How changing building shape and form can slash energy use

[Note: This post was originally published on The Fifth Estate website on 15 November 2016]

New guidance has just been issued to help architects, developers and designers understand more about how the shape and form of a building affects heat loss, so they can reduce the energy consumption of new buildings at little or no extra cost.

This guidance is contained in a new report published by the research arm of the British National House-Building Council, called The challenge of shape and form. The mission of the NHBC is to raise the construction standards of new homes and provide guaranteed protection for homebuyers.

Much of the focus on improving the energy efficiency of buildings has to date been in connection with building fabric, insulation and new technology, but their shape and form can be just as important. By paying attention to this, developers can add value to homes and gain a competitive edge.

Mathematical models are used to predict the energy consumption of buildings. These models correctly reflect the importance of the form factor. The form factor is a measure of the compactness of a building in the form of a ratio of the external area of the building to the floor area. In short:

Heat Loss Form Factor = Heat Loss Area / Treated Floor Area

This ratio can be anything between 0.5 and five. A lower number indicates a more compact, efficient building.

The Form Factor for different building styles and sizes. 

Passivhaus buildings aim to achieve three or less. Once the form factor is over three, achieving the Passivhaus Standard efficiently becomes more challenging.

The early design choices, such as how many storeys a building has, what shape the plan takes, the form and massing, all impact directly on the building energy efficiency.

A building can have a fairly simple massing, but if it has a lot of recesses or protrusions in the thermal envelope, the surface areas soon add up. Less (thermal envelope) surface area means less surface area for heat to escape through. This is shown in the following diagrams.

How changing a building's shape alters its surface area.

Form factor and insulation

The form factor has an effect on the amount of insulation needed to achieve the same U-value (measure of heat loss: – the 2013 UK building regulations have limiting U-values of 0.2 W/(m2.K) for a roof and 0.3 W/(m2.K) for walls). If a large compact block of flats had a form factor of 1.0, an average U-value of only 0.28 W/(m2.K) would be required.

The following figures illustrate this:

Heat loss area and U-values have a linear relationship. If the heat loss area of one option is twice that of another option, the insulation will need to be twice as thick!

The problem in Britain

In the UK, the energy and carbon requirements of building regulations do not explicitly give credit for housing designs with lower heat loss areas or more efficient shapes that will reduce heating costs for the building occupants.

The UK’s national calculation methodology, the Standard Assessment Procedure, does give appropriate weight to the form factor in calculating heat loss. But when the basic results from SAP model are fed into the buildings regulations compliance methodology, which follows, the benefits of form factor do not register.

The current Building Regulations in the UK are therefore unable to provide an incentive for industry to design and build homes that have a more efficient type and shape.

The NHBC says designers who focus solely on building regulations compliance may not even realise that they can reduce the energy consumption of homes by changing the form factor.

Doing so can be a low-cost or no-cost measure. The NHBC is calling on the government to consider ways of encouraging designers and developers to take advantage of this effect.

The effect of form and shape

Even though the form may be compact, the building can still be architecturally interesting and provide better comfort conditions for occupants. It need not have to lead to bland or monotonous housing designs.

The guide discusses how the most inefficient design features can often be avoided or replaced by alternatives that are still architecturally interesting. Many designs can provide better comfort conditions for the residents as well.

The NHBC hopes that form factor will gain a “currency” of its own, and will be included among the key parameters that are tracked and discussed as a housing development design evolves.

This is already the case in countries where alternative design approaches are popular; the Passivhaus standard, for example, lists efficient building shape as one of the five key design considerations when planning a new energy-efficient building.

---

David Thorpe is the author of:

• Best Practices and Case Studies for Industrial Energy Efficiency Improvement (with Oung, K. and Fawkes, S. UNEP, 2016)
• A London Conversation: Business Briefing on Green Bonds (The Fifth Estate, 2015)
• The One Planet Life (Introduction: Jane Davidson. Routledge, 2015)
• Earthscan Expert Guide to Energy Management in Buildings (Earthscan, 2013)
• Earthscan Expert Guide to Energy Management in Industry (Earthscan, 2013)
• Earthscan Expert Guide to Solar Technology (Earthscan, 2011)
• Earthscan Expert Guide to Sustainable Home Refurbishment (Earthscan, 2010)

Western China makes steps to sustainable building

Chongqing Taoyuanju Community Center by Vector Architects

China is increasing its efforts to make its buildings more sustainable with a new four-year program that kicked off following a two-day conference earlier this month in Chongqing.

The conference brought together more than 250 participants from national and local governments, Chinese enterprises and associations from all provinces in Western China as well as related German organisations.

Building energy consumption in China has increased by 40 per cent since 1990 and accounts for about 30 per cent of total final energy consumption. Although in recent years there has been a significant growth in green buildings in China, the development is still at an early stage in western China.

In this part of the world, micro, small and medium-sized enterprises (MSMEs) play a vital role in building sector but their staff often lack knowledge and skills in the field of sustainable building and have a limited access to financing.

