TM 5-6115-590-12 temperature    sensing    and    control    in    MUST    hospital elements that do not utilize the return air ducts.  When remote  temperature  sensing  is  not  used,  a  plug  with  a jumper wire must be plugged into the receptacle on the return air inlet panel. (1)   Cooled  Air  System  (fig.    1-8,  1-9).    The  cooled air  system  uses  two  independent  10  ton  (refrigerating capacity)  refrigeration  systems  for  maximum  flexibility of  operation.    The  two  refrigeration  systems  may  be operated   individually   or   together   to   provide   20   tons cooling  capacity.    Each  refrigeration  system  is  a  vapor cycle closed loop system consisting of an electric-motor- driven   refrigerant   compressor,   two   condenser   cooling fans,   a   refrigerant   receiver,   an   expansion   valve,   an evaporator,     two     recirculating     fans,     a     refrigeration solenoid valve, a compressor bypass solenoid valve, an overpressure switch, a refrigeration de-icing system, and associated   tubing,   fittings   and   refrigerant   level   sight gages.  All electric motors in the refrigeration system are powered by the 400 Hz electrical system and all control components   are   powered   by   the   24V   DC   electrical system.  Output temperature control of the refrigeration systems is automatic with variable adjustment provided. Refrigeration    output    temperature    control    is    accom- plished by three solenoid-operated valves, a refrigerant flow  control  valve,  a  compressor  bypass  valve,  and  a de-icing valve. The de-icing system functions automatically to prevent ice formation on the evaporator core. (2)   Heated Air System (fig.  1-10).   The  heated  air system    uses    two    independent    control    and    mixing systems   connected   to   a   single   source   of   heated   air. Each   system   uses   hot   compressed   air   from   the   gas turbine   engine   compressor   through   the   engine   load control   valve.      The   heated   compressed   air   passes through one or both thermostatically controlled, electrically  actuated  flow  control  valves  into  the  mixing chambers.  The heated air is mixed with recirculating air from the recirculating fans and is distributed through the air  outlet  ducts  to  the  elements  of  the  MUST  hospital. Output  temperature  control  of  the  heated  air  system  is automatic    with    variable    adjustment    provided.        The temperature  sensors,  installed  in  the  return  air  inlets, provide  automatic  temperature  control  of  the  output  air to the selected temperature by opening and closing the flow  control  valves  to  increase  or  decrease  the  flow  of heated     compressed     air     to     the     mixing     chambers. Overtemperature thermoswitches installed in the mixing chambers,  will  actuate  to  close  the  engine  load  control valve in the event heated air temperatures exceed safe maximum. (3)   Ventilating    Air    System.        The    ventilating    air system  provides  for  the  circulation  of  air  without  the addition  of  heated  or  cooled  air.    The  system  uses  the recirculating fans and ducts in the refrigeration systems and heated air systems to circulate ambient temperature air  through  the  other  elements  of  the  MUST  hospital. Vent   openings   in   the   return   air   inlet   panel   may   be opened as required to admit make-up air. e.    Water  System  (fig.    1-11  and  1-12).    The  water system, when provided with an external supply of water will  deliver  hot  and  cold  water  under  pressure  to  other elements   of   the   MUST   hospital.      The   water   system includes  a  cold  water  pump,  hot  water  pump,  exhaust- gas-to-water  heat  exchanger,  exhaust  gas  flow  control valve,   hot   water   storage   tank,   pressure   (surge)   tank, pressure    relief    valves,    check    valves,    pressure    and temperature  control  switches,  and  interconnecting  lines and  fittings.    The  cold  water  pump  receives  inlet  water and delivers the water to the cold water outlet and to the hot water heat exchanger.  A surge tank is connected to the  cold  water  system  to  prevent  the  noise  and  effects of  water  hammer  and  cycling.    The  water  is  heated  in the  heat  exchanger  and  goes  to  the  hot  water  storage tank.  The hot water pump draws water from the storage tank   and   delivers   it   under   pressure   to   the   hot   water outlet.  Pressure switches are utilized to activate the hot and    cold    water    pumps    as    required    to    maintain    a constant  water  pressure  in  the  system.    A  hot  water temperature    switch    controls    the    positioning    of    the exhaust  gas  flow  control  valve  to  regulate  the  flow  of exhaust   gas   to   the   heat   exchanger   and   maintain   a constant water temperature.  Temperature and pressure relief   valves   in   the   water   system   protect   the   system from   damage   due   to   excessive   temperature   and/or pressure.      A   thermostatic   switch   in   the   water   tank compartment   is   used   to   control   a   solenoid   valve   to bleed  hot  compressed  air  from  the  engine  compressor into   the   water   tank   compartment   to   prevent   freezing during   low   temperature   periods   of   operation.      Drain fittings   are   provided   to   completely   drain   the   water system during periods of inoperation. f.  Compressed Air System (fig.  1-10 and 1-13).   The compressed    air    system    consists    of    various    ducts, valves,  and  controls  utilized  to  deliver  compressed  air from  the  gas  turbine  engine  compressor  to  the  heated air system, water tank compartment, engine air cleaner ejector,    vacuum    system    eductor,    and    for    external pneumatic power requirements.  Compressed air to the heated  air  system  is  bled  off  through  the  engine  load control   valve   which   is   modulated   by   a   load   control thermostat m the engine exhaust to prevent the engine from being overloaded by excessive shaft and pneumatic loads.  Compressed air to the engine air 1-14