POWER GENERATION
HTM standby generation derogations explained
Geoff Halliday, Business consultant at WB Power Services, discusses the practical application of the guidance in HTM 06 to standby generators, the variance with how diesel generators are designed and built, and how some of the most common apparent ambiguities or variances can readily be overcome. He also discusses the generators’ critical role in the event of a utility power failure.
WB Power Services has a long and proud history of supplying standby generation solutions to the NHS and wider healthcare sector. Over many years the company has installed a large number of generating sets, both large and small, in applications ranging from basic containers to complex plant room installations. During this period, the business has acquired a significant experience base within its sales, project installation, and service teams. For those outside the day-to-day working of this sector, the size and scale of standby generation in a hospital setting is an unknown quantity. For those working from within the sector, on the other hand, the installation of a standby generating set probably isn’t an everyday occurrence, so this article seeks – from the standpoint of a specialist standby diesel generator installer, to ‘highlight, explain and clarify’: n How the guidance lines up with the way in which diesel generators are designed and built, and how this can be at variance with the HTM.
n How the guidance within HTM 06 can be practically applied.
n How some of the most common apparent ambiguities or variances can readily be overcome.
Starting point The starting point of any design should be with the relevant standards or guidance documents, which in this case – for Secondary Power Sources in healthcare settings – is HTM-06 (2017), and in the case of standby diesel generators, BS ISO 8528 (updated in 2018). As with any specification, BS ISO 8528 sets out the basic minimum standards for the equipment (some manufacturers exceed these), and often doesn’t move quickly enough in terms of recognising more cutting-edge product developments. For example, this can be across engine performance or market requirements, and has the tendency to look out of date even when newly published. It is likely to be a similar problem with some aspects
Figure 1: Generators installed within a plantroom.
of HTM 06, particularly as it is a guidance document, and by the nature of the review period, will not take into consideration more recent advances in technology and changes in the law; for example recent changes in emissions requirements. Hospitals are of course true 24/7
operations, forming a critical part of the local, regional, and national infrastructure, and varying greatly in terms of physical size, bed capacity, building age, and scope of services offered in that location etc. In the UK healthcare sector the Health Technical Memoranda (HTMs) are there to ‘give comprehensive advice and guidance on the design, installation, and operation, of specialised building and engineering technology used in the delivery of healthcare’. The primary reason that standby
generators are included within a hospital is to provide a Secondary Power Source (SPS), or simply to provide back-up power in the event of a power utility failure. A utility power failure can be anything from just a few seconds, to hours, or possibly
days. Uninterruptible Power Supplies (UPS) are one such SPS, installed mainly to provide power to highly critical equipment for relatively short periods of time, typically in the region of 5 – 30 minutes (up to 3 hours in some critical areas), which is more than sufficient to deal with any short-term ‘brown out’, or the 10 to 15 seconds required to bring the standby generator(s) online.
Diverse nature of equipment It is likely, in the case of more recently constructed hospitals, newly constructed wings, or recently refurbished areas, that the electrical load connected to a standby generating set is now the entire hospital / wing. This is due in part to the very diverse nature of the equipment used in all operational areas. When viewed in a more general context, the electrical loads can be considered to be: 1 The general building load, i.e. lighting and small power.
2 The mechanical load. 3 Critical area loads (ICU/CCU). 4 Critical equipment in general ward areas.
August 2024 Health Estate Journal 41
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