Technical Series 97-100
Previous studies have shown that energy consumption of residential high-rise buildings is comparable to that of single-family detached residences. This finding is unexpected, since high-rise buildings have better surface area to volume ratios and should use less energy per unit of floor area. A previous CMHC study1 rates of air leakage, a likely cause of excess energy use for a set of 10 buildings. By building on this information and on a variety of Ontario Hydro studies of energy usage in high-rise housing, this report details actual energy consumption and suggests means of reduction.
The report describes measurements of energy consumed and models of gains and losses in the 10 previously tested buildings over one heating season. The measurements are based on detailed information about building envelope, the mechanical and electrical systems and operating parameters. For each case, the report includes a description of the building, mechanical systems and operating schedules, weather data for the period of study, utility costs, and an energy analysis, including base loads, heat losses, air leakage profile, heat gains (including solar gain), an analysis of heat losses and recommendations for reducing energy consumption. The body of the report summarizes test results, and appendices provide building details.
The buildings are located in St. John's (Newfoundland), Montreal (Quebec), Ottawa and Toronto (Ontario), Winnipeg (Manitoba), and Victoria (B.C.), with two buildings constructed between 1960 and 1991, in each province. The largest building had 21 storeys and 240 apart ments, the smallest 8 storeys and 28 apartments. Two buildings had been retrofitted to improve airtightness (one in Ottawa, the other in Toronto). None of the buildings made use of energy- efficient lighting or ventilation heat recovery.
Each building was studied over a period from October or September to May or June of 1994-95, depending on location. Although the availability of utility bills varied, in each case the value of purchased energy was determined as accurately as possible and compared with estimated gains and losses based on weather, solar radiation at the site for the period, physical building attributes, estimated utilization factors and operational parameters. The cost of gas and oil was converted to energy terms according to conversion efficiencies based on information from the Gas Appliance Manufacturers Association and previously gathered by the consultant. In energy terms, estimated gains and losses agreed on average within 2 % of the total, with a variance of 4.5 kWh/in2.
Total purchased energy consumption ranged from 152 to 309 kWhIn2. Normalized for climate, the average consumption was 48.85 Whldegree day in2 with a variance of 7.02. From 25 to 58 % of this energy was used for space heating, 12 to 18 percent to heat domestic water, lighting, 3 to 9 % for elevators and 0.2 to 12.8 for space cooling (not including the cooling season). Other uses, including appliances, pumps and swimming pools, accounted for 8 to 20 %. The proportion of energy used for any particular purpose varied considerably from building to building.
Purchased Energy Use
In energy terms, purchased energy accounted on average, for 82% of all gains (61 % space heating, 21 % internal gains), with solar gain of 18 %. Solar gains were determined according to Environment Canada solar radiation records, using methods described by Duffie and Beckman2. Internal gains and utilization were determined using methods described by Barakat and Sander3and in the ASHRAE Handbook of Fundamentals.
Average losses in energy were due to windows (31 %) and air leakage, including leakage at doors and windows (24 %), ventilation (20 %), walls (16 percent), doors (4 %) and roof (5 %).
Conduction losses were determined from actual weather data for the period of study and U values were determined from the ASHRAE Handbook of Fundamentals, using building drawings and specifications with on-site confirmation of as-built conditions. Ventilation losses were determined by measurements of actual flows with systems in operation, calculated in terms of the operating schedules.
Gain and loss profiles varied considerably from building to building, as the
following graphs (Figures 2 and 3) show:
Gains as % of Building Total
Losses as % of Building Total
Air leakage was determined by the ALCAP method4, using the known air- leakage properties of the buildings, stack effect pressures based on monthly weather data, wind data and other factors to determine heat loss due to air leakage and occupant operation of windows. Base loads remained constant. Both conduction and ventilation load increased as linear functions of temperature difference. However, air leakage increased exponentially; hence, the colder the climate, the more important air leakage is in relation to other losses. One of the building load profiles illustrates this point (Fig. 4).
Load Profile for Ottawa Building
The results of this study should be helpful to designers and managers of high-rise
residential buildings, but more detail would be required for them to audit an
existing building using the same methods. The report recommends the following
general energy conservation measures:
· air sealing to reduce air leakage;
· improved window performance (including low-e films for retrofits);
· insulation upgrades for walls and roofs;
· energy-efficient lighting;
· scheduling of make-up air, central exhaust and laundry room exhaust systems;
· calibration of thermostats;
· lower thermostat set-points in garages, storage and service rooms; and
· water conserving measures (e.g., low-flow shower heads).
The largest losses are due to windows, air leakage, and ventilation. Improved windows, reduced air leakage, and ventilation heat recovery would appear to be the most promising prospects for designing buildings with reduced energy consumption.
Although losses, due to air leakage account for a substantial proportion of the typical heating budget, the consultant's estimate of a potential 4 to 6 % reduction in energy consumption after air-sealing, amounting to an average annual savings of $0.63/in2, suggests that hidden condensation and resulting deterioration of the building envelope is a more compelling reason to reduce air leakage. The two buildings that had been retrofitted do not stand out particularly (see Ottawa and Toronto in Figure 3, "Losses as % of Building Total").
Some strategies for energy reduction that focus on the decreased use of purchased energy may be offset by increases in other areas. For example, reduced air leakage may require improved ventilation. Or, energy-efficient lighting, at least indoors during the heating season, may require increased space heating. Better windows and improved ventilation systems incorporating heat recovery should be investigated as means of reducing energy consumption. Passive control, such as shading to reduce space cooling requirements without reducing usable solar gains, might be appropriate in Victoria.
Project Manager: Jacques
Research Report: Study report on the Energy Audits of High-Rise Residential Buildings, 1997
Research Consultant: Scanada Consultants Limited
1. Wardrop Engineering "Field Investigation Survey of Airtightness, Air Movement, and Indoor Air Quality in High Rise Buildings, Summary Report" July 1993
2. "Solar Engineering of Thermal
Processes", Wiley lnterscience, 1989.
3. "The Utilization of Internal
Heat Gains"ASHRAE Transactions, 1992.
4. "Development of Design Procedures and Guidelines for Reducing Electric Demand by Air Leakage Control in High-Rise Residential Buildings" for Ontario Hydro, 1991 (available from CMHC); "Comparison of airtightness, lAO, and Power Consumption before and after air-sealing of high-rise residential buildings" Paper #20, 12th AIVC Conference, Proceedings Vol. 1, pp315-322; "Identification, assess ment and potential control of air leakage in high-rise buldings" 6th Conference of Building Science and Technology Mar.'92; "Power Demand and Energy Savings through air leakage in high-rise residential buildings in cold climates" 5th conference on Thermal Performance of Exterior Envelopes of Buildings, ASHRAE/BTECC, December 1992.
full report on this research project is available
from the Canadian Housing Information Centre.
The information in this publication represents the latest knowledge available to CMHC at the time of publication, and has been thoroughly reviewed by experts in the housing field. CMHC, however, assumes no liability for any damage, injury, expense or loss that may result from use of this information.
©1999 CMHC-SCHL. All rights reserved.