Editing Active cooling (section)

== Building usage ==
Many buildings require high demands in cooling and as many as 27 out of the 50 largest [[Metropolitan area|metropolitan]] areas around the world are located in areas of hot or tropical weather. With this, engineers have to establish the heat balance in order to ensure proper ventilation throughout the structure.

The heat balance equation is given as:

<math>p \cdot c_p\cdot V \cdot dT/dt = E_{int} + E_{Conv} + E_{Vent} + E_{AC}</math>

where <math>p</math> is the air density, <math>c_p</math> is the [[specific heat capacity]] of air at constant pressure, <math>dT/dt</math> is the rate of [[heat transfer]], <math>E_{int}</math> is the internal heat gains, <math>E_{Conv}</math> is the heat transfer through the envelope, <math>E_{Vent}</math> is the heat gain/loss between indoor and outdoor air, and <math>E_{AC}</math> is the mechanical heat transfer.<ref name=":0" />

Using this, it can be determined how much cooling is required within the infrastructure.

There are three active cooling systems commonly used in the residential sectors:

=== Fans ===
{{Main|Fan (machine)|l1=Fan}}

A fan is three to four blades rotated by an electrical motor at a constant speed. Throughout the rotation, airflow is produced and having the surrounding being cooled through the process of forced convection heat transfer. Because of its relatively low price, it is the most frequently used out of the three active cooling systems in the residential sector.

=== Heat pumps ===
{{Main|Heat pump}}

A heat pump utilizes electricity in order to extract heat from a cool area into a warm area, causing the cool area to lower in temperature and the warm area to increase in temperature.<ref>{{Cite web|title=Heat Pump Systems|url=https://www.energy.gov/energysaver/heat-and-cool/heat-pump-systems|access-date=2020-11-11|website=Energy.gov|language=en}}</ref>

There are two types of heat pumps:<ref>{{Cite book|last=Lechner|first=Norbert|url=https://books.google.com/books?id=WjetCwAAQBAJ&pg=PR11|title=Heating, Cooling, Lighting: Sustainable Design Methods for Architects|date=2014-10-13|publisher=John Wiley & Sons|isbn=978-1-118-58242-8|language=en}}</ref>

==== Compression heat pumps ====
Being the more popular variant of the two, compression heat pumps operates through the use of the refrigerant cycle. The vapor refrigerant in the air gets compressed while increasing in temperature, creating a superheated vapor. The vapor then goes through a condenser and converts into a liquid form, dispelling more heat in the process. Traveling through the expansion valve, the liquid refrigerant forms a mixture of liquid and vapor. As it passes through the evaporator, vapor refrigerant forms and expels into the air, repeating the refrigerant cycle.

==== Absorption heat pumps ====
The process for the absorption heat pump works similarly to the compression variant with the main contrast being the usage of an absorber instead of a compressor. The absorber takes in the vapor refrigerant and creates a liquid form which then travels into the liquid pump to be turned into superheated vapor. The absorption heat pump utilizes both electric and heat for its functionality compared to compression heat pumps which only uses electricity.<ref name=":0" />

=== Evaporative coolers ===
{{Main|Evaporative cooler}}

An evaporative cooler absorbs the outside air and passes it through water-saturated pads, lowering the temperature of the air through water evaporation.<ref>{{Cite web|title=Evaporative Coolers|url=https://www.energy.gov/energysaver/home-cooling-systems/evaporative-coolers|access-date=2020-11-11|website=Energy.gov|language=en}}</ref>

It can be divided by:

==== Direct ====
This method evaporates the water which would then travel directly into the air stream, producing a small form of humidity. It usually requires a decent amount of water consumption in order to properly lower the temperature of the surrounding area.

==== Indirect ====
This method evaporates the water into a second air stream and then putting it through a heat exchanger, lowering the temperature of the main air stream without adding any humidity. Compared to direct evaporative coolers, it requires much less water consumption to operate and lowering temperature.<ref name=":0" />