HEAT RECOVERY TECHNOLOGIES

Alliance Air Products uses sever heat recovery technologies. Here is a review of some of these technologies:


heat wheel:

A heat wheel is a rotating apparatus generally used to reduce the energy consumed by air-conditioning equipment in locations with higher than normal outdoor ambient temperatures or humidity’s. It functions as a rotary heat exchanger, which means that it continually attempts to achieve thermal equilibrium. The device operates by having a warm air stream and a cold exhaust air stream flowing through its opposing halves, making use of these counter-streams to temper the incoming outside air (cooling hot outside air and to heating cold outside air).


Heat Weel

The physical structure of a heat wheel resembles a thick circular disk with a divider in the middle of two air ducts. One air duct has warm outdoor air passing through it, and the other duct has the return air stream passing though it on way to an exhaust fan. Filters also are in placed in both air streams in an attempt to keep the apparatus clean.

Heat wheels do require the most amount of labor intensive maintenance to keep their efficiency.

The heat wheel accomplishes thermal equilibrium by first being chilled by the cooler return air. When its cold portion rotates to encounter the warm outdoor air stream, it then absorbs heat from the air. As the device absorbs warmth from the air, the outdoor air stream temperature consequently drops. When the wheel rotates back to its starting point, it then sends the absorbed heat into the cooler exhaust air stream while simultaneously being once more chilled.


air to air heat exchanger:

Air-to-air heat exchanger is a fixed-plate (non-rotating) heat exchanger. It can be used in two (2) distinct applications - energy recovery and dehumidification.


Plate Type Heat Exchanger
  • Energy Recovery:
    In this application, the air-to-air heat exchanger is usually used to recover sensible energy. It is more cost-effective in smaller units (less than 10,000 cfm). It is also used in cases where cross-flow issues are critical (whereby the two air steams cannot be allowed to mix). The exchanger preheats the supply air during winter and precools the supply air during summer.

  • Dehumidification:
    In this application, the air-to-air, fixed-plate heat exchanger is used to create a dedicated, 100 percent outdoor-air unit that provides dehumidified ventilation air to a space at room-neutral temperature. It is also used where the ventilation cooling load accounts for the majority of the system cooling load, and in humid environments where comfort and moisture control are the primary concerns.


heat pipe:

A heat pipe is a thermal transfer technology that utilizes no moving parts, has two coils (pre-cool and re-heat), and uses a refrigerant that moves the heat from one coil to another through a phenomenon known as thermo syphoning. This is the same principle that causes heated air to rise and cooled air to fall.

Heat pipes may be described as having two sections: precool coil and reheat coil. The first section is located in the incoming air stream. When warm air passes over the heat pipes, the refrigerant vaporizes, carrying heat to the second section of heat pipes, placed downstream. Because some heat has been removed from the air before encountering the evaporator coil, the incoming air stream section is called the precool coil.

Air passing through the evaporator coil is assisted to a lower temperature, resulting in greater condensate removal. The "overcooled" air is then reheated to a slightly higher temperature by the reheat heat pipe coil, using the heat transferred from the precool heat pipe coil.

This entire process of precool and reheat is accomplished with no additional energy use. The result is an air conditioning system with the ability to remove 50 to 100% more moisture than regular systems.