Storing heat in sand?

[Guda]

People here don't value longevity in the same way that people do in Europe and other areas of the world. We have a disposable culture. I've spent a big hunk of my life fixing problems other people created because they didn't want to invest the time or money to do things right the first time. It is so sad. I've traveled around the world for my career, and even 15 -20 years ago saw technology that people here are just starting to think is "new".

Thats the garbage system called capitalism. Thats a system setup by & for sociopaths. All the isums are garbage because they were setup by people who know nothing, like lawyers. A new system setup by engineers is the only wat we will survive.

 

[Posplayr]

I think there is more involved that how much heat it will hold .... for instance what is the heat transfer rate as compared to water?

I think specific heat is most relevant. SH of water is 4182 J/Kg DegC
for sand it is 830 J/kg degC

Sand will get much hotter (5X as many delta DegC) containing the same amount of heat which means it will dissipate that heat much faster to the surrounding environment. Heat transfer (loss) is related to the temperature differential so.

 

[eXodus]

Thats the garbage system called capitalism.

capitalism is not the issue, there is capitalism in Europe for a few hundred years. You need a healthy market.

Cultural perception of time.

It's same with solar - People in the US didn't start installing those system got a return on Invest under 5- years. While in Europe people already jumped in at 20 year ROI.

 

[Wellbuilt]

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Interesting cultural difference, calling 4 inch thick concrete a "slab". In Europe that would not be sufficient for a walkway in your yard.
"Slab" begins at 10 inches thick. If you are building in frost zones in Germany we are using slabs of 50-80cm 20-30 inches.

Yes homes are more expensive there.

It’s not a money thing , all our slabs for radiant heat have a minim of 2” foam board on the bottom , and a max of 4” of concrete 4500 psi with glass fiber.
I allso use steel 6x6 wire so I can tie the pex tubing to it .
I use steel tubing chairs to keep the pipe in the top half of the slab .
The reason is a 4” slab with the heat tube 11/2 from the top gives the floor a fast recovery .
You can
I can run the water at 100o and it comes back @ 92o with a 200 foot loop .
My floor has 7 runs at 189 ‘ so it dosent cool much at all .
A 10” slab will not get hot enough to pass heat to the home , you would end up running the water at 120 o +
and that kills the efficiency.

 

[PVorBust]

Sometimes it is important to understand the WHY a phenomenon happens, not just that it does. Especially when applying things to other situations.

If I may, I'll reword that statement.

If you don't understand why a phenomenon happens, you can't (reliably) apply it to other situations.

A second point to remember is that if someone offers an analogy to explain a situation; the analogy doesn't prove the original statement is true and shooting holes in the analogy doesn't prove it isn't.

The analogy is just a tool to save you spending year at uni learning the math

 

[eXodus]

It’s not a money thing , all our slabs for radiant heat have a minim of 2” foam board on the bottom , and a max of 4” of concrete 4500 psi with glass fiber.
I allso use steel 6x6 wire so I can tie the pex tubing to it .
I use steel tubing chairs to keep the pipe in the top half of the slab .
The reason is a 4” slab with the heat tube 11/2 from the top gives the floor a fast recovery .
You can
I can run the water at 100o and it comes back @ 92o with a 200 foot loop .
My floor has 7 runs at 189 ‘ so it dosent cool much at all .
A 10” slab will not get hot enough to pass heat to the home , you would end up running the water at 120 o +
and that kills the efficiency.

My pex system in Germany is about 3 inches deep into the slab. It is not fast by any means, like I said before, you turn the temperature up and it takes 3 days to take effect.

We are actually running 29 Celsius - 84 Fahrenheit water in the living spaces and 33C - 93F in the bathrooms.

https://www.schwedenplatte.de/information/bodenplatte/fussbodenheizung/

basically you pour a 4-6 inch slab - then get the pex down and rebar and then pour another 4 inches on top.

A lot the Energy we get from Solar Thermal Panels - got about 6 sqm.

 

[Guda]

My pex system in Germany is about 3 inches deep into the slab. It is not fast by any means, like I said before, you turn the temperature up and it takes 3 days to take effect.

RMFAO!

basically you pour a 4-6 inch slab - then get the pex down and rebar and then pour another 4 inches on top.

Will pex last hundreds of years? Does it matter, or will the tunnel it creates last past the pex?

