Use your fans and cross ventilation to reduce air conditioning use this summer. Here’s how

My home office, originally the master bedroom, is the worst room in my apartment for cool down in the summerIt seems that the roof does not keep the heat out during heat waves.

It gets worse. The room is too big for a single central air conditioner to cool it sufficiently. A fan is always on not far from my desk. (Of course, 85ºF is not ideal for working.)

But a week ago I wore a hoodie to warm up after airing out the room all night with the windows open in cooler weather. It was fantastic. If I had kept the windows closed, my thermostat and air conditioner would have tried in vain to reach the same temperatures as two box fans.

Let’s take a look at how cross-ventilation works and the ways you can use it to reduce your energy bills.

How Cross Ventilation Can Cool Your Home

Cross ventilation works because the wind creates a pressure difference outside your home. The windward side of your home experiences a high-pressure airflow, while the windward side creates a low-pressure zone. The pressure differences exist whether or not your windows are open, so you better take advantage of them.

By means of open your windowsThe high-pressure air has a more direct path to the low-pressure zone — it flows more easily through a house than around it. It’s a great way to bypass your home’s insulation, which prevents thermal energy from entering and leaving your home. Once your home is cool enough, closing the windows and curtains will allow the air inside to warm up more slowly.

If you want to use natural ventilation for cooling, the outside air must be colder than the inside air.

For example, I close my windows and rely on my air conditioner after the outside temperature is above 75ºF. That’s usually when my thermostat kicks in — around 72ºF in my basement. I keep the windows closed during warm weather — unless the nighttime temperature drops below 70ºF before I go to bed.

Cross ventilation and air conditioning can coexist

If you are using an air conditioner or heat pump, you will see the best energy efficiency when every window is closed during operation. This is because open windows and doors create a large gap in the building envelope, separating the inside and outside air.

By limiting the amount of air the AC unit has to condition, it won’t have to work as hard as it would if the indoor air was constantly being exchanged with the outside air. In mild weather, free cooling is effective enough to offset the solar heat that ravages my home when temperatures rise.

You have to remember to close the windows daily, but the extra effort is generally worth it. Before I started using cross-ventilation regularly as a home worker, my air conditioning was running at least twice as hard. I have saved a lot over the years.

Effective natural ventilation depends on many factors

According to Energy.gov’s Energy saver office, the best candidates for natural ventilation are coastal and dry climates. On the coast, you can use cool ocean breezes to make your home more comfortable.

While these regions are most likely to experience dramatic nighttime temperature drops, you can use wind ventilation in other areas as well. It probably won’t be as effective, especially if your local climate is humid, but it’s still a good option for bringing in some fresh air.

Unfortunately, the effectiveness of cross-ventilation as a cooling method decreases as the outside temperature rises. If you leave your windows open all day, you can end up with warm air coming into your home and taxing your air conditioning system.

Even days with poor air quality are not ideal for open windows, so it is worth setting an alert if you live in a place with high air pollution.

It is not always easy to create a cross breeze. Passive ventilation works best when the wind blows directly through a window and in a straight line through the house.

Opening windows isn’t enough in a home where airflow must navigate complex hallways and rooms to find an exit. Any obstruction creates turbulence, so cold air can pick up a lot of heat as it tries to flow into an adjacent living space.

For example, the best windows for cross breezes in my house are on the upper floor, which is harder to cool than the relatively stable basement. This often means a temperature difference of at least 10 degrees in the summer — a comfortable 72º F downstairs and a balmy 85º up.

Unfortunately, the airflow has to move along multiple walls to connect them. Without my window fans, there is swirling turbulence in the hallway instead of a pleasant breeze through my office.

Create your own breeze with a window fan

It’s easy to use a window fan to create cross-ventilation. The simplest method is exhaust ventilation, which uses a single fan to push air out on the opposite side of the house from where you want the air to come in. This creates a negative pressure zone that pulls air through your home and out through the fan.

While this method is effective, it may not move the air fast enough to create a strong breeze, especially in large homes. Little air movement also means that potential cooling effects can be dissipated in turbulence before reaching the exhaust fan.

Fortunately, we can largely solve this by adding a second, incoming fan in the other window in a process called balanced ventilation. The incoming fan creates a high-pressure zone that flows more smoothly into the existing low-pressure zone.

Although I use a few Lasko box fans At Walmart you can also buy purpose-built window fans, such as this model from Bionairewith reversible air flow, thermostats and extension grilles for sealing windows.

Use smart home technology to control window fans

Let’s go over the basics of my window fan ventilation setup:

• Box fan 1 brings air in through the bedroom window.
• Box fan 2 draws air through the hallway and into the office before blowing it outside.
• Each fan is connected to a smart plug for easy control. I group them using a virtual switch so they run in unison.
• a Sonoff temperature sensor in the bedroom ensures that the fans run as long as the inside temperature is warmer than outside. It also prevents the room from getting too cold.
• I use a temperature dead band and a time delay to prevent the fans from continuously running near the desired temperatures.
• A window sensor in the bedroom prevents accidental activation when the window is closed, and at the same time activates the automation when I open a window.
  

While I don’t have a smart thermostat, you could integrate one into these routines so that the air conditioning stays off while the ventilation is running.

For this to work, you’ll need a smart home hub that can use temperature as an automation trigger. Your best bet is something like Home Assistant, Smart Things or Ezlo. Unfortunately, I was unable to find this option on Alexa or Google Home with my current smart home devices. I don’t have access to Apple Home, so I can’t verify how it uses temperature in smart home routines.

While window fans work well in my situation, you probably don’t need them if your home already handles crosswinds like a pro. Still, you can use smart home sensors to let you know when it’s time to close the windows and blinds for the day.

Fresh air fans

While window fans are probably best for renters and those on a budget, you can also outfit your home with a fresh air fan accessory for your HVAC system. As long as you have a compatible system, Ecobee smart thermostats support cross-ventilation through their Free cooling function. You can also get similar functionality from whole house ventilation products such as aprilAire.

I have no experience with ventilation systems for the whole houseTherefore, I recommend that you contact a local HVAC installer if you are considering adding one to your home.