First was that high-value item found in the metal cabinet.

Taking the blueprint out from his backpack, the virtual light screen actually displayed related information about this item.

【On the Application of Passive Geothermal Ventilation Ducts in Underground Buildings and Energy-Efficient Structures】

Quality: Rare

Introduction: Can optimize shelter ventilation duct structure, automatically adjust indoor temperature, energy consumption nearly zero. With auxiliary equipment installed, can achieve dust prevention, odor prevention, backflow prevention, humidity control, and extreme weather response effects.

Function: Underground shelter temperature remains constant around 10~25℃. After installing auxiliary equipment, room temperature adjustment becomes possible.

"This blueprint's effects are really good!" Yu Yuan's eyes revealed delight.

Automatically adjusts indoor temperature, energy consumption nearly zero...

Wasn't this basically a natural air conditioner?

Looking closely at these blueprints, line by line clearly depicted the geothermal ventilation ducts.

Several pipes buried deep underground connected the underground structure to the surface, with various professional terms and symbols marked at different positions along with detailed explanations.

Simply put, geothermal ventilation ducts were a natural ventilation technology that used the constant temperature characteristics of underground soil to regulate air temperature.

At depths of 1.5~3 meters underground, temperature remained stable year-round at 10~15℃. Therefore, when external air passed through buried pipes, it would be heated or cooled by the soil, achieving temperature regulation.

This system utilized natural air pressure differences, requiring no electrical equipment, thus naturally having no so-called energy consumption.

The blueprints also listed the advantages and disadvantages of different pipe materials, as well as layout pros and cons, mainly differences in pipe length, burial depth selection, and serpentine or straight-line arrangements.

Of course, there were also detailed markings for air intake vents, exhaust vents, and pipe slopes.

Especially the pipe slope—with just a slight 1%~2% incline, condensation water produced during cooling could be discharged into drainage pits, preventing backflow.

It could be called extremely comprehensive in detail.

Completing the above optimizations would achieve the goal of zero energy consumption while naturally regulating underground building temperature.

But if appropriate auxiliary equipment was added, even more comprehensive functions could be obtained.

For example, low-speed fans could adjust ventilation speed, while adding air filters or humidity control devices could achieve dust prevention, odor prevention, and dehumidification effects.

It could even enhance temperature regulation effects.

The virtual light screen again displayed a prompt asking whether to add the blueprint to the optimization path.

"Optimize, must optimize!"

Yu Yuan didn't want to wait a single moment, immediately choosing to add the optimization path.

The blueprint in his hand flickered slightly before disappearing.

【Shelter ventilation duct optimization path has been added, please check yourself!】

Opening 【Survival】——【Shelter Facility Management Log】——【Ventilation Duct Construction List】

Sure enough, 【Geothermal Ventilation Ducts】 had already appeared in the construction list. However, what embarrassed Yu Yuan was that to build 【Geothermal Ventilation Ducts】, he first needed to complete level 3 【Ventilation】 construction before he could proceed with optimization upgrades.

But he hadn't even built the most basic single-pipe ventilation port yet.

Damn!

The technology he obtained was too advanced to use for now.

Who could he complain to about this? Yu Yuan felt both amused and exasperated.

But this also gave Yu Yuan motivation—he'd make this geothermal ventilation duct his short-term goal!

After sorting and organizing everything, only three items remained before him that Yu Yuan couldn't decide about.

A wallet, a hotel key card, and a ten-centimeter-long key.

All three items came from Biao Ge's body.

Examining the key card, the surface was worn beyond recognition of the name, only vaguely showing characters for XX Grand Hotel and a symbol resembling a bauhinia flower.

The back still clearly showed the room number—Room 0813.

That key was clearly not a regular room key either. After some thought, Yu Yuan stored these two items properly and picked up the wallet.

It was a ladies' wallet containing a family photo, but the man in the photo wasn't that ugly bastard Biao Ge.

Instead, it was a quite handsome man in his thirties.

Wow, this was probably a wallet snatched from some unlucky fellow!

Raising an eyebrow curiously, he examined the wallet with interest. The wallet was clean, containing a neatly folded water bill and several banknotes Yu Yuan hadn't seen before.

And a few—condoms?

Yu Yuan blinked, momentarily stunned.

What kind of operation was this?

After checking all the loot, the hotel key card and that key made Yu Yuan smell resources.

Anything Biao Ge carried with him definitely had high value.

He just needed to figure out which hotel it was.

Next was upgrading shelter facilities. The system's reminder stayed in Yu Yuan's mind—upgrading the shelter with all his effort was his long-term goal.

For upgrading the shelter door, he now needed three units of wood and two hinges. The screwdriver and screws were already sufficient.

For building the rest area, he still needed one yoga mat. The lighter and old cloth were already gathered.

For the bathroom, he still needed a bucket. The towel had already been found...

After summarizing the facilities needed for construction materials, he opened the Taotao Hole page to search, but soon he started cursing.

"Damn, a bucket costs 200 survival points, a yoga mat 500 survival points? Are they crazy!" He currently had at most 300 survival points total, only enough to buy a bucket.

Anyone buying at these prices would be an idiot!

But he quickly discovered patterns among these materials.

Prices for industrial or daily necessities were generally high, while natural world products like wood, stones, and stream water had relatively normal prices.

One unit of wood or stone cost 5 survival points, one liter of clear stream water 20 survival points, while lake water and river water were only 10 survival points per liter.

But the price for a 500ml bottle of drinking water skyrocketed to 80 survival points per bottle.

Yu Yuan caught on!

This was pricing determined by material acquisition difficulty!

Industrial and daily necessities could basically only be obtained from human gathering places like cities, villages, and factories. But these places mostly had thugs, scavengers, and wasteland survivors present, greatly increasing danger while quantities were scarce.

Having fought with scavengers, Yu Yuan naturally understood their danger, not to mention those thugs with heavy weapons. If discovered, it meant certain death.

With high material acquisition difficulty, value naturally rose accordingly.

Understanding this, Yu Yuan's eyes lit up.

Looking at the massive haul from tonight, the corners of his mouth curved upward.

"Scarcity is good! Taotao Hole's trading methods aren't limited to survival point transactions—barter trading is also possible!"

He immediately started operating.

Before long, the player chat channel within the Social page began frantically scrolling.

Source: Webnovel.com, updated by lotustale.com