ventESI: Open Plan Office

Project Details

Part of Project n.: 85435; Funding body: UKRI – Innovate UK

Foreword

Elta working closely with OpenCFD Limited, proprietors for OpenFOAM®, are using CFD to assess air quality and measures to mitigate harmful aerosols through effective ventilation.

Objectives

  • to assess ventilation effectiveness within the occupied space during working hours whilst maintaining good IAQ, tempered temperatures for occupant wellbeing and comfort
  • to identify hot-spots of stale/aged air on the basis of the existing building management system ventilation and additional clear air measures (based on recommended air-changes)
  • to identify regions of reduced air quality (based on measure CO2 in ppm) towards the wellbeing of the occupants
  • to learn and understand air movement and aerosol transport within the occupied space under different breathing cycles (breathing/talking/coughing)
  • to monitor IAQ parameters continuously within the occupied space and support the validation of the CFD model
  • to use the CFD model to simulate the effects of different ventilation strategies
  • to learn and share the findings of this project with Professional Bodies and the wider community

Metrics Used

  • CO2 (ppm) as proxy for room occupancy / IAQ
  • Age of air / Fresh Air Andex (FAI, mins or secs)
  • Air temperature (°C)
  • Contamination superspreader effects
  • Effects of air filtration/cleaning

Summary

Upon installation of a mechanical ventilation system with heat recovery and the deployment of 3 class B RESET certified IAQ sensors, 1 wall mounted CO2 sensor and 1 uncertified mobile IAQ sensor in its open plan office, Elta produced a 3D model of the office space to facilitate the validation of a CFD model via ventESI tool (created by OpenCFD Limited, through the support of UKRI project grant No.85435). In order to achieve the objectives set out for this project, a series of preliminary CFD model iterations were run to fine tune the project boundary conditions, supply of outdoor air, exhaust of aged/stale air flow rates as well as spatial temperature profiles. Presently, the CFD model iterations are being adjusted to mimic/follow trends of live data from the IAQ sensors in order to support our understanding of the combined effects of different breathing cycle conditions, CO2 levels, age of air, fresh air index…All CFD model iterations consider full office occupancy (even though we’ve been through lockdowns and subjected to staggered working from home patterns). Ultimately, the use of a validated CFD model will further our understanding of ventilation effectiveness.

System Design

Mechanical ventilation system with heat recovery fully ducted on supply and extract split into 7supply grilles and 5extract grilles. Catering for 15l/s/person, 6 out of 7 supply grille discharges into the open plan office space 60l/s of clean, filtered and tempered outdoor air. 4 out of 5 extract grilles exhaust 90l/s of aged/stale air from the open plan office space. The remaining supply and extract grilles are located in the private office currently served at a balanced 30l/s thus catering for single occupancy plus one. Initially running on demand controlled ventilation based on CO2 measurements from the wall-mounted sensor, the mechanical ventilation system was programmed for maximum fixed speed and scheduled to run 2hours before and after office working times.

The CFD model uses OpenFOAM®, the fully ISO-9001:2015 quality assured standard release from www.openfoam.com. It’s built around a complete ensemble of validated underlying physics modelling, including turbulence, buoyancy and particulate (aerosol) transport. It reports on derived metrics to indicate air freshness (FAI) and particulate evacuation (log-reduction measures) and Air Quality (e.g. CO2 PPM). The tool is made available for non-expert users via the Cloud App, ventESI.

CFD Model - Findings So Far

  • Volume average of CO2(ppm) below 700ppm
  • Volume average of Age of air approx.. 1800secs = 30mins
  • Identification of CO2 hot-spot for Sales team cluster under breathing + talking cycles
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CFD model - Next Steps

  • Aerosol transport and clearance from AGPs (coughing … etc.)
  • CFD iteration for 3 different ventilation strategies
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