 

[noenegdod]

A 10” slab will not get hot enough to pass heat to the home , you would end up running the water at 120 o +
and that kills the efficiency.

This isnt true.

A slab with too much mass will react very slowly. Running really hot water is a way to get it to react faster but you will end up overshooting every time. If you get a huge swing in outdoor temperature, if the mass of the slab is too high, you will be too warm or cold for several days while it is cooling down or you are pouring heat into it waiting for it to actually warm up and freezing in the meantime.

Huge mass is very nice but you have to set the temperature of the mass for the warmest (outside) temperature you expect and then use a direct to air heater or water to air heat exchanger to manage the short term temperature swings. You have to watch the weather forcast a couple days (or more depending on mass) out.

If it looks like it is warming up, turn the slab heat off and run all your DHW through it if its an open system or through a heat exhanger to help start cooling it down. If its cooling down, start pouring heat in. It really isnt hard but each system has its own nuances and you have to live with them for a little while.

 

[Wellbuilt]

My pex system in Germany is about 3 inches deep into the slab. It is not fast by any means, like I said before, you turn the temperature up and it takes 3 days to take effect.

We are actually running 29 Celsius - 84 Fahrenheit water in the living spaces and 33C - 93F in the bathrooms.

https://www.schwedenplatte.de/information/bodenplatte/fussbodenheizung/

basically you pour a 4-6 inch slab - then get the pex down and rebar and then pour another 4 inches on top.

A lot the Energy we get from Solar Thermal Panels - got about 6 sqm.

That looks good , no one will design a system like that here , Every one says it won’t get hot .
I’m not a plumber , but im a builder and pex the floors out before we pour the concrete .
I like to run the 6x6 wire on the bottom then just zip tie the pipe to the wire , then run a second 6x6 wire on top and zip tie every thing together .
before we pour the concrete we place the chairs under the wire .
Then fill it with warm water . The water relaxes the pipe and holds it down .
If the pipe has a hole the water leaks out and we can fix it .
If some one pops a line we know about and can fix it .
Ive never found a hole in a pipe . Yet

 

[Wellbuilt]

This isnt true.

A slab with too much mass will react very slowly. Running really hot water is a way to get it to react faster but you will end up overshooting every time. If you get a huge swing in outdoor temperature, if the mass of the slab is too high, you will be too warm or cold for several days while it is cooling down or you are pouring heat into it waiting for it to actually warm up and freezing in the meantime.

Huge mass is very nice but you have to set the temperature of the mass for the warmest (outside) temperature you expect and then use a direct to air heater or water to air heat exchanger to manage the short term temperature swings. You have to watch the weather forcast a couple days (or more depending on mass) out.

If it looks like it is warming up, turn the slab heat off and run all your DHW through it if its an open system or through a heat exhanger to help start cooling it down. If its cooling down, start pouring heat in. It really isnt hard but each system has its own nuances and you have to live with them for a little while.

hmmmm I’ve never had a engineer Say anything like that ? It makes sense to me .
That sounds like a rough way to live , with the 4” slab I can see the floor warming up in a few minutes with a heat gun
The pump runs about 7to 10 mins an hour or 3 to 4 hours a day if it’s real cold .
Maybe insulating the bottom slab would help ?

RMFAO!


Will pex last hundreds of years? Does it matter, or will the tunnel it creates last past the pex?

I’m sure the pex will last 50 years , Probably a lot more if the water temp stays low .
Concrete is not water proof so the towels the pet leaves woul be no help

 

[eXodus]

Huge mass is very nice but you have to set the temperature of the mass for the warmest (outside) temperature you expect and then use a direct to air heater or water to air heat exchanger to manage the short term temperature swings. You have to watch the weather forcast a couple days (or more depending on mass) out.

yes our heating system has an outdoor sensor. The software is pretty good.

The pump runs about 7to 10 mins an hour or 3 to 4 hours a day if it’s real cold .

our pump runs 24/7 with variable speed from September to May. Further we got valves to adjust every run (a few per room)

Will pex last hundreds of years? Does it matter, or will the tunnel it creates last past the pex?

many of the first PEX pipes created in the 1960s are still in use today. Don't know about hundreds of years yet. But 50+ is very common.

