How to adjust the fresh air and recirculated air ratio in a vertical type air handling unit?

Hey there! As a supplier of vertical type air handling units, I often get asked about how to adjust the fresh air and recirculated air ratio in these units. It's a crucial aspect of maintaining good indoor air quality and energy efficiency. So, I thought I'd share some insights on this topic.

First off, let's understand why adjusting this ratio is so important. Fresh air brings in oxygen and dilutes indoor pollutants like carbon dioxide, volatile organic compounds (VOCs), and particulate matter. On the other hand, recirculated air helps save energy by reducing the need to heat or cool large amounts of outside air. Finding the right balance between the two can significantly impact the comfort and health of the occupants, as well as the operational costs of the building.

Factors Affecting the Ratio

Before we dive into the adjustment process, it's essential to consider some factors that influence the fresh air and recirculated air ratio.

Occupancy

The number of people in a space is a major determinant. More occupants mean more carbon dioxide is produced, and thus, a higher proportion of fresh air is required. For example, in a crowded office or a classroom, you'd need to increase the fresh air intake compared to a storage room with minimal human presence.

Activity Level

The type of activities taking place in the area also matters. Spaces where physical activities are common, like gyms or sports arenas, generate more heat and moisture, and may produce additional pollutants. In such cases, a higher fresh air ratio is necessary to maintain a comfortable and healthy environment.

Indoor Pollutant Sources

If there are significant sources of pollutants indoors, such as printers, copiers, or chemical storage areas, more fresh air is needed to dilute these contaminants. On the contrary, in areas with fewer pollutant sources, a higher recirculation ratio can be used to save energy.

Adjusting the Ratio in a Vertical Type Air Handling Unit

Now, let's get into the nitty - gritty of how to adjust the fresh air and recirculated air ratio in a Vertical Type Air Handling Unit.

Step 1: Know Your Unit

Before making any adjustments, you need to have a good understanding of your vertical type air handling unit. Familiarize yourself with the location of the fresh air damper, recirculated air damper, and the control system. Most modern units come with a control panel that allows you to monitor and adjust the airflow rates.

Step 2: Set Baseline Values

Start by determining the baseline fresh air and recirculated air ratios based on the factors we discussed earlier. You can refer to industry standards such as ASHRAE (American Society of Heating, Refrigerating and Air - Conditioning Engineers) guidelines. For general office spaces, ASHRAE recommends a minimum of 15 cubic feet per minute (CFM) of fresh air per person.

Step 3: Use the Control System

Once you've set the baseline values, use the control system of your air handling unit to adjust the dampers. If you need to increase the fresh air intake, open the fresh air damper further and close the recirculated air damper slightly. Conversely, if you want to increase the recirculation ratio, close the fresh air damper and open the recirculated air damper.

Step 4: Monitor and Fine - Tune

After making the initial adjustments, monitor the indoor air quality parameters such as carbon dioxide levels, temperature, and humidity. You can use sensors installed in the space to collect this data. Based on the readings, fine - tune the damper positions to achieve the desired fresh air and recirculated air ratio.

Comparison with Horizontal Type Air Handling Units

It's worth noting that vertical type air handling units have some differences compared to Horizontal Type Air Handling Units when it comes to adjusting the fresh air and recirculated air ratio.

Vertical units are often more suitable for buildings with limited floor space as they are designed to be installed vertically. Their compact design can sometimes make access to the dampers a bit more challenging, but the adjustment process is fundamentally the same. Horizontal units, on the other hand, are typically easier to access for maintenance and damper adjustments due to their horizontal layout.

Benefits of Proper Ratio Adjustment

Properly adjusting the fresh air and recirculated air ratio offers several benefits.

Improved Indoor Air Quality

By ensuring an adequate supply of fresh air, you can reduce the concentration of indoor pollutants, which in turn improves the health and well - being of the occupants. This can lead to fewer sick days and increased productivity in workplaces.

Energy Efficiency

Optimizing the ratio helps save energy. By using more recirculated air when appropriate, you can reduce the load on the heating and cooling systems, resulting in lower energy bills.

Comfort

Maintaining the right balance between fresh air and recirculated air helps regulate the temperature and humidity levels in the space, providing a more comfortable environment for the people inside.

Conclusion

Adjusting the fresh air and recirculated air ratio in a vertical type air handling unit is a crucial task that requires careful consideration of various factors. By following the steps outlined above and monitoring the indoor air quality, you can achieve an optimal ratio that provides a healthy, comfortable, and energy - efficient environment.

If you're in the market for a vertical type air handling unit or need more advice on adjusting the fresh air and recirculated air ratio, feel free to reach out. We're here to help you make the best choices for your building's ventilation needs. Let's have a chat and discuss how we can meet your specific requirements.

References

• ASHRAE Handbook of Fundamentals
• Various industry research papers on indoor air quality and ventilation systems.