Glasshouse production currently relies on the combustion of fossil fuels for heating. It is estimated that the sector used around 5,207 GWh and accounted for over 300,000 tonnes of carbon in 2005 (final report for Defra project AC0401). This project will aim to reduce the emissions from this sector.
To reduce emissions in the short to medium term, knowledge transfer activities will aim to encourage growers to adopt current best practice. A series of energy saving factsheets will be written which are aimed at the industry. This KT activity will be carried out in collaboration with the HDC (Horticultural Development Company; part of the Agriculture and Horticulture Development Board) who will design, print and distribute the factsheets, and use the information to form a web based energy saving manual. The factsheets will cover topics such as temperature manipulation, humidity control, CO2 enrichment, lighting, screens and general housekeeping and auditing.
We will also carry out a desk study which will aim to identify novel engineering technologies which, longer term, may be able to reduce the greenhouse gas emissions associated with heating, cooling, dehumidification and CO2 enrichment. Closed and semi-closed greenhouses are being examined in The Netherlands. In these systems excess heat in summer is being stored in aquifers and used for heating in winter where the temperature is boosted through the use of heat pumps, which in turn produces cold water for cooling in summer. However, most of the UK does not have access to suitable aquifers and so alternative solutions need to be found.
To provide a basis for the assessment of novel engineering solutions a specification quantifying the heating, cooling, dehumidification and CO2 enrichment demands for a typical tomato crop will be produced. Because the requirements are interrelated, technologies will be assessed in terms of their potential contribution to the system as a whole, rather than in isolation. We will initially consider a wide range of technologies including heat pumps, adsorption chillers, CHP, liquid desiccants, desiccant wheels, zeolites and inter-season heat storage. Technologies which show greatest potential will be identified and more detailed analysis of the carbon savings, capital costs and payback carried out so as to identify systems that might be commercially viable following further R&D.