Determining whether or not a room within a building is likely to overheat is essential for the thermal comfort of the occupants. The term ‘thermal comfort’ describes a person’s state of mind in terms of whether they feel too hot or too cold and it’s important as an unacceptable thermal comfort can result in occupants losing their ability to concentrate or removing protective clothing they may be required to wear.
At Ecodraw we will create a Dynamic Simulation Model of your proposed or existing building and accurately input its internal heat gains such as occupants, lighting and equipment. We will also model any windows, louvres or shading devices and then use actual weather data for the location of your building to simulate its amount of overheating throughout a typically hot year (Design Summer Year).
The overheating results we produce can then be compared against the relevant standards for your type of building such as BB 101 for schools, TM 52 for offices and CIBSE Guide A for care homes or other residential buildings.
The performance standards for summertime overheating in compliance with Approved Document L2A for teaching and learning areas are:
a) There should be no more than 120 hours when the air temperature in the classroom rises above 28°C
b) The average internal to external temperature difference should not exceed 5°C (i.e. the internal air temperature should be no more than 5°C above the external air temperature on average)
c) The internal air temperature when the space is occupied should not exceed 32°C.
In order to show that the proposed school will not suffer overheating two of these three criteria must be met.
The 2006 version of CIBSE guide A: Environmental Design outlined benchmark summer peak temperatures and overheating criteria shown in the table below:
This states that spaces such as Offices, Schools and living areas should not exceed 28°C for more than 1% of their occupied hours, and bedrooms should not exceed 26°C also for more than 1% of their occupied hours.
The latest 2015 version of CIBSE Guide A uses an equation to calculate the ideal comfort temperature and maximum indoor temperature based upon the average running mean of the outdoor temperature. The idea of using an adaptive overheating model is explored in more detail under the latest overheating compliance regulation TM52.
CIBSE TM52 uses an adaptive overheating methodology, meaning that the maximum indoor temperature that should not be exceeded changes based upon the current outdoor temperature. Unlike BB 101 where a maximum internal temperature of 32°C must not be exceeded at anytime, no matter what the external temperature.
To pass TM 52 two out of the three following criteria must be met:
Criterion 1: Hours of Exceedance – The number of hours during which the temperature difference between inside and outside is equal to one degree, between the period of May to September, shall not exceed 3% of the occupied hours.
Criterion 2: Daily Weighted Exceedance – The overheating weighted exceedance shall be equal or less to 6 in any one day. For example if a building has a temperature difference of two for two hours and a temperature difference of one for one hour this would equal a daily weighted exceedance of 5 (2×2+1×1=5), therefore satisfying the criterion.
Criterion 3: Upper Limit Temperature – The absolute maximum temperature difference of four degrees shall never be exceeded.
Before a building is occupied the only way to predict if overheating is likely to occur is to create a dynamic simulation model. We can show the amount of overheating occurring in your building for every hour in an entire year, allowing you to see exactly which rooms are likely to suffer from overheating and at what times.
If you would like us to model the overheating potentially occurring in your building, and compare the results to any of the regulatory standards, get in touch with us today.