Controlled Environment Agriculture Technologies

Adrienn Santa 

Engaged Learning Fellowship 

Mentors: Dr. Ali Beskok, Dr. Eva Csaky 

April 1, 2018 

I would like to thank SMU, Engaged Learning and the Hunt Institute for supporting this 

research. I would also like to show my gratitude to Dr. Ali Beskok, Dr. Eva Csaky, and 

Corrie Harris for sharing their thoughts and wisdom to help improve my findings.

Table of Contents 

Abstract ............................................................................................................................................................. 4 

1. Introduction ............................................................................................................................................... 1 

2. Technologies used in controlled environment agriculture ........................................................................ 3 

a. Orientation and structure ....................................................................................................................... 4 

b. Heating .................................................................................................................................................. 5 

c. Cooling ................................................................................................................................................ 15 

d. Ventilation ........................................................................................................................................... 18 

e. Glazing and insulation ........................................................................................................................ 21 

f. Lighting ............................................................................................................................................... 24 

3. Evie, design of low-cost cooling system ................................................................................................. 26 

a. Importance of Absorption Refrigeration Cycle ....................................................................................... 27 

b. Experiment .............................................................................................................................................. 29 

c. Results ..................................................................................................................................................... 33 

d. Implications of this project ..................................................................................................................... 35 

4. Conclusion .............................................................................................................................................. 37 

5. References ............................................................................................................................................... 38 

Signature and Approval of Mentor: .................................................................................................................... 43

Abstract 

Controlled environment agriculture (CEA) is technology-based food production system where 

growers are able to manipulate the inside environment according to the growing requirements of 

the specific plants. A greenhouse is a closed space where fruits, vegetables, herbs and other plants 

can be grown. Growing seasons can be expanded to the whole year if the inside conditions are 

controlled properly according to the requirements of the plants. However, often the land and 

building space available is small, and currently there are no low-cost solutions available to grow 

food efficiently in small urban spaces. CEA technologies are used for the purpose of controlling 

the temperature, humidity, airflow and light in the building. The best possible orientation and 

structures of a greenhouse, heating, cooling, ventilation, lighting and glazing as well as insulation 

materials are discussed in this report. Technologies and methods are compared as needed. Results 

show that the most efficient and sustainable technologies are currently more expensive initially 

than others. Due to this fact, most of the time small urban farmers are not able to afford sustainable 

and energy-efficient technologies. Further development, testing, and analysis needs to be done in 

order to make the CEA technologies affordable in low-income communities.

Controlled Environment Agriculture Technologies 

Adrienn Santa 

1. Introduction 

Food deserts are one of the biggest issues in low-income communities, not only in the Dallas 

area, but also in other parts of the world. According to the US Department of Agriculture, the term 

‘food deserts’ is defined as “parts of the country vapid of fresh fruit, vegetables, and other healthful 

whole foods, usually found in impoverished areas” [1]. In most cases there are no available quality 

grocery stores, farmers’ markets, or affordable fresh food nearby the affected area, which could 

result in serious health issues and other social consequences. According to the Economic Research 

Service of the USDA, an “estimated 2.1 million households, or 1.8 percent of all households (in 

the US) are in low-income and low access census tracts and are far from a supermarket and do not 

have a vehicle” [2]. Economic conditions often force grocery stores to relocate, which can result in 

having very few local stores. Some urban communities have access to public transportation, which 

can help residents to overcome the difficulties of accessibility of the nearest grocery store; however 

suburban and rural areas usually have very limited or no access to buses or trains. Climate change 

strongly affects the agriculture sector, as well. Farmers are unable to maximize their crop 

production with the unpredictable weather conditions. Thus, climate change forces farmers to 

switch to CEA in order to keep their crops healthy throughout the growing season. 

Figure 1: Store near San Antonio, Texas [3] 

The areas most affected by food deserts in the United States are around New Orleans (LA), 

Chicago (IL), Atlanta (GA), Memphis (TN) and Camden (NJ) [4]. Figure 2 shows the areas in the 

United States where a grocery store or a supermarket is further than a mile. It is evident that the 

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areas around New Orleans and Atlanta are critically affected by the issue of food deserts. 

Figure 2: Areas in the United States where the there are no available stores in a mile [1] 

Several movements and initiatives exist to reduce the number of food deserts and increase the 

availability of fresh food in impoverished communities. For example, with Amazon’s acquisition 

of Whole Foods, a major online grocery outlet was created, capable of delivering to all 

communities. However, this form of grocery shopping is currently very expensive, and in many 

cases, low-income populations cannot afford this type of service [5]. Digital distribution is another 

problem; many people affected by food deserts lack access to the Internet to take advantage of the 

service. 

Another potential solution to combat the issue of food deserts is to bring food production closer 

to the communities in need. This solution would create new jobs and opportunities for communities 

as well as make use of vacant lands and buildings. Often, the land and building space available is 

small, and currently there are no low-cost solutions available to grow food efficiently in small urban 

spaces. Existing solutions are not economically viable when used in small spaces because of their 

high costs of capital and operating, especially relating to energy. This report is a summary of the 

existing technologies such as heating cooling, ventilation, lighting systems, insulation, and 

materials used in controlled environment agriculture. I will first provide an overview of the most 

commonly used CEA technologies, then I will discuss a detailed design of a promising model for 

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low-cost cooling solution. 

2. Technologies used in controlled environment agriculture 

Greenhouses are promising solutions to provide better quality food for urban communities and 

protect plants against natural environmental effects on a year-round basis. The technologies used 

in greenhouses determine the installation and maintenance costs of the system. Various plants and 

seedlings have different optimal growing conditions (see Figure 3). They require different amounts 

of direct sunlight, temperature, humidity, and water. 

Figure 3: Germination and planting temperatures for some vegetables and fruits [6] 

The location of the greenhouse can make it difficult and costly to provide the required 

temperature for the plant. In Texas, greenhouses need to be cooled in the summer, while in very 

cold areas, heating has to be provided in order to keep the plants growing. This research is focusing 

on identifying and discussing the available climate control technologies used in controlled 

environment agriculture. First, the orientation and different structures are discussed followed by 

the heating technologies. Also, the usage of the various cooling, ventilation systems are analyzed 

as well as the most efficient ways to provide lighting for the plants, and the type of insulations 

used in controlled environment agriculture. The various aspects and technologies interact with 

each other, and the CEA system to create the optimal climate conditions. 

