What problems do air conditioning box preheating, heating and reheating solve respectively?

Preheating is usually used to warm up the cooler inlet air first. Heating is a general term for meeting the required heating tasks. Reheating is often used to restore the supply air temperature after air cooling and dehumidification. The three can use similar heat exchange components, but their processes, control objectives and enabling conditions are different.

Identify names by the processes the air undergoes

When low-temperature fresh air enters the treatment chain in winter, preheating can create conditions for subsequent processes; when there is heat demand in the room, the heating section is directly responsible for heating up the supply air; after cooling the air to a lower state for dehumidification in summer, if the supply air is too cold, it may need to be reheated. Just because you 'heat the air' doesn't mean you can use the same temperature setting to cover the entire process.

Preheating focuses on the inlet low temperature, subsequent processing conditions and antifreeze linkage; heating focuses on the target air supply status and available heat source capacity; reheating focuses on the temperature recovery and activation restrictions after dehumidification. The three names correspond to different positions and tasks and cannot be distinguished only by the amount of heating. How to arrange each section in the air treatment process, please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined?。

Preheating first serves antifreeze and subsequent processing

The preheating section is usually located after the fresh air inlet and before the coil. Its function is to raise the low-temperature air to a range where subsequent components can operate normally. If there is a lack of preheating in severely cold areas, the surface of the coil may freeze, and the heating section and humidification section may not operate stably. Preheating also assumes the antifreeze protection function, which is related to the low temperature alarm and valve linkage in the control logic.

When selecting the heat source and determining the capacity of preheating, you need to consider the local extreme low temperature, the proportion of fresh air, and the shutdown and anti-freezing arrangements. How to choose between hot water preheating and electric heating, please refer toHow to choose between hot water heating and electric heating for air conditioning boxes? . The location of the preheating section and anti-freeze requirements will also affect the sequence of functional sections. Please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined?。

The heating section is responsible for the task of heating the room.

The task of the heating section is to heat the air to the target supply air temperature to meet the room heat load. It can be located after the coil, before or after the fan, depending on the system flow and control. The heating capacity should be able to cover the heating requirements under design conditions and have the ability to adjust under partial load.

The heat source of the heating section can be a hot water coil, electric heating or steam. Different heat sources have different control methods and operating costs. For comparison between hot water heating and electric heating, please refer toHow to choose between hot water heating and electric heating for air conditioning boxes? . The names of the heating section and the preheating section are similar, but preheating is aimed at the inlet low temperature, and heating is aimed at the room heat load, and their tasks are different.

Reheating solves the problem of temperature recovery after dehumidification

The reheat section is usually located after the cooling dehumidification coil. In order to achieve the dehumidification target, the air is cooled to a lower temperature. The moisture content is reduced but the temperature may be too low, and it needs to be reheated to restore the supply air temperature to the target value. Rather than providing the main heat to the room, reheat compensates for the supercooling of the dehumidification process.

Whether the reheat section is enabled depends on the dehumidification needs and supply air temperature requirements. If the supply air temperature meets the requirements after dehumidification, reheating is not needed; if too much reheating is invested, cooling and heating will cancel each other out, increasing energy consumption. For the relationship between dehumidification capacity and cooling capacity, please refer toHow to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content? ;For the relationship between supply air dew point and reheat, please refer toWhat role does the supply air dew point play in the selection of fresh air air conditioning boxes?。

The technical requirement is to write the control relationship and not just the power.

It should be clear where each heating section is located, which measuring point is controlled by it, and its relationship with the fan, cooling valve and protection signal. If dehumidification and reheating are run at the same time, the triggering basis should be explained and ineffective confrontation should be avoided. Antifreeze design also involves shutdown and waterway measures, which cannot be judged by just the name of a preheating section.

The control logic needs to distinguish the respective set values ​​and allowable conditions for preheating, heating and reheating. If a temperature sensor or the same set of valve controls are shared, it may cause mutual interference between different sections. How to determine the sensor position, please refer toHow should the air supply temperature sensor of the air conditioning box avoid the influence of local airflow? . How to describe these signals in the control point table, please refer toWhat point tables need to be provided before the air-conditioning box is connected to the building automation system?。

Aili industrial supporting equipment

When Aili Industrial confirms the configuration of hot and cold sections and electronic control, it can check the control interface according to the independent tasks of each section; it is more effective to explain the winter and summer air flows at the same time during consultation. Aili Industrial can check coils, electric heating, humidification and control configurations together; the manufacturing end covers independent research and development and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The location, interface and control logic of each thermal section can be aligned in the same package.

Product form can be viewedAir handling unit andFan box page; clean air supply package can be combinedFFU fan filter unit andEFU equipment end fan filter unit verification; terminal particle filtration can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific heating effect, applicable environment and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. The actual effect is subject to on-site debugging and performance test results.

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Related questions and answers

Are preheating and heating the same thing?
no. Preheating targets the low-temperature air at the inlet, creating conditions for subsequent processing and anti-freezing; heating is responsible for the task of room warming, and their positions and control objectives are different.

Is reheating a waste of extra energy?
uncertain. When the air temperature after dehumidification is too low, reheat is used to restore the supply air temperature; if improper control causes a confrontation between cooling and heating, ineffective energy consumption will increase.

Can Aili Industrial help check the heating section configuration?
The location, heat source and control logic of preheating, heating and reheating can be checked based on winter and summer working conditions. The specific plan needs to be confirmed based on project conditions.

Related articles

1. How to choose between hot water heating and electric heating for air conditioning boxes?

2. On what basis should the sequence of functional sections of the air conditioning box be determined?

3. How to calculate the dehumidification capacity of air conditioning box from the difference in air moisture content?

4. What role does the air supply dew point of the air conditioning box play in the selection of fresh air air conditioning boxes?

Key points for selection and acceptance inspection