The engineering involved in building structures utilising insulated sandwich panels draws on two distinct engineering disciplines - structural engineering and heat transfer.  Generally, designers will be more familiar with one aspect at the expense of the other.  There can be a lot of uncertainty regarding these fields, so Reid aim to clear the waters and dispel the myths that relate to insulated concrete panels.  

Below are answers to some common questions asked about Nirvana Insulated Panels.

Why are different pin spacings used?

Nirvana connector pins tie each layer of the insulated panel together.  They function as a double headed anchor, which beds or anchors into each concrete layer.  The external wythe (layer) “hangs” from the internal structural concrete wythe in this manner, similar to a picture frame hanging from a hook.  The weight of the thinner external wythe is dependent on its’ thickness, which can vary according to the panel design.  The heavier (or thicker) it is, the more pins are required to support its weight.

How are pin spacings determined?

The external wythe “hangs” from the internal structural concrete layer.  The heavier the external wythe, the smaller the pin spacings are (ie. More pins per square metre).  This is calculated using well tested and verified concrete anchoring formulations, drawing on Reid’s expertise and experience in concrete lifting and anchoring to ensure pins can adequately support the load and bending moments experienced.

Why are certain pin diameters and pin lengths used?

The length of the pins is dependent on the thickness of the insulation, as each end of the pin is embedded in each concrete layer to a depth of 50mm.  Therefore, the thicker the insulation, where higher R-values are required, the longer the pin.
The diameter of the pin provides a cross sectional area of material to resist tensile loads and moment generation, dependent on the weight of the external concrete wythe.  The greater the weight, the more pins are used (smaller pin spacings) to provide greater cross-sectional area to support the applied loads and moments during lifting, transport, and service life.

What is the loading capacity of pins of different lengths?

For pure tension forces, the load capacity is the same for all pins, as they all have the same diameter, or cross sectional area.  In service however, the pins are exposed to tension and bending moments.  Bending moments are due to the distance between the two concrete layers (loads).  The Nirvana Technical data sheet details load capacities of the pins in shear and tension, and Nirvana software designs pin spacing with this in mind, such that the pins can safely support the applied load.

How thick should the internal and external concrete wythes be, and the insulation layer?

The internal concrete wythe is a structural element which should be designed by a qualified structural engineer.  This will ensure it will support the loads required in the structure.  The insulation layer thickness will depend on the R-value required for the building’s designed energy loading for heating and cooling, and Nirvana software can be used to assist in determining these values.  The external wythe is present to provide protection from physical abuse to the insulation layer.  It is typically 50mm thick.

How do the pins perform in a fire?

Nirvana pins are typically embedded in concrete and insulation, so would be hidden from the direct heat and flame of a fire.  Nirvana connector pins are manufactured from pultruded glass fibre encapsulated in a thermoset resin possessing a high glass transition temperature.  This product does not support combustion, and will self-extinguish once a flame is removed.  When exposed to high temperatures and flame, the resin can melt or burn, but the glass fibres retain full tensile strength.  This means that although the pin may soften, the effect on its’ performance will be incidental.

Are Nirvana pins chemically resistant?

In normal use, Nirvana pins will be completely encapsulated in concrete and insulation, making chemical exposure unlikely.  However, being manufactured from glass fibre and resin, the pins have very good chemical resistance to a wide variety of chemicals.  The pins are also unaffected by the alkalinity of concrete.

What is “Thermal Mass”?
Thermal mass refers to the heat capacitance properties of materials of construction, and is dependent on their mass and thermal heat capacitance values.  What this means is that a large amount of energy is required to heat up an object of high thermal mass, giving rise to a capacitance effect which can produce a “thermal lag” in temperature.  When properly insulated, the thick internal structural concrete wall of a Nirvana system is a large heat sink, with limited heat energy passing into or out of it.  When internal temperatures differ markedly from the external environment both during the day and night, the thermal mass effect can be best taken advantage of.  The insulation in a concrete sandwich panel allows only small amounts of heat energy to escape or enter the internal structural panel, which means temperature changes will take a long time to occur in the concrete, and hence the building’s occupied space.  When properly designed, this effect can significantly dampen temperature fluctuations in a building, greatly reducing the requirement for heating and cooling.

What is the difference between thermal resistivity, thermal resistance, and thermal conductivity?
Thermal resistivity is a scientific term referring to a material’s ability to resist the conductive flow of heat energy.  It is the inverse of thermal conductivity, which is a coefficient in the heat transfer equation which relates a temperature difference or driving force to the movement of heat energy through a material.  The higher the coefficient of thermal conductivity, the more heat will transfer through an object (ie. Metals have high heat transfer coefficients).  Thermal resistance includes a dimensional component, referring to the increased effect of using a thicker material.  Thermal resistance is the material’s thickness multiplied by its thermal resistivity.

What is the difference between “Static R-Value”, “Effective” R- Value, and “Dynamic” R-Value?
Static R-value is a measure of a material’s thermal resistance, where a rate of heat transfer through a material is measured when temperatures on either side of the insulation (the temperature driving force) are held constant (static).  This is a simple and easily measured value which provides a guide to the thermal performance (or conductance) of insulating (conducting) materials.  However, this measure does not reflect conditions in the real world where temperatures fluctuate over the course of a day/night cycle and over the year.  This change in temperatures is where a “Dynamic” R-value comes into play, but due to the multitude of variables related to these temperature fluctuations, this measure is very difficult to calculate and express as a “one-size-fits-all” value.  The “Effective” R-value is similar to the Dynamic R-value in that it takes temperature changes into account, but it includes the thermal mass dampening effect on temperatures.  This removes some of the uncertainty of the Dynamic R-value’s problems with temperature fluctuations.  To simplify it further, seasonal average temperatures are used for calculation purposes to provide a R-value that more accurately represents the performance of an insulated panel.

