Aquaponics /akwəˈpɒnɪks/: a system that combines aquaculture (the raising of aquatic animals) and hydroponics (cultivating plants in water) in a symbiotic environment.
Earlier this summer we were contacted by John Grant of Sheffield Hallam University to ask if we were interested in participating in his PhD research into the domestic application of aquaponics. We were, due to…
- Desire for water efficiency – aquaponics counter-intuitively is claimed to use a fraction of the water used in conventional food production
- Low maintenance – aquaponics offers automated water provision and no weeding
- Problems with slugs decimating conventional crops
- High yield and the potential to raise different fish
- Concern about soil degradation, and interest in alternatives
- Opportunity to reuse surplus food-grade IBCs
We are also able to test a system in a domestic setting, whilst also demonstrating it to visitors on our public and educational tours.
John visited us in July 2016 to consider site options. The factors considered were:
- accessibility, as the system will need checking each day to ensure fish welfare
- orientation, to maximise light
- existing shelter, or potential cost of a new shelter
- access to water and power
- available IBCs, which had previously been used to store water on a smallholding.
The key factor was the availability of space in an existing polytunnel. This is about 200m from the homes and offers good light. Access to filtered water and to power had to be installed, and the challenge remains to stabilise temperatures to ensure fish welfare.
System design and build
Two food grade IBC tanks were used:
- one for the sump tank (700l) and one for a grow bed (300l)
- the other provided two grow beds
Cutting IBCs with a thin metal angle grinder blade proved surprisingly efficient and produced a clean smooth edge on the plastic. The alternative using a jigsaw would have been more difficult to control on the bendy sides and produced a rougher cut edge. There seemed to be the possibility of fine plastic dust created by the grinding although mostly the plastic melted when cut and a dust mask was worn to protect against this, along with ear defenders and goggles. The containers were swept and washed to remove this “dust”.
Measuring to create an accurate cutting line was difficult with the slightly rounded shape of the IBC. Best estimates need to be used.
Metal work cut easily and it took about 5 hours for all cutting of the IBCs. Creating a lid for the sump tank out of spare bits took about 1 hour. This minimized waste materials from adapting the IBCs.
Fish health and welfare is a key requirement and has driven the design. To keep the water cool, the sump tank has been sunk into the earth floor of the polytunnel. Whilst the temperature of the soil surrounding the tank will vary with the seasons, it will remain cooler than the air temperature in summer and warmer in winter. The degree of difference will be monitored and recorded as part of this project. There is the additional benefit of keeping the sump tank dark to prevent (or at least slow) algae growth. It was for this reason that we chose a dark tank, when initally we thought a light tank could be useful to mark water levels.
The main challenge with burying the sump tank is the pressure of soil on the sides of the plastic part of the IBC. This is averted to some extent by the use of metal panels in the centre of each side.
An inverted growbed was used to protect the sump tank whilst the soil was tamped down, as it protected the water from soil. This was then replaced with a lid, made from a timber frame and the ‘waste’ from the IBC that had been cut to provide two growbeds.
The fish tank is located over the sump tank. The factors considered as part of this decision are access to the fish tank, the simplicity of plumbing, and temperatures. These two tanks are placed next to the doorway with an area in which to put a small table on which to keep records for research. This area is slightly cooler than the centre of the polytunnel, and it is (in broad terms) preferable to give warmer temperatures to the grow beds and a cooler temperature to the fish tank.
The fish tank is offset so that dense concrete blocks can take the weight of the tank on 3 sides, and to allow access to the sump tank (allowing for the potential need to remove and maintain/replace the pump). This access is on the grow bed side of the sump and fish tanks to reduce the complexity of plumbing. The tank is being filled gradually both to limit impact on the availability of water to HHP residents, and to monitor the stability and level of the fish tank.
The fish tank is dark as this is the preference for the fish under consideration, but there is the risk that this will increase the temperature of the water. Another way to manage the temperature is to insulate the tank, and we are considering the use of sheepswool from the HHP flock.
The next stage is to install the grow beds. This needs to take into account:
- Accessibility for planting, including the rinsing of roots, and harvesting
- Plumbing – length and complexity; any impact on accessibility
- Shading of other planting areas
The two options considered were linear and keyhole.