If you get a huge swing in outdoor temperature, if the mass of the slab is too high, you will be too warm or cold for several days while it is cooling down or you are pouring heat into it waiting for it to actually warm up and freezing in the meantime.

that's why the whole system only works with a good insulated house. When you would only have 4 inch wall that would be not the system for you.
It's a slow system that's why you have to keep the impact on it low. Double pan Windows and 12 inch Brick wall help.

 

[toms]

I agree that climate control is very area specific. We have a desert climate, and have had several days where it has gone from zero to 40°C.

We also often get several days of 40°C in a row, so all the houses with bulk thermal mass end up spending a lot of time using RC aircon anyway.

I guess we have a lot more sunlight hours than average, because it always confuses me when people go to huge effort and expense to attempt to maintain temperature in their houses when i find it is very simple and inexpensive to use a combination of ventilation and RC aircon.

 

[Supervstech]

yes our heating system has an outdoor sensor. The software is pretty good.

our pump runs 24/7 with variable speed from September to May. Further we got valves to adjust every run (a few per room)


many of the first PEX pipes created in the 1930s are still in use today. Don't know about hundreds of years yet. But 50+ is very common.


that's why the whole system only works with a good insulated house. When you would only have 4 inch wall that would be not the system for you.
It's a slow system that's why you have to keep the impact on it low. Double pan Windows and 12 inch Brick wall help.

I never heard of pex before the 90’s… and I can’t find anything saying it was around before the 60’s…

I did find this article claiming it was first created in the late 60’s…

Mr. PEX: PEX is polyethylene molecules chemically linked with each other to form a network. Engineers at BASF in Germany were experimenting making PEX both through use of peroxides and by exposing PE samples to radiation in the early 1960's. Thomas Engel is credited to start the first production of PEX tubing in the late 1960's.

 

[Wellbuilt]

wow the pump runs 24 /7 , how long do they last ?
Our pumps last 10/15 years and work 5 months out of the year
are you guys insulating under your slabs?

I agree that climate control is very area specific. We have a desert climate, and have had several days where it has gone from zero to 40°C.

We also often get several days of 40°C in a row, so all the houses with bulk thermal mass end up spending a lot of time using RC aircon anyway.

I guess we have a lot more sunlight hours than average, because it always confuses me when people go to huge effort and expense to attempt to maintain temperature in their houses when i find it is very simple and inexpensive to use a combination of ventilation and RC aircon.

Desert climate must be tough to heat and cool, my place has large temperature swings , I can see 85 /90o day time
And 40o over night .
my first floor seams to stay around 67o in side all summer the second floor could be 80o on a hot day .
I’m not temperature sensitive but at night its just to cool to be comfortable.
If I’m home I will start opening some windows to let in some warm air if not I have to lite my wood stove .
I’m a low tech guy , we sit around with blankets after dinner .
I don’t ever burn over nite , so I can burn a 1/3rd less wood every year .
I have friends that pay 4500 $ to heat 3 months out of a year .
I’ve never lived in a house with heat/ or central A/C .

 

[SolarPrep]

PEX has been around roughly 50 years. The first breaking test conducted to pressurize and then put tension on the PEX has been in continuous operation since then with no breakage. I've poured dozens of heated floors in both commercial and residential applications, and use nothing but Wirsbo. (Uponor) I used to do what the one poster said, and zip tie the tubing to mesh, but have since gone to using fiberglass rebar. I now plumb boilers with Wirsbo, and have used it up to 2". They make it bigger, but I don't have any use for it.

I use a slab temperature sensor, and run Caleffi and Uponor PEX manifolds with Grundfos Alpha 2 pumps. We use a minimum of 2" high density foam under the slab, and carefully seal all seams with a good 4" wide tape. Lately, we have been using 2 layers of foam with all seams overlapped, and both layers taped. If it is a basement, we compact the dirt before setting the first layer of foam. All water entering the slab runs through a 3/4 inch or 1" 3 way valve, and we typically set the entering water temperature at about 80 degrees. Loops should not be more than 250' each, and when longer we use a reverse return setup. We always set the direction of flow so that the hottest water heads around the perimeter of the slab where heat loss is more likely. We also tighten up our loop spacing around the perimeter.

Most people here in North America use 1/2 PEX for these applications. I used to use 5/8" because it has much better flow characteristics, but it has become almost impossible to get the fittings, and they cost too much. In Europe they use a lot of smaller tubing.

