Unlock the Secrets of Decrement Delay and Enhance Your Building’s Thermal Performance with Dynamic Envelope Design

Do you know that we spend about 80–90% of our time at home or in other public indoor environments? Are you aware of the great impact of indoor environmental quality on your health and working performance? Thermal comfort is a key factor influenced by the design strategies and the material choices you implement in your projects.

The building envelope works as a dynamic interface between indoors and outdoors by regulating climate variability, thereby impacting the heating and cooling loads. The thermal comfort quality that the envelope provides depends, among other things, on the thermophysical performance of the construction materials combined as wall and roof systems. In other words, the building envelope can be described as the third skin for the human body that supports keeping the body temperature steady even though the outside temperature fluctuates.

 

Highlights

– The thermal performance of building envelopes is complex and dynamic, with a great impact on indoor comfort and energy efficiency.

– Climate conditions, building orientation, envelope design and its specific construction materials, occupants’ behaviour, and HVAC systems (Heating, Ventilation and Air Conditioning) influence the global energy consumption of buildings.

– Global warming potential, decrement delay and other thermophysical properties of building materials are crucial for low-carbon and energy-efficient building envelope design.

– Biobased insulation materials (straw, cork, wood fibre, paper wool, hemp) show better thermal and carbon performance in comparison to conventional ones (foam glass, PUR, XPS), according to the joint research by @2050 Materials and @GHA Glenn Howells Architects.

Get familiar with relevant thermophysical parameters

Decrement Delay

Refers to the time it takes for heat generated by the sun, to transfer from the outside to the inside of the building envelope and affect the internal conditions. Units: hours.

Decrement factor

Ratio between the cyclic temperature variation on the inside surface of a wall or roof compared to the outside surface. In practical terms, it basically describes the stability of the inside surface temperature, typically over the course of a summer day. Units: hours.

Density

The mass (or ‘weight’) per unit volume of a material and is measured in kg/m3. A high-density material maximises the overall weight and is anaspect of ‘low’ thermal diffusivity. Units: kg/m3.

Diurnal temperature variation

The daily temperature shift that occurs from daytime to night-time.

Diurnal heat flow

The heat that flows to and from a building or space over the course of 24 hours.

Heat transfer

The transition of thermal energy from a hotter object to a cooler object. Units: kJ/kg.

Specific heat capacity

The amount of heat required to raise the temperature of 1kg of a material by one degree Centigrade. It is an important factor in slowing up the transfer of heat. Units: J/kg⋅K.

Thermal conductivity (λ-value)

It measures the ease with which heat can travel through a material. For ‘low’ thermal diffusivity, ‘low’ conductivity is an essential part of the equation. Units: W/m⋅K.

Thermal diffusivity

Rate of transfer of heat of a material from the hot end to the cold end. It is calculated as the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. In effect, it is a measure of thermal inertia or ‘buffering’. Units: m2/hr.

Thermal mass

A concept in building design that describes how the mass of the building provides “inertia” against temperature fluctuations. Units: J/K

Thermal resistance (R-value)

The measure of a component’s ability to restrict the passage of heat across its thickness. The R-value is calculated by combining the thermal conductivity and the thickness of the material. Hence R=t/λ, where ‘t’ is the thickness. Used in connection with insulation, the higher the R-value, the more effective the insulation. Units: m2⋅W/K.

Thermal transmittance (U-value)

A measure of the overall rate of heat transfer, by all mechanisms under standard conditions, through a particular section of construction. This measure takes into account the thickness of each material involved and is calculated from R-values of each material as well as constants accounting for surface transmittance (Rsi and Rso, inner and outer surfaces respectively) and also for a small standard air gap (Rso).

Units: W/m2⋅K.

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