The SusBuild project aims to foster sustainable building practices among these small companies in Chongqing City and Yunnan province. It is funded by a European Union project called Switch Asia II. This is concerned with capacity building, providing technical support and raising awareness of large-scale commercial buildings, strengthening the capacity of financial institutions for providing green loans to these kind of companies, and promoting the idea of a sustainable building sector to decision-makers at national and local levels.

For Europe there is the added benefit of fostering a business network locally and between the EU and China.

The conference addressed three topics: sustainable building materials and components, sustainable building design and construction, and energy management in buildings.

Lena Tholen and Christopher Moore from the influential German Wuppertal Institut, which initiated the project, shared European experiences of energy management in sustainable buildings, giving a policy perspective, and the design and construction of sustainable buildings.

Participants visited pilot project buildings and an industry park aiming at developing modern building industry clusters in Chongqin Quijiang District.

Amongst the buildings that the delegates saw were the green roofs of the Chongqing Taoyuanju Community Center, designed by Beijing-based Vector Architects. This is blanketed with plants, from vine-covered walls to the undulating green roof that mimics the shape of the surrounding hillside. The design includes a rainwater collection and reuse system, passive ventilation, permeable pavement, and locally sourced materials.

Chongqing Taoyuanju Community Center by Vector Architects

One building in the complex has earned LEED Gold certification. Xizi Otis Chongqing Plant won the award for its sustainable construction, reduced water use, energy efficiency and indoor environmental quality, among other measures. It also recycled 90 per cent of the waste generated during its construction phase, which used locally sourced materials to reduce its carbon footprint. It utilises an ongoing operations management process to minimise environmental impact.

The factory manufactures an elevator design that is a favourite of green buildings. The Gen2 elevator reduces energy consumption by up to 75 per cent compared with traditional elevators by using a regenerative drive, LED lighting and sleep mode for elevator lights and fans.

Also in the area is a regeneration project for a 22-hectare former iron and steelworks dating back to the 1930s in the Dadukou district that is designed to make it economically, socially and environmentally sustainable. The former gasometer is now a business hotel for an area that has a mixed economy with compact planning to ensure good connectivity; and sustainable forms of transport – buses, trams and pedestrian route.

'Magic Mountains'.

In this district the authorities recently held a contest to design a new green business district. One entry, from the CEBO/Chongqing University team, was for a development populated with buildings that resemble prismatic mountain peaks called Magic Mountains.

The tops of the buildings have plants growing out of them and the design includes passive cooling and heating, a plan that encourages biking and walking, and measures to reduce the overall consumption of resources and energy by 22 per cent.

The university hosts a low carbon green building international joint research centre which this entry was intended to showcase.

SWITCH Asia II will continue until the end of 2019.

How to save millions on air conditioning by designing passively cooled buildings

Air conditioning is by far the greatest consumer of electricity in buildings in hot countries, but it needn't be so.

Architects designing buildings for regions that otherwise would require air conditioning can use passive solar techniques to keep them cool, and in many cases successfully eliminate the need for expensive air conditioning.

Right: A design for a mosque using passive solar and evaporative cooling.

Passive solar cooling operates in two stages:

1. Do your best to prevent the sun from reaching the building or gaining the interior of the building during the periods when it is in danger of overheating.
2. Then employ passive techniques to remove unwanted hot air.

Different techniques are available depending upon the climate, i.e. whether it is dry or humid.

Passive cooling for warm/hot, dry climates

Here is a summary of the techniques available for hot, dry climates with a large temperature variation from day to night use:

• high interior thermal mass;
• exterior superinsulation;
• highly-reflective OR green roofs, with insulation and a radiant barrier beneath;
• night ventilation;
• phase change materials;
• air vents;
• diode roofs;
• roof ponds;
• wind towers;
• ensure correct exterior shading on windows;
• closing windows and deploying shutters at sunrise to keep out the hot daytime air;
• direct evaporative cooling.

Above: How a wind tower on a building is used for cooling cooling.



Cooling is provided by radiant exchange with the massive walls and floor plus optional techniques explored in more detail below. Open staircases, etc. may provide stack effect ventilation, but observe all fire and smoke precautions for enclosed stairways.

Curved roofs and air vents are used in combination where dusty winds make wind towers impracticable: a hole in the apex of a domed or cylindrical roof with a protective cap over the vent directs the wind across it and provides an escape path for hot air collected at the top.

Arrangements may be made to draw air from the coolest part of the structure as replacement, to set up a continuous circulation and cool the spaces.

Passive cooling for warm/hot and humid climates

This is a summary of the techniques available for warm and humid climates, with little temperature variation from day to night:

• airtight and superinsulated construction;
• a radiant barrier beneath the roof deck;
• highly-reflective or green roofs, with insulation beneath;
• phase change materials;
• daytime cross-ventilation to maintain indoor temperatures close to outdoor temperatures.
• fresh air brought in through a dehumidifier through the crawlspace or basement by using underground pipes or use solar-powered absorption chillers;
• avoid drawing in unconditioned replacement air that is hotter or more humid than interior air;
• avoid open areas of water such as pools;
• the Passivhaus standard permits 15 kWh/m².yr of cooling energy to be used, which has proven to be sufficient in almost all cases because the Passivhaus system is highly effective in reducing unwanted heat gains;
• As above, curved roofs and air vents are used in combination where dusty winds make wind towers impracticable.

