Thermal admittance of building materials
Thermal admittance (Y) is a measure a material's ability to absorb heat from, and release it to, a space over time. This can be used as an indicator of the thermal storage capacity (thermal mass) of a material, absorbing heat from and releasing it to a space through cyclical temperature variations, thus evening out temperature variations and so reducing the demand on building services systems.
Thermal admittance is expressed in W/(m^2K), where the higher the admittance value, the higher the thermal storage capacity.
Thermal admittance is calculated as the heat transfer (in watts W) / area (m^2) x the temperature difference between the surface of the material and the air.
Typical admittance values based on a 24-hour cycle might range from 1.0 for a timber frame wall with brick outer leaf, to 2.65 for a cavity wall with 100 mm dense aggregate block (ref. The Concrete Centre).
The admittance time lead, ω (expressed in hours), is a measure of the time delay between the peak heat flow between the material surface and the space and the time of the peak temperature in the space.
Admittance is dependant primarily on a material's density, thermal capacity, thermal conductivity, surface resistance and the time cycle of the temperature variation.
As the thickness of a material increases, so the admittance approaches a constant value. It is generally considered that in the UK, with a 24-hour thermal cycle, heat energy can only penetrate up to 100 mm into materials such as concrete and masonry.
[edit] Related articles on Designing Buildings Wiki
[edit] External references.
- ISO 13786:2007. Thermal performance of building components -- Dynamic thermal characteristics -- Calculation methods.
- The Concrete Centre: Thermal Mass Explained (2012 update).
Featured articles and news
RTPI leader to become new CIOB Chief Executive Officer
Dr Victoria Hills MRTPI, FICE to take over after Caroline Gumble’s departure.
Social and affordable housing, a long term plan for delivery
The “Delivering a Decade of Renewal for Social and Affordable Housing” strategy sets out future path.
A change to adoptive architecture
Effects of global weather warming on architectural detailing, material choice and human interaction.
The proposed publicly owned and backed subsidiary of Homes England, to facilitate new homes.
How big is the problem and what can we do to mitigate the effects?
Overheating guidance and tools for building designers
A number of cool guides to help with the heat.
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.
UK Infrastructure: A 10 Year Strategy. In brief with reactions
With the National Infrastructure and Service Transformation Authority (NISTA).