If you have an application other than in a slab, take a close look at Warm Board. It is an expensive product, but if you factor in what you get for the money, it is money well spent. Sheets of prefabricated and CNC cut plywood delivered to your job-site with all the grooves cut, and a complete layer of aluminum transfer surface on the one side. It is awesome for use under tile, etc. The key to Warm Board is planning...you have to be willing to take the time to carefully think through the plan, and then not make changes unless absolutely required.

With some simple controls that are readily available, we don't see huge swings in temperature, and we live in the Midwest. In fact, I can tell you that for the last 5 years, my home theater room has not varied more than 2 degrees from the setpoint. The vast majority of time it is dead on. The pump maintains the setpoint.

 

[eXodus]

I never heard of pex before the 90’s… and I can’t find anything saying it was around before the 60’s…

that was typo of mine. 1960s you are correct I'm referring in the same sentence to 50 years.
Our house was built in the 80s.

wow the pump runs 24 /7 , how long do they last ?
Our pumps last 10/15 years and work 5 months out of the year
are you guys insulating under your slabs?

we are on the second Grundfoss in 35 years, and we did exchange the pump while it was still working - the new pump just needs much less power.
The old pump needed about 50-75w while the new one runs between 5-7W. (five to seven watt)

Actually starting and stopping a pump it what kills lifespan. Electric motors want to run all day.

Our house is not insulated under the slab - only the walls (below grade) but in the Basement the heated floors are in a bed of loose sand (it's not really sand, it's very light and contains a lot of air)
So basically a slab sandwich - Slab - Sand (with the Pex pipes sit on top) Slab

newer construction I think starting in the 90s have under slab insulation.

 

[740GLE]

High pressure steam becomes very unfriendly if something goes wrong.


My recommendation is sourcing one of these bad boys

American Solartechnics, LLC.

Last Updated: March 6th, 2024 December 2nd, 2022 - Between the fire we had this summer and our other business endeavors keeping us busy, we have been considering stepping back from the Heat Bank...

www.americansolartechnics.com

We have an 800 gallon unit for our indoor wood boiler mainly for heating. With a DHW coil and mixing valve we have 5+ days of hot water for the wife and I if the tank was at 180f. Showers start to get a little cool when the tank temp gets under 130f.


You could use sand, burry a huge swimming pool size sand pit with a few hundred feet of Pex coils, you’d just need to insulate the heat from the escaping to the rest of the ground.

 

[Wellbuilt]

Grundfous makes good pumps , I try to use them when I can .
My well is a grundfos solar pump .
Is it a Sand /cement lose mix ?

 

[Wellbuilt]

High pressure steam becomes very unfriendly if something goes wrong.


My recommendation is sourcing one of these bad boys

American Solartechnics, LLC.

Last Updated: March 6th, 2024 December 2nd, 2022 - Between the fire we had this summer and our other business endeavors keeping us busy, we have been considering stepping back from the Heat Bank...

www.americansolartechnics.com

We have an 800 gallon unit for our indoor wood boiler mainly for heating. With a DHW coil and mixing valve we have 5+ days of hot water for the wife and I if the tank was at 180f. Showers start to get a little cool when the tank temp gets under 130f.


You could use sand, burry a huge swimming pool size sand pit with a few hundred feet of Pex coils, you’d just need to insulate the heat from the escaping to the rest of the ground.

This sounds good .
Even better if it’s under the house ?

 

[Supervstech]

I have heard all my life that starting and stopping is what kills a motor... I do not think that applies across the board to all motors. Sure, combustion motors that need lubrication certainly suffer from this.
But electric motors? Perhaps a pump that has to suction water prior to pumping maybe... but most pumps don't. Starting capacitive start motors would develop wear of the sling switch, or the winding itself heating up during starting.
But many motors use brushes and bearings that wear during use.
I'm sure, surge starting amps don't do the windings good...
I just wonder, what wears an electric motor out most? Starting repeatedly, or constant load?

 

[eXodus]

I'm sure, surge starting amps don't do the windings good...
I just wonder, what wears an electric motor out most? Starting repeatedly, or constant load?

There are various electric motor designs. And everyone has a different way of failing.

