DC Space heaters and BTUs per square feet

[plateauhops]

Hi, I'm looking into heaters than run on DC and am wondering if anyone has used DC heaters with batteries run on solar. [Edit: I started writing this thread because I was interested in understanding heating utilities but have updated it to include what type of multi-utility system it could be useful for]. I may plan to use LiPO4 batteries and I know that's not really common yet, but if you have knowledge on batteries that work with DC space heaters, I would be very interested in discussion.

One measurement I am reading is BTUs, and most of them recommend an average of 5,000 BTUs per 100 square feet. I'm using Tumbleweed Tiny Houses as a research model, since they are built with a standardized quality of insulation, and have many testable examples around 90-120 sq ft.
http://tinyhouseblog.com/stick-built...german-weebee/ (this one used an AC space heater, but 500 watts was turned on twice an hour for 10 minutes and was reported to keep the entire house warm).
From that link: "These houses are energy efficient when well insulated! Currently there is a electric convection heater (500W) at work until I

[Mike90250]

Using solar electric is very inefficient for heating. If you install solar thermal panels, you can harvest almost 3x as much BTU for either hot air or hot water.

Battery capacity for heating is also difficult, as you need batteries to be 6x your nighttime power needs, to allow for a day or 2 of shade/clouds, and to not destroy batteries by deep discharge.

[plateauhops]

Using solar electric is very inefficient for heating. If you install solar thermal panels, you can harvest almost 3x as much BTU for either hot air or hot water.

Battery capacity for heating is also difficult, as you need batteries to be 6x your nighttime power needs, to allow for a day or 2 of shade/clouds, and to not destroy batteries by deep discharge.

Ok thanks! So, if I used a solar thermal for the day, would it store anything for the night?

For solar electric, I'm making a moderate estimate of 12 hours for nighttime, which by one calculation is 166W/h x 12= 1992 Wh. So I'd need 12kwh of batteries... Unless I could use a storage heater?
https://secure.wikimedia.org/wikiped...Storage_heater ( I don't know how it works, but maybe it could be useful. Edit: that link doesn't even work on mine)

[Mike90250]

Even something as simple as a 55 gallon drum, with a low flow circulating pump, would store heat overnight, and slowly release it all night. 35ga might work too. Water is a very good storage medium for heat. you could also use rock in the drum, to take up space, and use less water/anti-corrosion mix too, water circulating will heat the rock, and it will still release it overnight.

Solar thermal also works on cloudy days when solar PV will generate little power (my 3,000 watt array only produces 300 watts on a cloudy day, just 10% of nameplate)

[plateauhops]

Even something as simple as a 55 gallon drum, with a low flow circulating pump, would store heat overnight, and slowly release it all night. 35ga might work too. Water is a very good storage medium for heat. you could also use rock in the drum, to take up space, and use less water/anti-corrosion mix too, water circulating will heat the rock, and it will still release it overnight.

Solar thermal also works on cloudy days when solar PV will generate little power (my 3,000 watt array only produces 300 watts on a cloudy day, just 10% of nameplate)

I'll definitely go with solar thermal. That's a great idea- 55 gallons seems enough. Not sure how much much I will be able to produce with 4PVs, but LEDs and an efficient fridge I'll get. I guess there will be days where I'll only get a couple hundred watts, so a battery system that doesn't "leak" many watts is something I'm looking into.

[Sunking]

Sounds like you live up north with poor solar insolation of 2 hours or less of sun. If that assumption is correct you will need at least 2000 watts of solar panel for each Kwh of usable power, or $4000 just for the panels. That should make up your mind real fast.

[Mike90250]

AGM batteries are currently the winners for high effiencecy, with low standby losses.
Some forms of lithium batteries may be better, but the tech is more set up for high power car usage, not off grid solar, yet.

[plateauhops]

Sounds like you live up north with poor solar insolation of 2 hours or less of sun. If that assumption is correct you will need at least 2000 watts of solar panel for each Kwh of usable power, or $4000 just for the panels. That should make up your mind real fast.

It's already been made up- I would go with solar thermal instead of DC space heaters from solar electric. Yes, I live in the north.