Keyhole: a permaculture approach which minimises path to bed ratio, reducing the distance travelled to work on a bed. This has a particular value with aquaponics as plant roots must be cleaned prior to planting. Plumbing would be to the rear of the beds, with ease of access dependent on the distance of the beds from the polytunnel wall. Planters can be placed at the end of the paths, and potentially incorporated into the aquaponics system at a later date. Additional beds would be added in a similar fashion.
Linear: A more efficient approach in terms of materials used as plumbed routes are marginally shorter (the above diagram is not to scale). The pipework from the fish tank to the growbeds, and from the growbeds to the fishtank each have one less joint. It also allows for planting on a 20cm strip on the south of the polytunnel. The access path will need to be wider than for the ‘keyholes’ as it will need to allow for a working area to clean roots. Additional beds could leave a break to allow easier access to the south edge, with plumbing bridging any gap.
The impact on ease of use will only be fully understood from practice.
Over the past 18 years we’ve hosted thousands of students of energy, water, and environmental sciences but increasing number of visits from other strands of academia is both heartening and fascinating.
Recently we hosted Nottingham University’s School of Mathematics, as part of their work on MASS: ‘Modelling and Analytics for a Sustainable Society‘, and are delighted to hear we were cause for both inspiration and optimism.
“HHP showed me that I was wrong and it is possible to live in a (much more) sustainable way without diminishing our quality of life. I would even argue that the ‘Hockerton lifestyle’ might even be far more enjoyable than the busy, consumption-focused lifestyle most of us enjoy”
“Highlights on the day included “the house tour as we got to see how it all came together in reality”, “the aquaponics, as this was not something I was aware of before, the conservative and careful use of water (e.g. less filtered water for showering and the toilet), their own water filtration systems and being off the grid for water”.
“[we] were all surprised at the toasty warm floor despite the absence of any central or secondary heating!”
You can read their views in full here, or contact us to find out how we can bring your area of work or study to life for your students, colleagues or clients.
Today the Committee on Climate Change published its ‘Next Steps for Heat Policy‘.
Heating and hot water for UK buildings make up 40% of our energy consumption and 20% of our greenhouse gas emissions. It will be necessary to largely eliminate these emissions by around 2050 to meet the targets in the Climate Change Act and to maintain the UK contribution to international action under the Paris Agreement.
It’s been widely welcomed for highlighting the stalling of Government policy in recent years. But one point sticks out to us in particular:
New-build. Buildings constructed now should not require retrofit in 15 years’ time. Rather, they should be highly energy efficient and designed to accommodate low-carbon heating from the start, meaning that it is possible to optimise the overall system efficiency and comfort at a building level.
The document expands on the potential for heat pumps and district heating, but where is the option of zero-heating? Why not build homes so they don’t need central heating? Whose heating system helps with summer cooling? And use solar PV and wind to top up efficient immersion heated water stores when renewable power supply surpasses time-critical demand?
It can be done, with existing technology and skills, at roughly the same cost as a new home built to building regulations alone, and here’s our energy use from the last 15 years, and a related temperature study to prove it.
The average energy use by the homes at Hockerton Housing Project has consistently been less than a third of that used by the ‘average’ UK household, and two-thirds of that demanded by the Passive House standard.
So why is this approach not being followed more often?
- The Government’s preferred energy performance calculation (RdSAP and SAP) can’t calculate the benefits from interseasonal storage.
- There is no great commercial incentive to lobby for this low-tech and affordable approach. It profits residents rather than manufacturers or standard-setters.
- There’s an assumption that high thermal mass, in the form of concrete, is inherently bad. It’s not if it removes the need for heating, reduces maintenance, and increases the durability of the home. Parity with timber-framed homes is reached at about 20 years.
- That’s it.
And here’s the small print:
- 5 homes, averaging 2 adults, 1-2 children
- Increase use over time reflects increased home-working and children becoming teenagers. Savings in the general population are not mirrored as homes at Hockerton have always had energy efficient lightbulbs, sought the most efficient appliances, and had energy-aware residents.
