When installing lightning protection systems for mission-critical projects, there is daily interaction between electrical equipment and the fixtures installed at the roof level.
In this article, Hadi Baik Daraei, Senior Design Manager at LPI Group, outlines what a coverage study is, how you can protect your data centre roof and electrical equipment against lightning strikes, best practices and standards for protecting electrical equipment at roof level, and the exceptions for protection requirements of a mission-critical data centre.
As experts in the design, procurement, and engineering of lightning protection, earthing, and surge protection devices, LPI Group’s technical design team is specified by clients to complete a coverage study on their data centre to assess if the data centre and its fixtures installed on the roof are fully protected against direct lightning strikes.
This complex study can be conducted using different in-house software such as AutoCAD 3D, XGSLAB, and SES Shield 3D by the highly skilled electrical engineering team at LPI. As part of the coverage study, there are three methods of protection that should be specified which includes:
- The Rolling Sphere Method
This method simulates how lightning will interact with a building should there be a direct strike. The design team will illustrate a sphere with a certain radius rolling over the surface of a building, and anywhere the sphere touches are where lightning can strike.
This method is the most comprehensive methodology that is usually used for complicated structures such as data centres, pharmaceutical plants, and battery plants.
- Mesh Method
This method does not depend on the height of the structure. A caveat to using this method is that it cannot be used on curved surfaces and requires use on flat surfaces.
It is important to note that using the ‘Mesh’ method is not appropriate for protecting equipment on the roof.
- Angle Method
This method is a 3D concept, where the protected area is the cone that is swept by the line that emerges from the tip of the air termination rod and ends at the surface of the structure. The protected area will be cone-shaped in the case of a simple air termination rod, but it can also be a tent-shaped protected area.
The image below showcases a coverage study on a pharmaceutical project in Europe.
Design Phase Considerations
As part of the coverage study PV (Solar) cells and HVAC Systems are audited. When installed on a roof these items are known as roof fixtures, therefore it is paramount to also include these in the complete building envelope protection.
As part of the design phase considerations the standard IEC 62305-3, Protection Against Lightning – Part 3: Physical Damage to Structures and Life Hazard, states that metal roof fixtures do not require additional protection if their dimensions do not exceed all of the following values:
- Height above the roof level of 0.3m
- Total area of the fixture 1.0m2
- Length of the fixture 2.0m
PV Cells and HVAC Equipment are excluded from the above-mentioned conditions.
Roof fixtures contained in building models such as PV cells and HVAC Systems are electrical devices which are connected to the internal wiring system of the building and the earthing connection point. This may lead to excess pressure on the system and result in issues such as surge propagation into the internal wiring system and circuits. Failure to protect against surge propagation will lead to outages in the data centre, or any other building.
HVAC equipment has a crucial role in the amount of availability of IT equipment. This is because normal operating conditions exist when the HVAC system provides the necessary air conditioning to maintain the IT room within specifications. Even in IT rooms with moderate densities, loss of the HVAC system (whether through loss of power, or cooling equipment failure) can result in steep temperature gradients and subsequently high space and equipment inlet temperatures.
According to the standard IEC TR 63227, for PV Cells, the minimum protection of ‘Level III’ is recommended. This standard states, “In special cases, e.g., for objects of cultural value or requirements for increased availability of the system, additional measures or a different lightning protection system class may be required.” As a result, there is then a need to consider some protection measures to control the side effects of the surge propagation into the internal wiring and circuits to prevent potential outages or loss of life.
LPI Group’s technical design team conducts coverage studies using two different software’s as a minimum to compare the results and ensure that the electrical equipment on the data centre roof and the building are well protected against direct lightning strikes.
When lightning strikes electrical equipment installed on the roof, there will be extended side effects to the internal equipment which is connected to the roof fixture like PV cells and HVAC Systems.
To reduce the risk of downtime, LPI recommend that it is essential to provide complete lightning protection for all electrical roof equipment. This can be achieved by including roof fixtures in a coverage study. On a building where roof fixtures are not protected from lightning, LPI’s technical engineers suggest that a coverage study is performed to install adequate lightning protection for the fixtures, particularly if regulatory conditions or requirements of insurance companies exist.
The result of no protection against lightning strikes involves operational downtimes, loss and damage to equipment and potential loss to human life.
Upon completion of the coverage study and the new lightning protection is installed, LPI Group will carry out annual maintenance on the system to ensure complete building envelope protection.
Fill out the contact form to speak to our technical design team about coverage studies for your mission-critical project.
LPI Group – Cloud to Ground Protection
By Hadi Beik Daraei, Senior Design Manager at LPI Group