The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.
Here’s an excerpt:
A New York City subway train holds 1,200 people. This blog was viewed about 4,000 times in 2014. If it were a NYC subway train, it would take about 3 trips to carry that many people.
Some look at wind farms and find them an ugly scar on an otherwise beautiful landscape. I disagree. I think they are grand, graceful, wonders of modern engineering and with every powerful rotation they are working to preserve the beauty of the natural surroundings in which they stand.
Wind turbines are a great source of renewable energy, but they are not the correct solution for anywhere and everywhere. In this post I am looking at what factors influence the suitability and feasability of Wind Turbines.
The first thing to consider is the SUITABILITY. What is the annual average wind speed in the proposed location? If data suggests thats the average is LESS that 4.5m/s (meters per second), then the context is actually not suitable and one should consider and alternative such as Solar PV.
Next consideration is a location for the turbine. There are a few factors that influence how well the turbine will work in a given context. Buildings and trees disrupt that passage of wind causing turbulence which has a negative impact of the efficiency of the turbine (see image below. Source). The ideal setting is the top of a rounded hill which is why you often see the very large turbines in rural settings on a high point or out at sea.
Wind speed also increases with height so the higher the better. There is a limit to this of course – building control may have regulations that govern the maximum height of turbines – particularly in urban settings. Also, one needs to consider the cost and ease of maintenance with a taller installation.
The turbine should be installed to face prevailing winds. Work out what these are in the specific context. The turbines have some flexibility around their pivot point but for maximum benefit, position them carefully.
There are some useful calculations or ratios to consider (Source: Energy Savings Trust):
Have you ever seen a turbine or group of turbines and they dont seem to be working even though there is some wind… well that is because turbines work to minimum and maximum wind speeds. The CUT IN speed refers to the minimum speed that the wind must be for the blades to start rotating and generating electricity. The smaller the turbine the earlier the cut in speed. So a small 500W turbine may cut in at 3.5m/s but the very large industrial ones will start around 10m/s.
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As shown in the graph above, there is also a CUT OUT speed. Turbines have an in-built braking system to protect the motor from over-use and strain. For domestic / smaller turbines (typically 500W – 25kW) cut out speed is around 25m/s. Look out for the maximum design wind speed which should be around 50 – 60m/s. These are rare gust speeds but turbines must be designed to withstand such forces.
ENERGY OUTPUT
Every turbine will advertise a RATED / PEAK OUTPUT. It will come as a 1500kW Turbine for example. What this is essentially saying is that at an ideal wind speed of x, you will get 1500kW of power. The system should say what the wind speed is for the rated output – in the case of the 1500kW Turbine, it may be 12m/s.
In reality, the wind will not blow consistently at 12m/s. One can expect about 25% to 30% of the theoretical rated output. To use the example of the 1.5kW Turbine with rated speed of 12m/s. The theoretical output is 13 150 kWh/yr (1.5kW x 8760hrs), when in actual fact due to fluctuations in the wind (even if the annual average is 12m/s) as well as inefficiencies such as turbulance – 30% of that is your likely yeild = 4000kWh/yr. This is why one must be careful not to size the system based on the rated output but take into account the annual average wind speed and allow for inefficiencies. The average American household consumes 10 000kWh/yr (28kWh/day) (Source) so this 1.5kW turbine would only provide 40% of the demand. They might thus consider a larger 3kW system if budget and site restrictions allow.
An oversized system may be very lucrative where excess electricity is fed back to the national grid, generating money. This is demonstrated in the example below:
A 250-kW turbine installed at the elementary school in Spirit Lake, Iowa, provides an average of 350,000 kWh of electricity per year, more than is necessary for the 53,000-square-foot school. Excess electricity fed into the local utility system earned the school $25,000 in its first five years of operation. The school uses electricity from the utility at times when the wind does not blow. This project has been so successful that the Spirit Lake school district has since installed a second turbine with a capacity of 750 kW. (Source)
Payback periods are determined if you work out the annual savings (cost of electricy / kWh) relative to the cost of the installation and maintenance. If you are able to generate money by feeding excess energy back to the grid this will definately improve the feasability as the payback period deminishes.
