WeTried Translations
Translator/Editor: Ceaseless
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◈ The Medieval Heretic King is Too Good at Developing ◈
Chapter 100: The Winter of Prague (2)
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The standard heating device of this age was the fireplace.
Firewood was crammed into a firebox built of stone or brick, and the heat and light warmed the room.
The problem was efficiency.
Anyone who has ever built a fire knows this.
When you sit before a campfire, your front gets hot while your back remains cold.
The heat does not wrap around a person. It only radiates in one direction, like light.
A fireplace was no different.
Its practical thermal efficiency was only around 10 to 15 percent.
In other words, 85 percent of the heat energy from burning firewood escaped through the chimney.
On top of that, firewood burned out within a few hours. If the fire died in the middle of the night, you had to sleep shivering like Šárka.
Of course, there were alternatives.
Kachelofen.
The German word meant tiled stove. It was a high-end medieval European heating device designed to overcome the limitations of the fireplace.
When firewood was burned inside a sealed firebox clad in ceramic tiles, the hot smoke did not escape straight up the chimney. Instead, it wound through flues built inside the stove before leaving.
As the smoke traveled through those passages, the ceramic tiles steadily absorbed the heat. Even after the firewood burned out, they continued to radiate warmth for three or four hours.
It was excellent in terms of performance, but it had two fatal flaws.
First, it was expensive. Every heat-resistant ceramic tile had to be fired in a kiln, then craftsmen had to fit and stack them over several weeks. It was a luxury item for a noble's castle or a wealthy merchant's mansion, not something to put in a commoner's hut.
Second, it cracked. It was ceramic, after all. If sudden temperature changes caused the tiles to fracture, poisonous smoke leaked through the gaps. Repairs were no simple matter either.
Fireplaces were the height of inefficiency.
Kachelofen was expensive and difficult to maintain.
I needed a new alternative that would offset both their shortcomings.
The answer was already in my head.
* * *
A few days later.
The third annex of Prague's royal palace.
It was the most secluded part of the palace. I had converted the deserted, dust-covered space into my private workshop.
Afternoon sunlight slanted in through the small window, but the air inside still held January's chill.
Wearing a leather apron and gloves, I gave the brick structure beside the workbench one last inspection.
Thud, thud.
Footsteps approached through the corridor outside.
Perfect timing.
“Your Majesty, I came because you called for me...”
Šárka's words stopped halfway as she entered.
“Brr, it's cold! Why is it so cold in here, Your Majesty?”
Šárka wrapped her arms around herself and shivered. It seemed colder inside than it had been outside.
János Hunyadi entered behind her.
“My lord. Why did you summon us?”
The moment János opened the door, he frowned as well. His breath rose white before him.
“Why is it so cold in here? You should at least light the fireplace... Huh? Where did the fireplace go?”
János's eyes swept over the wall.
The fireplace that should have been there was gone.
In its place stood a strange structure.
A long construction of brick and clay.
The first thing that caught the eye was the firebox at one end, the opening where fuel was fed in.
But unlike a fireplace, its opening did not face upward. It was a horizontal hole, like the entrance to a rabbit burrow.
Directly above it, a vertical passage built from tightly packed bricks stretched straight toward the ceiling.
A brick structure reaching waist height ran along the wall in an L shape, while a chimney at the opposite end passed through the wall and outside.
Overall, it looked like a long, narrow brick bench.
It was long enough for three or four adults to sit side by side.
“Your Majesty, what is this?”
Šárka examined the structure with curious eyes. She tapped the brick surface with her index finger, then tilted her head.
“A brick chair?”
“You can sit on it, so it is a chair.”
I took off my leather gloves.
“But it is also a stove.”
Ondol, the Korean heating system as familiar to Koreans as air. What would happen if I combined it with a Western-style fireplace?
The answer was a rocket mass heater.
A hybrid stove that brought the core principle of ondol into a Western setting.
Šárka spoke with a puzzled expression.
“A stove? But isn't the firebox too small? How are you going to put firewood in there?”
It was a natural question.
The fireboxes people of this era knew were large enough for someone to crouch inside, filled with piles of firewood as thick as an arm.
But this opening was so narrow that even a cat would have to squeeze through it.
“I don't plan to put firewood in it.”
I took out the item I had prepared beneath the workbench.
Thud.
A black, heavy cylinder.
A pitch-black lump about a handspan wide and two handspans tall.
Nineteen holes pierced its face.
János frowned and asked,
“What is that, my lord? It looks like leftover cheese.”
“What kind of cheese looks like this? This is Bohemia's new fuel. It is called a briquette.”
It was something no Korean could fail to recognize.
A coal briquette.
