Utilizing Fan Coil Unit return to fullfill fresh air requirements

In summary, the conversation discusses concerns about outside air compliance and humidity control in a common but problematic configuration. The question is also raised about the fans being constant or variable speed and always running or cycling. Ultimately, the concern is maintaining positive pressure in the building for better indoor air quality.
  • #1
tj00889
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TL;DR Summary
Hello,
I'm currently working on an HVAC Villa project in Dubai where the client has requested that he does not wish to pay for a dedicated fresh air fan to provide fresh air. He added that the common method of doing this in commercial projects in Dubai is to extend a fresh air duct from outside to the FCU return plenum as shown in the drawing. Can this provide sufficient control of how much fresh air will enter to be compliant with ASHRAE 62.1 and what problems can I expect.
Thank you very much
Schematic.PNG
 
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  • #2
Great question, with multiple facets/layers. I'll get back with more when I have more time, but yes you are right to be concerned about outside air/62.1 compliance. Also, this configuration will not adequately control humidity. It's a bad idea, but unfortunately a common shortcut.

Question for you: are the fans constant or variable speed? Always running or cycling?
 
Last edited:
  • #3
russ_watters said:
Great question, with multiple facets/layers. I'll get back with more when I have more time, but yes you are right to be concerned about outside air/62.1 compliance. Also, this configuration will not adequately control humidity. It's a bad idea, but unfortunately a common shortcut.

Question for you: are the fans constant or variable speed? Always running or cycling?
The fans are constant speed and cycling.
What I am worried about is if the positive pressure buildup in the room would stop fresh air supply all together. There is also the issue that seeing as there is no way to maintain the building at positive pressure with this configuration, I was wondering if there is anything in ashrae i could use that states that maintaining the building at positive pressure is a requirement or at least a suggestion for better indoor air quality
 

1. What is a fan coil unit (FCU) and how does it work?

A fan coil unit is a type of air conditioning unit that uses a fan and a coil to cool or heat air. It works by drawing in air from the room, passing it over a coil filled with cold or hot water, and then blowing the conditioned air back into the room.

2. Can a fan coil unit be used to provide fresh air?

Yes, a fan coil unit can be used to provide fresh air by utilizing the return air from the room. The return air is filtered and then mixed with fresh outdoor air before being conditioned and distributed back into the room.

3. How does utilizing fan coil unit return help fulfill fresh air requirements?

By using the return air from the room, the fan coil unit can help fulfill fresh air requirements by providing a continuous supply of fresh air to the room. This helps improve indoor air quality and maintain a comfortable and healthy environment.

4. Are there any limitations to utilizing fan coil unit return for fresh air requirements?

Yes, there are some limitations to utilizing fan coil unit return for fresh air requirements. The amount of fresh air that can be provided may be limited by the size and capacity of the fan coil unit, and the outdoor air temperature and humidity levels may also affect its effectiveness.

5. What are the benefits of utilizing fan coil unit return for fresh air requirements?

Some benefits of utilizing fan coil unit return for fresh air requirements include improved indoor air quality, energy efficiency, and cost savings. By using the return air from the room, less energy is required to condition the air, resulting in lower energy bills. Additionally, the use of a fan coil unit can also help reduce the need for separate ventilation systems, saving on installation and maintenance costs.

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