ENVIRONMENTAL SYSTEMS_ 425/PASSIVE HOUSE/Energy Flow/Monday Feb 1 THE THERMAL ENVELOPE.

ENVIRONMENTAL SYSTEMS_ 425/PASSIVE HOUSE/Energy Flow/Monday Feb 1 THE THERMAL ENVELOPE. Looking back at the passive house key principles, the top three out of five guiding concepts – thermal insulation with no thermal bridges; air tightness; high thermal performance windows – relate to the efficiency of the envelope specifically in terms of restricting thermal transmittance. To achieve the extremely high targets for minimal energy use, the exterior of the building on all sides – roof, ground, walls, and any penetrations such as windows, skylights, structure, exhaust ducts – is scrutinized in terms of design strategy and then analyzed and adjusted with calculations based on the physical properties of the materials being used, as well as the geometrical organization of the components. MAININTING THE INTERIOR THERMAL ENVIRONMENT In terms of the ability of the envelope to prevent the interior thermal condition being ‘lost’ to the exterior or ‘ambient’ condition, we look at two key issues: TRANSMITTANCE and AIR MOVEMENT 1. TRANSMITTANCE. The overall quantitative ability for the wall, roof, or ground floor to resist thermal transmittance through the physical materials that lie between the interior and exterior environments (obvious examples are building insulation, concrete, masonry, wood, glass, steel). We call this ability to resist thermal transmittance, the envelope’s R-VALUE This is a factor of the sum of each of the physical thermal resistance properties plus a number of other factors that we will outline later. Typically, once we know the R-value of a material in terms of its ‘resistivity per inch’, a simple picture is built up of the overall envelope composition based on total thicknesses of each material. For example, if a mineral wool insulation has a thermal resistance value of R5/inch, and if we use 4” total thickness as we assess it in section, we would achieve R20 for that component of the envelope. We would then look at all the other components on either side, and create a full understanding of the overall wall makeup. Any given material’s inability to resist thermal transmittance, is simply called its transmittance. We call the thermal transmittance of a property its U-VALUE While opaque building elements are often referred to by the R-Value, the more inefficient components of wall assembly, such as windows and exterior doors, are often described in terms of their U-Value. The U-value is very simply the inverse of the R-value i.e. U-Value = 1 or R-Value = 1 R-value U-value Effect on thermal gradient from interior to exterior adding insulation to the interior of a solid masonry wall In the diagram above, we can see the dramatic effect of the high resistivity material - insulation - on the overall wall make-up. Apart from the typical make-up of wall and window components, Passive House also requires ‘NO THERMAL BRIDGES’. This means the removal of one-off interface moments where some kind of penetration or atypical building component causes a disruption to the typical, high performing thermal resistance, often causing an increased level of energy flow, or ‘transmittance’ with both energy losses and the potential for condensation with the exterior envelope assembly. ’cold’ balcony structure is causing condensation, and consequent mold in the interior cavities of the building 2. AIR LEAKAGE. The amount of interior air, that literally passes from the interior to the exterior as a factor of building geometry and the barriers - or not - to that movement. In this aspect we are focused on air changes per hour within the building envelope. The greater volume of air lost to the outside in an uncontrolled way (without being directed through heat recovery systems) the greater the loss of the internal thermal environment to the ambient exterior. In the Passive House strategy, a number of techniques are adopted to reduce air leaking. These techniques include: A continuous air barrier material, located as some component of the wall, roof and floor makeups; lapping of materials at key interfaces; high quality window frames with thermally broken interlocking components; the use of sophisticated window tapes between various building components; filters and valves at points of building penetrations, taped windows, foil backed insulation (high impermability to vapor) and plywood (medium impermeability) are used to varying effects in the aim to reduce heat loss through air leakage blower door test, performed to monitor the amount of air forced into the building leaks out over time WEEKLY ASSIGNMENT 03: ENERGY FLOW Assignment 03 – set Feb 08, 2016, due Feb 15, 2016 to be submitted to Moodle as a PDF by end of day: 1. Based on the formula for calculating the R-value of adjacently installed materials, and referring to the R-Value page of the PHPP, provide the working method and final R-value for a wall that the following components sited adjacently moving from the exterior to interior as follows: A 6” concrete exterior wall 2’-0” thickness of straw bale laid on edge 4” stud at 2’ centers with no insulation between 1 layer of 5/8” drywall to form the interior face Assume that the Exterior Surface Film Resistance is for a screened location (i.e. that there is some kind of exterior shading that is not part of the thermal make up of the wall – this could be a tree, an adjacent house or some intentional shading structure, low less likely for an ‘opaque wall’) and that the Interior Surface Film Resistance is for a upward heat flow. 2. Assuming that this gives an indication of the R-value for the envelope generally, would this be appropriate in R-value terms as a starting point for any passive house projects in North America, and if so, in what part of the country / climate zones? 3. Draw a simple freehand section through the wall that shows an estimate of change in temperature through the various components of the wall. Note the interior and exterior sides, and assume the exterior is ‘cold’ and the interior is ‘warm’. No actual quantitative temperature data is required, but the section should be to scale. 4. Name one benefit of this suggested wall make up. 5. Name one disadvantage of this suggested wall make up where space is limited and what you might adjust without losing the benefit of the answer to 3. above. 6. In 20 words describe the mechanism for an internal thermal environment to be lost to the exterior OTHER than by thermal transmittance of adjacent materials, and list a highly performing material that would limit the phenomenon being so much of an issue. 7. Name a material that has a high resistance to thermal transmittance (R-value) but a low impermeability, listing both R and Perm value. 8. Name a material that has a low resistance to thermal transmittance (R-value) but a high impermeability, listing both R and Perm value.