{"id":4499,"date":"2023-11-01T10:40:00","date_gmt":"2023-11-01T10:40:00","guid":{"rendered":"https:\/\/www.bcta.group\/attma\/?p=4499"},"modified":"2023-10-27T08:14:16","modified_gmt":"2023-10-27T07:14:16","slug":"understanding-the-importance-of-environmental-readings","status":"publish","type":"post","link":"https:\/\/www.bcta.group\/attma\/2023\/understanding-the-importance-of-environmental-readings\/","title":{"rendered":"Understanding the Importance of Environmental Readings"},"content":{"rendered":"\n

The environmental readings taken on a test are the barometric pressure, external temperature and the internal temperature or the average internal temperature from several readings in taller buildings. All of these readings are taken before the test and then they are taken again at the end of the test.<\/p>\n\n\n\n

Recording the Barometric Pressure<\/h3>\n\n\n\n

The barometric pressure can be recorded inside or outside the building and needs to be recorded both before and after the test.  According to the ATTMA test standards this can be recorded in hPa or mBar to 1 decimal place which will be a number roughly around 1000 or in Pa to no decimal places which will be a number of roughly 100000.<\/p>\n\n\n\n

If your software only has a single data entry point for barometric pressure then you need to record the readings within your notes section of your software for traceability. The mean average of the two readings is then entered into the data entry point.<\/p>\n\n\n\n

Recording the Temperature Readings<\/h3>\n\n\n\n

The temperature readings are recorded in degrees Celsius to 1 decimal place and need to be allowed to stabilise when moving from the inside to the outside of the building or vice versa.  Depending on the response time of the probe and thermometer and the amount of difference between the temperatures this can take between 2-10 minutes.  The most common type of probe and thermometer used within the UK by air tightness testers typically takes 5-8 minutes to stabilise.<\/p>\n\n\n\n

Internal temperatures are recorded at the approximate geometric centre of the building, so basically by the internal pressure tube.  In the ATTMA test standards when you have taller buildings a temperature reading needs to be recorded for every sixth floor or part thereof i.e. 1-6 is one, 7-12 is two, etc.  There\u2019s no guidance on the location of where the multiple readings are taken but it makes sense to spread them evenly in the building.<\/p>\n\n\n\n

External temperatures are to be taken by the fan.<\/p>\n\n\n\n

Why do we record environmental readings?<\/h3>\n\n\n\n

The environmental readings are used to apply adjustments to the calculated flow values in the test because they are used to determine the weight of the air in kg\/m3<\/sup>, which is known as air density. The weight of air determines how much volume of air can be moved through your fan with heavier than normal air reducing the volume and lighter than normal are increasing the volume.  In air tightness testing we use a standardised air density of 1.2 kg\/m3<\/sup> so whether the air is light or heavy is relative to this value.<\/p>\n\n\n\n

Click Page 2 to read more<\/p>\n\n\n\n\n\n\n\n

Flow of air going through the fan<\/strong><\/h5>\n\n\n\n

When the flow pressure readings are converted to flow based on the equipment calibration variables this flow is adjusted by the difference between the air density that the calibration variables are given at on the calibration certificate and that of the air going through the fan.  This gives us the flow of air going through the fan corrected to the test conditions.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n
Qm<\/sub><\/em><\/em><\/td>The flow of air going through the fan adjusted by the air density of the air going through the fan<\/td><\/tr>
QC<\/sub><\/em><\/em><\/td>The flow of air calculated from the flow pressure readings using the calibration variables<\/td><\/tr>
\u03c1C<\/sub><\/em><\/td>The air density at calibration<\/td><\/tr>
\u03c1m<\/sub><\/em><\/td>The air density of the air going through the fan<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The Air density that you use for the air going through the fan depends whether you are pressurising or depressurising the building.  If you pressurise then the air is being drawn from outside the building through the fan to inside the building so the external air density (\u03c1e<\/sub><\/em>)  is used. if you are depressurising the air is being drawn from inside the building through the fan to the outside of the building so the internal air density (\u03c1i<\/sub><\/em>) is used.<\/p>\n\n\n\n

Location<\/th>Temperature<\/th>Barometric Pressure<\/th>Air Density<\/th><\/tr><\/thead>
Internal (\u03c1i<\/sub><\/em>)<\/strong><\/td>20\u00b0C<\/td>1000.00 hPa<\/td>1.1884<\/td><\/tr>
External (\u03c1e<\/sub><\/em>)<\/strong><\/td>10\u00b0C<\/td>1000.00 hPa<\/td>1.2303<\/td><\/tr>
Calibration (\u03c1c<\/sub><\/em>)<\/strong><\/td>20\u00b0C<\/td>1013.25 hPa<\/td>1.2041<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Depressurise<\/strong><\/p>\n\n\n\n

Reading<\/th>1<\/th>2<\/th>3<\/th>4<\/th>5<\/th>6<\/th>7<\/th>8<\/th><\/tr><\/thead>
Flow in m3<\/sup>\/h<\/td>711.5<\/td>655.0<\/td>605.0<\/td>557.0<\/td>502.6<\/td>444.4<\/td>368.2<\/td>289.7<\/td><\/tr>
Qm<\/sub><\/td>720.9<\/td>663.7<\/td>613.0<\/td>564.4<\/td>509.2<\/td>450.3<\/td>373.1<\/td>293.5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The air density on the depressurisation test is lower than at calibration therefore it\u2019s easier to move air through the fan under these conditions so a greater volume of air is moved than at calibration.<\/p>\n\n\n\n