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a. Orientation and structure 

Optimization of the orientation, structure, shape and location of a greenhouse have significant 

effect on energy consumption. The best possible orientation is where the greenhouse has the 

maximum interception to sunlight, which provide adequate nutrients for crops. To find the optimum 

orientation of a greenhouse, the climate conditions, latitude, hemisphere of the Earth, and time of 

the year for maximum production need to be considered. The most common type of orientations 

is east-west and south-north. Snezana Dragicevic from University of Kragujevac made a 

comparison about the two different types of orientation for each month of the year at different 

latitudes in the northern hemisphere and computed the total solar radiation input though each wall 

[7]. According to her findings, the uneven-span shape receives the most radiation of all the 

compared shapes. This type of greenhouse is suggested to have an east-west orientation greenhouse 

at latitudes of 44°N and 54°N “as it receives less solar radiation in summer with small differences 

in receive solar radiation in winter month” and “with increase of the latitude angle, the difference 

in the radiation received during winter month increase as compared to lower altitudes” [7]. Another 

researcher, Wael M. El-Maghlany recommends orienting the greenhouse with respect to south 

direction in latitudes between 24° and 31.2°; however, in latitudes below 24° it is better to align 

the greenhouse towards east and west. By choosing the most optimal orientation of the enclosed 

place, total heat gain can be maximized, and radiation heat can be used as supplementary heating 

which could reduce the running cost of the heating system [8]. 

The structure of the greenhouse plays an important role in efficiency and productivity. The 

growing structure provides shelter for the crops from unforeseeable weather conditions. Selecting 

the type of the greenhouse depends on the crops produced inside, use of space, and extension plans 

[9]. There are three types of greenhouses: lean-to, detached, and gutter connected (ridge or furrow). 

The most favored type of structure is the lean to, but very few of them are used in commercial food 

production because of its limitations. The detached greenhouse stands by itself, and the most 

common type of detached greenhouse is the Quonset. Solid walls support the end of the structure 

while arched rafters are found throughout the body. This is not the most efficient type of 

greenhouse, as near the walls the growing area is restricted for smaller crops [10]. Ridge or furrow 

greenhouses are “two or more greenhouse structures joined together at a common intermediate 

gutter” which increases their efficiency [9]. There are several different shapes used as gutterconnected 

greenhouse, such as arch or gothic, A-frame or even-span, sawtooth, Venlo and open 

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roof. 

Figure 4: Greenhouse structures: A-Gutter connected, B-Quonset, C-Single gable [10] 

b. Heating 

According to Jim Rearden an estimated $250 million is spent annually on commercial 

greenhouse heating in the United States [9]. In most parts of the world, it is necessary to provide 

some form of heating to the plants in either winter or summer (depending on the location of the 

greenhouse on Earth) because of the heat loss through the walls and the ground. Taking Texas 

weather into consideration, the average low temperature in January 2018 was -1.3°C, and the 

lowest temperature reached was -15°C [11]. The light winter and a good greenhouse structure can 

help eliminate the usage of heating. However, this is not always the case. Before choosing the 

proper heating design, variables such as heat source, availability, and cost need to be considered [9]. 

Heat sources can be: natural gas, liquified petroleum gas, fuel oil, wood and electricity. The 

dynamic environment of the greenhouse needs to be taken into consideration as well in order to 

choose the most appropriate form of heating. Greenhouses tend to lose heat in a very short time, 

but they also gain heat very quickly because of their solar collector properties [9]. Moreover, being 

able to control where the heat is going is very important, as not all the zones are necessary to be 

heated inside the greenhouse. For example, the temperature requirement can change according to 

the stage of growing. Consideration of all of these factors can create an energy efficient and cost- 

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effective way for raising the temperature. Furthermore, 30% less energy is required for heating if 

insulation and other coverage are utilized to protect the greenhouse from the cold days. 

There are many options to maintain the required temperature inside the building during the 

cold days, but the two major types are hot air or hot water. Many times, the combination of different 

heating systems result in the most efficient solution. 

Unit heaters are one way to create supplemental heating in a greenhouse. “In the United States, 

unit heaters enjoy a market dominance of approximately 60% of all the heating equipment dollars 

spent on greenhouses” [9]. On the other hand, in the other parts of the world, the water heating 

systems are more popular. There are several unit heater types available for use, but all of them 

have basically the same function. They generate hot air then distribute it in the available space with 

a help of an internal fan. Unit heaters mainly utilize propane, natural gas, or oil, but electric units, 

hot water, and steam styles are also available on the market [9]. There are two major types of unit 

heaters used for greenhouse heating: vented and unvented. “The traditional vented, gas-fired unit 

heater transfers heat from the combustion gases to the air through a heat exchanger and exhausts 

the combustion gases outside the greenhouse through a flue pipe” [12]. Yet, in an unvented unit 

heater, all combustion gases are exhausted straight in the greenhouse after burning the gas, which 

means that all of the heat is utilized for raising the temperature of the inside air. The overall 

efficiency of most unit heaters is rated between 50-90%. 

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Table 1: Advantages and Disadvantages of unit heaters [9] [12] 

Advantages 

Disadvantages 

Low initial/capital cost 

Lack of focused heating 

Low installation cost 

Longevity can be poor 

High reliability 

Undesired shadows by cast 

Low cost for lots of BTU 

Can be noisy 

Quick response 

Limit the ability to hang plants near heaters 

Ease of zoning houses 

Water condensation 

Ease of staging multiple heaters 

Potential fungal diseases 

Can be used for CO 2 enrichment Byproducts of combustion (ethylene, sulfur 

dioxide, nitrous oxide, carbon monoxide) can 

be harmful for plants and humans 

- Plants are unlikely to use all generated CO 2 

Figure 5: Unit heater in a greenhouse [13] 

Unit heaters are typically mounted near one of the end walls of the greenhouse. This position 

enables the system to deliver heat towards the middle section of the building. Most of them are 

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placed high, especially the gas-fired units, to avoiding damaging the crops. The cost of the unit 

heaters depends on the size and type that will be installed. The average cost of a design with 

minimal complexity in the northern region in the United States ranges from $0.40 to 0.80/ft 2 for a 

1-acre application [9]. Table 2 represents an example of the manufacturer suggested retail price 

for the specified vented unit heaters as well as their thermal and seasonal efficiencies. 

Table 2: Heater efficiencies and costs of vented unit heaters with propeller fans and 

stainless-steel heat exchangers and burners [12] 

Another type of heating system which is usually installed near the peak of the greenhouse is 

infrared heating systems. They are classified into two categories: high-intensity infrared heaters 

and low-intensity infrared heaters. The system runs near the roof through the length of the whole 

greenhouse and reflects down the heat energy to the plants below it, the infrared rays passing 

through the air. A metal heating tube that runs throughout the whole heater system is heated with 

combusted fuel (natural gas or propane). Infrared pipes can be used for the same purpose. The 

system efficiency can be increased by installing fins of the infrared pipes. “Low-intensity infrared 

heaters are safer to use in a greenhouse than high-intensity infrared heaters, because the pipes are 

heated up to 1100°F (594°C); the pipes of a high intensity infrared heater can be heated as high as 

1800°F (982°C)” [14]. 

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The heat radiated from the pipes can be adjusted by changing the height of the heating system. 

