Zero carbon housing

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Zero-carbon housing is housing that does not emit greenhouse gasses (GHGs) into the atmosphere, either directly (Scope 1), or indirectly due to consumption electricity produced using fossil fuels (Scope 2). Most commonly zero-carbon housing is taken to mean zero emissions of carbon dioxide, which is the main climate pollutant from homes, although fugitive methane may also be emitted from natural gas pipes and appliances.

Contents

Definition

There are nevertheless a number of definitions of zero carbon housing, particularly concerning the scope of emissions in the housing lifecycle (eg construction vs operation or refurb), and whether it is acceptable to count off-site emissions reduction (eg due to renewable energy export) or other external reductions against any residual emissions from the house to make it a Net Zero Home. The Chancery Lane legal climate project gives 6 definitions of zero carbon housing or buildings, [1] of which 2 explicitly allow for the inclusion of off-site emissions reductions, via off-site renewables or other carbon offsets, and one is a net zero definition, allowing for net renewable energy export to be included. Some definitions are at odds with the apparent meaning of zero carbon, with the UK government at one point proposing to define a zero carbon home as one with "70 per cent reduction in carbon emissions against 2006 standards" [2] - ie by definition not literally zero, as it allows up to 30% of conventional emissions.

Construction vs operation: Some scopes cover operation only, some give the option of including construction too. [3] For the purposes of present day policy to reduce emissions, it is most useful to include construction and operation in the scope of new buildings, and refurbishment and operational emissions in the scope for existing buildings (as their construction impacts cannot be changed in retrospect). For a refurbishment to be genuinely zero-carbon, the embedded carbon needs to be "paid back" by the emissions saved by the house within a timescale relevant for action on climate change (normally within a few years), and well within the lifetime of the equipment concerned. Where a new zero carbon house is constructed, the embedded carbon of the whole building must be considered and paid back. As there is substantial embedded carbon in conventional building materials such as brick and concrete, a new zero carbon home is a bigger challenge than a retrofit and is likely to need more novel materials.

Another way in which a home can become zero carbon in operation is simply that it is powered, heated and cooled purely by a zero carbon electricity grid. While these are currently (2024) few (eg Iceland, Nepal [4] ), a significant number of countries are targeting zero carbon electricity grids by 2035, including Austria, Belgium, Canada, France, Germany, Luxembourg, the Netherlands, Switzerland and the UK. [5]

Retrofitting existing conventional homes to become zero carbon in use

The following main changes are required:

Eliminate direct greenhouse gas emissions

Most conventional houses in countries where space heating is required use fossil fuels or wood for space heating, hot water and cooking. In order to become zero carbon, these heating systems need to be replaced with zero emission heating methods. The main options are:

The cost of these measures to householders is naturally a critical factor. Because conventional systems benefit from economies of scale and installation skills are widely available, new zero carbon technologies may have a higher capital cost, although this may be offset by lower operating costs or efficiency savings, depending on the relative costs of electricity and fossil fuels. For this reason some governments provide householders with grants or subsidies towards the cost of the shift, for example the Boiler Upgrade Scheme [12] in the UK, which helps to fund heat pump installations.

Ensure that the house generates more electricity than it consumes from the grid

Solar panels installed on the roof Installation of solar PV panels - panels in place - geograph.org.uk - 2624288.jpg
Solar panels installed on the roof

In almost every case the renewable source of choice for dwellings is solar photovoltaic (PV) power. Use of solar PV power is now becoming routine worldwide, as solar power costs have fallen to become the cheapest source of electricity. [13] Solar panels are typically placed on roofs, outhouses, or on the ground near the home, and it is practical for almost all scales of dwelling and most parts of the world. The only exception may be flats / apartments in dense urban areas, which may lack a roof or even any exposure to the sun.

