Effective ventilation is vital to ensure safe, comfortable, and efficient indoor environments. For hospitals and healthcare facilities in particular, ventilation is a critical component in a building’s life-support system. There are a number of reasons that specifications for hospital ventilation systems are significantly more stringent than for typical commercial buildings. Use of healthcare premises is particularly intensive, with high-power requirements and high occupancy and traffic levels due to the constant flux of patients, staff, and visitors. Patients may be highly susceptible to airborne infection risks, and their medical condition may require close control of the indoor environment.
A significant contributor to the UK climate footprint
In terms of environmental impact, healthcare is a significant contributor to the UK’s climate footprint. Health Care Without Harm reports that in 2019, hospitals and related buildings were estimated to account for around 5.4% of the UK’s total greenhouse gas emissions.
Given the wide range of equipment and engineering systems needed to maintain an optimum indoor environment, the legal and technical requirements applying to ventilation for healthcare premises are complex. Valuable guidance is provided by the Health Technical Memoranda (HTM) reference series, produced by National Health Service (NHS) estate specialists and expert cross-industry panels. Guidance on hospital ventilation is explained in HTM 03-01: Specialised ventilation for healthcare buildings. Published in 2021, this provides updated guidance drawing on the healthcarespecific aspects of current standards and best practices. While not mandatory by law, unless specifically stated, HTM 03-01 is considered an authoritative overview of ventilation requirements for NHS and other healthcare premises. It makes clear that any departure from the guidance it contains requires detailed written justification, as part of the works approval process.
Guidance in two parts
The guidance comes in two parts. Part A covers design, specification, installation, and acceptance-testing of healthcare ventilation systems. Part B deals with the ongoing management, operation, and maintenance, of existing healthcare ventilation systems. Together, the documents provide an essential reference for specifiers, designers, suppliers, installers, and Estates and facilities managers
There have been many changes since the previous edition was published in 2007. A central element in the updated version is a focus on achieving carbon reduction targets, in support of UK legislation to reduce greenhouse gas emissions to Net Zero by 2050. The main principle is that, as far as possible, ventilation should be delivered by natural means, passively, without requiring power input. Next in terms of priority is mixed mode ventilation, involving a combination of natural and mechanical systems. Mechanical ventilation is the next most preferable option
Given the often high heat loads and intense use of hospital buildings, along with the importance of fine control in managing indoor climate, the guidance acknowledges that it may be difficult to achieve total ventilation requirements through passive means alone. Some element of hybrid and/or traditional mechanical ventilation may be required
Minimising energy consumption
The overriding principle in HTM 03-01 is to minimise energy consumption by choosing ventilation solutions with the lowest lifecycle environmental cost. To this end, the guidance is to switch systems ‘off’ when not needed, and, when required to support set conditions, set-back to the minimum necessary to achieve and then maintain the desired state. The guidance points out that since the previous edition, there have been significant changes in legislation covering energy use, as well as technical developments that improve equipment efficiency. As a result, system designs that simply follow the pattern of previous installations ‘will not meet the revised energy or operational standards, and will not produce a compliant result’. The revised guidance incorporates the relevant changes relating to healthcare ventilation, and system designers are highly recommended to follow the updated parameters set out.
For reducing energy consumption by mechanical systems, it points out that one of the biggest potential areas for savings is fans, as they account for around 40% of the total electrical energy used by ventilation systems.
Improved fan efficiency
Recent technical advances have significantly improved the efficiency of fans and related motors. This has partly been driven by the Energy-related Products (ErP) Directive 2009/125/EC, and by substantial investment by manufacturers in the fundamental technology of impeller design, motors, and electronic speed controls. There is a presumption against use of older-style approaches, such as belt-driven fan systems, on both safety and inefficiency grounds. The default choice for fans is now electronically commutated (EC) motors, which offer significant improvements in performance and efficiency
As a result of their ability to vary fan speed according to the airflow needed, EC motor efficiency can be above 90%. When part of a system, EC fans consume up to 70% less energy than conventional, singlespeed fans, delivering large reductions in emissions and running costs. In addition to the efficiency of individual components, the guidance highlights the importance of zoning and control strategy to overall ventilation system efficiency. Zoning has to take account of a number of factors related to how the treated building and specific spaces within it are used.
For example, the guidance says zoning should be configured in the light of:
Occupancy over time.
Resilience requirements.
Fresh air / ventilation requirements.
Fire and smoke management strategy for the building or space.
Where the ventilation system is designed to provide full heating and / or cooling, the following additional factors also must be considered:
Internal or peripheral location.
Orientation of windows.
Variation of internal loads.
Level of control required.
Monitoring through a BMS
In terms of control strategy, the guidance is clear: hospital ventilation systems should be controlled and monitored through a central building management system (BMS). It is no longer acceptable for individual items of equipment, or separate air-handling systems, to be equipped with local control only. No matter how good such controllers are, the big gains in efficiency come from a fully integrated, building-wide approach to energy management and environmental control.
