Did You Know? Essential Facts About Commercial HVAC Coils

Commercial HVAC FAQ’s

  • Fins are responsible for 70% of heat transfer of  HVAC coils.  Which obviously means the tubes are only responsible for 30%.
  •  The performance between copper fins vs. aluminum fins is very minimal.  The only reason to ever use copper fins is if there is a problem with corrosion.  Unless you like paying almost triple the cost!Chilled Water Coils
  • The air that travels across the face of the HVAC coils must be specific to what type of coil it is.  For instance, steam or hot water face velocities are not the same as chilled water or direct expansion.  For steam or hot water, 800 feet/minute is ideal.  For chilled water or refrigerant, 500 feet/minute is ideal.
  • While we build 1/2” OD and 5/8” OD HVAC coils, there is very little difference in performance.  The reason for this is the overall tube surface is almost the same. 5/8” tubes are larger, but 1/2” coils have more tubes per row.  And given that tubes are only responsible for 30% of heat transfer in HVAC coils, you’re not missing out on much by going with 1/2” tubes.
  •  There’s no such thing as right hand or left hand in hot water booster coils. If you need a right hand coil, just flip it over and install!
  •  You can use hot water booster coils for low pressure steam.  Don’t let the manufacturer up-sell you into a custom steam coil if you don’t need it.
  • You always want to minimize the number of passes on a steam coil.  The less times the steam has to pass through the coil, the better.  Two passes through any steam coils should be the maximum.

 

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Did You Know? Shell & Tube Heat Exchanger FAQ’s

tube bundleThere are basically three kinds of shell and tube heat exchangers:

  • “U” Tube heat exchangers where it is possible to remove the entire bundle
  • Fixed tube heat exchangers where the tube sheet are welded to the shell and stationary and the bundle is not removable
  • Floating tube heat exchangers where one tube sheet is fixed and the other floats axially.  This tube bundle is also removable.

Capital Coil & Air builds all three of these heat exchangers types, but more importantly, the replacement bundles for heat exchangers.  The shell portion of the heat exchanger can often last 40+ years without corrosion or something to seriously damage the shell.  The tubes and the bundles can be replaced fairly simply, but you must do (5) things to accurately duplicate the bundle.

  • You must duplicate the tube surface area in the bundle first.  You can use different size tubes if you choose, but however you do it, you must use the same surface area.
  • You must duplicate the baffles on the bundle to allow whatever is traveling through the shell to pass back and forth in the same number of passes.
  • You must duplicate the length of the bundle exactly. Making a bundle too long is a very costly mistake.
  • You must duplicate the materials of construction on the bundle including the tubesheet, tubes, and baffles
  • Last, you must duplicate the bolt hole pattern exactly because the bundle flange is bolted between the head flange and the body flange and all the bolts go through all the holes simultaneously.  There are also those really lucky times where the tube sheet is sandwiched between and there are no bolt holes.

Shell & tube heat exchangers can last an extremely long time.  The bundle, unfortunately, cannot.  Capital Coil has a real expertise at replacing bundles and heat exchangers for emergency situations.  Many times bundles fail and the turnaround time is essential.  Capital offers 5 day and 10 day shipments regularly.  Give us a call or shoot us an e-mail when downtime needs need to be minimal!

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