To deliver a zero carbon house, the size /generation capacity of the PV array must match the annual consumption of the house. This is often straightforward, even if the home is using electricity for heating, directly or via a heat pump, or for cooling. In the case of cooling the solar energy availability will match the cooling demand quite well, but this is not the case with winter heating in higher latitudes. In this situation the house will typically import electricity for heating and other purposes in the winter, and export excess solar power in summer. To be net zero the export must exceed the import.

Home batteries are widely used with solar power, to provide electricity at night or dull conditions, and for cost advantage where export rates are low. In this situation it may make financial sense to store rather than reimport electricity.

Other forms of renewable power are possible in domestic situations, including micro hydro and wind turbines, but the larger size of this equipment restricts it to larger farms or estates, or to communal facilities, eg a wind turbine on an apartment block.

Maximise energy efficiency

Energy efficiency is not strictly necessary to achieve zero carbon housing, so long as the house is able to cover its electricity demand with renewable energy generated on site. However, greater energy efficiency reduces the scale of renewable generation required, and the cost of electricity imported, and may increase comfort by reducing temperature variations. At a national / economy level greater domestic energy efficiency reduces the need for large scale grid generation and transmission infrastructure, and electricity imports. The main energy efficiency approaches are:

Building fabric insulation to reduce space heating and cooling needs: Existing buildings can have their energy consumption cut significantly by insulating walls, floors and roofs, and by related measures such as draughtproofing. While some measures, eg loft/attic insulation using rockwool, are cheap and simple, others such as external wall insulation are more disruptive and expensive. Householders have to make careful analysis of the costs and benefits in terms of energy costs saved. In some countries there is state support for some home insulation measures.

Energy Star Label Energy Star logo.svg
Energy Star Label

Efficient appliances and lighting: these enable a cut in energy consumption without any change in occupant behaviour. For example, modern LED lighting uses 75% less electricity than traditional incandescent bulbs. [14] Almost all appliances including white goods, computers, TVs and refrigerators have been developed to use less electricity, such that even since 1995, when they were a mature product, refrigerators in the EU are estimated to have had their power consumption cut by 60%. [15] But more efficient appliances can more expensive, and consumers find it hard to know or calculate whether the more efficient products are worthwhile. For this reason certification including the Energy Label in the EU, and Energy Star in the United States have been developed to help consumers.

Efficient behaviour: home occupants have a large influence on the energy consumption of the a home. Typical behaviours include:

Fabric first?

A major topic of debate in housing circles is whether retrofit should focus on "fabric first": [16] i.e. maximising energy efficiency before updating energy supply approaches to eliminate fossil fuel use and add renewable generation. Proponents suggest that this approach is necessary to avoid over sizing energy supply systems such as heat pumps and to minimise overall energy demand in the economy. Opponents of fabric first suggest that major building upgrades such as wall and floor insulation and new windows are expensive and disruptive, and may deter residents from taking any action at all to move their homes towards zero carbon. By comparison, they say, energy supply equipment such as heat pumps and solar PV panels are cheaper and deliver larger reductions in carbon emissions and bills.

Design Considerations for new Zero Carbon Housing

There are two main areas to consider in designing and building zero carbon housing:

Design for maximum energy efficiency and zero carbon energy supply in operation

The same approaches as set out in the above section are required, and it is normally cheaper to design these features into a house from the start, than to build a conventional house and retrofit it later. Key design approaches include:

Orientation of the home: In cooler climates the home should be orientated to take full advantage of active (eg PV) and passive solar heating. This involves making roofs face south (in the northern hemisphere) to maximise solar power, and specifying large south facing windows to maximise passive solar heating. Measures must also be taken to minimise overheating in summer, such as blinds, shutters and shading. In hotter climates a house can be orientated North-South to minimise insolation in the middle of the day and reduce overheating and cooling demand, although having a south facing roof for PV is still an advantage.

