Low Cost Cooling

Saturday, August 25th, 2007

David Friedman wonders why this Low Cost Cooling idea isn’t in wider use:

A common hot weather strategy, especially for people living in big old houses without air conditioning, is to open windows at night when it is cool out, close them in the morning.

It should be straightforward to automate the procedure, using windows or vents that can be set to open when the temperature outside is cooler than the temperature inside, close when it is warmer, with fans to increase the airflow when desired. I would expect both the capital cost and the operating cost of such a system, used to replace or supplement air conditioning, to be trivial relative to the cost of air conditioning itself.

Yet I do not think I have ever seen such a system. Have I missed it? Or is there some non-obvious problem with the idea?

An anonymous commenter has this to say:

When I was in engineering school about 25 years ago, I did a project studying such systems. They were entirely possible (and in fact some had been built as demonstrations), but the cost was prohibitive. One key enabling technology has blossomed since that time: networking over power wires. You’ve got to run power wires to each window for the motor, so you use them for the control network also.

However, it still costs too much. The cost of networking has plummeted, and a 3-GHz PC costs much less than the TRS-80 8-bit computer I used in that project, but a motor in each window costs just as much as it ever did, and the cost of installation labor is higher.

This is the idea that seemed natural to me:

A more practical idea is to rig the central heat/air with high-volume controlled vents to the outside. You leave your windows closed, but the system detects when it is appropriate to circulate outside air rather than recirculating artificially heated or cooled inside air. A mass-produced system like this should only cost $200 more than a regular high-efficiency furnace & central air (that is, about the same as the building permits required to install a new furnace!), and I think in the climate here it would pay off in the first year. But I just don’t see anything like that on the market…

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