Everything you want to know about using Solar Energy is here!

Knowledge – as well as solar energy – is power! I'm very proud to announce the publication of not one but two new titles that I've been working on for a long time.

These distil much of my learning over this period about two essential topics that will help us fight climate change:

1. Passive Solar Architecture Pocket Reference
2. Solar Energy Pocket Reference

Get 20% off! E.g. paperback or e-book would be £20.79! Just enter code FLR40 on checkout. Order here:

• Passive Solar Architecture Pocket Reference
• Solar Energy Pocket Reference  

Passive Solar Architecture covers: the principles of passive solar building and passive house, a ten-step design and build strategy, calculating solar irradiance, factors affecting the choice of building materials, passive heating and cooling principles and techniques in different climates, the Passivhaus Standard and natural and augmented lighting and notes on technology and building occupation.

The book also includes conversion factors, standards, resources and is peppered throughout with helpful illustrations, equations, explanations, and links to further online resources.

Passive Solar Architecture is ideal for practitioners, architects, designers, consultants, planners, home builders, students and academics, and those working in development contexts.

This book is intended to act as an aide memoir, a reference supplement, a resource and an overview of the field. Rich in background detail, the book also includes at-a-glance tables and diagrams, equations and key definitions.

Solar Energy covers: solar radiation and its detailed measurement, the emissivity and absorption properties of materials, solar thermal energy collection and storage, photovoltaics (both at all scales), solar cooling, and the use of solar energy for desalination and drying.

The book also includes conversion factors, standards and constants and is peppered throughout with helpful illustrations, equations and explanations, as well as a chapter making the business case for solar power.

Solar Energy is for anyone with an interest in solar energy, including energy professionals and consultants, engineers, architects, academic researchers and students.

They will find a host of answers in this book – a practical assimilation of fundamentals, data, technologies and guidelines for application.

They're available in hardback, paperback and as ebooks.

Get 20% off! E.g. paperback or e-book would be £20.79! Just enter code FLR40 on checkout. Order here:

• Passive Solar Architecture Pocket Reference
• Solar Energy Pocket Reference  

Innovative eco-social housing neighbourhood reaches completion in Wales

A version of this article was published on The Fifth Estate on 17 May.

Glen Peters standing outside one of the two-bedroomed semi-detached houses.

The first tenants have moved into Pentre Solar, an eco-social housing neighbourhood being constructed in Glanrhyd, Wales. ('Pentre' means village in Welsh.)


Dr Glen Peters, chief executive of Western Solar, has an ambition for his company to supply 1000 homes and to work with housing associations and local authorities to provide social housing.

The South-facing front of a three bedroomed house with plenty of glazing to capture the sun's heat. Inside it falls onto a black, melamine-covered concrete floor to absorb the heat.

The North-facing rear of a three bedroomed house. The homes are clad in local larch. This is projected to last at least 25 years before it needs replacing. Much care in the detailing of the design should extend the cladding life well beyond this point.

Peters estimates the build cost is about £120 per square foot (AU$19 a square metre). This has led him to set a rental cost of the two-bedroom houses of £480 a month (AU$836), a level in line with the local 106 planning condition of no more than 80 per cent of local market rents. The three-bedroom houses are set at £620 a month (AU$1080). For the developer, this gives a 3.5-4 per cent return on investment.

A pair of two-bedroomed semi-detached houses. All the homes have solar roofs.

Local materials and labour

Costs have been kept low and as much as possible of the houses manufactured locally from local materials. In total 80 per cent of the building is manufactured locally out of local timber and 40 per cent – the airtight frames – are manufactured in a nearby factory – a converted cowshed – to be assembled on site.

Peters says the multiplier effect of the benefit to the local community for every £1000 invested is £2200, a factor of 2.2.

The timber frames are kept out of direct contact with the ground to prevent damp from rising:

A footing protected from damp on the patio.

The homes’ design builds upon the developer’s experience of a prototype house, Ty Solar:

The prototype Ty Solar (Ty is Welsh for House so the name means Solar House in English) in West Wales. In the background can be seen the first solar farm in Wales which finance the building of Ty Solar.