The average cost of an infrared system with minimal complexity in the northern region in the 

United States ranges from $1.00 to 1.60/ft 2 for a 1-acre application [9]. This type of heating is 

cleaner, more environmentally friendly, and more effective at heating than the traditional heating 

systems. 

Figure 6: Infrared heating system [15] 

Table 3: Advantages and disadvantages of infrared heating [9] 

Advantages 

Energy efficiency 

Dry leaves 

Reduction in diseases such as botrytis 

Reduced heat loss 

Disadvantages 

Shadowing 

Proximity-dependent heat transfer 

Uneven heat transfer 

Limited lifespan 

Hot water systems are the most common type of heating systems used across the world in modern 

greenhouses because of their ability to be managed. The thermal properties of the water enable it to 

carry large amounts of energy over long distances with only a small loss to efficiency. “Water can 

carry 3,500 times the energy that air can carry,” which means that heating air is far less efficient 

than heating water [9]. The heat carried by hot water can be transferred in a multitude of ways. The 

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water can be utilizing for floor heating, bench heating, top heating, perimeter heating, snow and ice 

removal, or preheating irrigation water. Usually, the central boiler system is used to heat the water 

between 120°F and 180°F, and then it is distributed through a pipe system. However, solar 

collectors can be installed on the roof to use the energy from the sun for heating purposes. Pumps 

and valves help to provide even distribution in the system and can control the amount of heat added 

to the building [16]. The pipe system can be placed closed to the crops under the bench (Figure 8), 

in the soil, or the hot water can be circulated in a floor heating system (Figure 9). 

Figure 7: Piping of hot water heating system [16] 

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Figure 8: Under bench heating distribution [16] 

Figure 9: In-floor heating distribution [16] 

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Another way of utilizing hot water is heating a coil connected to a fan to blow hot air out into 

the greenhouse. Hot water systems are more energy efficient as the heat is radiated from below 

and it heats up only the close environment of the plants instead of heating up all or most of the air 

in the greenhouse. This is especially important in the different vegetation stages. This system is 

recommended for larger scale buildings due to the higher initial costs. The average cost of a hot 

water system with minimal complexity in the northern region in the United States ranges from 

$1.50 to $4.00/ft 2 for a 1-acre application [9]. 

Table 4: Advantages and disadvantages of hot water systems [9] [14] 

Advantages 

Disadvantages 

Energy efficient 

Takes time to reheat the space 

Quiet 

Higher Initial cost 

Good manageability 

Complexity 

Carry great amount of energy in long Special skills needed for proper installation 

distances 

Can transfer the energy in different ways - 

Environmentally friendly - 

Good control of temperature - 

Flexibility - 

Other type of heating methods used in controlled environment agriculture include electric 

heaters and burning wood in a furnace or boiler. Electric heaters are not very popular, as it is one 

of the least efficient ways to heat a greenhouse due to their significant operating costs. Wood is a 

great source of fuel in areas that it is widely available. It can be used in a furnace to create hot air 

or in a boiler to heat water. In recent years, boilers have been more commonly used. 

Renewable energy sources have become more popular in the controlled environment 

agriculture sector in the past couple years. The effects of global warming increase the heating and 

cooling loads for buildings which result in greater energy requirements and the relatively high 

price of fossil fuel makes owners to move towards other alternative energy sources. Solar panels, 

solar collectors, heat pumps, biomass and cogeneration systems are the most utilized ones. 

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A solar greenhouse is a passive way to help maintain the required temperature inside the 

building by maximizing the southern glaze exposure to the sun by orienting the greenhouse in such 

a way to reduce the amount of fossil fuels used for heating. The solar greenhouse collects a mass 

of thermal heat from the sun during the day and the insulation prevents the loss of heat at night. 

The northern side of the building is usually well-insulated and has very minimal glazing. “The heat 

storage and thermal insulation of greenhouse is one of the key technologies for improvement of 

solar energy utilization and the reduction of manual concurrent heating power consumption” [17]. 

This type of method can require supplemental heating such as usage of solar collectors or heat 

pumps. 

The easiest way to generate renewable energy is photovoltaic solar panels. The photovoltaic 

panels convert the sunlight into electricity using semiconducting materials that exhibit the 

photovoltaic effect. The panels can be mounted somewhere high or on the roof of the greenhouse 

for maximum exposure of the sunlight. The optical lenses can be mechanically operated to track 

the sunlight which could generate 15% more electricity over the standard photovoltaic system 

according to James Holloway’s testing [18]. The greenhouse’s equipment can be powered by the 

electricity generated by the solar panels. Off-grid photovoltaic systems need to be equipped with 

banks of batteries to be able to store the excess power and utilize it when there is very little or no 

sun. These systems are recommended for operations in which the nearest electrical grid is far. 

While solar panels do have high initial costs, the system does not require fuel, they have low 

carbon-dioxide emissions, and they require very little maintenance. The system payback period 

depends on the size and the amount of exposure to sunlight. The utilization of free energy from the 

sun is a sustainable way for heating and cooling as well. 

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Figure 10: Solar panel system on the roof of a greenhouse [19] 

Geothermal energy uses a thermal mass of soil underground to store (cooling) and dispense 

energy (heating). The tubing system is installed at least 4-6 feet underground so that air can be 

circulated back and forth with the building. Deeper, at around 10-12 feet, the soil has a more even 

temperature which can be useful if the plant has a small range of optimal temperature. In summer, 

humid hot air is circulated in the pipes where the cool temperature of the earth reduces the air 

temperature coming from the greenhouse and condenses the humidity on the wall, which is 

transferred to the soil around the tubes. The ground becomes a store of energy which can release 

the heat on cold days. In the winter, the higher soil temperature raises the temperature of the air 

coming from the greenhouse by drawing off the stored summer heat. Similarly, a liquid system can 

be installed in the soil. Through heat exchanges, the heat can be released or absorbed according to 

the season. This type of heating and cooling is very sustainable in long term. The initial cost of the 

system is very high, but the “free” heating and cooling eventually outweighs the initial costs [20]. 

This is one of the most economical options that currently exists for temperature regulation of a 

greenhouse. 

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Figure 11: Geothermal energy used for heating and cooling [20] 

c. Cooling 

Due to high solar radiation, the average high temperature in Texas in August is 96 °F [11], and 

the temperature inside a greenhouse can be several degrees higher. In order to keep the crops 

growing and provide fresh vegetables and fruits year-round in the southern regions of the United 

States, the temperature must be reduced inside the greenhouse during the hot summer days. In 

northern areas, ventilation techniques provide enough air circulation so that the plants can 

evaporate enough (cool themselves), and additional cooling becomes optional. There are several 

active and passive ways to maintain the temperature cool inside. 

One of the passive ways to block some of the sunlight is using shading. This can be done by 

shade paints or shade cloth. Paints are a very quick and cost-effective way to protect the plants 

from the strong direct sunlight. The number of layers can be adjusted according to the temperature. 

