Is 100mm of concrete enough in naturally ventilated buildings?
A question often asked by architects and designers is: "Will 100mm of concrete provide enough thermal mass?" The answer largely depends on the extent to which you want to optimise the building design. It is sometimes thought that a 100mm of concrete is sufficient, but this fails to take account of a range of factors including how buildings actually respond to real weather conditions. For example, a naturally ventilated office with exposed 100mm concrete composite floors (steel decking/soffit with insitu concrete topping) might have sufficient heat capacity to cope with a simple 24 hour heating and cooling cycle. However, in addition to a building’s daily cycle, there are also longer cycles related to a typical hot spell (usually three to five days) and also the five working days per week cycle, from which heat will reach different depths within the available thermal mass. In the case of floors in a non-air conditioned building for example, the greater the slab depth, the longer the time period it responds to; the core of a 300mm thick concrete slab responds to the monthly average condition and draws heat in deeper over an extended period of hot weather.
For longer time periods these factors are important because it is the longer-term average room temperatures that define the thermal storage core temperature and hence the temperature gradient that draws heat in to the concrete. So, whilst a 100mm of concrete offers some useful thermal mass, thicker slabs provide greater temperature stability and increased cooling performance across a range of conditions including hot periods.
To help visualise what this means in practice, the graph below shows how the soffit temperature of exposed 100mm and 300mm floors in a naturally ventilated office respond to hot weather. This was produced using finite difference modelling to calculate the heat transfer at the soffit and into the floor slab over the course of several days, during which there is a shift to warmer weather.
This publication assists engineers in understanding the common challenges of building tall.
An all-you-need-to-know guide on the specification of sustainable concrete.
Guidance on how concrete can be used to achieve credits under the latest version of BREEAM NC:2014.
This book summarises the reference material that will be used in the design of reinforced concrete buildings to Eurocode 2.
This document provides information on the material and resource efficiency of concrete and masonry.
This guide sets out how concrete's attributes can be used to minimise CO2 emissions.
This eighth annual report report presents the concrete industry’s sustainability performance in 2014.
This publication explores the key themes of whole-life, including future flexibility, resilience and ease of maintenance.
This guide focuses on the use of concrete at Coin Street Neighbourhood Centre and its part in creating a low energy building.
This publication summarises the material used in the design of reinforced and prestressed concrete bridges using Eurocode 2