Blue sky thinking for green build

Cover story

4 renewable energy focus Green Building supplement November/December 20084 renewable energy focus Green Building supplement November/December 2008

Blue sky thinking for green buildDESPITE BEING A GOOD FIRST STEP, SUPERINSULATED, HIGH THERMAL

MASS BUILDING ENVELOPES AND PASSIVE TECHNOLOGIES CAN ONLY GO

PART WAY TO ACHIEVING BUILDING TARGETS SET BY GOVERNMENTS IN

MANY COUNTRIES; ACTIVE RENEWABLE ENERGIES WILL BE NEEDED TOO,

AND BUILDINGS WILL HAVE TO BECOME THEIR OWN POWER GENERATORS.

BUT WHAT TECHNOLOGIES WILL BE READY AND MATURE ENOUGH TO

ENABLE THIS, ASKS GEORGE MARSH?

Governments have been setting dates by when

they want new homes and other small premises

to be zero carbon, zero energy or both. The

UK, for example, wants net zero-carbon homes

by 2016.

Despite the renewables industry forging ahead

with micro-generation technologies in the hope

of addressing this need, many people, such as

Dr David Strong, ceo of RES subsidiary InBuilt

Consultancy Ltd, caution that active renewable

technologies should not be seen as a panacea

– rather energy effi ciency and passive renewa-

bles should always be targeted fi rst. Unfortu-

nately, he acknowledges, passive benefi ts derive

largely from intelligent architectural design, and

do not have the commercial push behind them

that actual “devices” have.

He also regrets that highly visible technologies

are often favoured over lower-profi le solutions

that may, nevertheless, be more productive.

For example, a well conceived ground source

heat pump installation, he says, though virtu-

ally unseen, can be more eff ective than a micro

wind generator.

Another specialist who has as much know-how

and practical experience in this area as almost

anyone else alive is British architect Bill Dunster.

He and his team at Bill Dunster Architects ZED

Factory Ltd have been responsible for several

noteworthy zero-energy (fossil) developments

(ZEDs). Most have been wholly or partially resi-

dential. And while the majority have been in

the British Isles, where the variable nature of

the climate complicates the challenge, Dunster

has also been responsible for projects in conti-

nental Europe, China and elsewhere.

When can renewables fi t the bill?

When it comes to renewable energy technolo-

gies, Dunster emphasises that much depends

on geographical location, climate and housing

density. For UK/north-western Europe and

densities of under 50 dwellings per hectare,

Dunster favours solar and biomass solutions.

Typically, he might specify the use of evacu-

ated tube solar thermal systems located on

south-facing elevations to provide domestic

hot water for half the year, and a wood pellet-

powered boiler for the other half of the year

when solar energy is scarce.

He is also an advocate of solar PV, integrated

into roofs and facades. He argues that payback

for solar PV can be faster than detractors

suggest, especially in countries that have good

incentive schemes – such as Germany – not to

mention regions where electricity is expensive

(California, for example). Obviously the type of

PV technology varies enormously according to

country/application etc., but as far as the UK

goes, he says, “working with an 8% escalator

for the price of fossil fuel, which we consider

realistic in the long run, and buying PV in bulk,

we achieve payback of less than 12 years in the

UK. In France, it’s less than fi ve years because

of the better fi nancial incentives there. We

specify high quality monocrystalline PV

because available roof area is limited and we

therefore want high conversion effi ciency. The

technology is proven, there’s minimal technical

risk and it so happens that this type of PV is

best for durability as well.”

A number of the partnership’s buildings also

feature micro wind generation, but only where

siting conditions are favourable. As Dunster

contends, “having a wind turbine for every plot

is worthwhile only if the location is well

endowed with wind resource and there’s a

good master plan. Community-scale wind can

be better, and we have included it in develop-

ments such as Jubilee Wharf in Cornwall.”

