Active Thermal Mass Cooling -- Using Night Air to Fan Cool Thermal Mass

 This page describes a scheme and some experiments in using night air to cool thermal mass inside the living space to store "coolth" for the next day.  Fans are used to circulate outside air at relatively high velocity over over the thermal mass during the evening hours when the outside air is cool.  For the system described here, the thermal mass comes in the form of barrels filled with water, but other forms of thermal mass could be used.


The system is VERY simple -- basically a fan on a timer.  There is not much of anything to go wrong or leak or require maintenance.

I have been using this scheme to cool my 25 by 25 ft shop.  The thermal mass consists of 4 water barrels arranged inside a cooling "tunnel".   A fan pulls outside air in through a vent in the wall, and forces the air down the cooling tunnel to cool the water mass.  The cooling tunnel channels the air to keep the air velocity up near the barrels, which increases the heat transfer.  To retrieve the stored "coolth", I reposition the fan so that it blows shop air over the cool barrels and cools the air. 

I go over the calculations involved in designing and sizing this system in some detail because I get feedback that these calculations are helpful to people who want to design their own systems.  If the calculations are not your cup of tea, just skip over them and go to the build and performance sections.



Scoping Calculations

Picutures of the setup

Previous page on this

Test run on the new setup -- should show both cool down and coolth recover



This method relies on cool night air temperatures -- its really a way of averaging out the day and night temperatures.  For example in our climate even if it gets to a very hot (for us) 95F during the day, the night temp is likely to get down to 55F, so the average temperature is a comfortable 75F. 

A lot of the western US has this type of climate.



Other Options

There are lots of other ways to transfer the coolth of night air into thermal mass -- here are a few possibilities: