Write short notes Roof Pond, Stack Effect, Wind Catchers, Cross Ventilation, Axial Fan, Diffusers

(a) Roof Pond 

The roof pond concept combines the traditional functions of a roof with a means of natural heating and cooling. The key elements of the concept are:

  • Use of water for heat storage and as an interim heat sink.
  • Thermal coupling of the water with the occupied spaces.
  • Exposure of the water pond to sunshine for heating.
  • Exposure of the water pond to the night sky for cooling.

The principal constituents of a roof pond system are the container for the water, the supporting structure, and the thermal insulation with which the thermal coupling and decoupling of the water are achieved. With these elements, a roof pond can contribute to thermal comfort in all seasons.

Evaporation in a pond is proportional to the air-water contact area. Such area, increases considerably with the incorporation of fountains and sprayers, thus producing an extra decrease in water temperature. The smaller drops, the greater the air-water contact surface is increasing evaporation. A single water drop moving through still air experiences two processes: Heat flows from the air to the drop (if the air is hotter than the drop). Water evaporates from the drop to the surrounding air. The hotter the drop is, the more water will be evaporated. Inward heat transfer will warm it up but evaporation will cool it down.

As a result of these two opposite tendencies, an equilibrium drop temperature is reached (the wet-bulb temperature of the air). Once the drop has reached the wet-bulb temperature, the extra energy needed to evaporate more water has to come from the surrounding air. Cooling by fountains is achieved simultaneously in two different ways, by cooling directly the air of the surrounding space and by cooling the water of the pond.

(b) Stack Effect 

The stack effect or chimney effect is the movement of air into and out of buildings through unsealed openings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences.

In architectural design, the stack effect refers to passive air movement throughout a building due to variances in vertical pressure initiated by thermal buoyancy. If the air within a building grows warmer than the temperature of the surrounding outdoor air, the warmer and lower-density air will rise.

The stack (or chimney) effect occurs in tall buildings when the outdoor temperature is substantially colder than the inside temperature. Hot air rises, so the warmer, indoor air is buoyant and presses upward to exit the building through a variety of openings in the upper floors.

(c) Wind Catchers 

A Windcatcher, also known as a wind tower, wind scoop, Malqaf, or Badger, is a traditional cooling architectural element that has been used for thousands of years in countries with severe hot climates. Wind catchers are one of the parts of Persian traditional houses, the main function of which is generating thermal comfort. They generate cool air in two ways: moving air and generating evaporative cooling. Wind catchers may be defined as traditional air conditioners operating by using renewable wind energy. 

Ryan Frayne spent his life inventing--even when his time was drawing short. In his mid-20s, before he was diagnosed with terminal pancreatic cancer, he created Windcatcher, a mattress pad that fully inflated with just a few breaths. 

Windcatchers are traditional in Persian architecture, as well as in Ancient Egypt, and can be found across the Middle East. They generally take the form of small towers installed on top of buildings, although they can be found in several different shapes and structures.

(d) Cross Ventilation 

Cross ventilation (also called Wind Effect Ventilation) is a natural method of cooling. The system relies on wind to force cool exterior air into the building through an inlet (like a wall louver, a gable, or an open window) while the outlet forces warm interior air outside (through a roof vent or higher window opening).

Ventilation is necessary in buildings to remove 'stale' air and replace it with 'fresh' air: Helping to moderate internal temperatures. Reducing the accumulation of moisture, odors, and other gases that can build up during occupied periods.

Windows or vents placed on opposite sides of the building give natural breezes a pathway through the structure. This is called cross-ventilation. Cross-ventilation is generally the most effective form of wind ventilation. It is generally best not to place openings exactly across from each other in space.

(e) Axial Fan

Axial fans are generally used for cooling applications like the ones mentioned below: Process cooling in systems or machinery. Spot cooling of transformers and generators and industrial equipment. Ventilation in warehouses, factories, foundries, laundries, garages, equipment rooms, and engines.

An axial fan is one in which the extracted air is forced to move parallel to the shaft about which the blades rotate. Centrifugal fans extract air at right angles to the intake of the fan and spin the air outwards to the outlet by deflection and centrifugal force. Vane-axial fans tend to be the most efficient fans available for HVAC air-handling units—with efficiencies reaching up to 85%—largely because the direction of the airflow is little changed as it passes through the fan.

Axial fans create low-pressure air, as the design of such fans allows these devices to distribute air somewhat evenly in a defined area. Radial fans, conversely, generate high-pressure air. In other words, they'll create a steady flow of air that can be used to target a concentrated area.

(f) Diffusers.

Plain and simple, a diffuser is used to fill the air in a room with tiny, breathable particles of beneficial essential oils—giving the room a calmer, more pleasant-smelling ambiance. “It's well known that scent is associated strongly with memory,” says Benjamin. Put simply, essential oil diffusers work by emitting essential oils into the air. This means you can inhale and absorb the benefits into your body, which can aid relaxation but also works wonders for your senses. For example, if you're looking to relax after a stressful day, it can make all the difference.

What is a diffuser in ventilation? A ventilation diffuser disperses pressurized air exiting heating ventilation and air conditioning ductwork and provide a decorative finish over the grill box hole holding the ductwork in place. Without an air diffuser, the air exiting the HVAC system would travel in a straight direction.

A diffuser system is an effective means of disposing of heated water from power plants. They mix and dilute the heated water so that temperature rises are rapidly reduced with little environmental impact. In HVAC systems, the air supply diffuser is a device that delivers and ventilates conditioned air in an area, mixes indoor air, and manages air output. It works by reducing the air duct velocity by increasing the static pressure.

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  • Best Overall: InnoGear Ultrasonic 200ml Diffuser.
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