“János, what do you think this is made from?”
“Well, it looks like coal...”
“Exactly. It is coal. But not ordinary coal. It is made from coal waste.”
Coal dust was a by-product produced during the making of Coke.
When coal was baked in a kiln to make Coke, fragments too small to form lumps piled up on the bottom. Dust was also constantly created while breaking and transporting Coke.
This coal dust usually had nowhere to go. It was discarded along the riverbank or left abandoned in some corner.
Even if it was used as fuel, it could not burn like lump coal in powdered form. Air could not pass through it. No matter how tightly it was pressed together, only the surface charred before it gave off smoke and went out.
That was why it had merely been piled along the riverbank beside the steelworks.
“I sifted that waste to gather only the fine powder, then mixed it with clay at a three-to-one ratio and pressed it into a mold.”
Šárka peered into one of the holes in the briquette.
“Then why are there holes in it? Are they handles?”
“They are not handles. Those holes are the key.”
I stood the briquette on the table so they could see its face.
The round holes lined up like a honeycomb were plainly visible.
“What does a fire need to burn?”
“Firewood.”
Šárka answered confidently.
“That is fuel. Other than fuel.”
“Um... flint?”
“That is a tool for making a spark. I am asking about something more fundamental.”
János cut in.
“Air, is it not? If you light a fire inside a sealed chest, it soon goes out.”
“Correct. More precisely, it needs one component in the air. That is complicated, so we'll skip it. The important part is that a fire must come into contact with outside air to burn.”
I spread my palm over the top of the briquette, covering all the holes.
“What happens if I block the holes like this?”
“The air can't get in... so it won't burn?”
“Right. Then what if there are holes?”
I lifted my hand.
The holes in the briquette were visible again.
“Air travels through those holes deep into the briquette. They are passages that make it burn evenly all the way through instead of only charring the surface.”
János tilted his head.
“But, my lord, you said you mixed in clay. Does dirt burn? Wouldn't it put the fire out?”
“Of course clay doesn't burn. But it acts as a binder, holding the powder together. More importantly, it controls the rate of combustion. If I compressed coal alone, it would burn too quickly. With clay mixed in, it burns slowly and for a long time.”
One demonstration was worth a hundred explanations.
I pushed the briquette into the firebox.
The bottom of the L-shaped combustion chamber had been prepared with dry sawdust and tinder.
Scrape, crack!
I struck flint and dropped a spark.
The dry sawdust caught fire, and a small flame rose.
At first, there was little reaction.
It did not flare up like firewood. It only slowly licked at the bottom of the briquette.
“Your Majesty, is it not burning?”
Šárka whispered carefully.
“There is no smoke, and I can't feel any heat...”
“Wait. It needs to warm up first.”
One minute. Two minutes.
In the silence, only a faint crackle could be heard.
Then, a subtle vibration began.
The sound gradually grew louder, as if some great beast deep inside the firebox were stretching awake. It could not yet be seen, but something was definitely waking.
Then a bright red glow began to spread through the briquette's holes like veins.
“Huh?”
Šárka's eyes widened.
The briquette, which had been completely black, gradually heated from below. Soon, every hole glowed red like lava.
Then, the next moment.
Whoooosh!
A fierce rush of wind roared from the mouth of the firebox.
Air was being sucked in.
As though an invisible giant had placed its mouth against the firebox and taken a deep breath, the workshop's cold air was drawn inside.
“W-What is that?!”
János instinctively stepped back. Šárka's bangs fluttered toward the firebox.
“What is this...? There is nothing there, yet the wind is being sucked in on its own!”
With my hands behind my back, I nodded.
It was going exactly as planned.
“János. Where does hot air go?”
“It rises. Like smoke rising into the sky.”
“Then what happens if the air inside that narrow, long vertical passage becomes hot in an instant?”
János looked at me in disbelief.
“The air... gets sucked in? Like it is now?”
“Correct.”
This was the principle of the rocket stove.
Its core was the insulated vertical flue above the firebox.
The heat riser.
As high-temperature air surged upward through the riser, the powerful updraft drew in the air around the firebox like a vacuum cleaner.
The incoming air intensified the fire, which created an even hotter updraft. It was a chain reaction.
Šárka cautiously approached the firebox.
“Wow... It really is warm! No, it is hot!”
She crouched in front of the firebox and held out her hands. Her face quickly flushed red.
“But, Your Majesty, why did you make this huge brick chair? It just takes up space and looks uncomfortable...”
Šárka's observation was sharp.
If all I wanted was a good fire, there was no reason to build such a long brick structure.
I smiled and pointed toward the bench-shaped structure.
“Šárka, go sit on that chair.”
