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What is PAHU in an HVAC System?

PAHU is an abbreviation for Precision Air Handling Unit. It simultaneously controls the temperature and humidity in a building. It is purposely designed for cooling server room environments and datacenters rather than residential or commercial buildings. They have a high ratio of cooling capacity and offer superior design and reliability. Main parts of precision air handling units include cooling coil, air filters, blower and motor, heater, actuator valve, and humidifier bottle. It is sometimes referred to as precision control units or precision air conditioning systems. This article discusses role of PAHU in a communication network HVAC system and the way it differs from typical comfort or commercial HVACs.

How Does it Work?

central heating and cooling air handling system control
The movement of heat from electronic equipment in a server room is achieved through a refrigeration cycle. A fan blows warm air from the computer room across the evaporator while the pipes in the coil are supplied with a cold liquid refrigerant to facilitate cooling. Even if the evaporator coil remains cold, the refrigerant running inside the coils continues to boil and evaporate, changing from liquid to gaseous state. The vaporized cool refrigerant is then drawn into a compressor causing a rise in temperature inside the loop. The computer room heat energy is carried by the compressed refrigerant to the condenser coil, which transfers heat to another medium. It exits the condenser coil as a hot, high-pressure liquid and channeled to the expansion valve that is normally located at the entrance to the evaporator coil. This process is repeated in a continuous cycle until the heat energy from the computer room is pumped into the outside atmosphere.

The Role of Precision Air Handling Units (PAHU) in an HVAC System

  • Temperature Control

The high-density heat load produced in server rooms and datacenters goes far beyond the capacity of ordinary air conditioning systems in residential or commercial buildings. To maintain telecommunications equipment in a stable environment, precision air handling units provide just enough cooling capacity for maximum efficiency and operation. The HVAC systems in these areas prevent wide temperature fluctuations. Therefore, they require the precision to react quickly to a drastic change in heat load.

  • Humidity Control

It is crucial to protect telecommunications equipment from static electricity discharges and internal condensation. PAHU is not only responsible for maintaining proper temperature but must also maintain the correct level of humidity in the computer room. Too much humidity within the telecom equipment increases the potential for hardware damage. If the level of humidity is too low then the operation of the systems could be disrupted or shut down by static electricity. An ordinary HVAC system is not capable of controlling the environment within these boundaries.

  • Protection

Precision air conditioning is purposely designed to protect equipment. It is separate from ordinary air conditioning systems that are designed to provide the necessary comfort for people. The primary loads for an HVAC system in residential or commercial sites are often people and ventilation air. However, pressurization, building construction, people, electronic equipment, and ventilation air determine the complete cooling load for telecommunication systems in the room. This means that server rooms and data centers will require heavy-duty air conditioning as well as precision controls that react quickly to any drastic changes within the electric systems.

  • Air Volume and Filtration

Telecommunication systems demand greater air volumes that cannot be provided by ordinary air conditioning systems. A server room requires up to 30 air changes per hour while a typical office space only requires two air changes per hour. The high-density heat load requires more changes of air in a relatively small space than a less dense comfort application in residential buildings. Hot spots and temperature fluctuations can develop within the space if there is no proper air volume. Precision air handling units also filter the recirculation air in a communications site to increase efficiency.

Precision air handling units maintain proper temperature to IT equipment with precise processor-based temperature control. These air conditioning systems are designed to maintain high levels of sensible heat produced by machines while standard air conditioners manage latent heat produced by people and their environment. Precision air conditioners demonstrate better air distribution because they operate at higher speeds than standard air conditioning units. Several units can be coordinated with each other to control individual AC loads automatically for efficient cooling in larger premises. The ideal feature of precision air handling units is that they can be enhanced or incorporated with new features because their firmware is regularly updated to keep up with technological changes.

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