Air Differential Pressure Transmitter across AHU Chilled water coil

[Mansoor1982]

Hello All,
We have been using Air Differential Pressure Transmitter (DPT) across filter to identify the pressure drop to take preventive action on filter maintenance. One of our customer raised a query asking "Why is it not a standard practice to use Air DPT across Chilled water coil?". Would appreciate if knowledgeable HVAC experts throw some light on this topic. Does it make a strong case to have an Air DPT across Chilled water coil? If yes, why? And if no, why? Thank you in advance.

 

[BronYrAur]

What would be gained from the DP information? With proper filter maintenance, the coil should be kept clean. DP would change based on airflow (if variable) and on the amount of condensation. If you were to use it to identify when your coil is clogged, I'm sure you would find out by a lack of cooling performance anyway. Just my initial thoughts.

 

[SAK9]

Coil chemical or brushing is done once in 8~10 years.There is no justification to install a monitoring for such a maintenance activity that so infrequent.Couple of ports on either side of the coil will be useful to check pressure drop once every few years

 

[Compositepro]

The question is somewhat contradictory. Are you measuring DP across filter or coil? Measuring filter DP to detect when filter must be changed just cost money and is a cost/benefit analysis. HVAC systems are usually designed for absolute minimum cost.

 

[willard3]

If you know the delta p across the filter and maintain it, there's no reason for one on the CW coil.

Condensation and differing inlet/outlet conditions on the CW coil will just mislead you.

 

[ChasBean1]

I suppose if you have a unique situation such as a very low temperature (<32°F) CHW system or a DX cooling system that serves a critical situation (a system that may be prone to cooling coil frost), the DP sensor and alarming might prove beneficial. I’d suggest a 0-2” or 0-5” device with a 1.0” or 1.5” alarm. Otherwise you’ll typically find a higher DP in the summer while condensation occurs on the coil and a lower DP in the winter. This would not be necessary in a typical HVAC system.