Mass heat storage - indoor water tank??

[gotwind2]

Over on Treehugger.com I read/ watched a very interesting article.

A smart guy in Idaho has built a clever passive and active solar home, and converted his car to electric.

http://www.treehugger.com/files/2009/05/selfbuilt-solar-home.php

Pretty obvious stuff, what interested me was his comment on using passive solar heating to warm a 120 gallon tank, Aquarium (i think) indoors, not sure how the fish would react to it??

The benefit being, the stored heat is slowly released throughout the colder evening/ night time through mass water storage compared to rapidly cooling solar heated air.

It seems a very simple inexpensive idea tp me, that's maybe worth discussing.

Ben.

[Airstream]

Idaho can be COLD. When it is say -15 (C or F) and below and that cold air is 15% relative humidity, when you warm it it becomes extremely dry which feels like fire to breath day in and day out. We keep aquariums just to give supplemental moisture - and on the driest, coldest days just walking by the aquariums you notice the vapor pressure as 'heavier' air, 'much more pleasing to be around' air, like you find at the base of a waterfall or in a canyon down by the water.

You mention the articles 120 gallon water tank being used for heating. With 120 gallons weighing 1000 pound and allowing 1 BTU per pound per degree F specific heat if you heated that water 10 degrees above room temperature it would store an extra 1000*10 Btu which equals the same heat as 7 sq feet of solar collector receiving 5 hours average sun. If it could go to 100F over room temperature its nearly 30 Kilowatt Hours worth of power, or 140 Btu per hour released for a month!

BUT to transfer that heat efficiently you need a larger temperature difference than 10 degrees, yes it would be pleasing to sit next to, but perhaps if it is really an aquarium I expect its for quality of living, pleasure and humidity since any higher temperatures would not support fish or plants.

[Fish4Fun]

I agree with Airstream that an "open aquarium" will certainly help with maintaining relative humidity and help provide some passive heat storage, but I do not think it is the most efficient way to provide passive heating to a home where someone has invested in a 2244W Solar Array!  Assuming an installed cost of $10/W he's @ $22,440 with his "best day" at ~15.3kWh (roughly $1.53 return with a loan for the same amount @ 6% costing $3.69/Day).  If he replaced his "heat tubes" with a couple of good quality solar collectors totaling 6M^2 (~65 sq ft) they could provide upwards of 20kWh of low grade heat with his 3.3 Winter solar hours.  He could probably install the two collectors and a 120 gallon heat storage tank filled with sodium sulfate combine it with his domestic hot water system and a couple more heat exchangers for $4k, less if he does the labor and some homework.

I am all for solar power, but the first investment IMHO should be domestic hot water and low grade heat.  Solar PV is very difficult to cost justify.  His "Electric Car" for instance, he added 4 solar panels and said they would give him an additional 4 miles in the summer, I think that may be a stretch, but let's just assume they can.  Let's assume he got a real deal on the panels and that they were $400 each ($1600 total).  At $0.10 per mile he would need to travel 16000 miles on the solar panel provided energy to "break even".  At an average of 10 miles per day (1/4 of his max range) this would translate to 1600 trips, or a minimum of 4+ years.  Assuming his panels put 125Wh each into his batteries, he can charge them up to 500Wh per sun hour.  His battery capacity is 10.5kWh (48V * 220Ah), and his range is ~40 miles.   this means he is using 260Wh/Mile (which is a very low figure).  So, his 10 mile trip will consume roughly 2.6kWh which in turn will require 5.2 sun hours to recharge @ 500Wh (net).  Assuming an average speed of 20MPH, a half hour drive will take 5.2 hours to charge!  I think there might be a future in electric cars, but only if they are carefully engineered to be electric cars, not conversions from the junkyard and the internet and Costco.  

I applaud Mr Weber for his enthusiasm, intentions and commitment, but I think much of his investment is wasted.

Fish  

[electrak]

You mention Sodium Sulfate in a heat storage tank, is that Sudium Sulfate solid as phase change, or is it in water of better heat density?

[Jon Miller]

Phase change,

Being done with cars to store the waste heat.

I agree, low grade heat should be solar solar solar! space heating requirements at 40% of the UK energy demand and cooling loads in the USA could be met with cleaver use of passive gain and appropriate deployment of technology.

Sadly in the UK the buzz is all about heat pumps, which is a cock and bull story.

I attended a public talk with so called experts in policy and the national electricity grid and they both talked about heat pumps as being the future.  I pointed out during Q and A about passive heat and they looked at me as though I was backwards!  

Retro fitting is the future for low grade space heating hence my attempts:

Which I have proved to produce around 1200kWh of heat per annum for a £200 total build and install cost!

http://www.otherpower.co.uk/costings%20for%20can%20solar%20www,cansol,co,uk.pdf

Regards

[CmeBREW]

Interesting info Ben.

    Even though I am just more of a 'beginner' with this type of stuff, I suspect it is a great idea also.  I have been fliping around a very simple design myself.

Currently I am working on a Solar Hot Water system using a homemade collector (1/2" PEX tubing) out in the yard and a 55 gal plastic drum in the basement, right beside the electric HWH.

I just got the tiny circulating pump going yesterday, and even though it was totally cloudy, the plastic tank heated up the little utility room a bit I noticed, since I don't have the R13 insulation around the tank yet.

It seems like a very simple idea.  Pex tubing is only $25 bucks per 100'. (1/2"diam)

So one 100' section goes for the collector and the lines to the plastic tank, and the other 100' section for the heat exanger inside the tank. (which is easy to put into it, cutting alittle square out the top)

And then a tiny CPU/or pond pump ($15 bucks) circulates the hot water at nightime.

It is a neat idea for less than a couple hundred bucks.

Soon, I will show my posting for my simple Solar hot water heater.

[sbotsford]

Storing hot water is effective.  Aquariums aren't the way to do it, unless you want poached fish.  Most fish get really unhappy with more than a few degrees temp change in a day.  Water contains less oxygen as it gets warm -- which is why trout need cold water to grow.

A 100 degree F temperature swing on a 55 gallon barrel of water is a bit over 40,000 BTU.  Which  is also about half an hour output of a household furnace.  Now a furnace hopefully isn't running night and day, so that barrel of water can be several hours heat for your house.

It's not unreasonable to put, say 12 barrels, in your house next to the furnace. Insulate them well, and provide to shutter vents on them.  One connects to the cold air return for your furnace.

Set the house up with 2 thermostats.  The first one just turns on the blower.  It pulls air out of the barrel box, and pushes it through the house.

The second one, set a bit lower, turns on the burner.  Note that even when the burne comes on, it's using air pre-warmed by the barrels.  You may have to fiddle with the high temp cutoff to allow hotter air through your vents.