our power plant generators.