Oil in vacuum tubes

[renewablejohn]

We last heard from WillyP near the end of May 2021.
Wondering how they did with solar heat storage.

Maybe the warning of the construction of a potential bomb came to late.

 

[rin67630]

Oil will be much harder to pump when it gets cold.

Why would you want to pump it when it is cold?
Arent't you supposed to transport heat?

 

[Insolation]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

 

[upnorthandpersonal]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

You could build a sand battery, and use a heat exchanger with water to extract the heat.

Thermal energy storage - Wikipedia

en.wikipedia.org

Cheaper and safer than hot oil, no leaking.

 

[Mart Hale]

I suggest you watch this guys videos ->

he has out of the box thinking and the comment section is gold.

 

[Mart Hale]

You could build a sand battery, and use a heat exchanger with water to extract the heat.

Thermal energy storage - Wikipedia

en.wikipedia.org

Cheaper and safer than hot oil, no leaking.

This guy heats it up with a fire outside and brings it inside.

 

[Warpspeed]

Pumped solar thermal systems used to be the big thing a few decades ago, and we all know the problems of boiling and freezing, constant maintenance, leaks and so on.

Technology has come a long way since the old days, heat pumps are now vastly more efficient, and solar panels and batteries have improved as well, and come down in cost.
Water is pretty difficult to beat as a cheap non toxic bulk thermal storage medium.

These days, a solar/air sourced heat pump working into a large water thermal storage, powered from solar panels, might be worth investigating.

 

[WillyP]

Maybe the warning of the construction of a potential bomb came to late.

LOL! I'm still here. Don't be sendin' DHS to the house yet. I did get delayed due to a car crash. I won't be building anything for at least another year. But I am healing and growing stronger.

 

[WillyP]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

that would work. But I am designing a system tht will actually heat the house all winter. I'm not looking to supplement a different system.

As to heat transfer fluid, it is formulated to cool quickly. Usually it is used in large machines that need to be cooled.

 

[WillyP]

Pumped solar thermal systems used to be the big thing a few decades ago, and we all know the problems of boiling and freezing, constant maintenance, leaks and so on.

Technology has come a long way since the old days, heat pumps are now vastly more efficient, and solar panels and batteries have improved as well, and come down in cost.
Water is pretty difficult to beat as a cheap non toxic bulk thermal storage medium.

These days, a solar/air sourced heat pump working into a large water thermal storage, powered from solar panels, might be worth investigating.

you do make some great points about the cost of PV solar. But I really really want radiant floor heat. I will get my electricity from PV solar. It will run the AC.

 

[WillyP]

As an update. I have been convinced oil is a bad idea. It has many good points, but the bad outweighs the potential.

I will be using water in the vacuum tubes to heat underground storage tanks. The main reason I am doing it that way, is so I will have a constant supply of water heated to a specific temperature (95°F).

As for building this system and more importantly my new home. I had a pretty severe car crash in September of 2021. I will be needing another year (or two) before I can start a project this huge. For now I am living in my house in Dale City VA.

 

[Warpspeed]

I have some practical experience with a fairly large (25,000 gallons) solar powered hydronic heating system that was installed in a school.
Your hope of maintaining a constant water temperature is hopelessly impractical.

Any heat added or removed from the storage will greatly change the water temperature, and its that temperature change that represents the useful energy. The greater the temperature swing, the more energy is stored/released per unit volume.
You quickly reach the point of either of boiling, or the water cools so much its not hot enough to do anything useful with.

Its all very well to say increase the volume of water, we had a tank about twenty five feet high and about fifteen feet in diameter (from memory).
It was HUGE.
But it really needed to be about five times that volume to work the way it was supposed to work.
I was not involved in the original planning, that was before my time, but I was the poor bugger that had to monitor the project and maintain it.
It simply did not work, and was ripped out and replaced with heat pumps a few years later.

I suggest you do all the thermal calculations before you spend a single dollar.

 

[WillyP]

I have some practical experience with a fairly large (25,000 gallons) solar powered hydronic heating system that was installed in a school.
Your hope of maintaining a constant water temperature is hopelessly impractical.

Any heat added or removed from the storage will greatly change the water temperature, and its that temperature change that represents the useful energy. The greater the temperature swing, the more energy is stored/released per unit volume.
You quickly reach the point of either of boiling, or the water cools so much its not hot enough to do anything useful with.

Its all very well to say increase the volume of water, we had a tank about twenty five feet high and about fifteen feet in diameter (from memory).
It was HUGE.
But it really needed to be about five times that volume to work the way it was supposed to work.
I was not involved in the original planning, that was before my time, but I was the poor bugger that had to monitor the project and maintain it.
It simply did not work, and was ripped out and replaced with heat pumps a few years later.

I suggest you do all the thermal calculations before you spend a single dollar.

It sounds like a really poorly designed system. I really don't think keeping water at a certain temperature is all that hard. Especially if I use heat exchangers and a discharge tank. My system is designed to be under ground, inside a greenhouse with an insulated bottom. I could see some over heating as a problem. But not enough to render the system unusable.

 

[Hedges]

Sure, you can keep water at a certain temperature. All you have to do is put in exactly the amount of energy lost.