Attention should also be paid to the layout of multiple houses and surrounding features such as trees, so home solar panels are not shaded by trees or other houses. Tree felling to stop shading should be avoided as this is counterproductive in carbon terms. Joining houses as terraces or semi-detached housing is also advantageous as these houses insulate each other and reduce heat loss. In hotter climates trees should be retained or planted so that they can provide shading to homes and streets and reduce cooling needs.

High insulation and air tightness: this applies to all elements of a building envelope, ie floors, roofs, walls, windows and doors. Building codes and standards in many countries specify levels of insulation required by law in new buildings. For discussion of building insulation codes and technologies worldwide see building insulation. Modern building codes, if complied with, may be adequate to achieve zero carbon in operation if linked with an appropriate energy supply. They may specify either or both of materials performance, normally in terms of the U-Value of a material or combined materials, measured in Watts/m2/K, and/or overall building performance in kWh/m2/year. For example, UK regulations specify walls should be <0.18W/m2K. [17] Building energy consumption rates vary enormously: the UK holder houses use 259kWh/m2, while new houses use 100kWh/m2. [18] However there are indications that better performance is possible, with achievement of 50kWh/m2/yr relatively straightforward through retrofit. [19] Meanwhile the high Passivhaus standard requires no more than 15kWh/m2 [20] (for space heating only) which is achievable, though currently considered specialist and high end.

Air tightness refers to minimising air leakage or draught into and out of a building. If cold air leaks in and/or warm air leaks out, this increases heating requirements (or cooling, in hot climates). Air tightness is measured in air changes per hour or AC/H. An example of a high standard of air tightness is the PassivHaus standard which requires less than 0.6AC/H. There is also a need for a minimum air change level, so that damp and stale air does not build up, with negative health impacts for occupants. In order to achieve both requirements a MVHR system is often specified, though this increases costs.

Renewable energy supply integrated into the building: Solar PV panels can be integrated into a roof rather than mounted above conventional roofing materials like tiles. This enables saving on roofing materials and may improve appearance. A house can also be designed for heat pump heating, by specifying underfloor heating which is the best heat emitter for a heat pump: it allows lower flow temperatures which increase heat pump efficiency.

Minimising embedded carbon in the building fabric

See Green Building.

Additional Benefits of Zero Carbon Housing

Health

Zero carbon houses offer much cleaner indoor air because they curb fossil fuel combustion which releases volatile gases and pollutants. Appliances such as gas stove, heaters, dryers, and ovens that rely on burning fuel inside the home worsen the air quality indoors and can lead to respiratory issues for the occupants. Not only is the indoor air quality affected, but so is outdoor air quality. Pollution from residential buildings is noted to be responsible for about 15,500 deaths per year in the United States alone. [21] Replacing appliances that run on fossil fuels can improve indoor air quality and reduce asthma symptoms in children by up to 42%, as well as decrease fire hazards in homes. [21]

Costs

As previously mentioned, energy efficient homes can save the occupant on their utility bills by both replacing their appliances with energy efficient appliances as well as updating their insulation and building envelope. For every $1 invested in improvements towards creating a zero carbon home, approximately $2 are saved in electricity generation and utility costs. [21]

Success with Zero Carbon Housing

It is now routinely possible to achieve net zero carbon housing, even without significant energy efficiency retrofit, by combining heat pump and solar PV technologies. For example, in the UK the average house uses 12,000kWh pa for heating, and 2,900kWh per year for electrical appliances. [22] Using a heat pump to supply this amount of heat will require about 3,000kWh (assuming sCOP of 4). This gives a total electrical demand of 5,900kWh per year, which can be supplied by a solar array of about 6.3 kW (figures derived from Energy Saving Trust calculator in 2024 [23] ), which is about 16 panels. This approach relies on the grid to supply energy in winter and receive it back in summer, as batteries cannot provide seasonal energy storage. Additional insulation would reduce the heat demand and therefore solar array size needed.

