How to compare greenhouse proposals in humid tropical climates
In humid tropical climates, evaporative cooling loses most of its effect because the wet-bulb temperature is already close to the air temperature, so compare proposals on four normalised lines before price: effective ventilation and air-exchange rate after insect-screen derating, the declared humidity or VPD band and the equipment that actually holds it, the cooling approach and its installed electrical load at the site's design wet-bulb, and annual humidity-related operating cost — dehumidification energy, fan runtime, crop protection and condensation-driven maintenance. A cheaper bid in the tropics almost always drops dehumidification capacity, air movement or condensation management, and each of those reappears as disease pressure and yield loss rather than as a line on the invoice.
Hot-and-dry and hot-and-humid are different engineering problems, and a proposal written for one is usually wrong for the other. In a humid tropical site the wet-bulb temperature can sit within two or three degrees of the dry-bulb for much of the year, which means pads and fog deliver a fraction of the cooling they deliver in an arid climate while adding moisture the crop then has to lose.
The consequence is that the deciding lines shift. Ventilation and air movement matter more than installed cooling capacity, dehumidification and condensation control move from optional to central, and the largest cost differences between bids show up in humidity-related operating cost rather than in the structure price.
This page is the normalisation sheet for those projects. Restate every bid on the same lines, resolve non-compliance in writing, and only then compare price. Nothing here ranks suppliers or declares one technology better — the right approach depends on crop, altitude, wet-bulb profile, energy tariff and disease pressure at your specific site.
1. Ventilation and air exchange — the primary humidity tool
In the tropics ventilation is not only a cooling strategy, it is the main way moisture leaves the greenhouse. Require effective figures after screen derating, and require the air-exchange rate to be stated at a condition, not as a brochure number.
- Total roof plus side vent area as a percentage of floor area, after insect-screen derating
- Insect screen mesh (thrips, whitefly or aphid grade) and the airflow derating factor applied to it
- Air-exchange rate per hour claimed, and the wind speed, vent position and outside condition assumed
- Ridge configuration: open roof, rolling roof, sawtooth or fixed vent, and behaviour in heavy rain
- Rain protection over open vents, and whether vents are forced shut in storms — and what holds humidity then
- Horizontal air-flow or vertical air-flow fans: count, kW, placement, and control logic at night
- Gutter height and internal volume, which drive buffering capacity against humidity spikes
2. Dehumidification — the line that separates serious tropical bids
In a high wet-bulb climate the crop's transpired water has nowhere to go on still, saturated nights. Require every bidder to state how humidity is removed, with capacity in measurable units, or to state explicitly that no dehumidification is included.
- Declared humidity or VPD band by crop stage, day and night, and the hours per year it is expected to be exceeded
- Dehumidification method: forced ventilation with heating, mechanical (refrigerant) dehumidifiers, desiccant systems, heat-exchanger units or none
- Installed moisture-removal capacity in litres or kg of water per hour, and at what inside and outside condition
- Electrical load in kW for dehumidification, and expected annual runtime hours
- Whether any heating is included — dehumidifying by ventilation without a heat source does not work on saturated nights
- Condensate handling: collection, drainage, and whether recovered water is reused
- Control integration: which sensors trigger dehumidification, and the alarm behaviour when the band is missed
3. Cooling approach at high wet-bulb — restate the design condition
Evaporative cooling is limited by the wet-bulb temperature. Declare the site's design dry-bulb, wet-bulb and radiation in the RFQ and require each bid to restate them, otherwise capacity figures are not comparable.
- Design outside dry-bulb, wet-bulb, relative humidity and peak radiation used in the calculation
- Realistic achievable delta below outside temperature at the design wet-bulb, not at an arid reference condition
- Whether fogging or pads are proposed, and what the humidity consequence is at the design condition
- Shading strategy: fixed whitewash, movable shade screens, diffuse covering, and the shade percentage
- Any mechanical or semi-closed cooling: installed kW, cooling medium, and grid capacity required
- Night strategy: what the system does when outside air is saturated and cooling by ventilation stops working
- Total installed electrical load in kW attributable to cooling and air movement
4. Condensation, covering and disease-risk detailing
Most humidity damage in tropical greenhouses arrives as condensation drip and prolonged leaf wetness rather than as a temperature failure. These details are cheap in the tender and expensive afterwards.
- Covering material and anti-drip / anti-condensation treatment, with stated lifetime in tropical UV
- Gutter and condensation drainage detailing, including internal condensate channels
- Screen material choice and its condensation behaviour when closed
- Minimum-pipe or air-movement strategy to break the boundary layer at night
- Leaf-wetness or dew-point monitoring, sensor positions and count
- Corrosion protection specification for structure, fixings, fans and electrical enclosures in humid, coastal or saline conditions
- Rainwater discharge capacity for tropical rainfall intensity, and site drainage scope
5. Humidity-related OPEX gaps — convert every bid into annual cost
Two proposals with the same CAPEX can differ substantially in annual running cost once humidity management is priced. Require consumption and consumable figures in measurable units so they can be priced with your own tariffs.
