High-precision constant temperature and humidity laboratory air conditioners must have high-precision temperature and humidity sensors. Required sensor accuracy: ±1.5%RH, ±0.3℃ (at 23±2℃). Repeatability: better than 0.5%RH and 0.1℃. Stability: better than 1.0%RH and 0.1℃ per year. For ordinary computer room air conditioner sensors, the accuracy is about ±3%RH and ±1℃.

There are currently two ways to adjust the cooling capacity of air conditioners on the market:

Frequency regulation: In fact, it is to change the power of the compressor by changing the power supply nature, so that the compressor can work under load or overload, and adjust the throttling amount of the refrigeration system at the same time, so a lot of cumbersome links must be added, and each link must be perfectly matched, otherwise there will be failures. This is indeed the case in reality, and the failure rate is very high.
Chilled water type unit: Use cold water at about 7℃ as the cold source, and control the water flow by opening or closing the electric valve, so as to easily control the cooling capacity. The electric valve structure is as simple as a household faucet, so the failure rate is almost zero, and the control effect is the most stable. By reasonably calculating the heat and humidity load and air dew point of the room to match the air volume, cooling capacity, heating capacity, and humidification capacity, and then control the stepless regulation of each component through PLC, and select sensors with high sensitivity and good linearity, the temperature can be ±0.5℃ and the humidity can be ±2%. This method requires calculation and matching based on the actual area and load of each laboratory, so there is no standard molding unit, and all are customized processing types.
Due to the accuracy requirements, high-precision constant temperature and humidity laboratory air conditioners require adjustable heating capacity, cooling capacity, humidification capacity, and dehumidification capacity.
(1) For heating, multi-stage heating is used for adjustment according to the temperature difference. When the temperature difference is small, only the first stage of heating is turned on. When the temperature difference is slightly larger, the 1st and 2nd stage heating are turned on at the same time. When the temperature difference is larger, the 1st, 2nd and 3rd stage heating are turned on at the same time.

(2) For humidification, proportional humidification is used to control the humidification amount according to the humidity difference.

(3) For the adjustment of cooling and dehumidification, there are three adjustment methods:

a) The first generation adjustment method uses multi-stage cooling, which is generally used for high-power equipment and is mainly used for temperature adjustment. It has little effect on humidity adjustment.

b) The second generation adjustment method uses variable frequency cooling, and the cooling capacity is between 50% and 100% to achieve stepless cooling adjustment. This adjustment range is sufficient to solve the problem of temperature and humidity stability. It is used for high-precision constant temperature and humidity laboratory air conditioning, and the effect is remarkable. However, due to control needs, many auxiliary control links need to be added, and the various accessories must be closely coordinated.

c) The third generation of regulation mode, chilled water type refrigeration mode, uses chilled water (designed according to the general central air conditioning water temperature) as the cold source, and the coil runs ordinary cold water at about 7°C. The computer motherboard easily achieves 0% to 100% stepless adjustment of cooling capacity by controlling the opening of the water valve. Moreover, the integral valve structure is as simple as a household faucet and has a very long service life. However, the equipment requires a lot of maintenance and it is difficult to repair after a problem occurs. It is recommended to avoid using it as much as possible.

Operation characteristics of constant temperature and humidity laboratory:

1. The constant temperature and humidity laboratory adopts a direct evaporative independent constant temperature and humidity air conditioning system, which has the advantages of simple system, easy adjustment, convenient operation and management, and energy saving. In engineering design, it is necessary to reasonably select the system according to the temperature and humidity accuracy requirements of the laboratory, and calculate the load of the room as detailed as possible and select a matching constant temperature and humidity unit.
2. In order to meet the requirements of indoor constant temperature and humidity accuracy, the ventilation frequency of the constant temperature and humidity air-conditioned room is large. According to experience, the ventilation frequency of the constant temperature room of ±2℃ is about 10-15 times/h; the ventilation frequency of the constant temperature room of ±1℃ is about 15-20 times/h; the ventilation frequency of the constant temperature room of ±0.5℃ is about >20 times/h; the ventilation frequency of the constant temperature room of ±0.2℃ is about >30 times/h.
3. The airflow organization design is also one of the main factors affecting the accuracy of the constant temperature room. The following principles should be considered when designing the airflow organization in the high-precision constant temperature and humidity room: reasonable airflow organization process, give full play to the cooling or heating effect of the air supply airflow; establish a stable and uniform temperature field to ensure that when the airflow reaches the working area, the difference between its average temperature and the temperature of the working area does not exceed the allowable temperature fluctuation value; when the airflow reaches the working area, its flow velocity is about 0.25m/s. ±2℃ and ±1℃ high-precision constant temperature and humidity laboratories use full-hole plates and partial-hole plates for air supply, and uniform return air at the bottom, which has a better effect.
4. In the construction of a constant temperature and humidity laboratory, its thermal insulation and airtightness are also very critical; a laboratory with good thermal insulation and airtightness has the advantages of saving energy, improving temperature and humidity accuracy, and reducing operating costs.