This mixed-use development, completed at

Penryn in 2006, has workshops, a community

hall, café and 6 maisonettes. Four pole-mounted

6 kW Proven wind turbines together with a 75

kW communal wood pellet boiler provide power

for water and under-fl oor heating. An evacu-

ated-tube solar thermal system preheats the

water throughout the year. Given a highly

energy-effi cient building structure with high

thermal inertia, super-insulation to about three

times conventional building standards and

eff ective sealing against entry of unwanted

George Marsh

ref_green_build_p4_11.indd 4ref_green_build_p4_11.indd 4 03/11/2008 12:02:0103/11/2008 12:02:01

renewable energy focus Green Building supplement November/December 2008 5

Building/Renewable Energy


outside air, these renewables are said to make

Jubilee Wharf a zero carbon and near-zero

energy development. The future addition of

more wind turbines and solar PV allowed for in

the master plan should enable the develop-

ment to export energy to the grid.

For higher density developments of 50-100

dwellings per hectare, Dunster does not rule

out biomass combined heat and power (CHP),

despite mixed experience at the practice’s early

fl agship scheme, the Beddington Zero Energy

Development (BedZED) in the London borough

of Sutton. This project was a joint venture

between Dunster Architects, BioRegional

Developments and the Peabody Trust housing

association. Unfortunately, a 100 kW wood-

chip-fuelled CHP installation that has provided

heat and power for some 240 residents and

200 working people is currently unserviceable.

According to Dunster, the plant was incinerating

wood at too low a temperature and this led to

a build up of carbon that eventually compro-

mised operation. He points out, however, that

the CHP technology used at BedZED, which saw

its fi rst residents in 2002, is a decade old and

that “we are in a diff erent place now” with the

latest biomass CHP generation. He predicts that,

once present funding diffi culties are resolved,

CHP will return to BedZED and start contributing

again. Biomass-CHP economics should, he says,

improve as community-scale schemes become

commonplace, leading to shared use of mainte-

nance assets.

BedZED also features Dunster’s trademark roof-

mounted wind cowls – downwind-swivelling

ventilating cowls that incorporate passive heat

exchangers for recovering heat from outgoing

stale air. As these cowls require some wind to

be fully eff ective, they can be said to rely on

renewable energy.

Dunster says that systems performing well at

BedZED are those that are simplest with the

fewest moving parts.

Experience has reinforced his preference for

technologies that are mature and well proven

with long track records. He points out that

active renewable technologies may not be

appropriate unless the building structure is

engineered to require only small amounts of

energy for space heating and cooling, water

heating and other functions. This implies high

reliance on passive technologies such as storage

of heat/cool within the building structure (high

Despite the renewables industry forging ahead with micro-generation technologies in the hope of addressing this need, many people, such as Dr David Strong, ceo of RES subsidiary InBuilt Consultancy Ltd, caution that active renewable technologies should not be seen as a panacea – rather energy effi ciency and passive renewables should always be targeted fi rst.

Continued on page 8...



6 renewable energy focus Green Building supplement November/December 2008

Case study: Build in Freiburg

Vauban (images – below)

After the second world war, French soldiers

moved into barracks on the outskirts of

Freiburg. After the troops moved out, this

offered the city the opportunity to create

a model residential area for 5000 people,

just minutes away from the city centre;

One feature is the energy concept, which is

based on the wood-chip fi red cogeneration for

district heating. A number of buildings, many

of them passive houses, are equipped with

solar thermal or PV installations and almost all

were subsidised by Badenova (the local energy

supplier);

The project’s structure integrates legal, political,

social and economic actors from grass-roots

level up to the city’s administration;

An ecological traffic/mobility concept is

implemented with a reduced number of

cars (40-50%), which are parked in solar car

parks on the edges of the development.

Public transport is at the heart of Vauban,

with a tram system that goes into the

heart of the development;

The development is made up of joint building

projects, about 30 groups of building owners, a

co-operative (Genova), and a self-organised

settlement initiative.