In rural settings it may be both suitable and feasible to install a larger turbine to feed a group of houses – a 25kW Turbine might provide ample power for 5-8 houses. Due to it’s larger size it would be located further away where noise and visual disruption can be minimised.
INDEPTH LOOK AT AN EXAMPLE OF A TURBINE
The AWP 3.7 from African Wind Power is one I came across on the web while browsing. It has a rotation diameter of 3700mm and would be suitable for domestic type usage.
The following graph is helpful to explain the relationship between wind speed and power output:
The peak output of 1.5kW is achieved at wind speed of 12m/s. Cut in speed is shown at around 2.5m/s.
Furthermore, the manufacture notes that the predicted energy yield per day for differing wind speeds is as follows:
PROS & CONS
Pros:
Cons:
LOCAL WIND DATA
Interesting fact – Cape Denison in Antarctica is the windiest place on earth with annual average wind speed of 20m/s. Joburg, Cape Town and Durban are 4.5m/s, 6m/s & 5m/s respectively.
For useful weather data for South Africa visit: Windfinder
For more technical detail and calculations visit: www.wind-power-program.com
Article about scientific response to claims that wind turbines make people sick: Discover
“Architecture is much more than art. And it is by far more than just building buildings”
There are few architects that are as humble and community-focused as Francis Kere. He is an absolute inspiration to me. The son of a Chief, Kere had the rare opportunity to be educated from the age of 7. He was sent far from his home in Gando, to join 150 other children in a basic school, where he excelled. He was awarded a scholarship to study Architecture in Berlin, Germany.
Kere recalls how the women in his village would give him their last pennies when he would return to school from holidays. A deep sign of affection, these women wanted to support his education in the hope that he would be able to use his knowledge to benefit the community in the future. This had a deep impact of the young man, and he carried the hope of his community with him throughout his education. While still a student in Berlin, he started drawing up plans for a new school for Gando and set about fundraising amongst his peers and further a-feild. He eventually returned with $50000.00 to start work.
In a TED talk he explains how the community were thrilled at his proposal for the school but they were shocked that he would use clay as a primary building material. Clay is the typical building material for the huts in Burkina Faso and the villagers were hoping that Kere would propose building components like one would find in flashy cities. But it is precisely Kere’s solution for buildings that hit the bulls-eye of sustainable architecture. Use locally abundant building materials, & techniques that can be taught to the community who will be the ones to do the work. Not only does this keep costs manageable but there are almost zero carbon emissions and the buildings respond well to the context and climate. (Despite the durability of the clay walls, they do need to be protected from the heavy rains, by wide overhangs of the roof.)
Clay is used in the form of compacted bricks, and compacted floors:
Steel rods (typically used as rebar in concrete) span between beams that hold the clay brick roof:
An elegant but brilliantly functional floating roof of corrugated iron acts as a sun umbrella, shading the building below from the direct solar energy, while allowing ventilation in the void below to remove hot air. This passive cooling strategy proves highly affective at regulating the indoor temperature.
The children love the building and it has aged very well.
The success of the school enabled Kere to embark on other projects in Gando and beyond. An extension to the school saw the use of an arch of clay bricks where Kere had to physically demonstrate the safety of the rather fanciful looking structure. It survived when Kere jumped up and down on the top and his community was satisfied!
Another beautiful project is the Library. Again, using local craftmanship, clay pots were sawn in half and cast into a concrete roof slab.
The affect is beautiful. Mottled natural light as well as escape points for hot air.
Clay walls have excellent thermal mass which is idea for hot climates. The walls slow the passage of heat from outside to inside, but this is further assisted where the walls are shaded by wide eaves / roof overhangs.
Francis Kere has definitely delivered on the hope held by his community. Not only has he seen it that they have beautiful buildings to improve the lives of the Gando people, but he has brought skills to the men and women who are now eligible to work on other projects around the country. Kere has won a number of awards for his buildings, while utterly deserved, it is clear that winning awards is not the reason Kere does what he does… it is to give back, and to improve the lives of the people he loves.
This is Sustainable Design in action. It is truly beautiful and I am totally inspired!
