Innovative Energy Engineering



Ventilation & Exhaust

Pollutants or noxious gases such as CO2, VOCs, and odors need to be removed and fresh air with O2 needs to be supplied. Good Indoor Air Quality (IAQ) is required to protect health and life safety.

Supply air requirements typically are based on occupancy loads and exhaust requirements typically are based on pollutants produced. For most spaces these requirements don't balance. It is best to balance the supply and exhaust flows (chose the higher of the two) because any imbalance is balanced by uncontrolled infiltration or exfiltration. In some cases this imbalance is desired to control pressure between spaces. An example would be a garage being kept at negative pressure compared to an adjacent office to prevent any pollutant transfer to the office. Air from spaces requiring exhaust must be "exhausted" to the outside and must not be recirculated. Few exceptions may be that locker room air can be used as makeup air for bathrooms etc.

Code determines minimum requirements and the Jurisdiction Having Authority (JHA) makes final decisions. Most codes are based on the International Mechanical Code (IMC), but States' and local codes may differ in some aspects. ASHRAE Standard 62 is the basis for many codes and often is required by clients (i.e. for LEED certification).

Energy Recovery and Dedicated Outside Air Systems

Ventilation loads can be reduced by up to 75% by use of Energy Recovery Ventilators (ERV) that recover latent (moisture transfer) and sensible energy. In winter outside air (OA) is preheated, and in summer OA is precooled and de-humdified. Heat Recovery Ventilators (HRV) only recover sensible energy. Costly downstream equipment can be downsized or eliminated. Very dirty air with high filtration requirements can make ERV impractical. Grease-laden air (kitchen exhaust) can not be routed through the heat exchanger. All ERV have minor cross-contamination (1-5% depending on type and pressure differences). This is not critical in most building applications but may be a problem in biohazard and other applications.

Especially for cooling, wheel ERV are more efficient than Plate ERV. Sensible-only runaround loop use water or glycol coils in in supply and exhaust air flows. Those are less efficient and require a pump, but don't allow any cross-contamination. Heat pipe systems work similarly but without the need for a pump.

Air leaving the ERV is pre-treated, but not at the required condition. In most cases it is beneficial to further treat the air before it enters spaces or other equipment. This can be done by addition of cooling, heating and other energy recovery devices. Especially for dehumidification this treatment is beneficial. The system for this treatment of air typically is referred to as Dedicated Outside Air System (DOAS).

Opportunities for Improvement

Specialty Applications

Many applications are proprietary to certain industries and follow industry-specific guidelines. The National Institute for Occupational Safety and Health and OSHA also provide reference material:

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