Very much more efficient, but you won't be able to reach very high temperatures because a heat pump like that can't handle that.
Storing heat in sand?
- Thread starter Guda
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And you are slowly coming to my solution. Instead of storing heat energy, I store electrical energy in the battery. And when heat is needed I start the heat pump. The pros - no heat energy losses and close to constant round trip energy losses (~20%). And electricity can do a lot more than heat. It can cook, it can cool, it can run the TV.
Common heat pumps lose efficiency when you push their output to high temperatures. The lower the output is, the higher the efficiency is. If you plan to heat the oil to 30-35C then yep, it will work. If you plan to heat it up to over 100C - nope, it won't work.
Common heat pumps lose efficiency when you push their output to high temperatures. The lower the output is, the higher the efficiency is. If you plan to heat the oil to 30-35C then yep, it will work. If you plan to heat it up to over 100C - nope, it won't work.
Mart Hale
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Yeah, the more I look into it, it may need to be something custom...
I am hearing numbers like for 1 unit of energy you put into a standard coil heater you get 80 % energy out, but with a heat pump you get 200% back ( provided you have optimal conditions ) ....
This makes me want to learn far far more about heat pumps, I have seen people hack them on youtube.... and makes me more want to follow down this path...... of exploring what options are our there.
Mart Hale
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Yeah, I am off grid, and have like 30 KWH of storage. I have been always looking of how to use that energy even wiser, I am interested in the heat pumps that run directly from solar, that has my attention.
Coil heaters are 100% efficient. Every unit of electric energy you put in, you get back as heat. Heat pumps can be way more than 200% - it is determined by the COP of the device together with ambient temperatures. For example, I have a heat pump that has a COP of 4 (and over). This means that for every kWh of electricity I put in, I get 4 kWh of heat energy out of it.
MyK3y
Hack
Using an air-to-air heat pump to heat sand seems counterproductive - they're designed to heat and blow warm air throughout your house. I owed have one, except my wife doesn't like them - she's not a fan of having air blowing all over the place, cold or hot.
They are very common in NZ and Australia.
The colder the climate the less effective they are, as they are basically a thermal condenser, extracting low levels of heat from the air and concentrating them.
They are, in essence, the opposite of an AC unit or fridge.
Decent heat pumps can operate in reverse in summer and cool you down.
Their popularity here comes form the fact you get 3+x the electrical energy you put in back in heat energy. We are now seeing heat-pump water heaters for the same reason - bang for buck there is no better off-the-shelf domestic heating system. We are likely to replace our gas instant/tankless hot water heater with a heat-pump water heater. They were prohibitively expensive, but you can get a decent one now for $2k.
However, when your temps get below 20C, they don't really work that well, if at all, which is why they are less popular in the northern cold climates. In that case, wter-to-air and ground-source heat pumps come into their own, but the installation costs are the prohibitive factor. If we had a decent supply of ground-source heat pumps here, we would get one of those and run radiators, but they're rare and expensive. Running costs are trivial, which is why they're popular. Basically paying just to run the pump - 50-100W.
They are very common in NZ and Australia.
The colder the climate the less effective they are, as they are basically a thermal condenser, extracting low levels of heat from the air and concentrating them.
They are, in essence, the opposite of an AC unit or fridge.
Decent heat pumps can operate in reverse in summer and cool you down.
Their popularity here comes form the fact you get 3+x the electrical energy you put in back in heat energy. We are now seeing heat-pump water heaters for the same reason - bang for buck there is no better off-the-shelf domestic heating system. We are likely to replace our gas instant/tankless hot water heater with a heat-pump water heater. They were prohibitively expensive, but you can get a decent one now for $2k.
However, when your temps get below 20C, they don't really work that well, if at all, which is why they are less popular in the northern cold climates. In that case, wter-to-air and ground-source heat pumps come into their own, but the installation costs are the prohibitive factor. If we had a decent supply of ground-source heat pumps here, we would get one of those and run radiators, but they're rare and expensive. Running costs are trivial, which is why they're popular. Basically paying just to run the pump - 50-100W.
MyK3y
Hack
Like magic all the bits I needed came together - will head to the beach tomorrow with a bunch of sacks for sand to make a prototype. Our local sand is black - titanomagnetite - Fe2TiO4, a mix of iron and titanium. The downside is that it is electrically conductive, so I will need to attach my conductors through the side of the drum using exhaust gasket or similar high-temperature putty, rather than laying bare copper in the sand itself.
As I have two of everything, I might go to the builders merchants and pick up a couple of hundred kilos of sharp sand as well and run them back-to-back..
As I have two of everything, I might go to the builders merchants and pick up a couple of hundred kilos of sharp sand as well and run them back-to-back..
Mart Hale
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I used to collect this with magnets for making cores for my Muller motors, ahh those were the days.
MyK3y
Hack
The whole of the west coast of the island I live on has black sand beaches. This one is only about 6 miles from my front door.
It was purely coincidental - I was looking for sand and saw our regional plan (covers all the things you can do to trees, rivers, beaches, etc.) said I could take 300kg a year for personal use.
Did you smelt it yourself? (He who smelt it, cast it!)
Mart Hale
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No, I never made it that far, I made several "free energy" devices and came to the conclusion I was putting too much $ in and getting zero energy gain out that I moved on to systems that give me energy every time like solar..... I have been working on looking at ceramic kilns, and I was thinking of running one off direct DC... TOOOO many projects, but I would like to melt aluminium and use my 3d printer to make the molds....
orangezero
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Is there already a thread? I've seen a few decent designs for DC induction heaters which can get hot enough to melt aluminum. With enough solar you could skip the expensive power supplies and it all suddenly becomes quite inexpensive. Add in some insulation...
Hedges
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Mart Hale
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orangezero
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Sorry, yeah like one of those. The power supplies needed can be crazy expensive, but if you have a huge DC battery from solar... Same with some audio equipment I've noticed.
Induction heater has lower efficiency (~80%) compared to resistive heater. There are even OOB MPPT devices for resistive loads like water tank heaters. I don't see benefits in considering inductive heating here.
MyK3y
Hack
Back to sand batteries: the guy I was buying the barrels off lives near my Dad (130km away) so I was going to kill two birds with one stone.
Of all the days he is not working a Saturday it's this one, when we were already aiming to go to that town.
I'm not going to spend $30 worth of gas to go get a $20 barrel, so it looks like no sand battery this weekend
And, the weather has gone from glorious early spring sunshine to three days of misery - bad enough that it screwed our power connection from the street and I had to call the power co to come and fix the pole.
The best laid plans, and all that...
Of all the days he is not working a Saturday it's this one, when we were already aiming to go to that town.
I'm not going to spend $30 worth of gas to go get a $20 barrel, so it looks like no sand battery this weekend
And, the weather has gone from glorious early spring sunshine to three days of misery - bad enough that it screwed our power connection from the street and I had to call the power co to come and fix the pole.
The best laid plans, and all that...
You know how induction work ? There is nothing like DC induction, induction imply changing magnetic field => AC current. Well of course you can create AC from DC .. but this is in no way DC induction, appart if i missed something .. :D
Mart Hale
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So using nitrol wire to make a kiln may be a better choice.... The advantage would be for convenience for bending metal..... they are very handy if you want to put a bend in metal and not heat up the entire bar.
Do you really not get that he is talking about the source of power being DC? Of course the induction side is AC. I haven't been following along that closely and immediately understood that "DC induction heater" meant "induction heater powered by DC".
