Fuel is Fuel.... An alternative view to economy
 

....... I look at fuel efficiency a bit more broadly than just gas mileage............. About 80% of the energy in a gallon of gasoline goes out as waste heat...... and we cannot improve much on that. However in my part of the world we heat our houses burning propane or natural gas..... That's fuel too!!! If I could capture my waste heat.... some % of it, and use it for home heating, I can greatly improve my fuel efficiency, but it cannot be measured by a simplistic figure like "gas mileage". If 20% of the energy in my fuel goes to propelling my car, and I can utilize even 10% of that energy to heat my house, I've achieved a 50% increase in fuel economy. If I can utilize coolant heat and exhaust heat, and lets say store it in molten salt in a tank, and actually utilize 20% of the energy in the fuel for heating, and 20% for propulsion, I've DOUBLED my fuel economy.

This would only be of value during the heating season........ but it might be possible to get my 18 mpg pickup up to an effective 36 mpg.......... better than my car.

We need to look at our overall energy consumption not just gas mileage...... In an ideal world, one would have a thermal solution in an insulated tank, and when you filled your car with gas, you would pump out the solution and replace it with cold solution, and get credited for the thermal value based on seasonal demand, and it would be used in homes and buildings..........

H.W.

I bought a Nissan leaf.
If happen to charge it with mostly natural gas then the power likely came from a natural gas combined cycle plant which can easily be 50% efficient.
If it's from a coal plant, less than 38%.
For wind power I'm just going to say it's about 100% efficient.

In Europe they seem to have figured out how to use waste heat for home heating, but in the US no one really seems interested.

You'd need to choose the salts correctly. https://duckduckgo.com/?q=eutectic+salt

A little research should tell you how big a trailer you'd need to move the salt from the vehicle to the house.

Put an overhead door in the living room, drive on in. :thumbup:

That's not a new idea of mine, but for an entirely different reason. I used to have tenants and even though the driveway was RIGHT FREEKING THERE, they always parked on the grass to save that THREE STEPS. So I thought they might like an overhead door into the house, the lazy ****s. :rolleyes:

Florida couple heeds Dorian warnings and moves their cars
-mort

Good reason to have french doors.

Problem is going to be weight, takes a lot of mass to hold fairly few BTU. Water holds 1 btu per lb per degree F temperature change. To hold 1 gallon worth of LP BTU's (91,500 btu/gallon) assuming a 140(70-210) degree temperature difference in the water/antifreeze you'd need 657 lbs of water (79 gallons). My furnace is 80,000 btu so that would be 68 minutes or run time. I think my last LP fill was $1.25 a gallon but has been over $3 in the past.

So I'd need 2 (40) gallon hot water heaters sized tanks, an heat exchanger in the exhaust (wrap exhaust pipe with copper tube and insulate), an expansion tank and a circulating pump.

Then a way to put the heat into house (already have some radiant hot water floor heat in part of my house so that part would be easy for me. Park in the garage, hook up 2 hoses and turn on the 12v circ pump.

I don't know the specific heat of brine or how that would change things.

Just need to concentrate the heat into smaller and smaller space... sounds like the beginnings of a fusion reactor.

So I used the link I provided and found this:
https://www.cedengineering.com/userf...%20Storage.pdf

It's about cooling instead of heat, but phase change is phase change.

Somebody below linked to a site that presumably explains phase change.... We are NOT talking about brine here, but phase change of a salt from solid to liquid. The principle is the same as melting ice. It takes approximately 80 times as much energy to change ice to liquid water, as it does to raise the same amount of water one degree C. Molten salts or eutectic salts if you will, are engineered to have the phase change of the salt from solid to liquid at the temperature you need it.... this would presumably be around 180F, or a bit lower. The latent heat of fusion of these salts probably is not as high as water, but even at 1/2 that, you would need only a fraction as much as you would need water.
The only reason for having an actual brine, is for mobility in the solid state, and faster distribution of the energy through the mass of salts.

H.W.

Not familiar with the salts, the one linked is for cold storage Freeze/thaw temp of 47 dF wouldn't work well for heat storage, but the latent heat of fusion of 50 btu/lb if that is the same or close for a mixture the that has a freeze/thaw of 180 would work well and obviously give 50 more btu per lbs vs the normal 1 or less btu/lb/dF. I've seen the plastic balls filled with water used inside tanks for chilled storage, I think it would have to be similar here with solid salt inside plastic balls inside a tank circulating anti-freeze to get the heat from exhaust to heat then melt the salt.

So energy wise, to get the same 1 gallon worth of LP (ignoring the antifreeze) assuming the same 140 dF delta + 50 btus latent heat of fusion we get 190 btus/lb, so it would take 481 lbs of brine balls.

