Net Zero Buildings

The New Buildings Institute (NBI) in the USA turned 15 years old in April. The NBI is a non-profit ‘working to improve the energy performance of commercial buildings. The NBI has two very interesting initiatives that deserve wider attention, ‘Getting to 50’ i.e. achieving savings of at least 50 per cent compared to current building code (regulations) and ‘Zero Energy’, which is about getting to net zero energy buildings, i.e. buildings that consume no more energy in a year than they produce. Even the ‘getting to 50’ is an ambitious goal, getting to net zero even more so. So on their 15th birthday it is interesting to look at how things are going with both of these really useful initiatives but particularly net zero energy.

A recent report released by the NBI summarized the progress on net zero buildings and took a first look at costs and features of these buildings. The report covered 21 buildings with sufficient data to analyze, 15 of which had actual results and 6 with modeled consumptions. They covered most climate zones in the US and a wide range of buildings including offices, schools and sports facilities. They were small, generally less than 15,000 ft2 but this is representative of the US building stock. The total number of net zero energy (or zero energy capable) buildings in the US is expected to reach 100 by the end of 2013.

The average Energy Use Intensity (EUI) for US commercial buildings is 93 kBTU/ft2. The least efficient of the 21 buildings had an EUI of 35kBTU/ ft2 – i.e. 62% less than the average. The most efficient achieved EUIs of about 10% of the average – i.e. energy consumptions 90% less than the average.

The techniques used included; integrated design, extensive use of day lighting, high efficiency envelopes, high efficiency glazing and advanced heating and ventilating systems and all the buildings included photovoltaic solar systems. All the technologies used were widely available and not particularly innovative in themselves. As energy used for heating and lighting is reduced, the proportion used for plug loads is increased and more effort is then needed to reduce this through both design and better operations.

Measuring incremental costs of buildings is notoriously difficult but it is possible to measure actual costs and compare them to other buildings. The NBI concluded that incremental costs were in the range of 0 to 10% but less than the modeled costs, with paybacks less than 11 years. It is likely that more experience in design teams and the supply chain will reduce costs and there are now plenty of examples where integrated design can reduce total costs.

The NBI’s programmes and reports show that designing and building real buildings with net zero, or close to net zero energy use is possible and possible at low (or possibly even zero) costs. What is needed to make it happen more widely is more clients who see the possibilities and the advantages in reduced life cycle costs, and designers schooled in integrated design and appropriate technologies. More aggressive improvements in building codes (regulations) would of course have a major part to play.