Can Metal Pins Increase Heat Transfer in Concrete Walls?

[AnonLinear]

TL;DR

Given a cement wall, if I were to put a series of metal pins embedded within, or on the surface, could I transfer the heat that would have been absorbed by the wall to travel along the metal instead?

I had an idea thinking about heat transfer and how placing water over a hot surface will transfer the heat to the water. It got me thinking, in a case where water could not be an option for a medium could I use metal, which would still have a higher heat transfer to absorb more of the heat, which would "travel" along a path to somewhere else?

 

[hmmm27]

The heat still has to get from the wall to the pins, and from the pins to <whatever>. Why would you think it would not work ?

 

[berkeman]

Welcome to PF.

Summary: Given a cement wall, if I were to put a series of metal pins embedded within, or on the surface, could I transfer the heat that would have been absorbed by the wall to travel along the metal instead?

It got me thinking, in a case where water could not be an option for a medium could I use metal

Can you post a sketch of what you have in mind? I'm having trouble visualizing what you are asking about. Just click the "Attach files" link below the Edit window to upload a PDF or JPEG image of your sketch. Thank you.

 

[kuruman]

Remember that there has to be a temperature difference between the ends of the pins to drive the heat from one end to the other.

 

[Arjan82]

What you are referring to is called a cold bridge (or thermal bridge). But do note that water has a very high heat capacity, which means that it can absorb a lot of heat without increasing temperature too much. But steel much less so. So you can use it much better to transfer heat more quickly from one place to another, rather than absorb heat.

 

[Baluncore]

Summary: Given a cement wall, if I were to put a series of metal pins embedded within, or on the surface, could I transfer the heat that would have been absorbed by the wall to travel along the metal instead?

It got me thinking, in a case where water could not be an option for a medium could I use metal, which would still have a higher heat transfer to absorb more of the heat, which would "travel" along a path to somewhere else?

The type of metal will be important. Avoid stainless steel, use copper, brass or maybe aluminium if possible. Look up the thermal conductivity of different available metals.
https://en.wikipedia.org/wiki/List_of_thermal_conductivities

The ideal would be water circulating through a loop of copper tube.
Black plastic pipe is used to circulate water in solar water heaters.
https://en.wikipedia.org/wiki/Thermosiphon

 

[AnonLinear]

This would be how it would be structured, more or less. With the blue being the more conductive material. I would want the heat to "move" and centralize along this grid. Preventing heat from reaching the other side of the wall. Instead all being stored in the blue grid

 

[AnonLinear]

Remember that there has to be a temperature difference between the ends of the pins to drive the heat from one end to the other.

ah excellent, I did not account for that, I will now.

 

[AnonLinear]

What you are referring to is called a cold bridge (or thermal bridge). But do note that water has a very high heat capacity, which means that it can absorb a lot of heat without increasing temperature too much. But steel much less so. So you can use it much better to transfer heat more quickly from one place to another, rather than absorb heat.

sweet, its got a name. I can't use water because then it would require a new active system to keep the wall cool and then there's mechanical parts. Where the grid (doesn't need to be steel) just needs to be installed and left alone. Thank you.

 

[AnonLinear]

The type of metal will be important. Avoid stainless steel, use copper, brass or maybe aluminium if possible. Look up the thermal conductivity of different available metals.
https://en.wikipedia.org/wiki/List_of_thermal_conductivities

The ideal would be water circulating through a loop of copper tube.
Black plastic pipe is used to circulate water in solar water heaters.
https://en.wikipedia.org/wiki/Thermosiphon

Excellent, Thank you very much. I will take this into account
Would there be a copper tube to capture more of the heat, where the water would store it?
And would the water need to be flowing. I'm looking for a system as passive as possible, with the least amount of mechanical parts.

 

[AnonLinear]

Welcome to PF. Can you post a sketch of what you have in mind? I'm having trouble visualizing what you are asking about. Just click the "Attach files" link below the Edit window to upload a PDF or JPEG image of your sketch. Thank you.

Sure can

 

[Arjan82]

Excellent, Thank you very much. I will take this into account
Would there be a copper tube to capture more of the heat, where the water would store it?
And would the water need to be flowing. I'm looking for a system as passive as possible, with the least amount of mechanical parts.

'capture' is synonymous to 'store' I would say in this context. Normally it is called conduction, so copper is very good at conducting heat.

If you let the water flow it is better at extracting heat from the source. What you would say is that forced convection (water flowing over a heat source) is has a higher heat transfer rate than natural convection, when the water is not flowing (actually, it is still flowing due to the temperature differences, but at a much lower speed).

 

[anorlunda]

And would the water need to be flowing. I'm looking for a system as passive as possible, with the least amount of mechanical parts.

https://en.wikipedia.org/wiki/Heat_pipe

 

[Lnewqban]

Welcome @AnonLinear !