Obviously we cold heat it up to 220-240 dF and store a little more heat.

Actually thinking about it now, it would probably work better to us a small liquid to liquid heat exchanger and use the engine coolant on one side and the heat storage anti-freeze on the other side. That would automatically limit max temperature to engine temperature to make controlling it easier. Not sure how to limit max temperature using the exhaust.

I wonder if those plastic bags for water storage have large enough openings to get the balls in. It would form fit to the trunk when filled up and wouldn't need an expansion tank since it's flexible.

This is a very pertinent point. An EV may be 80-90% efficient from outlet to road miles, but there's also the efficiency of power plants to account for, and transmission of that power.

Honda and Toyota both have engines which can make 40% of energy in gasoline usable.

How does one compare the fuel "efficiency" of a solar panel or hydro?

Cost per mile is one way of looking at things, but over what period do you calculate it? A projected lifespan of the vehicle? Do you calculate only cost you have to pay, or should overall cost of production and disposal (and even pollution) be accounted for?

If you have natural gas or lpg or diesel home heating,

Get an EV and a generator. Use the generator to charge the car and use the waste heat from the generator to heat the house.

On the plus side you only have heating when you are in the house.

Why not just design the house to use such little energy that supplemental heating is very minimal? :)

I utilize what you are suggesting when I need to work on my car in the winter, make sure it is nice and warm before pulling into the garage for the free heating.

What we really need is an exhaust heated oven to cook our dinner on our drive home. Simple heat exchanger... Or how about a engine coolant heated crock pot.

My issue with the phase change material is that they tend to loose their effectiveness over time.

Toyota had the vacuum insulated canister to store heated coolant to preheat the engine for the next trip, it would be cool to see that idea on steroids.

It frustrates me in the winter to see industrial cooling towers running expelling waste heat from industrial process water, and then to see the same plants burning natural gas to heat water for building heat. Not even trying...

Excellent question. That would be a hemisphere with an oculus.

Do you have designs for such a house?

Preferrably one in a very hot climate.

Wonder how much work it is to convert a gasoline generator to natural gas.

This is the only one in my albums.
https://ecomodder.com/forum/member-f...1-hausboot.png
This one is suspended on an Eiffel-tower post with decks that shutter the fenestration. I've got everything from McMansions to tiny houses, but not in shape to show. The example is unviewable, isn't it?

Unviewable?
I can see the picture and understand the concept. Is that a vertical wind turbine on top?

Back to the orginal question. Storing heat will be a bit of a problem. (transporting such a mass may be a big problem). There are things like this:

https://www.amazon.com/HotSnapZ-Reus...8243843&sr=8-8

they do a phase change. I am not sure of the thermal capacity of these at the moment.



Another aspect of climate control is humidity. Humidity has a strong effect on how you
perceive temperature. A dehumidifier can be recharged using excess exhaust heat. That would be a worthy use of exhaust heat...

I personally was thinking of using the exhaust to distill water.

The lighting is bad, the reflection is unnecessary. It looks like it's floating on a ring and standing on five legs at the same time. I forget.

The decks that pivot up to cover the doors and windows would work for a wilderness cabin.

I've saved some other models from before but I'm trying to migrate to different software, and I'm having to relearn materials and lighting.

Heat and humidity can be controlled with an enthalpy wheel

I've thought it would be neat to have an interior wall of water to absorb excess heat of the day and release it at night to stabilize temperature.

My favorite idea is an infrared light with tracking to follow people in a room, heating individual people rather than a whole mass of air.

The house temps dipped down to about 68F today, and I found my fingers weren't keeping warm. I'm still adapted to summer temperatures.

Which materials lose their effectiveness? I mean, water never gets better or worse and converting between solid, liquid, and gas.

Teoman,
I have built two. Another one of my hobbies. All you really need to do is achieve very high R values in the floor, walls, and ceiling and do good air sealing. Stay away from scam products that lie about R values. Radiant barriers and air sealing products are bad about this, they work but their effects can’t be quantified in terms of an R value. You don’t need fancy products, just add more of the same insulation for what is usual in your area for construction which keeps the cost affordable. I had to quit posting on energy efficient housing forums as this advice is contrary to what lines the pockets of the forum sponsors.

They look just like normal houses, except the exterior walls usually end up very thick. For example my brick faced double stud wall is 21 ¾” thick and has a true R-67 after discounting for thermal bridging. Insulated with Recycled (used) polyisocyanurate foam (unbelievably cheap, get fiber faced not foil faced for moisture reasons) between the stud walls and fiberglass. The internet is full of wisdom here (search Passive House), you just have to shovel through the garbage. In order to transplant a design from one climate to another you must pay attention to humidity and moisture. Do not just grab a design from up north and build it down south.

