Multi-Unit Residential Buildings (MURBs) consume a significant amount of energy. Understanding how MURBs use this energy is essential to developing strategies for reducing energy consumption and costs to building owners and occupants, though very few studies have been performed to benchmark or understand real-world consumption.
Energy use within MURBs is relatively unknown. Very little measured data exists to benchmark MURB energy use within North America, let alone understand where the energy is being used for such large components as space heating, hot-water, or ventilation.
The thermal performance (effective R-values) and airtightness of the building enclosure plays an important role in the energy efficiency of a MURB, yet fully understanding the actual in-service performance and the role these factors play has not fully been demonstrated with actual data.
In addition, numerous building enclosure rehabilitations have been performed to address moisture problems within MURBs in the past few decades, with little understanding of how this has resulted in space-heat and energy savings in these buildings.
A landmark industry sponsored research study was performed by RDH in conjunction with local electricity and gas providers (BC Hydro, Terasen Gas and Fortis BC), local municipality (City of Vancouver), and government agencies (Canada Mortgage and Housing Corporation and the Homeowner Protection Office) in a joint effort to benchmark and understand the energy consumption and energy efficiency of mid- to high-rise residential buildings.
The study is unique in that it involves the analysis of a large number of in-service buildings, with similar usage and exposure conditions over a decade. The study also included several buildings which underwent full building enclosure rehabilitation work so that the energy savings attributable to building enclosure upgrades could be assessed with actual energy data.
Detailed energy consumption data was analyzed for over 39 multi-unit residential buildings within the Lower Mainland and Victoria to understand how much energy was being used and where.
We found that the average energy use intensity for the MURBs within the study was 213 kWh/m2/yr with a range between 144 to 299 kWh/m2/yr as shown in the figure below.
- 51% of this energy use was attributable to the burning of natural gas (make-up air units, hot water and gas fireplaces)
- 28% was attributable to electricity used in individual suites (electric heat, lighting, appliances, outlets, etc.)
- 21% was attributable to electricity supplied to common areas (lighting, elevators, fans, pumps, common space heating, etc.).
The figure below from the study shows how energy is typically consumed in a MURB so that opportunities for improvement can be determined.
The study found that newer MURBs (built after about 1990) typically used more energy than older buildings. This is due, in part, to increased ventilation requirements for new buildings, which require heating more outdoor air as it’s brought into the building.
Additionally newer buildings typically have more amenities such as pools, saunas and exercise rooms. Gas fireplaces that are relatively inefficient at space heating were also found to be more common in newer buildings.
The study also looked at the energy savings attributable to building enclosure rehabilitation and renewals work. Energy use was analyzed in thirteen of the study buildings and found that the effective thermal performance was increased substantially, and on average space-heat energy savings of 14% (total energy savings of 8%) were being achieved.
This was substantial given that energy efficiency was not a primary design concern for the rehabilitations due to the owners desire to minimize construction costs. Energy use was reduced during these rehabilitations primarily because of the improved thermal efficiency and improved airtightness of the building enclosure, but in all cases could have been much higher had efforts been made to incrementally improve insulation, airtightness or window performance.
Whole building energy modeling, calibrated with the actual energy consumption, was performed to assess various energy savings measures for MURBs. Several opportunities for improvements to new and existing MURBs were identified, including improvements to the building enclosure. This includes improved windows, more effective insulation, and increased air-tightness, as well as tune-up items such as adjustments to make-up air set-point temperatures, thermostat controls, improvements to elevator controls, lighting upgrades and metering of fireplaces and hot-water.
Several publications including reports, conference papers and industry bulletins have been published on the MURB study for further information and reading.