Thermal energy generation in machines

[Calecute]

I'm sorry for the simple question, but i couldn't find a straightforward answer searching on google or in the forums.

I'm a bit unsure about how heat generation works. Machines have a DTU/s generated, but how it relates to inputs/outputs is kinda confusing. Initially I thought the machines DTU/s would be the thermal energy difference between inputs and outputs, but with outputs temp not being a function of input temp this cannot be true.

So I guess the total thermal energy generated by a machine is:
Machine DTU/s +(output temp*output mass*output specific heat)-(input temp*input mass*input specific heat)
?

So as an example running a petrol gen at 40ºC with 40ºC ethanol for 1s (so outputting 500g of carbon dioxide at 110ºC and 750g of polluted water at 40ºC) it would be:


20,000DTU +(110ºC*500g*0.85(DTU/g)/ºC) +(40ºC*750g*4.18(DTU/g)/ºC) -(40ºC*2,000g*2.47(DTU/g)/ºC) 

This would give 20kDTU(machine) +47kDTU(carbon dioxide) +125kDTU(polluted water) -198kDTU (ethanol)=~-5.5k

So runing a pretty normal petroleum gen on ethanol is heat deleting? This can't be right can it?

 

[JRup]

You might want to look into the wiki to check the heat economy section on petroleum generators:

https://oxygennotincluded.fandom.com/wiki/Petroleum_Generator

 

[blakemw]

15 hours ago, Calecute said:

So runing a pretty normal petroleum gen on ethanol is heat deleting? This can't be right can it?

It is entirely possible for buildings to be heat-deleting. The game makes zero effort in terms of conservation of energy.

But the problem can be difficult to frame usefully. We may want to know if a system is self-cooling (or cooled by the inputs), or we may want to know where the most efficient place to apply cooling is, like how it's far more efficient to cool the outputs of an Electrolzer than the input water.

The Petroleum Generator, if sealed insulated box, will indeed be kept cool (below the boiling point of ethanol, in this case), by 40 C ethanol.

The same is true of Coal Generator, Hydrogen Generator and Natural Gas Generator, all can be successfully kept cool - including their outputs - by their fuel.

For example I've happened to analyze the Coal Generator for use in Spacefarer Modules. The Coal Generator consumes 1 kg/s of coal, produces 9kDTU/s of heat and 20 g/s of 110 C CO2. The 9kDTU/s of heat increases the temperature of the coal by 12.67 C, and the CO2 increases the temperature of the coal by 1.8 C. So if fed with 20 C coal pooped out by 20 C Hatches the equilibrium temperature is 34.47 C, for normal amounts of heat generation in a Spacefarer module, the Coal Generator fed 20 C coal would thus keep temperatures below 40 C, rather than heating it up as one might expect. (and this analysis stands up perfectly to sandbox testing)

The equilibrium temperature is much more complicated to determine for buildings that output at building temperature, made even more complicated if it's not perfectly thermally coupled with the inputs and outputs, like a Gold Amalgam generator can run a good deal hotter if it's not immersed in liquid. It is of course easier if the building temperature is fixed by an active cooling system.

Oh also tooltips are usually accurate but aren't always accurate, like the Natural Gas Generator actually produces CO2 at building temperature and it's not floored to 110 C. This seems to be a glitch that only affects secondary outputs, in the case of the NGG it seems to have something to do with the gas output being piped, buildings that vent directly to the environment aren't effected.

[ghkbrew]

20 hours ago, Calecute said:

So runing a pretty normal petroleum gen on ethanol is heat deleting? This can't be right can it?

In addition to @blakemw's points it's worth pointing out that there's a difference between net heat deletion and a thermally stable system.  In your example if you run a 40C generator running on 40C ethanol using insulated pipes, you can be net deleting heat, but the system will still increase in temperature as the generator adds heat to itself.  To make a stable system you generally need to have the inputs absorb the heat from machine itself (and optionally from the outputs).

 

In the specific case of ethanol power generation, a sweet spot in the design space is to put the distillers and the generator in an insulated room and snake the lumber through it on a rail.  The ~20C lumber will absorb enough heat to keep the whole system stable at 50-60C.

[Calecute]

 

So the thermal energy math is correct. 

On 8/11/2022 at 7:25 PM, JRup said:

You might want to look into the wiki to check the heat economy section on petroleum generators:

https://oxygennotincluded.fandom.com/wiki/Petroleum_Generator

 

Thanks! I had checked the wiki on heat, but hadn't though to check the heat part of the petrol gen. It is indeed very informative.

On 8/12/2022 at 5:54 AM, blakemw said:

It is entirely possible for buildings to be heat-deleting. The game makes zero effort in terms of conservation of energy.

But the problem can be difficult to frame usefully. We may want to know if a system is self-cooling (or cooled by the inputs), or we may want to know where the most efficient place to apply cooling is, like how it's far more efficient to cool the outputs of an Electrolzer than the input water.

The Petroleum Generator, if sealed insulated box, will indeed be kept cool (below the boiling point of ethanol, in this case), by 40 C ethanol.

The same is true of Coal Generator, Hydrogen Generator and Natural Gas Generator, all can be successfully kept cool - including their outputs - by their fuel.

For example I've happened to analyze the Coal Generator for use in Spacefarer Modules. The Coal Generator consumes 1 kg/s of coal, produces 9kDTU/s of heat and 20 g/s of 110 C CO2. The 9kDTU/s of heat increases the temperature of the coal by 12.67 C, and the CO2 increases the temperature of the coal by 1.8 C. So if fed with 20 C coal pooped out by 20 C Hatches the equilibrium temperature is 34.47 C, for normal amounts of heat generation in a Spacefarer module, the Coal Generator fed 20 C coal would thus keep temperatures below 40 C, rather than heating it up as one might expect. (and this analysis stands up perfectly to sandbox testing)

The equilibrium temperature is much more complicated to determine for buildings that output at building temperature, made even more complicated if it's not perfectly thermally coupled with the inputs and outputs, like a Gold Amalgam generator can run a good deal hotter if it's not immersed in liquid. It is of course easier if the building temperature is fixed by an active cooling system.

Oh also tooltips are usually accurate but aren't always accurate, like the Natural Gas Generator actually produces CO2 at building temperature and it's not floored to 110 C. This seems to be a glitch that only affects secondary outputs, in the case of the NGG it seems to have something to do with the gas output being piped, buildings that vent directly to the environment aren't effected.

Yeah i guess it's possible to a heat deleting engine to go up in temp for ever since it's also mass deleting, and depending on how heat is distributed between outputs and the machine itself. And yeah i imagine the output at machine temp with lower bound can lead to runaway heating, as theres a feedback loop between machine getting hotter and outputing even more heat. Interesting to know also about the bug in some output temps. 

On 8/12/2022 at 10:54 AM, ghkbrew said:

In addition to @blakemw's points it's worth pointing out that there's a difference between net heat deletion and a thermally stable system.  In your example if you run a 40C generator running on 40C ethanol using insulated pipes, you can be net deleting heat, but the system will still increase in temperature as the generator adds heat to itself.  To make a stable system you generally need to have the inputs absorb the heat from machine itself (and optionally from the outputs).

 

In the specific case of ethanol power generation, a sweet spot in the design space is to put the distillers and the generator in an insulated room and snake the lumber through it on a rail.  The ~20C lumber will absorb enough heat to keep the whole system stable at 50-60C.

The input absorbing heat trick seems quite useful, since input thermal energy is deleted. I guess you can even run the inputs through a room with a aquatuner to take some heat of other stuff before you burn it. Will definitely try it.

Thanks for the help!