HVAC Coil manufacturers can over emphasize the need to designate left or right hand. The different reference points used can be intimidating and confusing. Often times, it just doesn’t matter.
Do you need to specify a left or right handed steam HVAC coil?
Not generally. Most steam HVAC coils are universal. Steam coils are normally 1 or 2 rows deep. This allows you to reverse the piping connections. The supply connection must be on top and the return connection must be on the bottom. Return connections on steam coils need to be as low as possible for proper condensation removal. As long as you have the return connection lower than the supply connection, it does not matter if you have a right handed or left handed steam HVAC coil.
Do hot water HVAC coils need to be left or right handed?
Hot water and steam coils are almost identical since both are typically only 1 or 2 rows deep. The major difference is the supply and return feed. If possible, feed the bottom connection and return the top connection. This helps promote the removal of air that can get trapped in the HVAC coil.
Which HVAC coils require a ‘hand’ designation?
Cooling coils that are larger than 2 rows require a hand designation. All coils except steam coils should be installed in a counter-flow arrangement. This is particularly true for HVAC coils with three rows or more. Counter-flow refers to the direction of the air across the fins relative to the fluid in the tubes. A counter-flow arrangement will produce the most capacity. Using a chilled water cooling coil as an example, the coldest water entering the coil should be cooling the coldest air leaving the coil. See below for a more detailed explanation of counter-flow.
A detailed explanation of counter-flow:
A HVAC coil is an air to fluid heat exchanger. Air is traveling on the outside of the tubes and fluid is traveling on the inside of the tubes. The most important principle in designing any heat exchanger is put the air and the fluid in a counter-flow arrangement. This means that the air and water travel in opposite directions through the heat exchanger. You always want the water, refrigerant or steam entering on the side of the exchanger where the air is leaving. This means that as the air goes from left to right, the fluid is traveling from right to left. All coils are tested in counter-flow arrangements and it provides maximum efficiency. You can lose 15% of the capacity when a HVAC coil is piped backwards. This is the primary reason why deeper HVAC coils are designated as right or left hand. Counter-flow has negligible effect on 1-2 row coils.
How to reference left or right hand?
When you stand in front of a coil, the connections will either be on the right or the left side. This is what they mean by “hand” connections. Most manufacturers determine left and right while facing the entering airside of the HVAC coil. A few manufacturers determine left and right while facing the entering airside of the coil (the air hitting you in the face) When facing the end of the coil with the pipe stubs, the supply connection should always be at the bottom, leaving air side of the coil. The return connections should always be at the top entering air side of the coil.
Is there a proper hand for replacement coils?
When you are replacing a chilled water coil the connections are almost always on the bottom right and top left. Once you determine the supply and return feeds, hand designation is not important. The HVAC coil is either bottom right / top left or bottom left / top right. The most important factor with replacements is to match what was there, unless you realize the original coil was not piped in a counter-flow arrangement. This is a great situation, you can share your expertise with your customer and show them how to save money!
In summary, hand designation isn’t a difficult concept, but many HVAC coil manufacturers make it seem more difficult than it needs to be.