In the past, integration of local systems with a BMS sometimes presented challenges, due to the different communications protocols in use. Today, this has been greatly streamlined, and most of the mainstream manufacturers have made connection of equipment quick and easy. Another key element in optimising efficiency is specifying correct equipment capacities. HTM guidance advises that particular attention be given to the correct sizing of equipment at the design stage. Key to this is determining the true ‘in-use operating condition’. Overestimating this fundamental parameter at the outset will result in the selection of oversized equipment, that will be less easy to control, and result in higher energy use throughout the lifetime of the system
Design and selection of set-points
A connected issue is the design and selection of set-points. This can have a big impact on energy consumption, and requires careful calibration to ensure that the required conditions are met without overshoot and resultant excess energy consumption. Improving health and safety is another key driver of the updated guidance. It provides a new approach, based on the concept of the Ventilation Safety Group (VSG) in healthcare organisations. This follows a similar approach adopted in recent guidance on water and electrical safety in their own respective HTMs.
A VSG is a multidisciplinary group with responsibility for the safe and resilient operation of ventilation systems on healthcare premises. As part of a hospital’s governance structure, the group reports to a designated board member. The group typically includes an Authorising Engineer to act as an independent adviser, an infection prevention and control specialist, a representative of the authorised ventilation contractor, estates staff, clinicians representing individual departments, and finance staff. Other specialists may advise, as required.
Design of new systems
As well as being responsible for all aspects of ongoing ventilation safety and resilience, the VSG’s remit includes the design of new systems and modifications to existing systems, annual verification and performance testing, and prioritisation of equipment for replacement.
Any proposed changes that may affect the safety or resilience of ventilation systems must be reviewed and signed off by VSG. This includes the potential impact of proposed building work on site, and its possible effect on air intakes.
While the revised HTM was produced before the emergence of COVID-19, the guidance takes account of all known transmission evidence available at the time of publication
In this context, it states that ventilation is firmly established as one of the principal mitigations against the virus, and should be part of a package of infection prevention and control measures. The authors conclude that the recommended ventilation rates proposed ‘are likely to provide a lower risk environment for COVID-19 airborne transmission’.
Welfare and maintenance of staff
The safety and welfare of maintenance staff attending to hospital ventilation is also addressed. There is a requirement to provide covered access for staff while servicing air-handling units located externally on a rooftop or on the ground. This is to ensure that staff are protected, and that equipment is shielded from possible water ingress, while access panels are removed during maintenance. For our own part, CIAT has developed a weatherproof enclosure made of galvanised steel that runs alongside the unit, to provide complete protection from the elements during servicing work, and prevent dirt and moisture from entering the unit to minimise contamination risks.
A further measure to reduce environmental impact requires that components such as bypass dampers and related gears, must not be made of plastics. Manufacturers are now using alternative solutions made of steel that perform just as effectively without reliance on single-use plastics. In a further design refinement, CIAT has developed a new drain pan made of stainless steel, which is easier to clean and helps maintain hygiene. The design also helps minimise the overall height of the unit, which is valuable in situations where space is tight
Effective management of condensate
To minimise the risk of Legionella and other sources of contamination, effective management of condensate water remains a key consideration. In compliance with the requirements, drain pipework on our own air-handling units for hospitals is fitted with specialist borosilicate glass, enabling service staff to quickly see any build-up of deposits
Certain spaces within hospitals may require tailored ventilation systems to address specific needs. For example, endoscopy rooms where invasive examinations are carried out are required to have negative pressure. This helps protect staff from exposure to waste anaesthetic gases released in the room, and airborne infection risks
The role of refrigerants as contributors to global warming and equipment efficiency should also be considered. The guidance advises that selection should be made carefully with reference to the current F-Gas Regulations, which are subject to constant review. The main consideration is to select the refrigerant with the lowest global warming potential for a given application. It also advises taking account of the life expectancy of equipment versus the future availability and increasing cost of the refrigerant.
A ‘head-start’
The detailed, up-to-date guidance contained in HTM 03-01 provides an excellent head-start and reference for designers, HVAC practitioners, and building managers responsible for delivering high quality ventilation for hospitals. It takes account of the complex needs of all stakeholders – patients, staff, and visitors, as well as the handson professionals who install and service equipment during its lifecycle, balancing these needs with the requirement to improve energy efficiency and reduce environmental impact.
Lee Jenkins-Skinner
Lee Jenkins-Skinner has spent nearly a decade working in the HVAC industry, and brings a wealth of knowledge in air-handling units and ventilation solutions to CIAT. Having studied design and industrial engineering at The University of Manchester, he started his career as a mechanical product designer, but soon found his true vocation in HVAC as an application engineer.
Joining CIAT in 2018 as a pre-sales engineer, in 2022 he was promoted to AHU Product manager, UK & Ireland. In this role, he is responsible for supporting the development of the company’s air-handling and roof-top units. He supports the products by providing internal and external training specific to users’ needs, and developing or modifying selection tools to increase productivity. In the early stages of his career, he was involved in selecting HTM 03-01-certified AHUs to meet stringent guidelines. CIAT’s air-handling units have been installed in hospital operating theatres, inpatient, and outpatient units, and other healthcare settings, throughout the UK and Ireland. Today, Lee Jenkins-Skinner provides the CIAT team with advice and guidance on a variety of standards-related topics, and assists with the design and build of AHUs.