3 ms·

So basically, as I understand it, the full process is as follows, starting with dry dessicant: 1. External air is blown over the dessicant, which pulls moistur

So basically, as I understand it, the full process is as follows, starting with dry dessicant: 1. External air is blown over the dessicant, which pulls moisture out of the air. 2. That dry air is then blown over water, which rehumidifies the air and also cools it by evaporative cooling. This part here is essentially the same as a swamp cooler. 3. The air is then cooled further by what is essentially a normal air conditioner, but which doesn't have to work as hard because the water is already cooler from step #2. 4. The dessicant, though, needs to be dried out, so as the article explains it I think the desiccant is heated by a heat pump to dry it out. Please someone correct me if my understanding is wrong. It's an interesting design which basically combines a swamp cooler with a heat pump (after all, AC is just a heat pump that pumps heat out of the house). I'm skeptical of the 60% number though given the extra energy that needs to be applied to dry out the desiccant.

malfist 3y ago
I wonder if it's using the waste heat from the AC to dry the dessicant
sushibowl 3y ago
Could you use the heat pumped out of the house by the AC to dry the desiccant?
0xfae 3y ago
You could use the waste heat from the heat pump (standard A/C) in step 3 to heat/dry the desiccant in step #1. That heat is, like you said, just dumped outside now. Why not make use of it?
- ilyt 3y ago
  Similarly we could use air exhaust from home itself to heat up AC in the winter
xenadu02 3y ago
With regard to regenerating the desiccant: Presumably the same heat pump used for the normal A/C cycle would be used to handle this. Add some valves and controllable dampers which are potential failure points but not expensive. Instead of dampers you could have a separate exhaust fan but either way you need to extract the hot and very humid air from the regen cycle to avoid dumping it into the building. There's a tricky optimization problem for a system like this. In heat pump mode your ideal time of day is around solar noon when temps are hottest... with an inverter (fully variable) compressor and fan you can run both at lower power to generate just enough heat needed for regen. That can clash with your cooling load and electric rates though so it may make more sense to run at night when you need to run longer or higher power to generate enough heat. Most consumer A/C systems sold in the US don't even have inverter compressors yet so that is some added cost/complexity. Many have variable speed indoor and outdoor fans but not all. There may be some decent gains to be had just by adopting the latest "conventional" refrigeration tech.
- adrianmonk 3y ago
  I wonder if you could just pump the liquid desiccant outside, do the drying outdoors, and then pump it back inside. Then you wouldn't need to worry about air handling for the moist air. When retrofitting a house to replace traditional AC with this, it may not be easy to get air from where the AC is located (usually the middle of the house) to the outside. If you pump desiccant outside, maybe you can squeeze desiccant hoses in right next to your refrigerant lines. Also, there's all that waste heat outside at the condenser anyway. It seems like you could use that heat to help dry the desiccant. I guess that creates a different tricky optimization problem: if you wait too long to start drying your desiccant at night, when you finally do, you risk making the house too cold because you are stealing its heat. Maybe you just pause desiccant drying until whenever AC is needed again.
ramses0 3y ago
There was a neat "trash tv" show that I saw a while back talking about A/C's and Vacuum cleaners being invented and the "necessities" behind them (complete with obviously fake/acted "scenes from the 1850's with corresponding gigantic moustaches"). They talked about the rationale of A/C being related to "consistency in humidification in a printing press environment" - https://www.theatlantic.com/business/archive/2017/09/tim-harford-50-inventions/540276/ https://www.theatlantic.com/business/archive/2017/09/tim-har... Literally an "Air, Conditioner", with cooling being a byproduct. The line in the video was something like: "he recognized that you could simply dry out the air completely, and _then_ re-introduce the appropriate amount of humidity". To dry it out, you cool it down and "condense" the humidity. This seems like a neat continuation of the idea: Dry out the air before you cool it, and effectively time-shifting (and having separate systems) for the drying, the cooling, and the baking/restoration of desiccant.

malfist 3y ago

I wonder if it's using the waste heat from the AC to dry the dessicant

sushibowl 3y ago

Could you use the heat pumped out of the house by the AC to dry the desiccant?

0xfae 3y ago

You could use the waste heat from the heat pump (standard A/C) in step 3 to heat/dry the desiccant in step #1. That heat is, like you said, just dumped outside now. Why not make use of it?

ilyt 3y ago
Similarly we could use air exhaust from home itself to heat up AC in the winter

xenadu02 3y ago

With regard to regenerating the desiccant: Presumably the same heat pump used for the normal A/C cycle would be used to handle this. Add some valves and controllable dampers which are potential failure points but not expensive. Instead of dampers you could have a separate exhaust fan but either way you need to extract the hot and very humid air from the regen cycle to avoid dumping it into the building. There's a tricky optimization problem for a system like this. In heat pump mode your ideal time of day is around solar noon when temps are hottest... with an inverter (fully variable) compressor and fan you can run both at lower power to generate just enough heat needed for regen. That can clash with your cooling load and electric rates though so it may make more sense to run at night when you need to run longer or higher power to generate enough heat. Most consumer A/C systems sold in the US don't even have inverter compressors yet so that is some added cost/complexity. Many have variable speed indoor and outdoor fans but not all. There may be some decent gains to be had just by adopting the latest "conventional" refrigeration tech.

adrianmonk 3y ago
I wonder if you could just pump the liquid desiccant outside, do the drying outdoors, and then pump it back inside. Then you wouldn't need to worry about air handling for the moist air. When retrofitting a house to replace traditional AC with this, it may not be easy to get air from where the AC is located (usually the middle of the house) to the outside. If you pump desiccant outside, maybe you can squeeze desiccant hoses in right next to your refrigerant lines. Also, there's all that waste heat outside at the condenser anyway. It seems like you could use that heat to help dry the desiccant. I guess that creates a different tricky optimization problem: if you wait too long to start drying your desiccant at night, when you finally do, you risk making the house too cold because you are stealing its heat. Maybe you just pause desiccant drying until whenever AC is needed again.

ramses0 3y ago

There was a neat "trash tv" show that I saw a while back talking about A/C's and Vacuum cleaners being invented and the "necessities" behind them (complete with obviously fake/acted "scenes from the 1850's with corresponding gigantic moustaches"). They talked about the rationale of A/C being related to "consistency in humidification in a printing press environment" - https://www.theatlantic.com/business/archive/2017/09/tim-harford-50-inventions/540276/ https://www.theatlantic.com/business/archive/2017/09/tim-har... Literally an "Air, Conditioner", with cooling being a byproduct. The line in the video was something like: "he recognized that you could simply dry out the air completely, and _then_ re-introduce the appropriate amount of humidity". To dry it out, you cool it down and "condense" the humidity. This seems like a neat continuation of the idea: Dry out the air before you cool it, and effectively time-shifting (and having separate systems) for the drying, the cooling, and the baking/restoration of desiccant.