Large buildings will require detailed modelling. Power may be required for anti-stratification fans and ducts.

Shading tactics

Some tactics for providing shading to prevent the sun from reaching the building are:

• Covering of rooves and courtyards with deciduous vegetation (allowing winter access) such as creepers or grapevines permits evaporation from the leaf surfaces to reduce the temperature. At night, this temperature is even lower than the sky temperature.
• Green rooves, earthenware pots laid out on the roof, and highly-reflective surfaces (e.g. painted with titanium oxide white paint/whitewash) are all techniques practiced widely.
• Coverings that in the daytime insulate the roof but automatically withdraw at night exposing the roof to the night sky, allowing heat to leave by radiation and convection.
• Horizontal overhangs or vertical fins prevent overheating while preserving natural daylighting.
• For east and west walls and windows in summer: vertical shading and/or deciduous trees and shrubs.
• For south-facing windows: horizontal shading.
• Shutters, closed in the day.
• Highly textured walls leave a portion of their surface in shade.

Right: A summary of different shading types.

Natural ventilation

The design of natural ventilation systems varies on building type and local climate. The amount of ventilation depends on the careful design of internal zones, and the size and placing of openings.

Wind-induced ventilation is helped by siting the ridge of a building perpendicular to summer wind direction, with minimal obstruction to the wind.

In a multi-storey building, the rooms or zones on the outside faces may be separately controlled, depending upon the degree of sophistication present in the building, its size and location. If hot air is present above a set temperature, it is allowed to escape at whatever rate is necessary to preserve the comfort of this zone’s occupants, via controlled venting into a vertical space – atrium or stairwells/lift shafts – positioned centrally or on corners (with glass sides to aid the process).

At the top of this space, louvres, perhaps in clerestories or skylights, allow a controlled amount of hot air to escape, again, at whatever rate is necessary for comfort of the whole building’s occupants. Basement windows allow cool air in.

• Offset inlet and outlet windows across the room or building from each other.
• Make window openings operable by the occupants but controlled by the building management system.
• Provide ridge vents at the highest point in the roof that offers a good outlet for both buoyancy and wind-induced ventilation.
• Allow for adequate internal airflow.
• In buildings with attics, ventilate the attic space to reduce heat transfer to conditioned rooms below

It's not always possible for a building to be completely natural ventilated. In such cases fan assistance is required. Thermostats, dampers and fans would be connected to a building energy management system.

Ventilation chimneys include caps to prevent backdrafts caused by wind. These adjust according to the wind intensity and direction and increase the Venturi effect.

Turbines may be deployed to increase ventilation. Self-regulating turbine models are available. There are several styles of passive roof vents: e.g., open stack, turbine, gable, and ridge vents, which utilise wind blowing over the roof to create a Venturi effect that intensifies natural ventilation.

Bernoulli's principle

This uses wind speed differences to move air, based on the idea that the faster air moves, the lower its pressure. Outdoor air farther from the ground is less obstructed, with a higher speed, and thus lower pressure. This can help suck fresh air through the building.

Bernoulli’s principle multiplies the effectiveness of wind ventilation and is an improvement upon simple stack ventilation. However, it needs wind, whereas stack ventilation does not. In many cases, designing for one effectively designs for both.



The BedZED development in south London (above) utilises specially-designed wind cowls which have both intakes and (larger) outlets; fast rooftop winds get scooped into the buildings. The larger outlets create lower pressures to naturally suck air out.

Solar chimneys for cooling

Solar chimneys are employed where the wind cannot be relied upon to power a wind tower. The chimney's outer surface (painted black and glazed) acts as a solar collector, to heat the air within it. (It must therefore be isolated by a layer of insulation from occupied spaces.)

Pre-cooling air with ground source intakes

Right: Earth-air tunnel.

Also known as an earth-air tunnel this is a traditional feature of Islamic and Persian architecture.

It utilises pipes buried a few meters down, or underground tunnels, to cool (in summer) and to heat (in winter) the air passing through them.

They can lower or raise the outside replacement air temperature for rooms which are buffer zones between the interior and exterior temperatures.

Trombe wall effect for cooling and heating

A double skin façade is employed, the outer skin of which can be glass or PV panels. The cavity between the array and the wall possesses openings to indoors and outdoors at both high and low levels. operate more efficiently anyway).

Evaporative cooling

Evaporative cooling is used in times of low or medium humidity. As water is evaporated (undergoing a phase change to water vapour), heat is absorbed from the air, reducing its temperature. When it condenses (another phase change), energy is released, warming the air. This is the same for all phase change materials.

Right: passive solar cooling with a courtyard.

Evaporative cooling can be direct or indirect; passive or hybrid.

