Why AHU compliance to HTM-03-01 is important for healthcare applications

Adam Waters, Daikin Applied AHU Product Manager and HTM-03-01 specialist examines why AHU compliance to HTM-03-01 Healthcare Technical Memoranda is important, not only for the health and life expectancy of the AHU itself, but also to the patients and staff within the Healthcare estates.

What is HTM-03-01?

HTM-03-01 is the healthcare technical memoranda. It is an NHS published document that is supported by the British government which sets the standard and expectation for ventilation equipment in healthcare applications. There’s been 4 previous iterations of the HTM guidance spanning from its initial introduction in 1983 to the latest release in 2021. A new release of the guidance occurs roughly once every decade, bringing with it more stringent guidelines, higher efficiency targets and engineering design adjustments in line with advancements in market legislation and technology.

Though the guidance is not mandatory, it is an accumulation of research and experience of many important bodies within the HVAC and healthcare industry, setting definitive targets for engineering solutions with the interests of the end user (the public) at the forefront of its requirements. For this reason, the consideration of the guidance when designing ventilation equipment for healthcare applications is of the utmost importance.

What are the main requirements of the latest guidance with regards to AHU design

The latest HTM-03-01 guidance provides many significant updates over the 2007 edition, the main one being that the overall design parameters are much clearer for AHU manufacturers to interpret and follow.

From an engineering perspective, the panel construction requirements have been updated to now require a dual skin construction with Euroclass A insulation, providing greater fire & noise resistance, whilst also offering a more robust solution. The primary solution is for all AHU’s to be internally mounted, where logistically this is not possible, all external units must come complete with integrated maintenance corridor & pitched roof arrangement creating an enclosed plant-room.

Access requirements are also more clearly defined with access doors of minimum 500mm width (600mm to units <1m in deck height) required both sides of all coils, and upstream of all filter banks.

In addition, legislation for filter requirements has been updated to ISO 16980, which in turns requires higher efficiency PM pre & final filters to improve IAQ.

Similarly, heat recovery efficiency requirements have been updated in line with updates to EU1253, and thermal wheel solutions are now permitted under the premise that only sensible type rotors complete with purge sector and enhanced tightness seals are proposed. This allows for more spatially effective AHU solutions to be permitted.

Newer EC fan technology has been recognised as the most favourable fan solution due to their high efficiency, low maintenance requirements and spatially effective solutions. EC fans also have the advantage by being able to offer more redundancy through installation in an array/wall arrangement. Previous requirements for maximum 2m/s face velocity are no longer required provided moisture eliminators are included to cooling coils. There’s also no limitation on coil sizes and the need to split or stagger coil pieces.

These are just a few of the many items defined by the latest guidance, for a more in depth, comprehensive overview, consider enrolling for our CPD on the design of AHU’s to HTM-03-01 (2021).

Why compliance to the guidance is important

Ultimately, the guidance offers the best solutions to suit the critical application. It considers a multitude of parameters from material choice to efficiencies, indoor air quality (IAQ), future maintenance and even wider regulations to form a well-engineered, cohesive solution. The risks of not following the guidance can be extremely detrimental not only to the health and life expectancy of the AHU itself, but also to the consumers i.e the patients and hospital staff.

  • Poor access requirements can result in a longer maintenance time and personnel safety risks, which in turn affects downtime and hygiene, compromising the IAQ of the space.
  • Poor material choices can lead to corrosion and the growth of microorganisms within the air stream again compromising the IAQ.
  • Poor filter design can result in air bypass at filter sections resulting in contaminants being delivered to the space.
  • Lack of consideration for drainage requirements can result in water pooling within the AHU leading to corrosion and the growth of legionella.
  • Lack of consideration for the optimal positioning of intake and exhaust can lead to contaminated air being re-delivered to the space.

The above lists only a few of the consequences of poor non-compliant AHU design, but it also highlights the significance and need for the guidance to be followed when designing new AHU and ventilation systems.