HEALTHCARE VENTILATION
transmittance and thermal bridging of the AHU needs to comply to BS EN 1886 Class T2 and BS EN 1886 Class TB2 respectively to be considered HTM 03-01-compliant. We aware that some manufacturers detail thermal transmittance in their healthcare AHUs as complying to T3 TB3 standard. These manufacturers are not doing anything deceitful in sharing their full specification, but it is important that clients recognise that T3 TB3 on your specification will mean that the AHU doesn’t comply to HTM 03-01. There will be instances where T2 TB2 perhaps is not required for performance, but is required for compliance, and therefore while a manufacturer might recognise this, if they claim it also meets the HTM 03-01 (2021) guidelines this would be incorrect. Also, and this of significant concern, we
have seen quotes for air-handling units that are claimed to adhere to HTM 03-01 and, within that, comply to T2 TB2, that sadly don’t. This wouldn’t necessarily be obvious to someone outside of the industry, and of course if a specification claims to be compliant, most would take that at face value.
A familiar technique However, we have looked at their construction technique in detail. This particular unnamed example uses a technique we have worked with on other projects, and as such we have good reason to believe that it would be nigh- on impossible to achieve a mechanical performance of T2 TB2 using this method of manufacture. We currently hold data on file showing that T2/TB2 is not possible using this method of framework. This is further illustrated by the diagram in Figure 1, which shows a direct thermal link between the inside and outside air. We can only assume that the reason
that lower classifications of thermal bridging are being employed is due to the impact on cost. Sometimes clients do push for price reductions, and it is in these areas that savings can be made without impacting on profitability, but it will impact on the unit’s ability to adhere to HTM 03-01.
Thermal performance As a means of assurance, we work with a solution that has been tested by both
‘‘ Rockwool Pre Filters: ISO ePM10>50% insulated panels
Return Filters: ISO ePM10>50%
Main Filters: ISO ePM1>50%
EC fans as standard
Stainless & HDX Granite Internals
Aluminium framework to achieve: Thermal performance T2/TB2 Class L2/L1 leakage Casing Strength D2/D1
Figure 2: A diagram of an AHU, with some of the basic features that would lead to it being HTM 03-01-compliant shown.
ourselves and an esteemed third party to ensure that there is no doubt around compliance. We can and do offer price- competitive value-engineered solutions to clients who want it, where compromise might be made on areas such as thermal bridging, but there has to be transparency around this, because in this instance, a value-engineered solution would not meet HTM 03-01 guidelines, and therefore would not be suitable for many of our NHS and other healthcare clients.
Fans
Another area where costs can be cut, but inefficiencies subsequently incurred, is the use of AC direct drive fans which require inverter drive. HTM 03-01 Part A clause 9.40 specifies that fans should be EC direct drive type fans. Again, these have a higher upfront cost, but offer considerable savings over the lifespan of the AHU due to reduced energy consumption, and so, for the end-user, are more cost-effective long term. Away from the cost side, a significant consideration for the NHS at the moment is sustainability. Energy efficiency is a huge part of this, and as such EC fans are preferable, both as regards HTM 03- 01 guidelines, and to be part of a more sustainable solution.
Fan derogations Alternative fan types, such as AC and PM
Away from the cost side, a significant consideration for the NHS at the moment is sustainability. Energy efficiency is a huge part of this, and as such EC fans are preferable, both as regards HTM 03-01 guidelines, and to be part of a more sustainable solution
54 Health Estate Journal October 2023
fans, can sometimes be energy-efficient, but this very much depends on the project specification. Belt and pulley-driven fans are not HTM 03-01-compliant, due to low efficiency. These alternative fan types may reduce the upfront cost of a unit, but may also render it non-compliant with HTM 03-01 (2021), and therefore it is important to understand the context of the project before making a decision on fan type, recognising that price isn’t usually the most informed way of finalising a specification. When price is being used as the driver for decision making, we often see that true lifecycle costs are not being considered, because a more energy- efficient solution with harder-wearing components will over time prove more economical.
Other specifications This article could go on for many more pages, as we interrogate the requirements of HTM 03-01 (2021)-compliant AHUs set out in Table 1, the alternatives we have seen presented, and what these mean to the industry and the end-user. The recurring theme is, however, obvious at this point: n Cost savings are being made, probably due to pressure on budgets.
n The cost-saving alternative does not have the supporting paperwork required to verify it still meets HTM 03-01…
n …thus the AHU is no longer HTM 03-01 compliant.
n This non-compliance is not being made clear, or is explained away as the HTM not being legislative
n The AHU installed is now not meeting specification, but this gets lost in the process that started with a HTM 03-01 specification, and ended with a value- engineered solution
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