• Direct: the humidity of the cooled air increases because air is in contact with the evaporated water – can be applied only in places where relative humidity is very low.
• Indirect: evaporation occurs inside a heat exchanger and the humidity of the cooled air remains unchanged – used where humidity is already high.
• Passive: where evaporation occurs naturally; incoming air is allowed to pass over surfaces of still or flowing water, such as basins or fountains;
• Hybrid: where mechanical means are deployed to control evaporation.

Phase change materials (PCMs)

PCMs utilise the air temperature difference between night and day. In the daytime, incoming external air is cooled by the PCM-storage module, which absorbs and stores its heat by changing its phase state (e.g. solid to liquid).

At night-time the substance reverts to solid form, releasing its heat by being cooled by the now cooler external air. Commercially available PCMs are chosen based on the temperature of their phase change relative to that required in the space to be moderated.

Night cooling

Night ventilation, or night flushing relies upon keeping windows and other openings closed during the day but open at night to flush warm air out of the building and cool thermal mass which has heated up during the day.

It relies upon significant temperature differences between day and night time (which must be below 22°C / 71°F) and some wind movement.

The above combines edited extracts from one of my published books, Solar Technology, and a forthcoming title: Passive Solar Architecture Reference Pocketbook.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development
• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, and
• Energy Management in Industry: The Earthscan Expert Guide

4 Ways to Plan Neighborhoods and Buildings to Minimize Energy Use

Conventional buildings consume much energy for heating and cooling to protect them from the temperature effects of climate and seasons. But some basic thought and planning, in combination with these 10 passive solar building design techniques, can help to radically reduce these energy costs. Here's 4 key ideas:

1. Optimize the spatial layout

 

Inappropriate (left) and appropriate (right) spatial layouts for settlements in hot climates. Grid layouts borrowed from other climates, and wide spacing of buildings, do not provide shade or wind shelter. Organic, non-grid layouts do provide shade and can be designed to block winds, preventing issues with wind funnelling. Credit: author.



Right: Sample layout for housing estate in higher latitudes such that each property has both privacy and an equator-facing aspect and roof to maximise potential use of solar energy. Grey circles are trees, grey lines are hedges (preferably) or fences. Credit: author.

2. Optimize the building form and layout

A low surface area to volume (S/V) ratio is optimal for a passive, low-carbon building. This is the ratio between the external surface area and the internal volume.

Compactness C = Volume / Surface Area

Size is also a factor: a small building with the same form as a larger one will have a higher S/V ratio. Buildings with the same U-values, air-change rates and orientations but differing S/V ratios and/or sizes may have significantly different heating demands. This has the following consequences:

• small, detached buildings should have a very compact form (square is close to the perfect optimum, the circle);
• larger buildings may have more complex geometries;
• high S/V ratios require more insulation to achieve the same U-/R-value.

In temperate zones, aim for an S/V ratio ≤ 0.7m²/m³.

Form factor

The ratio of the usable floor area, F, to above-grade enclosure area E is more useful, because it favours buildings that require less floor-to-floor height.

Form factor = F/E

The more compact the form, the higher the ratio, which is better. Large buildings (e.g., 172,800 ft² over 12 stories) have a much more efficient form than small buildings or large high-bay buildings for heating load (but not cooling, where the opposite is true).

This metric permits comparisons of the efficiency of the building form relative to the useful floor area. Achieving a heat loss form factor of ≤3 is a useful benchmark guide when designing small Passivhaus buildings. This also reduces the resources required and the cost. Most building uses do not require volume but floor area. This metric also does not include the ground contact area, but does include the roof.

A building with a more complex form is also likely to have a higher proportion of thermal bridges and increased shading factors that will have an additional impact on the annual energy balance.

The effect of form on total energy consumption for a given floor area is reduced as buildings increase in size. Besides permitting greater design flexibility, this lets designers use daylighting and natural ventilation cooling strategies also to reduce energ demand, as these require one dimension of the building to be relatively narrow (between 45 and 60ft (14–18m).

Example:

For a small office of 20,000 ft2 (1800 m2) a narrow two-storey form, ideal for natural ventilation and daylighting, may have a form factor ratio of 0.88, whereas a deep square plan have one of 1.02. For the former to have the same enclosure heat loss coefficient as the latter, its overall average enclosure R-value would need to be 1.02/0.88 = 16% higher. This would require a significant increase in the opaque wall area R-value, a reduction in window area, or a more expensive window.

 

An increase in the S/V ratio of 10% (the building in the middle) would require 20mm of insulation more than the good form on the left to achieve the same level of insulation. The one on the right (a 20% higher S/V ratio) would require an extra 40mm of insulation.



Optimum room layouts in dwellings according to the climate.

3. Adapt the dwelling forms and room layouts according to latitude

For latitudes above 25°: the sun-facing glazing area should be at least 50% greater than the sum of the glazing area on the east- and west-facing walls. Orientation is long on the east-west axis, which should be within 15 degrees of due east-west. At least 90% of the sun-facing glazing should be completely shaded (by awnings, overhangs, plantings) at solar noon on the summer solstice and unshaded at noon on the winter solstice. The room plan should – if it is a dwelling – incorporate the main living rooms on the equator-facing side, with utility rooms, less used rooms and garage if any on the north side. Morning rooms are typically bedrooms. On the side away from the equator windows should be kept to a minimum and as small as possible for lighting to minimise heat loss. This wall should also have high thermal mass or/and be externally insulated, to retain heat in the building.

