INTEGRATING AN INDOOR AIR BIOFILTER INTO A BUILDING

As described thus far, the use of an indoor air biofilter involves the creation of a wall of hydroponic plants with circulating water and air that is integrated into the various other systems of a building such as the structure, HVAC and electrical systems. The place to start is by first assessing where and how large an area to make available for the indoor air biofilter. Typically, this means that a vertical wall area in an open area of the building needs to be available such as in an atrium or open stairway area. It could also be the wall of a gathering place, lobby, a central area, or a passageway. This vertical wall approach provides the maximum possible green space with minimum use of floor space. The vertical wall itself serves as the basic structural support for the components of the system and will need to be confirmed that it can accommodate the additional load. Typically, an indoor air biofilter will add approximately 11 to 16 pounds of dead load per square foot of green surface area. Allowing for this additional load should be readily accommodated in most building designs.

Once the location and loading are accounted for, the next area to integrate with is the HVAC system. Two different approaches are possible here. First, the indoor air biofilter can be constructed with internal or onboard air handling fans that can be used to draw air through the biofilter then release that cleaned air directly back into space that it is serving. This makes it a fairly closed system that serves the immediate surrounding space but not the rest of the building, although it is certainly possible to duplicate this approach multiple times throughout a building. Air flow generated by the building HVAC system would not likely be impacted by this first approach, although supply and return grilles would need to be located to complement, not compete with the biofilter fans. The second approach is to connect the biofilter directly to the HVAC system. In this case the HVAC fans draw the indoor air through the biofilter and distribute the cleaned air throughout the building.

A biofilter mounted directly on the wall can be constructed in a variety of sizes and in a variety of locations. Image courtesy of Nedlaw Living Walls Inc.

 

WESST CORP.

Built: January 2009 Architects: Diamond and Schmitt Architects Address: Albuquerque, New Mexico This LEED Silver building was among the first indoor air biofilters constructed in the United States. A great project that incorporates great natural light emitted through the glass fronting exterior wall.

When looking at the HVAC integration, it is important to consider both the quality of clean air generated and the quantity of air treated. Quality speaks to the efficiency and effectiveness of the indoor air biofilter removing contaminants as discussed previously. The quantity of air comes into play when determining what rate clean air can be delivered either to a contained area or to a full HVAC system. This is captured as a clean air delivery rate (CADR) which is calculated as the removal efficiency (expressed as a percentage) multiplied by the velocity of the air flowing through the system usually measured in cubic feet per minute (cfm). Hence, if a biofilter is working at 85 percent efficiency, then it will produce 85 cfm of clean air for every 100 cfm of air brought into the system. Note that this means the output of clean air is not limited by the biology of the system rather it is limited only by the amount of air flow into biofilters. Within typical operating conditions, the more air that goes in, the greater the quantity of clean air that goes out.

Since this is a hydroponic (water-based) system, a good quality water supply is needed. The typical approach is for a catch basin or reservoir to be included at the base of the biofilter to hold a small reserve of water. This water is then pumped from this basin up to the top of the system and flows down through the biofilter to nourish the plants that are hosting the beneficial microbes. Note that if this basin is kept filled with water and in some cases stone, then it could reach over 130 pounds per square foot of floor area which will need to be accommodated. The basin will need occasional maintenance, so a drain must be provided for that purpose or simply for the purpose of regulating the water level in the basin. Note that depending on the quality of the water provided, there may be some occasional salt build up in the basin or the rest of the system that will require periodic draining and cleaning.

Plants of course need light to grow and an indoor air biofilter needs light too. Natural daylight is certainly preferred and part of green building designs in general since people also thrive when they have views and access to daylight. In cases where natural daylight is a possibility, it should definitely be worked into the space where the biofilter is located so that the daylight will shine on the plants. In cases where this is not practical or possible, then supplemental electrical lighting can be used. Those lights will only need to be lit for a portion of the day, not 24 hours, and can be selected to be very energy efficient. In this way the added energy use of the biofilter remains small.

Finally, similar to any botanical system, indoor air biofilters generate humidity and some dripping or splashing may occur. This should be taken into account when determining the placement of the system and choosing the finishes around it. Only the materials forming the reservoir or basin need to actually contain water and be waterproof. The rest simply need to be tolerant of occasional spray or a little localized increased humidity. For the most part, a full range of commercial building finish products can be used that can be selected to blend with the interior design of the rest of the building.

Biofilter Design Options Section

With the above basics established, it is now possible to look at the various choices available for the design of the indoor air biofilter itself. The first fundamental choice has to do with wall mounting options. The biofilter will require a basic infrastructure and framework to support the plants, draw air through it, and provide the hydroponic watering. In the simplest manner, this framework can be mounted directly to a portion of an interior wall. Since there is some depth to the framework, there will be an exposed edge on each end that will need to be covered with finish or trim material. The plants will protrude out from the frame and the water basin at the base will likely extend a bit further, but can be finished appropriately.