posted 2 years ago
Hi, Dave. As a DIY project, it is impressive.
Let me discuss the technology. It is cooling the house as an evaporative cooler. The principle is to increase relative humidity in the air (RH) to lower the temperature where evaporation is taking place. This method has two major issues. First issue is that it increases RH until it saturates indoors, then it works no more, that's why this system is mostly used outdoors. For avoiding saturation, a way for drying the air is needed. There are several methods for doing this: Absorption, adsorption and other technologies that require an energy input.
The second issue is that the power of the cooling is limited by how much heat can be stored in the air humidity. If you don't want to sweat, you typically keep your house under 70% RH. In these conditions, an evaporative system can only lower the temperature up to 10 degrees, regardless of the power of the unit. This means that you don't get comfortable temperatures in really hot summers. But if you can't pay the bill for a heat pump, then 10 degrees is better than nothing.
A third issue, although this is minor, is that this system depends on many things for it to keep working: reliable electricity for the pumps, electronics for control, plumbing materials and a source for the desiccant. When a system depends on many things out of your control, it's not very resilient.
Now, I don't get what is really doing calcium chloride. It usually is used as an absorption desiccant, and it is consumed in the process. If that's the case, then we need to add the costs of replacing the consumable. 50lb of calcium chloride costs 45$ in Amazon.com right now. If it is used as adsorption, then yes, it just takes energy. I remember adsorption fridges that worked on propane, for off-grid applications. And I've seen a few years ago, rooftop solar panels on sale that delivered cold water by the adsorption process. None of these technologies were competitive enough, because the units were much more expensive than their counterparts using heat pumps.
The place where adsorption is competitive is, curiously, in the industry sector. The cost of building the units is rapidly offset by the savings. They are big ugly metal boxes that takes hot water from solar panels, store heat in a container, and deliver cool air or water through a pipe. This design is only missing the heat storage. Well now, a DIY adsorption solar cooler might be affordable. This one is probably not as efficient as a commercial one, and it is certainly bulkier, but if you can make it cheap for yourself, it's a cheap cooling unit to add to your other passive cooling solutions.
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