I. Three Major Challenges in Extreme Scenarios

The traditional logic of museum environmental control is based on relatively stable external climatic conditions, but 

extreme weather has completely disrupted this balance.

First is the “extended” high-humidity rainy season. During a typical rainy season, relative humidity usually ranges 

between 70% and 80%, but in recent years, there have been repeated extreme cases lasting nearly two months with 

average daily humidity exceeding 90%. In such conditions, the air approaches saturation, causing the cooling and 

dehumidification efficiency of conventional air conditioning systems to decline sharply. More problematic is that 

the thermal inertia of the building envelope leads to condensation forming inside the walls; even as the air temperature 

drops, the walls continue to radiate moisture into the interior, creating a tug-of-war between dehumidification and 

moisture regain.

Second is the reheat load impact caused by extreme heat waves. As the number of hot days in summer increases, 

solar radiation enters the venue in large quantities through glass curtain walls and roofs. To cope with the sensible 

heat load, the air conditioning system must cool the space significantly, but this often leads to excessive dehumidification, 

causing the indoor relative humidity to drop too low. At this point, the constant temperature and humidity unit 

must activate “reheating compensation”—that is, heating the air after cooling and dehumidifying it to maintain 

the set temperature and humidity points. Frequent and intense reheating compensation not only significantly increases 

energy consumption but also puts a strain on the compressor’s response speed and the heating elements’ control precision.

II. Core Technical Capabilities: From “Functional” to “Reliable”

To address these challenges, constant temperature and humidity units must undergo targeted upgrades in both hardware 

architecture and control logic, rather than relying solely on increased cooling capacity.

Rapid dehumidification capability is the cornerstone of managing high-humidity environments following flooding. 

This requires units to feature a high sensible heat ratio and high airflow design, enabling them to handle more latent 

heat load per unit of time. The key lies in optimizing evaporator layout and airflow organization to ensure that saturated 

humid air entering the unit is rapidly cooled below the dew point as it passes through the coils, while efficiently draining 

condensate. At the same time, the control system must feature an “emergency dehumidification mode” that temporarily 

relaxes temperature fluctuation thresholds to prioritize bringing humidity back to a safe range, with temperature accuracy 

restored once conditions stabilize.

The precision of reheat compensation is central to managing heat waves. Traditional reheat methods, such as electric 

heating or hot-water coils, suffer from lag and overshoot issues. Modern high-performance units typically employ 

variable-frequency compressors paired with electronic expansion valves to achieve stepless regulation of refrigerant flow, 

creating a dynamic coupling between cooling and reheating operations. During peak heatwave periods, the system can 

intelligently determine whether to prioritize sensible or latent heat, avoiding energy waste caused by the “cool first, then 

heat” sequence. More advanced solutions utilize total heat recovery technology, harnessing waste heat from the compressor’s 

discharge for reheating, which not only improves energy efficiency but also accelerates response times.

Anti-frost protection and operation under low-temperature, high-humidity conditions are often overlooked yet critical details. 

During the rainy season or after flooding, outdoor air humidity is extremely high. When the unit operates in dehumidification 

mode for extended periods, the evaporator surface temperature can easily drop below freezing, causing frost or even ice to 

form on the fins, which blocks airflow channels and, in severe cases, can lead to compressor damage due to liquid slugging. 

Effective countermeasures include: using hot gas bypass defrosting, operating at reduced frequency via variable-frequency 

control to minimize the likelihood of frosting, and installing an outdoor air preheating coil. More importantly, the unit must 

be equipped with “adaptive defrost logic” that actively determines the optimal timing for defrosting based on changes 

in coil temperature and air pressure differential, rather than relying solely on a time relay, thereby ensuring continuous, 

uninterrupted operation even under adverse conditions.

III. Power Supply Assurance: The Invisible Line Between Life and Death

All precision functions ultimately depend on a continuous supply of electricity. During periods of frequent extreme 

weather, momentary power outages or sudden voltage drops occur from time to time. A single unexpected shutdown 

of a constant temperature and humidity unit can cause drastic fluctuations in temperature and humidity within half an 

hour—the damage of which is no less severe than that caused by a minor flood.

Therefore, the configuration of dual power supply lines and backup generators has been upgraded from a “recommendation” 

to a “requirement.” Dual power supply ensures that when one mains power line fails, the backup line can switch over 

within milliseconds to maintain the operation of the compressor and fan, thereby avoiding the lag caused by a restart. 

Diesel generator sets serve as the ultimate backup and must be capable of starting under load; their power output should 

cover the peak current drawn during the startup of the constant temperature and humidity unit. It is also crucial to 

recalculate the generator’s fuel reserve—in extreme scenarios where flooding disrupts transportation, the fuel supply 

must be sufficient for at least 72 hours of full-load operation. Additionally, a communication protocol must be established 

between the power supply system and the generator control cabinet; when a power supply mode switch is detected, the 

generator should automatically freeze its current settings and delay restarting to avoid the period of frequency instability 

that occurs immediately after the generator comes online.

IV. Rapid Recovery Plan: The Critical First 24 Hours After a Disaster

First, mobile emergency dehumidification units must be on standby. These units, equipped with independent power 

supplies and rapid takeover capabilities, can be connected to the museum’s ductwork or placed directly in critical 

areas within 30 minutes of a main system failure. Second, the control system should feature a built-in “disaster recovery 

mode”—when sensors detect that temperature and humidity have continuously exceeded preset thresholds, the system 

automatically switches to high-power dehumidification and constant-temperature modes, temporarily overriding certain 

energy-saving settings to restore standard values as quickly as possible. Finally, on-site teams must conduct advance 

drills for duct switching operations and emergency generator startup procedures to ensure smooth execution even in 

extreme conditions—such as darkness and slippery surfaces—and to prevent secondary errors caused by panic.

Global warming is rewriting the environmental control standards for museums. Climate control units are no longer 

merely quiet “background equipment”; they have become active defense units that must engage in precise maneuvers 

during heat waves, wage a relentless battle during the rainy season, and provide emergency relief after floods. From the 

robust performance of rapid dehumidification to the sophisticated logic of anti-frost protection, and from dual power 

supply to fuel reserves—every technological upgrade represents a deep commitment to the concept of “preventive 

protection.” As extreme weather becomes the new normal, the resilience of museums is reflected in these unseen 

corners—in the steadfast maintenance of every degree of temperature difference, in the assurance of every watt of power, 

and in the composed response to every rapid post-disaster recovery. Only by building this line of defense sufficiently strong 

can the tangible evidence of civilization navigate the increasingly violent turbulence of climate change and safely reach the future.