Chen Hao stared at the temperature curve on the screen, his fingers tapping three times on the keyboard. All the data from the past seventy-two hours had risen without any sign of decline. He turned to Nana, "We can get started now."

Nana's optical lens flashed. "Implement the 'Heating Gradient Adjustment Plan'?"

“Yes,” he said. “Turn off the heating in the warehouse and garage first, and use the saved heat in the living area.”

After the command was input, the main boiler's output power began to decrease. The red pipe on the screen gradually thinned, and the speed of the light representing heat flow also slowed down. Five minutes later, the alarm light on the north-side return water valve turned yellow.

“Pressure fluctuations,” Nana said. “The rapid drop in pressure leads to uneven thermal expansion and contraction.”

Chen Hao grabbed his notebook and flipped through a couple of pages. "Then let's change the plan. Reduce the food supply by five percent every two hours, don't cut it off all at once."

“Adjusted.” Nana reset the parameters. “At the same time, start the solar preheating cycle and increase the geothermal pump unit to 70% load.”

The solar collector array slowly rotated, its absorption surface facing the gray-white sky. Deep underground, the geothermal well also began pumping water at an accelerated pace. These two new energy sources gradually replaced the fuel boiler.

"It's like a jigsaw puzzle now." Chen Hao leaned back in his chair. "We have to put it on piece by piece, not just the whole thing."

Nana didn't reply; her system was running a simulation. The new energy allocation model showed that during the day, solar energy could handle 40% of the heat load, geothermal energy provided a stable 30%, and the remaining 30% would have to be supplied by coal. At night, solar energy would drop to zero, geothermal energy would reach 50%, and fuel would make up the rest.

"How much can we save this way?" he asked.

"Based on the current consumption rate, the fuel reserves can extend the service life by 68 days," she said.

Chen Hao whistled, "Then we've essentially lived for two more months."

"It's a result of improved resource utilization," Nana corrected.

"If you insist on speaking like a human, there's nothing I can do." He grinned and casually pushed the water glass next to the control panel away to prevent it from being knocked over.

The alarm sounded again, this time indicating a slight heat loss from the main pipeline in the east wing living area. A red dot was flashing on the infrared detector.

"It might be due to aging of the sealing rings." Nana pulled up the structural diagram of the utility tunnel. "It needs to be inspected manually."

"I'll go." Chen Hao stood up and rummaged through the cabinet to find anti-slip boots. "You keep an eye on things up there. Call me if anything happens."

The entrance cover to the underground utility tunnel made a dull thud as it was pushed open. Moist air rushed in, carrying the smell of rust and dirt. Chen Hao ducked inside, his headlamp illuminating the wet ground ahead.

"Ten meters behind the third pillar on the left," Nana's voice came through the earpiece. "Watch out for the water under your feet."

He moved forward step by step, his shoes slipping twice. After turning the corner, he noticed that the protective plate at the main pipe connection was loose. Upon closer inspection, he found that the edge of the gasket was blackened and would crumble into dust at the slightest touch.

“It’s broken,” he said. “It needs to be replaced.”

"There are spare silicone gaskets in the second compartment of the toolbox," Nana reminded, "the low-temperature resistant type."

He took out a new gasket, installed it, and tightened the bolt. During the process, his hand brushed against the outside of the pipe and got burned.

"This pipe is still quite hot." He shook his hand.

"The current surface temperature is 63 degrees Celsius," Nana said. "It's within the safe operating range."

After fixing the last screw, he patted the connector and said, "Okay, now check the data over there."

The system was repressurized and tested. The heat transfer efficiency returned to 98.6%, and the alarm was extinguished.

"Passed," Nana said. "We can proceed to the next stage."

Chen Hao climbed out of the utility tunnel and put his toolbox back in its place. His coat was covered in mud, but he was too lazy to change it. Back in the control room, he noticed that the solar panel output had suddenly jumped a bit.

"Increased sunlight?" He leaned closer to the screen.

“The clouds briefly parted,” Nana explained. “It was expected to last seventeen minutes.”

"Take this opportunity to store up more hot water," he said immediately. "Let the water tank heat up first."

After the command was given, the water pump began filling the rooftop water tank. The solar heating elements hummed, and the thermometer reading slowly rose.

“These devices were all idle before,” Chen Hao said, looking at the flowchart. “Now they’re finally coming in handy.”

