Difference Between Pre-cooling and Thermal Mass Cooling

Whole house fans are the best way to cool down your home without hurting your budget. They’re energy-efficient appliances that circulate air throughout the home and exhaust trapped hotter air.

Not only are whole house fans great for staying cool and enjoying a nice breeze inside the home, but they can also be used to cool the home in anticipation and as a result of hot days due to their pre-cooling and thermal mass cooling abilities.

What is Pre-Cooling?
Thanks to modern data weather, we can pretty accurately forecast hot days and heat waves ahead of us. Pre-cooling allows you to use your whole house fan to suck the heat out of your home in anticipation of these hot days.

When hot air gets into your home, it not only raises the indoor air temperature but can also increase the surface temperature of your home and warm the structure itself. If your home is already warm when the hotter weather comes, it’s going to be significantly harder to stay cool inside.

Pre-cooling pulls the heat out of your home. Simply run the whole house fan at night and during cool mornings before the heat wave to ensure that your home is “pre-cooled”.

Thermal Mass Cooling
Pre-cooling involves the concept of “thermal mass”, which describes how objects (or building materials) absorb and retain heat. Materials that have a high thermal mass, like concrete and brick, can absorb a lot of heat.

However, these materials also have a long thermal lag time of about 12 hours, meaning it will take brick and concrete about 12 hours to discharge the heat they’ve absorbed during the day.

High thermal mass building materials are great for winter energy efficiency because they retain heat at night and slowly release it, reducing heating costs. However, they can be a problem if thermal mass cooling isn’t considered during hot summers.

To ensure your thermal mass isn’t heating your home during the summer, do the following:

  1. Shade: Keep thermal mass shaded to prevent them from absorbing too much heat and releasing it overnight. This means drawing blinds and curtains during the day and using landscaping techniques to provide some external shading.
  2. Ventilation: Use passive cooling by opening up windows or active cooling with a whole house fan to draw the heat from thermal mass overnight so that by the time the sun comes up again, they’ve released most or all of the heat they absorbed the previous day.

Now is a great time to add a whole house fan to your room before the dog days of summer really kick in.  Call us with any of your questions. We’ll be happy to help. 1-661-775-5979 M-F 7 am – 5 pm PST