In the California desert there are two primary ways to cool down a house: closed loop air conditioning and open loop swamp cooling. A central air conditioning unit works by using electricity to compress a refrigerant fluid, typically outside the house, which is then sent under high pressure to a heat exchanger located inside the house, where it passes through an expansion device to a lower pressure. The refrigerant cools down from the expansion process, and through the heat exchanger cools the warm indoor air. The inside air never contacts the outside air directly, and cooled inside air is moved through the house via ducting and a blower unit. The warmed refrigerant then goes back outside the house where it is compressed again and repeats the cycle.
Swamp cooling (aka evaporative cooling) works in a more direct method. A large pad of absorbent material is located at the inlet of a blower. Water is sprayed on the top of the pad, and as very dry outside air is pulled through the pad by the blower some of the water evaporates into the air. This cools and humidifies the air, which the blower then blows into the house. As one might expect, though, if the house is closed up tightly there is no place for this cooler and more humid air to go, so a means to exhaust the same amount of air as the blower brings in needs to be available. When this is the case the system works efficiently and can keep a house comfortably cool with much less energy usage than an air conditioning system. When it is not the case the blower works inefficiently against a higher house pressure and the house not only remains warm but also becomes potentially uncomfortably humid.
I have both systems installed. My preference is to use the swamp cooler as much as practical, but there are times when conditions are such as make it a secondary choice – such as when air quality is bad from either dust or smoke, or on the rare days when a burst of monsoon humidity hits the area. As the system currently stands, I have to manually turn the cooler on and off several times a day. I run it on low speed with water off overnight when the outside temperature of cool desert nights is lower than the inside temperature so I can cold-soak the house with “free” outside air, then turn it off when I go to work, then when I get home it goes back on with the fan on high and water on to cool down the heat buildup from the day, then once the temperature either gets cool enough or the outside temperature starts to drop close to the house temperature I turn it off until it’s cool enough to start cold soaking again. While I would like to automate this process, I’m not comfortable with leaving several windows wide open during the day while I’m away from the house, particularly since if the swamp cooler isn’t running then the house will just heat up that much faster from the hot daytime air, which may well kick on the air conditioner that I have set to turn on if the house gets too hot.
Enter the Up-Dux. The concept is fairly simple: cut a hole in the ceiling so air can blow out of the room, into the attic, and then eventually vent out of the attic. As a side benefit, this also helps to cool the attic, which then helps to reduce the amount of heat coming through the ceiling into the rooms below. Since there are various good reasons to keep the hole closed when the cooler isn’t running, what the Up-Dux basically consists of is a metal liner for the hole with a lightweight lid on it. It works on a very simple principle: the cover is counterbalanced by a small spring so it only takes a small amount of force to open it, but is still heavy enough to close by itself. When the swamp cooler blower starts, the pressure inside the house becomes higher than the pressure in the attic, causing the lid to open. Once that happens air begins to flow through the hole and its momentum pushes the lid more open until the point is reached where the force exerted by the air on the lid is equal to the force exerted by the weight of the lid on the air. As pressure decreases (by, for example, opening a window, or the blower turning off) the lid closes to rebalance, as it increases (closing a window or turning the blower back on) it will open to rebalance. It’s a purely mechanical “dumb” system, and it’s very well suited to exhausting a swamp cooler when no one is around to open or close windows and doors. As an added safety feature there are two spring loaded dampers held in place by plastic pins which, in the event of a fire, melt and release the dampers to close off the vent.
So far so good. In theory it’s a great idea, but the question that naturally follows is how much air does one exhaust? The manufacturer has a guideline recommending one up-dux vent per 900 CFM of cooler capacity, or more simply putting one in each normal size room and two in larger areas. For my application that would come out to approximately 7 vents. Not a huge number, but at about $45 each it’s outside the range of a trival cost. So I opted to get one as trial and see how it worked.
The unit itself comes fully assembled and ready to pop into an appropriately sized hole (a bit over 11 inches by 11 inches). Cutting a hole in the ceiling is a somewhat messy job, but one saving factor is that it’s designed to be installed from the room below rather than having to go up and do it from the attic. In my case, I had an attic access panel with sufficient space so I was able to pull the panel and do the installation on my workbench. The unit is relatively lightweight, and the mounting method is 4 metal tabs which are folded over the ceiling material, then small screws are screwed through the side of the duct into the tabs before closing off the bottom with a plastic grate assembly. A thin piece of plastic is provided with the unit to slide into the grate to block it off to reduce heat loss in the winter, but my guess is I’ll make a foam cover of some nature so there is a bit more insulation. I then put the panel with the vent back up and turned on the swamp cooler with no other ventilation in the house (e.g. doors and windows all closed). As designed, the up-dux opened fully, and as I opened and closed windows and doors the up-dux responded.
With the trial successfully completed, I decided to step into adding more one at a time. I’m not looking for an optimum installation with only the up-dux as my venting option, but to provide enough venting that when I am not home to open additional vents there is still a reasonable venting capability. My guess is I’ll need another one or two.
All in all I’ve found the up-dux pretty much does what it advertises. Quality control is a bit iffy – on the first one I bought there was about an inch where the piece of foam weather stripping which the lid rests on was too short, and on the second one, one of the corners of the duct had either not been assembled or come loose in shipping. Relatively minor issues, but for a unit that at $45 I feel is already at least 2x overpriced I would have expected relative perfection.