These post-war buildings containing 60 apartments were renovated between 2006 and 2008. The design was worked out using PHPP software, and the result monitored for two years afterwards and found to have almost met the Passivhaus Standard by achieving an annual heat energy demand of 17kWh/(m²a). The work included 260mm of exterior insulation, triple glazing, central ventilation with heat recovery, reduction of thermal bridges, and 7.5m² (80ft2) of solar collectors on the sloped roofs of six
staircases leading to the new attic apartments. A pressure test prior to the refurbishment indicated an average air change rate of 4.41/h. After refurbishment, the average was reduced to only 0.461/h. The result is dramatically shown in the thermographic images taken before and after the work.
Figure 2.57 Terraced apartments in Frankfurt, Germany. Source: © IEA-SHC (Task37-540-Frankfurt)
to optimize the light and heat input. If the property is being renovated, then the windows are already in a fixed position. However, there are ways to improve the amount of light available from an existing window, such as:
by painting the reveal, lintel, window sill and opposite walls a light colour
•
to reflect more light;
possibly slanting the sides of the reveal to increase the amount of light
•
entering the room (Figure 2.59);
by positioning mirrors in the reveal and opposite the window to reflect
•
more light into the room.
Light shelves
In some places (e.g. high windows in communal areas in offices, blocks of flats and modern dwellings), installing light shelves may help to save electricity used for lighting. Light shelves reflect daylight deep into a room from horizontal overhangs above eye-level. Highly reflective surfaces bounce light onto the ceiling and up to four times the distance between the floor and the top of the window into a room. They are generally used in Continental, not tropical or desert climates, due to the intense heat gain (Figure 2.60).
Sun pipes
Light tubes or sun pipes can transport natural daylight from roofs to rooms that do not have direct access to good natural light (Figure 2.61). They are common in dense, urban areas in Japan, for example. Compared to conventional skylights, they offer better heat insulation, and are silvered inside to reflect light down them. They can help to remedy seasonal affective disorder.
Figure 2.58 Classical mastery of daylighting: the Pantheon in Rome,
Italy. The building dates from around 200AD.
Source: © Clare Maynard
Figure 2.59 Angled reveal on a
skylight to admit more light into the room (the white paint also helps to reflect more light inside).
0.2m2 (2.15ft2), which can therefore let in a lot
of air.
Frames, lintels and sills must be insulated inside to prevent thermal bridging. Detailing is available online for free, for example at the UK Energy Saving Trust’s Enhanced Construction Details (ECDs) minisite (see the
Resources chapter). Figure 2.60 Light shelves can be positioned to reflect indirect summer light deeper into the room while blocking direct glare.
Figure 2.61 A sun tube
or pipe fitted into a roof, which takes light down to a windowless bathroom.
Source: (a) German Wikipedia, http://de. wikipedia.org (b) Sun tunnel image courtesy of Greenworks and Velux
(a) (b)
Figure 2.62 Shafts with reflective sides,
opening in a ceiling, channel daylight from rooflights deep into this building.
The apartment block shown in Figure 2.63 is located in Linz, Austria, and is almost 50 years old but in relatively good condition. The pictures show it before and after renovation in 2006, which made it exceed the Passivhaus Standard for energy efficiency by achieving an annual heat energy demand of only 11kWh/(m²a). Part of the reason for its astonishing success is due to an innovative cladding system, which the designers call the ‘Gap-Solar Façade’. It consists of a special cellulose honeycomb protected behind a glass facade. This is warmed by solar radiation creating a warm buffer zone in the honeycomb on the outside wall, which reduces heat losses from the interior. Efficiency depends on the amount of sunlight and the facade orientation. On the south-facing side, the losses over the heating season are drastically reduced, with an average dynamic U-value for the wall of approximately 0.08W/m²K. Other features of note are triple- glazed windows, including an anti-glare shield, decentralized mechanical ventilation with heat recovery and air heating, closing off the balcony openings with windows, high insulation and domestic hot water delivered by a district heating system.
Reference
Preisack, E. B., Holzer, P. and Rodleitner, H. (2002) ‘Raum-klimatisierung mit Hilfe von Pflanzen’, Programmlinie Haus der Zukunft des bm:vit, Neubau Biohof Achleitner, Gebäude aus Stroh & Lehm, p42
Figure 2.63 Apartment block in Linz, Austria, (a) before and (b) after renovating, including use of innovative solar
cladding.
Source: © IEA-SHC
not to. The city is Kunming, capital of southwestern China’s Yunnan Province. Perhaps construction companies in Kunming will complain at the cost of having to install these systems. Yet at just 3000 Renminbi, it represents only one half of a per cent of the total cost of the average house. It will pay for itself within three or four years.
Kunming is not alone in China. Rizhao – it means ‘sunshine’ in Chinese – has over half a million square metres of solar water heating collectors with 99 per cent of households in the central districts using solar water heaters and more than 30 per cent doing so in the outlying villages.
On the other side of the world in sunny California, families in solar-panel equipped homes are also enjoying free hot water. They have solar collectors to heat their swimming pools and pump water to flat collectors on the roof. The water is pushed through tiny tubes. ‘It’s almost the equivalent of the garden hose sitting in your yard. Turn on the faucet and hot water comes out’, solar expert Graham Owen of GoSolar Company explains. The California Energy Commission says 28,000 homes in the state are now solar and more families are installing it (NBC, 2010). According to the California Energy Commission and California Public Utilities Commission, Californian systems cost around $5000.