Pressurise<\/strong><\/p>\n\n\n\n

Reading<\/th>1<\/th>2<\/th>3<\/th>4<\/th>5<\/th>6<\/th>7<\/th>8<\/th><\/tr><\/thead>
Flow in m3<\/sup>\/h<\/td>711.5<\/td>655<\/td>605<\/td>557<\/td>502.6<\/td>444.4<\/td>368.2<\/td>289.7<\/td><\/tr>
Qm<\/sub><\/td>696.3<\/td>641.1<\/td>592.1<\/td>545.1<\/td>491.9<\/td>434.9<\/td>360.4<\/td>283.5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The air density on the pressurisation test is higher than at calibration therefore it is more difficult to move the air under these conditions through the fan so a lower volume of air is moved than at calibration.<\/p>\n\n\n\n

Flow of air going through the building fabric<\/strong><\/h5>\n\n\n\n

This flow is then converted again by looking at the difference of the air density of the air going through the fan and that of the air going through the building.  This gives is the flow of air going through the building fabric and there are two equations with one for when you are depressurising and the other for when you are pressurising.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

Depressurise<\/p>\n\n\n\n

Reading<\/th>1<\/th>2<\/th>3<\/th>4<\/th>5<\/th>6<\/th>7<\/th>8<\/th><\/tr><\/thead>
Flow in m3<\/sup>\/h<\/td>711.5<\/td>655.0<\/td>605.0<\/td>557.0<\/td>502.6<\/td>444.4<\/td>368.2<\/td>289.7<\/td><\/tr>
Qm<\/sub><\/td>723.9<\/td>666.4<\/td>615.5<\/td>566.7<\/td>511.3<\/td>452.1<\/td>374.6<\/td>294.7<\/td><\/tr>
Qenv(in)<\/sub><\/td>696.3<\/td>641.1<\/td>592.1<\/td>545.1<\/td>491.9<\/td>434.9<\/td>360.4<\/td>283.5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Pressurise<\/p>\n\n\n\n

Reading<\/th>1<\/th>2<\/th>3<\/th>4<\/th>5<\/th>6<\/th>7<\/th>8<\/th><\/tr><\/thead>
Flow in m3<\/sup>\/h<\/td>711.5<\/td>655<\/td>605<\/td>557<\/td>502.6<\/td>444.4<\/td>368.2<\/td>289.7<\/td><\/tr>
Qm<\/sub><\/td>696.3<\/td>641.1<\/td>592.1<\/td>545.1<\/td>491.9<\/td>434.9<\/td>360.4<\/td>283.5<\/td><\/tr>
Qenv(out)<\/sub><\/td>720.9<\/td>663.7<\/td>613.0<\/td>564.4<\/td>509.2<\/td>450.3<\/td>373.1<\/td>293.5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Adjustments of the trendline through the readings to standard conditions<\/strong><\/h5>\n\n\n\n

The trendline through the data is calculated at the conditions on the test but to compare tests with each other they need to be corrected back to a standardised air density.  If this wasn\u2019t done you would get different results on the same property depending what time of year it was tested. The Air Flow Coefficient (Cenv<\/sub><\/em>) is the start point of the trendline and this if what gets adjusted to give us the Air Leakage Coefficient (CL<\/sub><\/em>)<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

For the depressurisation test if you were to calculate the flow at 50Pa (Q50<\/sub><\/em>) from the Cenv<\/sub><\/em> it would give you a value of 651.191 m3<\/sup>.h-1<\/sup> whereas with the CL<\/sub><\/em> corrected back to standardised conditions this is 653.298 m3<\/sup>.h-1<\/sup>.<\/p>\n\n\n\n

For the pressurisation test if you were to calculate the flow at 50Pa (Q50<\/sub><\/em>) from the Cenv<\/sub><\/em>it would give you a value of 676.943 m3<\/sup>.h-1<\/sup> whereas with the CL<\/sub><\/em> corrected back to standardised conditions this is 679.131 m3<\/sup>.h-1<\/sup>.<\/p>\n\n\n\n

These are a minor adjustment because the environmental readings are not extreme relative to the standard air density.<\/p>\n","protected":false},"excerpt":{"rendered":"

The environmental readings taken on a test are the barometric pressure, external temperature and the internal temperature or the average<\/p>\n","protected":false},"author":3,"featured_media":4504,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[29],"tags":[97,61,30],"class_list":["post-4499","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-air-leakage","tag-airtightness","tag-attma"],"publishpress_future_action":{"enabled":false,"date":"2026-05-07 07:39:03","action":"change-status","newStatus":"draft","terms":[],"taxonomy":"category","extraData":[]},"publishpress_future_workflow_manual_trigger":{"enabledWorkflows":[]},"_links":{"self":[{"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/posts\/4499","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/comments?post=4499"}],"version-history":[{"count":7,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/posts\/4499\/revisions"}],"predecessor-version":[{"id":4510,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/posts\/4499\/revisions\/4510"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/media\/4504"}],"wp:attachment":[{"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/media?parent=4499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/categories?post=4499"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bcta.group\/attma\/wp-json\/wp\/v2\/tags?post=4499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}