Air conditioners use refrigeration to chill indoor air, taking advantage of a remarkable physical law: When a liquid converts to a gas (in a process called phase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds to evaporate and condense over and over again in a closed system of coils. The compounds involved are refrigerants that have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these serpentine, air-chilling coils. When hot air flows over the cold, low-pressure evaporator coils, the refrigerant inside absorbs heat as it changes from a liquid to a gaseous state. To keep cooling efficiently, the air conditioner has to convert the refrigerant gas back to a liquid again. To do that, a compressor puts the gas under high pressure, a process that creates unwanted heat.

All the extra heat created by compressing the gas is then evacuated to the outdoors with the help of a second set of coils called condenser coils, and a second fan. As the gas cools, it changes back to a liquid, and the process starts all over again. Think of it as an endless, elegant cycle: liquid refrigerant, phase conversion to a gas/ heat absorption, compression and phase transition back to a liquid again. It's easy to see that there are two distinct things going on in an air conditioner. Refrigerant is chilling the indoor air, and the resulting gas is being continually compressed and cooled for conversion back to a liquid again. On the next page, we'll look at how the different parts of an air conditioner work to make all that possible.Most  forced-air  furnaces  are  designed  for  the addition  of  a  cooling  coil.  The  coil  is  placed  on  the output  side  of  the  furnace  and  uses  a  forced-air  furnace blower to circulate the air over the cooling coils.

addition of a dehumidifier reduces moisture in the air.general electric hvac units The  cooling  unit,  placed  in  any  convenient  locationdoes a window ac unit have to be tilted outside the building, produces chilled water that ishvac units on sale circulated  through  the  cooling  coils  near  the  air-The air to be conditioned is then blown over the cooling coils and is cooled by the chilled water absorbing the heat from the air. is then returned to the unit. You have probably seen fan-coil units in a school orThese  units  contain  a  fan,  coil,  falter, condensate drain, and sometimes, an outside-air inlet. central unit furnishes air to the unit, and duct coils heat

or cool the air. The amount of air moving over the coils and the temperature of the coils can be manually orA  piping  system  provides hot or cold water to each unit. (a foldout at the end of this chapter) shows  a  heating  and  air-conditioning  layout  for  aYou can see that the air- conditioning plant consists of four separate self- contained units, three of which  are  located  in  the  mechanical  equipment  room, and one on the porch of the ward. towers,  that  have  not  as  yet  been  mentioned.   water-cooled air-conditioning system, cold water is run over the coils of the condenser (rather than air being blown over the coils). The purpose of the cooling tower is to cool the water. Water is sprayed at the top of the tower, and as it falls through the redwood louvers, it is cooled by the air. Sometimes, large blowers force air through  the  water,  making  the  cooling  tower  more

You   can   read   more   about   cold-water air-conditioning  systems  in  the  UT2  TRAMAN. In12,  you  can  see  the  line  of  air- conditioning  ducts  running  from  each  of  the  air-Note that the section dimensions of each length of specified size are noted on the drawing. Notice, too, that these dimensions decrease as distance away from the unit increases. You should notice, also, that some spaces are heated by  radiators,  rather  than  the  air-conditioning  system. These spaces (all the toilets, for example) may contain odors or gases that would make it inadvisable to connect them with the air-conditioning duct system. the radiators, the heating capacity, in British thermal units (BTUs), is inscribed. In each space not connected to the air-conditioning system, you can see an exhaust fan (for ventilation) shown. On each fan, the air capacity, in cubic feet per minute (CFM), is noted.

In each air-conditioned room, you see a circle (or more than one circle) on the duct. outlet for the conditioned air. In this case, the outlets are diffusers, and the capacity of each diffuser, in CFM, isNote that this capacity varies directly with the size of the space serviced by the outlet. Steam  lines  from  the  boiler  in  the  mechanical equipment  room  to  the  air-conditioning  units  and radiators appear as solid lines. Small diagonal lines on these  indicate  that  they  are  low-pressure  steam  lines. Returns appear as dashed lines. In the upper left corner, a detail shows the valve arrangement  on  the  steam  and  condensate  return  lines to  each  of  the  air  conditioners.   mechanical symbols specified in MIL-STD-17B, the detail indicates that in the steam line, the steam headed for the unit passes agate valve, then a strainer, and then an electrically operated modulating valve.

reduces the pressure to that for which the unit coils are The steam condensate leaving the unit first passes a gate valve, then a strainer, then a union, and then a steamThis trap is a device that performs two functions: (1)  it  provides  a  receptacle  in  which  steam  condenses into water and (2) it contains an automatic valve system that periodically releases this water into the rest of the Beyond the steam trap, there is another union, next comes a check valve, and finally a gate valve. valve,  as  you  know  from  the  EA3  TRAMAN,  is  aIt permits passage in one direction and prevents  backup  in  the  opposite  direction. Every  drawing  prepared  in  the  drafting  room  must be  checked  and  edited.  As  a  capable  EA2,  you  maybe delegated  the  job  of  doing  so.   drawing, you are inspecting it to make sure that it accurately conveys the information contained in the data