Back-up generators are essential for providing power to the data centre in case of a utility outage. However, back-up generators also generate a lot of heat, which needs to be dissipated by a cooling system. The cooling system may rely on water supply, either from the municipal network or from a dedicated tank. If the water supply fails, the cooling system may not function properly, leading to overheating and potential damage to the generators. This could compromise the reliability and availability of the data centre power supply and cause downtime or data loss.

1: CDCP Preparation Guide, page 18, section 2.3.2 2: Data Center Generator Cooling Systems3, page 1, section 1 4: Data Center Cooling Systems5, page 1, section 1

According to the IEEE definition, reliability is the ability of a system or component to perform its required functions under stated conditions for a specified period of time. Reliability is a measure of how often a system or component fails, and how long it takes to recover from a failure. Reliability is closely related to availability, which is the degree to which a system or component is operational and accessible when required for use. Reliability and availability are both affected by factors such as design, maintenance, testing, and environmental conditions.

The main difference between an Environmental Monitoring System (EMS) and a Building Management System (BMS) is that an EMS monitors only, while a BMS monitors and controls. An EMS is a system that collects and records data from various sensors and devices that measure environmental parameters, such as temperature, humidity, air quality, power, and water. An EMS provides alerts and reports based on the data, but it does not control or adjust the environmental conditions. A BMS is a system that integrates and manages various building systems, such as HVAC, lighting, security, fire, and access. A BMS not only monitors the data from these systems, but also controls and optimizes them to achieve the desired performance and efficiency. A BMS can also communicate with an EMS to receive data and provide feedback.

1: Environmental Monitoring Systems vs Building Management Systems2, page 1, section 1 3: Building Monitoring System vs Environmental Monitoring System4, page 1, section 1 5: BUILDING AND ENVIRONMENTAL MANAGEMENT SYSTEMS AND HOW THEY MEET GMP ...6, page 1, section 1 7: Environmental Monitoring System vs. Building Management System8, page 1, section 1

A computer room air handling unit (CRAH) is a device that uses circulating chilled water to remove heat from the data center environment. A CRAH consists of a fan, a coil, and a filter. The fan draws the warm air from the data center and passes it through the coil, where the heat is transferred to the chilled water. The chilled water is supplied by a chiller or a cooling tower, and the cooled air is returned to the data center. A CRAH is different from a computer room air conditioning unit (CRAC), which uses a refrigerant instead of chilled water to cool the air.

* EPI Data Centre Professional (CDCP) Preparation Guide, page 36

* Chilled Water Systems: Applications and Common Uses

* The Principles of Basic Refrigeration: What is a chiller?

Waveform distortion is a type of AC power quality anomaly that occurs when the shape of the voltage or current waveform deviates from the ideal sinusoidal shape. Waveform distortion can be caused by nonlinear loads, such as rectifiers, inverters, variable frequency drives, and electronic devices, that draw current in pulses or harmonics. Waveform distortion can result in overheating, reduced efficiency, malfunctioning, or damage of equipment.