This solution is not always applicable; therefore, it can be replaced with shade cloth like nets and 

blinds. Shade cloth can lower the temperature up to 10 degrees [21]. Blinds can be internal or 

external. With the external blinders the sunlight is filtered before it passes through the glass and 

traps inside which make this type of blinders more efficient. Internal blinders can be installed in 

front of the windows. Both types are removable when their usage is not necessary and can be 

automated if the budget allows [22]. The cost of these depend on their size and the type that is 

needed. It is also important to note that too much shading can result in reduction of plant height 

and number of trusses [23]. 

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Figure 12: Shading on a greenhouse roof [22] 

Another passive method to reduce the average summer temperature inside the growing space 

is trenching the greenhouse. By trenching the greenhouse about 36 inches beneath the ground level, 

where the soil temperature is around 60-70 degrees, the energy requirements can be reduced. The 

inside ambient temperature will be lower than usual due to the utilization of lower soil temperature, 

and this will decrease the amount of heat that needs to be removed from inside [24]. 

Evaporative cooling pads are one of the most common ways to provide cooling in a greenhouse. 

The system is based “on the conversion of sensible heat into latent heat through evaporation of 

water” [23]. The operation of evaporative cooling pads requires air flow through a pad medium. 

The pad can be placed on one side of the greenhouse and exhaust fans, which help pull the air 

through the pad, can be placed on the opposite wall. Temperature reduction can be achieved by 

releasing the energy from the air. “The air released to the outside has absorbed 8,100 BTU of heat 

energy for each gallon evaporated” [9]. Water distribution helps the liquid circulate through the 

material. The original evaporative cooling systems were about 2 inches thick, while the modern 

pads are 4-6 inches thick. The newer cooling pads are made of corrugated cellulose material which 

helps prevent rotting. The medium usually sits in an aluminum or plastic trough. Although it is 

simple to operate the system, it has high installation and operating costs as well as amplified 

possibility for fungal diseases [23]. The ability of a well-design system is capable to reduce the 

dry bulb temperature inside to around 85% of the difference between the outside dry bulb and wet 

bulb temperature. The evaporative cooling system needs to be oversized in areas where the 

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humidity is constantly high in the summer, such as in Dallas [9]. 

Figure 13: Evaporative cooling pad [21] 

Fog (mist) cooling and humidifying systems tend to cost less than the evaporative cooling pads. 

The system is getting more popular in the agricultural sector due to its ability to provide even 

temperature reduction and levels of humidity. These advantages persist in both humid and dry areas 

as well. The principles of the fogging system are very similar to the evaporative cooling system, 

with the only difference being how efficiently the water is utilized. In the fog cooling system, water 

is fogged and sprinkled over the crops from the sprinkler system installed close to the roof. The 

fog is evenly distributed throughout the greenhouse and “because of the flash evaporation 

characteristics of fog, 100 % efficiency is achieved” [9]. The minimum lowering temperature can 

be as low as 1°F with the fogging system, while the minimum temperature differential in the 

evaporative cooling system is 7-10 °F. The mist cooling system consists of a high-pressure pump 

and fine fog nozzle which requires proper maintenance [9]. High-pressure fog systems can 

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change the environmental conditions quickly. Fog systems are designed for all types of greenhouse 

configurations and all types of plants [25]. 

Cooling with water through pipe system has the same principles as heating with water. The 

water must be cooled and pushed through a pipe system which is installed close to the crops. This 

is one of the less common types of cooling systems used in controlled environment agriculture. 

Geothermal heating and cooling are paired together in a single package; if you install the 

system you will get both. Low grade geothermal cooling has a high initial cost but is very 

sustainable and economical in a longer term. On hot days, the air from the greenhouse is circulated 

through underground pipes, and when the water vapor condenses from the hot, humid air on to the 

outside of the pipe, energy gets released into the soil. 

As discussed previously in the heating section, the solar-powered air conditioning system is a 

sustainable choice to achieve heating or cooling. Solar energy can be attained by solar collectors 

or solar panels. Solar collectors use water to store the energy, while solar panels generate electricity 

which can be used for heating, cooling, lighting, or powering other equipment around the building. 

Further explanation about this system can be found in the heating section. 

An absorption refrigeration cycle is another sustainable way to provide cooling in controlled 

environment agriculture. The advantages and disadvantages of the system is discussed in detail in 

section 3, but in summary, this system is a promising low-cost cooling solution and is similar to 

the regular vapor compression air-conditioning system. 

d. Ventilation 

Ventilation is necessary year-round in order to maintain the required humidity and CO2 levels for 

the crops. Before discussing the various ventilation methods, it is important to highlight the 

difference between open and closed greenhouses. An open greenhouse has some form of air flow 

from outside of the structure and has more interaction with outside air. In contrast, a closed 

greenhouse is similar to indoor growing, and there can be more control over the inside conditions 

as there is no direct contact with the outside air. The open greenhouse mostly relies on natural 

convection, but it can be equipped with supplemental ventilation system. In the case of natural 

ventilation, the differences in air pressure move the air through the space. On the other hand, the 

forced ventilation method is primarily used in closed greenhouses and utilizes fans to move to air. 

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On an average summer day in the United States, the noontime solar radiation input can be around 

300-350 BTUs per hour/ft 2 of floor area. This heat contributes to the temperature and humidity rise 

inside, resulting in a higher evaporation rate from the plants [9]. Too significant a humidity level 

can result in moldy surfaces, pests, and diseases on the plants. 

Fan ventilation systems can be used in all weather conditions. The most common recirculation 

fan used in controlled environment agriculture is the overhead horizontal airflow fan [9]. Fans 

create a positive air flow through the greenhouse. Bottom air flow systems and vertical airflow 

fans are commonly used in dense plant canopies. Exhaust fans help release the heated air from the 

greenhouse, and by creating a vacuum, they bring cool, fresh outside air inside the building through 

inlets like open doors or cracks. “Cooling effectiveness of the greenhouse reduces as it travels 

across a greenhouse, resulting in a temperature gradient between the air inlet and exhaust” [9]. 

This problem can be solved by designing a shorter greenhouse and increasing the airflow velocity 

of the fans. The most effective distance between the inlet and the fan outlet is 150 feet or less. It is 

more efficient to have a few larger fans than several smaller fans. The maximum distance between 

the installed fans can be 25 feet in order to provide uniform airflow in the greenhouse. Fans are 

usually selected based on static air pressures; the average value used is 0.125 inches of water 

column. “The volume of air to be moved (or exchanged) is calculated as the number of volumetric 

air changes per minute (usually 1.0-1.5/min)” [9]. The most energy-efficient fans have properly 

sized motors and are maintained regularly. Fans are fairly cheap to install and operate, and they 

can be used as supplemental equipment with evaporative cooling pads, infrared heating, or other 

heating and cooling methods as well. The power for the fan operation can be generated by 

photovoltaic panels. 