See also

Related Research Articles

<span class="mw-page-title-main">Heat pump</span> System that transfers heat from one space to another

A heat pump is a device that consumes energy to transfer heat from a cold heat sink to a hot heat sink. Specifically, the heat pump transfers thermal energy using a refrigeration cycle, cooling the cool space and warming the warm space. In cold weather, a heat pump can move heat from the cool outdoors to warm a house ; the pump may also be designed to move heat from the house to the warmer outdoors in warm weather. As they transfer heat rather than generating heat, they are more energy-efficient than other ways of heating or cooling a home.

<span class="mw-page-title-main">Energy conservation</span> Reducing energy consumption

Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively or changing one's behavior to use less and better source of service. Energy conservation can be achieved through efficient energy use, which has some advantages, including a reduction in greenhouse gas emissions and a smaller carbon footprint, as well as cost, water, and energy savings.

<span class="mw-page-title-main">Water heating</span> Thermodynamic process that uses energy sources to heat water

Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.

<span class="mw-page-title-main">Solar water heating</span> Use of sunlight for water heating with a solar thermal collector

Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications.

<span class="mw-page-title-main">Environmental impact of electricity generation</span>

Electric power systems consist of generation plants of different energy sources, transmission networks, and distribution lines. Each of these components can have environmental impacts at multiple stages of their development and use including in their construction, during the generation of electricity, and in their decommissioning and disposal. These impacts can be split into operational impacts and construction impacts. All forms of electricity generation have some form of environmental impact, but coal-fired power is the dirtiest. This page is organized by energy source and includes impacts such as water usage, emissions, local pollution, and wildlife displacement.

<span class="mw-page-title-main">Low-energy house</span> House designed for reduced energy use

A low-energy house is characterized by an energy-efficient design and technical features which enable it to provide high living standards and comfort with low energy consumption and carbon emissions. Traditional heating and active cooling systems are absent, or their use is secondary. Low-energy buildings may be viewed as examples of sustainable architecture. Low-energy houses often have active and passive solar building design and components, which reduce the house's energy consumption and minimally impact the resident's lifestyle. Throughout the world, companies and non-profit organizations provide guidelines and issue certifications to guarantee the energy performance of buildings and their processes and materials. Certifications include passive house, BBC—Bâtiment Basse Consommation—Effinergie (France), zero-carbon house (UK), and Minergie (Switzerland).

<span class="mw-page-title-main">Sustainable architecture</span> Architecture designed to minimize environmental impact

Sustainable architecture is architecture that seeks to minimize the negative environmental impact of buildings through improved efficiency and moderation in the use of materials, energy, development space and the ecosystem at large. Sustainable architecture uses a conscious approach to energy and ecological conservation in the design of the built environment.

<span class="mw-page-title-main">Superinsulation</span> Method of insulating a building

Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss by using much higher insulation levels and airtightness than average. Superinsulation is one of the ancestors of the passive house approach.

<span class="mw-page-title-main">Electric heating</span> Process in which electrical energy is converted to heat

Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators.

<span class="mw-page-title-main">Heating system</span> Heating of air in buildings or vehicles

A heating system is a mechanism for maintaining temperatures at an acceptable level; by using thermal energy within a home, office, or other dwelling. Typically, these systems are a crucial part of an HVAC system. A heating system can be categorized into central heating system or distributed systems, depending on their design and method of heat distribution.

<span class="mw-page-title-main">Zero-energy building</span> Energy efficiency standard for buildings

A Zero-Energy Building (ZEB), also known as a Net Zero-Energy (NZE) building, is a building with net zero energy consumption, meaning the total amount of energy used by the building on an annual basis is equal to the amount of renewable energy created on the site or in other definitions by renewable energy sources offsite, using technology such as heat pumps, high efficiency windows and insulation, and solar panels.

Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technologies include renewable biofuels, solar heating, geothermal heating, heat pumps and heat exchangers. Insulation is almost always an important factor in how renewable heating is implemented.