Ty Solar was constructed in 2010 using the profit from Peters’ solar farm, the first in Wales. It cost about £75,000 (AU$130,640) to build with a £47,000 (AU$81,870) grant from the Sustainable Development Fund.

The unit costs of the Glanrhyd houses, built on the site of a now-demolished garage, were higher than normal, mainly because of the land reclamation, provision of services and unusual weather-related costs, as well as complying with planning conditions in an area of outstanding natural beauty.

The three-bedroom homes occupy 100 square metres, the two-bed ones slightly less, but still feel spacious.

The company is focused on providing social housing as Peters believes there is a reasonable business in creating good quality affordable housing, as none of the large developers seem to interested in doing so.

While it is economic and technically feasible to build these homes, politically Peters’ route has not been easy.

”Politicians have been unduly influenced by volume building companies, and while they love the houses it has been difficult to persuade local authorities and housing associations of the benefit of backing this design, despite the fact that occupants have virtually zero energy bills. The key performance indicators imposed on housing associations are unduly skewed towards capital costs rather than tenant and community welfare,” he says.

He is hoping that when he has occupancy data to back up his case, more housing associations and councils will be interested in the model.

Zero energy bills

The timber frame houses are built according to passive house principles, though are not validated as such due the cost of doing so, versus the benefits.

Each monopitch roof sports 8kW of integrated photovoltaic panels. Over a year these generate surplus energy, providing an income from a feed-in tariff, as well as giving the occupants free electricity. Total energy demand is about 12 per cent of a conventionally built home. Beneath the solar panels is a galvanised steel sheet that laps over the timber frame.

They sit on a concrete slab, unlike the prototype, which was constructed using the box beam method with a suspended timber floor. Peters says concrete is more durable, with more thermal mass and has a lower maintenance requirement, although with a greater carbon footprint.

The windows are double, not triple-glazed, to keep costs low as Peters believes that the incremental benefit of the extra pane of glazing is cancelled by the cost in the mild local climate.

The insulation is all 27cm of recycled newsprint pumped into the cavity. This type of eco-insulation is in general the most economic and ecological. The paint is clay-based – breathable and with no off-gassing. Although more expensive per litre, it requires fewer coats on bare plaster.

The houses all come fitted out with the most efficient washing machine, condenser drier, kitchen, water-saving bathroom with occupancy sensors in areas such as toilets, internet connection, Wi-Fi and an outside socket for charging an electric vehicle. There are LED lights throughout.

All of these relatively spacious homes are provided with the most energy-efficient appliances and exceptional attention to detail.

Communal electric car

The Nissan Leaf charging outside one of the houses.

The occupants of the estate have been given a Nissan Leaf to use collectively, charged by the solar panels on the roofs.

“It’s a way of getting neighbours to cooperate with each other and eliminate the need for a second car,” Peters says.

Energy storage

The South-facing homes are generous in their space, their form determined by the maximum depth allowed by the passive heating.

The rest of the heating is provided in a surprising manner, using the best of old technology with new: solar electricity and storage heaters.

An installed storage heater; proven, old technology meeting the new.

Storage heaters contain thermally massive blocks that are heated up by an element. They then release that heat gradually over many subsequent hours.

This form of energy storage was introduced to British homes in the 1960s and ’70s on a special tariff called Economy 7. Since nuclear power stations could not be switched off, unlike other forms of electricity generation, these tariffs allowed people to use nuclear electricity at night – at a lower rate when national demand was low – to charge the storage heaters.

The problem was that by the time the heat was needed, the following evening, they were often too cool and many people subsequently removed them and installed central heating instead.

Here, the idea is to let the storage heaters be heated up during the day by the solar panels on the roof, meaning they are able to provide adequate heating through the evening and night provided that there has been average sunshine (50 per cent of a June summer’s day) during the day.

This may not be the case in the depths of winter and so the homes are also grid-connected. They export surplus energy when there is some – after the electric car and storage heaters have been topped up – and purchase it when not enough has been generated.

“Storage heaters are incredibly cheap,” Peters says, “and a well proven technology. Whereas the storage we had to start with in the prototype house – lithium-ion batteries – were designated a fire risk and we had them taken out. They are also much more expensive.”

