Whoa! This looks boring already! Just wait…

Today, I would like write about what questions to ask when coordinating the heating and cooling system in a residential apartment. What I won’t talk about today is how big a system needs to be, how to balance a system, or any of the more technical stuff. I leave all the technical loads to the mechanical engineer. What I will talk about is which system to use, and what questions to ask when using that system.

To simplify the discussion, I have chosen to talk about the most common types of conditioning systems. There are all types of new and interesting systems such as hydronic systems, passive solar systems, and so on, but the most commons systems are still packaged wall units and more traditional central air conditioning.

Packaged Wall Units are the types of air conditioners that you might see in motels. They are a bit noisy, not incredibly efficient, but they are the least expensive of the lot. The only reason I would consider a packaged unit in an apartment it if I was on an incredibly tight budget.
Traditional Central Air Conditioners are those air conditioners that you might see in every typical suburban home. The system can be gas powered or electric powered, and generally they are more efficient and cheaper in the long run than the Packed Wall Units. Central Air Conditioners are much more expensive to install, though, and also take up quite a bit more space. Traditional Central Air Conditioners are composed of 6 basic parts:

• A Condenser which creates the cooling element by condensing freon gas and then letting it expand which creates a cooling effect.
• A Fan Coil which blows the air into the rooms as well as holds the heating coils which heat a room.
• An Outside Air Duct which draws fresh air in to the system from the outside.
• Supply ducts which supply the conditioned air into the rooms and…
• A Return Air Duct which recycles the air in a room back into the fan coil.
• A drain pan and drain.

condensing units on roof will be located here

fan coil with supply and return ducts

Also, regardless of which system you choose to use, there are several constants that will affect the design of the system. For instance, you will always have to exhaust the kitchen and the bathrooms with a fan of some sort. Some important general questions include:

• Where will the bathroom exhaust go to, and where will the kitchen exhaust go to? For both of these exhaust systems, they will need to get to the outside somehow. You can either take the exhaust out of the roof or out of the wall. If you take the exhaust out of the roof, then you will need to have some sort of shaft that take this up to the top of the building. If you take this out of the wall, then you will have to put this exhaust duct in either the joists, in a dropped ceiling, or in soffits.
• Will the system be in the joists, in a dropped ceiling, or in soffits? If you want a really clean looking ceiling, then you will most likely drop the ceiling below the joists to accommodate for all of the ducts running everywhere. If you have really deep joists, truss joists, or some other special joists then you may be able to just put all the ducts in the joist space (depending upon the what is allowed by code). The simplest and cheapest option for moving ducts through a space, though, is to simply have a dropped soffit wherever the duct is running.
• Do the intakes and exhausts conflict with the shear walls? A very important item that often gets overlooked is where the shear walls (solid structural walls that often can not be penetrated) are located. I’ve seen this many times where someone runs a duct along the edge of a wall, and come to find out, the duct can’t penetrate to the outside because there is a shear wall in the way. This means that the duct has to go somewhere which usually means having to create an unsightly soffit you had not planned. Ugly!
• Do the intakes and exhausts conflict with the window or door headers? Not only do you have to think of the shear walls, but any time you have a window or door, you will have a solid header that you will not be able to penetrate.

More questions come up with the most two common air conditioning systems, for instance:

Central Air Conditioning:

• Where will the condensing unit go? This is almost always on the roof or in a side yard away from the residence. I like t keep the compressor as far away as possible from human contact. It sucks that bad. The cooled liquid then travels from the compressor to the fan coil.
• Where will the fan coil go? This usually goes inside the ceiling or standing up in a closet. To preserve space in apartments on a tight budget, I have often put the fan in the ceiling. The only thing weird about this set up is you will need a drain somewhere to drain off condensate. I usually drain to a tub or shower.
• Will the fan coil get a ceiling or wall mounted return air grill? Let’s say the fan coil is ceiling mounted. Right next to the fan coil should be a return air plenum or duct. I suggest a side duct through the wall of a soffit because this method is quieter than if the return air was directly below a unit.
• Will the fan coil need sound dampers? The fan coil will likely need excess sound insulation below and above the unit, and the unit might be mounted on springs to stop the vibration from transmitting to other apartments or rooms. These units are very annoying if you do nothing.
• How deep is the fain coil, and will the fan coil make drop the ceiling below 7’-6”? The fan coil is about 10” deep, so when all is said, you will need about 1’-4” for the whole ceiling drop which includes air space, gypsum board, and metal studs. If this ceiling drop falls below 7’-6” then consider moving the unit to a closet. 7’-6” is sort of the code cutoff point for a livable ceiling height.
• How will the fan coil get fresh air? The fan coil is required to use some fresh air in the mix. This means, just like the exhaust air, you will need to get something in to the fan coil from the outside. Sometimes the fan coil is right in the middle of the house or apartment, so keep in mind where and how far you have to go.
• Are the kitchen exhausts far enough away from the fresh air intakes? There are codes that require that fresh air and exhaust be a certain distance apart. Check your code books for minimum distances or consult your mechanical engineer.
  How will the fan coil get air to the various rooms? Finally, the supply takes a bit more room because it’s covered in soft insulation. Where are these ducts going to fit?

fan coil after installation

Packaged Window Units:

• Why would I use this system? Because it’s cheap and easy to install.
• How many units do I need? I ask this because you may need two or three of these things depending upon the size of your apartment. Let’s just say, you would need two of these for a small two bedroom.
• Where do the units go? Let’s say a small two bedroom gets one unit in the master bedroom and one unit in the living room.
• Do I need transfer fans? Then, you would stick a transfer fan between the living room and the bedroom to cool or warm the second bedroom. This fan is unsightly, so think about its location.
• What do the units look like on the façade of the building? I would really consider what grill you use and if the grill can be integrated into the windows some how. This thing is ugly regardless.
• Will this fit with the window system and floor to floor height I’ve chosen? Finally, I’ve noticed that you really want to lay out a wall section to make sure that you can fit the windows, header, top plate, bottom plate, and wall unit all within the constrained floor to floor height. Often times, a smaller than desirable window needs to be used which might test your light and air requirements.

packaged wall units can be installed like this if you want extra room on the interior, but I don’t advise this because of how it looks on the building.

Here are some links for more information:

• http://www.firstco.com
• http://www.residential.carrier.com/
• http://www.amana-ptac.com/
• http://www.mcquay.com
• http://www.colemanac.com/