HVAC SYSTEMS
Above left: This fluid-filled (empty) manometer would be better replaced with a pressure transducer linked to the BMS for improved control. Above right: Ageing critical ventilation plant (with the manometer no longer used).
Even before we start to look at a strategic replacement
Dr Scott Brown
Dr Scott Brown PhD, Med, CEng, CSci, MIPEM, MCGI, is a Chartered Engineer and Chartered Scientist with over 30 years’ experience in hospital and biomedical engineering. He is also registered as a Clinical Scientist with the Health and Care Professions Council, and has gained certification in MGPS (AP) and HVAC(CP). He established Health Tech Solutions Ltd in 2014, and offers consultancy services to the healthcare sector, along with engineer and user training on medical devices, dental operating units, and hospital infrastructure systems, both in classrooms and remotely. He has worked as an independent consultant with several NHS hospitals – introducing strategic equipment replacement planning, has published widely on hospital and biomedical engineering – including contributing to four textbooks, and is an invited speaker at national conferences.
programme, we need to ensure that we have the necessary data from which to plan. Essential therefore is an accurate asset list of all HVAC systems. Having an up-to-date, well-informed dataset supports a much more robust argument, and enhances Estates Department credibility when approaching the director of Finance or the Capital Investment Committee for monies. While this might seem obvious, there are plenty of hospital Trusts with this basic information not at hand. Changes in the way records are held – with the switch from paper-based to electronic records, or, for example, changes between different software applications, may have led to some valuable historical information being lost. Therefore, even if an asset register is available, its accuracy should be verified. The HTM gives us guidance on compiling an asset register or inventory, and suggests the list is subdivided into four categories: n Local exhaust ventilation (LEV) systems. n Critical healthcare ventilation (CHV) systems. n General ventilation systems (GVS), and General extract systems (GES)1
(page 141).
A unique identifier Each system should be assigned a unique identification code or asset number. HTM 03-01 sets out a list of important information to capture about a system, but for strategic replacement planning, only a subset of this is required. Along with the identification code we need to know the purpose of the system, the equipment installed, the date of installation, and the area served. While the purpose of the system might seem obvious, hospitals are in a continuous state of reconfiguration, and clinical areas are frequently moved, which may impact on the requirements of the HVAC system. Furthermore, by removing any ‘ghost’ assets (those that no longer exist), a true picture can be painted of the asset base. We could of course introduce a plan to replace all
HVAC systems based purely on age. We have already mentioned that capital budgets are constrained, and have competing priorities, so a replacement plan based purely on the HTM guidance of 20 years may be unrealistic. So, do we say ‘Replace at 25 years or 30 years’, although this doesn’t take into account the impact of unavailability due to failure. Failures to some extent can be reduced by regular maintenance, and HTM 03-01 also talks about replacing motors within the lifespan, and, of course, other routine maintenance. An approach informed by risk factors may thus offer a sensible alternative. The most common way of looking a risk is to grade each factor, with the granularity of the grading a compromise between detailed
40 Health Estate Journal September 2025
knowledge and easy application. For most circumstances three or five levels are commonly used, and this is familiar with our 5 x 5 matrix model created by the National Patient Safety Agency (NPSA).2
Clinical risk The clinical risk of unavailability should be considered, and should reflect the risk to an individual patient, or many patients. If we were to use a High, Medium, and Low grading system for simplicity, then a good example of a high risk would be an operating theatre with a UCV system. The failure of the UCV system could lead to unacceptable levels of colony-forming units (cfu), thereby increasing the risk of surgical site infection (SSI) for the patient. UCV theatres are traditionally used for higher risk surgical interventions such as orthopaedics, and it follows that here SSIs have a much higher consequence on successful clinical outcomes. Of course, this failure would only affect one patient at a time, assuming a single operating theatre, and if detected quickly, with further surgeries cancelled, only one patient may be affected. If we consider a Critical Care Unit, infection would impact potentially much higher numbers of vulnerable patients. Looking at this another way – and an isolation room housing an infectious patient could also be construed as a high risk, because failure may mean that other patients and staff are put at risk. Conversely, with a neutropenic patient in an isolation room, a failure in the ventilation would only impact the one patient. Lower risk grades may be assigned to failure of a HVAC
system supplying a general ward – where the impact may be more on patient comfort than infection risk. Clearly, the grading of clinical risk due to unavailability is complex, and is influenced by the type of patients and procedures conducted in a hospital. Furthermore, consideration should be given to future respiratory-related pandemics, and incorporating lessons learned from the Sars-Cov-2 pandemic in clinical areas designed to minimise spread by incorporating suitable pressure regimes. The service impact is a measure of the degree of
disruption that any significant failure of ventilation plant failure would have on the clinical service. This could range from insignificant disruption at one end of the spectrum – perhaps with the closing of one isolation room – to a complete cessation of the service, such as closing an operating theatre. Such plant failures can be even more significant in the case of older HVAC systems, where multiple operating theatres are supplied from a single plant. Instances of four or more theatres being supplied from a single HVAC plant are not unknown, and any plant failure in such a scenario would mean a suite of operating
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