heating coil sizing
heating coil sizing
(OP)
Can somebody give me a good explanation why typically when you size heating coils in VAV systems (either reheat coils for VAV boxes or in the VAV AHU) is it customary to size the coil for about 50% of the maximum (cooling) airflow rate. I usually see in the sequence of operation that when heating is called for in the space the boxes close down to 50% and then the heating coil is activiated. why is it done this way ??
Thanks for your help.
Thanks for your help.





RE: heating coil sizing
This will allow a reduction in fan energy (why move 100% of the air when you don't need it all).
The sequences I write tend to be more based around free cooling: boxes open to minimum for heating and cooling, boxes open to 100% for free cooling.
RE: heating coil sizing
RE: heating coil sizing
Them's my two cents worth...
Good on y'all,
Goober Dave
RE: heating coil sizing
RE: heating coil sizing
So the heating process is designed in two main steps: 1) reduce cooling airflow, then wait and see if that warms the space enough. If the space is still too cool, 2) begin to bring on reheat (while still at the reduced flow) to control room temperature.
RE: heating coil sizing
That is my biggest pet-peeve of misconception of HVAC people.
Reheat does not dehumidify. It removes NO moisture. It does reduce the RH of the supply air, but the ONLY thing that removes moisture is a cold coil. The reheat allows the cooling coil to run and supply dehumidified air, without overcooling the space. Essentially, it nothing but a false load for the zone.
Jabba
RE: heating coil sizing
Please read the attached pages and your doubts will be cleared.
RE: heating coil sizing
RE: heating coil sizing