Very general:
All Motors will fail mechanically eventually. Any bearing wears out at some point. That might be 5 years or 1000 years.
Depends how it was designed and sealed. Many bearing contains a grease fluid - when that is in constant motion and warm - it's pretty good for a long time. But you when you stop it - and it's getting old - it might seize up on you.

On the electric side of things - usually heat cycles damage a motor. So turn the motor on - it gets warm - you turn it of - it cools down.
You do that a few thousand times and some connection gets loose or a wire brakes because of that cycling.
Further in the windings of a motor you only got a thin layer of "paint" coating between the individual wires. The just need to rub against each other, with the heat cycles enough that its getting you a short.

On your computer fan the bearing will probably fail long before the electric motor does. They are usually poor sealed and either drying out or getting dirt inside.

While on a A/C compressor the windings burn out from the heat cycles long before the bearing budges. The A/C system is completely sealed with oil contained for the compressor - those things usually fail rather rapid when a winding gets damaged

 

[Supervstech]

Absolutely on ac sealed compressor motors, I would say what kills them is a poorly installed system... refrigerant floodback, or overheat from condenser fan failures, or capacitor failures causing winding overheats... don't get me started on Air conditioning stuff... years in the field looking at those failures.

But on water pumps as this thread is discussing, since most are likely brushless, and capacitive wound... run windings... ya think it is heat cycling? Makes sense. The bearing being submerged constantly likely aren't more or less stressed starting or running... impellers cavitation may damage the impeller... hmmm

 

[Bob B]

I used to do control work for slab heating in commercial environments.

The control specifications varied, but the most common method was to control the return water temperature .... If a space temperature was being controlled, that space temperature would be used to reset the return water temperature setpoint thru a range.
Sometimes variable speed pumps were used, and other times a fixed volume pump was used in conjunction with a mixing valve that would mix the return water with the hot water supply. A Belimo actuator on a 3 way valve isn't all that expensive.
The pump would generally be specified to run below a certain outdoor air temperature.

Controlling the hot water supply was a different control loop.

 

[eXodus]

But on water pumps as this thread is discussing, since most are likely brushless, and capacitive wound... run windings... ya think it is heat cycling? Makes sense. The bearing being submerged constantly likely aren't more or less stressed starting or running... impellers cavitation may damage the impeller... hmmm

the new grundfoss pumps have magnetic levitation bearings. As long there is water in the pump the impeller never touches anything.
In theory those bearings should last very very long (1000 year design life)

The impeller "lands" only when you shut it off. In my use-case - we shut off the system once year over the summer - so we get one heat cycle and one touching event a year.

Someone here in that threat mention he runs the pump 10 minutes an hour - so don't know if that is an average - but that could mean 24x a day start and stop - his pumps goes through more heat cycles in a day - then my pump in 20 years.

Anyone who understands thermodynamic expansion and contraction should see which part will last longer. Could be that the pump is mounted right against the boiler/reservoir and always stays a constant temperature - who knows.

You can destroy anything with enough heating and cooling cycles, whole mountains are coming down over centuries that way. Over time microfractures accumulate and then stuff falls apart

The control specifications varied, but the most common method was to control the return water temperature .... If a space temperature was being controlled, that space temperature would be used to reset the return water temperature setpoint thru a range.
Sometimes variable speed pumps were used, and other times a fixed volume pump was used in conjunction with a mixing valve

Our radiant floor system employees all of those, - 3 point valve, variable speed pump, measuring the outgoing and return water temperature. and outdoor.

The software does some magic, controlling all those things. It adjust temperature and flow depending return and outdoor temperature, further how hot currently the solar tank is. Starts and stops the natural gas furnace.

Sometimes it uses fairly hot water and low flow and sometimes it used lots of flow and only warm water.

 

[glenkleidon]

Well, I can see one reasoning flaw that will limit it's application. First you make the statement that sand can be heated hotter than water. Then you say you'll be heating the sand with hot water plumbing. So, isn't the maximal heat level controlled by how hot you can heat the water? Unless this is a presurized water system, the maximal temperature will never surpass 100C.

Yes, the problem is that when the sand gets hotter than the water, the heat would leak back into the incoming plumbing rather than add to the sands heat. But if you used a liquid other than water with a higher boiling point (dont know what that would be though) OR increased the pressure in the incoming plumbing....