f Kiwa Energy Domestic Ventilation Report

The report provides an evaluation of the effect of the levels of ventilation on hydrogen concentrations that could result from leaks.
A mathematical model has been developed using data collected from air tightness testing of real properties, to simulate maximum gas in air concentrations achieved within a domestic property following a leak of hydrogen. The model is based on well-established theories in fluid dynamics and has been validated (by the model developers) by comparison with real experimental data, gained from the Hy4Heat, H100 and HyHouse programmes of work. A comprehensive range of scenarios have been modelled to assess leaks of varying severity, under a range of ventilation regimes. Modelled hydrogen leak rates range from 0.02 m3/h to 51.7 m3/h and levels of property air permeability range from 4.2 to 24.7 m3/h/m2 @ 50 Pa, by convention 0.21 to 1.24 Air Changes per hour (ACH).
As expected, spaces with greater ventilation are predicted by the model to result in lower maximum gas in air concentrations and adding vents (internal and / or external), is effective at reducing concentrations within a room.
A general finding from air permeability tests of dwellings was, kitchens and hallways within properties were less airtight than living rooms. This implies greater ventilation to/from these spaces. Consideration has been given in this work to the co-use of audible alarms where they are most likely to alert the occupiers. If pipework and appliances are in rooms connected to a central space, typically a hallway, an alarm (with integral detector) located at the highest point of that space should detect hydrogen from a leak in the connected rooms. In general, this is the most likely location to form the audible alarm to be heard in the various rooms in a dwelling. However, there will be cases where appliances and pipework are not in a room connected to a central location, or where a large build-up of gas may occur (e.g. due to high ceilings relative to door height) before tracking to a central location. Adding internal high-level vents to facilitate tracking to the alarm location should aid timely detection of a leak in these cases. An alternative could be to install more alarm units which may be more practical and preferred.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.