A pair of two-bedroomed semi-detached passive solar houses.

The prototype house has been monitored and has well exceeded the predicted generation capacity, providing twice the electricity used over the year.

Peters says: “We have spent £2 million (AU$3.5m) researching and developing a sustainable timber building system that is 100 per cent British, powered by solar energy. We hope now to create 1000 homes across Wales and the UK, once the current political uncertainty is out of the way and we have won the argument on the efficacy of timber housing.”

David Thorpe is the author of a number of books on energy efficiency, sustainable building and renewable energy, including:

• The Expert Guide To Energy Management In Buildings
• The Expert Guide to Solar Technology and
• The Earthscan Expert Guide to Retrofitting Homes for Efficiency.

Find out more and buy the books here.

UNEP backs Passivhaus to help meet climate targets

[This post originally appeared on The Fifth Estate website on 9 November.]

As the latest round of global climate talks begins, the UN Environment Programme is calling on nations to ramp up their action to reduce greenhouse gas emissions and is explicitly backing the use of the Passivhaus Standard to reduce emissions from buildings.

Thermal image showing how a Passivhaus refurbishment/makeover of a terraced home (the blue one) means it radiates (loses) no heat compared to its neighbours (red and yellow - meaning they are radiating heat. The more red, the more heat is being lost).

Delegates in Marrakesh for yet another climate conference, the 2016 UN Conference of the Parties (COP22), have been studying a report by UNEP on what the world needs to do to meet the requirements of the Paris Agreement and halt dangerous global warming.

COP22 is about following up the just-ratified Paris Agreement. The agreement marks a turning point in the history of the world, establishing both the commitment and the framework for dealing with climate change. COP22 is about fleshing out the detail, and there is a great deal of detail to be fleshed out.

The Intended Nationally Determined Contributions from COP21 form the basis of the Paris Agreement; they are the pledges that each country laid out at year’s negotiations, showing their contribution to tackling climate. But these presently fall well short of achieving COP21’s “well below 2°C” temperature goal.

The Emissions Gap Report

Just in advance of the conference the UNEP issued its “Emissions Gap Report“, which notes the “troubling paradox at the heart of climate policy”.

Erik Solheim

In the words of Erik Solheim, the head of the program, the paradox is that “on the one hand nobody can doubt the historic success of the Paris Agreement, but on the other hand everybody willing to look can already see the impact of our changing climate”.

(Everybody, that is, apart from the Republicans in the US who elected Donald Trump and his cronies. But that is another story.)

This report estimates that we are actually on track for global warming of up to 3.4°C – way over the target. The current commitments made by nations “will reduce emissions by no more than a third of the levels required by 2030 to avert disaster”, he says.

“So, we must take urgent action. If we don’t, we will mourn the loss of biodiversity and natural resources. We will regret the economic fallout. But most of all we will grieve over the avoidable human tragedy.”

Global greenhouse gas emissions continue to grow. UNEP is calling for accelerated efforts now, prior to 2020, and for nations to increase their ambitions in their INDCs.

“Pathways for staying well below 2°C and 1.5°C require deep emission reductions after, and preferably also before 2020, and lower levels of emissions in 2030 than earlier assessed 2°C pathways,” the report says.

The report does identify where solutions are available that can deliver low-cost emission reductions at scale, including the acceleration of energy efficiency.

Much has been said, including by myself, about the effect on emissions by actors who are not nations, such as cities, regions and companies. It’s possible, the report notes, that these could reduce emissions in 2020 and 2030 by a few additional gigatonnes, but it is difficult to assess the overlap with INDCs because these are not usually detailed enough and non-state actions can overlap or mutually reinforce each other.

The importance of energy efficiency

The report emphasises that ambitious action on energy efficiency is urgent. Well-documented opportunities exist to strengthen national policies on energy efficiency.

Studies based on the Fourth Assessment Report of the Intergovernmental Panel on Climate Change show that for a cost range of between US$20 and $100 per tonne of carbon dioxide, 5.9 gigatonnes of emissions could be saved from buildings, 4.1 for industry and 2.1 for transport by 2030. These estimates are conservative and the real potential in each sector is likely to be bigger.

