HEATING | LOW-ENERGY GREENHOUSES To minimise carbon emissions, developers behind two huge greenhouses in East Anglia are using heat from nearby wastewater treatment plants to provide perfect growing conditions. Phil Lattimore reports on the innovative engineering behind the facilities GROWING INTEREST C ould two new sustainable giant greenhouses being built in Norfolk and Suffolk be part of the answer to a growing problem? Sustainability and reducing greenhouse gas (GHG) emissions are increasingly important issues for the agricultural sector, which is estimated to account for up to 9% of total GHG emissions produced in the UK. The National Farmers Union (NFU) is targeting net-zero emissions in British farming by 2040, and while most of the sectors GHGs come from sources such as methane produced by cattle and nitrous oxide released by fertilisers, the food supply chain from transport and distribution to infrastructure and buildings has a key role to play. The recent announcement that two of the largest greenhouses in the UK are to be powered by low carbon sustainable energy sourced from waste heat from water recycling centres is, therefore, a significant development. And, its backers claim, it could offer a model for the decarbonisation of agriculture in this particularly energy-intensive, and conventionally energyinefficient, part of the sector. Sustainability The two innovative greenhouse developments are located at farmland sites near Norwich and Bury Crops are grown on a hydroponics-based vertical system St Edmunds, covering 16 and 13 hectares respectively a larger area than Londons O2 arena and use more than five times as much glass as The Shard. They are part of a 120m project being developed by Oasthouse Ventures thats backed by asset management firm Greencoat Capital (the UKs largest investor in renewables). The carbon footprint of the food produced there is expected to be 75% lower than equivalent European greenhouses, and Greencoat estimates they will be capable of producing 20 tonnes of tomatoes a day some 12% of the UKs needs. The 7m-high greenhouse structures, which are being built by Dutch glasshouse specialist BOM Group, rely on a hydroponics-based vertical growing system that includes 177km of growing gutters for a range of plants and vegetables. Conventional gas warming will be replaced with heating supplied via closed loop heat pumps that use waste heat from nearby wastewater treatment plants run by Anglian Water. The Smart Energy Services business unit at Irish utility Electricity Supply Board (ESB) has been selected by Greencoat to design, install and manage the closed loop heat pump system, as well as combined heat and power (CHP) plants at each site. The CHP units will provide electricity to power the heat pumps and will also transfer supplementary CO2 into the greenhouses to accelerate crop growth, recapturing a high proportion of the carbon created. All of the heat and electricity produced by the CHP units will be used on site, making it one of the most efficient CHP systems in the UK, according to ESB. The systems being developed by ESB will constitute the highest installed capacity of heat pump technology so far in the UK, capable of generating a combined total of 70MW peak of thermal power. The system will also result in the treated water outflows from the recycling centres being cooled sufficiently before they are released back into the river, benefiting local ecosystems. www.cibsejournal.com November 2019 51 CIBSE Nov19 pp51-54 Heating Tomatoes.indd 51 25/10/2019 15:29