That is like keeping decoupling capacitors at a specific voltage. Easy enough, but they provide absolutely zero energy storage. Only by cycling in voltage (temperature in the case of water) do you get to store/extract energy. With the exception of phase-change materials, but many of those work over a temperature range. Ice in water is one with a set temperature.

You could use a hot water tank plus tempering valve to deliver constant-temperature water.

 

[WillyP]

Sure, you can keep water at a certain temperature. All you have to do is put in exactly the amount of energy lost.

That is like keeping decoupling capacitors at a specific voltage. Easy enough, but they provide absolutely zero energy storage. Only by cycling in voltage (temperature in the case of water) do you get to store/extract energy. With the exception of phase-change materials, but many of those work over a temperature range. Ice in water is one with a set temperature.

You could use a hot water tank plus tempering valve to deliver constant-temperature water.

The tempering valves are usually used in gas fired systems. Or at least that is how I understand it. In a closed system, the water doesn't cool when some of it is removed. The only way that would happen is, if the cold water was returned to the storage tank. I plan to have a discharge tank that will store the cold water, then heat it before returning it to storage. Of course the storage could cool if it wasn't kept at a constant temperature. But being buried in an insulated vault should keep it warm.

 

[Hedges]

OK, you're varying the volume of hot water, rather than varying the temperature of a fixed volume. That works to store energy too.
Do you recirculate from hot tank to make up for it cooling over time?

With an elevated hot tank, pumping would only occur when the sun shines, and gravity could feed hot water through radiators.
You would prefer to extract most of the heat in a single pass. Reverse-flow water to air heat exchanger?

 

[Warpspeed]

It sounds like a really poorly designed system. I really don't think keeping water at a certain temperature is all that hard. Especially if I use heat exchangers and a discharge tank. My system is designed to be under ground, inside a greenhouse with an insulated bottom. I could see some over heating as a problem. But not enough to render the system unusable.

Yes it was poorly designed. It was planned by the Public Works Department for a newly built "energy efficient government school" built with state government money. Lots of publicity, politicians making speeches, media fanfare the whole works.

I was working for a different department at the time, responsible for monitoring and maintaining these white elephant projects, of which there were several... All jolly good fun and quite interesting, all at the taxpayer expense, of course.
But even as another failed alternative energy project, there was plenty to be learned, and it was all pretty interesting from the personal perspective.

Until you have heard 25,000 gallons of water boiling and rumbling and gurgling in a steel tank, from imploding steam bubbles.....
It was pretty terrifying up close.

So I do speak from some practical experience.
I wish you luck with your project.

 

[Warpspeed]

The original concept of this project was that the coldest water at the base of the tank was circulated through the solar/thermal collectors, and returned quite hot to the top of the tank.
The idea was that the top of the tank always had the hottest water due to stratification.

If, on a bad day, solar was insufficient to heat the tank, electric heating elements were placed at two thirds the way up the tank to be heated at night with off peak power. One hundred amps per phase at 240v was pretty expensive to run, even at a reduced night time tariff.

On a really cold morning, the hottest water was drawn from the top of the tank, and used to heat the school, then the barely warm water returned to the bottom of the tank.

There were several issues, the main ones were that the top one third of the tank was the only part electrically heated, the bottom two thirds essentially stone cold on a mid winter early morning.
As soon as either the solar circulating pump, or the heating circulating pump started up, the turbulence in the tank instantly destroyed any stratification.
The hot water at the top quickly mixed with the cold water down lower, resulting in luke warm water, which was insufficient to do any heating.
The heating worked for about one hour early in the morning, by mid morning everyone was complaining about the cold.

The school principal asked me to do whatever I could to fix it, regardless of cost.
There was not much I could really do. My job was purely monitoring and maintenance not to totally rebuild the system.
But I came up with a sort of sneaky solution.
I wired up a small circulating pump to the heating element circuit, to continuously circulate water in the tank at night, top to bottom. That caused the whole tank to be heated at night, instead of only the top third.

It was better, but still inadequate.
The increased electricity bills from my demon modification were eye popping !!!
This "low energy school" was fantastically expensive to heat, and the Education Department that were paying the bills were having hysterics.

Finally sanity prevailed, and a whole bunch of heat pumps were installed, one per classroom.
This was all about forty years ago, the school is still there, I may go back one day and see if that huge tank is still there. It probably is.

 

[Hedges]

Perhaps a bladder or moving piston, separating hot from cold portions, would have made it work.
Similar to separate tanks.

 

[Warpspeed]

Quite a few possibilities there.
I had thought of numerous horizontal partitions with only a few small interconnecting holes. That would still allow slow water circulation without much mixing either side of each partition.

In aircraft and high performance race cars, its pretty much universal to fill the fuel tank with a solid foam material, that only takes up a couple of percent of total volume.
But it very effectively prevents sloshing of the fuel, which would be devastating to stability during rapid maneuvering.

I don't know if it is suitable for water, but possibly so. That would pretty much kill any turbulence or thermal mixing in a large water tank.
It would probably be detrimental for electric heating with the usual immersed element which relies on convection, but should work well with pumped storage.

Stratification only works in dead still fluid, the density gradient is after all, very small.
Any slight stirring or turbulence, and its game over for any stratification.