A more recent analysis by the International Energy Agency indicates that the cumulative direct and indirect emissions estimates to 2035 are 30 gigatonnes for buildings, 22 for industry and 12 for transport.

The two studies are not comparable due to differences in approaches, but together illustrate the significant potential in the three sectors.

Improving energy efficiency also offers many other benefits like reduced air pollution and local employment.

It is an integral part of Sustainable Development Goal 7, which aims to “ensure access to affordable, reliable, sustainable and modern energy for all”.

The energy efficiency target is to double the global rate of improvement in energy efficiency by 2030, from 1.3 per cent per year to 2.6 per cent. Achieving this goal will be important for achieving many of the other goals:

• Building energy efficiency will be increased by ratcheting up the ambition of energy codes, and increasing monitoring and enforcement of building regulations with the use of energy performance certification and with encouragement to create highly efficient buildings.

• Industrial energy efficiency will be helped the more that companies introduce energy management by adopting ISO 50001 an energy performance monitoring. Energy performance standards need to be enforced for all industrial equipment.

• Transport energy efficiency is improved by the adoption of vehicle fuel economy standards and electric mobility for passenger transport. For freight movements sustainable logistics can be deployed.

There is a huge role for energy service companies to offer these services.

All of these efficiency savings can be encouraged by planning policy. For example:

• Successful zoning can reduce the need to travel, and neighbourhood layouts can reduce the need for heating or cooling.

• Spatial planning can help to improve transit options, increase and co-locate employment and residential densities, and increase the amount of green spaces.

• Heating, cooling and electrical energy services can also be more efficiently delivered at a neighbourhood scale than at a building scale, with distributed renewable or low-carbon energy supplied by local energy service companies.

The Passivhaus standard

The report explicitly advocates the adoption of the Passivhaus standard. Passivhaus, originating in Germany, is primarily a tough quality assurance standard, which demands great attention to detail during the design and construction process to achieve certification.

Key to it is a target that annual final energy use for heating and cooling should not exceed 15 kilowatt hours a square metre a year.

The report says that the global floor area covered by Passivhaus buildings has grown from 10 million sq m in 2010 to 46 million sq m in 2016, with most activity occurring in Europe.

And importantly, it says the price for new Passivhaus buildings in several countries is comparable to standard construction costs.

Initially developed for mid and northern European climates, Passivhaus has been proven to work extremely well in hot climates too. High levels of airtightness and insulation work equally well in protecting buildings from overheating provided there is adequate solar shading.

Controlled mechanical ventilation allows options to pre-cool or pre-heat the supply air and also to humidify or dehumidify the ambient air depending on the relative humidity. In combination these strategies are capable of significantly buffering the daytime temperature swing.

Conventional cross ventilation through open windows and night purge ventilation strategies may also be used as part of the Passivhaus cooling concept when appropriate, such as during the cooler evening of a hot day.

In order to achieve the Passivehaus standard in hot countries, the outer wall must have a U-value between 0.20-0.45 W/m2K.

Depending on the heat-insulating properties of the loadbearing outer walls and on the thermal conductivity of the insulation material used, it may be necessary to install an external thermal insulation system of up to 30cm thickness.

Modern external thermal insulation composite systems based on mineral raw materials combine the best insulating properties with ease of handling. Compared to conventional insulation systems, the additional expense pays off after only a few years.

In climatic regions where the daytime temperature does not drop low enough to purge the accumulated heat gains from the building at night there will be a residual cooling load.

In such cases the Passivhaus standard permits 15 kWh/m2.yr of cooling energy to be used. A small cooling load has proven to be sufficient in almost all cases because the Passivhaus concept is highly effective in reducing unwanted heat gains.

The blower door test is used to detect leaks in the building envelope. The smaller the measured value, the higher the airtightness. Passive houses in hot countries require a value =< 1.0. This means that during the measurement at most 100 per cent of the indoor air volume is allowed to escape through leaky spots within one hour. Experience has shown that values between 0.3 and 0.4 are attainable.

