Final Design

Overview

Functional requirements

The completed design achieved the following main functional requirements

- Is completely portable
- Dissipates 100 W of heat from the body
- Operates for at least 1.5 hours per battery
- Is a watertight system
- Reach target temperature within 2 min

This project proposes a cooling vest design that utilizes thermoelectric cooling devices, or Peltier devices, to directly convert electrical power to a temperature difference.

Generally, Peltier devices consist of alternating p- and n-type semiconductor pillars connected on either side by thermally conductive plates. When electrical current is applied to the semiconductors, heat is drawn from one end of the semiconductor to the other. The plates heat or cool depending on which end the semiconductor they are in contact with and form the hot side and cold side of the Peltier device.

Fully Assembled System

In the proposed vest, both sides of the Peltiers are in contact with custom-designed water blocks that allow direct contact with running water. The water loop in contact with the cold side distributes cold water throughout the vest. The water loop in contact with the hot side cools the Peltier device to maintain efficiency.

This system provides the user with almost immediate cooling across the torso for at least 1.5 hours per battery by simply turning the device on.

Depiction of final system loop

Water Block and Peltier Assembly

Hot Side

The hot sides of the Peltier devices were directly cooled by the water running across the Peltiers. Heat was absorbed by the water which was cooled by a radiator and fans; heat was expelled to the environment. The components making up the hot side were kept inside the backpack. The only component exposed to the environment were the fans and radiator. The front faces of the fans were covered by fan guards in order to avoid a stall. Rubber was added to the perimeter of the radiator in order to protect it from possible bumps or falls. The water blocks sit in the lower part of the backpack, with the radiator in the upper compartment.

Cold Side

Vest Inside and Outside View

23 meters of tubing were woven through a mesh vest in a series of 5 circuits. Cold water circulated through the tubes which ran across the user’s torso. Body heat was absorbed by the water which was then cooled by the Peltier devices. The Peltier devices, water pump, and water blocks were located in the backpack. A compression vest was worn over top to ensure proper contact between the tubes and the user’s skin.

Control System

Power Management System

The purpose of the control system is to deliver energy from the battery to the Peltier devices, pumps, and fans. The battery voltage (22.2 V) is not at the correct input voltage for these systems. To get the correct input voltages, the battery voltage is stepped down with buck converters; buck converters reduce a higher DC voltage to a lower one.

One of the buck converters converts the battery voltage to 12 V, for the pumps and the fans, which run at 12 V. The other buck converter converts the battery voltage into a variable lower voltage for the Peltier devices. This voltage is controlled by the user with a potentiometer dial. The user also has a switch to shut off the system.

The control system also utilizes a battery management system (BMS). This device ensures that each battery does not over-discharge.

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