There have been debates about whether or not COVID-19 can be spread through airstreams and poor ventilation. Linked below are two articles with a more detailed look at this subject.

Whether or not COVID-19 is spread in this fashion, the fact remains that many types of pollutants and bacteria can be spread through air mixing and there are means to prevent these types of airborne contaminants. In fact, there are means to prevent this while also accomplishing more efficient operation.

One important area in HVAC systems is the ability to operate efficiently and reduce long term energy costs. Heat exchanger technology selection is a significant operational cost driver. Most Air Handlers, especially in large buildings, implement some type of “energy recovery” heat exchanger to help condition incoming/fresh air. By implementing a HX at this point, it relieves the load on the higher operating cost heaters and cooling coils. Therefore, the two main design considerations to recover energy with heat exchangers are thermal performance and operating cost:

  1. Thermal Performance: The more effective your heat exchanger, the closer you can get the incoming air to the desired building temperature, which leads to reduced operating costs.
  2. Energy Recovery Component Operating Cost: These heat exchangers are typically passive (no energy) or low energy consumption components to the system. Therefore, the operation of the heat exchanger is much cheaper than allowing heaters or cooling coils to fulfill the entire heating/cooling process.

Two of the more effective options in terms of energy recovery for side-by-side airflow systems are Enthalpy Wheels and Air to Air Heat Pipe Heat Exchangers (AAHX).

An Enthalpy Wheel essentially mixes fresh outdoor air with the conditioned exhaust air of the building by spinning. An example is shown in Figure 1. The direct contact mixing is effective from a heat exchange perspective; however, it does pollute the fresh air with any contaminants collected through the circulation of air within the building. Additional filters and maintenance are often required to meet clean airflow requirements, and can lead to downtime or added costs.

Energy Wheel www.1-act.comFigure 1. Energy (Enthalpy) Wheel Operation

Air to Air Heat Exchanger www.1-act.comFigure 2. Air to Air Heat Exchanger Operation

AAHX technology shown in Figure 2, completely isolates the two airstreams, making it an ideal choice of heat recovery heat exchanger for HVAC systems in hospitals, cleanrooms and other high occupancy facilities where air cleanliness is of critical importance.

The heat pipes provide extremely efficient heat exchange to fin stacks that span the entire volume of the air duct. Click here for more information on how heat pipes achieve efficient heat transfer:  While the heat pipes span both airstreams, the AAHX is designed such that no air enters the opposite duct. See Figure 2 for operating principles of ACT’s AAHX.

Any debris, dust, bacteria, etc. that is collected within the building, is safely exhausted to the outside without any risk of recirculating or contaminating the fresh incoming air. Many buildings with clean requirements often state “no cross-air contamination” in their HVAC specification.  The AAHX can meet his requirement, can provide efficient heat exchange, requires no energy consumption and can be implemented into almost any geometric configuration. When suggesting a product for clean air buildings, the AAHX should be the top consideration.

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