Use fewer larger windows (save cost for same amount of light) and spring for triple panes or better. (Vinyl replacement triple panes are affordable, only 10-20% more than similar double.) Get the R values high enough and all you need to condition the space is one or two mini split air conditioners. Lighter exterior colors and cool roofing products reduce the temperature of the outside surface, aka if you want a dark exterior you need even more insulation to get the same performance.


Redpoint5,
I was talking about phase change solutions, usually waxes or salts, sold in packets and marketed as PCM. I can’t explain it either, but the data sheets show a drop of in performance after a number of cycles. I assume the chemistry degrades over time? Obviously normal materials don’t normally stop absorbing heat when they phase change…

The problem being is that if you need a specific temperature of phase change there are relatively few options other than those solutions. I purchased a quantity of PCM packets that change phase at like 40 degrees for my refrigerator due to the monthly power outages in my rural area. Got to keep the fridge cold until I have time to start the generator.

I believe you were responding to my link of the amazon instant heat packs.

Yes they do lose « performance » over time.

http://www.zonbak.com/knowledge/pass...taway_opt.jpeg
Passive Solar Design Guide page 13

It's been getting down to low 50s, high 40s at night here, and we still haven't run the heat yet. Every few days the sun will break out long enough for me to open the shades and soak up the heat, which will get us by a couple more days without running the heat.

This summer I ran the AC about 2hrs each day that was above about 85 degrees. Just dehumidifying the air made a big difference. I set the temp to 78 degrees for cooling.

I call BS on the statement about phase change materials losing their effectiveness over time. The melt point and freeze point of a chemical does not change over time, nor does the amount of energy required for phase change....Water of course being the obvious example......... of course if an eutectic material is not chemically stable and breaks down, or reacts with itself to produce something entirely different this would not be the case. Otherwise there is no possible change in the heat of fusion of a chemical. If an eutectic material is not stable by itself, it should never be sold for that application. If it reacts to it's environment (containment), then it needs to be contained with something that is not reactive to it. It's that simple.

H.W.

Oops........ I didn't read this before posting. It should have been a "qualified" statement from the start.


H.W.

I used to cook on the manifold when traveling....... There are vacuum insulated containers for cooking........ called of all things "thermal cookers"..... Isn't all cooking "thermal".... Kind of an absurd term. But it's like a thermos..... you heat it to cooking temp, and it holds that temp within a few degrees for hours, cooking your food. Ideal in an RV or sailboat. I use Sous Vide extensively in cooking, most often at a mere 130F for meat. A super insulated container would be perfect for this........... Heat a piece of chuck steak to 130, and hold it for 48 hours, and it is as tender as rib eye... or more, and a perfect pink medium rare all the way through, requiring just a minute or two of searing on the outside to make a perfect steak such as you cannot possibly do on a grill... it tenderizes while never exceeding a medium rare state, rich pink and juicy. Many things can be cooked to perfection this way.
Precision temp control is the challenge... With 180F coolant, how do you regulate temp at 130F in your water bath? The food is sealed in a food saver or zip lock, submerged in closely regulated water. Veggies can be cooked to the perfect crispness / softness, eggs to a perfect custard yoke.......... an awesome tool if you haven't tried it yet!
H.W.

Sounds too complicated trying to store thermal energy instead of converting it into chemical or electrical. Well, maybe a good alternative would be recovering exhaust heat, repurposing an old absorption fridge to serve as an air conditioner, and then if you use the moisture taken out of the interior of your vehicle as a source of water for supplemental injection you'd be able to go leaner and using that moisture to avoind knocks and keep the temperature under control.

I've been planning to store engine heat for my micro-RV, and had spent decades waiting for Glauber's salt to hit the shelves. That's not going to happen in the foreseeable future, but paraffin has nearly the same heat of fusion and its temperature can be readily increased with stearic acid. I've been thinking of using a water muffler to recover the heat and steam from the exhaust, with a pump to circulate it to a tank containing mostly paraffin in thin plastic tubes. The coolant could also circulate to a similar tank. The wax would slowly melt, storing heat near the boiling point for water. To use that heat in your house, you'd only have to hook up two hoses, and circulate water to a radiator.

If we would put a mini-split in the garage and the house, we could use the garage as a heat source in the winter to get heat from for the house. -- This really means we need smarter HVAC/mini-split systems to allow using a garage or other area as a secondary heat source/sink rather than just an inside vs outside perspective. Even stealing heat from another section of a building and moving it to another is preferable (with a lower delta T) vs inside vs outside fairly often. Especially with some minisplits getting high heat transfer ratings.

