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Retrofitting a Light Industrial Space with a Renewable Energy-Assisted Hydroponics Facility in a Rural Northern Canadian Community: Design Protocol.

INTRODUCTION

Small-scale hydroponic farming is a relatively new crop production method that presents benefits over conventional agriculture in terms of product yield, land use, and water efficiency (Barbosa et al. 2015). Such a method of production could be extremely beneficial to rural indigenous communities in northern Canada, which often suffer from high import costs (Leblanc-Laurendeau 2019; Mercier et al. 2018). Various indoor farming setups have been researched for remote communities, with a focus on utilizing renewable energy systems. Ground source heat pumps (Yildirim and Bilir 2017; Russo et al. 2014; Esen and Yuksel 2013), solar photovoltaics (Bambara and Athienitis 2019), and latent energy storage (Baddadi et al. 2019) have all been proven successful to indoor farms in mild-climate regions. However, the downside of indoor farming is the higher energy requirement of space conditioning that does not exist in open-field agriculture (Grewal, Maheshwari, and Parks 2011). For this reason, 60 % of Canada's greenhouse area is in the warm regions of southern Ontario (Ontario Ministry of Agriculture, Food, and Rural Affairs 2016). As such, the greatly reduced import costs associated with switching to local indoor farming in Canada's territories and northern regions of provinces could be significantly diminished by the reduction of operating energy costs.

This study presents a procedure for assessing the feasibility of retrofitting an existing medium-scale light industrial building in a northern Canadian rural community with hydroponic farming operated by renewable energy sources. The purpose of such retrofitting is to serve as an alternative to importing fresh produce from warm climates. As such, the first objective of the study is to estimate the operating demands for heating, cooling, electricity, water, and carbon dioxide consumption. Next, the operation of a hybrid system consisting of renewable sources shall be simulated and compared with traditional energy sources to evaluate the potential reduction in operating costs and greenhouse gas (GHG) emissions. This procedure shall be presented in the context of a case study building in Fort Chipewyan, Alberta, and the feasibility evaluation results are presented here.

METHODOLOGY

Load Calculation

The building targeted for retrofit must be surveyed prior to the commencement of the design and evaluation. Heating energy consumption is highly dependent on the location and structure of the building. Additionally, the internal operations, with regards to occupancy and space uses, are critical to accurately estimating operating energy consumption. The next step is to select and model the hydroponics system. Particularly, the required electricity and water, operating schedules, and crop cycle are preliminary variables that have significant impacts on the productivity and profitability of the space. Then, it is necessary to evaluate the operating loads of the building. Specifically, these include sensible and latent heating and cooling, as well as carbon dioxide (C[O.sub.2]) supplementation, water consumption and electrical demand for equipment.

Sensible Load. The sensible load consists of losses associated with conduction, ventilation, infiltration, and the evaporative cooling effect by the plants, as well as any gains from internal equipment and the sun. For this, the indoor temperature setpoints are necessary and should be determined based on the requirements of the occupied spaces, as well as the requirements of the specific crop being farmed. For plant factories, the ideal range of average total air change (infiltration and ventilation combined) is between the minimum of 0.02 ACH to deal with potential contaminant buildup (Niu, Kozai, and Sabeh 2020), such as ethylene (Daunicht 1997), and the maximum of 0.1 ACH, above which C[O.sub.2] supplementation is uneconomical due to the high exfiltration of C[O.sub.2] to the atmosphere (Kubota 2020). Given that this procedure targets cold climate locations, it is critical to pursue a low ventilation operation with supplemental C[O.sub.2], which means that the retrofitted building must be well sealed. The internal gain from indoor equipment and the solar heat gain through fenestration should be considered. Hourly solar irradiance estimates can be obtained from a solar position calculator (National Oceanic and Atmospheric Administration), and clearness index data for the target location (HOMER Pro 2020).

