With the 2020 Pandemic that developed earlier this year and the CDC and WHO guidance provided, there has been a renewed focus on indoor air quality. There are a wide range of approaches that have been presented through technical resources, ie. American Society of Heating, Refrigeration, & Air-Conditioning Engineers (ASHRAE), as well as product driven technology from suppliers.
While there has been much interest from the Commercial, Educational, and Residential communities, much of the earlier focus has been on hospitals and medical facilities. Additionally, while ASHRAE has provided guidelines for improving conditions, the standard which sets the minimums for healthcare facilities is ASHRAE 170 – Ventilation of Healthcare Facilities. This standard addresses important requirements useful in minimizing airborne transmission of infectious agents. The standard specifies ventilation requirements for total air changes, outdoor air changes, as well as filtration requirements. While this standard and the parameters set forth are specific to healthcare organizations, the overall approach can be applied to other types of facilities (ie. commercial, educational, municipal, etc.), which also parallels recommendations that have been provided by the governing authorities (CDC and WHO).
While there are other, lower cost measures available, such as ultraviolet and germicidal irradiation, through the use of strategically located devices which provide localized treatment of air, but the effect may be limited depending on the air velocity where the UV lights are located and the distance of the air-flow from the point of treatment. Another technology would be ion point sterilization where positively charged ions are injected into the air-stream which kills airborne germs. The effectiveness of this methodology would depend on the concentration of the airflow and distance from the point of treatment as well. When increased filtration and higher levels of outside air are utilized, they provide a more effective system approach which has an improved effect on all of the spaces served by the equipment.
When reviewing and exploring options to implement increased filtration and higher levels of outside air, an important consideration is the capability of existing systems. When media type filtration is increased, the increase to overall pressure drop of the duct-work system has to be considered. Unless adjustments are made to the system, the resulting higher pressure drop can cause lower air-flow in both total and outside air changes which are counter-productive to the overall goal.
When outside air quantities are elevated, there is an increased demand to temper (heat and cool) the outside air being taken in so that the space temperature and humidity conditions can be maintained. Before these measures are implemented, the systems must be carefully evaluated.
Upon evaluation, if the systems do not have the capabilities to support the increased filtration and ventilation, other options such as separate units that will deliver tempered air to the existing mechanical units can be investigated. Possibly higher supply air fan horse-power may be required. Alternately, separate units to supply only tempered ventilation air into the spaces can be utilized.
Overall, there are a variety of options, some with more effective results than others, which should all be evaluated to ensure the right solution for the application is being provided. This article serves to provide a high-level discussions of the issues surrounding this technical topic, all of which could not be summarized in this article.
Engineering Humor
At a training session in the fire station, the team was assembled around the kitchen table.
The training officer was discussing the behavior of fire. “You pull up to a house and notice puffs of smoke coming from the eaves, blackened out windows and little or no visible flame. What does this tell you?” he asked.
He was expecting to hear that the house is in a possible back draft situation, a condition very dangerous to fire fighters. Instead he heard the following from one quick wit in the back, “You got the right place!”
The cleaning lady comes to the bank manager…
“Can you please give me the key of the safe vault?”
“What?! What for?”
“It’s always so time consuming to have to use my hairpin in order to clean it!”
The FBI and the DEA are joining efforts and will be assigning some of their agents to a quasi-FBI/DEA enforcement team specifically targeting the illegal allergy pills sales that occur on the black market.
The agents will be called “Pseudo Feds!”