What is a thermal bridge?
A thermal bridge refers to a high conductor of heat energy spanning an insulation layer, which allows heat energy to bypass the insulation layer and pass into the cooler side.  Estimates of up to 30% reduction in R-value can occur where thermal bridging exists.

What is conductive, convective, and radiative heat transfer?
Conductive heat transfer occurs where heat energy flows through a material where a temperature differential or driving force is present, such as thawing frozen food in ambient air.  Convective heat transfer refers to the physical movement of a material, such as air or water, which transfer heat energy.  Using the example of air, a heater heats the local air, which rises to the ceiling and draws cooler air in to the heater, only to be heated and rising to the ceiling again.  The air’s density decreases as it is heated and expands, so it rises above the cooler dense air.  This is also how hot air balloons work.  Radiative heat transfer refers to heat energy transferred through radiation.  This can be as simple as the sun shining on a surface and heating it up, or a hot concrete pavement radiating out its heat once the sun has gone down, cooling it in the process.  Nirvana relies on preventing conductive heat transfer, and should be employed with appropriate designs to avoid unwanted radiative and convective heat transfer through the use of shading and air circulation fans.

How does Insulation work?
Insulation is used to restrict the flow of heat energy from a high temperature to a lower temperature environment.  It is made from materials possessing low thermal conductivity.  In doing this, it prevents the material or environment from heating up or cooling down.  The insulation resists the passage of heat energy through it, and so can be used to maintain and control temperatures with little additional energy input/output.

What types of insulation can be used in the Nirvana Insulation system?
Almost any type of insulation can be used in a Nirvana system, with the only restriction being that it must be able to support the weight of wet concrete without being compressed, and slurry ingress into the insulation must be prevented during manufacture.  The insulation must also meet the R-value requirements of a particular project, which is dependent on the stated BCA R-value and the climate zone in which the project is to be built, and this can be done by varying the thickness of insulation used.

What is the difference between EPS and XPS?
Both XPS and EPS are manufactured from polystyrene, though they are formed in 2 different methods.  Expanded Polystyrene (EPS) is formed from expanding small beads of polystyrene with heat, and blowing agents, to produce large blocks of this common material, which can then be cut into whatever shape is required.  This product is commonly seen in eskies and fresh fruit/produce packs and is white.  Extruded Polystyrene (XPS) is made from one continuous piece of heated polystyrene, where blowing agents are used to create air cells within to expand its volume and assist in insulation properties.  EPS is softer, more flexible, and allows vapour passage through it to some extent.  XPS is stronger and does not allow vapour passage through it.  Both products can be used very effectively in the Nirvana Insulated panel system with long service lives.

Can mineral wool insulation, such as Rockwool or Glasswool, be used in the Nirvana System?
These products can be used, but care is required in their selection and placement during manufacture to ensure they are not overly compressed/squashed by the weight of the concrete, and concrete slurry and bleed water do not penetrate the insulation.  This can be achieved using plastic sheets and dense grades of mineral wools.  However, due to these factors, the cost, and the difficulty in pushing connector pins through these materials, other types of insulation are preferable to achieve a good result without undue difficulties.

What about Dew Point?
The dew point refers to the temperature and pressure at which water condenses from the air (morning dew) once it reaches 100% relative humidity.  This is commonly seen where warm humid air condenses water on the surface of something recently taken out of the fridge, such as a cold bottle.  This can cause problems in improperly designed building envelopes where condensation occurs in the indoor environment on plasterboard and wooden frames, causing water damage and mould.  Because Nirvana systems are made from concrete panels and insulation with minimal porosity, there is essentially no air present in the wall system for condensation to occur, nor any avenue for fresh air to enter the concrete to condense further to leave any presence of water.  Ideally, a dew point temperature should occur outside the building envelope, and by using a Nirvana system, the dew point can occur somewhere in the external wythe or insulation layer without any concerns over condensation.

How can I be sure that the panel sections won’t delaminate?
Reid, and our sister company Ramset, are the experts in concrete panel lifting and anchoring.  Nirvana has been developed using this vast experience to ensure a Reid design will provide a durable and energy efficient wall, fully functional for many years of service life.

How long will a Nirvana Panel last in service?
Nirvana panels are simply extensions of standard concrete panels, and can be expected to last for similar durations in standard service conditions.  Because the insulation is protected from the weather, physical damage, and vermin by the two concrete panels, it will function as designed during this service life, with minimal expected decline in performance.

Are Nirvana Panels easy to manufacture, and are there any pitfalls?
Provided Nirvana connector pins are installed at the design spacings, the manufacture of Nirvana panels is a simple extension of standard manufacture of concrete panels, involving two concrete pours rather than one.  Due to the circular cross section of a Nirvana pin, correct orientation of the pin during installation is fool proof (how can you place a circle on its side – looks the same however it is placed).  Beware of systems with non-uniform cross sections, as their design parameters change dramatically if installed incorrectly – up to 70% reduction in load capacity is possible!  This is not the case with Nirvana, reducing potential liabilities and taking complication out of the installation process.

How will using Nirvana panels save me money?
The enhanced thermal performance of Nirvana panels, especially in climates with large differences between day and night time temperatures, greatly reduces the energy loads required to maintain the internal environment within the comfort zone for occupants.  By dampening out the temperature fluctuations indoors, less heating and cooling is required.  The capacitance effect of thermal mass reducing temperature swings indoors results in reductions in a building’s initial capital costs in larger heating and cooling equipment, and flows through to lower service costs to operate this equipment.