Energy and Economic Analysis for Greenhouse Ground Insulation Design
Abstract
:1. Introduction
2. Energy and Economic Analysis
2.1. Greenhouse Characteristics
2.2. Energy Analysis
2.2.1. Thermal Module
- Xm is the moisture capacitance multiplier (dimensionless)
- ρa is the density of air (kg m−3)
- Vi_c is the volume of the crop zone airnode (m3)
- is the rate of change of the inside air humidity ratio (kgwater kgdry_air−1)
- is the rate of change of time (s)
- mvent is the mass transfer rate of water due to ventilation (kg hr−1)
- minf is the mass transfer rate of water due to infiltration (kg hr−1)
- mET is the mass transfer rate of water due to evapotranspiration (kg hr−1)
- mcpl is the mass transfer rate of water due air movement between the airnodes (kg hr−1).
- Xth is the thermal capacitance multiplier (dimensionless)
- cp_a is specific heat of air at constant pressure (kJ kg−1 °C−1)
- is the rate of change of the inside air temperature (°C)
- Qconv_si is the energy flux due to convection (W)
- Qvent is the energy flux due to ventilation (W)
- Qinf is the energy flux due to infiltration (W)
- QTSS is the energy flux from the thermal shading screen (W)
- QAL is the energy flux from artificial lighting (W)
- Qheat is the energy flux from auxiliary heating (W)
- Qcpl is the energy flux due air movement between the airnodes (W).
- Qcond is the energy flux due to conduction (W)
- Qswr_si is the energy flux due to absorbed shortwave radiation (W)
- Qlwr_si is the energy flux due to longwave radiation (W).
- Qconv_so is the energy flux due to convection (W)
- Qswr_so is the energy flux due to absorbed shortwave radiation (W)
- Qlwr_sky is the longwave radiation energy flux to the sky (W)
- Qlwr_gnd is the longwave radiation energy flux to the ground (W).
- Qswr_c_AL is the energy flux due to absorbed shortwave radiation on the crop surface (W)
- QET is the energy flux due to evapotranspiration (W).
2.2.2. Energy Modeling Key Assumptions
- mcpl is coupling mass flow of air between the airnodes (kg hr−1)
2.2.3. Values of Greenhouse Design Parameters
2.3. Economic Analysis
- D is the nominal discount rate (%)
- I is the inflation rate (%).
- Cgas is the natural gas price ($ m−3)
- egas is the electricity cost escalation rate (%)
- n is the study period (yr).
- Ains is the area with replaced with permanent or movable insulation (m2)
- Cins_mat is the material cost of insulation ($ m−2)
- Cins_inst is the installation cost of insulation ($ m−2).
- Qp_heat is the rated thermal output of the nearest commercially available boiler that can satisfy the simulated peak thermal energy demand (kW)
- Cboil_mat is the material cost of the boiler ($ kW−1)
- Cboil_inst is the boiler installation cost ($ kW−1).
- Cstru_tot is the installed cost of the greenhouse structure per unit area ($ m−2)
- CHVAC_tot is the installed cost of the HVAC system per unit area ($ m−2)
- CAL_tot is the installed cost of the AL system per unit area ($ m−2).