Latent Load. The evaporative cooling effect occurs when plants convert liquid water into water vapor with sensible energy taken from the air as part of photosynthesis (Resh 2013a; Graamans et al. 2017). As a result, additional input is required by the system, equivalent to the product of moisture evaporation rate and heat of vaporization of water (ASHRAE 2017). This conversion of liquid water into water vapor by photosynthesis causes humidity in the space to increase, which, if not controlled, can cause plant transpiration rates to decrease over time and can create a potential for developing mold and mildew (Brechner, Both, and CEA Staff 2013).

Carbon Dioxide (C[O.sub.2]), Water, and Electricity Supply. A common practice in indoor farming facilities, especially in cold climates, is to maintain an elevated C[O.sub.2] concentration to enrich the indoor environment for expedited growth. This allows less fresh air to be brought in, thereby reducing heating energy consumption, while boosting plant growth beyond what would normally be achieved in traditional cultivation. Elevated concentrations of 800-1200 ppm are common in these applications but can vary based on crop type and crop growth stage (Jones 2005; Resh 2013b). Since water is crucial to the hydroponics process, water consumption serves as another critical load to be included in the performance model. Similarly, an essential component of a plant factory is lighting. This component drives the basic process of photosynthesis, by which plants consume carbon dioxide, circulate water, and grow, so it is essential to ensure that adequate light can be achieved, either natural or artificial.

Cost and Greenhouse Gas (GHG) Emissions Analysis

Once the space heating load has been determined, the next step is to evaluate available energy options for each of the calculated loads. This is highly dependent on the location, time of year, and other socio-economic and political factors. Furthermore, the specifications of every device and equipment selected to fulfill the calculated loads are necessary for calculating operating costs and GHG emissions. This must also include miscellaneous resources such as the cost of water and supplemental carbon.

CASE STUDY

Existing Building Retrofit

The existing case study building is a 270 [m.sup.2] (2900 [ft.sup.2]) fish processing plant that is in Fort Chipewyan, Alberta (58.770N, 111.120W). It is a 2-storey, wood-frame, slab on grade building with RSI-4 (R-22) walls and RSI-7 (R-40) roof and three small clear double-paned glass windows on the south-eastern side. The main space makes up most (31 %) of the building floor area at 84 [m.sup.2] (900 [ft.sup.2]) and is to be retrofitted with a hydroponic growing setup. The building also includes two chilled rooms: a cooler (5 % of floor area) and an ice room (8 % of floor area). As well as a processing room (20 % of floor area), a break room (16 %), and an office (4 %). The remaining 16 % of the building is dedicated to a combination of corridor, stairway, and mechanical room. The occupancy schedule was modelled as two workers in the hydroponics and processing areas, and one person in the office working for 8 hours per day.

The hydroponics equipment is modelled based on a commercial vertical farming setup with 240 2.1 m (7 ft) towers and a combination of 24 75 W and 48 150 W variable RGB spectrum LED lights. The crop to be produced is a generic species of lettuce. Water demand, electricity consumption, and annual yield are modelled based on estimates and calculators provided by the manufacturer. The facility operation is modelled as 365 days per year, with the hydroponics equipment operating 24 hours per day and a lighting schedule of 16 h/8 h photoperiod/dark period based on similar case studies for lettuce (Frantz et al. 2004; Hiroki et al. 2014).

Load Calculation

Sensible Load. Heating and cooling calculations followed typical ASHRAE load estimation procedures (ASHRAE 2017) using the heat loss and heat gain factors simulated for an average meteorological year using the bin method. In the case study, the indoor temperature in the hydroponics space was as an average in the range of 17-24 [degrees]C (63-75 [degrees]F) to account for the potential variation in plant requirements through the various stages of growth (Resh 2013; Brechner, Both, and CEA Staff 2013), and the outdoor temperatures were taken from ASHRAE climatic data as discretized bin data for a typical meteorological year (ASHRAE 2017). The other spaces in the building were considered to have a setpoint of 21 [degrees]C (70 [degrees]F), with the cooler and ice room set to 5 [degrees]C (41 [degrees]F), and -5 [degrees]C (23 [degrees]F), respectively. The air change rates in the main growing space were assumed as an average in the range of 0.02-0.1 ACH, as per the preferred plant factory operating conditions (Niu, Kozai, and Sabeh 2020; Kubota 2020). The break room, preparation area, and office were assigned healthy ventilation flowrates for human comfort ranging between 10-30 L/s (22-64 CFM) based on floor area and expected occupancy (ASHRAE 2016). Given that the lights are an essential component of indoor farming, average heat output for LED efficiency of 60 % (Ahn et al. 2014; Liu et al. 2017) was considered to maximize waste heat gain. Although the size of glazing units in this case was relatively negligible in terms of contribution to heat losses and gains, solar heat gain through fenestration was considered based on hourly solar irradiance (National Oceanic and Atmospheric Administration; HOMER Pro 2020), and knowledge of the building orientation and coordinates.