I see we are getting into masters of science in engineering problems.
I'd say a lot of the heat energy from car to house ideas would probably only be really feasible on RVs. ie: At warmest my garage is usually 20 degrees colder than my house in the winter. If I run a 2000w heater on full blast 24/7 I can pull it up to within 8 degrees.
For the most part a lot of the recoup energy storage ideas are very cool, but a lot aren't feasible because of initial investment vs roi.
Also, natural gas for heat appliances is just about the most efficient way to go.
I do think that the black water box on the roof idea would work. Then you could pipe it to a radiant heating pad in an insulated foundation slab and even a bypass for your water heater. Roofs get unbearably hot pretty much all year round. (radiant walls wouldn't be as efficient... less sun exposure)
White roofs are a way to go too. 90% reflection vs like 2% for black tar. I think its even mandated in nyc building code now. Drops inside temps by a couple of degrees C which is significant.
For the most part, if you were going to do energy saving projects the most bang for your buck would be to:
Reinsulate with High R-value materials, airtight to like 99% so no leaks, clean air management system, updated high-efficiency appliances, and all natural gas heating appliances (ofc tankless water heaters).
If you bought a place in need of a remodel/update and are not replacing good components it could pay for itself.
Then your energy bill would be so low it wouldn't matter. That's my goal. Do that as my first 90%, then my last 10% would be adding renewables/recap. The only problem with those is as stated: initial investment, ROI, doesn't add to value of the house... You would have to take it with you or anchor yourself. Also, here locally you're not allowed to be on the grid while you're generating solar.
Also for reference:
NGCC power plants are up to 62% efficient.
Honda Toyota are up to 41% efficient now.
LS cars are up to 36% efficient.
90's jap cars non lean burn were up to 32-36% efficient per bsfc charts.
Coal is actually up to 40% efficient.
Nuclear is up to 35% efficient.
A cool note in the spirit of the op:
My advisor has a patent on a device that captures the steam of the stack if the steam turbine at a power plant, and can recoup that water back into the system in areas where water is very scarce (ie: middle east, certain areas in far east).
Also, we had an ashrae meeting the other day and one of the firms in Little Rock is bidding the new Walmart Campus System in Bentonville. The project requirement: The entire campus is beyond net zero. It makes more power than it consumes and sends it to the grid.
Supposed to be big ****.
**Add step 2. Roof water capture system. Easy money right there.
Back to the fuel is fuel idea.
So imagine you have a power grid that is 32% coal, 32% natural gas, 32% nuclear, and ~4% renewable.
(0.32)(0.4)+(0.32)(0.62)+(0.32)(0.35)+0.04(100)= ~47.84% efficient
Then the power transfer efficiency at 10% loss -> 43.056% -> then ev charger to road ~87% = 0.37.5%
Disclaimer: exact specifics are a close ball park... not too exact. The main point to bring is that when comparing direct and indirect emission with the current power grid it really just depends on where you live if your EV is actually cleaner than a new efficient hybrid. But the $/mi cost of the EV is a little better than the hybrid.
I think the end goal will be all-electric end users so we can choose from many different sources of energy to avoid price hikes like gasoline.

Heat from an in-vehicle storage tank can be recovered from a cold garage. An insulated hose would help more to a vehicle outside.
My roof gets a nice blanket of snow for several months, and chipping ice from the colder eaves to prevent pools of meltwater getting under the shingles is a springtime chore.
Burning natural gas should be done with a condensing vent, not a heat-operated chimney at a minimum. Realistically, high-grade energy should always be used to run a heat pump to multiply the yield for low-grade heat.

Why even store the energy as heat?
 

Storing the energy as heat is inefficient. Use the heat from the exhaust to boil water and generate steam to turn a generator and charge batteries. When the batteries are full, turn the gasoline motor off and just run on battery power.

If heat is needed, storing it makes sense. The secondary steam engine has been an obvious option for a century, but steam engines are only efficient with a much higher temperature difference, so they would dissipate most of any remaining heat.

How about a sterling engine powering the generator?

Even with high-grade heat, sterlings only get 20%. In heat engines, efficiency is totally dependent on temperature difference. That's why jet engines use such expensive high-temperature materials, and diesels still beat them by letting ordinary metal cool off between thermal peaks. https://en.wikipedia.org/wiki/Carnot...thermodynamics)

No, not necessarily. While modern batteries have poor energy density compared to gasoline, they're still way lighter and more compact than hauling a water heater tank around in your Prius. The other thing to think about is, in a hybrid car, you ALREADY have a storage mechanism - the batteries - built in. All you have to do is build the steam generator and add a heat exchanger to condense the steam back into water.

As for the efficiency of the steam generator, so what if it's not as efficient as a modern steam plant? You're recovering waste heat anyway, so anything you get back is a win. I would think that the reason they don't already have this technology on hybrid cars has more to do with weight, complexity, packaging and safety than thermal efficiency.

That's a good idea. It would probably be more compact and lighter than a steam turbine.