DX Air Handler RFQ Checklist: Airflow, ESP, Coil & Controls

Start HereQuick Answer for Buyers

A direct expansion air handler should be selected when a standard DX unit cannot meet the project’s air-side requirements. Choose it when the space needs ducted air distribution above 500 Pa ESP, outdoor air above 20%, special filtration such as ISO 16890 ePM1 class, or humidity control coordinated with coil leaving-air temperature.^[1]

The practical rule is simple: use a packaged DX unit for straightforward comfort cooling, and use a DX air handler when the air path is the project risk. The air handler gives more control over coil face velocity, fan selection, filters, drain pan, casing, mixing box and controls — and that control matters because pressure drop, wet-coil behavior and condensate drainage can reduce real capacity even when the compressor size looks correct.

Decision LogicWhen a Direct Expansion Air Handler Fits

A direct expansion air handler fits projects where air treatment is more important than only nominal cooling capacity. It combines an evaporator coil using direct refrigerant expansion with AHU sections for fan, filter, mixing, drainage, casing and control logic.

This matrix matters because a direct expansion air handler is not just a bigger indoor unit — the coil, fan and refrigerant circuit must work as one system. If a filter bank loads from 80 Pa clean pressure to 200 Pa final pressure, airflow can drop because the fan operating point moves left on the fan curve.

Product RangeSongXin DX Air Handler Configurations

SongXin’s air handling unit production line covers three main DX-ready configurations. Each is built on an aluminum-frame, polyurethane-foamed galvanized panel casing with copper-aluminum coils, 100% leak-tested and assembled under ISO 9001 quality management.^[9]

All three platforms can be specified with multi-stage filtration (panel / bag / HEPA), optional UV sterilization, IP54 protection and IoT-ready BMS controls. Energy efficiency on optimized configurations reaches 94%, with reference projects across 40+ countries and reported uptime around 99.8%.^[9]

Cross-reference: see modular air handling unit supplier for split-shipment large units, and modular AHU selection guide when site access limits transport size.

RFQ FoundationsCore Selection Parameters

A reliable direct expansion air handler RFQ should define the real operating envelope before model selection. The supplier needs air-side data and refrigerant-side data, not only the room area.

Numbers should be distributed across the air side, refrigeration side and maintenance plan because one missing value can change the final configuration. A 90 kW air handler at 600 Pa ESP is not the same selection as a 90 kW air handler at 1000 Pa ESP.

The Heart of the UnitDX Coil Sizing: Face Velocity, Rows & Fin Spacing

The DX coil is the bridge between the air side and the refrigerant side. Three coil parameters drive whether the unit will reach its nameplate capacity in the room.

A practical buyer’s check: if the supplier quotes the coil at 3.2 m/s face velocity to “fit a smaller cabinet”, ask for the wet-coil carry-over test result. SongXin’s coil section follows 100% leak and pressure tests before assembly, and selection sheets state face velocity, rows, fin pitch and dry/wet pressure drop on every offer.^[9]

Worked ExampleAirflow, ESP & Coil Screening

A simple calculation helps the buyer see whether a direct expansion air handler is needed. Assume an industrial support room has 96 kW total load, 72 kW sensible load and a target supply-air temperature difference of 10 K.

By Room TypeConfiguration Matrix

A direct expansion air handler should be configured by room duty, not by a generic catalog name. The matrix below gives a buyer-facing starting point.

The key mechanism is pressure loss. Filters, coils and ducts convert fan energy into pressure drop. As resistance increases, airflow falls, and lower airflow can reduce sensible capacity because less room air passes across the coil.

Cost DecisionDX Air Handler vs Chilled Water AHU

Many buyers ask whether a DX air handler is “cheaper” than a chilled-water AHU. The honest answer: only when the project is small or standalone. Once the building has multiple zones, central energy management, or run hours above ~4,000 per year, chilled water usually wins on lifetime cost.

The table below is a procurement-planning model for a single 96 kW load running 2,500 vs 5,000 hours per year. Use it as a screening tool; replace with site-specific quotes before purchase.

Procurement guidance. For a single 96 kW industrial support room at 2,500 hrs/yr, a DX air handler is usually right. For a campus of 6 zones × 80 kW running 5,000 hrs/yr, the air-cooled screw chiller + multiple AHU layout (see the 50 ton air-cooled screw chiller selection guide) is the safer long-term choice. On the boundary, ask the supplier to quote both and compare 10-year total cost.

Climate DeratingHigh-Ambient & Part-Load Behavior

DX systems lose capacity as outdoor ambient temperature rises, because condenser heat rejection becomes harder. This is a critical RFQ point in Middle East, South Asia and African projects.

A common mistake is rating the unit at 35 °C and installing it in a 46 °C climate. The same dynamic applies to air-cooled chillers — see air-cooled screw chiller ambient temperature capacity for the equivalent chiller behavior. At part load, a DX air handler with multiple compressors and interlaced coil circuiting keeps coil temperature uniform; single-compressor DX units cycle on/off, causing humidity swing and reduced equipment life. For continuous-process rooms, request a minimum 2-stage compressor configuration.

Send ThisRFQ Data & Specification Checklist

A direct expansion air handler RFQ should make the supplier responsible for a measurable operating point. Send the data below when asking SongXin for engineering support or a quote.

Specification checklist

When you send your project conditions, SongXin can compare a direct expansion air handler with a standard air handling unit supplier solution or with a chilled-water system using how to select a water cooled chiller and single screw vs twin screw chiller for plant-side selection.

Field StoryProject Case Study: 21,456 m³/h DX AHU

Avoid TheseCommon Mistakes

1. Buying the compressor size and forgetting the fan. A 96 kW DX air handler that cannot deliver 21,456 m³/h at 1,000 Pa will not perform like a 96 kW system in the room.
2. Ignoring fresh-air moisture. Outdoor air above 30 °C and 60% RH adds latent load, increasing condensate and pushing the coil toward a colder leaving-air condition. State the fresh-air ratio before the coil is finalized.
3. Treating filtration as an accessory. Fine filters raise pressure drop because smaller particles need denser media or deeper banks. If the fan is selected only for clean-filter pressure, airflow falls as filters load.
4. Using a DX air handler where chilled water is better. For a campus with 10+ large zones or continuous operation above 4000 hrs/yr, compare a chiller plant first — see SongXin’s air-cooled screw chiller content.
5. Accepting a rating at 35 °C when the site is 43 °C or hotter. Always ask for the capacity table at the actual site design temperature — not the catalog reference.

Why It WorksWhy Buyers Choose Direct Expansion

ComplianceCertifications & Quality Documentation

A DX air handler is a regulated piece of equipment in most export markets. Ask for the supplier’s certifications before placing the order, not after delivery.

SongXin’s manufacturing follows ISO 9001 with 100% per-unit leak, pressure and airflow testing, supports CE-compliant builds for European projects, and keeps documentation aligned with AHRI, ASHRAE, RoHS and REACH frameworks for export tenders.^[9][10] Detailed references and audit-ready files are on the certification and compliance page and quality control testing page.

Q & AFrequently Asked Questions