Solarsiedlung an Schlierberg (see images above right)

With 58 “Plusenergiehäuser” in total and

one combined residential and office block

– the Sonnenschiff – the Solarsiedlung am

Schlierberg is reputed to be one of the

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most modern solar housing projects in

Europe;

The development´s structure is focused on

the circuit of the sun. All the terraced houses

face south, and the distance between the

rows of houses is designed to guarantee

insulation over the winter;

The community´s supply of heat is provided

by a local network of solar energy. The heat

is generated by hot water vacuum collectors

on the ‘Sonnenschiff ’ and a central timber

power station which supplies heat and elec-

tricity. Thus, energy is generated in an exclu-

sively regenerative way;

Solar energy plants on the roof of the houses

turn solar radiation into electricity. The elec-

tricity produced is fed back into the public

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grid and generates a profi t of at least 0.42

€/KWh for 20 years;

“Plusenergiehäuser” aim to cover the total

energy requirement of the house in a

regenerative way and even to produce a

surplus. Therefore, each of the houses has

a solar power station of its own on its roof

with an output of 3,0 to 12,0 kW, depending

on the size of the houses;

All the “Plusenergiehäuser” share the same clear-

cut layout concept: The large windows and the

main living rooms behind them face south. This

makes the rooms very bright, and the heating

of the houses is performed by the sun;

Information courtesy of www.rolfdisch.de

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The Solarsiedlung am Schlierberg: Solar energy plants on the roofs of houses turn solar radiation into electricity.

The Vauban district – home to 5000 people – includes many innovative house designs; the development of units was implemented by individual groups of diff erent social status (no

commercial property ‘developers’ were permitted to buy land), and the resulting diversity of housing and community is striking. Vauban also contains one of the fi rst “Passive Houses” (right),

which demonstrates that a building can have 80% less CO2 emissions than a traditional building.


http://www.rolfdisch.de



thermal inertia); maximising the solar energy

that enters the building naturally; and massive

insulation against heat/cool loss.

Dunster has little use for ground-source heat

pumps in individual north-European proper-

ties. For most developments, he contends,

there would be insuffi cient ground area to

enable devices to produce more than a token

amount of energy, perhaps not even enough

to exceed that needed to drive the system.

The alternative of digging deep boreholes is

expensive and not always feasible. Even so,

Dunster’s team continues to keep heat pump

technology under review, as a potential

means both to exploit ground heat and to

recover exhaust heat from buildings. Similarly,

micro CHP is being monitored as having

future potential.

For densities of 100-200 dwellings per hectare,

Dunster adds that he is looking towards possible

future use of synthetic gas (syngas) made from

waste, and fuel cells. Upper storeys of buildings

would, however, still incorporate substantial solar

PV. The highest dwelling densities, of 200 or

more per hectare, will inevitably be high-rise

towers and for these Dunster envisages building-

integrated wind as well as some PV and biomass-

CHP.

On display

A chance to see Dunster’s ideas translated

into reality was aff orded by this year’s

EcoBuild exhibition at Earls Court, London.

Among the several “green” homes on display

was the ZED factory’s RuralZED house,

intended for the “under 50 homes per hectare”

scenario. The timber-framed prefabricated kit

house, which can rapidly be assembled on

site, gains energy self-suffi ciency from the use

of solar roof panels and a biomass boiler

fuelled by wood chips.

RuralZED owes much to the earlier evolution of

Dunster’s own home, Hope House, in which

technologies currently in place include a small

wood stove for space heating, an automated

pellet boiler for domestic hot water in winter,

solar thermal collectors providing hot water

from spring to autumn, a 1.1 kW peak PV array

and a 600 W wind turbine. Adapting the house

design for factory construction, producing in

volume and buying in bulk have enhanced

aff ordability.

According to Dunster, “you could move into a

RuralZed home today and your total monthly

payments, including mortgage and utility bills,

will be not higher than for a comparable new-

build conventional home.”

Another concept aired at EcoBuild was the

Sigma home designed by the PRP Architec-

tural practice and produced by the Stewart

Milne Group, well known for its timber-framed

housing (see image on page 10). Features

include passive ventilation via an open stair-

well and integrated solar thermal, solar electric

and micro-wind renewables.