“Me? There? It will be cold...”
Šárka hesitantly perched herself on the brick bench.
At that moment.
“...Ah!”
Her eyes went round.
“Y-Your Majesty! This...! It is warm! No, my bottom is getting hot!”
As if she could not believe it, Šárka shifted her hips and ran her palm over the brick surface.
“How can a block of stone be this warm? The fire is over there.”
Unable to contain his curiosity, János came closer and laid a hand on the brick. His eyebrows twitched.
“Huh. It is true. Warmth is seeping out from inside the stone.”
“Of course it is. Smoke is passing through it.”
I pointed to the top of the vertical passage, then slowly traced the outline of the L-shaped brick bench along the wall.
“An ordinary chimney throws the hot smoke straight outside, but this one is different. The rising heat does not leave immediately. It passes through that long horizontal passage and warms the bricks. Brick and clay also retain heat for a very long time. Once heated, they will keep giving off warmth for half a day even after the fire goes out.”
It worked on the same principle as ondol.
The only difference was that this was installed along the wall instead of beneath the floor.
“My lord, how long will one briquette last?”
“About ten hours.”
“Ten hours?”
János's expression changed.
“Firewood has to be added every hour... Are you saying that one lump no bigger than a fist will burn all night?”
“Yes. Replace one before you go to sleep, and it will last until morning. You will no longer need to wake up shivering at dawn to add firewood.”
János swallowed.
“And you said the material is... coal waste?”
“Yes. The black powder that was thrown away by the river.”
“Then it will be nearly free. We only have to pay for labor and clay.”
Šárka had already pulled both legs up onto the brick bench and curled up like a cat.
“Ah... This is wonderful. It feels like my back is being roasted. I want to live here...”
Her expression was one of pure bliss.
It was the magic of deep warmth, understood only by those who had endured cold that seeped into their bones.
Šárka spoke in a drowsy voice.
“Your Majesty, can you put one of these in my room? Please...”
“There is no reason I can't. But building such a heavy brick bench in your room would require quite a bit of construction.”
A rocket mass heater was fixed in place. Once installed, it could not be moved, and it took up considerable space.
It might work in a spacious workshop or sitting room, but it would be difficult to install one in every maid's room in the palace or every ordinary home.
“That is why I prepared one more thing.”
I pulled away the cloth covering the space beneath the workbench.
Clatter.
Another black object appeared with a dull metallic sound.
This time, it was not made of brick.
It was a smooth, sturdy cylinder cast from iron.
It stood about knee-high. Long vertical grooves ran down its body, and a small sliding door at the bottom controlled the air vent.
János stroked his chin.
“Is this... a stove?”
“It is a cast-iron briquette stove. The principle is the same. You put a briquette in and burn it.”
It gave up brick's heat-retention properties in exchange for portability and immediate heat.
It was a fifteenth-century reinterpretation of the familiar briquette stoves once commonly found in Korean schools, construction sites, and snack shops.
“It is heavy, but it can be carried around. No installation is needed. You only have to run the flue pipe out through the window.”
I opened the lid, put in a briquette, and lit it.
“I lined the inside with a thin layer of Refractory brick to preserve heat. The cast-iron exterior releases heat quickly and warms the air. It is perfect for small rooms or tents.”
János stared at the stove with shining eyes.
“This is perfect for military use. Every winter march brings a flood of frostbite cases. If we put one in every barracks, it will change our combat strength. We will not need to drive soldiers so hard just to gather firewood.”
“That is not all.”
I placed a kettle of water on top of the stove, which had already been heated to the right temperature.
Sizzle.
“You can put a pot on it to cook, or a kettle to boil water. It solves heating and cooking at the same time. Šárka, this would be better for your room. You cannot lie on it like the bench, but it will warm the entire room in no time.”
“Wow... This is good too! And if I leave a kettle on top, the room will not get so dry...”
Šárka climbed down from the bench and approached the stove.
“Your Majesty, when can we use this? In winter, my hands freeze stiff and hurt so much when I do laundry. Please put just one in the laundry room. Please?”
“Don't worry. I already sent the design to the steelworks.”
There was no farming in winter, so if I put the blast furnace that had been producing farm tools to work making stoves, the Prague marketplace would be filled with briquette stoves in a few days.
The only concern was carbon monoxide poisoning, but I could explain the stove's operation in detail in the newspaper.
Once the stoves spread, poor people would be able to survive winter without worrying about expensive firewood.
If firewood was no longer needed, fewer trees would be cut down, preserving the forests.
This winter, the sight of Prague... no, of Bohemia, would surely change.
Every home would be piled high with briquettes instead of firewood.
Footnotes:
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