<span class="mw-page-title-main">Underfloor heating</span> Form of central heating and cooling

Underfloor heating and cooling is a form of central heating and cooling that achieves indoor climate control for thermal comfort using hydronic or electrical heating elements embedded in a floor. Heating is achieved by conduction, radiation and convection. Use of underfloor heating dates back to the Neoglacial and Neolithic periods.

Domestic housing in the United Kingdom presents a possible opportunity for achieving the 20% overall cut in UK greenhouse gas emissions targeted by the Government for 2010. However, the process of achieving that drop is proving problematic given the very wide range of age and condition of the UK housing stock.

<span class="mw-page-title-main">Air source heat pump</span> Most common type of heat pump

An air source heat pump (ASHP) is a heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapor-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. ASHPs are the most common type of heat pump and, usually being smaller, tend to be used to heat individual houses or flats rather than blocks, districts or industrial processes.

<span class="mw-page-title-main">Ground source heat pump</span> System to transfer heat to/from the ground

A ground source heat pump is a heating/cooling system for buildings that use a type of heat pump to transfer heat to or from the ground, taking advantage of the relative constancy of temperatures of the earth through the seasons. Ground-source heat pumps (GSHPs) – or geothermal heat pumps (GHP), as they are commonly termed in North America – are among the most energy-efficient technologies for providing HVAC and water heating, using far less energy than can be achieved by burning a fuel in a boiler/furnace or by use of resistive electric heaters.

<span class="mw-page-title-main">Photovoltaic thermal hybrid solar collector</span> Solar energy technology

Photovoltaic thermal collectors, typically abbreviated as PVT collectors and also known as hybrid solar collectors, photovoltaic thermal solar collectors, PV/T collectors or solar cogeneration systems, are power generation technologies that convert solar radiation into usable thermal and electrical energy. PVT collectors combine photovoltaic solar cells, which convert sunlight into electricity, with a solar thermal collector, which transfers the otherwise unused waste heat from the PV module to a heat transfer fluid. By combining electricity and heat generation within the same component, these technologies can reach a higher overall efficiency than solar photovoltaic (PV) or solar thermal (T) alone.

<span class="mw-page-title-main">Sustainable refurbishment</span>

Sustainable refurbishment describes working on existing buildings to improve their environmental performance using sustainable methods and materials. A refurbishment or retrofit is defined as: "any work to a building over and above maintenance to change its capacity, function or performance' in other words, any intervention to adjust, reuse, or upgrade a building to suit new conditions or requirements". Refurbishment can be done to a part of a building, an entire building, or a campus. Sustainable refurbishment takes this a step further to modify the existing building to perform better in terms of its environmental impact and its occupants' environment.

The INTEGER Millennium House is a demonstration house in Watford, England that opened to the public in 1998. It was renamed The Smart Home after being refurbished in 2013. The house was originally intended to showcase innovations in design and construction, building intelligence, and environmental performance. The INTEGER design included many innovative features, including environmental technology such as a green roof and a grey water recycling system, home automation that included a building management system and an intelligent security system, and innovative technical systems such as under-floor trench heating. In 2013, the house was refurbished and retrofitted with a variety of new and upgraded features, including a building-integrated photovoltaic (BIPV) array, which altogether halved its carbon emissions and increased its energy efficiency by 50%. Since its creation, the house has garnered numerous awards, appeared on Tomorrow's World on BBC Television, hosted thousands of visitors, and influenced mainstream construction.

<span class="mw-page-title-main">Zero heating building</span> Building without heating demand

Zero-heating building or nearly zero-heating building (nZHB) is a building having essentially zero heating demand, defined as having heating demand, Q’NH, less than 3 kWh/(m2a). The zero-heating building is intended for use in heating-dominated areas. The purpose of the zero-heating building is to supersede net-zero energy buildings as a way to bring building-related greenhouse gas emissions to zero in the EU. Zero-heating buildings address flawed net-zero energy buildings: the requirement for seasonal energy storage, in some cases poor comfort of living and narrow design options.