See more Kere Architecture HERE, I will be writing more posts on his other projects in the future.
Images source: KERE ARCHITECTURE
I have been toying with the idea of becoming a LEED Accredited Professional and looking at the benefits of the time and money that it requires. This is an illuminating article on the pitfalls of the system which I found very interesting…
LEED works well if you’re a wealthy person building within a Northern city. But that probably includes about 1% of the world’s population. We need a green building rating system for the rest of us.
Read the article on ARCHDAILY here.
Furthermore I found the reader’s comments entertaining and illuminating – I love the passionate expression!
The LEED certification program is a massive, creativity-snuffing bureaucratic boondoggle and the enemy of intelligent & responsible site-specific and client-specific design.
The building for UN CITY in Copenhagen was completed in 2013 and it boasts some impressive green building aspects.
LIGHTING
CREDITS
Location: Copenhagen, Denmark
Client: FN Byen (Copenhagen Port & City Development)
Gross Floor Area: 52.000 m2
Cost of Construction: 134.000.000 Euros
Architects: 3XN
Interior Design: PLH / UN Common Services
Contractor: E. Pihl & Son
Consultants
Engineering: Orbicon
Landscape: Schønherr
We have just returned from a dreamy week on the Island of Kefalonia in Greece. There is much about the island that makes for interesting contextual analysis of buildings and the how they suit the climate and way of life on the island.
CLIMATE
A typically Mediterranean climate with hot dry summers (up to 35C) and cold wet winters (lows of 6C). These extremes typically mean that cooling and solar-exclusion is required in the summer and heating and solar-inclusion is required in the colder months.
LOCAL ECONOMY
Residents on the island make a living though various industries – in the thriving tourist trade (hotels, restaurants, shops, excursions); or farming olives – beautiful old trees have been tended for literally thousands of years; wine making; farming of crops, goats, sheep and some cattle.
Living off the land is quite common as the island yields all sorts, from vegetables to olives, honey and animal products – fish & goats being most abundant.
TRANSPORT
Ferries link some of the key town on the island as well as to other local islands. There is a basic bus service on the island which is particularly helpful for the islands many aged folk.
As tourists, we needed to hire a car to get around, or take taxis and the bus routes are limited and buses quite infrequent.
Wind power:
I noticed that a number of buildings did have solar thermal panels to make use of the abundant solar energy, and a few had domestic scale wind turbines.
EDF Energies Nouvelles have a 30MW wind farm positioned on the hilly centreparts of the island which seemed to be constantly active. The company owns 90% with the remaining 10% held privately. (Source)
Now I don’t have access to the efficiency of the wind farm but if I was to say that the wind conditions for optimum yield of electricity was only good half of the time (quite possible over a year), the 30MW farm would generate: 4380hrs x 30MW = 131 400MWh.
Assuming an average annual consumption per capita of 5500kWh, this farm supplies enough energy for almost 24000 people. Given that the island has around 33000 inhabitants, this is a good effort towards a completely green energy solution.
What my calculations don’t consider are the number of tourists that occupy the island over the summer, and also the non-domestic energy use of the island. But this at least gives one an idea of how the output of this wind farm may be used.
Solar farms:
There are a few solar electric farms on the island which I would guess are privately owned by hotels to service the needs of these buildings. Especially relevant as the months with the greatest energy demand – tourist season, correlate with the months of greatest solar irradience – long hot summer days.
Further reading –
Thesis on domestic energy consumption in Greece
Power and energy consumption explained
TYPICAL CONSTRUCTION
Kefalonia is prone to tremors and earthquakes and a particularly devastating earthquake in 1953 reduced almost all buildings to rubble (save for the northern village of Fiscado). Since then building have to withstand tremors up to 7.5 on the richter scale. As such, most of the buildings are now built in a concrete bunker style. Strong concrete structure with clay brick infill.
The island is an abundance of lightly coloured sandstone. It was this stone that historically provided the base for all structures and many of these are still visible as ruins around the island.
The stone is still used in modern construction but generally only as cladding or as retaining walls. It is beautiful the way it just roots the buildings to the island though. Golden, authentic, abundant.
