C.2 Path B Performance Limits

Part C: Case Study

In accordance with the City of Vancouver Energy Modeling Guidelines the project aims to comply with the Path B targets of the Green Building Policy for Rezoning, which sets performance limits for total energy use (TEUI), heat loss (TEDI), and greenhouse gas emissions (GHGI) limits. The table below indicates the targets and the modeled values as part of the rezoning application.

City of Vancouver Zero Emissions Plan for New Buildings: Path B Rezoning Performance Requirements

TEUI (kWh/m2a)

Path B 121

Performance Limit*

TEDI (kWh/m2a)

29.8

Rezoning Application 98.2 28.7

Energy Model

* Limits are determined by an area weighted average of the Residential 7+ storey and Retail occupancy performance limits

GHGI (kgCO /m2)2

5.9

4.2

The thermal energy demand intensity (TEDI) target provides a measure of the amount of energy a building requires to maintain an indoor temperature that is thermally comfortable for occupants, per meter of conditioned floor area per year; It is a measure of the annual heat loss from a building’s envelope and ventilation, after accounting for all passive heat gains and losses14. Thus the performance of the building envelope, and therefore any heat loss through the balcony connection detail, is critical to meeting this target.

Per the City of Vancouver rezoning submission requirements under the Zero Emissions Plan for New Buildings, an energy model must be undertaken and the results form part of the Sustainable Design Strategy Report for the rezoning application submission.

Listed below are the main areas under the designer’s control that will dictate how the project will perform in meeting the TEDI performance limit, four of which are envelope related:

1. Form / Massing: A more articulated building results in greater heat loss area, and therefore, more difficult to meet the targets.

2. Effective R-values of assemblies, accounting for all thermal bridging. 3. Glazing: Both the specification of the glazing units themselves and the amount of glass as per the window to wall ratio (WWR).

4. Level of infiltration or airtightness of the building. 5. The use of a heat recovery ventilator (HRV).

To meet the Path B rezoning performance requirements the following targets were determined for this project. The proposed design will:

1. Have a simplified compact form; 2. Have an effective R15 opaque assembly (including all thermal bridging);

3. Use good quality windows (triple pane fixed glazing and double pane operable/doors) with a 45% window to wall ratio;

4. Have a presumed infiltration rate as per the defined City of Vancouver target of 2.0L.s/m2@75Pa; and,

5. Use a 78% effective heat recovery ventilator (HRV).

Of these five targets two are impacted by the balcony connection detail: compactness of form and the effective R-value of a wall system.

Impact of Form

As described in section B.1, the form of a building and configuration of balconies can have a significant impact on the amount or length of thermal bridging associated with a balcony. Above and beyond thermal bridging, building form and articulation is a significant factor affecting a building’s ability to meet TEDI performance targets. In general, a more compact building is more energy efficient, making it easier and less expensive to achieve the performance targets.

The compactness of a building form can be measured using the ratio of a building’s vertical surface area to floor area ratio (VFAR). A case study which compares an articulated building form versus a simplified form with the same floor plate area illustrates the impact that compactness has on a project.

As an example, a multi-unit residential building with a simplified compact form has a VFAR of 0.49 whereas a more articulated version of the building with the same total floor area has a VFAR of 0.7. The articulated version nearly doubles the linear length of thermal bridging related to the balcony connection and adds 4500m2 of additional wall area. This addition of wall area reduces the window to wall ratio by over 10 percent without reducing the amount of glazing as the ratio is based on surface area of wall.

VFAR: 0.49 VFAR: 0.7

Total Floor Area: 17,400 m2 Wall Area: 5,320 m2

Window to Wall Ratio: 45%

Length of Balcony Thermal Bridging: 1,634 m Total Floor Area: 17,400 m2 Wall Area: 9,835 m2

Window to Wall Ratio: 32%

Length of Balcony Thermal Bridging: 3,145 m

Part C: Case Study

Building Envelope Thermal Bridging Guide

VERSION 1.1 2016

Building Envelope Thermal Bridging Guide2

Thermal Bridging and the Effective R Value

The effective R value of a wall system is calculated through a combination of three values:

1. Clear field transmittance: The heat flow from the wall, floor or roof assembly represented by a u-value.

2. Linear transmittance: Additional heat flow caused by details that are linear, represented by Psi (Ψ).

3. Point transmittance: Heat flow caused by thermal bridges that occur only at single, infrequent locations, represented by Chi (χ).

Clear field transmittance can be calculated based on values listed in the Building Envelope Thermal Bridging Guide2 , but to understand the thermal bridging calculation, the thermal bridge linear transmittance value (known as the Psi Ѱ-value), or the point transmittance value (known as Chi χ) of the detail needs to be determined. There are two main ways of doing this: 1. The detail can be modelled in a software such as

THERM, HEAT 2 & 3 or Flixo.

2. The values can be taken from a reference guide such as Building Envelope Thermal

Bridging Guide2 .

The methodology for calculating an effective R value for an assembly through a combination of the clear field effective R-Value of the assemblies and any thermal bridging (balcony, parapets etc.) is outlined in the extensive supporting documentation accompanying the Building Envelope Thermal Bridging Guide2. A spreadsheet calculator (Enhanced Thermal Performance Spreadsheet) is included in the Building Envelope Thermal Bridging Guide2 to assist in this calculation. Once the effective R value has been calculated, the wall, floor and roof assemblies (clear field transmittance) and the thermal bridging details (linear and point transmittance) can be adjusted to achieve the target effective R-value.