McMaster University · Capstone Project · 2023–2024

Smart Modular
Greenhouse

A self-regulating hydroponic greenhouse designed to maintain stable growing conditions across an outdoor ambient temperature range of −20°C to +35°C. Eight months of engineering, from thermal modelling to embedded control systems to physical build.

FEA · Nastran Thermal Analysis Embedded C / Python ESP32 Control Loop Hydroponics 8 months · ~$194 budget
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01 · Overview

Project at a Glance

55°C
Total operating temperature range
±1°C
Temperature regulation tolerance
$194
Total build cost after 20% BOM reduction
147W
Glycol heating loop output capacity

The goal was to engineer a modular, self-regulating growing environment capable of year-round operation in Northern Canadian climates. The project required integrated analysis across thermal physics, structural mechanics, embedded control systems, and hydroponic growing, each informing the others. The system was designed with scalability in mind: modular units can be combined end-on-end or side-by-side to increase growing capacity and passive solar heat intake proportionally.

02 · Thermal Analysis

Solar & Heat Transfer Modelling

Solar Irradiance Model

Using Iqaluit (63.75°N) as the reference latitude, a conservative mid-point for Northern Canada, daily solar irradiance was modelled across a full year using NASA-derived equations for sun declination and daylight duration.

Θ = 23.5° · sin(2π · dt / 365.25)
σ_D = 137 mW/cm² · cos(L − Θ)

The daily energy across all polycarbonate faces was computed by integrating irradiance over daylight hours. Front and back faces were estimated at roughly half the top-face irradiance based on angle of incidence geometry, and 1.6× the surface area, contributing a combined factor of 2.6E_D total daily solar intake.

Glycol Heating System

For winter operation, a 60% propylene glycol mixture (freeze point −52.8°C) was modelled using a 1800 L/h pump, establishing the supplemental heat budget.

q = ṁ · c_p · ΔT
= 0.516 kg/s · 3.563 kJ/kg·°C · 80°C = 147.3 W

Convective and radiative losses were evaluated under laminar flow assumptions using Prandtl and Reynolds number analysis referenced against CERN detector cooling data for glycol mixture properties.

Passive Solar Heat Intake: Watts/Day vs. Calendar Date

Peak: ~137 W/day (July) · Minimum: ~10 W/day (January)
Viable passive heating window (>80W): May 9 – Oct 3 (~5 months)

03 · Control System

Embedded Temperature Regulation

Architecture

A closed-loop PID-style temperature control system was implemented across two layers: an ESP32 microcontroller running firmware in C for low-level sensor reading and actuator control, communicating continuously with a Python desktop GUI for monitoring, setpoint adjustment, and data logging. The system maintained ±1°C regulation tolerance under steady-state conditions.

Wireless communication was handled by the ESP32's onboard Wi-Fi stack. All hardware connections, sensors, pump relay, heating element control, and LED grow lights, were hand-soldered to COTS components to minimize cost and maximize integration density within the enclosure.

Control System & GUI Demo
Temperature Regulation in Action
Hydroponics & Water Circulation System
Capstone Fair Demo
System Overview
04 · Physical Build

Construction & Materials

Greenhouse front view showing polycarbonate panels, wood frame, and hydroponic tray
Fig. 1 - Front view: polycarbonate glazing, wood frame, hydroponic tray with drip irrigation
Greenhouse three-quarter view showing pump system, sensor array, and tubing
Fig. 2 - Three-quarter view: pump system, sensor array, glycol tubing, and hinged access panel

Bill of Materials

Component Description Est. Cost
Raspberry PiMain compute unit for GUI and logging$66.90
ESP32 Dev BoardEmbedded microcontroller, sensor I/O, Wi-Fi~$15
Polycarbonate Sheet0.05″ thick, glazing for all faces$15–30
Structural WoodPine frame construction$5–20
Submersible Water PumpUltra-quiet brushless, hydroponic loop$15
Water Pipes & FittingsPVC supply lines, drip emitters$10–15
Hydroponic Growing TrayMicrogreens/seedling tray with drain$20–40
UV/Full-Spectrum LED LightsSupplemental grow lighting$11
Heat RadiatorAluminum heat exchanger for glycol loop~$15
VentilationVent cover and circulation system~$15
Misc. (fasteners, sensors, wiring)Building materials, temp sensors, relay~$10
TotalAfter 20% BOM reduction from design optimization~$194
05 · Findings & Conclusions

Engineering Conclusions

✓ Passive Solar Window

Passive solar heating exceeds 80W from May 9 to October 3 sufficient for unaided warm-season growing without supplemental heat.

✓ Glycol Loop Capacity

The modelled glycol heating loop delivers 147W of thermal output, sufficient to compensate for the ~10W passive solar minimum in deep winter, with significant margin.

✓ Scalability Validated

Modular end-on-end expansion doubles glazing area and solar intake. Side-by-side expansion increases it by 1.5×. Both configurations are viable for full-year operation with a heat exchanger.

✓ Control Loop Performance

The ESP32-based closed-loop system achieved ±1°C steady-state regulation, validating the control architecture for real deployment conditions.

△ Heating Unit Lead Time

The external heater did not ship in time for the capstone demonstration. The glycol heating system was validated analytically but not tested under live winter conditions.

△ Model Limitations

Solar model does not account for atmospheric refraction. Front/back face irradiance estimates are geometric approximations. Night-time supplemental heating requirements require further analysis for spring/autumn shoulder seasons.

Next Steps

Future work would focus on live winter thermal testing with the glycol loop installed, detailed insulation R-value measurement to validate the passive heat retention model, and iterating the control firmware to support adaptive setpoints based on external weather data. A scaled-up two-module prototype would directly validate the modularization analysis presented here.