How Much Do You Really Know About Coils and Air Handlers?

swcoil_superadminAir Handlers, Questions, Quiz

There are many different types of coils, fan coil units, air handlers and tube bundles.  Test your knowledge on these application questions.  NO PEAKING AT ANSWERS!

1. What’s the #1 reason for replacing steam distributing coils?
  1. Condensate corrosion
  2. Stress corrosion
  3. Freeze event
  4. Air temperature fluctuation
2. What’s the main difference between a double deck and a multizone air handler?
  1. Single versus multiple zones
  2. Air flow control near the space versus at the unit
  3. Hot deck is smaller in double deck unit
  4. Air flow control near space versus at unit
  5. Better control with the more expensive multizone design
3. On chilled water coil projects, what’s the #1 system problem that differs from the design specification?
  1. Fans don’t produce the needed CFM to allow the coil to meet its capacity
  2. GPM flow is much less than specified
  3. Coil connection sides are incorrect
  4. Entering coil water temperature higher
4. #1 reason why fan coils fail to cool a space?
  1. Lack of air throw into the space
  2. Lack of water flow
  3. Higher entering water temperatures
  4. Clogged valves and less than stellar thermostats
5. What’s the negative to replacing inefficient filters with high efficiency filters in a central station unit?
  1. They won’t fit in the existing filter rack
  2. You will need better filter controls
  3. Filters will require more frequent cleaning
  4. Air flow may be reduced
6. Why are hot water coils usually 1 or 2 rows and chilled water or dx cooling coils 4 rows and up?
  1. There’s usually a much larger temperature spread between water and air
  2. One needs to lower temperature and the other must also remove moisture
  3. Moisture on the surface reduces the heat transfer
  4. Cooling coils need a lower air velocity
7. Steam distributing (tube-in-tube) coils exist for what major reason?
  1. Better air flow across the coil
  2. Lower resistance to the steam
  3. Separation of steam and condensate
  4. Works better with steam valves
8. What’s the #1 reason why u tube bundles fail in steam and water heat exchangers?
  1. Water and condensate quality problems
  2. System pressure
  3. Tube sheet stress
  4. Vibration

ANSWERS:

#1 – This is a close one, but condensate problems (A) barely win over (C) freeze event.  Most new steam systems do not have corrosive agents in a large enough volume to cause leaks in copper coils. However, as they are treated, and oxygen enters the system, the corrosive agents build and cause pitting tube leaks.  The big 3 are 1) oxygen, 2) carbon dioxide and 3) ammonia. 

#2 – The answer is (B).  In a dual deck unit, the heating and cooling duct are run almost all the way to the mixing box and the controls that determine how much cooled air and heated air flow into the box.  On a multizone unit, the heating duct is very short, and the control of the damper with mixing air is done at the unit.

#3 – All these answers are a problem.  However, 8 out of 10 systems never receive the temperature of water required by the specifications, so the answer is (D).  Many cooling coils that were selected at 45 degrees entering water have 48 degrees water entering the coil which produces less heat transfer.

#4 – All these answers are applicable.  (A) is the one we see the most, and it’s a problem for a myriad of reasons.  Sometimes the location of the unit is too far from the area of the space to be cooled, and the unit fan is too small to project the air the needed distance.   The additional ductwork also reduces the overall flow creating much less CFM flow.

#5 – The answer is (D).  Higher efficiency filters are better, because the air is in touch with the surface more often to remove foreign material.  However, this also causes more air resistance.  The air flow volume will decrease unless you change the speed of the supply fan to overcome this extra resistance.

#6 – The answer would be both (A) and (B).  Water can be 80-100 degrees difference on a hot water coil system, whereas a cooling coil system can be 25-30 degrees difference.  It also requires more surface in the direction of the air flow (rows of tubing) to remove the moisture if it’s present.

#7 – The steam distributing coil was introduced and designed to be able to separate the steam and the condensate.  The answer is (C).  The steam goes down the inner tube giving it a straight path to the other end of the finned surface.  Since the steam starts to change to condensate, these inner tubes have holes to allow that condensate to move into the outer tube.  This unique arrangement allows steam to flow and condensate to return to the condensate connection leaving the coil.

#8 – All the answers listed are systematic problems, but most tube bundles are replaced over time because of corrosion to the tube material.  The answer is (A).  Systems change over time, and so does the buildup of corrosive agents, which eventually creates pitting in the tubes. 

If you were correct on 7 or 8 of these questions – you are very well informed!  A good score is still 5 or 6.  These are not easy questions, but it’s indicative of how many situations can cause HVAC problems in and around coils and air handlers.  After 4+ decades of acquiring knowledge and experience, Southwest Coil, who exclusively represents USA Coil & Air, has the answers and the products and services it takes to provide you with great ways to increase your company profit. 

Contact the experts at Southwest Coil for all your coil needs!

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