Greenhouse Technology Decisions: Technology Level, Ventilation, Cooling, Energy and Automation

1. High-tech vs mid-tech greenhouse

Technology level is a commercial decision, not a prestige one. It should follow from the price the market pays for continuity and quality, not from what looks most advanced in a brochure.

• Mid-tech typically means a robust structure with natural ventilation, basic screening, drip irrigation with a fertigation unit and simple controls — lower CAPEX per m², lower fixed cost, wider yield variance across the year.
• High-tech typically adds a taller gutter, full climate control, energy and shade screens, active cooling or heating, humidity management, drain recirculation and a climate computer — higher CAPEX and fixed OPEX, tighter yield and quality control, longer production window.
• The deciding question: does your market pay a premium for out-of-season supply, consistent grade and guaranteed weekly volume? If it does not, high-tech capital is often better spent on more mid-tech area or on water and post-harvest infrastructure.
• High-tech also raises the operating skill floor. A house that depends on setpoint strategy needs a grower who can run it; without that, measured performance drifts toward mid-tech results at high-tech cost.
• Phasing is legitimate: build the structure and utilities to accept screens, cooling or CO2 later, and instal them once the market and the team justify it. State the future-provision requirement explicitly in the RFQ.

2. Natural vs forced (mechanical) ventilation

Ventilation is the first climate tool, and the cheapest one to run. Active cooling should only enter the scope after ventilation has been sized properly.

• Natural ventilation relies on roof and side vents driven by wind and thermal buoyancy. It has near-zero running cost and few moving parts, but its capacity is limited on still, hot days and it becomes ineffective when insect screening restricts vent area.
• Forced ventilation uses fans to guarantee a defined air exchange regardless of wind, at a continuous electrical cost and with more maintenance. It is normally chosen where insect screening, cyclone loads, humidity control or a very tight climate target rules out relying on vents.
• Screening interacts directly with this decision: fine mesh can cut effective vent area substantially, so vent area, mesh specification and design air exchange must be quoted together, never separately.
• Ask every bidder for the design ventilation rate, the vent area as a percentage of floor area, the assumed wind data set, and the mesh porosity used in the calculation. Two proposals with the same vent count can differ materially on all four.
• In humid climates the binding constraint is often moisture removal rather than temperature, which can make air exchange and dehumidification strategy more decisive than fan power.

3. Pad-and-fan vs fogging (high-pressure misting)

Both are evaporative and both are limited by the same physics: the drier the incoming air, the more cooling is available. Wet-bulb data for the hottest weeks — not average temperature — decides whether either is worth its capital.

• Pad-and-fan pulls air through a wetted pad and along the house. It delivers a strong temperature drop in dry climates but creates a gradient from pad to fan, needs a closed house, and consumes water and fan energy continuously.
• Fogging atomises water into the air above the crop, keeping the climate more uniform, working with natural ventilation and allowing humidity to be raised deliberately. It needs high-pressure pumps, very clean water and strict nozzle maintenance, and it can raise humidity to unhelpful levels in already-humid air.
• In humid or coastal climates neither delivers much cooling; the realistic levers become ventilation capacity, shading and screening, crop timing, and — where economics allow — mechanical cooling or dehumidification.
• Water quality is a scope item, not a detail: pad systems foul and fog nozzles block on hard or high-EC water, so filtration or treatment belongs in the same package.
• Require every cooling bid to state design outside conditions, design inside target, installed cooling capacity, water consumption per hour and per season, and electrical load — otherwise the two systems cannot be compared at all.

4. Grid-only vs solar-hybrid energy supply

The energy decision follows the climate system, because it is the cooling, heating, dehumidification and irrigation loads that define what has to be supplied and what happens when supply fails.

• Grid-only is simplest where supply is reliable and tariffs are moderate. Its real risk is not price but interruption: pumps, fans and controls stopping during peak radiation can damage a crop within hours.
• Solar-hybrid (PV with grid and, where needed, storage or a generator) fits sites with high daytime loads that coincide with irradiance — irrigation pumping, fans, fogging pumps — and sites where the grid is weak, expensive or capacity-constrained.
• Load profile decides the value, not annual kWh. Map hourly demand across a peak week and a shoulder week before sizing anything; PV that produces when nothing is running has poor economics.
• Critical-load backup is a separate question from cost saving. Define which circuits must never stop (controls, main irrigation, ventilation actuators) and specify the autonomy required in hours.
• Grid-connection lead time and export rules vary by jurisdiction and are a common schedule risk; confirm them before the tender rather than after award.

5. Manual vs automated operation

Automation earns its place where it removes a measurable constraint — labour availability, response speed or consistency — not where it adds features nobody will use.

• Manual or semi-manual operation stays viable at smaller commercial scale, with a stable and affordable workforce and a forgiving climate. It keeps CAPEX and integration risk down and depends heavily on grower skill.
• Automation of climate, irrigation and fertigation is usually the first step with the clearest return: it holds setpoints and dosing consistently overnight and at weekends, which is where manual operations lose most performance.
• Internal logistics automation (trolleys, harvest handling, sorting) is justified mainly by labour cost and availability at scale; it also imposes layout requirements that must be fixed in the structural design, not retrofitted cheaply.
• Every automated system needs data ownership, protocol compatibility, remote access, alarm routing, spare parts and service response defined in the contract. Unstated integration is the most common source of variation orders.
• A useful test: state the specific decision or task each automated function replaces, and who would otherwise perform it. Functions that fail this test can be deferred to a later phase.

How to carry these decisions into the RFQ

• State the chosen technology level and the reason, so no bidder silently substitutes another.
• State the design outside conditions and inside targets used for every load calculation, plus the climate data set and its source.
• State the ventilation strategy, target air exchange, vent area and screening specification together.
• State whether active cooling or heating is in scope, and the design capacity basis if it is.
• State the energy model, connection capacity, tariff assumption and required backup autonomy.
• State the automation level per system, and the integration, data and service requirements attached to it.
• Require a written exclusions list from every bidder — technology-level differences hide there more often than in the headline price.

Questions buyers ask before selecting a greenhouse company