Renewable Energy for Indoor Agriculture

Transcription

1 Renewable Energy for Indoor Agriculture Lucas Semple 1, Rupp Carriveau 2,3,4, David S.K. Ting 2,3,4 1 Engineering Manager, UnderSun Acres 2 Environmental Energy Institute 3 Turbulence and Energy Lab 4 Ed Lumley Centre for Engineering Innovation, University of Windsor

2 Background Over 2500 acres of Greenhouses in Leamington-Kingsville alone. In Ontario, the maintenance of suitable growing temperatures can account for 90% of the energy utilized by greenhouses. In Ontario this is achieved on the back of natural gas.

3 Idea! Let s offset some of this reliance on natural gas with solar thermal panels! BUMMER: When we need the heat the most the solar system output is weakest. DISCOVERY: Over 20% of natural gas usage occurs over the summer months for morning preheating.

4 Objectives 1. Design a supplemental solar thermal energy system to reduce natural gas consumption in commercial greenhouses. 2. Assess the economics of such a design. 3. Consider additional measures to improve the economics of reducing natural gas consumption in commercial greenhouses.

5 Method: Overview 1. Develop a transient model of the greenhouse indoor microclimate. 2. Validate model performance against historical greenhouse natural gas usage. 3. Design array of supplemental solar thermal panels to integrate into existing climate management processes in the facility. 4. Examine outcomes and evaluate system technoeconomic feasibility. 5. Propose next steps. Trimble 2015.

6 Method: Major Model Parameters TRYNSYS is a transient simulation modeling environment. TRNSYS AIR CHANGE APPROACH 3D venlo-type, 1 acre greenhouse modeled. 5.5 m gutter height, 10 X 5 m bays, 25 o roof slope. Double polyethylene cover used with a heat transfer coefficient of 3.2 W/m o K. Multi thermal zones were created throughout the domain. A constant crop density of 6kg/m 2 was considered and air change dynamics were adjusted to account for crop growth.

7 Method: Major Model Parameters MODEL CONTROLS LAYOUT Day and Night temperatures were set at 22 o C and 18 o C respectively. Heat is (at least) supplied between 0400 and 0600 hrs. Infiltration was set at 0.4 ACH. When indoor temperature exceeded 25 o C ventilation through roof cover vents at a rate of 60 ACH. Thermal curtains are closed when solar radiation is less than 5 W/m 2, curtains are not used in Summer. Indoor air velocities are assumed to be 0.15 m/s based on the literature. Transpiration was modeled as an internal humidity gain.

8 Method: Major Model Parameters System mimics that typical to SWO. HEATING SYSTEM LAYOUT Steam near the roof and hot water near the floor. Steam boiler maintains water temperature in the storage tank between 60 o C and 65 o C. Water is drawn from the top of the storage tank and circulated through the piping system at a rate of 1000 kg/hr. Natural Gas usage from 12 recent growing years from 3 different operations were used to calibrate.

9 Checking Model Model comparison to 12 recent growing years from 3 different operations.

10 Solar System Design SOLAR SYSTEM LAYOUT Glazed flat plate collectors were chosen to best suit the desired tank temperature of between 60 o C and 65 o C. Working fluid was even split of water glycol to reduce risk of freezing. An effectiveness rating of 0.8 was used for the solar heat exchanger. Water was drawn from the bottom of storage tank and returned to the top.

11 Model Outcomes Impact of solar energy system on boiler energy usage.

12 Conclusions 1. Transient model of the greenhouse indoor microclimate was developed. 2. Model was used to evaluate the technoeconomic feasibility of a supplemental solar energy system designed to offset natural usage for heating. 3. Annual heating loads were reduced by about 35%. 4. Simple payback for the solar system ranged between 11 and 15 years. With a carbon tax payback reduced to 9 to 11 years. 5. CO 2 equivalent emissions were reduced by 120 tonnes/acre/year.

13 Next Steps 1. Evaluate the impact of integrated seasonal energy storage on system efficacy. 2. Integrate also the electrical side of energy demand what combination of solar thermal and solar pv would be most strategic to greenhouse growers (particularly those running lights)?

14 Environmental Energy Institute