Developed as an experimental project, the

building will be monitored over the next

two years, with families living in it much of

the time, so that its performance can realis-

tically be assessed. Interestingly, Stewart

Delgarno, director of product development

with the Group, places a higher premium on

effective building fabric and passive tech-

nologies than on active renewables, at least

as incorporated into individual homes.

“There’s more work to be done on micro

generation technologies before they are

mature enough to make a significant contri-

bution,” he says. “That time could be 10

years away. More focus is needed, for

instance, on the way systems interface with

the building and with each other.”

Delgarno believes that certain technologies,

particularly wind and CHP, are not well suited

to application on the scale of individual plots

and that implementing them on a larger,

community scale is a more promising

approach. Of those that could nevertheless

be suitable at the plot-specifi c level, he

regards solar thermal as the most productive.

He believes solar PV to be still too expensive

and micro wind to be useful only in a few

locations where there is adequate wind

resource and little turbulence. He points out

that an eco home, with its high specification,

could cost up to 40% more than a compa-

rable conventional house. Active renewables

at the level incorporated in Sigma could

account for some £40,000 per unit.

An eco home that can be inspected at the

UK Building Research Establishment’s (BRE)

Innovation Park at Watford near London, is

the Kingspan Lighthouse from Kingspan Off-

Site. This features a 2 kW wood-pellet

biomass boiler, a wind catcher for mechan-

ical ventilation with heat recovery, plus solar

electric and solar thermal arrays integrated

with a 40 degree pitched roof. Solar thermal

generates all the hot water in summer and

some in the spring and autumn, reducing

demand on the biomass boiler and the

amount of wood used. PV panels of 46 m2

area supply 4.7 kW (peak) for the whole

house.

The super-insulated, airtight timber-based

building includes external shutters for solar

control. Smart meters monitor and record

energy consumption. As an alternative to

plot-specifi c micro generation, Kingspan says

the building can easily be connected to

larger-scale renewables serving multiple

homes. In this case, local wind turbines of 45

kW to 400 kW could be included and biomass

options could typically extend to a 450 kW

boiler or 100 kWe biomass CHP.

Innovative use of a ground source heat

pump distinguishes another of the Innova-

tion Park’s buildings, the Hanson EcoHouse.

External paving allows rainwater to pass

through it and into a tanked sub-base. This

Visible technologies are often favoured

over more productive lower-profi le

solutions; a well-conceived ground

source heat pump installation though

virtually unseen can be more eff ective

than a micro wind generator.

Continued from page 5...




combines with a layer of flexible piping

linked to the heat pump to provide space

heating and domestic hot water. The house

also features a solar collector. Photovoltaics

and a mechanical heat recovery system could

be added to move the home further up the

sustainability scale.

Another heat pump solution, this time air-

sourced, serves the Barratt Green House, which

was the fi rst home to be constructed on the

Innovation Park by a mainstream builder.

Conceived by Barratt PLC, the house extracts

thermal energy from the air to heat the house

and hot water. Use is also made of passive

solar heating, while computer controlled shut-

ters limit heat build-up from strong summer

sunlight. Solar PV on the south-facing roof

provides electricity for the home’s electrical

equipment. Mechanical background ventila-

tion ensures the house has clean, fresh air. The

house is also designed to be part of a cluster

of homes connected to a district electricity

generating/heating system.

Experience gained from two years of inten-

sive testing of this house will benefit a

development due to be built on the site of

a former hospital near Bristol in the UK.

Selected as preferred bidder by English

Partnerships, the Government’s national

regeneration agency. An on-site biomass

powered CHP plant will deliver energy to all

homes and commercial premises in the

development.

Also involved in the project are HTA Architects,

ARUP, Kingspan Off site and the Sovereign

Housing Group. The Hanham Hall hospital site

was the fi rst site identifi ed under English Partner-

ship’s Carbon Challenge, an initiative intended to

deliver zero-carbon homes and communities as

examples to show that high sustainability targets

are feasible – and can be commercially viable.

