Heater element? (not for water)

[DThames]

I am looking for ideas to heat a block/pile of concrete or metal mass with extra PV energy. So looking for some heater element ideas, other than for water.

Total available watts, about 3000 at 135v open circuit. Several heaters in series or parallel would be okay.

 

[acdoctor]

In the past I have seen commercial kitchen hot tables with 3 or 5 kw electric. In a inch thick aluminum plate. You might find something salvage and add more mass. Also in floor heating mats like for bathroom floor maybe.

 

[DThames]

I wonder what the results would be if you embedded a grill type heating element into a slab of castable refractory cement.

 

[Rednecktek]

I wonder what the results would be if you embedded a grill type heating element into a slab of castable refractory cement.

That's pretty much what we use on ships, but you don't want to embed the element in the refractory because of the expansion and contraction. Instead you cast the plate then dremel out a groove in the bottom for the element to sit in, then sandwich the element between 2 plates. Works well if you have the amperage.

 

[12VoltInstalls]

Does the ‘mass’ of which you speak exist now?

I’m not certain but I think an insulated concrete water tank may be a better thermal storage system. Other than soapstone or some ceramics I don’t think other solids like concrete holds heat as well.

I have been in homes of people who have poured concrete containing a big percentage of soapstone aggregate around a plastic water tank then insulated that with foam for wood-fired and solar heat storage in water.

 

[DThames]

Does the ‘mass’ of which you speak exist now?

I’m not certain but I think an insulated concrete water tank may be a better thermal storage system. Other than soapstone or some ceramics I don’t think other solids like concrete holds heat as well.

I have been in homes of people who have poured concrete containing a big percentage of soapstone aggregate around a plastic water tank then insulated that with foam for wood-fired and solar heat storage in water.

The mass does not exist. I am just kicking around the idea.

 

[efficientPV]

Water heater elements are cheap. You could sink a couple in concrete with connections exposed. If straight expansion wouldn't be a problem. Concrete doesn't transfer heat well so I would operate them at reduced voltage for low heat density.

 

[12VoltInstalls]

kicking around the idea

Concrete doesn't transfer heat well so I would operate them at reduced voltage for low heat density.

That’s sorta why I mentioned water storage rather than solids. Other than tulikivis and soapstone-clad woodstoves any thermal storage I’ve ever seen was water or water/glycol.
I guess a couple advantages to water are the ease of “moving” the energy from one place to another; you can transfer energy from one medium to another fluid simply; and the ‘cost’ of the medium is very low.

Concrete and rocks can never be relieved of their weight and volume and even heating is more complicated.

Just my opinion.

 

[rcrracer]

https://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html
Plus, water is cheap and easy to move.

 

[efficientPV]

Storing heat in massive chimneys is old technology. A concrete block would be a good way to store excess energy for overnight cheap. Just hard to move around and support. It would be interesting to sleep on. Electrodacus heats his concrete floor with just imbedding TTHN copper wires.

 

[Quattrohead]

Heating elements from clothes dryers or HVAC heaters could possibly just have concrete gently poured around them or have a block system stacked over them.
Kind of like the old Economy 7 storage heaters in the UK.

Amazon.com : Furnace Replacement Heating Elements

Amazon.com : clothes dryer heating element

 

[circus]

https://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html
Plus, water is cheap and easy to move.

Plus, water stores twice as much per pound.
Like cheap batteries, the holy grail of thermal storage is phase change. If you could find something that would turn to solid at say 70°F, heating and cooling costs would plummet. Raising water from 31.5°F to 32.5° takes the same energy as raising it from 33° to 177°

 

[DThames]

My interest is not so much in storing heat for a specific period or use but to smooth out the delivery of that heat into the house. On these sunny less than cold winter days, I could take 3000+ watts into the house that otherwise would be unclaimed potential. I don't need 3000 watts for 5 hours. If I could add 1000w to the house and 2000w to a mass, the mass could then cool (into the house) after the sun goes down.

I found some range elements on Ebay that might be worth messing with. I have some 3s, 60cell, strings coming into the house. So 105-120v on a 240v element might be a place to start. Certainly will not get anywhere near rated watts but running cooler would be fine.

 

[rcrracer]

My interest is not so much in storing heat for a specific period or use but to smooth out the delivery of that heat into the house. On these sunny less than cold winter days, I could take 3000+ watts into the house that otherwise would be unclaimed potential. I don't need 3000 watts for 5 hours. If I could add 1000w to the house and 2000w to a mass, the mass could then cool (into the house) after the sun goes down.

I found some range elements on Ebay that might be worth messing with. I have some 3s, 60cell, strings coming into the house. So 105-120v on a 240v element might be a place to start. Certainly will not get anywhere near rated watts but running cooler would be fine.


View attachment 81312

A mini split that heats water. Resistance heating has a COP of 1 while mini splits, in heating mode, can have a COP of up to 5.5(?).

 

[rcrracer]

Plus, water stores twice as much per pound.
Like cheap batteries, the holy grail of thermal storage is phase change. If you could find something that would turn to solid at say 70°F, heating and cooling costs would plummet. Raising water from 31.5°F to 32.5° takes the same energy as raising it from 33° to 177°

Frequently asked questions about phase change materials - PureTemp

What are phase change materials? Phase change materials (PCM) are substances that absorb and release thermal energy during the process of melting and freezing. When…

puretemp.com

 

[efficientPV]

I would prefer a heating element with a metal sheath because of possible corrosion. I saved an old dishwasher element and it is easy to make gradual bends into other shapes.

 

[DThames]

I put two of those stove top burners (image above) between some concrete blocks/pavers and wired them parallel to 3 series, 60 cell panels for about 105v max power. Plugged into 120v AC, each burner was consuming a bit over 300w, of its 1200w rating, so not red hot like on the stove top. So connected to the 105v solar, it will be less than 300w per unit. My temp sensor display maxed out at 110C, but it was somewhat hotter than that on this cloudy day. It took a few hours to reach 110C and a few hours to cool back down, which is my goal, to spread out the heat over time.

If I built this for some real use, I will put it inside a metal box so the concrete can be taken on up in temp a bit. With some ventilation of that box, the heat can be dumped to the surrounding air but at a slower rated than the solar heating on the concrete. That is the concept, anyway.

 

[Quattrohead]

Yep looking good.
I am so happy I have the opposite problem here in Florida, I need a cool thermal dump. I guess I will make my house slab 10 foot deep

 

[rearden]

I have played with 5 gal water containers with 250w coffee mug heaters (with a home automation controller, emonpi and a zwave switch.) Heat the water and let it cool down over night. I have thought about a horse trough with a deicer. I could then transport the heat via pex. But a stack of bricks with some old heater elements have the benefit of not steaming up or leaking in the basement.
There should be some kind of thermal paste which you could put around a heating element to transfer the heat into the mass. Something which you could buy in affordable larger quantities than cpu grease. Something to pot the element which would expand and contract, but could directly transfer the heat by conduction.

 

[rearden]

A mini split that heats water. Resistance heating has a COP of 1 while mini splits, in heating mode, can have a COP of up to 5.5(?).

Do you have any recommendations?