Passivhaus principles can also be applied to refurbishment of existing buildings and achieve impressive results. In the UK there are many examples of ultra-low energy, low carbon retrofits.

At the same time, the Passivhaus Institut has launched a Passivhaus standard for refurbishment projects, known as “EnerPHit”, covering a range of property types, including tower blocks, terraced houses and community centres.

Given that costs are around the same as for conventional buildings but energy costs of using the building are drastically reduced, why are they not more widely adopted?

The main reasons are the lack of ambition in building codes, the lack of awareness, trained construction workers and appropriate monitoring. For the aims of the Paris Agreement to be realised this is just one opportunity that needs to be grasped.

Since the US election, the need to grasp these opportunities has become even more urgent.

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)

It's time to make carbon negative buildings the norm

Climate change has entered into a new phase that could last generations even if governments act to curb human activity that leads to global warming. But the Habitat III New Urban Agenda agreed ten days ago offers a chance for the built environment to become negative carbon. Buildings can now begin to withdraw carbon dioxide from the atmosphere. This article gives a few tips on how.

Globally averaged concentration of carbon dioxide in the atmosphere reached the symbolic and significant milestone of 400 parts per million for the first time in 2015 and surged again to new records in 2016 on the back of the very powerful El Niño event, according to a new bulletin issued last week from the World Meteorological Organization's annual Greenhouse Gas Bulletin.

"The year 2015 ushered in a new era of optimism and climate action with the Paris climate change agreement. But it will also make history as marking a new era of climate change reality with record high greenhouse gas concentrations," WMO Secretary-General Petteri Taalas said in a statement.

The data "predicts that carbon dioxide concentrations will stay above 400 ppm for the whole of 2016 and not dip below that level for many generations," the WMO said. “The El Niño event has disappeared. Climate change has not. Without tackling carbon dioxide emissions, we cannot tackle climate change and keep temperature increases to below 2^oC above the pre-industrial era. It is therefore of the utmost importance that the that the Paris agreement does indeed enter into force well ahead of schedule on 4 November and that we fast-track its implementation.”

The El Niño event triggered droughts in tropical regions and reduced the capacity of “sinks” like forests, vegetation and the oceans to absorb CO₂. Besides this it also led to an increase in CO₂ emissions from forest fires. According to the Global Fire Emission Database, CO₂ emissions in Equatorial Asia – where there were serious forest fires in Indonesia in August-September 2015 - were more than twice as high as the 1997-2015 average.

Habitat III's New Urban Agenda

But there's hope. Habitat III, which took place in Quito last week with around 36,000 people attending from 167 different countries, adopted the New Urban Agenda which, amongst other things, urges cities to tackle climate change.

Joan Clos, the Executive Director of the UN Human Settlements Programme (UN-Habitat), called the Agenda "a common roadmap for the 20 years to come” at the closing plenary of the conference.

Cities are both the source of most of the world’s carbon-dioxide emissions and the place where the most impactful interventions can occur — to reduce automobile driving, improve energy-efficiency in buildings and switch to renewable energy sources, among other opportunities.

“By making the Paris Agreement one of its antecedents and quoting its long-term goal, the New Urban Agenda is acknowledging the climate challenge in cities, and putting climate action at the core of urban policies at national and local levels — and that’s a good thing,” said Mark Watts, executive director of the C40 Cities Climate Leadership Group.

The agenda does not bind Member States or city governments to specific targets or goals, but is rather a “shared vision” that set standards for transforming urban areas into safer, resilient and more sustainable places, based on better planning and development.

The Quito Implementation Plan is now set up to support the outcomes of Habitat III and the New Urban Agenda.

Negative carbon buildings

Amongst the potential strategies to help with the Quito implementation plan is for building specifiers, developers and architects to generate buildings which are at least zero carbon on balance, when totalling the carbon impacts of materials, construction, use and demolition. But what does this mean?

Some features of zero or carbon negative buildings 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;
• construct and manage it in such a way that it minimises the emission of greenhouse gases during its lifetime and eventual demolition;
• encourage the capture, generation and even export of renewable energy;
• make the structure very airtight;
• make the structure breathable;
• make it durable, resilient, low-maintenance, fire- and weather-resistant;
• incorporate a large amount of insulation. 

