HVAC SYSTEMS
preference for the use of corrosion- resistant alloys such as stainless steel is underpinned in the document. Alongside the selection of appropriate materials for the air-handler casing, the prevention of unwanted condensation and standing water in the surfaces of the unit is of the utmost importance in averting the aforementioned issues, as well as the risk of Legionella. Emphasis on the use of suitable protection from rain ingress, appropriate draining, the avoidance of evaporative cooling solutions, and setting minimum requirements to eliminate thermal bridges, in the casework have also been addressed.
Classification of casing
Finally, the classification of the air-handler casing to established standards is also recommended, with the products now preferably adhering to a classification of D2, L2, T2, and TB2 to BS EN 1886. These are important in ensuring low leakage and infiltration, which can undermine the fresh air delivery, filtration, and energy efficiency of the equipment, and the thermal performance of the units, which may predominantly affect the likelihood of condensation forming on the casing, and heat loss or gain through their fabric. Any leakage, and the mechanical strength of the equipment in particular, must be proven both through factory and in situ testing.
Service, maintenance, and refurbishment
Perhaps one of the most important changes to come about with HTM 03-01 (2021) is the increased focus on installation, commissioning, validation, and maintenance standards, with the recommendations and guidelines being fully revised to ensure that the equipment is not only compliant at the point of installation, but also throughout its lifecycle. Most of the design blunders with air-handling units are not evident at the point they are installed, but quickly become apparent when, for example, maintenance cannot be carried out properly due to poor access facilities, or cleaning becomes impossible due to a cluttered design inside the unit. Emphasis has been put on providing appropriate access for cleaning and maintenance facilities for servicing the units. Validation acceptance standards and methodology, and guidelines on the commissioning process, routine inspection, and maintenance, have also been completely revised. Furthermore, guidance is also given on the expected lifecycle of the units – 20 years –and the updating of mid-life plant which should be taken out of service, deep cleaned, its controls renewed, and recommissioned after 10 years.
The resiliency of the ventilation system is crucial to safeguard the operation and capacity of the healthcare building.
Resiliency
As we established already, the resiliency of the ventilation system is crucial to safeguard the operation and capacity of the healthcare building, and the health and lives of those working and being treated within. Long system shutdowns are absolutely not acceptable. It is only natural then that the new guidance emphasises the need to quickly and effectively maintain and service, the plant, especially in those areas where failure of the equipment can have irreversible consequences – the so-called critical areas.
To this end, fan walls are suggested to provide resiliency and increased capacity of the systems, which, in the event of a fan failure, should still be able provide at least 80% of the design capacity. Fan walls also provide advantages in facilitating the quick replacement of faulty fans, as they are composed of several small fan assemblies, rather than a single large one. The revision also requires that fans in critical areas can now be replaced in 20 minutes or less, with the use of quick- release plug and socket connectors to facilitate this. It should be noted, however, that in non-critical areas a single fan might still be the preferred option, as multiple fans come with the disadvantage of increased capital cost, and inefficiencies associated with the use of multiple motors and impellers.
Efficiency and sustainability In line with the demand for more energy- efficient solutions, another key revision covers new technologies in air movement, heat recovery, and controls. Fan technology has come a long way since 2007, with Electronically Commutated (EC) fans now being widely used for their energy-efficient motors, ease of control, flexibility, and compact size. Heat recovery devices are now capable of achieving significantly higher efficiencies, yielding major energy
savings when properly applied, and building management systems are commonplace in most buildings. The new guidance steers designers towards these new technologies, and highlights their importance in achieving an efficient and sustainable design.
Furthermore, energy-intensive requirements – such as the need for HEPA filters in critical areas, droplet eliminators to prevent water carryover, and protective mesh guards on fan inlets – have been reconsidered to being included only where strictly necessary. This change can have a huge impact on the lifecycle energy consumption and the efficiency of the equipment, and it’s remarkable that we are finally seeing their inclusion being re-considered.
Interpreting the revisions As with all new legislative or guidance instruments, understanding the content is key to effective implementation, and this can often be inconvenient, time-consuming, and costly, especially if these are published half way through the construction or design of a building, as has no doubt happened on many projects when the HTM 03-01 revisions were published.
These difficulties can arise because while the guidelines are thorough and all- encompassing, they cannot be absolute or too prescriptive, as they need to be interpreted in the context and demands of the project they are to be applied to. It is crucial that when recognising the revisions, and making appropriate changes to current working practices, those responsible for adjusting the specifications have the experience and critical thinking skills to implement the changes appropriately and purposefully. This is where the engineering expertise of manufacturers can become important. The revisions made to the document are mostly appropriate to deliver
September 2021 Health Estate Journal 39
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