The Regenerative Dual Duct TM/SM System

System Origin:

Classical HVAC systems are almost all derived from a common basic configuration based on the concept that recirculation of air provides for the most economical operation and outdoor air is introduced through a mixing process when it is thermodynamically appropriate. From a thermal perspective, this is correct, especially in a heating mode. However this technique is an inefficient way to introduce ventilation. It fails to produce any energy savings over a combination of recirculation and a 100% outside air side stream without energy recovery during the cooling season. It fails to produce effective distribution of ventilation air.

The Regenerative Dual Duct System^TM/SM was developed by starting with the most efficient possible method of meeting individual space thermal and ventilation requirements, determined on the basis of eliminating any energy other than what is required to meet space thermal comfort requirements. It completes the process by efficiently processing air in a manner that makes the use of 100% outdoor air significantly more efficient than is otherwise possible with recirculation based systems. 

• To achieve verifiable compliance with ANSI/ASHRAE Standard 62.1 it is necessary to monitor ventilation air delivery rates. The lowest permissible air delivery rate is the minimum amount of outdoor ventilation required to be delivered to each space.

• To meet the need for ventilation most efficiently, the ventilation process must, at worst, be thermodynamically neutral to the heating process and at best provide what cooling benefits can be achieved while minimizing the use of refrigeration. To achieve this heating, cooling and ventilation processes must be functionally independent from a control standpoint, and ventilation air must be of an acceptable humidity condition.

• To effect this in a multiple space environment, heat should be provided locally and be deliverable without the air handling systems being in operation. A dual path ventilation system comprised of a cooling and ventilation air flows, both consisting of 100% outdoor air, should be provided.

  • Ventilation management can be controlled and verified through total flow measurement with a common VAV air terminal unit controller which would be used to control the ventilation deck. The minimum flow would be full shut-off when the space is unoccupied as determined through the use of occupancy sensors. When occupied, the ventilation deck would be used to maintain minimum flow conditions to the space.

  • Cooling is controlled in a manner consistent with a shutoff VAV system, providing cool air to meet cooling loads only.

  • By providing 100% outdoor air in both decks, the ability to minimize air delivery to individual spaces is preserved.

The Regenerative Dual Duct System^TM/SM achieves these goals.

Benefits:

Energy Use Reduction: The Regenerative Dual Duct System^TM/SM minimizes energy use by minimizing total air flow to each space, efficiently processing the air flow delivered, by making maximum use of waste and free cooling energy before using new energy assets, by reducing parasitic system losses, and by eliminating the need for the HVAC system to create it's own loads to maintain comfort conditions. This makes the strategy anywhere between 2.7 (vs. VAV Reheat) and 10 (vs. Terminal Reheat) times more efficient than classical HVAC systems. (ES_IECDDVAV_4_05.pdf)

Indoor Air Quality: Recirculation of air sets up a cycle of concentration of contaminants within a building until the rate of contaminant generation is offset by the rate at which it is exhausted from the space. It also serves to transmit contaminants generated in one space throughout all spaces served by the system. The Regenerative Dual Duct System^TM/SM minimizes indoor air quality problems by disrupting the cycle of concentration, by assuring at least minimum rates of outdoor air delivery to dilute and remove contaminants from individual spaces, and by eliminating the redistribution of contaminants between spaces.

Applications:

Educational Facilities: Educational facilities are high density occupancies with a variety of different occupancies and substantial needs for ventilation. With the energy use of the typical high school in the upper Midwest over 150,000 Btu/sf/year, and energy costs for code compliant designs approaching $2.00/sf/yr, schools are logical applications for Regenerative Dual Duct Systems ^TM/SM. Ventilation is usually the first thing cut by maintenance staff to save energy. Educational facilities are notorious for poor air quality and are the major locus for the transmission of disease throughout communities. Respirable particles given off by a student in one classroom can, and often are, transmitted through a classical air handling system to reach students and staff in other areas, where they are taken home and given to other family members. Regenerative Dual Duct Systems ^TM/SM can save the typical high school about $1.25/sf/year at current energy costs, which is sufficient to return the entire cost of the system in about 6 years at a 15% annual rate of energy cost inflation. Finally, high levels of CO₂ are known to reduce children's attention span. Children taught in schools with good air quality score about 15% higher on standard achievement tests.

