EcoCasa won the Ashden Award for sustainable buildings in 2014

Buildings account for a large share of global energy use. Designing and upgrading them to use less energy is key to reducing fuel bills, increasing energy security and building a low-carbon world. Design techniques include optimising the amount of natural light and the volume of air that flows in and out of the building.

Low energy buildings techniques

Energy is used in buildings to deliver comfortable conditions for occupants and to power appliances: this is known as ‘energy-in-use’. Energy is also used in the production of building materials and during construction: this is known as ‘embodied energy’. Currently the energy-in-use over the lifetime of most UK buildings greatly exceeds their embodied energy.

UK Award winner Architype is an architectural practice designing to the PassivHaus standard, using active systems and renewables to reduce energy-in-use, as well as trying to cut embodied energy. St Luke’s Primary School, designed by Architype, uses passive techniques including day lighting, windows and roof lights that let in sunlight when the sun is low in winter but block it in summer, high levels of insulation and airtightness, and natural ventilation for cooling in summer. Energy-efficient active systems are also incorporated, including a biomass wood-chip boiler that supplies the underfloor heating. It is predicted to use less than half of the statutory energy targets.

The Greater London Authority’s RE:FIT programme helps public sector organisations deliver ‘spend to save’ environmental retrofit projects that improve their estates and reduce carbon emissions. If provides expert advice and a procurement framework that simplifies the process, with the suppliers guaranteeing energy and financial savings. 

Measures installed range from boiler upgrades and solar PV to insulation and LED lighting, Cooling and ventilating commercial buildings drains money and energy. Monodraught’s COOL-PHASE® low-energy cooling and ventilation system reduces the running costs of buildings, creating a fresh and healthy indoor environment. 

Through its novel application of phase-change material (PCM) technology in a thermal energy store, temperatures are kept within a comfort zone, while energy consumption is reduced by up to 90% compared to conventional cooling systems. Indoor air quality is also improved as the system monitors and responds to CO2 and humidity levels.

The office of UK Award winner Architype, an architectural practice designing to the PassivHaus standard

Ashden Award winner GERES incorporated many passive techniques into the design of greenhouses for the bitterly cold but sunny climate of Ladakh. The greenhouses are aligned East-West with tough, transparent agricultural plastic on the South face to maximise solar gain: a blanket is pulled over the plastic for night-time insulation. The North, East and West walls are made from mud and stone with high thermal mass to store heat during the day. With these passive techniques, vegetables can be grown throughout the winter even when the outside temperature falls to -25 degrees C.

Techniques and principles

Low energy buildings use a mixture of passive techniques and active systems to deliver a comfortable environment with low energy use and low greenhouse gas emissions. Passive techniques relate to the shape of the building and the materials that it is built with, while active systems use machinery to provide services to the building which minimise energy use. Incorporating renewable energy generation on site can reduce emissions further. However, low energy use should be the first priority, since this is the cheapest way to cut greenhouse gas emissions. In addition, low energy use makes the adoption of renewable energy technologies more viable because less capacity is required to meet the building demand.

It’s possible to reach the point where a building produces net zero greenhouse gas emissions in use, known as ‘zero carbon in use’. Embodied energy can also be reduced by using low-carbon building materials and construction methods.

Passive techniques

High levels of insulation and airtightness are used to reduce heat loss from the building, and hence the need for heating during winter. Using dense materials in the building construction creates ‘thermal mass’, which reduces temperature fluctuations by storing heat and releasing it later in the day, helping limit overheating during hot weather or times when there are a lot of people in the building.

Buildings can be designed to make the best use of sunlight by orientating them relative to south and arranging windows to maximise daylight and allow sunlight in during winter, but to limit direct sunlight penetration during summer when it can cause overheating. The use of high efficiency, low emissivity glazing allows high levels of daylight in whist reducing heat losses through windows.

Passive design can use wind-driven and stack-driven natural ventilation to provide cooling in summer without the need for air conditioning. To minimise heat losses during cold weather, airflow is reduced to the minimum needed to provide fresh air.

Passivhaus Trust, a 2017 finalist helped with the UEA ADAPT building, with straw thatch wall and solar shading

Renewables

Renewable heating systems including biomass boilers, active solar water heating and ground source heat pumps can be used to supply heating and hot water needs with reduced greenhouse gas emissions. Solar photovoltaics can be mounted on or integrated in the building roof, to provide renewable electricity. Wind turbines can be included within the site as another means of providing renewable electricity.

Cost

At present constructing a ‘Zero Carbon in use’ building can add as little as 5% to construction costs depending on the building type and other details, and some projects have achieved zero carbon status with no extra cost. Energy bills for a Passivhaus home would typically only be around 35% of that of an average house, saving the residents several hundred pounds a year.

The future

Most countries are planning how to reduce their fossil fuel reliance and associated greenhouse gas emissions. For example, the UK Climate Change Act of 2008 is targeting a 34% reduction in greenhouse gas emissions by 2020 (compared with 1990 levels) and an 80% reduction by 2050. As energy-in-use decreases, attention will shift to reducing the energy embodied in the construction of new buildings.

However, it is estimated that the majority of the homes that will exist in 2050 have already been built so it is also crucial to retrofit existing buildings with energy efficiency measures.