Hacker News Reader

Comment by lr | Hacker News Reader

Articles like this remind me of this house, which was built in Iowa City, IA by a Physics professor (he was my professor for several classes). At the time this house was being built, ISU had an "active solar" research facility, i.e., using all kinds of mechanical means to turn solar energy into heat for homes. Once this house was built, ISU shut down the "active solar" research because, as this house showed, passive solar was just so, so much cheaper and efficient: https://lhodges.public.iastate.edu/house.htm

View on HN

It's actually remarkable how much heat a simple "soda can solar panel" or "downspout solar panel" can inject into a room. Add a photovoltaic panel to run a 12v brushless 100CFM fan to stir the air and inject the hot air into the room, and you have a "free" source of 120F air to heat a few hundred square feet. Add a south-facing window shining sunlight onto a dark grey slate tile floor (which acts like heat sink) and the floor will release that heat well into the night. So with two very simple passive elements, one can, to a large degree, supplement a traditional heat source (heat pump, gas furnace, etc.). I've seen this approach work with vacation cabins in the mountains, and RVs, a well as the traditional house-on-the-cul-de-sac.

These heat collectors are cheap and simple to make (<$500), and should be quite reliable, giving a +50 degree F delta with almost zero maintenance and no utility consumption. The only moving part is the inexpensive and reliable fan.

* https://www.pinterest.com/jayhike/soda-can-solar-heater/ and https://lifehacker.com/build-your-own-soda-can-solar-heater-...

You might enjoy this: http://www.iedu.com/Solar/Panels/index.html

Ah, a high-efficiency version of the simple soda can version. Yes, it's of great interest to me. Thank you!

Compare also the Passive House (Passivhaus in German) concept, which makes use of similar techniques:

https://en.wikipedia.org/wiki/Passive_house

These are particularly suited to cold climates, where thermal capture and storage are possible. I'd first run across this concept via Thorsten Chlupp's Reina, LLC, in Fairbanks, Alaska, where he builds (and lives in) net-zero energy homes based largely on passive designs. The key consideration is thermal energy, though his designs incorporate some PV electrical generation as well.

http://www.reina-llc.com

Chlupp has numerous videos detailing methods and results. The longer ones really get into the weeds, and are fascinating:

https://www.invidio.us/search?q=thorsten%20chlupp%20passive%...

Passive cooling and dehumidification, both critical to interior comfort in the American midwest, are more challenging. I'd like to see how Hodges accomplished those aspects.

Rocky Mountain Institute (Amory Lovins) is another example of passive / conservation-based energy design, including the firm's landmark facilities in Snowmass, Colorado. I've seen the banana "orchard" within the structure's foyer, as well as other design elements.

That equation is definitely changing with modern PV prices and heat pumps: https://www.greenbuildingadvisor.com/article/solar-thermal-i...

Yes. Successful passive solar homes typically aren't all that passive, as they often need fans to transfer heat between the solar space and the storage medium (e.g., Hodges's house had pipes in the cement floor with fans; it was also common in other passive solar houses to have a massive rock bed beneath the foundation with air ducted through it). The traditional passive solar house where a mass floor is heated really only works in climates where it's sunny on a regular basis in winter (basically, the Plains, Rockies, and Southwest). If it can get cloudy, the house will need far more thermal storage and a means of heat transfer and control. The capital cost of the storage and system is considerable, and then operation requires maintenance. Also, the glazing typically needs to be covered overnight to keep from radiating all the heat out. It's not very passive. (I own a so-called passive solar home which is woefully lacking in storage; on a sunny day it'll heat up to 78F inside, but it will lose all the heat out the windows overnight).

Contrast with the one-two punch that is heat pumps and solar panels, each benefiting from mass manufacturing economies of scale. The heat pump can pull in 3KW of heat for every 1KW of electricity applied, and the solar panel can provide the electricity. The total cost is probably less than $20K, works just about anywhere, and provides air conditioning in the summer.

But there's something special about having a low-tech solution which isn't as likely to break, and doesn't require a genius to troubleshoot. As an engineer myself, I prefer a calmer, low-tech approach when possible.

Solar tempering is great! But the point is to get to 100% heating from "passive" solar, you'll need a lot of expensive storage and an active means of controlling heat transfer to/from the storage. It's cheaper to use heat pumps, and, when coupled with solar panels, it lets you get to net-zero, and in existing houses that weren't designed for passive solar.

About 10 years back, I didn't understand why people didn't put up solar thermal panels on their roof, because it was such an efficient way to convert solar energy into hot water.

But since that time, the price of solar PV has dropped so much that panels + wires + an electric water heater is probably the cheapest most maintenance free thing you could do.

That said, I suspect a hydrionic floor system with thermal panels outside for heat and a groundwater loop for cooling might still be the best solution for heating/cooling because of the energy requirements.

I think you mean Ames, IA, not Iowa City, IA... which is a curious mistake to make. :-) I had Prof. Hodges for Physics 221 in 1998.

LOL, Freudian, perhaps... Thanks for catching that! Given how much time I spent at school in Ames vs. Iowa City, I can't believe I made that mistake!

What's even more efficient now is solar panels running a heat pump.

Reply on news.ycombinator.com