Friday, 26 January 2018

Passive Energy Buildings and Insulation


Fact: buildings account for 40% of total energy consumption and 36% of total CO2 emissions





Passive building: Passively maintains its contents at the right temperature, without the need for active cooling or heating.

So we realize that in specific conditions there are buildings that will not need heating or cooling systems.  For such buildings, any kind of energy source, including renewable energy, will be unnecessary.


 Five key factors (passive building)


The building envelope


  1. Insulation
  2. Windows
  3. Ventilation with energy recovery
  4. Airtightness
  5. Thermal Bridges


Thermal Insulation


Thermal insulation is the reduction of heat transfer between objects in thermal contact.

Reducing heating and cooling costs is an effective step in controlling climate change and also contributing to the increase of energy efficiency. Current solutions are based on increasing the thickness of the insulating material itself, but are likely to lead to negative economic, architectural and environmental impacts. 

Noteworthy: Only when a building achieves a 'LowHeat' state, the integral carbon of the insulation becomes important. This occurs when the energy retained through the insulation exceeds the energy used for the production of the insulation materials.

Let's assume that the same heating energy is spent in three identical houses.





In the absence of insulation, the temperature is maintained at 15°C. With classic insulation, the temperature reaches 18 °C. While using advanced insulation the house maintains a temperature of 20 °C.


Criteria for material selection


Performance

The most important aspect for the insulating material is its performance, i.e. whether it is designed to provide consistent resistance to heat passage throughout the life of the building.

Easy installation

The final performance is determined by how effectively a manufacturer can install the material (know-how and technical expertise). For instance, the insulation slabs must be installed so that no gaps exist between the adjoining slabs or between the slabs and other construction components that are part of the overall insulation envelope.

Progressive quality degradation (shrinkage, compaction, settlement)

Some materials may be unstable during their installed life. This can be prevented by standardized performance measurement (smart grid - smart insulation), careful design and installation methods.

Moisture protection

Certain insulating materials are affected by increased moisture. If the humidity is high (inflow or above 95% relative humidity) then a suitable resistant material should be specified. Click here to redirect to the relative humidity and dew point tool.


What are the performance terms?


Thermal conductivity (╬╗)

Thermal conductivity is defined as the ability of the material to transmit heat through conduction. The lower is, the better the performance.

Thermal Resistance (R)

Thermal resistance is the ability of a material to resist the flow of heat and it is the number that connects the thermal conductivity of a material with its thickness (m²K / W). Higher thickness means less heat flow and so there is lower conductivity. These two parameters constitute the thermal resistance of the construction. A layer of construction with high thermal resistance is a good insulator.
Thermal resistance = Thickness (m) / Conductivity (W / mK)

Thermal Transmittance (U-value)

It is the heat transfer rate through a structure, divided by the temperature difference in this structure. The units of measurement are W / m²K. The better the structure, the lower the U value.

Specific Heat Capacity

It is considered as the amount of heat required to raise the temperature of 1 kg of material by 1K (or 1 ° C). A good insulator has high specific heat capacity because it takes more time to absorb heat to increase its temperature: This delays heat transfer.

Thermal Diffusivity

The specific parameter measures the ability of a material to conduct thermal energy in relation to its ability to store thermal energy (units: mm2/s). For example, metals are rapidly transmitting thermal energy as opposed to wood. Insulators have low thermal diffusivity. In order to calculate thermal stress during rapid temperature change you need the thermal diffusivity of the material instead of thermal conductivity.
Thermal Diffusion = Thermal Conductivity / Density x Specific Heat Capacity

Density

The density of a substance is its mass per unit volume (unit: kg / m3). A high density material maximizes total weight and is an aspect of "low" thermal diffusivity and "high" thermal mass.

Embodied Carbon

It is not an aspect of the thermal performance of an insulating material, but it is a basic concept of managing climate change. Embodied carbon is considered to be the total amount of carbon released over the life cycle of a material (production, transport, use, demolition, disposal).

Vapour Permeability

It is the extent to which a material permits the passage of moisture through it. It is the flow rate of water vapor through a unit of material of a specific thickness caused by the difference in water vapor pressure between two surfaces under certain conditions of temperature and humidity.


Insulation materials - Commercially available


Wood fibre
Cellular glass
Cellulose (blown/sprayed) 
Mineral Wool
Polyurethane foam
Phenolic foam
Expanded polystyrene (EPS)
Extruded polystyrene (XPS)
Aerogels




References

ISO 14001
Horizon 2020
eipak.org
Homeskin
Passivehouse.com (Passivhaus)
Sustainability Workshop
Greenspec

 

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