In museums, precision laboratories, data centers, high-end wine cellars, and other environments with stringent requirements, 

we consistently enjoy a constant comfort akin to “spring-like conditions all year round.” The unsung hero behind this is the 

constant temperature and humidity unit. Unlike ordinary air conditioners that merely regulate temperature, it precisely controls 

both the ambient temperature and humidity simultaneously.

So how does this remarkable machine operate? Today, we lift the veil on its inner workings. Its core lies in the precise coordination 

of four major systems: the refrigeration system, heating system, humidification system, and dehumidification system.

Core: Four Functional Systems

First, let's examine its workflow through a schematic diagram:

I. Refrigeration System: The “Cooling” Element

Refrigeration is the foundation of constant temperature and humidity control and the key to dehumidification.

Working Principle: Similar to air conditioners, it follows the compression refrigeration cycle.

• Compression: The compressor compresses low-temperature, low-pressure refrigerant gas into high-temperature, high-pressure vapor.

• Condensation: The high-temperature, high-pressure vapor enters the condenser, where a fan dissipates heat to the outside

  environment, cooling and liquefying it into high-pressure, room-temperature liquid.

• Throttling: The high-pressure liquid flows through the expansion valve, causing a sudden pressure drop and transforming it

  into a low-temperature, low-pressure misty mixture of gas and liquid.

• Evaporation: This low-temperature, low-pressure mixture enters the evaporator. Here, the humid, warm air from the room is

  blown over the evaporator fins by a fan. The refrigerant absorbs heat from the air, evaporating into a gas. Simultaneously,

  he air temperature drops, and its excess water vapor condenses into droplets on the cold evaporator surface (the dehumidification

  process). These droplets are then drained away through a drain pipe.

Visual Analogy: Imagine taking a chilled beverage from the refrigerator—water droplets quickly form on the bottle's surface. 

The evaporator acts like that “chilled bottle”; when moisture in the air encounters it, the vapor condenses into liquid water, 

thereby reducing air humidity.

II. Heating System: The “Warmth” Source for the Environment

When the ambient temperature falls below the set value, the heating system activates.

Working Principle: Primarily operates in two ways:

• Electric Heating Element (Common): Directly uses resistance wire heating, functioning like a large “hair dryer.” When

  heating is required, the heating element is energized to generate heat. A fan blows air over the heated element, warming

  the air before it is circulated into the room. This method features simple construction and responsive control.

• Heat Pump Heating (Higher Energy Efficiency): By switching the four-way reversing valve, the refrigerant flow direction reverses.

  The condenser, which previously dissipated heat outdoors, now releases heat indoors, while the evaporator, which previously

  absorbed heat, now draws heat from outside. This effectively “transfers” outdoor heat indoors, achieving a much higher

  energy efficiency ratio than electric heating.

Visual Analogy: Electric heating elements function like a household space heater; heat pump heating operates as a “heat 

transporter,” bringing outdoor warmth indoors during winter.

III. Dehumidification System: The Environmental “Dryness” Expert

The dehumidification function of constant temperature and humidity units is typically integrated with the refrigeration system 

but can also be independently controlled through specialized technology.

Working Principle:

• Refrigeration Dehumidification (Primary Method): As described above, when humid air flows over a cold evaporator coil,

  its temperature drops below the “dew point temperature,” causing water vapor to condense and separate as liquid water.

  This is the most direct and efficient dehumidification method.

• Reheat Dehumidification (Precision Control): Pure refrigeration dehumidification simultaneously lowers ambient temperature,

  potentially causing “supercooling.” To address this, advanced constant temperature and humidity units employ reheat technology.

  This involves first cooling and dehumidifying air through the evaporator, then passing this cooled, dry air over the condenser

  (or a separate reheat coil) for isothermal heating. The air is raised to the setpoint temperature before being delivered indoors.

  This achieves humidity reduction without lowering temperature, even accomplishing complex tasks like “cooling + dehumidification”

  or “heating + dehumidification” simultaneously.

Visual Analogy: Reheat dehumidification is like “wringing out a towel before drying it”—first “wringing out” moisture from the 

air through cooling (dehumidification), then “drying” the air temperature to a comfortable state through heating (temperature control).

IV. Humidification System: The Environment's “Moisturizing” Assistant

When the environment becomes excessively dry, the humidification system activates.

Working Principles: Common types include:

• Electrode/Electric Heating Humidification (Mainstream): Water is directly heated to boiling point via electrode rods or electric

  heating tubes, producing pure steam. A fan then mixes this steam into the supply air to achieve humidification. This method

  offers high efficiency and precise control.

• Wet Membrane Humidification: Water pumped onto a humidification membrane absorbs moisture. As air passes through the

  damp membrane, it naturally draws moisture, achieving humidification. This is an isenthalpic process, mimicking natural evaporation.

• Visual Analogy: Electrode humidification functions like an “efficient kettle,” continuously generating steam; while wet-membrane

  humidification resembles air passing through a damp towel, naturally absorbing moisture.

• Synergistic Operation: The Intelligent “Environmental Manager”

• The four major systems do not operate independently but are centrally coordinated by an intelligent control system (the “brain”).

• Sensing: High-precision temperature and humidity sensors monitor environmental data in real time.

• Judgment: The control system compares monitored data with preset values.

Execution:

• Scenario 1: High temperature and humidity (summer conditions) -> Activates the [Cooling System] to lower temperature while

  automatically dehumidifying. If dehumidification causes excessive cooling, it may trigger the [Heating System] for reheating to

  maintain precise temperature control.

• Scenario 2: Low Temperature & Low Humidity (Winter Conditions) -> Activates the 【Heating System】 to raise temperature

  while simultaneously activating the 【Humidification System】 to replenish moisture.

• Scenario 3: Comfortable Temperature but Excessive Humidity (Rainy Season) -> Activates the 【Cooling System】 for dehumidification,

  potentially complemented by the 【Heating System】 to compensate for temperature drop caused by dehumidification, achieving

  constant-temperature dehumidification.

• Scenario 4: Temperature is comfortable but humidity is too low (dry winter) -> Activate the 【Humidification System】 independently.

In summary, the constant temperature and humidity unit functions like an unflagging intelligent steward. Through the precise coordination 

and dynamic compensation of its four internal systems, it continuously adjusts the balance of “cooling, heating, drying, and humidifying.” 

Ultimately, it creates and maintains a stable, comfortable, “spring-like year-round” ideal space for us amidst complex external environmental conditions.