APC ACPDX21-86 manual Scalable Solution for Critical Environments, Air Quality, Low Humidity

Scalable Solution for Critical Environments

Temperature and Humidity Design Conditions

Maintenance of temperature and humidity design conditions is critical to the smooth operation of a technology room. Based on ASHRAE TC9.9, the recommended design conditions for class one and class two environments should be 20–25°C (68–77°F) and 40–55% relative humidity (R.H.). Precision air conditioning is designed to maintain temperature at ±2°F and humidity at ±3–5% R.H. 24 hours a day, 365 days a year. Vapor barriers and sealed rooms are required to maintain these tolerances. In contrast, comfort systems are designed to maintain ±5°F from the temperature setpoint. There is usually no dedicated humidity control and the simple controllers cannot maintain the setpoint tolerance required for temperature, allowing potentially harmful temperature and humidity swings to occur. This is not acceptable for sensitive electronic equipment.

Air Quality

Precision air conditioners provide a high volume of air flow, around 600 CFM/ton (286 L/m, 150 CFM/kW). This high CFM moves more air through the space improving air distribution and reducing the chance of localized hot spots. It also allows more air to move through filters, ensuring a cleaner environment. This requires a moderate-to high- efficiency filter bank to minimize airborne particles.

Low Humidity

Low humidity greatly increases the possibility of static electric discharges. Static discharges can corrupt data and damage hardware.

High Humidity

High humidity can result in tape surface deterioration, head crashes, condensation, corrosion, paper handling problems and gold and silver migration leading to component and board failure.

High & Low Temperature

A high or low temperature or rapid temperature swings can corrupt data processing and shut down an entire system. Temperature variations can alter the electrical and physical characteristics of electronic chips and other board components causing faulty operation or failure. These problems may be transient or may last for days. Transient problems can be very difficult to diagnose and repair.

Efficiency and Reliability

The use of energy efficient, direct drive fans along with fewer moving internal parts eliminate most potentials for failure. Scroll compressor technology provides unparalleled efficiency and con- stant, reliable operation with an ability to withstand liquid refrigerant ‘slugging’ which is a major cause of compressor fail- ure. The compressor is also equipped with an internal high pressure sensor which opens a bypass valve in case of high pressure. This ensures internal pressure compensation takes place and damage to the compressor is avoided.

APC InRoom -

The Right Solution

The APC InRoom cooling unit provides the maximum amount of precision cooling in a compact footprint with the lowest operating cost and noise level.

Dedicated Dehumidification Cycle

A dedicated dehumidification cycle allows the system to increase latent capacity without boosting compressor capacity, and also lowers the requirement for reheat. To achieve dehumidification, the electronic expansion valve is first partially closed. The reduction of the refrigerant mass flow makes the evaporation temperature drop, which lets the surface temperature in a part of the evaporator fall below the dew point of the air, causing dehumidification. For increased dehumidification, the fan speed is reduced. With a constant cooling capacity, the temperature of the air which flows through the heat exchanger coil passes below the dew point. The moisture contained in the air condenses on the heat exchanger, gathers in the condensate pan, and is carried away by the drain. To achieve humidification for the DX units with cabinet size 1 and all CW units, the fan speed is reduced. For the DX units with cabinet size 2–5, approximately one third of the evaporator is isolated from the refrigerant flow by a solenoid valve to achieve dehumidification by lowering the evaporator temperature below the dew point.

2 InRoom Precision AC Tech Data Manual