fan coil units

Fan coil units are a very common way to heat and cool the individual apartments in high rise and other multi-unit buildings.  Here’s some information on fan coil units.

In some buildings heat and cooling are created at a single central plant.  This can be a very efficient way to operate at large scales.  But now comes the problem of moving that heat or that cold into the individual apartments.  Heating or cooling air and then moving that air through a large building isn’t practical – the ducts would have to be enormous, it would probably be very loud, and the air pressure needed would create its own set of problems.

So water is used as the heat transportation medium.  The building’s central plant creates hot or chilled water and pumps it through the building to the fan coil systems in the individual apartments.  There the water runs through a heat exchanger.  A fan pulls air from the apartment and blows it over the heat exchanger where it picks up heat (or gives up heat to the cold water) and then blows the conditioned air back into the apartment.  Each fan coil unit will have a filter, so the air that’s pulled in is run through the filter before it hits the heat exchanger.  So the filters need to be changed on a regular basis.  Sometimes the apartment owner is solely responsible for buying and changing the filters.  Sometimes the building will drop new filters at the front apartment door but let the owner or tenant change them.  And sometimes, usually in very pricey areas, maintenance crews will actually come in to replace the filters for you.  However it works in your building, be sure that the filters get changed regularly – ideally at least every three months.  Here’s a schematic diagram of a typical fan coil unit.

There’s always some sort of thermostatic control, but the type can vary greatly.  The most basic system just has an on/off switch for the fan, so you’re on your own to control the temperature.  Turn on the fan switch for more heating (or more cooling in the summer), turn it off when you’re satisfied.  Some systems have a variable speed fan to give you a little more precise control of the temperature.  And some systems will have a thermostat so that you can control the temperature in the room quite well.

A small apartment might have just one fan coil unit, but bigger apartments will have as many as it takes to cover the entire space.  Each fan coil unit will have its own air filter and its own thermostat control.

Most older buildings in the Chicago area use a 2-pipe fan coil system.  There are two pipes – one bringing water into the fan coil and one taking it away.  In these systems only hot water or chilled water can be provided, but not both at the same time.  And by both law (in most places) and by common sense the building has to err on the side of providing heat.  In the middle of January that’s not generally a problem, but there are some times in the early spring or late fall when the building has switched over to heat but you’d like cooling instead.  A 2-pipe system is cheaper to install, but that’s one of its downsides.

Many newer buildings use a 4-pipe system.  With this type of system the building can be supplying both heated and chilled water at the same time, so you’re better protected during those times of year when mother nature might throw either warm or cold temperatures at us.

Some fan coil units are installed in a wall.  There’s an access panel to get at the equipment (fan, filter, heat exchanger, and control valves) for servicing, and vents where air is pulled in and pushed out.  Some fan coil units sit on the floor and project out into the room.  They look a little bit like radiators.  With this type of system air is drawn in underneath the unit and pushed out the top.

Almost all fan coil systems provide cooling with chilled water, and that means handling the water created by condensation.  There will be a pan underneath the heat exchanger coil to catch the dripping condensation, and there will be a drain pipe to drain it away.  This pan can crack and leak, and the drain pipe can become clogged allowing the pan to overflow.  So these are problems that can cause water leaks and damage.