*3.4.2. Heat pump units*

**3.4. Refrigeration systems**

**Figure 11.** Air compressor system

*3.4.1. Rooftop units*

RTUs, HPs, CRAC units, and chillers.

**3.4. Refrigeration Systems**

include RTUs, HPs, CRAC units, and chillers.

compressor.

178 New Applications of Electric Drives

compressor power is reduced.

a gas heater or an electric heater.

the demand and energy consumption are reduced greatly.

control the space temperature.

the RTU as shown in Figure 12.

*3.4.3. Computer Room Air‐Conditioning Units*

*3.4.2. Heat Pump Units*

**Figure 12.** Single-stage DX rooftop unit

heating capacity.

the demand and energy consumption are reduced greatly.

Refrigeration systems are also good candidates for VFD applications. The compressor is the major device where the VFD is installed in a refrigeration loop. The typical applications include

Figure 11 Air compressor system

Refrigeration systems are also good candidates for VFD applications. The compressor is the major device where the VFD is installed in a refrigeration loop. The typical applications

Compressed air has many applications in the manufacturing process. In the HVAC industry, air compressors can be used to generate the pressurized air to drive the pneumatic actuators for dampers and valves in air‐handling units. The compressed air is stored in a pressurized tank, which serves as an air source to the end users. Traditionally, the pressure of tank is maintained by the on–off control of one or multiple air compressors. Figure 11 shows a schematic diagram of an air compressor system with a VFD installed on each

Typically, staging control is used to maintain the compressed air pressure. When the end users require less compressed air and the compressed air pressure is higher than the set point, the compressor will shut off. On the contrary, one more compressor starts when the end user utilizes more compressed air and the compressed air pressure drops down below the set point. This inefficient control causes frequent compressor start–stops, which definitely shortens the lifetime of the compressor. However, when a VFD is installed, the wear and tear on the compressors is less so that their lifetime is prolonged. In addition, the

Rooftop unit is one type of unitary air handler designed for outdoor use, usually on the roof. There are two types of configurations: packaged unit and split unit. A typical packaged rooftop unit has a refrigeration system delivering cool air into the space. Therefore, it is also called the direct-expansion (DX) unit. Meanwhile, most RTUs provide heating to the space using either

In an RTU, the supply fan (or indoor fan) and compressors are usually running at a constant speed. At partial load conditions, excessive fan and compressor power are consumed due to constant speed operations. With the installation of VFDs on the fan and (or) compressors, significant power consumption could be saved. In addition, compressors account for the largest part of power consumption in an RTU. With the reduction of compressor speed, both

In an RTU, the supply fan (or indoor fan) and compressors are usually running at a constant speed. At partial load conditions, excessive fan and compressor power are consumed due to constant speed operations. With the installation of VFDs on the fan and (or) compressors, significant power consumption could be saved. In addition, compressors account for the largest part of power consumption in an RTU. With the reduction of compressor speed, both

Figure 12 Single‐stage DX rooftop unit Figure 12 is a typical single‐stage RTU. The supply fan circulates air through the evaporator and heater. Traditionally, the supply fan and compressor run at a constant speed. Initially, the VFD is used on the supply fan to modulate the fan speed and maintain the space temperature set point. This type of RTU can be called variable capacity RTU. Later, the VFD is used on the compressor as well. Both fan and compressor speeds can be modulated to

Heat pump units are very similar to RTUs as both systems utilize a refrigeration system. However, heat pump units can use the refrigeration system to produce heat as the first stage. At colder weather conditions, auxiliary heat is turned on to provide additional

A VFD can be installed on heat pump units as well. The schematic diagram is very similar to

Heat pump units are very similar to RTUs as both systems utilize a refrigeration system. However, heat pump units can use the refrigeration system to produce heat as the first stage. At colder weather conditions, auxiliary heat is turned on to provide additional heating capacity.

A VFD can be installed on heat pump units as well. The schematic diagram is very similar to the RTU as shown in Figure 12.
