Lancaster, Pennsylvania – June 15, 2015.Advanced Cooling Technologies, Inc. (ACT), Lancaster, PA., was chosen by the Penn State area Centre Area Transportation Authority (CATA) to provide heat pipe heat exchangers for incorporation into the make-up air units for its new state-of-the-art bus transfer terminal building and maintenance facility, Figure 1. The heat pipe heat exchangers will preheat the incoming cold air, during the winter season, by transferring energy from the exhaust air stream. The transport authority has a fleet of 92 natural gas engine buses serving 32 routes with over 7.3 million riders annually. ACT’s energy recovery systems have the ability to save over $2,500/week in heating utility costs.
Project Background: CATA’s fleet of busses, Figure 2, are powered by natural gas, which is significantly cleaner and less polluting than traditional diesel powered busses. However, when the busses are stored indoors or when they are being serviced in the maintenance bays, the engine exhaust products can still be potentially hazardous to the people that work in these facilities. Therefore, the make-up air units are designed to provide a significant amount of fresh air to prevent unhealthy concentrations of carbon monoxide and other byproducts of the combustion process. The requirement for numerous air changes per hour puts a high demand on the heating systems during the winter season.
While large amounts of fresh air are being drawn into the facility, a nearly equal amount of air that has already been heated to the space temperature is being exhausted from the building. ACT’s air-to-air heat pipe heat exchangers are placed across these two air streams. The heat pipe coil, which is in the warm exhaust stream, extracts thermal energy from the exiting stream. This energy is transferred to the heat pipe coil that is the incoming air stream through the highly conductive heat pipes. The heat pipe coil in the incoming stream delivers this thermal energy to the incoming air stream, effectively preheating it prior to passing through the active portion of the air handler (gas burner). The result is a significant reduction in the amount of energy required to heat the incoming air up to the space temperature.
The Application: While there are other types of energy recovery devices, for example plate heat exchangers and enthalpy wheels, the heat pipe was a much better fit for this application. Plate type heat exchangers where too large to fit into the energy recovery section of the make-up air handlers. Typically, the energy recovery section of the air handler is designed to incorporate a sensible or enthalpy wheel. However, in this application, with hazardous (exhaust fumes) and potentially explosive (natural gas) gases, the wheel is not an acceptable solution because of the significant amount of exhaust gas recirculation that is inherent to the wheel design. Therefore, the heat pipe heat exchanger with the same slim profile as a wheel and the near zero leakage between the exhaust and incoming air streams was the best solution. The heat pipe heat exchanger has the additional benefit of decades of maintenance free service. There are no motors, bearings, drive belts or that require periodic maintenance or replacement.
Project Scope and Payback: The scale of the project involved the engineering and manufacturing of 11 air-to-air heat exchanger (AAHX) systems ranging in size from approximately 4 ft. x 5 ft. all the way up to 6.5 ft. x 8 ft. Each self-contained AAHX unit was sent to the air handling manufacturer for final installation into the make-up air handlers.
The calculated energy savings versus the cost of the ACT AAHX units results in a payback period of less than two years. A few other key statistics are provided below.
- Total energy transferred for the 11 systems is over 3,500,000 Btu/Hr.
- At design conditions, the CATA ACT-AAHX systems save over $2,500/week.
- ACT-AAHX reduces Greenhouse gas emissions by approximately Five (5) tons/day
- The ACT-AAHX units are rated for over 20 years of continuous operation
- No required maintenance other than replacing the air handlers air filters