Latent Load. The required moisture removal rate by the dehumidifier is approximated to be equal to the water supply rate to the irrigation system, which in this case is 260-280 L/day (69-74 gal/day) on average. This load contributes a vital load to the water removal system, which in this case was an electric dehumidifier. Latent effects for the other spaces are generally not essential to the growing operation, so they were neglected.

Carbon Dioxide (C[O.sub.2]) Supplementation. In this case, the required carbon concentration is assumed to be an average in the range 400-900 ppm due to the variations in air change rates mentioned earlier. Plant consumption of C[O.sub.2] is taken as a general range between 0.12 kg/hr per 100 [m.sup.2] (0.53 lb/hr per 1076 [ft.sup.2]) (Ontario Ministry of Agriculture Food and Rural Affairs 2020), and 7 g/[m.sup.2] per hour (0.02 lb/10 [ft.sup.2] per hour) (Castilla, Baeza, and Papadopoulos 2012). Given the fact that the ventilation and infiltration would create fresh air change, an average C[O.sub.2] flowrate is calculated by a mass balance with an air distribution effectiveness of 0.8 (ASHRAE 2016).

Water Demand. The watering rates to the hydroponics system were assumed as 260-280 L/day (69-74 gal/day) on average. Additional water demands for other spaces in the building are estimated based on fixtures layouts of one lavatory with a sink, and two kitchen faucets. Fixture usage is estimated based on the occupancy schedule. This also includes heating water energy consumption, which is determined as a product of hot water demand and average temperature rise between municipal feedwater temperature of 8 [degrees]C (45 [degrees]F) and boiler supply temperature of 50 [degrees]C (120 [degrees]F).

Electrical Demand. The lighting system consisted of 120 LED grow lamps with a total power consumption of 9 kW, operating for 16 hours per day. Additional components included plumbing and climate control equipment as listed by the manufacturer, which were assumed to operate 24 hours per day. Lighting estimates for other spaces involved standard 32 W ballasts operating for a typical working schedule of 8 hours a day in the occupied areas and intermittent use of 4 hours a day in the freezer and cooler.

Cost and Greenhouse Gas (GHG) Emissions Analysis

Fuel Consumption. Table 1 shows a biomass boiler, propane furnace and an oil furnace. The wood boiler is designed to be the renewable system due to the local availability of the resource, and when regrown sustainably, wood is generally accepted as having significantly lower GHGs than the combustion of fossil fuels (US EPA 2003; Evans, Strezov, and Evans 2010). Additionally, in this case, the wood fuel option has the potential to provide local employment, so investment in this option would help the community. Wood combustion was compared to both propane and heating fuel oil, both being heating fuels commonly available in the region. Furthermore, the water heating demand from a propane-fired hot water tank was added for completeness but was not targeted for critical fuel comparison. Fuel prices in the location are listed in Table 1.

Electrical Consumption. Cooling and moisture removal were modelled using electric air-conditioner and dehumidifier appliances on the performance of commercially available units with efficiencies of EER = 2.9 W/W (10 BTU/W) and 2 L/kWh (0.5 gal/kWh), respectively. In addition to the lighting and hydroponics equipment, these make up the total electrical demand, which can be supplemented with renewable electricity generation. An on-site ground-mounted solar photovoltaic (PV) array is modelled with PVWatts[R] based on the monthly average generation (NREL 2020). The breakdown of the assumed PV system is summarized in Table 2.

