Net-zero new buildings are beginning to enter the market. Getting to net-zero with existing office buildings presents a bigger challenge. The first step on the practical pathway to net-zero is implementation of all cost-effective energy efficiency opportunities, including operations and control improvements and building system retrofits which meet required returns on investment. For jurisdictions with low-carbon electricity grids, the emphasis will be on fossil fuel efficiency.
Most commercial office buildings generate large amounts of internal heat, not only from lights, plug loads and people but also from data centres and mechanical and electrical equipment rooms. Typically, this heat is rejected in winter through so-called air-side free cooling, or by cooling towers, air cooled condensers or district cooling systems. Reclaiming all internal heat, wherever practical, can provide a major step towards net-zero.
While every building is different, and some system configurations are more advantageous than others, in most cases reclaimed heat is collected through the building’s chilled water system. Small, high-temperature heat recovery chillers extract the heat from the chilled water loop and generate heating water hot enough to meet the building’s needs for much, or all of the heating season. Domestic hot water loads can be met year-round.
Analysis of several commercial office buildings in Toronto shows gas savings due to this type of heat recovery in the range of 1.7 to 4.5 ekWh/sf, amounting to displacement of between 35 and 90 percent of the energy efficient target. This level of reduction makes the remaining net-zero steps of on-site renewables and carbon offsets far more manageable. Ongoing development is expected to further increase the magnitude of the heat recovery step towards net-zero.
Read our full report on advanced heat recovery as a crucial step on a practical pathway to net-zero for existing commercial office buildings.