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Steam Heating

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					Steam Heating

Calculating the “A”
   Dimension
            Water seeks its own level
               (most of the time)

In this example, the weight of the
atmosphere is pressing down on
both sides of the “U” tube equally.
Thus, the water level remains the
same on both sides
                                      Water Level
              Water seeks its own level
                 (most of the time)
Suppose we add more
weight to one side of the
tube. For every pound (per
square inch) we add to one
side, the water will rise 28
inches in the other.

This number shows up a lot
in heating!
Water seeks its own level
   (most of the time)
Water seeks its own level
   (most of the time)
          Here we’re pumping air OUT of
          the right side. That lowers the
          pressure and causes the right
          side to rise.

          It’s important to note that it’s not
          the vacuum pulling the water UP,
          it’s the greater weight of the
          atmosphere on the left side
          pushing down that causes the
          right side to rise.
The All Important “A” Dimension


                    Think of the piping
                    from the end of the
                    supply main back to
                    the boiler as the
                    previously shown “U”
                    tube. The waterline
                    will remain equal
                    across the system,
                    when the boiler is
                    not firing.
The All Important “A” Dimension
• Typically, residential steam piping is sized for a
  two ounce pressure drop. ½ psi is used for
  larger systems (>100,000Btuh)
• This means that if you start out with 1psi in the
  boiler, you wind up with about 7/8 psi at the end
  of the system. (1/2 psi in larger systems)
• With this in mind, the water inside the boiler will
  always be higher pressure than the condensate
  attempting to come back!
The All Important “A” Dimension
• Because of this, we need to ‘stack’ the
  condensate up vertically, to overcome this
  pressure differential.
• The stacked-up condensate must NOT be
  allowed into any pipe containing live
  steam, or massive problems will occur!
The All Important “A” Dimension
   (Systems > 100,000Btuh)
  The All Important “A” Dimension
     (Systems > 100,000Btuh)
Steam pressure drop across the system
  (1/2psi)……………………………………14”
Condensate pressure drop…………….......4”
Storage space for the extra condensate
That occurs at start-up……………………...8”
Extra safety margin (future pressure drops
  due to dirty returns, etc)……………….…2”
Total “A” dimension………………………..28”
The All Important “A” Dimension
   (Systems < 100,000Btuh)
 The All Important “A” Dimension
    (Systems < 100,000Btuh)
Steam pressure drop across the system
(2 ounces/1/8 psi)..……………………..…3.5”
Condensate pressure drop……………....3.5”
Storage space for the extra condensate
That occurs at start-up……………………...7”
Total “A” dimension………………………..14”
What can go wrong?
How do I fix that???
The Hartford Loop

				
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posted:10/13/2012
language:English
pages:15