Saving energy a room at a time

My air conditioning unit outside recently went kaput. The compressor just overheated and locked up. I spent two days sleeping in an 80+ degree house.

First I want to say that those two days resulted in a big energy savings. And a desire to leave the state or check into a cushy hotel. But what does this have to do with green?

In my Internet travels I have run across multiple articles and advice blogs about closing off rooms in your home to save energy. I pay attention to these as I have three rooms that are seldom used. Many say it's a great idea to close the vents, the door and place something under it to stop the airflow. In fact I have a friend who is in the business of selling remote controlled dampers for your duct work just for this purpose.

In theory if you close off 1/3 of your house you could save 1/3 on heating and cooling. But of course it's never that simple.

A forced air furnace has a fan that forces the air either over a flame or heating element in the winter and over the cooling coil in the summer. That air continues to be forced, once cooled or heated, down the duct and into the room. That air came from a return duct, either one big one or lots of small ones by being sucked in by the same fan. Its just one big loop.

Now if I close a vent, that air backs up and increases the pressure on the fan to work. It also reduces the amount of air running over the flame or coil. In the case of the coil, the refrigerant doesn't properly transfer the temperature and it's sent outside to the compressor improperly. (I don't really understand this part as it is either too liquid or too gas for the compressor thus making it work too hard). But whatever the details are, it isn't good to reduce the airflow over the coil.

When the system works too hard, your efficiency goes down and if you do that long enough the system fails.

So what I have found is the green and DIY sites all say it's a good idea. The three Heating and air conditioning people I talked to all say its a bad idea for the reasons mentioned. Given my neighbors unit also failed this week, it seems that problems exist that aren't obvious and limiting air flow below the system's design is one of them.

Bottom Line #1 - If you want to close a few rooms I would have your trusted heating and air guy come out and measure the pressures and airflow as you close off the ducts. Its possible your ducts leak so much there wont be much back pressure or that there is enough flow from the returns to properly work with your coil. Or there are more ducts than system pressures can fill up, so closing a couple wont matter. The smaller the system the more likely a problem.

It's also worth noting that the room in question will not be insulated between the room and the house. You also have to be careful about letting it get too cold in the winter around water pipes.

It may be that the whole idea is fraught with enough problems or potential problems to render it more trouble than its worth. I intend to get my AC guys out in the fall when they slow down and have them do the tests I described. It's all measurable and can be quantified.

Bottom Line #2 - Heating and air guys understand how to make stuff cool or hot. However, they don't spend much time making it cool or hot for the least amount of energy used, carbon released etc. We have to encourage them to help us save energy.