Common greenhouse conditioning plants compared with versatile geothermal system in Ames, Iowa

Energy consumption is one of the most important factors related to profitability in greenhouse systems, and it is a factor in both financial considerations and environmental impacts. Competitiveness in the greenhouse industry is highly dependent upon the energy demand of heating systems. This paper focuses on the use of geothermal energy in agricultural sector. A ground source heat pump system was designed for a new greenhouse complex in Ames, Iowa. An accurate study of the external air temperatures, solar radiation, time, wind speed, and boundary conditions was conducted. Electrical and heating energy, and power demands were analysed. For the greenhouse design presented, the greatest power demand was 350 kW for heating and 620 kW for cooling. These values permitted the greenhouse to be maintained at the temperature of 16.7 ºC, when the external temperature ranged from -20 ºC to 30 ºC. An economic analysis was conducted considering only the energy demand cost, and this cost was compared with the equivalent energy cost of fuel oil and natural gas systems for heating and the equivalent energy cost of the fan and pad systems for cooling. For heating purposes, the economic analysis showed that the total energy demand cost over the nine years of using a closed-loop GWHP was around 120,000 USD, whereas the fuel oil system was 364,000 USD, and the natural gas system was 253,000 USD. This yields cost savings of 67 % and 53 %, respectively. For the cooling purposes, the economic analysis is inconsistent, and the fact, the energy cost difference between the closed-loop ground source heat pump cooling system and fad and pad systems is huge, 83,000 USD for closed-loop ground source heat pump cooling and around 5,200 USD for the fan and pad system energy in nine years.