ac split system

Maybe. It depends on whether you want to transfer air into the room or out of the room. If you don't want to transfer air, you do not need a grille.

Do the room accupants have any way to get fresh air into the room if they want it?

What does the local building code require?

I would recommend it. A limitation of split-type systems is there is no method to introduce outside air into the conditioned space.

Whether a door grille, vent, or any other method, it is recommended to allow some outside air into the conditioned space. It becomes more important if you have a lot of occupants inside.

Of course, by allowing outside air in, you will pay an "air quality penalty", since the outside air needs to be cooled also.

Several of the split ac systems do have an option to add small amounts of fresh air (outside air) into the unit.

Split system is: Condenser and fan coil separated.

For home air conditioner, there is no additional ducting, only the fan coil inside the room with a circulating fan and a evaporating coil after an expansion valve.

If you have a grill for example, the question would be: how to bring in the fresh air through the grill, if you do not have a fan?

Most commercial, central systems have Condensers chilling a brine system, which is circulated through a distribution pump and fed to fan coils heat exchangers, which are installed in a ducting. The inlet side of the fan coil has a damper controlling recirculating air and another damper for fresh air.

However, I have yet to see this configuration on house air conditioning system. So far, not one as the house air conditioner fan coils are of smaller capacities of 18,000 to 20,000BTU or so for a small apartment room of 1000 m3.

tijit

_{Digital is our name, Portable is our game.}

There are several manufacturers offering "mini-splits" for small room air conditioning. Carrier, Daikin, Carrier, Sanyo, are a few. Stock units do not have ducting, and therefore do not provide outside air. However, Carrier and I suspect others offer optional fan kits or OA duct kits to allow outside air to be brought to the unit. It is more money and more work to properly set these kits up for operation, but if you need or are required to bring in fresh air, it can be done.

And yes, airflow in needs to be balanced with some provision for airflow out.

Get real.

If the door has an air tight seal, use a grille.

No inside door has an air tight seal and therefore no inside door needs a grille. Outside sealed doors typically have no desire to pass gass.

Calculations: 1/8" wide crack x 6' high x 2 plus 1/8" crack x 3' wide x 2 (top & bottom) equals grille size or larger. Install a corn stove and the heat loss will no longer represent a significant cost. www.msnusers.com/cornstoves

Any room with AC going to it with no air return needs somewhere for the air displaced by that coming from the AC to go or you will slightly pressurize the room and the room will loose flow from the AC system. So YES, a grill might be a good idea if there is no return in the room, and if the door is typically shut, and there's nowhere else for the air to flow out.

I have installed 5 split systems. (Not a lot by some standards but enough to have some hands on experience.)

For the split system to cool/heat the room no additional air supply is needed. However keep in mind without some type of air turnover the air will become "stail" for lack of a better word. In small spaces usually entering and exiting the room will provide fresh air. (Depending on the frequency.)

I have installed multiple units in the same room (large room with a considerable heat load) with no additional supply air and had no problems with that either.

Based solely on the installation of a split system adding a door grill will not add or remove any air from the room as the system does not create any positive or negative air pressure. It simply recirculates the air the same as setting a fan on top of a desk.

In the case where an air handler is floor mounted in a closet (typical) a vent is added to a door to facilitate a return air flow. While the gap around the door might provide enough air for a small unit it is not likely to be enough for most units. You will have the noise of air sucking in through the gap indicating the fan is starved. This results in poor air distribution through out the space(s) being served and, in the case of fans with forward curved blades, an additional load is placed on the fan reducing the life of the motor (not to mention making the door harder to open. At any rate it is a low cost add to put in a grill. The noise problem goes away, the door is easier to open and the space is more comfortable.

It is a really smart idea to introduce pre-treated outside air to slightly pressurize the zones being served as is the case in large buildings with varying requirements for interiors. There are a number of very important reasons for doing this to include health, safety, maintenance and productivity.

In a home, however, it is a small area (for most of us) and the doors and windows which will not be air tight are also opened and closed frequently enough that fresh air is not a problem. Cooling the outdoor air here in the south don't make no sense especially when you aint home to enjoy it none most times!