Calling all thermodynamic engineers ... Sand Battery

[ChrisGreaves]

"Gladwin says the sand battery is great for heating houses in countries with a cold climate, but warns that the efficiency drops off when it is used to return power to the electricity grid."

I am thinking of sand/grit/pebbles only as a heat reservoir in my bedroom.

My new windows in the bedroom, study, and guest room, with their ability to heat rooms, have amazed visitors. During October our average temperatures (ºc) were 14.3, 7.9, and 11.1 as maximum, minimum, mean.
The bedroom (one window facing south) and study (one window facing south, one facing west) would leap to 22 during the day. I left both doors open so that heat would bleed into my living-room, and the temperature there rose to 20.

We were not then mid-winter, and we did not have 36 hours of strong snow-laden northerly winds, but still I am encouraged. Sunny days in winter are common; can I continue to attract heat in this passive manner?

"Management Measures", and it does so so that management can compare. I have not worked out how to compare conditions in a parallel test. I could record hourly temperatures in each room through the next six months of cold conditions, and repeat that next year, with the weather bureau's record of outside temperature, but that is too much work for me.

$5,000 of window installation means I will not have a positive $ROI in terms of energy ($0.13/KwH). The windows are being installed to reduce heat-loss through draughts, and to boost my mood; I like to see the world, either rampant pumpkin vines or a fresh blanket of snow.

That said, I have space under the bed in my nine foot by ten-foot bedroom. And over the past four winters I have harvested cleaned road-grit and now have about fifteen gallons of grit.
If I load the grit into containers, and for the next six months store those containers under my bed, will they absorb heat during the day and release the heat at night?

Here I am interested in the principle. Right now I have no way of measuring whether or not the scheme will work.
Nor am I considering mechanisms to pump hot air through the grit; just small enough containers so that the heat can travel within the hour. That is, I suspect that a 55-gallon drum would not warm up in the centre during the day, and stored heat would not escape during the day, whereas a 355ml tomato paste can may be sufficiently efficient.

Thoughts welcomed
Chris

[LineLaline]

Oh wow, this is so interesting!
Thank you so much for sharing

[John Gray]

Is that US gallons or UK gallons?
Litres would be less ambiguous, of course...

[ChrisGreaves]

Litres would be less ambiguous, of course...

I agree, but we have to give our American cousins something that they can grasp, even if it is inaccurate

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How are my new windows performing?
I did a very crude calculation this morning.
The table above shows data for the first thirteen days of November for 2021 and 2022 from my local data site.
In 2021 the average minimum was 3.5 degrees, in 2022 2.9 degrees, so this year is "colder" than last year.
In 2021 my total heating co$t was $47, in 2022 $49.

A very crude measure is the cost of energy to heat my home. I spent $49 in the first thirteen days of this month, but only $47 for the same interval last year, a rise of 3%.
But last year's daily minimum temperature was 22% lower, so, crudely, I think that I am better off.
There are many factors that might improve my view;-
(a) Wind speed. Stronger winds pump away more heat.
(b) Wind direction. Northerly winds pump away heat.
(c) Temperature maintained indoors. Lowered thermostats consume less heat.
(d) A higher external maximum lowers the temperature gradient.

Then I have to consider those "Heat degree" days.

At 11:30 the bedroom is at 19, the daytime thermostat setting is 13, so I open the door and heat floods into the living-room. Hooray!

Cheers, Chris

[ChrisGreaves]

This you tube video focuses on using a kitchen electric jug element to heat a tub of sand, and then using the hot tub of sand to regenerate electricity.
My starting thought last Fall was to capture heat from the hot days and use it to offset the chill that same night; a short-term transfer of heat energy.
I was not thinking of storing seriously hot sand.
cheers, Chris

[GeoffW]

Sure, that's possible. Check out Passive Solar Building Design - in particular thermal mass.

Stone may be more effective than sand - I have seen stone and brick used for this. Naturally, you'd want darker colours.

[BobH]

Look into trombe walls.

[GeoffW]

Look into trombe walls.

You can't look into walls unless you have windows (as distinct from Windows) - and Chris has them covered. Or uncovered.

[Graeme]

The UK uses storage heaters which are high mass bricks with heater elements inside all wrapped up in an insulating material. They come on at night consuming a lower tarrif off peak electricity and let the heat seep out during the day.

They're ok if you are indoors all day but if you're not then you are paying to heat empty rooms.

They are especially good at helping to level the peaks and troughs of the power station output graphs!

Using the free energy from the sun to do the job is a much better idea.

[ChrisGreaves]

Sure, that's possible. Check out Passive Solar Building Design - in particular thermal mass.

The house in Gawler (Adelaide) had 18" thick limestone walls. It stayed cool in summer for the first couple of weeks, then gradually warmed up and in winter time we kept at least one of the five fireplaces stocked with large mallee-roots, so the living-room at least stayed warm through the bitterly cold winters (which dropped as low as 5c on a few nights hah hah hah!)

Passive is what I was thinking of. Just push containers of sand under the bed and leave them there. That gave me the hurdle of containers - in the limit, storing sand in foam containers wouldn't work, and wood would not be much better. Passive heating of sand seems difficult.

Stone may be more effective than sand - I have seen stone and brick used for this. Naturally, you'd want darker colours.

One thing we do have in Newfoundland is ROCK and I now suspect that this might be a better option. Dig them out, leave them in the rain overnight, then slide the biggest ones under the bed.

Then I am faced with a problem of measuring effectiveness - daily temperatures, daily consumption of electricity, and daily temperature readings.

That is why this winter, my first winter with four larger windows, I am suspecting that I lose more heat than I could have imagined through these 24 square foot windows. In spring and fall they are great, but unshaded in summer they may well turn my house into Bonavista's greatest meringue producer, and in winter, well, $300/month for electricity (this time last year $200-$250 tops) tells the story.

Cheers, Chris