How to compare greenhouse proposals in hot climates
In hot climates, compare greenhouse proposals on five normalised lines before price: total ventilation area as a percentage of floor area after insect screen derating, installed cooling capacity and the design outside temperature it was sized against, humidity control at peak load, annual water and electricity consumption in measurable units, and the explicit exclusions list. A lower price almost always means one of these five was reduced, and a screen, pad bank or chiller added after award costs several times what it costs inside the original tender.
Hot-climate greenhouse bids diverge more than any other project type. Two suppliers can quote the same 3-hectare structure with an 80% price gap simply because one sized cooling against a 42 °C design day and the other against a seasonal average, or because one derated ventilation for a 50-mesh insect screen and the other did not.
This page is the normalisation sheet. Put every bid on these lines first, resolve non-compliance in writing, and only then look at price. Nothing here ranks suppliers or claims a technology is universally better — the right cooling strategy depends on crop, humidity, water cost and energy tariff at your site.
1. Ventilation — normalise the effective area, not the headline
Ventilation is the cheapest cooling in any climate, and the most commonly overstated line in a hot-climate bid. Ask every bidder to state effective area after screen derating, not the gross vent opening.
- Total roof plus side vent area as a percentage of floor area — state the number, not the vent type
- Insect screen mesh specification and the derating factor applied to airflow
- Vent drive: continuous rack-and-pinion, rolling side, or manual, and the opening time from closed to full
- Wind-side and lee-side vent control, and the wind speed at which vents are forced shut
- Whether ventilation was sized for the design day or for an annual average
- Air exchange rate per hour claimed, and the conditions at which it was calculated
2. Cooling — capacity means nothing without the design condition
Installed cooling capacity is only comparable when every bidder used the same outside design temperature, humidity and radiation. Declare those three values in the RFQ and require each bid to restate them.
- Design outside dry-bulb and wet-bulb temperature, relative humidity and peak radiation used in the calculation
- Cooling strategy: natural ventilation only, shading, high-pressure fogging, pad-and-fan, or semi-closed
- For pad-and-fan: pad area and thickness, fan count, installed airflow per m², air path length and expected temperature gradient end to end
- For fogging: nozzle count, working pressure, water quality requirement, droplet size and pump redundancy
- Achievable inside temperature at the design condition — as a stated delta below outside, not as a marketing claim
- Shading and energy screens: number of layers, shade percentage, and whether they are movable
- Installed cooling electrical load in kW, since this is the line that dictates OPEX
3. Humidity control — the line most hot-climate bids omit
Evaporative cooling raises humidity. In coastal and greenhouse-dense regions the resulting VPD and condensation behaviour is a disease and yield problem, not a comfort detail. Require an explicit answer.
- Target VPD or humidity band by crop stage, and how it is maintained during peak cooling
- Behaviour when outside wet-bulb is high: what the control strategy does when evaporative cooling stops working
- Dehumidification equipment, if any, with capacity and energy demand
- Night-time condensation management and minimum-pipe or air-movement strategy
- Horizontal air-flow fans: count, placement and control logic
- Sensor set and positions used to control humidity, and alarm thresholds
4. Water and energy OPEX — convert every bid into annual consumption
Two proposals with identical CAPEX can differ substantially in annual running cost. Require consumption figures in measurable units so the comparison can be priced with your own tariffs.
- Annual electricity consumption in kWh, split between cooling, pumping, lighting and controls
- Peak electrical demand in kW, which drives connection capacity and any generation requirement
- Annual water consumption in m³, split between crop irrigation and evaporative cooling
- Evaporative cooling water losses and blowdown, plus the water quality required to protect pads or nozzles
- Drain water recirculation percentage and disinfection energy demand
- Consumables: pad replacement interval, filter and nozzle replacement, screen and film life
- Maintenance labour hours per year attributable to cooling and ventilation systems
5. Scope gaps that turn a cheap hot-climate bid into the expensive one
The exclusions list is the most important page in any proposal. These are the items most frequently absent from hot-climate quotations; require each bidder to mark every one as included, excluded or not applicable.
- Water treatment ahead of pads or fog nozzles — filtration, softening or reverse osmosis
- Buffer storage tanks and the pump station serving cooling demand at peak
- Electrical connection, transformer, main distribution and backup power for critical loads
- Civil works: levelling, drainage, foundations, concrete floors and access roads
- Insect screening and its ventilation compensation
- Second screen layer, blackout or shade cloth where the crop plan implies it
- Commissioning at design-day conditions rather than a mild-weather handover
- Operator training, as-built documentation and a first-season spare-parts package
- Import duties, inland transport, offloading, cranage and site accommodation
- Any performance figure that is stated in marketing text but excluded from the contract
6. A workable evaluation sequence
Score technical compliance before price. A bid that fails normalisation should be returned for restatement, not discounted mentally and left in the comparison.
- Restate all bids on the five lines above using the buyer's own design conditions
- Issue one written clarification round; require answers in the RFQ structure
- Reject or re-tender lump-sum bids without a breakdown by structure, climate, water, electrical and civil
- Price the OPEX difference over at least five years using your own tariffs before comparing CAPEX
- Check warranty per component group and service response time in-country
- 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.
Hot-climate cooling strategies — what to verify in each bid
Neutral summary of trade-offs commonly discussed in protected-agriculture engineering. Suitability depends on crop, wet-bulb temperature, water cost and energy tariff at your specific site, and must be confirmed by the qualified engineers on your project.
| Strategy | Works best when | Main constraint | Verify in the bid |
|---|---|---|---|
| Natural ventilation + shading | Moderate peak temperatures and reliable wind | Limited delta on still, high-radiation days | Effective vent area after screen derating; shade percentage and whether screens are movable |
| High-pressure fogging | Hot and dry air with low wet-bulb | Adds humidity; needs clean water and pressure stability | Nozzle count, working pressure, water treatment scope, pump redundancy |
| Pad-and-fan | Hot, dry, large uninterrupted spans | Temperature gradient along the air path; continuous fan energy | Pad area and thickness, installed airflow per m², path length, gradient, kW load |
| Semi-closed / mechanically cooled | High-value crops, high humidity, or tight climate targets | Highest CAPEX and electrical demand | Installed cooling kW, design condition, grid capacity, backup power scope |
Normalisation sheet — the lines every bid must answer identically
| Line | Unit to require | Common distortion |
|---|---|---|
| Ventilation | % of floor area, after screen derating | Gross vent area quoted without screen effect |
| Cooling capacity | kW installed at a stated design condition | Capacity sized to an average, not a design day |
| Inside temperature target | Delta below outside at design condition | Marketing claim with no stated condition |
| Humidity control | VPD or RH band maintained at peak load | Line absent from the proposal entirely |
| Electricity | kWh per year and peak kW | Only equipment ratings, no consumption |
| Water | m³ per year, irrigation vs cooling split | Irrigation only; cooling losses omitted |
| 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 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.