Building owners have multiple choices for saving and recapturing energy, each with advantages and disadvantages, including heat recovery wheels, air-to-air heat exchangers, glycol runaround loops, and heat pipes. Heat pipes are thermal transfer devices capable of transferring heat and energy several hundred times faster than conventional methods. They are highly efficient, relatively inexpensive, require no energy, have no moving parts, no chance for cross contamination, and little to no maintenance is required. Heat pipes can be installed with new air handling units, or retrofit to existing units. They are frequently used on 100% outside air systems.
A traditional heat pipe is a vacuum-tight hollow cylinder filled with liquid that vaporizes when heat comes in contact with the surface of the pipe in the evaporator section. The vapor then travels along the heat pipe to the condenser section where it condenses and gives up its latent heat. The liquid then returns to the evaporator by capillary action via a wick structure, by centrifugal force in a rotating system, or by gravity, and the process repeats.
PJM recently completed a heat pipe retrofit on multiple air handlers for a New Jersey R&D laboratory as part of an air handler renovation. The client, looking to recoup lost energy on exhaust, wanted a low-maintenance option that eliminated the risk of cross contamination. Installation was accomplished by opening the air handler, sliding in a heat pipe cassette, and making the necessary connections. Accommodations were made to capture additional condensate that would be produced when the coil reached dewpoint.
Upon startup of the new heat pipe system, the outside dry bulb temperature (DBT) was 92°F, and the wet bulb temperature (WBT) was 78°F. Within a short amount of time, DBT was reduced to 82°F and WBT was 60°F. All in all, the heat pipe was achieving 17 tons of free cooling.
PJM Mechanical Contractors, Inc. is a multi-faceted mechanical contractor providing construction and installation, service and maintenance, and design/build services in a comprehensive range of mechanical disciplines that include HVAC, plumbing, controls, refrigeration, custom metal fabrication, piping, fire protection, and backflow preventer testing. PJM primarily serves clients in pharmaceuticals, manufacturing, healthcare, institutional, and other various commercial and industrial sectors.