Gas absorption heat pumps with borehole energy storage in organic greenhouse horticulture E. Eriksson, N. Vergote, J. Dewitte, T. Beyers and K. Declerq | PCG Vegetable Research Centre, Belgium, [email protected] - BACKGROUND Energy saving measures Summer situation (or warm periods) 1. Insulation greenhouse • Polycarbonate outer walls • Total K-value = 2.75 W/m².K • System runs on CO2 and heat is additional • Excess heat is stored in the short term heat storage • Cold is used for dehumidification and cooling. • Heat is stored in the drillhole energy storage (DES) when short therm heat storage is full and CO2 demand is still high. 2. Energy screen • 63% energy saving / 65% light screening 3. Climate screen • 45% energy saving / 14% light screening 4. Air treatment unit (ATU) • Dehumidification, cooling and heating 5. Low temperature • Ø 51 mm heating pipes • Max 55 °C tube temperature Winter situation (or cold periods) 6. Gas absorption heat pump (HP) • CO2 for fertilisation • System runs on heat and CO2 is used in the greenhouse. • Low value heat from DES (stored in summer) is used by the heat pump. 7. Drillhole energy storage (DES) • Cold for dehumidification and cooling • Heat production with COP: 1.3 to 1.7 • • • Low value heat storage/source Higher COP heat pump More CO2 dosing - GOAL An energy efficient system as an alternative to CHP for smaller (organic) companies - METHOD Climate control parameters Measurements • Energy use and climate parameters for two compartments of 400 m² • In culture of tomato and pepper in 2012 • In culture of tomato and cucumber in 2013 • • • • • • T: 19 °C day / 17 °C night RH: 80 % - 85 % day / 85 % - 90 % night Close ventilation Februari – March ATU for dehumidification and cooling Semi-closed growing: open windows when RH ↑or heat ↑ Limited use of minimum tube - RESULTS Tomatoes 2013 Tomatoes 2013 Start End Total energy use (kWh/m²) COP Heat Pump Energy use Heat Pump (kWh/m²) 22/01/2013 20/11/2013 301.4 1.41 20/01/2012 27/11/2012 418.3 1.40 213.6 297.2 Reference situation (kWh/m²) 410.0 410.0 Energy use for 400 m² Energy saving Heat Pump 29% 29% Total energy savings 48% 28% Energy measurements for a 400 m² compartement with tomatoes in 2012 and 2013 Loose type tomatoes Total production kg/m² Admiro 35.0 Aromata 30.4 Arvento 40.2 Bocati 36.9 DRW 7749 (Rebelski) 37.7 EZ 1259 35.9 Kanavaro 35.7 V470 HF1 = EDDA 37.5 Average yield 36.1 Yield tomatoes in 2013 Total production Beefheart tomatoes kg/m² Arawak 38.0 Couralina F1 46.7 Corazon 40.9 Rugantino 39.4 ST 7639 42.5 Tomawak 43.2 Average yield 41.8 Yield tomatoes in 2012 - CONCLUSIONS This system has a potential energy saving of 50 % or higher compared to a reference situation of 410 kWh/m². Finding the balance between energy saving and controlling humidity still remains a challenge. So a proper climate control strategy is necessary to obtain a stable climate and good product quality. For more info: www.proefcentrum-kruishoutem.be