The World Ends In 27 Days

Shichen had designed Xiling to survive an exterior temperature of 70 degrees.

At the time, the number had seemed excessive.

Zhiyi’s records showed that the first Heat could push Yunzhou beyond 60 degrees, but Xiling sat at a higher elevation and remained protected by the mountain. Shichen had added another ten degrees to the anticipated maximum, duplicated every essential system and insisted that nothing critical depend upon a single cooling loop.

By seven in the morning, the temperature at Xiling’s exterior air intake reached 70.4 degrees.

The residential level remained at 21 degrees.

Shichen stood in the mechanical control room and watched the primary cooling system compensate. Pumps forced chilled water through the residential walls and ceilings, while another closed loop carried the collected heat into exchanger lines buried deeper within the mountain.

The system was working exactly as designed.

That didn’t mean it could continue doing so indefinitely.

Zhiyi entered carrying her tablet, with Hanchuan following closely behind her. Her hair had been tied back, but she was still wearing the clothes from their overnight watch.

"You were supposed to sleep after four," Shichen reminded her.

Zhiyi looked at him. "I slept before four."

"You slept for three hours," Shichen pointed out.

"And three hours is not zero," Zhiyi replied with a casual shrug.

Hanchuan rested his hand against the side of her neck. "We’re going back to bed after this."

Zhiyi looked at the system display instead of answering him.

Shichen understood why Hanchuan had followed her into the mechanical section. Once Zhiyi found a problem, she treated everything else as an interruption until she understood it.

"The primary loop is operating at 63 percent," she observed.

"It will reach 70 percent before the exterior temperature stabilizes," Shichen replied. "I’m activating the secondary loop."

"Running them together will increase power consumption."

"It will reduce the strain on each compressor and keep both systems within efficient operating ranges."

Zhiyi considered the explanation before nodding. "Alternate the deep exchanger fields every six hours. The inactive field will have more time to disperse stored heat into the surrounding rock."

Shichen adjusted the program. The suggestion would extend the useful capacity of the system, although he disliked needing it on their second day underground.

He activated the secondary cooling loop.

The vibration beneath the floor changed as another set of pumps began operating. Status lights moved from standby yellow to green while the system divided the load between the two loops.

No alarm sounded.

Hanchuan examined the power consumption. "How long can it run like this?"

"Longer if we reduce unnecessary heat inside the shelter," Shichen told him. "The residential level is our largest active zone, but the kitchen, laundry and vehicle level are adding loads we don’t need."

They returned to the common area and found the other three men gathered around breakfast. Zeyu had prepared eggs on the induction range and appeared personally offended by the restricted selection of cooking equipment.

"The ovens are off-limits," Shichen announced.

Zeyu looked toward the two built-in ovens. "Both of them?"

"Both," Shichen confirmed.

Zeyu frowned. "What if I need to bake something?"

"You don’t," Shichen replied.

"That feels unnecessarily absolute," Zeyu complained.

Shichen gestured toward the other appliances. "Every appliance that produces heat forces the cooling system to remove it. The induction range, pressure cooker and microwave transfer more of their energy into the food. Use those."

Zeyu glanced at the microwave. "You expect six adults to survive the apocalypse on reheated food?"

Jingwei accepted a plate of eggs from him. "You made eggs."

"The principle matters," Zeyu insisted.

Qinghe set a bottle of water beside Zeyu’s hand. "The principle can matter after you drink that."

While they ate, Shichen divided Xiling into active and restricted zones.

The residential level, medical room and essential storage areas would remain fully cooled. Guest rooms would be closed unless someone needed isolation. Lights and ventilation in unused corridors would switch on only when motion sensors detected someone.

Laundry would run during the coolest available hours. Showers remained unrestricted for hygiene, but hot water use would be reduced.

The vehicle level would stay isolated until the mobile base, SUVs and concrete floor released the heat they had carried inside.

"The vehicles have been underground since yesterday," Zeyu pointed out. "They can’t still be that warm."

"The mobile base contains several tons of metal, batteries and mechanical equipment," Shichen reminded him. "It retained heat from the drive and continues producing heat through its maintenance systems."

Zeyu immediately opened the vehicle diagnostics. "I can shut down everything except battery conditioning."

"You should have done that when we parked."

"I was distracted by the forest being on fire."

Shichen looked at him until Zeyu lowered his attention to the controls and began shutting systems down.

Zhiyi added the new restrictions to Xiling’s operating schedule. She calculated the expected reduction in heat load, then adjusted it when Qinghe insisted that everyone needed warm meals and enough light to maintain normal sleeping patterns.

Survival required more than keeping the air cold.

If they remained underground for four years, the shelter also needed to preserve their health, judgment and ability to tolerate one another.

Shichen had accounted for that in the design. He had included private rooms, artificial daylight, acoustic separation and redundant living spaces because six people couldn’t spend years sharing a single concrete room without consequences.

He hadn’t anticipated needing every feature immediately.

After breakfast, he led Zeyu and Jingwei to the vehicle level. The freight elevator opened onto air several degrees warmer than the residential section. Heat radiated from the armored body of the mobile base, although its systems were already powering down.

Zeyu checked the tire pressure and battery temperatures while Jingwei inspected the garage entrances. Shichen closed the workshop, spare-parts rooms and fuel-storage corridor behind insulated fire doors, reducing the amount of space connected to the vehicle-level ventilation.

"The fuel rooms need to remain ventilated," Zeyu reminded him.

Shichen continued securing the doors. "They have an independent system."

"I know," Zeyu replied. "I helped pay for it."

Shichen glanced at him. "Paying for something doesn’t mean you understand it."

Zeyu placed one hand over his chest. "You become cruel when you’re tired."

Shichen ignored him and checked the air flowing from the garage vents. The exhaust system was operating at minimum capacity, preventing fumes from accumulating without drawing unnecessary exterior air into the mountain.

Everything remained within acceptable limits.

They returned to the mechanical level shortly before noon.

The two cooling loops were sharing the load evenly. Residential temperature remained stable, power consumption had declined and no section had exceeded its assigned limit.

Shichen began to believe the shelter had absorbed the first increase.

Then an alert appeared on the control panel.

WESTERN SERVICE TUNNEL: TEMPERATURE VARIANCE

Jingwei moved closer. "How large?"

Shichen opened the sensor history.

The sealed tunnel should have been warmer near its outer entrance and progressively cooler as it approached the underground garage. Instead, the temperature near the center had risen nine degrees in less than four minutes.

"That isn’t exterior heat moving through the door," Shichen stated.

Zeyu stopped beside him. "Then what is it?"

A second warning appeared before Shichen could answer.

WESTERN SERVICE TUNNEL: PRESSURE LOSS

Something had breached the outer seal.

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