“That’s what they were designed for,” Nana said.

“I know, but nobody cared before,” he shrugged. “It’s like having a can of food that’s three years past its expiration date in the fridge; you can still open it and eat it, but who would dare?”

Nana paused for two seconds, then said, "This analogy doesn't hold true."

"Anyway, the sentiment has been conveyed." He waved his hand.

The two then adjusted the energy distribution rhythm. During the day, when there was plenty of sunshine, they maximized the use of solar energy; geothermal energy maintained a basic supply; and the boiler was only started during periods of extreme demand. At night, the order was reversed: geothermal energy became the primary source of energy, the boiler provided supplementary energy, and solar energy was shut down.

"The problem is how to strike a balance." Chen Hao scratched his head. "On sunny days, the sun produces too much energy, which is wasted; on cloudy days, it's not enough."

Nana retrieved the off-grid energy dispatch algorithm from the robot's knowledge base, "Based on historical data, a dynamic model is built to predict the next day's sunlight intensity in advance and automatically adjust the output ratio of each system."

"It sounds like fortune telling," he said.

“It’s mathematical modeling,” she corrected.

"Alright," he nodded. "Let's give it a try."

After the program started running, it automatically generated a scheduling table. Chen Hao looked at it for a few minutes, but found it too complicated, so he simply added a shortcut button to the control panel.

He typed: "Winter → Spring transition mode".

“From now on, we’ll call it the ‘Spring Switch,’” he said with a smile. “Just press it, and warm air will come on its own.”

"The naming does not conform to technical specifications," Nana said.

“I’m not an engineer.” He sat back down. “Practicality is enough.”

In the first hour of the new trial operation, the overall situation was stable. The temperature in the living area was maintained at 18 degrees Celsius, and energy consumption decreased by 22%. The fuel consumption curve flattened significantly.

"At this rate, we can reduce the boiler to minimum load by the end of the month." Chen Hao took a sip of water. "Then we can finally get a good night's sleep."

“You slept for three hours and forty-seven minutes last night,” Nana said. “That wasn’t a good night’s sleep.”

“I’ve improved.” He glared. “I even stayed up all night last week.”

As we were talking, the temperature sensor in the east zone went off. The reading dropped from 18 to 15 and was still going down.

"What happened?" He jumped up.

"The geothermal branch valve in this area is responding slowly," Nana quickly checked. "It might be blocked by ice."

"Didn't you say it would be dissolved?" He grabbed the wrench.

"There is still residual ice in some low-lying sections." She pulled up the pipeline slope diagram. "Manual clearing is required."

This time, there was no need to go down into the trench; the valve box was at the end of the corridor. Chen Hao pried open the cover and found the valve body stuck. He tapped it gently a few times with a wrench, then twisted it, and finally it came loose.

Hot water resumed circulation, and the temperature began to rise.

“Next time, we’ll do a clearing plan,” he said, panting. “We’ll run the hot water through the system regularly, instead of waiting until it gets clogged.”

"It has been added to the maintenance list." Nana finished recording.

They continued to monitor the system. Four hours later, the new model stabilized. The three energy supply lines moved in parallel on the screen: solar power surged during the day, geothermal power remained steady, and fuel was only added when there was a short delay.

"It looks like three people are taking turns on duty," Chen Hao said.

"The analogy is inappropriate," Nana said, "but the understanding is correct."

He stretched, his coat sliding to the floor without him picking it up. His eyes were a little sore, but he didn't want to sleep yet.

"What if the weather suddenly gets cold?" he asked.

“The energy storage tank can maintain heating for six hours,” Nana replied. “The boiler can be restarted in eight minutes.”

"It's enough," he nodded. "Much better than before."

On the screen, the spring indicator light is green. The energy mix is ​​updated in real time, and the proportion of fuel continues to decrease.

Chen Hao picked up his pen and wrote a line in his journal:

"We didn't burn as much coal today, and the house isn't cold."

After finishing writing, he closed the notebook and looked up at Nana.

"Shouldn't we be organizing the supplies next?"

Just as Nana was about to answer, a notification popped up in the lower right corner of the console:

The greenhouse lighting system has completed its self-check and is ready to be started.

Chen Hao stared at the line of text for two seconds, then reached out and clicked close.

"Not now," he said. "Wait a little longer."