At any point of the wall, where metal and cement are in contact, the temperature will be the same.
It is only when metal is leaving the hot wall and going inside a cooler mass, that some heat flow can happen, part of which will be transferred to the surrounding air and insulation of the energy-accumulator mass.

The substantial heat flow happens from the exterior to the interior surfaces of the wall.
Sun radiation is reaching the exterior surface (point of higher temperature) and progressively heating the cross section of the cement wall to lower and lower values of temperature.

The temperature reached by the interior surface is what determines how much of that radiating energy is transferred to the shaded indoor air and residents.

If located midway, your metal grid will capture only a fraction of that flowing energy (see how little blue surface your sketch shows, compared to the cement surface); and only a percentage of that can be finally transferred to the device that could use it.

 

[AnonLinear]

Welcome @AnonLinear !

At any point of the wall, where metal and cement are in contact, the temperature will be the same.
It is only when metal is leaving the hot wall and going inside a cooler mass, that some heat flow can happen, part of which will be transferred to the surrounding air and insulation of the energy-accumulator mass.

The substantial heat flow happens from the exterior to the interior surfaces of the wall.
Sun radiation is reaching the exterior surface (point of higher temperature) and progressively heating the cross section of the cement wall to lower and lower values of temperature.

The temperature reached by the interior surface is what determines how much of that radiating energy is transferred to the shaded indoor air and residents.

If located midway, your metal grid will capture only a fraction of that flowing energy (see how little blue surface your sketch shows, compared to the cement surface); and only a percentage of that can be finally transferred to the device that could use it.

View attachment 315634

This is fantastic. Thank you for your model. So, say if the metal grid was in contact with a body of water, there would be heat transfer? If this is true, I know that metal will transfer that heat slowly, is there another kind of material I could use to transfer heat?

My original idea of the thermal batteries that would store solar radiation before it could travel through the cement, is it feasible?

 

[AnonLinear]

https://en.wikipedia.org/wiki/Heat_pipe

excellent, thank you.

 

[Tom.G]

Not exactly what you were asking, but some alternatives.

Here are a couple more ideas for thermal storage that have actually made it into some custom homes. Probably neither of them are worthwhile for existing structures though.

Thermal solar panels to heat a bed of rocks (coarse river gravel) under the home. The system blows heated air thru the rock bed during the day. At night that circulation is stopped and room air is circulated thru the hot rocks.

A 'thermal mass wall' of concrete (or brick) in the living area facing large South-facing windows. At night, thick thermal draperies are closed to block off the windows. The wall then heats the living area at night.

And one more approach that can help in colder climates. This was done in Snow Country in the mountains. The owner bought some styrofoam insulation panels (a few inches thick) that have foil on their surface. He cut them to fit the windows and placed them in the windows at night.

Just for general information, in older houses the greatest heat lose is generally the cracks around the windows and door.

About the same amount is thru the window glass. Double pane or triple pane windows can be a big help, but kinda expensive to both purchase and install. Storm windows on the outside can be a low cost alternative that are effective. Even lower cost is clear plastic sheeting attached on the outside of the building covering the window. Have a few inches air gap between the plastic sheeting and the window and do not completely seal the air space. Have about 6 to 12 square inches vent space to the outside air. This is to avoid condensation collecting in the dead air space.

The third greatest heat loss is usually from the ceiling. Get some insulation up there above the ceiling. If the rafters/joists are accessable, the easiest to use is probably the stuff that comes in rolls, either paper or fiberglass based. If the that space is not readily accessable you can use particle insulation that is blown in, this is not a do-it-yourself job for most people.

Finally there are the walls, treat the same as the ceiling.

Oh! The floor, especially if the underfloor area is open to the weather. Some air circulation is required under the floor if it is above soil, so you can't completely block it off. Your local city building department can likely tell you what the minimum ventilation area is.

Of course heavy carpets with padding will be much help. But try to get some insulation on the underside of the floor if you can. An alternative, and expensive, option is insulate the the living area side of the floor then put a false floor over it. This is hardly ever done, you have to trim all the doors, and if you are really energetic, rip out and reset all built-in cabinets, replumb the toilet and tub, etc.

 

[Lnewqban]

This is fantastic. Thank you for your model. So, say if the metal grid was in contact with a body of water, there would be heat transfer? If this is true, I know that metal will transfer that heat slowly, is there another kind of material I could use to transfer heat?

My original idea of the thermal batteries that would store solar radiation before it could travel through the cement, is it feasible?

Again, heat transfer into the metal grid (and out of it) is only possible when a temperature differencial exists between it and the surrounding substance.
The greater that differential, the more thermal energy would be transferred per unit of time.

 

[256bits]

If located midway, your metal grid will capture only a fraction of that flowing energy (see how little blue surface your sketch shows, compared to the cement surface); and only a percentage of that can be finally transferred to the device that could use it.

If there are metal pins embedded within the concrete wall from the exterior extending inwards, the 'insulation' properties of the concrete itself is being circumvented.