Health Care Facilities:

Health care facilities are in crisis. 24-hour-per-day operation and energy use characteristics on the order of 300-450,000 Btu/sf/yr make them attractive energy conservation targets. Hospitals also are breeding grounds for antibiotic resistant strains of bacteria, like MRSA, which have now made it out into the rest of the world. Nosocomial infections involving antibiotic resistant bacteria can quickly and easily turn the cost of an $8,000 hospital stay to an $80-160,000 stay which one in ten infected patients do not survive. Last year, some estimates hold that as many as 100,000 Americans died from these infections.

The Regenerative Dual Duct System^TM/SM has the ability to disrupt two of the primary infections paths: direct- and indirect air-to-wound transmission paths. Outdoor air has long been recognized as superior to recirculated air because outdoor air is naturally sterilized by the UV radiation from the sun. Nosocomial infections involving the air path invariably originate inside the facility. The Regenerative Dual Duct System^TM/SM not only has the ability to sharply reduce the energy requirements of this facility type, but by virtue of the fact that employs 100% outdoor air, it is inherently superior to other strategies with respect to sepsis control. In addition, the process employs technologies that permit the system to act as a microbial scrubber: capturing, killing and removing from the system virtually all viable particles containing bacteria and other pathogens. It also actively removes many gaseous contaminants known to cause problems for respirably impaired patients.

Finally, air handling systems employing recirculation and air-side economizers create pressure imbalances within all types of facilities. When used in health care facilities, these systems cause varying air migration patterns within facilities which result in the migration of air-borne particulates through all areas.

The Regenerative Dual Duct System^TM/SM can easily be configured to serve any and/or all occupancies found within a health care facility while simultaneously addressing these problems.

Research & Development Facilities:

This is the application that the Regenerative Dual Duct System^TM/SM was originally developed for. Requiring high rates of ventilation, close control of pressure relationships between spaces, and positive separation of supply and exhaust sides of the systems, when constructed with corrosion resistant polymer heat exchangers the super efficient Regenerative Dual Duct System^TM/SM is the perfect HVAC system for laboratory applications. It does not require reheat for summer application and reduces the heating and cooling capacity requirements and energy footprint of these energy intensive facilities to about the same as a conventional office building.

Places of Assembly:

Meeting halls, conference centers, exhibition halls, banquet halls, gymnasiums, auditoriums and theaters are all examples of spaces which can be used to support large gatherings of people requiring high rates of ventilation. Anyone who has spent any time in these facilities knows how quickly a person can become uncomfortable in a crowded room. This is a physiological response to excessive levels of CO₂, a known vasodilator, which causes blood vessels close to the skin open up, creating increased blood flow, and causing people to feel warm. Because the Regenerative Dual Duct System^TM/SM is 100% outdoor air, it far more effective in removing odors and excess CO₂ and produces a superior environment with substantially lower operational costs.

Casino's:

Casino's may be the ultimate challenge for HVAC systems. Research by the gaming industry has shown that smoking, like gambling, are addictive behaviors and that 70% of gamblers are also smokers.

Cigarette smoke quickly contaminates duct systems, so any HVAC system which recirculates air anywhere in casinos is a bad design, period. Within a matter of 2-3 months, all areas served by recirculating systems will smell like dirty ashtrays. Most casino's have begun to move to 100% outdoor air systems based on heat wheel, but these carry smoke from the exhaust into the supply, particularly in mid-winter when the wheels see moisture condensation.

The Regenerative Dual Duct System^TM/SM is a far superior solution because there is no mechanism for cross contamination of smoke from exhaust to supply air to occur. Contamination is limited to the exhaust side of the system making the task of keeping both the supply air and supply side system elements clean is much easier.

The energy recovery basis for the system and high levels of heat from gaming equipment satisfied most heating requirements without the need for much supplemental heat in most geographical regions. Casino's would also benefit from displacement ventilation strategies to more quickly and effectively remove most cigarette smoke from occupied spaces. The combination of displacement ventilation and 100% outdoor air makes for a much more pleasant environment, eliminating the problems associated with recirculation and cross contamination, and keeping the indoor environment much sweeter, much longer than any other alternative.