References

  1. ↑ "Zero Carbon Housing and Zero Carbon Homes". The Chancery Lane Project. 2023-04-21. Retrieved 2024-06-19.
  2. ↑ Ares, Elena (27 April 2016). "House of Commons briefing paper no 6678, Zero Carbon Homes" (PDF).
  3. ↑ "Net Zero Carbon Buildings: A Framework Definition". UKGBC. Retrieved 2024-06-19.
  4. ↑ Ritchie, Hannah; Roser, Max (2024-02-29). "Which countries get the most electricity from low-carbon sources?". Our World in Data.
  5. ↑ "Zero-carbon electricity: powering grids with wind and solar". Zero Carbon Analytics. Retrieved 2024-06-11.
  6. ↑ Niranjan, Ajit (2023-11-23). "'You can walk around in a T-shirt': how Norway brought heat pumps in from the cold". The Guardian. ISSN   0261-3077 . Retrieved 2024-06-19.
  7. ↑ "Heat Pumps Outsell Gas Furnaces Once Again: What's the Difference?". CNET. Retrieved 2024-06-11.
  8. ↑ Finnegan, Jones, Sharples (15 December 2018). "The embodied CO2e of sustainable energy technologies used in buildings: A review article". Energy and Buildings. 181: 50–61. Bibcode:2018EneBu.181...50F. doi: 10.1016/j.enbuild.2018.09.037 .{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. 1 2 Emission factors for gas and grid electricity (28 June 2023). "Greenhouse gas reporting: conversion factors 2023". Gov.uk.
  10. ↑ Average boiler efficiency = 85.3%. "In-situ monitoring of efficiencies of condensing boilers and use of secondary heating" (PDF).{{cite web}}: CS1 maint: numeric names: authors list (link)
  11. ↑ Gabbatiss, Josh (2023-02-23). "Heat pumps 'up to three times cheaper' than green hydrogen in Europe, study finds". Carbon Brief. Retrieved 2024-06-13.
  12. ↑ "Boiler Upgrade Scheme (BUS) | Ofgem". www.ofgem.gov.uk. Retrieved 2024-06-11.
  13. ↑ "Solar energy the most affordable electricity generation technology in many parts of the world: Executive summary – Solar PV Global Supply Chains – Analysis". IEA. Retrieved 2024-06-11.
  14. ↑ "LED Lighting". Energy.gov.
  15. ↑ "Fridges and Freezers - European Commission". energy-efficient-products.ec.europa.eu. Retrieved 2024-06-11.
  16. ↑ "Think first before fabric first | Environmental Change Institute". www.eci.ox.ac.uk. 2024-01-15. Retrieved 2024-06-11.
  17. ↑ "2021 Update to Part L Building Regulations – Volume 1: Dwellings". Elmstead Energy Assessments & Building Services - EEABS. 2022-03-28. Retrieved 2024-06-13.
  18. ↑ "New build houses save homeowners £2,600 in annual energy bills". www.hbf.co.uk. Retrieved 2024-06-13.
  19. ↑ Fausset, Rupert (2024-01-23). "The surprisingly easy trip to a Net Zero Home". Net Zero Home. Retrieved 2024-06-13.
  20. ↑ "Passivhaus Institut". passiv.de. Retrieved 2024-06-13.
  21. 1 2 3 Said, Evana; Rajpurohit, Sujata (2022-09-23). "The Health, Economic and Community Benefits of Zero-carbon Buildings".{{cite journal}}: Cite journal requires |journal= (help)
  22. ↑ "Average gas and electricity usage | Ofgem". www.ofgem.gov.uk. Retrieved 2024-06-13.
  23. ↑ "Home | Solar Panel Calculator". pvfitcalculator.energysavingtrust.org.uk. Retrieved 2024-06-13.
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