The ideal features of zero-carbon, solar buildings.

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 and storing atmospheric carbon in its structure.

Neighbourhood design

From a planning angle, different neighbourhood layouts for developments are appropriate depending on the regional climate as shown in these figures:

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

Higher latitudes: in this housing estate each property has both privacy and an equator-facing aspect and roof to maximise the potential for the use of solar energy. Grey circles are trees, grey lines are hedges (preferably) or walls.

Carbon intensity

On average the carbon impact of the construction of conventional buildings is between 10 and 20% of their use during their lifetime. But it is self-defeating to construct a zero carbon building with materials that cause high carbon emissions in their manufacture.

Conversely it is ideal to use materials which lock up atmospheric carbon, for situations where well-performing and suitable alternatives exist, usually made from natural cellulose-based materials. (Plants absorb atmospheric carbon while growing and 'lock it up' in their mass.)

Steel is a possible exception, despite its high embodied carbon, as it is long-lasting, but many large and high-rise structures are now being made using frames made of timber products.

‘Natural’, ‘green’, ‘bio’ or ‘renewable’ building materials can be classed together as ‘cellulose-based’. Amongst their benefits are that they:

• lock up atmospheric carbon in the building;
• have varying degrees of insulation ability;
• are easy to work with;
• make structures that are breathable.

They are also biodegradable or easily recycled at the end of the building's life and may support local agroforestry.

Wood has a greater tensile strength relative to steel – two times on a strength-to-weight basis – and has a greater compressive resistance strength than concrete.

Sustainably sourced timber and timber products specially designed for structural use must be specified. These include glued laminated timber ('glulam') and Cross-Laminated Timber (CLT).

The tallest building in the world made with timber frame is 14 storeys high and is in Bergen, Norway. It uses metre-thick columns of glulam and CLT, plus two concrete decks above the 5th and 10th floors. See the video below.


Glulam can produce columns, beams and curved, arched shapes and has a much lower embodied energy than reinforced concrete and steel, although higher than solid timber.

CLT is an engineered timber product with good structural properties and low environmental impact able to provide dry, fast onsite construction, with good potential for airtightness and a robust wall and floor structure suitable for most finishes internally and externally. It requires only limited new site skills and can be assembled without the use of adhesives using mechanical fixing. Its low weight means that a high degree of offsite manufacture is possible.

Other useful timber products include:

• Plywood, wood structural panel;
• Oriented strand board (OSB);
• Laminated veneer lumber (LVL);
• Parallel strand lumber (PSL);
• Laminated strand lumber (LSL);
• Finger-jointed lumber;
• I-joists and wood I-beams – "I"-shaped structural members designed for use in floor and roof construction;
• Roof trusses and floor trusses.

Other natural carbon- negative materials currently used in construction include:

Material	Application
Flax	Roofing insulation
Hemp fibres	Insulation
	Medium density fibre board
	Oriented strand board
Hemp shiv	Monolithic construction ofwalls, floors and roofs
	Insulation
	Panel construction
Jute	Carpet
	Plastering mesh
	Scrim
Paper	Recycled and shredded forinsulation
	Mixed with cement to formblocks
Reed	Thatching
Reed mats	Plastering base (like laths)
Sisal	Carpet (mixed with reinforcedcement in some countries)
Straw	Bales as building blocks
	Wall panels
	Thatching

For reporting purposes, it may be useful to report the carbon storage capacity of a building, to add to the carbon saved from using renewable energy to heat and power it. For buildings a web-based calculator like the one on this page may be used.

Phase shifting Phase shifting is another useful tool for building designers. It denotes the time taken for an extreme external temperature to reach the interior, travelling through the building envelope.

The aim of passive cooling in hot, non-humid areas is to have a phase shift of 12 hours, so that the midday heat only reaches the interior in the middle of the night. With good amplitude dampening, its effect will also be very much moderated.

Some of the stored energy in the fabric is thus automatically transferred back outside, ensuring that temperature fluctuations and extremes on the inside are much less than outdoors.