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Figure 14: Exhaust fan on the side of the greenhouse [21] 

Desiccant-based ventilation systems are very useful in reducing humidity of the inside air in 

colder weather. Desiccant is a medium which absorbs moisture from the air and can be recycled in 

the desiccant wheel. The collected moisture evaporates with heat as it travels through the wheel 

[24]. “Rotary desiccant wheels can be used in HVAC systems to reduce the relative humidity in an 

incoming airstream through the adsorption of water molecules to the pore surface of a desiccant 

material, lowering the relative humidity” [26]. The regeneration temperature of the system depends 

on the desiccant material used, and while it could work in up to 120 °C, the development of new 

material can potentially reduce this temperature to 80 °C. Due to the high temperature of the 

regeneration process, additional heat energy needs to be added to the system. For airstreams, the 

pressure drop can be as high as 150 Pa with the typical rotary desiccant wheel structure [26]. 

Further reduction in regeneration temperatures and pressure is essential for the more efficient 

operation. This system is used for cooling purposes as well, and it is more environmentally-friendly 

than conventional cooling if the system is powered by free, or solar, energy. According to Amel 

Rjibi, the system powered with solar energy can save up to 24% of the electric energy and reduce 

CO2 emissions by 16% [27]. 

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A refrigerant-based dehumidification system is built similarly to the regular air-conditioning 

system, but it is designed for removal of water vapor from the air instead of cooling. It is equipped 

with an evaporator, condenser, expansion valve, water receptacle and motor-compressor unit (see 

Figure 15). Humid air enters on the evaporator side, where the cold coils of the element cool the 

air below its dew point. Subsequently, the removed moisture can be released to the water 

receptacle. The cold air is pushed through the condenser to increase its temperature, then released 

back to the room with higher temperature but less humidity [28]. This system uses about one 

quarter of the energy per pint when compared to the desiccant-based dehumidification [24]. 

Figure 15: Elements of the refrigerant-based dehumidification system [38] 

e. Glazing and insulation 

The glazing is the outside cover material or the “skin” of the greenhouse. The type of glazing 

used directly influences the amount of solar energy that enters the building. The solar energy both 

increases the temperature in the closed place and provides essential light for the plants [9]. Before 

choosing the right cover material, there are several factors that need to be considered: the type of 

plant being grown, the cost of the material and its maintenance, the durability, transparency and 

lifespan of the material, the location of the building, and the weather conditions of the area. The 

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following table summarizes the type of materials used in controlled environment agriculture and 

discusses their advantages and disadvantages: 

Table 5: Comparison of the different cover materials [29] 

- Advantages Disadvantages 

Glass 

Well-known, many different types to 

choose from, aesthetic, retain its 

transparency for long time, great 

thermal insulator, 

Durable 

Fragile, can be costly, the 

infrastructure needs to be 

able to support it 

Polystyrene (Rigid 

Plastic) 

Polycarbonate (Rigid 

Plastic) 

Glass-like panels, cheaper than glass, 

requires less structural support, 

strength and translucency are like 

glass, not easily damageable, fair 

insulator 

Strength and durability are second 

only to glass, leading option among 

plastics, double-wall configuration, 

admits up to 90% of sunlight, long 

lifespan (up to 20 years), cheaper than 

glass 

Lifespan is shorter than glass, 

not the strongest plastic, not 

the least expensive, clouding 

over a longer period 

More expensive than other 

plastics, may need additional 

insulation, can be an 

incubator for moisture, 

residue, dirt, or bacteria 

Polyethylene (Film) Cheapest option Easily damaged, short 

lifespan (usually less than 18 

month), requires frequent 

replacement, limited 

insulation possibilities 

Copolymer (Film) Cheaper than rigid plastic and glass Easily damaged, short 

lifespan (3 years), requires 

frequent replacement, limited 

insulation possibilities, can 

become brittle and crack in 

very cold weather 

Polyvinyl (Film) 

Most durable plastic film, cheaper 

than rigid plastic and glass 

Short lifespan (5 years), 

limited insulation possibilities 

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Chris Beytes made a general comparison of the different covering materials. More detailed 

specifications need to be requested from the manufacturers. This comparison can be found in Figure 

16. 

Figure 16: Greenhouse Coverage Comparison [9] 

The proper coverage material can help reduce heating and cooling costs during the winter and 

summer, respectively. Some techniques, such as installation of a double layer of film plastic while 

inflating it with a blower, can be both cheap and efficient insulation methods to apply. Usage of 

insulation material is required to increase the efficiency of a greenhouse system. Before choosing 

the right option, it is important to research the available types and understand their differences. 

Some insulation types can be left up all year around, while some require installation before the 

winter or summer arrives and removal at the end of the season. Double glazing is the most efficient 

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way to insulate the entire greenhouse. This type of insulation necessitates the installation with the 

greenhouse itself. It is not removable and is expensive, but this method provides the most benefits 

of any insulation method [30]. 

A clear bubble plastic cover can reduce heating costs by 35%. It is made of a double or triple 

layer of transparent plastic and is covered with air cells. This high UV- translucent insulator works 

just as effectively as double glazing and helps to prevent the greenhouse from overheating during 

hot summer days. The insulation works well with all types of glazing and can be left on yearround, 

but it is recommended to replace the bubble plastic cover every 3-4 years [31]. 

Figure 17: Clear bubble insulation [32] 

The third type of insulation is thermal screens. This insulation method consists of translucent 

material or clear plastic like cross laminated fabric. The material is attached to the eaves with wires 

and restricts heat from rising above the eaves by trapping the warm air inside the building. These 

screens are typically used overnight to conserve energy [30]. It is also possible to cover the 

greenhouse only partially and leave the remainder without insulation, which could be necessary if 

different plants are grown in each end of the structure. Finally, insulation can be installed on the 

floor as well. Base cladding blocks push out the incoming air at the intersection of the walls and 

floor. Polystyrene panels are often utilized for this form of seasonal insulation. 

f. Lighting 

Light energy is one of the major factors necessary for plant growth. In areas where natural 

sunlight is insufficient, some form of supplemental lighting is required to sustain the plants. 

Supplemental lighting enables the farmers to increase the growing season, plant productivity, and 

plant quality. There are several types of possible light sources, including high-pressure sodium 

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lamps and other metal halide lamps, fluorescent lighting, incandescent plant-grow lights, and LED 

lights [33]. 

Figure 18: LED supplemental lighting [34] 

High-pressure sodium (HPS) lamps and other metal halide lamps are not very efficient, as 

they generate significant amounts of heat through their operation. The HPS lamps have an orangered 

glow which can help trigger hormones in the plants, but it cannot be installed in close proximity 

to the plants because of its high heat generation. The average lifespan of the HPS lamps is 18,000 

hours, while the metal halide lamps produce light in the blue spectrum and have an average lifespan 

of 10,000 hours [33] [35]. The supplement of the metal halide lights can produce green leafy 

growth. HPS lamps produce up to 140 lumens per watt, while the metal halide lights only produce 

up to 125 lumens per watt. These values are significantly higher than those for incandescent or 

fluorescent light bulbs. A significant disadvantage of HPS lamps is that they are deficient in the 

blue spectrum, which is essential to the even growth of the plants. If using this type of lighting, the 

plants will require an additional source of blue light [35]. 

