HEATING | LOW-ENERGY GREENHOUSES system circulation pumps at the water recycling plant outflow are also duty/standby to ensure adequate redundancy in the system. Off the shelf The outfall from the sewage works is 3K or 4K higher than a typical river temperature CHINAS GREENHOUSE CITIES Lolli Olafsson is the founder and CEO of Geyser Thermal Energy, a sustainable energy and water treatment solution specialist that has been working on a huge, low carbon greenhouse project in China along with partners Qanbridge and FreshTeq, led by Tjerk Gorter and plant growth and water specialist Arnoud Tieleman. Plans are under way to construct massive agroparks across three provinces, covering around 100 hectares, with state-of-the-art greenhouses of 40-50 hectares that are designed to reuse 90% of their energy, with no use of pesticides and minimal use of water. We know that the future of food is going to be in sustainable greenhouses that are part of integrated fresh food chains, from seed to eat, says Olafsson. The more we can grow products locally, the more we can reduce our carbon emissions. Weve been working on a new, exible, next-generation design that will allow crops to be grown anywhere in the world at any time a breakthrough that will enable year-round production, which at the moment in many climate zones is not feasible. It will be low cost, and our aim is for them to be carbon neutral and use heat easily from any renewable source available. Innovative water treatment systems ensure water can be reused and not wasted. Hydroponic or aeroponic systems can be used, and the water and air treatment systems which are more effective than UV light mean the facilities are pesticide and chemical free. Lights above the plants will kill any bacteria or mould that may get in. Waste from the plants, such as old root systems, are reused, so no nitrates are released into the atmosphere; they are used to generate heat and biochar, a natural organic product that is used to clean water and air in the treatment system. A new revolution in fresh food is on its way, and it will most likely take place in China . insulated pipe, it makes it very cost-effective. What we potentially lose in the winter, we gain in the summer. The sites have a thermal store, so on particularly hot days that store can be charged, says Lawson. Roughly calculated, it would take around 3.5 days for the heat pumps flat out to charge that store from cold to hot. The conventional method of heating a greenhouse would be using a CHP to power an electrically led system, with a lot of the heat energy being discharged. But the systems used at the two sites are far more energy efficient, explains Lawson: In these systems, were supplying just the right amount of heat to meet the demand. We have multiple heat pump units in cascade 16 on the Norwich site and 13 on the Bury St Edmunds site, each one around 2.4MW and each has the ability to modulate, so we only have the required heat produced to meet the demands of the greenhouse. This system enables maintenance on heat pump units to be carried out at times of lower demand, so as not to affect capacity. The heat exchangers and While the scale of the East Anglian projects is challenging the current largest open loop ground source heating system in the UK has a 5.8MW capacity, compared with the 38MW and 32MW closed-loop systems that they will employ ESB will be relying on tried and trusted technology, says Lawson. Its based on our own experiences with deploying heat pumps. Were keeping it simple, were buying readily available off-the-shelf products that were putting together in a package theres nothing particularly bespoke about them. Within the greenhouses, the heat emitter system has been designed specifically with heat pump temperatures in mind to maximise efficiency. There are lower temperature heat emitter circuits, says Lawson. The lower the flow temperature of the heat pump, the more efficient it is. It works the same way as the source temperature a 1K drop in flow temperature equates to a 2.5% increase in efficiency. So weve sized all the growing rails to have a 50C flow temperature at worst case, and then we weather-compensate it from there. That means the heat pumps are more efficient than stipulating a 75C flow temperature and having to select a really high temperature heat pump. It doesnt really need to be that hot you can still get the full 38MW into the greenhouse at lower flow temperatures. Cost saving The project will benefit from the UK governments renewable heat incentive scheme. The projected capex cost per kilowatt of installed capacity of the GSHP system, according to ESB, is 249 per kW peak, with water extraction 100 per kW peak. And, with a relatively simple system compared with conventional CHP-based greenhouse heating with fewer moving parts involved maintenance costs are considerably lower too; ESB estimates the GSHP annual maintenance at 4.50 per kW peak and the CHP maintenance costs at 100 per kW peak. At current grid carbon levels, ESB Smart Energy Services projects the design of this energy centre will provide 1.2 million tonnes of carbon savings for both sites over the 20-year life of the project, compared with a standard CHP glasshouse. And as grid decarbonisation gathers pace, total carbon savings are expected to grow accordingly. As well as its capability to meet a large proportion of the UKs demand for vegetables such as tomatoes, the project will also boost local employment, creating around 360 permanent jobs and bringing a further 120 in high season. These greenhouses tick so many boxes when youre talking about Brexit and food security, employment and food miles, says Lawson. Is this type of solution the future of food production? Absolutely. CJ The greenhouse developments cover 29 hectares in total 54 November 2019 www.cibsejournal.com CIBSE Nov19 pp51-54 Heating Tomatoes.indd 54 25/10/2019 15:30