C[O.sub.2] and Water Demands. C[O.sub.2] supplementation is estimated as a supply of compressed C[O.sub.2] gas in medium cylinders supplied by a local gas supplier. C[O.sub.2] emissions to the atmosphere are neglected as it is assumed that any C[O.sub.2] released into space has assimilated and become consumed by the plants. As such, only the cost of supplying C[O.sub.2] is considered in this study. Similarly, the water demand for the building is included in the total operating costs for both the main hydroponics space consumption as well as the general potable water used in other fixtures for general purposes.

RESULTS AND DISCUSSION

Load Results

Space Conditioning Fuel Comparison. Shown in Figure 1 (a) is the monthly distribution of the heating and cooling thermal energy transfer requirements. Despite the building being in a northern climate, the maximum cooling requirement in the middle of summer, July, with an average cooling requirement of 11.4 MWh (39.0 MBTU), is greater than the maximum heating requirement in the coldest winter month, January, with an average heating requirement of 7.5 MWh (25.0 MBTU). This discrepancy between heating and cooling requirements is attributed to the heat gain from the lighting equipment, which lowers winter heating and increases summer cooling. Figures 1 (b) and (c) show the corresponding effect on space heating energies available in this study. It is evident that biomass combustion is by far the cheapest option; reducing average annual fuel spending by 66 % and 57 % compared with propane and heating oil, respectively. Furthermore, it has the smallest effect on greenhouse gas emissions, as recognized by energy authorities in North America (US EPA 2003; Environment and Climate Change Canada 2019), with a reduction in anthropogenic emissions of 98%, as compared with both propane and heating oil. However, as is shown previously in Table 1, this system is far more costly because it has a higher heating capacity and uses water as a transfer medium.

Electricity Consumption and Generation. Figure 2 (a) shows the electricity consumption of the various devices designed to meet the necessary loads. It is evident that the dehumidification and lighting loads are relatively constant throughout the months due to their constant steady-state operation in the growing process. Furthermore, the net amount of electricity generated from solar PV on-site array is shown in Figures 2 (b) and (c). This generated electricity can make a tremendous difference during summer months because of the availability of solar power, which can help offset the large loads from equipment, lighting, air conditioning, and dehumidification by a net annual reduction of 56 %. The size of the system could theoretically be increased to achieve 'net zero' status; a term used to describe a system that generates as much energy as it uses, or to assist an electric heating system in the winter, such as an electric resistance heater or heat pump.

Resource Consumption and Estimated Yield. The consumption of miscellaneous resources is summarized in Table 3. It is evident that the water and C[O.sub.2] consumption for the hydroponics space are very high. So, overall, even though these resources are not immediately identified as crucial material and energy flows in a system that is typically more concerned with climate control, they are certainly important to include in a performance feasibility assessment, and accurate pricing data must be determined. Also included is the annual average product yield. This is based on the variation in photosynthetic efficiency at varying C[O.sub.2] levels in the range of 400-900 ppm.

Economic and Emissions Results

Figures 3 (a) and (b) show the total annual operating cost and GHG emissions corresponding to the renewable energy system and two traditional fuel baseline systems. It is evident that the operation of a wood-fired boiler and a solar PV array could reduce operating greenhouse gas emissions by about 48 % with respect to both traditional systems, effectively cutting emissions by half. With regards to cost, the renewable energy options available to this project can provide cost savings of 39 % and 37 % relative to the propane and fuel oil space heating systems without PV. Taking into account the estimated average quantity of lettuce produced (8441 kg) from the facility, the cost results can be translated to average costs per kilogram of lettuce of 3.60 $/kg for the renewable system, 5.86 $/kg for the traditional system with propane heating, and 5.70 $/kg for the traditional system with oil heating. Comparing this with the approximate cost of lettuce of 5.00 $/kg; based on data extrapolated for the closest city of Fort McMurray, it would bring the costs down to those of Edmonton (Alberta's capital has costs of approximately 3.50 $/kg) (Government of Alberta 2019; CBC News 2020). However, these improvements come at higher initial costs for the biomass boiler and solar PV equipment (Tables 1 and 2). Given that remote communities are receiving greater investment in renewable technologies, such as Canada's largest microgrid project in Fort Chipewyan (ATCO 2020), the performance of the facility could improve in the near future without investment into these systems. Nonetheless, electricity and C[O.sub.2] supplementation appear to be the greatest costs, so additional efforts could be made to reduce these costs.

