Cooling  Coils 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. The addition of a dehumidifier reduces moisture in the air. The  cooling  unit,  placed  in  any  convenient  location outside the building, produces chilled water that is circulated  through  the  cooling  coils  near  the  air- conditioned space. 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. The warmed water is then returned to the unit. Fan-Coil  Units You have probably seen fan-coil units in a school or motel  room.  These  units  contain  a  fan,  coil,  falter, condensate drain, and sometimes, an outside-air inlet. A 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 or thermostatically  controlled.  A  piping  system  provides hot or cold water to each unit. HEATING  AND  AIR-CONDITIONING LAYOUT Figure 4-12 (a foldout at the end of this chapter) shows  a  heating  and  air-conditioning  layout  for  a hospital. You 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. Note the cooling towers,  that  have  not  as  yet  been  mentioned.  In  a 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 efficient.   You   can   read   more   about   cold-water air-conditioning  systems  in  the  UT2  TRAMAN. In  figure  4-12,  you  can  see  the  line  of  air- conditioning  ducts  running  from  each  of  the  air- conditioning units. 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. On each of 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. This indicates an outlet for the conditioned air. In this case, the outlets are diffusers, and the capacity of each diffuser, in CFM, is inscribed. Note 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.  Referring  to  the 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. This last reduces the pressure to that for which the unit coils are designed. The steam condensate leaving the unit first passes a gate valve, then a strainer, then a union, and then a steam trap. This 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 return  lines. Beyond the steam trap, there is another union, next comes a check valve, and finally a gate valve. A check valve,  as  you  know  from  the  EA3  TRAMAN,  is  a one-way valve. It permits passage in one direction and prevents  backup  in  the  opposite  direction. CHECKING AND EDITING CONSTRUCTION  DRAWINGS Every  drawing  prepared  in  the  drafting  room  must be  checked  and  edited.  As  a  capable  EA2,  you  maybe delegated  the  job  of  doing  so.  When  checking   a drawing, you are inspecting it to make sure that it accurately conveys the information contained in the data source. That source may be survey field notes, sketches, 4-10