Existing stock

New zero energy developments attract wide-

spread interest, but reality requires emphasis

on the vast stock of existing premises. At this

year’s annual Micropower conference,

Stewart Purchase, managing director of

heating specialist Viessmann UK, concluded

that a combination of solar thermal heating

and condensing boilers was the best option

today for consumers. Solar powered hot

water is the system most widely taken up at

present. Boiler efficiencies can be enhanced

still further by capturing energy from flue

gases with devices like Energy Saver and

EnergyCatcher.

Emerging technologies will augment future

choice, both for new developments and for

refurbishment of existing stock. Ceres Power

and Centrica, for instance, are collaborating to

bring fuel cell based CHP to the typical home.

Another concept aired at EcoBuild was the Sigma home designed by the PRP Architectural practice and produced by the Stewart Milne Group, well known for its timber-framed housing. Features

include passive ventilation via an open stairwell and integrated solar thermal, solar electric and micro-wind renewables.




Ceres is striving to make a wall-mounted fuel

cell CHP unit it has developed more aff ordable,

and expects to start residential trials within a

few years. Centrica is part-funding the project

and has placed a forward order for 37,500 CHP

units.

However, Martyn Coff ey of Baxi told Micro-

power delegates that the Baxi Ecogen, a micro

CHP appliance that can replace a wall-hung

boiler, will be available from next year, well

before fuel cell technology is ready for market.

Ian Stares of Energetix made a similar point for

Genlec, another relatively low-cost micro CHP

replacement for existing boilers. Meanwhile, stove

manufacturer Aga, noting that de-ashing wood

and solid fuel burning stoves can be a chore too

many for busy modern householders, has trial led

a wind-powered version of the iconic Aga!

Micro CHP, fuel cell based or otherwise, will

have its place, particularly in refurbishments.

However, many experts argue that large units

feeding multiple premises provide better

results. They champion community-scale

biomass CHP, as was pioneered at BedZED, as

the way forward.

Similarly, heat pumps can become more viable

when applied on a scale above that of individual

units. Thus ground-source heat pumps supplying

heat to six, 1950s-built homes in rural Hampshire,

UK, were recently installed as part of the Wood-

fi elds low-energy refurbishment project.

A number of cities, including Southampton on

the UK’s south coast, are embracing commu-

nity-scale CHP. A large plant planned for the

city’s Millbrook area is expected to provide

district heating for over 4000 households, 8

schools and 9 public buildings. About 50 MW

of electricity produced by the plant will provide

power for some 85,000 homes. Altogether, the

plant could deliver almost 80% of Southamp-

ton’s pledged carbon emission reductions,

saving 170,000 tonnes of CO2 per year. CHP is

also expected to be central to a large mixed-

use development planned by the City Council

for the site of a former shipyard.

Additionally, renewables are key to a district

heating scheme that Southampton has been

running since 1986. Water heated geother-

mally by hot rocks a mile below the city centre

is used to heat homes, offi ces and retail

premises around the centre. Briny water rises

up the geothermal well at 76 degrees C, and

passes through a heat exchanger, working in

conjunction with an absorption heat pump.

Spent brine at about 28 degrees C runs out to

the sea, having transferred its energy to clean

water in the heat exchanger. It is this clean

water that is circulated to premises.

CHP generators provide power for circulation

pumps and other associated plants, “waste”

heat from the CHP being used to augment the

geothermal heat. In summer, the absorption

heat pump provides cool water for the chilling

system of a fi ve-star hotel and for premises in

a major retail area. An innovative ice storage

system uses electricity from the CHP to fi ll the

store with ice at night, this then being utilised

during the day to provide cooling.

Southampton plans to augment its scheme

with energy-from-waste, fuel cells and other

sources in the future.

NB: Readers wishing to know more about Bill

Dunster’s visionary ideas and how they have

been expressed in sustainable buildings can fi nd

detail in the ZEDbook, recently published by

Taylor and Francis.

Joint authors Bill Dunster, Craig Simmons and

Bobby Gilbert clearly set out principles for sustain-

able living, building and upgrading to zero

carbon standards, and use of renewable energy

sources.


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Blue sky thinking for green build