For latitudes less than 25° or where topography significantly impacts insolation, the opposite should be the case. Bedrooms, for example, need light in the morning. The whole building needs to be protected from low angle heat.

Around 25° there is some leeway depending on local conditions. In these mid-latitudes different parts of a building may be used in the winter and summer, as equator-facing rooms become too hot and occupancy is switched in summer to rooms on the non-equator-facing side (not shown in the above left plan).

Table: The shape of the building has different requirements according to the local climate:

Climate	Elements and requirements	Purpose
Warm, humid	Minimise building depth	for ventilation
	Minimise west-facing wall	to reduce heat gain
	Maximise south and north walls	to reduce heat gain
	Maximise surface area	for night cooling
	Maximise window wall	for ventilation
Composite	Control building depth	for thermal capacity
	Minimise west wall	to reduce heat gain
	Limited equator-facing wall	for ventilation and some winter heating
	Medium area of window wall	for controlled ventilation
Hot, dry	Minimise equator-facing and west walls	to reduce heat gain
	Minimise surface area	to reduce heat gain and loss
	Maximise building depth	to increase thermal capacity
	Minimise window wall/window size	to control ventilation, heat gain and light
Mediterranean	minimise west wall	to reduce heat gain in summer
	Moderate area of equator-facing wall	to allow winter heat gain
	Moderate surface area	to control heat gain
	Small to moderate window size	to reduce heat gain but allow winter light
Cool temperate	Minimise surface area	to reduce heat loss
	Moderate area of pole-facing and west walls	to receive heat gain
	Minimise roof area	to reduce heat loss
	Large window wall	for heat gain and light
Equatorial upland	Maximise north and south walls	to reduce heat gain
	Maximise west-facing walls	to reduce heat gain
	Medium building depth	to increase thermal capacity
	Minimise surface area	to reduce heat loss and gain

4. Optimize the roof shape and orientation

In hot climate zones, vaulted roofs and domes dissipate more heat by natural convection than flat roofs. They give greater thermal stability and lower daytime temperature. The best orientation requires that the vault form receive maximum daily solar radiation in winter and minimum in summer.

A north-south axis orientation for a vaulted roof is better for winter heating, receiving the minimum direct solar radiation in the summer, while an east-west axis orientation will maximise summer heating, receiving the most irradiation in the morning and evening. The results are summarised by example for a 30° latitude site below.

Table: The effect of vault orientation on seasonal direct solar radiation.[i] CSR = Cross Section Ratio. This is the ratio between vertical height of the vault and the horizontal width.

Orientation	Season	Loss of direct solar radiation (%)
		CSR1 = 0.5	CSR1 = 0.8	CSR1 = 1	CSR1 = 1.25	CSR1 = 2
W-E	Summer	12.4	20.1	23.9	29	37.8
	Winter	9.8	17	19.6	23.2	30.4
N-S	Summer	17	28.6	35.1	42.1	56.4
	Winter	6.3	7.1	8	8.9	10.7
NE-SW	Summer	14.7	23.9	29.3	34.8	45.6
	Winter	8.9	13.4	16	18.8	24.1
NW-SE	Summer	14.7	23.9	29.3	34.8	45.6
	Winter	8.9	13.4	16	18.8	24.1

The effect of vault orientation on received seasonal direct solar radiation.

See this related post on passive solar building design techniques.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development
• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, and
• Energy Management in Industry: The Earthscan Expert Guide

---

[i] Mashina, GA and Gadi, MB; Calculating direct solar radiation on vaulted roofs using a new computer technique, Nottingham University Conference Proceedings, 2010. Available at: http://www.engineering.nottingham.ac.uk/icccbe/proceedings/pdf/pf196.pdf

10 stages to a passive solar building from design to build

Some aspects of a zero carbon building in the northern hemisphere, temperate zone.

Passive solar architectural principles have come of age. They have given rise to thousands of buildings of all sizes and purposes around the world, in all climate types, to demonstrate how buildings don't need to consume fossil fuel energy to support their occupants. They can even generate more power, or absorb more carbon, than they use. Below is a ten-step guide to how to go about designing and building one.

But  first, the benefits of passive solar architecture:

• Saves energy and running costs from the start;
• Comfort in all seasons and climates;
• Safe investment and resilience into the future;
• Added value every year through decreased operation costs;
• Longer useful life with high quality standard;
• Contributes to climate change protection.

Thanks to experience of the last 30 years, we know what works in different climates in the world and build costs have reduced to the same or just slightly higher than conventional builds. But lifetime costs are considerably cheaper – on average (dependent on purpose/design) being 87.5% savings (1/8 less to run) on heating and cooling.

Sustainable solar building is also known as passive house (Passivhaus in German), although this is also a strict standard.

