Two greenhouse proposals are not on the same weather basis just because both use an EPW file. Check what dataset each file contains, how it was prepared and which calculation used it. Then reconcile the annual simulation separately from the mechanical design conditions and the approved structural-hazard basis.
The practical outcome is a short list of calculations that are comparable, need an agreed rerun, or remain unresolved. This keeps a difference in weather evidence from being mistaken for a difference in greenhouse performance.
An EPW filename does not identify the dataset
EPW identifies a weather-data format. It does not, by itself, tell you whether the contents represent a typical year, a particular historical year or a projected scenario. EnergyPlus's Auxiliary Programs documentation, version 26.2, explicitly separates the procedures and purpose behind a dataset from the arrangement of data in a file format.
A typical meteorological year, or TMY, is selected to represent typical conditions using a stated method. It need not be a single continuous observed year. Conversely, an actual-year description does not establish that every variable was directly measured without gaps or estimates. The file's provenance and processing notes matter.
Ask for the actual file reference and provider documentation, not just “local weather” on the quotation. Record the provider and version, station or grid, location and elevation, source period, dataset classification and selection method. Preserve units, time convention, and known missing or estimated data so the modeler can judge comparability.
Separate the three records
Commercial greenhouse simulation workflows such as Hortinergy's documented process use typical hourly weather together with greenhouse and crop configuration. This establishes why the file belongs in an RFQ comparison. It does not independently validate the accuracy of a particular simulation or make its annual file suitable for every design task.
| Record | Evidence to reconcile | Outcome |
|---|---|---|
| Annual simulation | Dataset provenance, classification, variables, timing, file identity and calculation report. | Comparable annual basis, agreed rerun, or unresolved dataset. |
| Mechanical design conditions | Source and edition, relevant location, selected duty, coincident variables, designer and calculation reference. | Comparable duty basis, agreed rerun, or unresolved selection. |
| Structural-hazard basis | The separate, approved wind/snow and other applicable hazard-design reference. | Correct approved reference supplied, or structural clarification required. |
EnergyPlus's Climate Calculations guidance notes that a weather file may lack the conditions needed for equipment sizing. It also assigns selection of appropriate design conditions to the designer. A TMY file's warmest or coldest record is therefore not an automatic project design condition.
Ask the mechanical designer to identify the intended duty and the associated variables together. Do not assemble an artificial design hour from unrelated maximum temperature, maximum humidity and maximum solar values. Nor should the annual weather file be used to replace the governing structural-hazard submission.
Work through one paired proposal
Here is a hypothetical comparison with no invented energy results. Supplier A provides an EPW file described as a typical year assembled from a stated historical period. Supplier B provides an EPW file containing a particular actual year. Both annual reports use the same greenhouse area, but the file descriptions differ.
Record “different dataset basis” in the annual sheet. Ask the responsible designer to agree which dataset and model assumptions should be used for the comparison, then request the affected annual results on that basis. Converting or renaming B's file to EPW does not resolve the difference because it already uses that format.
Now suppose the two mechanical reports cite the same accepted design-condition source, edition and selected duty. That part can be reviewed on its own evidence. Do not discard a supported mechanical comparison simply because the annual runs need reconciliation. Equally, matching annual files would not close a missing mechanical design-condition reference.
Finally, compare each proposal's structural reference with the approved project basis. An attachment called “weather data” is not enough to show that the applicable hazard design has been addressed. This three-record approach tells the buyer exactly which response is needed from which specialist.
Read the package notes, including the limitations
Climate.OneBuilding documents the sources of its design conditions, including ASHRAE 2025 information, substitution from another location when needed, and calculation from source weather where ASHRAE conditions are absent. Check which method applies to the package being quoted. Receiving design information alongside an annual file does not establish that both came from the same source or method.
For projected weather, keep the scenario and method explicit. NOAA's TMY product page labels its product experimental and explains its typical-month selection and projection context. An experimental product or a single future scenario should not be presented as a verified worst-case forecast for the greenhouse.
Do not choose a station only because it is nearby, or impose a universal acceptable distance. Ask the modeler to justify the selected evidence for the site and calculation purpose. Retain the justification with the file version so the comparison can be repeated later.
Request the rerun that actually closes the gap
Use the three linked manual sheets: annual dataset comparison, mechanical design-condition comparison, and structural-basis reference. Enter the same proposal IDs on each. They contain no weather calculations or automatic engineering acceptance.
Complete the evidence fields before assigning “comparable,” “rerun on agreed basis,” or “unresolved.” For each rerun, name the agreed replacement basis, affected report and responsible designer. Use the separate heating-load design-input guide for the wider heating brief and the energy-efficient design discussion to examine the resulting system choices. The weather reconciliation should leave a specific, traceable request rather than a general demand for a better calculation.