How Will Rooms Operate on Loss of Mains Power?
Summary
The purpose of this technical paper is to describe the rationale and the evidence used to assess why HVAC Systems should not be supported by Uninterruptable Power Supplies at Stations, Shafts and Portals.
It discusses the resilience of the two independent electrical power supplies (A and B) and the requirements for a supplementary Uninterruptable Power Supply, UPS, system to provide additional power backup to HVAC systems to serve various critical equipment rooms.
The outcome of the paper is to establish whether there is a need for an HVAC UPS based on the probability of failure of the A and B power supply, maximum room operating temperatures and room construction.
The failure of both A and B power supplies is referred to as a Critical Occurrence.
During the early designs of the Stations, Shafts and Portals the ventilation and cooling designs for the Critical Rooms, such as Communication and Signalling Equipment rooms, were based on the best equipment heat load data available at that time. The heat rise calculations they performed using this data indicated that some Critical Rooms may overheat in the event of a power outage that disables the ventilation and/or cooling equipment (HVAC) while the critical Comms, Signalling, etc., equipment continues to operate on UPS power, and therefore continues to emit heat into these rooms.
To mitigate the potential risk of overheating, a range of solutions were developed all based around the principle of providing UPS power back-up for vent and/or cooling plant serving these Critical Rooms. This resulted in a significant increase in the UPS capacity required.
As the design progressed it became clear that the actual heat emissions from equipment in Critical Rooms would be significantly less than was perceived earlier. It was also confirmed that excessive heat rise in Critical Rooms is not a problem on existing LU, RfL, and NR infrastructure.
Based on this latest information, an assessment was made of the feasibility of deleting the UPS systems supporting the HVAC at all Stations, Shafts and Portals while still providing a solution that does not in any way compromise the reliability or lifespan of the equipment housed within these Critical Rooms.
This paper details that investigation and in particular the safety, reliability, maintenance and cost implications of omitting these UPS systems. The progression of these assessment activities, including sample calculations, modelling, measurements, etc. are detailed in this paper.
This paper confirms that omitting these UPS systems is fully justified with respect to all of the above criteria.
This assessment confirms that the continued operation of HVAC systems with loss of electrical power to the Station, Shaft or Portal is unnecessary.