Fluorescent lights contain filaments that require replacement from time to time. This type of 

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lamp consumes lots of electrical power and generate a great amount of heat, though less than the 

incandescent, metal halide, or HPS lights. The average lifespan of fluorescent light bulbs is 

estimated to be around 20,000 hours [33]. Because of their size limitations, it is only recommended 

to use for seedlings. Fluorescent bulbs provide a wide spectrum of light and have a better colorrendering 

property. To achieve the best results, it is recommended to place them no closer than a 

couple feet from the plants. The standard fluorescent grow light produces about 39 lumens per 

watt, but the newer versions are more energy-efficient and can produce up to 90 lumens per watt 

[35]. 

Incandescent bulbs are both the least expensive and the least efficient solution to supply 

artificial lighting in a greenhouse. The standard incandescent lightbulb can produce only 18 lumens 

per watt, much less than the other lighting options discussed [35]. 

LED is a type of semiconductor diode for which the spectral composition and light intensity 

can be adjusted according to the time of the day and the type of plants. Each type of plant has 

different requirements of light intensity, light quality (spectral distribution) of the radiation, and 

light duration (photoperiod) to perform photosynthesis. Spectral distribution affects the shape, 

development, and flowering of the plant. Plants are very selective about the wavelength of light that 

they will absorb, and they show the most reaction to red and blue lights [33]. One of the numerous 

advantages of LED light is the possibility to control its spectral composition and intensity. These 

characteristics can be adjusted according to the plant being grown and its developmental stage. 

Their lifespan is also significantly higher than the other light bulbs, reaching 30,000 to 50,000 

hours or beyond. Due to low-radiant heat production, they can be placed close to the crops without 

damaging them. Though LED lights have high capital costs, they are the most energy-efficient and 

sustainable method of supplemental lighting. 

3. Evie, design of low-cost cooling system 

A solar-powered absorption refrigeration cycle is a sustainable way of cooling commercial 

buildings. According to the size constraints of Evie (a mobile greenhouse built by the Hunt Institute 

for Engineering & Humanity at Southern Methodist University), a design model was fully 

completed by the ARC design team and compared with the regular vapor compression refrigeration 

cycle. 

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a. Importance of Absorption Refrigeration Cycle 

Figure 19: Evie at the State Fair (Photo Credit: Laura Graham) 

An absorption system has five main components: the generator, condenser, evaporator, 

absorber, and heat exchanger. Instead of using electricity as in vapor-compression systems, 

absorption refrigeration systems use a heat source to provide the energy needed for cooling. The 

absorption refrigeration system uses two different fluids and their mixtures in order to achieve 

cooling in a specified space. One fluid is used as a refrigerant, while the other is used as an 

absorbent. The two most common types of fluid pairs used for the cycle are ammonia-water and 

water-lithium bromide. In this design, ammonia was chosen as the refrigerant and water as the 

absorbent. 

The absorption refrigeration cycle has multiple advantages compared to the conventional vapor 

compression refrigeration cycle. One of its most important advantages is the method of 

compression of the refrigerant. In the regular vapor compression system, a compressor is used for 

the purpose of circulating the refrigerant in the cycle. This could be done by a centrifugal, 

reciprocating, or rotating type of compressor [36]. In the vapor absorption refrigeration cycle the 

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compression of the refrigerant is done by the absorber (water in this case), which absorbs the vapor 

refrigerant coming from the evaporator. Phase change can be observed in the absorber. 

The major power-consuming device in the regular vapor compression cycle is the compressor, 

while a pump is needed for the absorption refrigeration cycle. The compressor requires a large 

amount of power in order to run it, and the consumption increases as the size of the refrigeration 

system itself increases. The compressor is considered a major moving part in the vapor 

compression cycle but gets eliminated in the absorption refrigeration cycle, meaning that the only 

moving part is a pump, which requires significantly less power [36]. 

The type of energy used for the two aforementioned refrigeration cycles also differs. 

Mechanical energy is required to run the compressor in the regular vapor compression refrigeration 

cycle, while in the absorption refrigeration cycle, heat is used as an energy input. This heat could be 

residual heat coming from an engine, such as from a car, generated by solar collectors, etc. This 

project utilizes solar panels to generate electricity, which is used to provide power to the heating 

element. The heating element in the generator provides the required heat to separate the refrigerant 

from the mixture solution. 

The vapor compression cycle requires a lot of power, as it runs solely on electricity. Thus, the 

running cost of the system is expensive. The absorption refrigeration cycle depends on a natural 

energy source in this project, as solar panels provide the required power. This method of heat input 

minimizes the running cost of the refrigeration system. 

The compressor in the regular vapor compression refrigeration cycle usually operates at very 

high speeds, meaning significant amounts of vibration and noise. As the compression process is 

done by a generator and absorber in the absorption refrigeration cycle, the noise and vibration of 

the compressor is eliminated. Compressors also need strong foundations to resist the generated 

vibration and remain intact under the high pressure of the refrigerant. Thus, there are multiple 

advantages to replacing the compressor in our cycle [36]. 

The maintenance of the regular vapor compression cycle is more complicated and more costly 

than the maintenance of the absorption refrigeration cycle. Because the compressor is considered 

the main moving part in the vapor compression cycle, the regular lubrication and potential defects 

have to be checked regularly. Over time, it also requires replacing the piston, cylinder liner, piston 

rings, etc. Potential failure, and subsequent replacement, of the compressor is very expensive as 

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well. This type of maintenance also requires special care. In the absorption refrigeration cycle, on 

the other hand, the only moving part is the pump, which rarely fails and therefore requires 

significantly less maintenance. 

The absorption refrigeration cycle requires the usage of a mixture fluid. In this project, 

ammonia is used as the refrigerant and water as the absorbent fluid. Ammonia is an accessible and 

cheap refrigerant, while the halocarbons used in the regular vapor compression cycle are very 

expensive. The halocarbons are also dangerous to the environment, as they contribute to the 

greenhouse effect. Additionally, there could be multiple leaks in a vapor compression cycle because 

of the use of the compressor and its moving parts. In the case of leakage, the refrigerant has to be 

recharged regularly, which could be very costly. The absorption refrigeration cycle has very little 

or no potential for leakage, as there are no moving parts in the system other than a pump. This 

eliminates the potential cost of refrigerant recharge [36]. 

