VRV、MRV、MDV、VAV、VWV and KRV

VRV, MRV, MDV, VAV, VWV and KRV

来源：暖通高阶人才

KRV: Fresh air ventilator, total heat exchanger.

VAV: Variable Air Volume air conditioning system, it is the terminal equipment.

VWV: Variable Flow (Chilled Water) Air Conditioning System.

MRV: Fully variable multi-split air conditioning system. In essence, it is also a variable refrigerant flow system (some manufacturers call it MDV, GMV, etc.)

VRV: Variable Refrigerant Flow system air conditioning. The VRV technology is mainly developed by Daikin, so this name has been registered by Daikin. Now, as professionals in refrigeration and HVAC, we need to pay attention to the English abbreviation for the variable refrigerant flow system, which is VRF.

1. VRV Definition

The VRV system is a multi-linkage refrigerant flow system, which is an air conditioning system that controls the refrigerant flow rate and achieves cooling or heating through the direct evaporation or direct condensation of the refrigerant.

The VRV system was invented by Daikin Company in the 1980s. Since the VRV system only transports refrigerant to the sub-systems in each room, no independent ventilation ducts (the fresh air system has its own ventilation ducts) need to be designed. This achieves the miniaturization and quietness of the equipment. In terms of system structure, it is similar to a split air conditioning unit, with one outdoor unit corresponding to a group of indoor units (generally up to 16 units). In terms of control technology, it adopts a variable frequency control method, controlling the speed of the scroll compressor inside the outdoor unit according to the number of indoor units turned on, to control the refrigerant flow rate.

Compared with the all-air system, all-water system, air-water system, the VRV air conditioning system can better meet the individualized usage requirements of users. The equipment occupies less building space and is more energy-efficient.

The design of the VRV air conditioning system consists of two parts: 1) selection of air conditioning equipment and design of air conditioning pipelines; 2) control design of the air conditioning system.
2. Explanation of VAV

The VAV variable air volume air conditioning system, like the constant air volume air conditioning system, is also a type of air conditioning method in the full air system. It controls and regulates the temperature of a certain air conditioning area by changing the supply air volume rather than the supply air temperature, thereby adapting to the changes in the load of the air conditioning area.

The working principle is that when the load in the air conditioning area changes, the system's terminal device automatically adjusts the supply air volume to the room to ensure that the indoor temperature remains within the designed range. This results in a decrease in the supply air volume of the air handling unit at low loads, and the rotational speed of the air handling unit's blower also decreases accordingly, achieving the goal of energy conservation. Variable air volume systems usually consist of air handling equipment, supply (return) air systems, terminal devices (variable air volume boxes), supply air outlets, and automatic control instruments, etc.

Generally, the VAV system is suitable for the following systems: 1) In the same air conditioning system, there are significant differences and variations in temperature and load among different air conditioning areas, long periods of low-load operation, and separate control of the temperature of each air conditioning area is required. 2) Cold air needs to be supplied to the interior areas throughout the year in the building.

3. VWV Term Explanation

The VWV air conditioning variable water volume system is a technology that has been studied and developed earlier and more maturely compared to the variable air volume system (VAV) both domestically and internationally. There are many similarities and even identical features between VWV and VAV. In specific engineering practices, even the same control strategies can be adopted.

For instance, the variable-frequency constant-static-pressure control of the VWV system is similar to that of the VAV system; if the automatic control system can conveniently "capture" the opening degree of the water valve in the VWV system (by simply adding a valve position sensor), then the variable-static-pressure control of the VWV system can also be achieved. Furthermore, if the automatic control system can promptly "measure" the flow rate at each end of the VWV system, then we can also achieve the total water volume control of the VWV system.

4. Explanation of KRV

KRV fresh air ventilator - Total heat exchanger. The core component of the total heat fresh air ventilator is the total heat exchanger. The polluted air discharged from the indoor and the fresh air sent in from the outside both exchange temperature through the heat transfer plates and also exchange humidity through the micropores on the plates, thereby achieving the effect of ventilation and air exchange while maintaining stable indoor temperature and humidity. This is the total heat exchange process.

When the total heat exchanger is operating during the summer cooling period, the fresh air gains heat from the exhaust air, causing the temperature to drop and being dried by the exhaust air, thereby reducing the humidity of the fresh air. During the winter operation, the fresh air gains heat from the exhaust air, causing the temperature to rise and being humidified by the exhaust air. The fresh air ventilator is a device that filters, purifies, and undergoes heat exchange treatment of the outdoor fresh air before sending it into the room. At the same time, it also filters and purifies the polluted and harmful gases in the indoor area.

Currently, whether in China or abroad, the heat exchangers used in new air ventilators come in two forms: stationary and rotating. The rotary type heat exchanger also belongs to the rotating type. From the perspective of normal use and maintenance, the stationary type is superior to the rotating type. However, for large machines with a capacity greater than 2×10000m3/h, the rotary type heat exchanger is generally required for operation. Therefore, it can be said that both the stationary and rotating types have their own advantages and disadvantages.

To facilitate the arrangement of the airflow channels within the equipment and to reduce the overall size of the machine, the new ventilation fan adopts a cross-flow and stationary plate type heat exchanger. That is: the directions of the movement of the cold and hot gases are perpendicular to each other, and the airflow belongs to the convective heat transfer nature within the turbulent boundary layer.

Therefore, adequate heat exchange can achieve a high level of energy-saving effect.