There are currently 30,000 Passivhaus structures built around the world. The principle is that the architecture is designed to provide comfort for the occupants with minimum need for additional energy. This is achieved using design tools to establish the needs and requirements of all functions in the building and their inter-relationships. Energy savings are maximised by placing spaces in the most advantageous position for daylighting, thermal control, and solar integration.

This process may also reveal opportunities for multiple functions to share space and reduce the footprint of the building.

General principles of a passive solar building

Buildings should be at least zero carbon on balance, when totalling the impacts of materials, construction, use and demolition. Features of this are to:

• minimise the use of fossil fuel energy during the supply chain and process of construction;
• encourage the use of materials which store atmospheric carbon in the fabric of the building;
• encourage the generation and even export of renewable energy by the building;
• construct and manage it in such a way that it minimises the emission of greenhouse gases during its lifetime and eventual demolition.

Right: possible building designs for maximising the use of daylighting.

Such a building could, over its lifetime, become zero carbon, or even negative carbon by generating enough power to more than make up for the fossil fuels it has used.  To achieve this, the following features are needed:

• favouring the use of ‘natural’ and cellulose-based materials (timber products, and other products made from plant-originating materials);
• making the structure very airtight;
• making the structure breathable;
• making it durable, resilient, low-maintenance, fire- and weather-resistant;
• incorporating a large amount of insulation;
• taking advantage of free, renewable energy. 

10 steps to a zero energy building

So here, now is a summary of 10 steps in the design and build strategy of a zero-energy passive solar building, averaged for any climate zone in the world.

1. Site selection

• Secure optimum location, as free as possible from non-useful shading relative to the seasons and time of day. 
• Research the available solar resource and wind factors for the site using local and freely available data.
• Orient optimally.

Example of a sun chart to view the azimuth angle through a year at a building location.

2. Concept development

• Minimize shade in winter, minimizing parapets, projections, non-transparent balcony enclosures, divider walls etc.
• Choose a compact building structure with low skin to volume ratio. Use opportunities to combine buildings. 
• Use a simple shell form, without unnecessary recesses. 
• Survey and model the expected internal and external heat gains and cooling requirements, and other building energy loads.
• The following energy performance targets and air changes per hour define the Passivhaus standard and must be met in order for certification to be achieved:
• Specific heating demand ≤ 15 kWh/m²/yr
• Specific cooling demand ≤ 15 kWh/m²/yr
• Specific heating load ≤ 10 W/m²
• Specific primary energy demand ≤ 120 kWh/m²/yr
• Air changes per hour ≤ 0.6 @ n50.
• Optimize glazing, shading and aspect/form according to latitude and climate zone, to maximize the use of daylighting, balancing against the appropriate heat gains.
• Concentrate the utility installation zones, e.g. bathrooms, above or adjacent to the kitchen, in coolest areas in summer (temperate zones) or hottest (hot zones).
• Model and decide on the ventilation scheme making best use of the stack effect and Bernoulli principle. Is additional mechanical ventilation (with heat recovery) needed?
• Thermally separate basement from ground floor (including cellar staircase), make airtight and thermal bridge free. 
• Derive an initial energy use estimate.
• Evaluate the potential for renewable energy technologies: solar thermal, PV, wind, heat pumps, etc.
• Consider use of underfloor heating to save energy (water or electric).
• Check the possibility of government subsidies.
• Commence consultations with the building authority.
• Contract agreement with architects, including a precise description of services to be rendered.

3. Construction plan and building permit planning

• Select the building style – thermally massive or light. Sketch out a design concept, floor plan, energy concept for ventilation, cooling, heating and hot water. 
• Floor plan: short pipe runs for hot/cold water and sewage.
• Consider the space required for utilities (cooling/heating, ventilation etc.).
• Short ventilation ducts: cold air ducts outside, warm ducts inside the insulated building envelope.
• Further calculate and minimize the energy demand, e.g. with the Passive House Planning Package (PHPP) available from the Passivhaus Institut, Darmstadt. Climate data sets are available for most areas in the world which plug into this.
• Plan the insulating thickness of the building envelope and avoid thermal bridges.
• Calculate cost estimate.
• Negotiate the building project (pre-construction meetings).

4. Final planning of the building structure (detailed design drawings)

• Insulation of the building envelope: the absolute U-values will vary according to context (location, form etc), but in general aim for: 
• walls, floors and roofs ≤ 0.15 W/m²K; 
• complete window installation ≤ 0.85 W/m²K.
• Design thermal bridge free and airtight connection details.
• Specify windows that comply with passive house standard: optimize type of glazing, thermally insulated frames, glass area, coating, shading.
• 5. Final planning of ventilation (detailed system drawings)
• General rule: hire a specialist.
• Ventilation ducts: short and sound-absorbing. Air flow velocities below 3 m/s.
• Include measuring and adjusting devices.
• Take sound insulation and fire protection measures into account.
• Air pathways: avoid air current short-circuiting.
• Consider the air throws of the air vents.
• Provide for overflow openings.
• If MHVR/cooling is used, install in the temperature-controlled area of the building shell.
• Additional insulation of central and back-up unit may be necessary. Soundproof the devices. Thermal energy recovery rate should be > 80 %.
• Airtight construction to be checked at every stage.
• The ventilation system should be user-adjustable.
• Optional: ground or water-source heat pump (air or water as medium) and/or air pre-cooling/heating pipes; may be reversible for summer cooling and winter heating.