[plateauhops]

Even something as simple as a 55 gallon drum, with a low flow circulating pump, would store heat overnight, and slowly release it all night. 35ga might work too. Water is a very good storage medium for heat. you could also use rock in the drum, to take up space, and use less water/anti-corrosion mix too, water circulating will heat the rock, and it will still release it overnight.

Solar thermal also works on cloudy days when solar PV will generate little power (my 3,000 watt array only produces 300 watts on a cloudy day, just 10% of nameplate)

Would one ~36"x60" solar thermal panel be enough to heat 117 sq ft with enough storage in the drum for overnight? A better way of asking this is, how do I determine solar thermal BTU potential? Does insolation apply in the same way as PVs, just more efficiently? 1kwh= 3400BTUs is one figure I found. I could have it on the same side of the roof of four PVs in an array facing the sun snug with the dimensions of the roof border). (assuming I could fit 5 panels on one side of the roof) I haven't figured out if I'd need/want more for heating/boiling water... (though that would be practical too, even if I had less electricity for a TV, etc; for example my netbook uses an Atom processor at 2.5 watts+peripherals, lcd <15watts). I'm not sure how well solar thermal stores heat when it's facing 90 degrees or the other way (indirectly getting sun, if any), which I'd only do if the solar thermal panels could produce enough without facing the sun on the other side of the roof)

[Mike90250]

Since you are in the north, you will likely have freezing issues to deal with. You may need a drain back system with a differential controller to manage it and the pump.
I've been told http://www.solarroofs.com/index.html is reliable. YMMV.

30 - 50 gallons of 160F water, in a plain, un-insulated barrel, will slowly radiate heat all day and night. I know from making mead, it takes several hours to cool down just a 5 gallon batch before we can add yeast.

[Sunking]

I know from making mead,

Geez I though Moon Shiners was a right coast and south thing. :becky:

[plateauhops]

Since you are in the north, you will likely have freezing issues to deal with. You may need a drain back system with a differential controller to manage it and the pump.
I've been told http://www.solarroofs.com/index.html is reliable. YMMV.

30 - 50 gallons of 160F water, in a plain, un-insulated barrel, will slowly radiate heat all day and night. I know from making mead, it takes several hours to cool down just a 5 gallon batch before we can add yeast.

integrated water filter and heater 2.jpg

So i've been gathering solar, heating, and filtering systems and have illustrated a rudimentary idea of integrating many of the technologies that have been discussed here. I'm starting with a Tumbleweed because of the proximity and visualization of the faucet to the shower, the roof, and a water tank.

http://www.tumbleweedhouses.com/houses/tarleton/

http://www.flickr.com/photos/13664360@N08/3422302775

I'm interested in recycling all shower and faucet greywater into a filtration system, and plan to use an EcoloBlue or other atmospheric water generator that can be connected to two solar thermal water tanks (one for heat, one for shower/faucet hot water).
I would include a differential drain back system.

http://www.ecoloblue.com/30sDeluxeSolar

Apparently one ecoloblue w/ one 300 watt panel can generate 1-3 gallons of potable water a day running at 280watts, which I'd feed into the hot water system provided by the solar thermal, and filtered in a loop. Though there may be better options, as I might even find something that doesn't require the inverter in that package and instead perhaps buy a DC dehumidifier and just feed that into a different purification system. Other obstacles that would bring up would mean air that's too dry in the winter, nor might there be enough humidity to generate water. New questions are: how many watts are needed for the differential and water pumps. (note: the composter is not part of this cycle, and toilet water is not used)

So the goal is to get 4 Solar PVs and one solar thermal panel (or amounting to 3'x5', doesn't have to be exact) (denoted as "ST" in the diagram) to power electric, heat, and generate water using just the roof. It's a puzzle I'm interested in solving. Will update soon.