Walls and roofs are typically UNINSULATED, relying on the building materials for all regulation of indoor temperature.
ROOFING: Terracotta tiles on timber substructure
WALLS: Concrete structure with clay brick infill
FLOORS: Concrete floor slab
WINDOWS: Double glazed in aluminium frames
SOLAR STRATEGIES
Most houses have external shutters which are perfect for excluding the harsh summer sun even before it enters the building. Adjustable louvers are useful to allow natural ventilation through the dwelling.
Most modern buildings have double glazed windows as a defense against the cold. With temperatures as low as 6C.
By way of a bit of a case study, I will elaborate on the design and construction of the hotel we stayed in LEIVATHO HOTEL, on the South West of the Island. The hotel received the Architectural award for best building in Greece during 2011/2012.
Leivatho Hotel’s commitment to the environment is reflected in the water management, its recycling policy including composting, the use of organic locally produced food and the use of solar energy for water heating. A water recycling system cleans shower and bath water purely biomechanically and produces water which is re-used in the toilet and garden. Water consumption is lowered by up to 50%, which combined with the local flora contributes towards the conservation of a precious natural resource.
Eco- friendly food is served in an ever changing morning buffet, focusing on local specialties and products. Leivatho Hotel also uses 100% cotton linen and offers natural bulk soaps and amenities to its guests. – Hotel Website
Particular sustainable design features I noticed:
Opportunities for further energy and resource efficiency:
Kefalonia is a beautiful island with warm, friendly people. The lifestyle is relaxed and the land seems to produce much of what is required to sustain life on the island without putting it’s resources under stress. I am encouraged to see that renewable energy options are on the increase, and the simplicity of the lifestyle reminds us tourists that we do not need much to live comfortably and happily. I definitely hope to return one day!
As a waste product from Agriculture, haybales make a great sustainable building material. Haybales have excellent insulating properties and make for a very pleasing, organic finished result. Thatched roofs are common around the world so it was initially suprising to me that using haybales for walls is not more common. This is largely possible due to the fact that the mechanization that resulted and straw-baling formation only came about in the 1850’s!
The first documented haybale building was a school in Nebraska dating back to 1902. When the cows started to nibble at it, the builders decided the plaster the walls. Following this, numerous haybale buildings sprouted up in the area.
Haybales are treated much like over-sized bricks. Organised in a running bond, the bales are tied together using re-bar of bamboo or timber, or covered with a mesh. This can then be plastered with a lime, cement or clay based render.
A solid foundation is generally used, onto which the bales are placed. A moisture resistant membrane should be placed between the bales and the foundation.
The bales can be used as the structure of the building, or as the insulative infill to a steel / timber frame structure. A field bale will generally support 900kg per linear meter but it is possible to get highly compressed bales for greater structural loads, that can support up to 6000kg per linear meter.
‘Balehaus’ is a project of the University of Bath, where prefabricated panels with hay infill where fitted together and rendered with a breathable lime-based plaster. More about the ModCell concept here.
Haybale walls have very low thermal conductivity making them a great source of insulation. Thermal consuctivity of wheat is about 0.06 W/mk. For a bale wall 475mm thick this would achieve \ U-value of 0.123W/m2K. This exceeds the passivhaus requirement of 0.15w/m2K for walls.
Because the haybale walls are plastered, this prevents the unwanted concerns of rats and mice / fire damage / water ingress. It is important that a good covering of plaster is used – around 25mm thick. If looked after, haybale walls can last for centuries.
The NBS has now incorporated a guideline specification for Strawbale construction: http://www.thenbs.com/topics/Environment/articles/StrawBaleConstruction.asp
There is something about rammed earth walls that really appeals to me. The rich colour and texture of the compacted earth links the building so well with the natural surrounds – from which the soil should ideally come. The solid bulk of the walls has an anchoring, permanent effect that connects well with the concept of ‘Sheltar’. Rammed earth has been used for millenia as a solid, durable and thermally massive.
