When it comes to ventilating an apartment, especially if it's small, you hit a couple of bumps. Houses are easier to ventilate, because they have more design options available; houses can make use of their roofs to ventilate using pressure differences and solar chimneys, for instance, whereas apartments have no roofs to make use of (unless they're top floor apartments). So, the questions that arise are - what options do you have to ventilate your apartment, which one is the best one for you?
First, you have to know what you're working with, and to do that you'll need to make sure you have a good ventilation effectiveness. This will help you design your ventilation outlets (windows, ventilation louvers) and will let you know if the solution you're working with is appropriate for your ventilation needs.
The equation is:
Qwind= K*A*V, where Qwind is the air flow volume (m3/h), K is coefficient of effectiveness (unitless), A is the opening area (m2), and V is the outdoor uninterrupted wind speed (m/h).
K is a number between 0 and 1, adjusting for the angle of the wind and other fluid dynamics factors, like the size of inlet and outlet openings in your apartment. If the wind hits the window at a 45° angle it would have a coefficient of effectiveness of approximately 0.4, while wind blowing at an open window directly at 90 would show a coefficient of 0.8 (approx.).
Another important piece of information is the wind flow coefficient (ACH), which is important especially if you're also trying to cool your apartment; the higher the velocity, the faster a room cools and the higher the air renovating rate is. Keep in mind that the ability to cool doesn't help if the temperature of the air is too hot. If the heat inside the apartment is caused by radiant heat (lamps, household electric appliances, walls, ceiling) hotter air will still work.
The equation is as it follows: ACH= (Q/V)*(conversion factor), where Q is Volumetric flow rate of fresh air, V is the volume of the room (or space) being ventilated, and Conversion factor which is used when the time scales, volumetric flow rates, and volumes are of incompatible units.
Choosing a ventilation system:
After doing the calculations, you're ready to choose a ventilation system.
Mechanic ventilation: Natural ventilation systems are not advisable for apartments located in places with high noise pollution rates, as the noise will filter in. If you still want to try it out, you may use ventilation louvers- the louvers filter some of the noise and let a bit of light in. Another answer for this are mechanic ventilation systems powered by electricity- while is not the greenest alternative, it's the most efficient one and it allows you to filter dust and noise.
Using air pressure differences: This is the most efficient and common natural ventilation option available for apartments. Make sure you place the windows of your design strategically, previous study of local wind predominance, to create an artificial air stream inside your apartment. If you open windows or other ventilation openings in opposite sides, the differences will create a wind flow that will cool your apartment and increase the air renovation rate. If possible, design the whole apartment building so that every apartment gets to have windows in opposite sides of the wind flow. One option would be to create an interior airflow system in the center of the building, making the hallways encircle to an empty ventilated space- you can design the void as an interior garden for the atrium of the building, gaining oxygen in the process.
Trombe Wall: These walls are usually meant for cold places, as they heat up the inside of a building as they ventilate. They're double walls, where the interior one uses mass heating to heat the cold air coming into the space between the two; the air comes up and out of the interstice of the walls, heating up the place and moving the air inside, helping with ventilation.
Night purge: Night purge is only advisable for places where night and day temperatures differ considerably. The goal is to keep the apartment hermetically closed during the day, and opening every window and aperture possible at night, cooling the inside and the walls of the house, and ventilating it for the next day. During the day, the walls absorb heat and release it at night, using the temperature differences to create an artificial air stream.
Do you know of other ways of designing ventilation for apartments?