The Gaming Outpost

I am not certain whether it is cooler in the office today (the desktop thermometer–on the real, wooden, desktop, not the computer version–says 82 right now) because we now have two window air conditioning units working full time at opposite ends of the level and several fans driving the warm and cool air into various parts of the main floor, or because I got up early today and the heat has not yet overcome the house, or because despite my expectations today is not as hot as yesterday.  Yesterday I fought with the computer most of the day, and accomplished much less than I would have hoped because of repeated crashes and long periods of time spent elsewhere waiting for the system to cool.  Hopefully today will be somewhat more productive, although there are tasks on the list that must be addressed at some point, and the fact that I popped out of bed early has left me a bit tired despite the coffee.

I’m going to rant about the heat a bit more–not about the heat, exactly, but about people who don’t grasp concepts of physics related to managing it.  First, though, I’m going to mention the new temporal anomalies article at The Examiner, The Lake House part 12:  happy birthdays.  This piece looks at one event–the 2004 birthday party where Alex first meets Kate–and attempts in brief to outline the shifts it undergoes as Alex receives more information from Kate in newly-received letters.

Now for that promised rant.

Fans have motors.  When you run the fan, the motor gets hot.  The air driven through the fan serves to cool the motor; that is, the motor heats the air that it moves.  The net effect of running a fan is that air gets hotter.

People feel cooler when the fan is blowing, because the moving air is slightly cooler than their own skin, and so they, too, heat the air with their body heat; it also is the case that the warm air evaporates the perspiration on their skin, and that evaporation makes them feel cooler–again at the expense of making the room more humid in addition to being hotter.

The effective way to use a fan is to use it to move air from a cooler area to a warmer area, that is, to bring in the cool air from outside if the house is hotter than the outside air.  People can be deceived about this, though–it often feels cooler outside because of a slight breeze, particularly if you are near water (which cools air slightly in the early hours of the day and warms it slightly in the early hours of the night, resulting in convection currents) or pavement (which heats air in the sunlight causing it to rise, creating a vacuum filled by cooler air around it–again, convection currents). A thermometer is a better way to determine this than the feeling on the skin.  However, if you blow the cool air into the house, you have two inefficiencies at work. The more obvious one is that the fan is warming the air as it draws it from outside.  The less obvious one is that the pressure created by the impeller is rapidly dispersed through nearer windows, and your fan does not do much beyond the window of the room in which it is placed.  The more effective approach is to expel air from the hottest part of the house.  This not only removes the heat from the warmest location, it draws cooler air into that room from the cooler parts of the house, which in turn draw air through their open windows from the cooler outside.

This is why attic fans work so well:  they remove heat from the hot attic and draw it out of the lower floors, pulling cool air into the lower part of the house.  You accomplish the same effect on a smaller scale by using window fans to expel air from hot rooms.

There is a use for other fans within a house, but the effective use of such fans involves moving cool air into warmer areas, which in an enclosed environment means that the warm air will move to the cooler locations.  This is particularly useful if you have an air conditioner running in the cooler location and want that cooler air to reach the warmer rooms.  This happens naturally anyway, and that’s important to understand–simply putting a fan to blow air somewhere is not an effective way to accomplish the objective.  Cold air is heavier than warm air, and so it sinks; as it sinks, it pushes lighter warmer air up, and the warmer air spills over the top of the colder air, traveling in the opposite direction to fill the upper spaces of the area which the cold air is evacuating–that is, the cold air in the living room generated by the air conditioner falls to the floor and presses up the hall, creating a vacuum in the upper area of the living room and a pressure area in the hall, such that the now pressurized warm air in the hall rushes to fill the vacuum in the living room.  Again, that is convection.  You need to work with convection, not against it.

If you place a fan near the floor, you want it to blow the cool air into the warm area–exactly what the cool air wants to do already, but you are enhancing its motion.  People frequently do get this right, because they are usually thinking that they want that cool air over there to blow on them over hear, although sometimes they get it wrong because they’re sitting in the cool area using the fan to blow the cool air back at themselves against the natural flow (and, of course, heating it in the process) instead of getting the cool air to spread to warmer areas.

The problem, though, arises with fans that are elevated–fans on stands, fans on tables, fans that are not at floor level.  This problem is the more serious because rarely are these fans at ceiling level.  If you have a fan that is at the height of the top of the door, it makes sense for it to blow from the warmer room to the cooler room.  That’s the way the air is moving there anyway, and by placing the fan there you force the warm air out of the warm room which creates the vacuum on that side and draws the cool air into that room along the floor, where the cool air travels.  What I frequently see, though, is a fan about four feet high positioned to blow air from the cool room to the warm room.  This is very inefficient.  Given that the door is less than seven feet high, this puts the center of the fan above the midpoint.  The air is trying to flow through the door, cool air through the bottom three and a half feet and warm air through the top three and a half feet.  The effect of this fan is to impede the flow of warm air out of the warm room by blowing it back against the natural flow, and thus to maintain the pressure of the warm air against the influx of the cool air, keeping the warm room warmer than it would be if you removed the fan entirely.  A fan higher than the midpoint of the doorway should blow the air from the hot side to the cool side, so that the cool air can rush beneath it into the warm space.

This is all simple eighth grade physics, isn’t it?  Why don’t people get this?  I constantly find fans turned to point the wrong direction, moving air in ways that are going to make the house hotter and prevent the cool air from spreading properly through it.

Let me tag on one more fragment about oscillating fans.  I’ll admit that I don’t like them, because despite the cooling effects of breeze I prefer to avoid it–it chills sometimes, and it blows allergens at me.  Apart from that, though, there is a clear illogic to the use of such fans.&nbsp.  This morning I found one in a doorway oscillating such that it was blowing air first from the hot room to the cool, then from the cool room to the hot.  One of those directions is efficient; the other thus is obviously counter-productive.  That’s true in almost every case with oscillating fans: there is one direction that is optimal for the transfer of cool air into a warm space or warm air into a cool space.  Any other direction would be less optimal, by definition.

It might be argued that a fan placed near the floor in the doorway between a cool room and an occupied warmer room will provide greater comfort for the occupants if it oscillates.  It might; it will, however, be less efficient at cooling the warmer room.  If the fan is pointing in a constant direction, it will create a current which gains momentum, driving the cool air into one area of the room from which it spreads, pushing the warm air out in a constant current.  If the fan oscillates, though, its movement disrupts the current constantly, preventing momentum from being established, and reducing the efficacy of the heat exchange between the rooms.

So now you know how to use fans for maximum efficiency in cooling your spaces.  Perhaps someone will be able to benefit from this, despite the fact that I probably have to go out even now and find out whether someone has yet again moved my fans.

–M. J. Young