AIR MOVEMENT | CONTAMINATION CONCENTRATIONS Test concentrations for S1, S2, S3, S4, S5 and theoretical concentrations the industrial hygiene concept of effective flow VEFF, although he noted that ASHRAE uses the inverse of this, the Ez Factor, to evaluate air distribution effectiveness in a room. The two terms are consistent and enable the calculation of an effective air change rate (ACR). So in Case 1, ACR was 3.4, which compares reasonably to the actual supplied ACR of 4.1 (Figure 3 and Table 1). He then removed the mixing fan and, making no other changes, repeated the test to provide results as shown in Table 1. This indicates a different situation where, although mixing diffusers are used, there is no uniformity in mixing and the effective air change rate is 1.5 just 37% of the supplied air change rate of 4.1. Aside from the near field (S5), the most concerning result was that point S1 received a very high dose. A training centre used by Smiths organisation was tested as a real application. The highest dose (of 62 compared with the average of 36) was experienced by those sitting underneath the exhaust point, which also compared unfavourably with the theoretical dose rate of 13. Everyone in the room would have been exposed at a higher level than had been theoretically predicted (that was likely due to stratification). Smiths full presentation includes more examples showing startling spatial differences in contaminant concentrations and doses linked to the respective positions, flowrates and geometries of supply and extract points. View the presentation (at a cost) at bit.ly/CJASHTS23 CJ Figure 3: Tracer concentration with two high level 360 mixing air diffusers supplying 4.1 ACH and a separate mixing fan in the room [Source: Tom Smith, 3flow] Actual ACR (per hour) Effective Modelled Actual Actual Actual Actual Actual Average ACR average S1 S2 S3 S4 S5 actual (per dose dose dose dose dose dose dose hour) With mixing fan 4.1 0.15 7.01 8.32 5.60 7.52 6.08 15.40 8.56 No mixing fan 4.1 0.12 4.98 19.43 8.74 2.32 7.64 29.34 13.47 Table 1 : Actual and calculated air change rate, modelled and actual tested doses with and without mixing fan TM Ideal for up to 5 bed apartments/houses, the HRXE-ZEUS range operates by continuously extracting moisture-laden air from wet rooms within the property while simultaneously drawing in fresh, filtered supply air from outside. Recovers up to 95% of the normally wasted heat Summer bypass function No reduction in airflow when operating in bypass mode Listed on the SAP PCDB Visit our website to find out more about the HRXE-ZEUS, the Daddy of ventilation. YOUR VENTILATION SPECIALIST 03443 715 523 www.domusventilation.co.uk domusventilation_ 68 September 2023 www.cibsejournal.com V EN T IL AT ION DADDYS HOME HRXE-ZEUS