Some disadvantages of the absorption refrigeration cycle are its higher initial cost, the low 

coefficient of performance of the system, and the higher heat rejection rate. 

b. Experiment 

A thermodynamic analysis was performed on the cycle to achieve the working conditions of 

the absorption refrigeration cycle for Evie, the mobile greenhouse. The outdoor and indoor 

temperatures were assumed (36°C and 20°C, respectively) according to Dallas weather data and 

the required growing temperature for most plants [37]. Heat transfer calculations were done in 

order to obtain the heat load calculations on Evie. Some assumptions were made for the heat gain 

calculations, such as that Evie is made out of only glass like a regular greenhouse. 

Circuit analysis was utilized to study the required electricity for the system. As a result, the 

appropriate heat source could be picked to run the cycle. 

The theoretical cycle was modified according to the size of Evie. Since the mobile greenhouse 

has a limited space which requires cooling in the summer, the absorption refrigeration cycle had 

to be sized in accordance with its requirements. 

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The engineering specifications can be seen in Table 6, Table 7 and Table 8. 

Table 6: Objectives 

Objectives 

Cost-efficient 

Cool the given space 

Operate off-grid 

Details 

In about 5 years of operation, the 

overall cost should be less than the 

cost of operating a regular AC 

system 

Maintain a temperature of 20 °C inside 

of Evie 

Utilize solar-panels 

Have low capital cost Initial cost around $5000 

Table 7: Constraints 

Constraints 

Low maintenance cost 

Be able to operate within 

the given cooling load 

System size 

Details 

Must be less than regular AC system 

($300) 

The given cooling load for our system is 

1.68kW 

The size of the system including the solar 

panels should be less than 6.8 m 2 

Table 8: Functions 

Operate safely 

Functions 

Details 

Pressure should not exceed 2.85 MPa 

Operate efficiently The coefficient of performance is 0.2 

The cycle can be broken into different flows based on the presence of the ammonia-water 

mixture, ammonia gas, and ammonia vapor. States 1 to 6 are the cycle of the ammonium hydroxide 

solution, ammonia in liquid phase constitutes states 7 and 10, and states 8 and 9 contain ammonia 

vapor. The basic operation of an ammonia-water absorption refrigeration cycle is as follows. 

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The solution at state 1, rich in refrigerant, is pumped by higher pressure through the heat 

exchanger at state 2 into the generator at state 3, which contains the solution of ammonia-water, 

rich in ammonia. Heat is then added to the generator, causing high-pressure ammonia vapor to 

desorb the solution. The solution containing less refrigerant at state 4 is sent back through the heat 

exchanger to the absorber. The high-pressure ammonia vapor flows to the condenser, where it then 

loses heat to the surrounding environment by convection as it leaves the condenser. Then, the highpressure 

ammonia liquid (8) goes through a valve restriction to the low-pressure side (9) of the 

cycle. This liquid, at low pressure, boils and evaporates in the evaporator where heat from the given 

space is absorbed. The ammonia liquid (10) then returns to the absorber, where it is absorbed into 

the weak solution coming from the generator. The solution in the absorber, now once again rich in 

ammonia, is pumped to the generator (1), where the process starts again. The schematics of the 

absorption refrigeration cycle with the flow of solution mixture and ammonia vapor can be seen 

in Figure 20. 

Figure 20: Schematics of the Absorption Refrigeration Cycle 

The conditions at different states in Figure 20 is stated below, and the calculation can be 

found in Table 9 and Table 10. The cost of each element can be found in Table 11. 

1. Strong solution leaving the absorber (X1 =55.3% water, T1 = 30 °C) 

2. Strong solution entering the heat exchanger (X2 = 55.3% water, T2 = 30 °C) 

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3. Strong solution entering the generator (X3 = 55.3% water) 

4. Weak solution leaving the generator (X4 = 56% water, T4 = 60°C) 

5. Weak solution leaving the heat exchanger (X5 =56% water) 

6. Weak solution entering the absorber (X6=56% water) 

7. Refrigerant vapor leaving the generator which is heated at T7= 60°C, P7 = 2.61 MPa) 

8. Refrigerant liquid leaving the condenser (Saturated at 60°C, T8 = 60°C, P8 =2.61 MPa) 

9. Refrigerant liquid entering the evaporator (Saturated at 16°C, T9 = 16°C, P9 = 0.75 MPa) 

10. Refrigerant vapor entering the absorber (Saturated at 16°C, T10 = 16°C, P10 = 0.75 MPa) 

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c. Results 

Temperatures(T), pressures(P), enthalpies(h), mass flow rate of the fluids (m) and the quantity 

of water in the mixture fluid (X) were calculated at each state identified by a number in Figure 20, 

and the results are summarized in Table 9 and Table 10. 

Table 9: Thermodynamic Cycle Calculations 1 

Table 10: Thermodynamic Cycle Calculations 2 

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Table 11: Cost of the Elements 

Component Details Quantity Unit Price Total price 

Generator We need 36 " × 48 " 

& 

Aluminum sheets with 

1 $182 $182 

Absorber [38] thickness of 0.2” 

Condenser [39] Already exist in market. 

The cooling capacity is 

1 $718 $718 

1.5 tons 

Evaporator [39] Already exist in market. 

The cooling capacity is 

1 $ 254 $254 

1.5 tons 

Heat exchanger Already exist in market. 1 $150 $150 

Solar Panels [40] 

250-watt solar micro 

inverter kit 2 $579 $1158 

Battery 12 V/200 Amp-hr 3 $269 $807 

Steel pipe [41] 1/2" SCH 40. 

6 ft. long 1 $12.46 $12.46 

Pump [42] Red Dragon 5 ECO 25 

Watt 4.0m³ DC Pump 1 $458.3 $458.3 

Expansion Valve 

[43] 

90˚ Flanged 

Elbow [44] 

Heating element 

[45] 

TEA thermostatic 

expansion valve 

Smith Cooper 304 

Stainless Steel 1/2 in. 

90° Long Radius Elbow 

Weld Fittings - Sch 40 

1 $130 $130 

4 $3.70 $14.8 

material: stainless 

power:100 W 1 $10.44 $10.44 

Total $3895 

After preliminary design analysis and cost analysis, the ARC team has determined that this system 

will not meet the requirements set forward by our customer. The system with the solar panels will 

be too heavy to be placed on top of Evie, and the system components will be bigger than the given 

size requirement. Given Evie’s small size (about 7 m 2 ) and the requirement for a solar-powered 

system, we have concluded that our design will not be more efficient than the compression AC 

system that is already in place. However, from the design research, it is evident that this system is 

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feasible and could be efficient for a larger-scale cooling system where the cost of compression AC 

system is too high and sources like steam, geothermal energy, and natural gas could be used as heat 

input to the system. When used at such a large scale, this system will surpass the overall cost of 

regular AC system in about three to five years. 

d. Implications of this project 

Global Impact 

Upon success, this absorption cooling system could provide a significant advantage for 

farmers worldwide. This system provides an efficient, cost-effective method of cooling a 

greenhouse to an optimal temperature. Millions of people in the United States alone live in areas 

that face a lack of fresh, healthy food options and could greatly benefit if this system is used to 

produce food in a greenhouse setting. Moreover, there are many remote areas and households that 

do not have proper access to electricity, and this cycle could be used to provide AC in their homes 

or even cool their greenhouse. 

