Key Facts

Energy Savings

As buildings are very long-lived and a large proportion of the total building stock existing today will still exist in 2050 in developed countries, retrofitting the existing stock is key to a low-emission building sector. Numerous case studies of individual retrofit projects (in which measures, savings, and costs are documented) are reviewed in Harvey (2013), but a few broad generalizations are:

(1) For detached singlefamily homes, the most comprehensive retrofit packages have achieved reductions in total energy use by 50–75%;

(2) in multi-family housing (such as apartment blocks), a number of projects have achieved reductions in space heating requirements by 80–90%, approaching, in many cases, the Passive House standard for new buildings;

(3) relatively modest envelope upgrades to multi-family housing in developing countries such as China have achieved reductions in cooling energy use by about one-third to one-half, and reductions in heating energy use by two-thirds;

(4) in commercial buildings, savings in total HVAC energy use achieved through upgrades to equipment and control systems, but without changing the building envelope, are typically on the order of 25–50%;

(5) eventual re-cladding of building façades—especially when the existing façade is largely glass with a high solar heat gain coefficient, no external shading, and no provision for passive ventilation, and cooling—offers an opportunity for yet further significant savings in HVAC energy use; and

(6) lighting retrofits of commercial buildings in the early 2000s typically achieved a 30–60% energy savings. 

Technological Developments

There have been important performance improvements and cost reductions in many relevant technologies, and further significant improvements are expected. Examples include (1) daylighting and electric lighting; (2) household appliances; (3) insulation materials; (4) heat pumps; (5) indirect evaporative cooling to replace chillers in dry climates; (6) fuel cells; (7) advances in digital building automation and control systems; and (8) smart meters and grids as a means of reducing peak demand and accommodating intermittent renewable electricity sources. Many of these measures can individually reduce the relevant specific energy use by half or more. In addition to the new technologies, practitioners have also increasingly applied more established technology and knowledge both in new building construction and in the existing building retrofits.

The metrics of interest are the on-site energy intensity — annual energy use per square meter of building floor area (kWh / m2 / yr) — for those energy uses (heating, cooling, ventilation, and lighting) that naturally increase with the building floor area, and energy use per person for those energy uses — such as service hot water, consumer electronics, appliances, and office equipment — that naturally increase with population or the size of the workforce.

Dehumidification energy use is less amenable to reduction but can be met through solar-powered desiccant dehumidification with minimal non-solar energy requirements. Advanced lighting systems that include daylighting with appropriate controls and sensors, and efficient electric lighting systems (layout, ballasts, luminaires) typically achieve a factor of two reduction in energy intensity compared to typical new systems.  

Cool Room Cool Earth Campaign

“I would hope we would all have inverter-driven variable speed technology systems because we’d save energy and operating cost.”