If the concentration of C[O.sub.2] in the space were to be reduced to the absolute minimum level, cost savings of supplemental gas could be achieved in exchange for reduced production yield; elevated levels have been found to increase productivity by up to 20 % (Resh 2013). If the system modelled here were operated at 400 ppm year-round, 7597 kg of lettuce would be produced at the cost of 2.87, 5.38, 5.20 $/kg for the renewable, propane, and oil systems, respectively; this should be compared with 9285 kg at 4.12, 6.17, 6.03 $/kg for the same three systems at 900 ppm. This reduction in C[O.sub.2] supplementation could be further improved by supplying ambient levels of C[O.sub.2] from fresh air by increased ventilation during warm months, which would simultaneously reduce air conditioning electricity consumption. Since summertime cooling has been found to represent a major portion of the thermal energy transfer requirement (Figure 1 (a)), cooling by fresh air ventilation during warm months could provide further operational cost savings. This operational strategy would also affect the internal humidity of the space because it would not be sealed from the outside environment and the effects of outdoor air humidity, which varies with temperature, would have to be accounted for during dehumidification. Alternatively, carbon dioxide could be supplied as a product of fossil fuel combustion in a generator. Given the fact that buildings in this region require a heating system typically operated on the combustion of fuels (either the more renewable biomass option or traditional fuels), this could be a potential alternative. Furthermore, this could reduce the emissions generated since there would be a recycling effect that would help the emitted carbon be re-fixated into the plants (Chau et al. 2009; Dion, Lefsrud, and Orsat 2011; Kikuchi et al. 2018).

Other operational cost reduction strategies include the use of alternative passive designs, such as increased window area to provide natural light and reduce lighting electricity consumption. Once again, an optimal balance point would exist since increased window area would mean less electricity for lighting, but also less heat gain, which would result in a higher heating load. However, reduced electricity consumption for lighting and cooling could better use solar PV for an electric heating system, such as a heat pump or resistance heater. Ultimately, it is evident that operating a hydroponics space in the northern climate has some unique challenges, and indoor climate control is by far the most critical to be considered, and multiple options should be reviewed.

LIMITATIONS

The analysis in this study was simplified in several ways. Some climatic effects, such as outdoor humidity, wind speed, and solar irradiance on the opaque surfaces were neglected due to these parameters being secondary in importance to the level of detail explored here. Nonetheless, they would have some effect on the indoor environment. Additionally, it should be noted that distribution systems were not a point of comparison in this study, although this would certainly have other effects on the performance from an efficiency and maintenance perspective as well as overall cost. Emissions analysis was limited to greenhouse gas emissions only and was considered on the basis of annual operation. As such, carbon dioxide emissions from biomass combustion were assumed carbon neutral based on the view of energy authorities in North America (US EPA 2003; Environment and Climate Change Canada 2019). However, additional emissions would be included if a life cycle perspective were used to account for deforestation, land-use change, transport, and processing of biomass (Evans, Strezov, and Evans 2010). Furthermore, this analysis does not consider other gaseous emissions and solid pollutants, such as particulate matter (PM) and volatile organic compounds (VOCs). These can have additional adverse effects on air quality and human health and would be crucial to consider during an environmental impact assessment (Geng et al. 2019). The operating analysis for cost and emissions excluded processes such as labor, maintenance of equipment, and transport of resources (fuel, water, compressed C[O.sub.2]), all of which are recognized as having an additional impact on production cost and GHG emissions. Similarly, PV generation was analyzed on a monthly average basis, so any excess electricity that could be sold for profit during peak solar periods was not accounted for.