- Annual electricity in kWh split between dehumidification, air movement, cooling, pumping and controls, plus peak kW
- Dehumidification runtime hours per year assumed, and the sensitivity if the band is tightened
- Any heating fuel or energy demand used for moisture removal, in kWh or equivalent per year
- Annual water consumption in m³, split between irrigation and any evaporative cooling
- Crop-protection intensity assumed at the declared humidity band — tighter control usually reduces spray programmes
- Consumable and replacement intervals accelerated by humidity: screens, covering, filters, fan bearings, sensors, electrical enclosures
- Maintenance labour hours per year attributable to humidity, corrosion and condensation systems
6. Scope gaps that make a cheap tropical bid the expensive one
Require every bidder to mark each item below as included, excluded or not applicable. A single sentence referring to 'buyer scope' is not an exclusions list.
- Dehumidification equipment and any heat source needed to make ventilation-based moisture removal work
- Horizontal air-flow fans and their electrical distribution
- Anti-drip covering specification rather than a standard film
- Corrosion-grade structure, fixings and enclosures for humid or coastal sites
- Site drainage, levelling and rainwater discharge sized for tropical rainfall
- Electrical connection, transformer, distribution and backup power for climate-critical loads
- Water treatment, buffer storage and the pump station
- Commissioning during the wet season or at design wet-bulb, rather than a dry-season handover
- Operator training on humidity control strategy, as-built documentation and a first-season spare-parts package
- Import duties, inland transport, offloading, cranage and site accommodation
7. A workable evaluation sequence
Score technical compliance before price. A bid that fails normalisation should be returned for restatement, not mentally discounted and left in the comparison.
- Restate all bids on the four normalised lines using your own design wet-bulb and humidity band
- Require each bidder to state expected hours per year outside the declared humidity band
- Issue one written clarification round, answered in the RFQ structure
- Price humidity-related OPEX over at least five years with your own tariffs before comparing CAPEX
- Check warranty per component group, corrosion warranty, and in-country service response time
- Only then rank commercially
Financing note
SeedMatch Group is not a bank, lender, credit provider or financial adviser, and quotes no rates, approvals or commitments. Where a qualified commercial project requires funding, it may be introduced to independent third-party financing providers, who control all eligibility, pricing and decisions.
Humidity-management approaches — what to verify in each bid
Neutral summary of trade-offs commonly discussed in protected-agriculture engineering for high wet-bulb climates. Suitability depends on crop, altitude, wet-bulb profile, energy tariff and disease pressure at your specific site, and must be confirmed by the qualified engineers on your project.
| Approach | Works best when | Main constraint | Verify in the bid |
|---|---|---|---|
| High ventilation + air movement | Sites with reliable wind and moderate night humidity | Fails on still, saturated nights and during storms | Effective vent area after derating, air-exchange rate at a stated condition, HAF fan count and kW |
| Ventilation with supplementary heat | Cooler highland tropics and greenhouses with night condensation problems | Requires a heat source and its running cost | Heat capacity in kW, energy source, annual runtime, control interlock with vents |
| Mechanical dehumidification | High-value crops and tight VPD targets in lowland humid sites | Highest electrical load and CAPEX | Moisture removal in litres/hour at a stated condition, kW load, runtime hours, condensate handling |
| Semi-closed with active climate treatment | High-value production where climate must be held year-round | Highest CAPEX, grid capacity and technical operating demand | Installed kW, design wet-bulb, grid and backup scope, operator training and service model |
| Evaporative cooling (fog or pads) | Drier seasons or higher-altitude tropical sites with a lower wet-bulb | Limited effect at high wet-bulb and adds moisture load | Achievable delta at the design wet-bulb, water quality scope, humidity consequence at peak |
Normalisation sheet — the lines every humid-tropical bid must answer identically
| Line | Unit to require | Common distortion |
|---|---|---|
| Ventilation | % of floor area after screen derating | Gross vent area quoted without screen effect |
| Air exchange | Air changes per hour at a stated condition | Brochure figure with no wind speed or vent position |
| Humidity band | VPD or RH band by crop stage, day and night | Line absent, or stated without equipment to hold it |
| Dehumidification | Litres of water removed per hour at a stated condition | Equipment listed with no capacity or runtime |
| Cooling | kW installed at the site design wet-bulb | Capacity sized against an arid reference condition |
| Electricity | kWh per year and peak kW, split by function | Only equipment ratings, no annual consumption |
| Condensation control | Anti-drip covering spec, drainage detail, air-movement strategy | Assumed standard film with no condensation detailing |
| Corrosion | Protection grade per component group | Generic 'galvanised' with no specification |
| Exclusions | Itemised list, marked line by line | Single sentence referring to 'buyer scope' |
Questions buyers ask before selecting a greenhouse company
SeedMatch Group is not a greenhouse manufacturer, integrator, EPC contractor or installer, and has no exclusive relationship with any company named on this page. Several of the companies described here can be invited to quote through a structured RFQ. Capability descriptions summarise categories these companies present publicly and should be verified directly with each company for a specific project.
Normalise price per m² and flag missing scope across up to three quotations.
The 25-line normalisation method used before price is weighed.
The equivalent normalisation sheet for hot and arid sites.
The definition checklist that makes proposals comparable in the first place.
Section-by-section specification structure for a professional greenhouse tender.
Frame airflow, cooling load and water demand before the tender.
Lifecycle view: CAPEX, energy, water, labour, replacement and cost per kg.
The scope items that reappear as variation orders after award.
Structured intake that produces one comparable scope for every bidder.