The overall objective of this project is to demonstrate a passive condenser loop technology that can provide significant energy and water savings. Most current systems use a pumped condenser water loop to transport waste heat to an open loop cooling tower, and the heat is rejected via evaporative (wet) cooling. Compared to legacy processes, this technology is used for heat rejection instead of an open loop cooling tower, which enables dry operation to save water when ambient air has sufficient cooling capacity. The passive condenser loop is fully enclosed, has no freezing issue, requires no maintenance, operates passively, and is able to operate in both wet and dry modes, providing significant resilience improvement for building heating, ventilation, and air conditioning (HVAC) systems.

The passive condenser loop uses a two-phase loop thermosyphon to transport waste heat from the chiller to the cooling tower, instead of using the current pumped single phase water loop. A two-phase loop thermosyphon is a vacuum sealed loop filled with working fluid (e.g. refrigerant) that is able to transport large amounts of heat passively without additional energy input (e.g. electricity for mechanical pumps). The waste heat from the chiller condenser vaporizes the working fluid, drives the vapor/two-phase flow to the condenser. The condensate in the liquid return line provides a gravity head that forces the flow to circulate in one direction. Benefiting from this gravity aided passive two-phase system, the condenser has to be higher than the evaporator. It is not uncommon that the cooling tower is installed on the rooftop and the chiller is located on the ground. In addition to the passive operation, the two-phase system provides better thermal performance. First, the two-phase loop thermosyphon uses latent heat, in which the working fluid is able to maintain almost isothermal conditions. In contrast, the pumped water loop uses sensible heat, in which a 10 degree F temperature differential is typically required for the heat transfer. The isothermal condition of the two-phase loop thermosyphon minimizes the ∆T between the chiller and the evaporative condenser. Second, the heat transfer coefficient of the two-phase flow is higher than the single-phase flow, which further reduces the ∆T between chiller, working fluid, and evaporative condenser. Consequently, the reduced ∆Ts results in a lower condensing temperature of the chiller and therefore a higher coefficient of performance can be achieved. Advanced Cooling Technologies, Inc. (ACT) is a small business located in Lancaster, PA. ACT specializes in advanced two-phase thermal management with products sold to all major military primes. ACT has constantly applied advanced thermal management technologies to building HVAC and energy sectors. ACT will work with evaporative condenser provider, Baltimore Aircoil Company, engineering service company, and Department of Defense (DoD) energy manager from the demonstration site to conduct the demonstration. 

The technology can be applied to most of the water-cooled chillers, which are commonly used in larger buildings. For a 250-ton chiller system, it is estimated that the technology will be able to provide ~$330K life cycle saving (20 years) compared to the current pumped water loop with open loop cooling tower at equivalent full load hours = 2,000 hours, and around five years of the simple payback. The above estimation is based on the open loop cooling tower. Faster payback can be achieved if a closed-circuit cooling tower is used due to similar capital cost but much lower operational cost. (Anticipated Project Completion - 2028)