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Early to late game electrolyzer cooling

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I've been on a journey to reduce build complexity and increase heat economy. Saw this idea kicking around a while ago and finally got around to implementing it. I'm pleased with the way it works and want to share to help beginning and intermediate players.

This build uses a copper ore aquatuner to cool electrolyzed oxygen fed from a cool steam vent. No steam turbine. It is simple to build with basic tech. I set it up around cycle 70 and am still using it on cycle 302 with no intentions to change. It supports 9 dupes.

The build


Screenshots are from the spaced out dlc but will work in vanilla just fine.


I have a copper ore aquatuner sitting in about 20kg per tile of water and polluted water. Automation turns it on when the bath water is below 90°C and cooling is needed (coolant above 18°C).

Hot water at about 70°C from cool steam vents goes through the bath in copper radiant pipes drawing heat out and goes directly into the gold amalgam electrolyzer. Feeding hot water into an electrolyzer destroys heat.

Hot oxygen falls into the base across copper radiant pipes which rapidly cools the gas. The coolant then goes around the perimeter of my base - a nice clean method of keeping places temperature controlled.

Here's how the base looks at cycle 302. I added a second electrolyzer and replaced the bath water with oil but haven't modified the design or changed settings.



Coolant runs through granite pipes inside granite tiles around the interior of my base. I also circulate hydrogen in granite pipes just for a little extra heat carrying capacity (the hydrogen is not actively cooled). As you can see the core gets a little warm, but it's still cool enough for plants.



Build Plan:

Enclose as much of your base as you are able with insulated tiles and the interior normal tiles. This will help make the build more efficient and can be built as you go.

Make a bath for the aquatuner (2h x 5w works fine). Use bottle emptiers to put a 20-100kg layer of polluted water then another 20-100kg layer of water. That's 20-100 kg per tile, resulting 100 to 500 kg total of each liquid. Any two liquids that can tolerate 100°C temperatures will work.  Petroleum and crude oil are better choices, but not at all necessary. A single liquid is fine too, just takes more of it to make two tiles high.

Set up the plumbing and automation. Wire a thermo sensor and liquid pipe thermo sensor through an AND gate to the aquatuner. Set the thermo sensor to about 10 degrees C below the flash point of your liquids. Don't set it higher than 90-ish or you risk boiling the electrolyzer feed water and breaking pipes. (see where one of my pipes has damage? lesson learned)

Make your electrolyzer hat. Plumb the electrolyzer water through the bath in copper pipes, then insulated pipes to the gold amalgam electrolyzer. Use gold amalgam for the hydrogen pump.

Use mesh tiles and a pneumatic door to restrict dupes from going up into the hat. I caught them idling in 70° oxygen once 'cause dupes want to hurt themselves.

Copper radiant pipes between the hat and base will easily cool the hot oxygen before it falls into your base.

Easy cool steam vent taming:

Leave a few layers of natural tiles around the vent. Natural tiles have much more mass and will absorb a lot more heat from the vent. Surround the natural tiles with insulated tiles for good measure.

Put some tempshift plates (granite is fine) around the vent and a few touching the natural tiles to help heat move in to them.

Build a gold amalgam liquid pump in the collecting pool and plumb it straight to the machine.

A note about power economy:

The build will supply about half the hydrogen power needed to run the system in the beginning when everything is full on. Once the temperature settles down this build will be self-powering.

I'm supplying 45°C water to the bath, which goes into the electrolyzer at 65°C. Warmer supply water will decrease the efficiency, but I think this build is self powered all the way up to maximum operating temperature.

I don't know when they added this feature, but you can see the uptime of many buildings in the properties tab of its info card. The AT uptime is 14% over the last 5 cycles. Over the last 5 cycles the whole build has drawn 1,846,800 joules and created 2,607,360 joules worth of hydrogen.

Here's the math

Draw Qty Power (watts) Uptime Time (s) Draw (joules) Hydrogen produced (g)
Aquatuner 1 -1,200 14% 3,000 -504,000  
Electrolyzer 2 -120 49% 3,000 -349,200 325,920
Hydrogen Pump 1 -240 18% 3,000 -129,600  
Atmo suit Pump 2 -240 60% 3,000 -864,000  



Production Hydrogen (g/s) Power (w) Potential Generation (w) Coverage
Hydrogen Generator -100 800 2,607,360 141,2%



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Nice write up of the build. I like the pre-plastic heat deletion with the electrolysers.