6. Final planning of the remaining utilities (detailed plumbing and electrical drawings)

• Plumbing: Install short and well-insulated pipes for hot water in the building envelope. For cold water install short pipes insulated against condensation water. Use no greater bore than needed to conserve water and heat.
• Use water-saving fittings.
• Sub-roof vents for line breathing (vent pipes).
• Plumbing and electrical installations: avoid penetration of the airtight building envelope – if not feasible, install adequate insulation.
• Use the most energy-saving appliances/equipment.
• Situate switches for ring mains alongside light switches to enable easy switching off of phantom loads when leaving rooms/building.
• Plan installation of (perhaps wireless) building energy monitoring system.

7. Call for tenders and awarding of contracts

• Plan for quality assurance measures in the contracts.
• Set up a construction schedule.

8. Assurance of quality by the construction supervision

• Thermal bridge free construction: schedule on-site quality control inspections. Take photographs.
• Check of airtightness: all pipes and ducts must be properly sealed, plastered or taped. Electrical cables penetrating the building envelope must be sealed also between cable and conduit. Flush mounting of sockets in plaster and mortar. Take photographs.
• Check of thermal insulation for ventilation ducts and hot water pipes.
• Seal window connections with long-lasting adhesive tapes or plaster rail. Apply interior plaster from the rough floor up to the rough ceiling.
• n50 airtightness test: Have a blower door test done during the construction, when the airtight envelope is complete but still accessible, i.e., before finishing the interior work, but after completion of the electricians' work (in concert with the other trades), incl. detection of all leaks.
• Ventilation system: ensure easy accessibility for filter changes. Adjust the air flows in normal operation mode by measuring and balancing the supply and exhaust air volumes. Balance the supply and exhaust air distribution. Measure the system's electrical power consumption.
• Quality control check of all cooling, heating, plumbing and electrical systems.

9. Final inspection and auditing.

10. Conduct post-occupancy monitoring

...to determine if building performs as expected.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development

He is currently working on a Passive Solar Architecture Pocket Reference Book. Acknowledgements to Isover, St Gobain.

At last: the affordable solar house that makes a profit for residents

Glen Peters is a man with a mission to show how truly sustainable and affordable housing can be a solution to the housing crisis. Having made a good profit from a solar farm in his field (seen behind the house in the picture above) he's putting it to good use and demonstrating a new model for sustainable housing.

Working with a team of architects and designers he has produced a prototype two-storey detached three bedroomed house with a radical new take on passive house principles. Called Ty Solar (Solar House in Welsh) it is of timber frame construction and insulated with blown cellulose; and is potentially able to export more electricity to the grid than it consumes itself in a given year.

The larch used for the frame and cladding is sourced locally and assembled to specifications that are beyond those required by Building Regulations, giving it a Code for Sustainable Homes 5 rating (out of a maximum of 6). But this doesn't tell the whole story by any means.

By using recycled newsprint (the blown cellulose) as the only insulant around the entire building envelope and local timber, the house is locking up atmospheric carbon in its structure for an indefinite period, unlike buildings that use fossil fuel-based insulants that have emitted carbon during their manufacture.



The embodied energy of the house is therefore already very low, an important factor given that for normal buildings between 10 and 20% of their life-cycle energy consumption is used during the phase of extraction of raw materials and construction.

The final purchase price has been set at a maximum of £75,000. The principal watchword throughout the design process that has enabled this to be possible has been simplicity.

Almost heretically for passive house construction it eschews ventilation and heat recovery, and the only source of energy is solar: both passive solar through the abundance of south-facing windows and active through reliance on solar photovoltaic panels for electricity and top-up space and domestic water heating.

The demonstration house includes lithium iron batteries to store 12 kWh of power but is also grid connected to enable the export of unused electricity and the use of the grid as a backup at other times.

The battery bank is optional and really only for stand-alone houses. Glen says: “A group of 10 or more houses generating in tandem with a local smart grid could form a miniature power station and generate a considerable income, perhaps £1000 per year, for each of the households, or the power could be used to charge electric vehicles which could be shared between them."

Research commissioned by the Welsh Government estimates that over 14,000 new homes are needed every year in Wales for the next 15 years.

The hunger for affordable housing is reflected in lengthy waiting lists and increasing official homelessness figures. Wales' Minister for sustainable development has made the provision of affordable housing a high priority during his tenure.

All of this highlights the urgent need for houses of this nature. As Glen Peters says: "The bulk housing providers in the construction industry are ignoring affordable housing. They say that it doesn't work for them. I say they are missing a trick. We've proved it is perfectly possible to build low carbon housing that is truly affordable and that gives occupants zero energy bills."

With energy bills so high on the public agenda it is hard to see how local authorities and housing associations can ignore the potential that this house demonstrates.