Most people usually associate solar panels with shiny electricity-generating modules. However, solar water heating is usually far more efficient and worthwhile an investment at a small to medium scale. The paybacks are quick. It is a well proven technology. In fact, solar thermal for heating and cooling has been the more affordable technology for the domestic and small business sectors that have been its majority adopters. Worldwide, it dominates the solar renewables market, accounting for 84 per cent, as opposed to solar PV’s 14 per cent, of installed power. In 2007, over 90,000 GWh of thermal energy created by over 235 million square metres of collector area deployed across the world
saved the emission into the atmosphere of over 40 million tonnes of CO2.1
In the US in 2008, there were 485MWth of domestic SWH systems and 7000MWth of solar pool heating (SPH) systems. Approximately 37 per cent of all SWH systems installed were in Hawaii, followed by 20 per cent in Florida, 7 per cent in California and even smaller quantities in the other states. With over 80 million detached single-family homes in the US alone, the untapped potential for SWH as well as space heating and cooling is huge.
Figure 3.1 Kunming City in
China, where solar water heating is mandatory on most buildings.
Source: Alex Wang
Figure 3.3 151.7GWth of solar thermal collector capacity was in operation worldwide by the end of 2008, corresponding to 217 million m2 of collection surface. Of this, 131.8GW
th were flat-plate
and evacuated tube collectors and 18.9GWth were unglazed plastic collectors. 1.2GWth of air collector capacity was installed. China and Europe accounted for 86.3% of the total installations. The annual growth rate for installations since 2000 has been 20%.
Figure 3.2 Solar heating
ranks ahead of wind power in meeting global energy demand, after wood- burning and hydroelectric power, when compared to other forms of renewable energy. It yields much more than PV. Renewable energy policies still do not recognize this. Source: © IEA China 0 10 20 30 40 50 60 70 80 90 Europe GW US &
Canada Japan Australia & NZ Africa Country Asia Israel & Jordan Central & S. America Solar Thermal Installations worldwide in 2008
In nineteenth-century America, prospectors and farmers used a black metal tank to heat water during the day to save fuel. Then, in 1891, Clarence Kemp patented the world’s first solar water heater, the Climax, in Baltimore, Maryland. By 1900, 1600 of these covered the roofs of homes in southern California, including one-third of those in Pasadena. The Climax was essentially a batch heater (see below), which combines the tank and heater. But by 1911, it was already obsolete; many new patents had been issued, including one for the Day and Night heater. William J. Bailey patented his Day and Night in 1909. He cannily separated the solar water heater into two parts: a heating element exposed to the sun, and an insulated storage unit tucked away in the house where it was warmer, so families could have sun-heated water at night and early the next morning. Just like modern collectors, the heating element consisted of pipes attached to a black-painted metal sheet placed in a glass- covered box. The use of narrow pipes speeded up the heating effect. In the face of this technological advancement, Kemp went out of business. By 1918, Bailey had sold over 4000 heaters. By 1941, half of Florida was using solar power to heat water. Why did this trend not continue? Again, we have the fossil fuel industry to thank: it was a campaign to undercut solar prices by utility company Pacific Gas and Electric that put an end to this growth and stopped solar power in the US in its tracks. The company supplied grid-connected electric water heating, with its promise of greater flexibility.
It was Israel that continued the evolution of solar water heating. In the 1950s, after the formation of the Israeli state, it experienced a fuel shortage and water heating was not allowed between 10pm and 6am. Engineer and entrepreneur Levi Yissar designed a new solar water heater and began marketing it through his company NerYah in 1953. By 1967, the year of the Six-Day War, 5 per cent of the population were using Yissar’s system (Figure 3.5).
But then, and not for the first or last time, conflict fuelled by the demand for oil in the Middle East worked against the interests of solar power. Cheap oil from Iran, and from oil fields that Israel had captured during this war, made Israeli electricity cheaper and the demand for solar heaters dropped. It took the oil shortage crisis of the 1970s to provoke the passing of a law that required the installation of solar water heaters in all new homes (except towers, whose roofs were not big enough). Today, 85 per cent of the country’s households use solar thermal systems. This is estimated to save 2 million barrels of oil a year – Israel has one of the highest per capita uses of solar energy in the world at
Figure 3.4 Horace de
Saussure, who invented the first solar oven in 1767. It was a well- insulated box with three layers of glass to trap thermal radiation that reached a maximum of 109°C (228°F).
3 per cent of the primary national energy consumption. On the nearby island of Cyprus, a large number of heaters were also installed.
Now, of course, there are examples of the SWH technology almost everywhere, establishing its credentials in most climates. In Germany, over 5 per cent of homes use SWH and over a million systems are installed. In the UK and elsewhere in the European Union with a similar climate, solar water heating has so far been used mostly to heat domestic water supplies in detached and semi-detached houses. But now effort is being put into introducing the technology into apartment blocks, hospitals, hotels and the commercial sector, just as it is in the Chinese cities of Kunming and Rizhao, and in California.