Amplitude dampening and phase shifting should be particularly observed in roof areas. These may get very hot and so require large thicknesses of insulation with low thermal diffusivity. Aim for an amplitude dampening value of 10 (TAV 10%) and a minimum phase shift value of 10 hours.

There is now no excuse for building specifiers and designers not to give us at least zero carbon buildings.

---

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)

An off-site pre-fab approach to Passivhaus 'deep retrofit'

A new approach to retrofitting buildings for energy efficiency to a high standard has been deemed so successful that a British company is opening a new factory for offsite fabrication of a retrofit system that will be then taken on to the site for installation.

These kits involve a wrap-around solution for an existing building that also includes ventilation to ensure good air quality and, because it uses off-site construction, the upgrade process can take as little as three weeks and means that the occupants do not have to move out during the upgrade.

The company, Beattie Passive Retrofit, has secured patents in 57 countries for its innovative solution, which is called TCosy and been developed with funding from Innovate UK, that channels public financial support to private sector R&D to foster low carbon innovation.

The company’s approach, founded on the stringent and verifiable Passivhaus energy performance standard, also involves using locally-trained labour. Passivhaus standard is hard to achieve because it demands that the contractors achieve a high level of airtightness. However, due to the simple system and factory construction much of the uncertainty is taken out of achieving this. The standard can attain an 85% reduction, or £1000 per year, in heating fuel costs for the average house.

Residents of 6 flats in a 3-storey, apartment block owned by Solihull Community Council near Birmingham, England are amongst the first to benefit from the system, following a three-year collaborative R&D project between Encraft, a low-carbon buildings engineering consultancy, Coventry University and a local social enterprise called Jericho Foundation who trained people facing significant personal or occupational barriers to build the system.

Beattie's CEO Ron Beattie, who founded the company in 2008, said: "We have designed the retrofit process to be as simple and efficient for all parties involved. Having tested the processes we've proved we can deliver energy savings over the life of a building."

Ron Beattie provides an overview of the innovative Beattie Passive Build System and Retrofit System - The TCosy – filmed at the 2015 Passivhaus conference.

Gareth Cavill, Beattie Passive's lead architect, said that "the process begins by producing the architectural drawings in house. The information goes to the factory where the frames  are manufactured and then taken to the site where they are erected. We source the windows and doors from one of our supply partners in Europe due to their advanced quality and cost advantages."

He added that the insulation used within the timber frames consists of expanded polystyrene eco-beads.

Isabel Beattie, Head of Strategy and Development stated that "The estimated price for a retrofit is £550 per square meter of floor area including the frame, windows and doors," she said. "This makes a three-bedroom detached house retrofit typically cost £45,000. Our clients are expected to be social housing providers, developers and self builders."

The approach is similar to that offered by the Investor Confidence Project, in providing a guaranteed rate of return and financial package to investors, the key being the simplicity and certainty guaranteed to the investor and to the housing provider of the whole offer.

Ron Beattie believes this approach will solve a key problem facing what is called 'deep retrofit' agendas – financing their comparatively large upfront cost. "Once we can guarantee energy savings, we believe that pension funds and other long-term investors will be prepared to lend over 30 years, with a return after that. And we will have pulled people out of fuel poverty," he said.

"We showed estate agents in Birmingham what we’re doing and their studies suggest a £65,000 uplift in value on a £120,000 property, because you are putting a new building over the top of the old one. If redecorated, with a new kitchen and bathroom, you’re looking at a completely new house." This raises the possibility of generating a profit from deep retrofitting.

Isabel observed that they were already talking to some pension companies about investing in retrofits for future roll-out at scale. "We estimate that savings generated by the retrofit of on average 85% of heating requirements would help pay back the investment within 30 years. With this type of programme the tenants generally pay one fee that includes rent and energy, and it is from this income that the housing provider would pay back the investor. The fee would be reduced slightly for the tenant compared to the non-retrofitted rent, and they will also have warmer, healthier home."

Solihull homes before cladding.