It might be worth dumping some excess heat into the hydrogen going to the generators, too. Heating it up to 175C with a gold amalgam aquatuner will produce a fair amount of cooling.

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5 hours ago, ghkbrew said:

Nice write up of the build. I like the pre-plastic heat deletion with the electrolysers.

It might be worth dumping some excess heat into the hydrogen going to the generators, too. Heating it up to 175C with a gold amalgam aquatuner will produce a fair amount of cooling.

Yeah and you can do that once you get liquids that can handle that heat without vaporizing. Or maybe putting the AT in hydrogen instead of oil. Don't know how that would handle the heat - easy to sandbox though.

I love feeding max temp inputs into heat deleting machines. Sometimes it's difficult to generate enough heat.

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5 hours ago, SYS.Amadeus said:

Can you explain what is this setup, how it connects and what does it do ?


By using the bridges, it ensures that the flow never stops.  If the coolant is warm enough (via the pipe sensor) it goes into/out of the AT.  If it's too cool, then the AT is turned off by the sensor and the flow just continues past the input of the AT to move along.

Pretty normal, although you don't actually need it do use 2 bridges.  Put one bridge with the direct input coming from the AT's input line and route the AT's output line into the middle spot of the bridge.  Middle spot pass through takes precedence over the normal input of a bridge, so if the AT is outputting, it will go first.  If the AT isn't outputing, then the pass through flow just continues on.


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If one is a naughty boy, they can feed electrolyzers any temperature water by abusing small packets. After a game load, the first several packets will boil while in the electrolyzer but that quickly stops. Have a sump to collect the occasional water and ezpz heat deletion. Loop the packets and no problems occur when the electrolyzer becomes disabled from overpressure or automation. The smaller loop with the valve feeds small packets into the main loop only when there is room.


When the water inside the electrolyzer stops boiling off, it also stops exchanging heat with the surroundings. So definitely a bug somewhere in there. Why this happens after a few seconds and if it happens to the contents of other buildings is unknown. Interestingly, the contents of a reservoir don't boil off but still exchange heat. So whether the building is flagged as sealed in the code may have a role to play. I no longer have the decompiled code to look at, but I would guess electrolyzers don't have the sealed flag. Or maybe something else entirely, ONI is weird.

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That's brilliant @wachunga. This allows you to delete outside heat even when using a steam geyser with no turbine, which ordinarily has no room to do so. Even gold amalgam gives you plenty of room to exploit the SHC differences.

The reason for boiling only on load might be an order of operations thing. Something like this could be the normal order, but 2 and 3 are swapped on load?

  1. pipe feeds contents to building
  2. electrolyzer consumes contents
  3. debris exchanges heat
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Let's do some napkin math on the heat economy.

Say we start with 95C water condensed from a cool steam vent. Use a gold aquatuner to dump heat into it up to 170C. That's 313 kJ of cooling potential (per kg of water electrolyzed). The output oxygen will need to be cooled and for the sake of simplicity let's not bother separating out the hydrogen. Target temperature is 25C so we can farm bristle blossoms in the open. That's 168 kJ of cooling needed. Leaving 145 kJ of cooling potential. That's enough to condense 2.3 kg/s of 110C steam down to 95C water. Which is more than cool steam vents average IIRC. Neat.

Or to put it another way, the 145 kJ of excess cooling is equivalent to 12 hydrogen wheezeworts. Wheezewort buff when?


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My strategie from early to late game :

1. Use polluted water from the slime biome, to cool the oxygen by passing the pipe in a pool. It will fix the oxygen at around 30°C.

2. Find 5 wheezeworts / electrolyser.

3. Do a turbine/AT cooling system.

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Wahoo, starting again ONI after a year, the explainations makes it... harder to understand :)


Can you tell me if I get it right ?


It is a AT bypass and a way to compress the liquid bubles (10 kg buffer ?) ?




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1 hour ago, Argelle said:



Yes, that's right. The 2nd bridge inlet will work as a reliable 10kg buffer, which will be held there while the aquatuner is on. This can sometimes cause a pipe to burst if you are not careful, but it won't do that in this build.

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