[plateauhops]

Also, one part of this system which I've never seen tried is a thorough greywater recycler. I think this would be the most challenging aspect, and I didn't detail it enough. Instead of having the greywater flow out of the building and into topsoil or a greywater hookup at an RV park, it would be recycled as much as possible and looped back into a purification system. Every greywater system I've read always dumps it into the soil. I understand that it can pollute the soil if it's not filtered correctly, and thus I am not interested in outputting it to the soil. I only want to send it directly back to the purifier to reuse whatever can be reused for shower and drinking water, however the number of filtering steps that requires. I do not know how much water could be reused, nor how many watts/HP of pumps that would need (but if the PVs are too little, for the purpose of this puzzle, extra electricity could be assumed to develop the integrated utility system first, then to work on making it run on a low wattage system later). It would attempt to separate the solids from the water. This would certainly require some storage of waste, which would need to be delivered to a garbage facility once in a while, just like any other disposable, but it would be dehydrated waste. Considering water used for washing dishes will likely have microorganisms and soap suds in them from food and detergent, I am also interested in if perhaps some of the detergent could be recycled too using a sieve. If the dry food waste could be reliably separated, then I would consider adding that to the composter storage, such that only the composter would hold organic wastes.
Here is a list of wastewater treatment methods:

https://secure.wikimedia.org/wikipedia/en/wiki/List_of_waste_water_treatment_technologies

If anyone knows of ones that emulate a water treatment center at a residential scale, I would be interested in seeing how it could be integrated into the above illustration.
Also, the image I made be a bit blurry, I will try to redraw it with a more clear figures and jpeg compression. Also, the fridge is not an essential part of this system, and could be omitted in the image since it wouldn't be strictly required to run a solarwater tank, AWG purifier, drainback/controller. The AWG includes an ultra-violet light microbial irradiator. Additional technology considerations on possibly filtering urine, as NASA astronauts would do: http://www.wired.com/wired/archive/13.08/urine.html

Also, I know the original forum thread is less related to this, so let me know if I should repost this on a new thread.

In this model I attempt to develop a home that produces heat, water, and electricity. Heat eventually dissipates and is recollected using a solar thermal panel, water must be filtered and purified, and electricity helps run the systems that purify the water. The only thing it doesn't produce is food. The only thing that would occasionally need replacements would be the battery, and the parts for the filters... Everything else would last many more years and any unreusable waste would be removed manually.

[Mike90250]

Alas, greywater re-use is a tough one. It must not be allowed to become stagnant, and many cities have codes preventing it from being recycled except at the city plant. It can't be re-used anywhere for potable water use.
The major way is to use the rinse water from the washer, as the wash water for the next load, in the same day.
Otherwise, treatment usually consists of a tank and leach field like a septic system, but 50% smaller.

California has just (2010) allowed greywater systems to be permitted, but there is still a lot of restrictions. A cattail pond, or lagoon, seems to be a viable treatment system.

Pumping , filtering, straining are all power intensive, and require a lot of manual cleaning.

[plateauhops]

It can't be re-used anywhere for potable water use.

Except by NASA and at Water Security HQ in Reno
from the Wired Link:
"Back at Water Security HQ, the contents of the bucket get a final stir, and the experiment begins. The water is sucked through an intake hose and into the purification system - prefilter, carbon filter, iodinated resin, disinfectant holding tank, iodine scrub, and a polish. (Don't be shy with the polish, guys.)

After 30 seconds, water dribbles out of a nozzle and into a plastic cup. I raise it with a trembling hand. A toast to Alan Shepard and all the brave astronauts who endured the wrong stuff in their space suits for the advancement of science: This number one's for you. I take a big astronaut gulp, lower the cup, and wait for the noxious aftertaste. Nothing.

The water tastes pretty good - it's definitely not Evian, but it is better than most city tap."

So that's why I included the EcoloBlue or other sort of potable water maker. It would produce 1-3 gallons of potable water a day for cooking and drinking water, and then the greywater could be recycled for shower water and laundry... though I did consider recycling greywater to make it potable- it'd be extra-intensive, like what NASA does...I agree most pumps, strains, and filters are very energy intensive. Now I'm going to look for incredibly small systems that filter 3-5 gallons for shower water...(even as few as tens of mililiters might be needed to begin at a scaled down model, find the optimum efficiencies, and then scale back up. I'm interested in one that works like an instant drip coffee maker- processing a few drops at a time, over the course of the day, where 24 hours may be enough to process just the amount needed for shower water, and so it doesn't cause deep/sudden discharges on the batteries, but a gradual usage. Though, I know an instant drip uses a lot of power- and that only boils water..(and not that water needs to be boiled here, but I was using just part of that concept as an example...) though that might be a lot too, and am unsure if it could filter that amount at a lower power over the course of 24 hours using a combination of gravity-fed pumps and active-powered mechanics if I want to take a shower every day...