Using WiFi-Enabled Sensors For Smarter Restaurant Reopenings
Increasing the safety from virus transmission for indoor dining depends on the mode of transmission of COVID. Recently, a number of scientists petitioned the World Health Organization in their belief that there is credible evidence that aerosols, that is, droplets that remain infectious when suspended in air over long distances, are a mode of transmission. (Morawska, Environment International Volume 139, June 2020, 10573)
Aerosol transmission poses a challenge to the reopening of indoor areas of restaurants. Presently many states are allowing restaurants to open but these are mainly restricted to outside seating or extremely limited indoor service. The key difference between outdoor ventilation and indoor conditions is the rate of fresh air exchange indoors, described in terms of air changes per hour (ACH), both from designed systems and natural influx of fresh air. One air exchange per hour indicates the complete replacement of the volume of air in a room once per hour.
The Federal EPA recently called for increasing ventilation and indoor air filtration above “normal” pre-COVID industry standards. Previous standards are inadequate for the purposes of reducing airborne viral aerosol concentrations . Improving the typical present 1 ACH in a restaurant to 3 – 6 ACH can reduce inhalation exposure risk of airborne virus up to 100 times for diners in restaurants also practicing social distancing behaviors. (https://www.epa.gov/coronavirus/ventilation-and-coronavirus-covid-19)
Since air quality conditions in restaurants can change rapidly depending on occupancy, weather conditions and the proper functioning of ventilation equipment, real time monitoring of the air exchange rate is necessary to ensure the continued safety of customers. Informatics plays a key role in such monitoring. Fortunately, advances in internet of things (IOT) devices make such monitoring and reporting feasible and inexpensive. The Internet of things is any system of monitoring and digital devices capable of collecting and transmitting data to the internet.
Ventilation and IOT Monitoring Analysis Procedures
The basic procedure to analyze and design improved ventilation and monitoring in restaurants consists of four steps:
Assessment of the present ventilation and filtration system and estimation of the air exchange per hour rate
Design of enhanced ventilation/filtration systems to increase air exchange to 5 to 6 ACH
Change of the design of an air monitoring and IOT reporting system to ensure proper levels of ventilation given the occupancy conditions of the restaurant
The cost analysis of the ventilation enhancement and IOT systems
To demonstrate the cost effectiveness on viral transmission rates of this procedure, a “typical “restaurant case study is presented. Every restaurant will, of course, present its own specific conditions and opportunities, so the example is only illustrative.
Example Case Analysis
Step 1 - Present System
The example “typical” restaurant includes a 1200 square foot area with 12,000 cubic feet of air in the dining area and bar. The restaurant is served by a rooftop air handling unit (AHU) providing Supply Air (SA) flows (CFM) from the Mixed Air (MA) design proportion of 50% recirculated indoor Return Air (RA) + 50% Outdoor Air (OA (Fig.1). The existing ventilation system circulates just 1.5 air changes per hour, not enough to provide extra protection from aerosolized viral exposure in an occupied restaurant.
Step 2 - Enhanced Ventilation System
The dampers controlling the outside air intake are increased from 50 % open to 100% open, which doubles the air exchange rate to 3 ACH. In addition, applying duct mastic to seal leaky duct joints and using two window exhaust fans beneath existing ceiling fans to draw additional fresh air across the dining area raises the estimated ACH to 6. Upgrading two damaged restroom exhaust fans systems per CDC and OSHA guidance raises the ACH to 7. High-efficiency MERV-rated filters are placed across the Return Air flow to reduce aerosol levels before mixing and recirculating.
Step 3 - Design of IOT Monitoring System
ACH rates can be estimated from monitored carbon dioxide levels. IOT CO2 monitoring devices are placed as shown in Figure 2. In addition, IOT air flow devices are placed at the vents shown on Figure 1. Air flow monitoring ensures that the ventilation equipment is working properly. Figures 4 and 5 show two commercial IOT monitors and reporting screens presently on the market. The technology to inexpensively monitor and report ventilation conditions in real time to restaurant managers presently exists. The data from such systems can provide real time guidance to restaurant managers regarding safe occupancy rates.
Figure 2 - Placement of Carbon Dioxide Level Sensors With Enhanced Ventilation
Figure 3 - Fully Integrated Ventilation, Notification, Controller and WiFi System
Figure 4 - Low Cost Real-Time Airflow and Carbon Dioxide Sensors
A typical desktop model with battery-operated portable sensors provides real-time measurements, allowing manual adjustments as with a thermostat. Logged data is downloaded to confirm the design, track maintenance needs, and gather feedback for design improvements.
Step 4 - Cost Estimation
The estimation of the cost of installing the new systems would necessarily be approximate but the definition of cost categories should be reasonably accurate. A rough estimate of the system is provided below.
Figure 5 - Cost Estimate of CoVID Ventilation System Enhancements
Ventilation enhancements and monitoring do not by themselves ensure the safety of customers. Such actions can however play an important role in significantly increasing customer safety if employed with the use of masks, disinfecting surfaces, and maintaining a proper distancing of customers. None of these strategies are cost prohibitive. The intelligent adoption of the combined use of these strategies not only makes good public health sense but promotes safer work conditions and gives the potential customers more confidence to dine in safety.
