What exactly meaning of a fan coil unit's static pressure?

Answer 1

It is the pressure that the fan has to overcome due to ducts and fitting losses to give the required space ventilation and cooling requirements at least equal to the designed flow. It is a fucntion of the length, equivalent diameter, velocity, frictional losses (Tables) and density of the media flowing commonly air. A manometer of liquid filled gage (DWYER) is used to measure it. Fan manufacturers also rate the fans static pressure minimum requirements that the fan will operate normally.ESP is the static pressure created downstream of the air handling unit that the fan must overcome- this includes duct friction losses, room static pressures, etc. This could included a negative static pressure on the pull side of the fan and a positive pressure on the push side, or any combination of pressures the fan must overcome. ESP is different from total static pressure in that TSP adds the pressure losses of all internal units such as filter banks, heating coils and dampers to the ESP value to give you the total pressure the fan/s must overcome.

Answer 2

Fan coil units don't have inherent static pressures, but it has to overcome the static pressures when it will be ducted to a system. Static pressure and pressure losses however can be determined accordingly in ducts. The designer sizes up the ducts to overcomes this losses and give the fan's output to the point of application sizing the duct to overcome frictional losses as much as it could to meet the space requirements cooling load. This value is the amount of resistance the fan will be able to overcome within the system it is ducted to and still be able to provide the designed air flow. For example if your fan coil unit is ducted on the supply side and the total frictional resistance of the ductwork and diffuser is below that of the fan coil units static pressure you won't have a problem. If on the other hand, the frictional resistance is greater, you won't see the design air flow at the diffuser. In general you can calculate a system's resistance with the following rules of thumb: 0.1"/100ft of duct, 0.1" per elbow, 0.1" at the diffuser. The fan will probably rated between 0.3" & 0.7" of water gauge.

Answer 3

You have to size your ducts and fittings accordingly also to consider the length of duct to the space required otherwise you will not deliver the optimum output of your fan. This static pressure inside the ducts must be overcomed. Then chose the fan with the static pressure above your pressure and viola. I am not sure. I also want to know about this question.

Answer 4

The external static pressure of a fan is the pressure measured at the discharge of the fan and includes all the duct losses from the fan until it reaches the discharge point. When measuring the external static pressure you must subtract the velocity pressure of the airstream from the total pressure measured by the gage.

External static pressure is not total static pressure. Total static pressure is the difference between the external static pressure and the measured pressure at the fan inlet. If the pressure is measured at the inlet duct you must also subtract the velocity pressure from the measured pressure.