Enhanced Dehumidification and Energy Recovery in Tampa Bay

Whenever I visit Florida, I’m reminded of just how drastically climates can differ—even from one region of a country to another. My native Pennsylvanian summers certainly have their fair share of hot and humid air, but that first step into the Florida sun never ceases to amaze me; with the dependability of a German clock, I’m greeted by a wall of humidity so thick, you can practically smell the mosquitos on the breeze.

This solidifies two understandings in my life; the first is that Southern readers will invariably find amusement in my experience with real humidity; the second is how critical a quality climate-control system is. These systems must be capable of ensuring a comfortable and safe environment inside a structure, and they need to be optimized according to the specific climate outside. For hot and humid climates such as Florida, the necessity of such a system is heightened.

ideal solution: Wrap-Around Heat Pipe HEat Exchangers

At Advanced Cooling Technologies (ACT), we tackle a variety of thermal challenges for many different types of environments, each with its own set of obstacles. Experience in overcoming these obstacles allows us to strategize the best possible solutions for any number of scenarios. So, when ACT was approached to support the engineering and installation of an energy-recovery system for a high-rise in the Tampa Bay area, our team was prepared to develop an effective system to meet the customer’s requirements and the challenges that Florida’s climate presents.

The chosen system was ACT’s innovative Wrap-Around Heat Pipe Heat Exchanger (WAHX). The WAHX system allows buildings to have controllable reheat and enhance the dehumidification of the hot airstream. The result is a massive increase in HVAC efficiency and energy savings. Every WAHX system has tonnage capacity savings and MBTU/hr savings from the reheat it provides. In this particular case, the cost to install a WAHX system at the high-rise was $36,000; a payback analysis by the engineering teams at ACT and our Florida representatives determined that—thanks to the incredible Florida humidity—the installation cost would be paid back in just one-and-a-half years, with savings of $23,869 per year for the life of the air handler.

There is obviously a strong incentive to pursue these types of energy savings, and a WAHX system can be installed at any phase of the commissioning process, but a lot of careful planning goes into the installation of such a system.

There are three installation methods that vary in difficulty

The optimum installation point is at the air-handler unit (AHU) manufacturer’s factory. The next best choice is to have the AHU sent to ACT’s facility for installation. The final way (and the most challenging option) is to install the energy recovery system on site after the AHU has been assembled, as was the case with the Tampa Bay high-rise.

To complicate matters, the AHU—in this case, a Dedicated Outside Air Unit (DOAS)—was located on the 8th floor mezzanine of the office building with limited space for installing the WAHX system. These size constraints had to be accounted for at the engineering level in order to produce the most efficient system possible.

Installation

Always ready for a challenge, ACT’s engineering team, in coordination with our partners, was able to optimize the WAHX’s design for the available space. In conjunction with the DOAS unit, the WAHX system provides 12⁰ F of both precooling and controllable reheating. The DOAS system directly draws in warm, outside air that the WAHX system’s first coil lowers by the 12⁰F designed level, thus accomplishing tonnage savings by the reduction of the incoming air temperature. The combination of the cooling coil and the WAHX precooling helps to dehumidify the hot airstream. The adjoined reheat coil then raises the temperature to deliver dry, neutral air to the building’s lobby and hallways, ensuring that the Florida humidity stays outside, and occupants remain comfortable inside.

This installation also included ACT’s Active Thermal Valves (ATVs) to control the level of reheat per the requirements of the AHU and building-management systems. The ATVs individually control the heat transfer between the WAHX precool and reheat coils. Since this installation featured a two-row system, the valves were staggered into four on/off relay sets. As the outside air drops below the design point, more reheat is required to maintain the desired delivered air temperature of 61.9⁰.

Photo 1: Pipe-to-Pipe WAHX systems have individual heat pipes that connect to the pre-cool and reheat WAHX coils. Each pipe has its own thermal valve for reheat control.

To complete the installation, an insulated alcove cover was placed over the heat pipes, and the control enclosure was wired to the building’s HVAC management system, as seen in Photo 2. If this were a factory installation, the heat pipes would have been located inside of the air handler. However, as this installation occurred on-site, the project required the heat pipes to be located on the outside of the air handler, thus necessitating the cover. It should be noted that system performance is comparable between these two installation methods.

Photo 2: ACT-BMS interface cabinet. The four-stage control is wired to the four relays that turn 25% of the heat pipes on/off depending on temperature conditions.

In total, it took our team three days to install the retrofit. The system is now operational, and the high-rise is already benefitting from the massive dehumidification and energy-recovery benefits of ACT’s WAHX system. In this way, the customer is able to conquer the hot and humid Florida weather, and with the resultant energy savings, the system will be paying for itself in no time.