Project: Radical Water Retrofit of Victorian Semi
and Garden
Domestic: Nottingham Ecohome and urban permaculture
garden
 |
| vertical panorama showing green roofs and sustainable urban drainage |
The central aim of our radical eco
retrofit of a Victorian semi and garden was to see how far we could reduce our environmental
footprint through a systems approach to management of our energy, water and
food requirements. Our privately funded, ‘Whole Plot’ experimental approach to
retrofit led to the integration of water systems for the house and garden.
Through a range of internal and external measures and behaviour change, our
potable water use has been drastically reduced to around 55L pppd against UK
average of 150L and rainfall outlets and other surface water, which formerly discharged
to storm drains, is now 100% managed on site.
The whole site water management
strategy was undertaken to determine whether it was possible for a building and
the plot on which it sits to better manage the drought / deluge cycle that the
UK faces. Rainwater harvesting potential was limited by roof area and size of
garden meant soakaways were not feasible. Attenuation tanks were possible
because of reduced run-off. Also, collection efficiency reduces in heavier rain
(WISY filters).
Internal and external measures:
Internal
Rainwater
harvesting system supplies toilets, washing machine and irrigation – estimated
to meet 20% of total water demand. Saved 122m3 potable water over 14 years (note: the system was down for 2 years)
·
Ultra low flush
(2/4L) Ifo Cera toilets (x3)
·
Low flow
aerating shower heads – Ecocamel ‘Halo’
restricted to 6 l/m
·
Low dead leg
design using microbore pipes for hot and cold water and minimising distance to
mains pressure cylinder
·
Water saving
bath – 130L capacity
·
Highly
efficient washing machine – 39L / 6 kg load
·
Dishwasher –
Bosch 6L /cycle on eco setting (1820 l / year – the most water efficient model
in EU), hot fill from solar and wood heat
·
Behaviour
change
External measures
·
Installation of
sustainable urban drainage systems including attenuation tanks to front and
back gardens.
·
Porous surfaces
throughout – 30m2 tarmac
taken up
·
Installation of
4 edible green roofs for garden structures approx 8m2 delays and reduces run off
·
Innovative
design of horizontal wall mounted water butt to collect run off from green
roofs and use for irrigation
·
French drain
around building
·
Pond for
wildlife and aquatic food plants
 |
| House and garden work together - it's a whole plot approach to living |
Rainwater harvesting is estimated to
produce more CO2 than mains (due to pump energy, equipment and maintenance) but
other measures have CO2 benefits from pure savings and better management. Showers, hot fill dishwasher and low dead-leg
designs save additional CO2 as they save hot water.
Assuming 50% of the saved water is cold and 50%
hot, heated from 10ºC – 40ºC,
Hot water assumed to be generated by 50%
electricity (cheap rate immersion) with remainder met by renewables,
For hot water, energy saved per year 50 L pppd x
365 x (40-10º) x 4.187 kJ/kg.K = 2,292,383 kJ = 637 kWh / year,
Assuming cheap rate electricity @ 7.55p/kWh gives a
saving of £48.09 and assuming 0.56 kg CO2e/kWh on brown tariff, CO2 saved = 357
kg / year
Payback didn’t come into our strategy as water is so cheap, we wanted to
test out a range of emerging measures. Some costs are integrated into other
things such as hot water system.
Estimated cost of all water saving / management measures = £10,000
Surface water charges £60 / year saved
Cost of potable per m3 = £1.52
Saving 100L pppd x 4 people x 365 = 146m3
Saving is £1.52 x 146 = £222
Total saved / year = £60 + £222 = £282
Payback = all measures £10,000 / (water cost saving
£282 + energy cost saving (hot) £48.09) = 30.3 years
(Does not account for pump electricity or
maintenance costs for rain harvesting or fluctuations in charges - based on
current charges. Includes savings due to
behaviour, which need no outlay.
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