Performance Comparison of Air-Cooled Heat Pumps, Multi-Split Systems and Water-Cooled Units

I. Modular Air-Cooled Chilled (Hot) Water Units
The air-cooled modular chilled and hot water unit is a central air conditioning unit that uses air as the cold (hot) source and water as the medium for supplying cold (hot) air. As an integrated device for both cooling and heating, the air-cooled modular chilled and hot water unit omits many auxiliary components such as cooling towers, water pumps, boilers, and the corresponding pipeline systems. The system has a simple structure, requires a small installation space, is convenient for maintenance and management, and saves energy, making it widely applicable. Therefore, the air-cooled modular chilled and hot water unit is usually suitable for HVAC projects that have neither a heating boiler nor a heating pipeline network or other stable and reliable heat sources but require air conditioning throughout the year. It is a preferred solution in design.
The centralized and semi-centralized central air conditioning system composed of the main unit and terminal devices such as fan coil units and air handling units has the characteristics of flexible layout and diverse control methods. It is especially suitable for use in shopping malls, hospitals, hotels, factories, office buildings, and other places. The air-cooled modular chilled and hot water unit is equipped with standard water pipe interfaces and unit combination control functions, enabling the unit to operate freely. After installation, it can be used by connecting to the power supply and water circuit. When it is necessary to increase or decrease the main unit due to the increase or decrease of the air-conditioned area, its convenience is even more evident.
Advantages:
The upfront equipment investment is about 15% cheaper than that of the variable frequency multi-split (VRV) system;
The cooling capacity adjustment range is large, and it can achieve stepwise or stepless adjustment;
The technology is mature, the service life is long, no special machine room is required, and it can be directly installed on the roof or in an outdoor space;
The system structure is simple, and the installation space is small, especially suitable for areas lacking water sources;
It saves large auxiliary equipment or accessories such as cooling towers, water pumps, boilers, and the corresponding pipeline systems;
It has two independent working systems, and a failure in one system will not affect the normal operation of the entire unit;
The indoor air is cooled by water, keeping the relative humidity of the air within the range of human comfort.
Disadvantages:
In cold regions (such as Northeast China), electric auxiliary heating equipment needs to be configured during heating;
It is necessary to carry out maintenance and equipment cleaning once a year.
II. VRV Variable Frequency Multi-Split Units
The full name of the VRV air conditioning system is the variable refrigerant flow system. In terms of system structure, it is similar to a split air conditioning unit. It uses one outdoor unit corresponding to a group of indoor units. In terms of control technology, it adopts a variable frequency control method, controlling the rotational speed of the scroll compressor in the outdoor unit according to the number of indoor units turned on, and controlling the refrigerant flow.
Compared with the all-air system, all-water system, and air-water system, the VRV air conditioning system can better meet the personalized usage requirements of users. The building space occupied by the equipment is relatively small, and it is more energy-efficient. Precisely because of these characteristics, it is more suitable for office building construction projects that require frequent independent overtime work. The VRV air conditioning system also has a centralized control and management link, which can monitor and manage the remote VRV air conditioning systems in the control room. It is a relatively complete control method. For an intelligent building that has already designed a building automation system (BAS), it can reasonably and maximally exert the system functions, reduce the repeated investment in system equipment, and improve the system integration technology capabilities.
Advantages:
The multi-split system can automatically adjust the rotational speed of the compressor according to the change of the system load to change the refrigerant flow, ensuring that the unit operates with high efficiency. The energy consumption is reduced during part-load operation, and the annual operating cost is relatively low.

The piping of the multi-split system only includes refrigerant pipes and condensate pipes, and the refrigerant pipes are flexibly arranged and convenient for construction. Compared with the central air conditioning water system, under the condition of meeting the same indoor ceiling height, using a multi-split system can reduce the building story height and lower the construction cost.
The construction workload of the multi-split system is much smaller, and the construction period is short, especially suitable for project renovations. There are few system links, and all equipment and control devices are provided by the equipment supplier, ensuring the safe and reliable operation and management of the system.
The multi-split system is convenient and flexible to combine, and the system can be organized according to different usage requirements to meet the usage requirements of rooms under different working conditions.
It can be equipped with wired/wireless/centralized control/remote centralized monitors, with high temperature control accuracy; it has a fault self-diagnosis function, and a simple and complete self-diagnosis function; during the operation of the equipment, no special person is required for maintenance, effectively reducing the equipment maintenance cost.
Disadvantages:
The equipment cost is high;
The refrigerant exchanges heat with the air, resulting in a large temperature difference between the supply and return air, high air dryness, and poor comfort;
There are many system joints, which are likely to cause the leakage of Freon. At the same time, it will also form an ice blockage, hindering the circulation of the refrigerant and affecting the cooling (heating) of the unit;
There are many systems, the maintenance workload is large, and the refrigerant leakage is not easy to detect, making the maintenance difficult.

III. Screw Chiller Units
The screw chiller unit is a high-efficiency and energy-saving air conditioning cold source device developed through years of exploration, research, and development, drawing on the latest research achievements in engineering fields such as automatic control, refrigeration, heat and mass transfer, and multiphase separation at home and abroad. It has a variety of optional configurations such as large temperature difference, ice making and cold storage, heat recovery, and variable flow of the primary pump. Its comprehensive performance has reached the international advanced level and can meet various needs. It can not only provide chilled water for the central air conditioning systems of places such as hotels, hospitals, pharmaceutical factories, theaters, gymnasiums, entertainment centers, commercial buildings, office buildings, industrial and mining enterprises, etc., but also provide process chilled water for industries such as textiles, chemicals, food, electronics, and scientific research.
Advantages:
The compression ratio can be high, the EER value is high, the energy coverage range is wide, and users have a large selection range;
The unit can smoothly adapt to the changes in the air conditioning load through the slide valve adjustment, without surging phenomenon, with a low maintenance cost and a long motor life;
It can be adjusted steplessly within the range of 10% to 100%, with high efficiency during part-load operation and significant power savings.
It operates under positive pressure, and there is no problem of external air intrusion and corrosion;
It is not sensitive to the wet stroke.
Disadvantages:
The price is relatively high;
The lubricating oil system is relatively complex, and the oil consumption is large;
The noise is high;
The assembly accuracy is high, and the installation and debugging are complex;
The later operation cost is high.