Since this system does not rely on electricity to operate and could be run on energy sources 

like solar, gas, geothermal water, woods, kerosene etc., a broad set of applications for this system 

are possible. One option may be to use this system to make portable solar freezers which could be 

used to store blood and vaccines. This will be useful in the remote parts of the world where, due to 

limited access to electricity and refrigeration systems, establishing a blood bank has not yet been 

possible. It also has promising possible applications for fishermen and small dairy producers in the 

developing world who often lack access to electricity and require cooling for their highly 

perishable products. Without such technologies, they are under pressure to sell their product 

quickly, no matter the price. 

Economic Impact 

With this system running in their greenhouse, farmers will face a lower variable cost of 

cooling their greenhouse after the cost of initial setup. Since this system has only a few moving 

parts, there will be less maintenance required, also contributing to its cost-effective nature. With 

these greenhouses running efficiently, farmers can sell their food locally and bolster their local 

economy. 

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If the efficiency of this system could be increased to a level where it matches the efficiency 

of the AC systems currently used in households, this system could completely replace the 

compressor AC system. It can have a significant economic impact in the worldwide HVAC market 

since there would be great demand for a low-cost, low-maintenance system. 

If this system could be successfully implemented in cars to replace the compression AC 

system with a solar powered absorption cooling system, the car could maintain a constant 

temperature even while not running. Not only would car users save money on gas, they would also 

not have to waste time and energy waiting for their car to heat or cool to their desired temperature. 

Environmental impact 

By using the absorption refrigeration system, one could use renewable, clean energy 

instead of using electricity, one of the leading sources for greenhouse gas emissions. In this system 

we can use sunlight, wind, or water to generate power to run the system with minimal to no 

negative impact on the environment. 

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4. Conclusion 

This research focused on assessing the available technologies used in controlled environment 

agriculture and identifying a promising model for a low-cost cooling method. Based on the available 

literature, a detailed discussion is included on heating, cooling, and ventilation technologies as 

well as the best possible orientation, structure, insulation, glazing materials, and supplemental 

lighting methods for the greenhouse. A detailed design of a solar powered absorption refrigeration 

cycle model was designed for Evie, taking into consideration its size and limitations. The results 

show that the proposed design would be efficient in a larger scale, with costs lower than a regular 

air-conditioning system over a 5-year period. According to these findings, solar and geothermal 

energy are the most sustainable ways to heat and cool a greenhouse, yet currently their initial and 

installation costs are very high. Small-scale urban farmers and low-income communities are unlikely 

to be able to afford these technologies. Passive solar heating can be a great solution to reduce the 

heating costs during cold days, but this method requires some form of insulation. Clear bubble 

insulation has a relatively lower price when compared to the other insulation methods. The least 

expensive way to achieve ventilation is by natural convection, but natural convection is not always 

sufficient depending on the weather conditions of the area, the size of the greenhouse, and the type 

of plants grown. Light is one of the most important conditions for the adequate growth of the 

plants. While LED lighting has higher capital costs than other lighting methods, its numerous other 

advantages make it the most economical, sustainable, and energy-efficient solution to provide 

supplemental lighting to the plants. Communities interested in producing their own produce need 

to invest in these technologies to enjoy their long-term benefits. Further development, testing, and 

analysis are needed to improve the efficiency of the current technologies used in controlled 

environment agriculture and make them accessible to low-income communities. 

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[35] “Indoor Plant Grow Light Guide.” ACF Greenhouses, 

www.littlegreenhouse.com/guide3.shtml. 

[36] “Vapor Compression Refrigeration Cycle versus Absorption Refrigeration.” Brighthub 

Engineering, 17 Mar. 2010, . 

[37] Albert, Steve, et al. “Tomato Growing: Six Requirements for Success.” Harvest to 

40


Adrienn Santa 

Table, 10 Mar. 1970, 

www.harvesttotable.com/tomato_growing_six_requirement/. 

[38] Metals, Online. “0.25’ Aluminum Plate 6061-T651.” OnlineMetals.com, 

www.onlinemetals.com/merchant.cfm?pid=1248&step=4&showunits=inches&id=76&to 

p_cat=60. 

[39] “Goodman GSX140181 GSX14 - 1.5 Ton - Air Conditioner - 14 Nominal SEER - Single- 

Stage - R-410A Refrigerant.” EComfort, www.ecomfort.com/Goodman- 

GSX140181/p26109.html. 

[40] “1500 WATT SOLAR MICRO INVERTER KIT.” The Inverter Store, 

theinverterstore.com/product/1500-watt-solar-micro-inverter-kit/. 

[41] “Steel Pipe.” MetalsDepot® - Buy Steel Pipe Online!, www.metalsdepot.com/steel- 

products/steel-pipe. 

[42] Specialty, Aquarium. “Royal Exclusiv Red Dragon 5 ECO 25 Watt 4.0m³ DC 

Pump.” Aquarium Specialty, www.aquariumspecialty.com/royal-exclusiv-red-dragon-5-eco-25- 

watt-4-0m-dc-pump.html. 

[43] “TEA Thermostatic Expansion Valve, Complete Valves - Code Number Selector.” Danfoss 

Products, products.danfoss.com/productrange/list/refrigeration/thermostaticexpansion- 

valves/thermostatic-expansion-valves-exchangeable-orifice/tea/teacomplete-valves/?Conn-- 

size=1-2-in#/. 

[44] “Smith Cooper 304 Stainless Steel 1/2 in. 90° Long Radius Elbow Weld Fittings - Sch 40.” 

40-90- long-radius-elbow-weld- 

fittings/?gclid=Cj0KCQiA6enQBRDUARIsAGs1YQgYXiM87jjaNVehOP- 

Lca_AioLs1t7qSCteZBRSQ_7LlglFliY3H3AaAjtTEALw_wcB. 

[45] “2017 Four U Type Electric Heating Tube,U Shape Heating Element, 4u Cartridge Heater 

Tube,Liquid Heating Pipe, Tubular Heater Elements From Gdlees, $3.75.” DHgate, 

John M. Ellsworth Co. Inc., www.jmesales.com/smith-cooper-304-stainless-steel-sch- 

www.dhgate.com/product/four-u-type-electric-heating-tube-ushape/153428861.html. 

41

1

Signature and Approval of Mentor: 

I have reviewed and approve of this final report. 

Ali 

Digitally signed 

by Ali Beskok 

12:53:50 -05'00' 

Dr. Ali Beskok, Mechanical Engineering Department Chair 

1

Controlled Environment Agriculture Technologies

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