How Does A Fan Coil Work?

This is a question we get quite a lot, so why not post about it? I asked our engineer, Jack Devitt to provide a basic overview of fan coil operation, so here it is.

Fan Coil Basics

A fan coil unit is a single zone air conditioner, generally ranging in capacity from 200 to 2000 cfm. They are available in 115, 208/230, and 265 volts. Fan coils come in 4 general designs including vertical cabinet (VCAB), vertical concealed (VCON), horizontal cabinet (HCON), and horizontal concealed (HCON). The COIL in a fan coil is either a 2 pipe or 4 pipe arrangement. Fan coils are used in conjunction with a boiler for heat and a chiller for cooling.

First, we’ll look at a 4 pipe system. While this type of installation gives the user the most freedom, it is the more expensive arrangement. In a 4 pipe fan coil, 2 separate coils are needed, one for heat and one for cooling. Two pipes are used for heating and two for cooling (inlet and outlet for each). A valve, which is connected to the room thermostat, determines which circuit will be used, heat or cool. When heating is called for, the valve opens the heating circuit. Hot water form the boiler passes through the coil. A motor on the fan coil turns a blower, which blows across the coil and distributes the warm air into the room. When calling for cool air, the valve opens for the chilled water from the chiller, the coil is charged with cold water, and the blower distributes the cool air.

The most common arrangement for a fan coil is 2 pipe. These are sometimes used for cooling only, heating only, or both. There is only one coil in the 2 pipe system. When a 2 pipe system is used for both heating and cooling, the building engineer will switch the system from heat (boiler) of cooling (chiller) manually. With a 2 pipe system you can operate in only one mode, heating OR cooling, not both. This can be somewhat inconvenient during seasonal transitions where heat may be required one day and cooling the next.

Fan coils are controlled by cycling the fan with a thermostat, or controlled by a water control valve with a thermostat. The thermostats can be manually changed over from heat to cool, or automatically changed over with a pipe mounted aqua-stat.

Thermostats can be unit mounted in the return air path, or wall mounted to control the room temperature.

McQuay fan coils are used in a variety of applications, including residential, commercial, and industrial.

Air Distributors Company, Inc. is a factory authorized distributor for McQuay Parts and PTAC products. We also offer Fan Coil Units and Water Source Heat Pumps from various manufacturers. For more information, call us at 1-800-866-1210.

Written by Jack Devitt, edited by Greg McNary.

Tags: fan coil unit, fan coils, McQuay Fan Coil