CONCLUSION

We have presented a general design protocol and feasibility evaluation procedure of retrofitting light industrial spaces in northern Canada with hydroponics plant farming facilities. A building was analyzed as a case study to showcase the procedure in a medium-scale building in Fort Chipewyan, Alberta. The process involved evaluating heating, cooling, dehumidification, lighting, water supply and carbon dioxide supplementation loads as part of a typical year-round farm operation. Available energy sources to the specific case study were evaluated, and a selection of systems was compared. A renewable energy-assisted system comprised a biomass boiler for space heating and a solar photovoltaic (PV) array for electricity generation. The traditional systems for comparison did not include solar PV and spanned a choice of propane or fuel oil furnaces for space heating. The results show that producing hydroponically grown lettuce in Fort Chipewyan is a promising venture if renewable and local energy technologies are in place. However, further improvements can be made specifically with regards to alternative strategies of climate control (C[O.sub.2], humidity, heating, and cooling) inside the growing space. Overall, the design protocol and feasibility evaluation procedures, as well as the results from this case study, should be useful to other projects pursuing similar goals under similar circumstances.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC) Engage program. The authors also thank Mr. Rob Macintosh and Mr. Clayton Stafford for providing technical information on the facility design.

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Artur Udovichenko

Student Member ASHRAE

Brian Fleck, PhD, PEng

Member ASHRAE

Tim Weis, PhD, PEng

Lexuan Zhong, PhD, PEng,

Member ASHRAE

Artur Udovichenko is a Master of Science student in the Department of Mechanical Engineering, University of Alberta 9211-116 street NW, Edmonton, AB, T6G 1H9. Brian Fleck, Tim Weis, and Lexuan Zhong are professors in the Department of Mechanical Engineering, University of Alberta.
Table 1. Heating Fuel Options and Systems for the Case Study Building

Fuel Option   System Type   Fuel Cost, $/kWh
                            ($/BTU)

Cord Wood     Boiler        0.046 [+ or -] 0.005 (13 [+ or -] 2)
Propane       Furnace       0.133 [+ or -] 0.006 (38 [+ or -] 2)
Heating Oil   Furnace       0.095 [+ or -] 0.026 (27 [+ or -] 5)

Fuel Option   Efficiency   Heating Capacity,   System Capital
                           BTU/h (kW)          Cost, $

Cord Wood     85 %         400000 (120)        $ 6000
Propane       80 %         120000 (35)         $ 1300
Heating Oil   95 %         240000 (70)         $ 2100

Table 2. Electricity System Breakdown

PV DC   Physical        Tilt           Type
Size    Size

60 kW   400 [m.sup.2]   20 [degrees]   Standard
                                       Module, Fixed
                                       Array

PV DC   Local Electricity Price, $/kWh   PV Array Capital
Size                                     Cost, $

60 kW   0.25 [+ or -] 0.05 (Gwich'in     132600 (National
        Council International            Energy Board 2020)
        2017; NWT Power
        Corporation 2020)

Table 3. Resource Consumption and Product Yield

Item                   Annual Quantity

Water Consumption         134 [+ or -] 11 [m.sup.3]
                       (35313 [+ or -] 3000 gal)
Compressed C[O.sub.2]   11709 [+ or -] 11120 kg
Gas Consumption        (24732 [+ or -] 23434 lb)
Lettuce Production       8441 [+ or -] 844 kg (18609 [+ or -] 1861 lb)

Item                   Local Price

Water Consumption      3.0 $/[m.sup.3]
Compressed C[O.sub.2]  0.77 $/kg
Gas Consumption
Lettuce Production     5.00 $/kg (Government of Alberta 2019; CBC
                       News 2020)
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Author:Udovichenko, Artur; Fleck, Brian; Weis, Tim; Zhong, Lexuan
Publication:ASHRAE Transactions
Geographic Code:1CALB
Date:Jan 1, 2021
Words:5190
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