Posts by karlp

A guide to Volume Calculations for Passivhaus Air Tightness Testing and the Difference with the UK Method

Posted by on Aug 11, 2011 in Guides | Comments Off on A guide to Volume Calculations for Passivhaus Air Tightness Testing and the Difference with the UK Method

UK Methodology The UK standard measures Air Permeability, in m3/hr/m2@50Pa (the q50 measurement), or in other words the air leakage per square metre of building envelope. The ATTMA (Air Tightness Testing and Measurement Association) TS1 standard defines the building envelope as everything within the air barrier line ‘along the line of the component to be relied upon for air sealing’. This could be anywhere within the building envelope (even the external render). This is a measure of building envelope airtightness. Passivhaus Methodology The Passivhaus standard measures the Air Change Rate (ACH) @50Pa (the n50 measurement), or in other words the number of times the volume of air within the building is changed in an hour. So, it is a purely volumetric measure. The Passivhaus methodology considers the volume of air which needs to be heated. Therefore internal walls and floors are excluded. This is a measure of air infiltration, and hence the heating energy cost of the building. Calculating the Passivhaus Air Test Volume A straightforward way to calculate the volume required for the Pressure Test is as follows: Start with the Treated Floor Area (TFA) Add the space occupied by any stairs (imagine that they do not exist and that a standard floor construction occupies the void) Any areas treated at 60% for TFA purposes should be treated at 100% for this volume calculation The total TFA for each floor can be multiplied by each floor to ceiling height (averaged if necessary for sloping ceilings) to give a volume for each storey (not including internal floors) The total for all the storeys equals the Pressure Test volume Divide the measured air flowrate, in m3/hr, by the Pressure Test Volume (m3) to get the air change rate, n50 Note The two measures, Air Permeability and Air Change Rate, do not have a direct relationship with each other (so you can’t apply a conversion factor to one to get the other). Therefore the building needs to be measured to the right protocol, and the results calculated in the right way (n50 not q50), to get a result which can be used for certification. It is essential to use the correct volume for testing, even before the interior spaces are fully finished. Voids within wall and floor constructions cannot be...

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Does it actually work? Lessons from an exemplar scheme

Posted by on Nov 22, 2010 in news | Comments Off on Does it actually work? Lessons from an exemplar scheme

The recently published report ‘Low Carbon Housing: Lessons from Elm Tree Mews’, from the Joseph Rowntree Foundation, makes for fascinating reading, and highlights issues of critical importance as we strive to create low energy homes. The Elm Tree Mews development was conceived in 2005 as a small social housing development designed to energy and carbon standards just short of code level 4 of the Code for Sustainable Homes. Coheating and airtightness testing prior to occupation formed part of the assessment of the development as built, along with post occupancy monitoring over a period of 12 months. A number of areas in the report interested me in particular. Fabric First! A number of issues were highlighted with regard to the building fabric. These show the importance of a robust design process. The timber fraction was much higher than expected, meaning that the actual wall U-value of 0.3W/m2K was 65% higher than the designed U-value of 0.18W/m2K. The designed timber fraction of 2.5% was clearly incredibly optimistic, with the actual value being 25%. Product substitution meant that window performance suffered, with U-values slipping from 1.5W/m2K to 2W/m2K. The party walls were not considered a heat loss area in the design, but they were found to have a U-value of 0.3W/m2K. Losses through party walls have only recently been recognised as an issue, and are included in the 2010 Part L of the Building Regulations. The impact of thermal bridging on the performance of the design was underestimated. Envelope complexity contributed to the bridging at some challenging junctions. The as-built airtightness, at 7m3/hr.m2 was over twice the designed value, within current UK standards but much higher than that needed for low energy housing. Services which work! In terms of the heating and hot water services provision, there were shortcomings in the design, installation and commissioning processes. Component interactions and the complexity of control requirements were underestimated. Installation was poorly controlled and the commissioning process was not robust. Build for the occupiers! Resident interviews highlighted a number of shortcomings in the design. To create good architecture it’s essential to design spaces (and the control systems for those spaces) around the lives of the occupiers. The space needs to fit the people, not the other way round. In terms of layout, a lack of storage space was highlighted as an issue. Winter Gardens were seen by occupiers as difficult spaces, too cold to use all year round without introducing further heating, and taking up valuable outdoor space. Without radiators, but having no suitable clothes drying space, residents tended to buy tumble dryers. The control systems for the services were rather complex, with four controllers needed for the space heating, solar system, hot water and immersion heater. Room thermostats did not indicate temperature, making them difficult to...

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