"We have new sales staff and an architect. Work is coming in and growth is going to be very fast," added Ron optimistically. "We are due to start manufacturing in the factory soon and we’ve got seven or eight homes booked in, ready to go. They range from private client, multi-million pound houses to standard affordable homes for Hertfordshire Council – different ends of the market, but the same process."

To fill the demand the company will soon open a factory on the Scottow Enterprise Park, formerly RAF Coltishall. With 57 patents secured abroad, it is clearly confident that expansion on a large scale is possible one small proofs of concept are installed. With 20 million homes in the UK alone needing a low-energy retrofit, the market is clearly huge.

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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(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)

An Urban Permaculture Passivhaus Eco-Community

A plan of the development generated by architects RG+P.

We can get a glimpse of a sustainable, one planet urban community might be like by looking at existing projects. Presently, the largest permaculture-based, Passivhaus urban eco-community in Europe, is being developed in Leicester, England. When finished, the settlement will contain 68 homes for rent at affordable rates for essential workers. 

It is happening on the site of former, disused Whittier Road land on Heathcott Road, Leicester. The developer is East Midlands Homes, a provider of affordable housing, in partnership with Westleigh Homes. Westleigh is taking on new apprentices to learn building skills to help construct the homes.

At the edge of the site will be a farm, to be run on Permaculture principles, on which residents will be encouraged to work, to grow their own fruit, vegetables, other foodstuffs and supplies. When finished it will provide an urban oasis. The field pond will be refreshed, and hedgerows reinstated to connect a wildlife corridor on Saffron Heath, creating a diverse wildflower meadow and planting 800 new trees, many of which will be fruit trees, on the site.

Saffron Lane Neighbourhood Council (SLNC), a charity and social enterprise, is behind the “Building a Greener Future” project.

The site already contains a community garden, and has produced everything from striped beetroot and blue pumpkins, supplying a range of local restaurants with specialised herbs and vegetables and supporting local community projects, including their own brand and jam. This work is expected to expand upon completion of the estate.

The Neighbourhood Council exists "to provide a range of services to support disadvantaged residents of the Saffron Lane Estate and environs to reach their full potential". Its resource centre is around the corner from the 12 acre site.

Passivhaus homes

The 68 houses will be constructed according to Passivhaus principles which means that the annual running costs per year for heating will be just £13 per home, according to Standard Assessment Procedure software calculations (used by all developers to comply with Building Regulations). The majority of homes in the UK are constructed to level 3 of the Code for Sustainable Homes, meaning that homes comparable to these would use about 8801kWh per year and cost £735 per year to run.

Passivhaus is a standard for energy use in all building types. The homes will be of energy-efficient design, oriented to face south with increased south facing glass, super-insulated and with effective window shading and ventilation and moisture control, plus minimized building surface-to-volume area, protected from wind and with the cooler service spaces located on the northerly side.

The Standard requires the following:

• Space heating: less than 15 kWh/m²/yr;
• Total primary energy use (heating, hot water and electricity): no more than 120kWh/m²/yr;
• Air leakage: no more than 0.75 m³/m²hr @ 50 Pa (0.6 air changes per hour);
• The specific heat load for the heating source at the desired temperature is recommended, but not required, to be less than 10 W/m².

Neil Hodgkin, Head of Development at Saffron Lane Neighbourhood Council, said that "the original plan had been for the 68 homes to be built around the farm so that they would look onto it in a village green type construction, but this was not approved by the planners".

He added that since the houses are to be rented, the residents will have to sign a contract with the housing association, but "it will not be a feature of the contract that they have to do work on the farm, nevertheless they will receive encouragement and training".

It is very unusual to see a development which includes all of these features, and they are in line with the principles of 'one planet living' as espoused by the One Planet Council which notes that there are many benefits to this approach. They include:

• Sustainable, low impact homes;
• Sustainable livelihoods;
• Reduced ecological footprint for the community;
• Local food and products, with micro-enterprises and employment;
• Affordable housing;
• Increased land productivity;
• Skill training;
• Increased biodiversity at the site;
• Increased feelings of well-being and good health from residents;
• Increased sense of community;
• Efficient use of natural resources.

Watch a video about the community project up to now:

David Thorpe is the author of:

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

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

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[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