Values of Greenhouse LCCA Parameters
3. Results and Discussion
3.1. Portion of Heat Loss through Ground
3.2. Net Savings Achieved by the Ground Insulation Configurations
3.3. Impact of Insulation on Energy Consumption
3.4. Sensitivity of Net Savings to Energy Model Input Parameter Values
3.5. Sensitivity of Net Savings to Economic Parameter Values
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Material/Component | Parameter | Symbol | Value | Reference |
---|---|---|---|---|
Soil | Depth of arable soil layer | Dsoil_ar | 0.7 m | Assumed |
Depth of ground zone and far-field distanced | Dsoil | 10 m | Assumed | |
Smallest control volume size | CVmin | 0.1 m | Assumed | |
Specific heat | cp_soil | 0.84 kJ kg−1 K−1 | [15] | |
Density | ρsoil | 3200 kg m−3 | ||
Thermal conductivity | ksoil | 2.42 W m−1 K−1 | ||
Emissivity | εsoil | 0.9 | [22] | |
Solar reflectance | ρsoil | 0.75 | [23] | |
Deep earth temperature | Tde_soil | 5.9 °C | [20] | |
Amplitude of surface temperature | Amp | 15.3 °C | ||
Time shift | ts | 32 d | [16] | |
EPS ground insulation | Thickness | lins | 50 mm | Assumed |
Thermal conductivity | kins | 0.036 W m−1 K−1 | [24] | |
Specific heat | cp_ins | 1.5 kJ kg−1 K−1 | ||
Density | ρins | 20 kg m−3 | ||
Depth of vertical perimeter insulation | Dper_ins | 0.61 m | Assumed |
Parameter | Symbol | Value | Reference |
---|---|---|---|
Initial investment cost of greenhouse | Inv | $712,700 (concrete floor) $655,200 (soil floor) | Calculated based on [18] |
EPS insulation cost | Cins_mat | 6.51 $ m−2 | [25] |
EPS insulation installation cost | Cins_inst | 5.76 $ m−2 | [25] |
Floor Type | Insulation Location and Thickness | Energy Cost | Incremental Initial Investment Cost | Capital Replacement Cost | Residual Value | NS | Change in LCC |
---|---|---|---|---|---|---|---|
Concrete slab | BCGH (no insulation) | $1,582,202 | $0 | $84,949 | $25,586 | - | - |
Vertical perimeter | $1,579,716 | $912 | $84,949 | $25,586 | $1575 | −0.1% | |
Vertical perimeter and horizontal floor zones | $1,577,112 | $3192 | $84,949 | $25,586 | $1899 | −0.1% | |
Vertical perimeter and horizontal floor plus crop zones | $1,577,726 | $12,311 | $84,949 | $25,586 | −$7835 | 0.3% | |
Soil floor | BCGH (no insulation) | $1,567,120 | $0 | $84,949 | $25,586 | - | - |
Vertical perimeter | $1,564,725 | $912 | $84,949 | $25,586 | $1483 | −0.1% | |
Vertical perimeter and horizontal floor zones | $1,560,546 | $3192 | $84,949 | $25,586 | $3382 | −0.2% | |
Vertical perimeter and horizontal floor plus crop zones | $1,560,371 | $12,311 | $84,949 | $25,586 | −$5562 | 0.2% |
Floor Type | Insulation Level | Lighting Electricity Consumption (kWh yr−1) | Natural gas Consumption for Heating (m³ yr−1) |
---|---|---|---|
Concrete slab | BCGH (no insulation) | 114,971 | 61,903 |
Vertical perimeter | 114,971 | 61,690 | |
Vertical perimeter and horizontal floor zones | 114,971 | 61,466 | |
Vertical perimeter and horizontal floor plus crop zones | 114,971 | 61,519 | |
Soil floor | BCGH (no insulation) | 115,755 | 60,105 |
Vertical perimeter | 115,755 | 59,900 | |
Vertical perimeter and horizontal floor zones | 115,755 | 59,541 | |
Vertical perimeter and horizontal floor plus crop zones | 115,755 | 59,526 |
Item | Insulation Level | Internal Calculation of CHTC | CHTC Increased to 20 W m−2 °C−1 | % Change |
---|---|---|---|---|
Natural gas consumption for heating (m3 yr−1) | BCGH | 61,903 | 70,359 | 13.7% |
50 mm vertical perimeter and horizontal floor plus crop zones | 61,466 | 69,611 | 13.3% | |
Net savings | 50 mm vertical perimeter and horizontal floor plus crop zones | $1899 | $5521 | 190.8% |
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Bambara, J.; Athienitis, A.K. Energy and Economic Analysis for Greenhouse Ground Insulation Design. Energies 2018, 11, 3218. https://doi.org/10.3390/en11113218
Bambara J, Athienitis AK. Energy and Economic Analysis for Greenhouse Ground Insulation Design. Energies. 2018; 11(11):3218. https://doi.org/10.3390/en11113218
Chicago/Turabian StyleBambara, James, and Andreas K. Athienitis. 2018. "Energy and Economic Analysis for Greenhouse Ground Insulation Design" Energies 11, no. 11: 3218. https://doi.org/10.3390/en11113218