Low embodied energy

This successful and attractive-looking house goes against the grain in terms of many of the current developments in sustainable housing.

Compared to the Mark Group's demonstration house in Nottingham, BRE’s ‘Smart Home’, in Watford, and Velux’ CarbonLight demonstration home in Rothwell near Kettering, it scores very favorably on local sourcing, embodied energy, embodied carbon and simplicity of use. Above all it compares well on price.

All of these three supposedly cutting-edge demonstration homes contain extreme amounts of technology and sophisticated materials.

They represent corporate attempts to capture a high-end market in low or zero carbon housing.

The first utilizes an incredibly energy intensive over specified steel frame.

The second uses occupation sensors to control heating, lighting, ventilation, water and security, as well as heat pumps, solar thermal and PV.

The third is designed to be iconic in its extremely unusual shape and therefore expensive to reproduce. All of them make heavy use of smart electronics. And this is what puts up their price.

But although they may score highly on low operational energy use this does not make them necessarily sustainable.

The real target of sustainable housing should be overall life-cycle impact. This means that in fact small homes that are zero carbon in operation, whose materials are sourced locally and are of low embodied energy, preferably built in bulk and perhaps in a compact urban terrace or block, will be inherently more sustainable than stand-alone large homes packed with different technologies and comprising a high embodied energy.

This makes Ty Solar's closest antecedent perhaps the ecological evolution of Walter Segal Method timber frame construction, as pioneered at the Centre for Alternative Technology. The Segal Method was, pointedly, devised by its architect to produce affordable homes.

Even the low pitch of the roof is designed to minimize the heated but unnecessary interior loft space and increased requirement for materials that are result of higher pitched roofs, while still permitting the solar panels which the roof supports to take advantage of solar radiation.

The larch cladding will protect the building for years to come with minimum need for maintenance. The fact that it is screwed on in panels also makes it easier to access the interior of the walls if needed.

The Passivhaus certified windows and doors are even made locally rather than in Germany.

The house sits on footings raised slightly above the ground to remove the need for unnecessary concrete in foundations.

“Gareth, Jens and I come from very different worlds but we're united in our goal to be a disruptive influence of traditional thinking about building homes. In this, manufacturing becomes a key component and we see ourselves as manufacturers rather than builders,” says Glen. “We have created a lot of goodwill in our community and hope to continue to do so as we expand, creating local jobs, sourcing locally and above all keeping things small."

The test is whether day-to-day the homes do result in their occupants reducing their energy use and bills. This depends on their habits.

To this end simple controls will be easier to manage (see picture above right).

Some developers seem to believe that the occupants need a degree in energy management in order to keep down their running energy and carbon costs. Utility rooms contain a bank of sails and buttons worthy of the cockpit of the Star Ship Enterprise.

Ty Solar, by contrast, scores highly on ease of use since ventilation is controlled just by opening windows when required, and space and water heating is controlled in the traditional way, with thermostats. There are no other controls.

The house has not been formally tested for Passivhaus criteria, nor does it mean to be. It has also yet to be independently pressure tested.

It is a trial house that will be monitored for one year. However, with two floors each of 44.16 square meters and a volume of 254 m³ it has achieved a SAP rated figure of 0.12 air changes per hour.

This compares very favorably to the Passivhaus standard of 0.6 a change as per hour or a permeability rate of 3.0 m³/m²h. Over a 200-day heating period, a typical British house with eight air changes per hour and a 100m2 floor area, heated to 20°C, will cost thirty times more to heat than an equivalent house with 0.3 air changes per hour, according to an energy calculator (SIGA). The SAP-rated space heating requirement of this house is just 32.39kWh/m²/year.

This high performance is shown by the U-values, which are as follows:

Element	Average / Highest W/m2K	Maximum permitted W/m2K	Passivhaus standard
External wall	0.13	0.30	0.25–0.16
Floor	0.13	0.25	0.18–0.12
Roof	0.14	0.20	0.13–0.09
Openings	0.90	2.00	0.85

It can therefore be seen that the house, according to the SAP ratings, compares favourably with Passivhaus.

LED lights are fitted throughout, making the annual lighting consumption just 371.49kWh. With no pumps or fans, there are no further electricity requirements over and above that which is used in day-to-day living by a family in any home – for appliances and gadgets. It is therefore predicted by the SAP rating to have a negative energy use of -3253.56kWh (minus appliance use) and negative carbon dioxide emissions of -596.92 kg/year.

All of this means that the Energy Efficiency Rating on the EPC goes off the scale at 107, with an Environmental Impact (CO²) rating of 108. In the Code for Sustainable Homes assessment it reaches Level 5. The SAP Assessment also predicts that there will be only a medium likelihood of a high internal temperature, or overheating, in July and August, which can easily be catered for by opening the windows.

"We've just bought a 400m² cow shed to convert into our factory so we intend to minimize the impact on the land. We turned down offers of a brand new shed on a business park,” adds Glen.

Future houses could be semi-detached or terraced, and have one, two or three bedrooms, as demand dictates and housing associations or local authorities wish.

Clearly, Glen Peters is a man with an eye on the future - a sustainable future.