1 in 3 people (2.5 billion of the worlds population) do not have access to safe water and sanitation. Source: (wateraid.org). As demand for water increases, it is increasingly difficult to maintain the supplies of water to meet the needs of a growing population. On average, a person will use 150 litres per day (see graph below). Sustainable design guidelines recommend that fittings and fixtures reduce this to 80l/p/d through the installation of dual flush toilets and low flow taps and showers. One of the best options is to make use of greywater systems. In areas like the UK where there is high rainfall almost all the year round,greywater systems are less common than drier climates where, in my opinion, it should be a crime not to have a waterrecycling system in every building.
Greywater systems effectively collect wastewater from baths / showers / wash hand basins and washing machines, and use this water to flush toilets and irrigate gardens. (Waste water from toilets and kitchen sinks is classified as BLACK water and must be heavily treated prior to reuse).
Greywater systems collect water and filter it through a series of stages. A septic tank of sorts contains the water and allows solids to settle, while the ‘overflow’ is then filtered – gravel and bentonite clay are some common filtration stages. Thus particles are removed and the filtered water is pumped out for irrigation or into a toilet cistern.
The pros are:
- Higher savings for everyone
- Good and continuous irrigation
- Food supply is not interrupted
- Gardening and farm irrigation reduced to minimal or zero costs
- Demand for fresh water decreases
- Lower pumping and treatment costs
The cons are:
- Greywater cannot be stored for long or the nutrients in it will break down and it will start to smell bad.
- Quality of water may be different with high levels of boron that can destroy crop and plants
- If vegetables irrigated with contaminated water is eaten raw, it will cause health problems like diarrhoea
- Transmission of some infectious diseases through toxic chemicals from the used water to plants
- Too much nitrogen, sodium, and boron which could cause soil to degrade and groundwater to be contaminated
I do love the simplicity of the SINK POSITIVE… This is clever design!
Last post I looked at the importance of airtightness when it comes to low-carbon buildings. The lower the air infiltration, the greater the thermal comfort and less heating or cooling required to keep the indoor temperature comfortable.
The dangers of air-tight buildings are three-fold:
1. POOR AIR QUALITY
2. MOULD GROWTH
Diagram showing moisture within walls
Common sight at well sealed window frames as moist warm air cools when coming into contact with cold surface of external openings
External wall details showing typical problems due to moisture (A,B&C) and ideal solution (D)
Older buildings often make use of air-bricks high up on external walls so that warm, moist air can escape and allow fresh air into the building. But this totally conflicts with the intention of restriction indoor – outdoor air flow to preserve indoor temperature. Air-bricks are useful where the difference between indoor and outdoor temperature is not massive, for example climates where artificial heating or cooling is not generally used. Windows typically have trickle-vents incorporated into the frames to assist with the exhaust of moist air, but these also let unwanted cold air inside.
Victorian houses were actually designed and made to be quite leaky (rattling sash windows and open floor boards) to allow the smoke from coal fires to escape in an attempt to keep air healthy, however, thermal comfort was poor due to the draughty interiors and they were expensive to heat.
Where mechanical heating and / or cooling is required, air-tightness is vital to energy efficiency and thermal comfort. The best way of ensuring good air quality (low CO2 levels) and good humidity levels (below 60%) is to make use of MVHR – mechanical ventilation and heat recovery system. It is also worth noting that the MVHR can be switched OFF in the summer months to allow occupants to open windows and doors to naturally ventilate the building.
MVHR is only really necessary with air change rates of less than 4 per hour. However, I live in an apartment that has about 8 air changes per hour and while we have not issue with CO2 levels – typically 1000ppm, we have a big problem with humidity levels and condensation. In winter we use a de-humidifier permanently to control moisture levels. In summer we open the windows and the natural ventilation works just fine.
In summary, designers should design air-tight buildings but must consider efficient ventilation heat recovery systems which work to ensure healthy fresh air levels and extract moist air from kitchens and bathrooms to discourage mould growth. These should be commissioned properly before occupation and filter cleaned regularly. It is also imperative that the design considers good passive ventilation during summer months when the MVHR unit can be switched off.
INTERESTING LITERATURE ON THE SUBJECT:
USEFUL PRODUCTS:
Sustainable Building Design 