- Temperature tracking was undertaken when home was drying out and with low occupancy in that first winter, so not a perfect study, and overheating is now minimised through shading of conservatory sunspaces during summer. Even before this, the instances of overheating met the requirements of the Passive House standard.
- When space heating is required, it can be delivered by small electric heaters with far lower capital and operational costs. Such occasional use is included in the usage graph above.
- The ‘average household’ energy use data is taken from UK Government statistics for household energy use.
- Readings are taken manually so some of the quarters are thirds, or very small quarters. One particular peak can be put down to our Christmas party in 2012! If anyone wants to fund/test automated reads, do get in touch!
Every 3 – 4 months we read our 50 power and water meters to check how we are doing in terms of consumption, generation and export.
Each household pays for their share of consumption relative to use, with any income from the export of renewable energy shared equally between us.
The resultant figures help us remain aware of our use, not least because we see it relative to (or in competition with?!) our neighbours. It also reminds us how well these houses perform. This can become easy to forget when the house is your home – until heatwaves like this week, when we could feel the difference as the thermal mass soaked up any heat that made it through shaded windows.
* Our average daily energy use was around 23% of a standard house (per house, not incl the garages).
* We exported 38% of what we generated, compared with 48% in the winter
* We earn around 4p for a kWh exported but pay on average 7.5p per kWh we use, so over the last 4 months we’ve missed out on energy worth £145.
* In the last 4 months we’ve generated the equivalent of 95% of our total household use (not including our shares in our community-owned wind turbine of course).
* And we are using 260 litres of water a day per house on average. Potable: non-potable is 1:11. This is a similar ratio to that in the first quarter but an increase overall. Average usage per person is 82 litres, compared with Code for Sustainable Homes Level 5 and 6 target of 80 litres – perhaps due to higher number of washes during peak vegetable gardening season!
A 2 bed eco home, based on the Hockerton Housing Project design, has come up for sale.
This is a private sale, but if you want to find out more (price available on application), please contact us and we’ll pass on your details to the seller.
Half acre incl meadow, lake and woodland
View from above
The semi-detached bungalow is on a plot of land adjoining the Project. It was built by some of the original project members so shares the key design details and, importantly, has delivered on its promised performance. The house is south-facing, with a conservatory to the south overlooking a half acre of grounds and a car-port, storage and entrance area to the north.
- Built with high thermal mass, super insulation, buffer zones and high passive solar gain to capture heat in summer and avoid use of heating in winter.
- Earth sheltering helps insulate the home and minimises the impact on the natural environment.
- Triple glazed /low E/gas filled units.
- Mechanical ventilation heat recovery.
- Electric car charging port.
- Energy costs of about £500 a year, less than half the national average.
- Water is supplied through a shared rain water catchment and storage system.
- There is no mains sewage system in the village. The house shares a septic tank and floating reed bed sewage treatment system.
- Boot room with storage.
- Utility /shower room including hot water cylinder, sink, washing machine and storage together with basin, wc, shower and towel radiator.
- Inner hall [3.1m x 3m] currently used as office and library.
- Kitchen/ dining area 6.2m x 3m, with tall glazed French doors with windows over leading into the conservatory.
- Sitting room 6.2m x 3m. Window on north wall and tall glazed French doors with windows over leading into conservatory. The rear section of this room [2.2m x 3m] could be adapted to form a third bedroom.
- Master bedroom suite includes a dressing area [3m x 1.45m], shower room [1.6 x 3m] and bedroom [3.2m x 3m] with tall glazed French doors with windows over leading into conservatory.
- Bedroom 2 [3.2m x 3m] with mezzanine floor over. Tall glazed French doors with windows over [3.25m x 1.8m] leading into the conservatory.
- The fully double glazed timber conservatory [12.6m x 3m] has 4 velux roof lights and a wood burning stove.
- Double french doors lead into the south facing garden approx 24m x 45m with a shared large pond. There is a hedge to the west boundary and woodland leading down to the stream to the south boundary.
- Total internal floor area approx 127m2.
- There is a phone and super fast Broadband connection. No TV points.
- The property is leasehold with a 999 year lease subject to a token peppercorn ground rent.
- Maintenance of the septic tank sewage system and rain water catchment system is shared with the adjoining dwelling.