Nov 04, 2026

What Is a DX Cooling Coil? How It Works, Types and Applications

Quick answer: A DX (direct expansion) cooling coil is a heat exchanger in which refrigerant evaporates inside the coil tubes and absorbs heat directly from the air passing over the fins. It needs no intermediate fluid such as chilled water, so it is a compact and efficient cooling solution for air handling units (AHUs), packaged units and split systems.If you are designing, buying or maintaining an HVAC system, understanding DX coils helps you choose the right cooling technology. This guide explains what a DX cooling coil is, how it works, its main types, where it is used, and how to select one.What Is a DX (Direct Expansion) Cooling Coil?A DX cooling coil is the evaporator section of a refrigeration circuit, built as a finned-tube heat exchanger. “Direct expansion” means the refrigerant expands and evaporates directly inside the coil, rather than cooling a secondary fluid first.Warm air from the room or outdoors is blown across the coil. The refrigerant inside absorbs heat from that air, changes from a low-pressure liquid-vapour mix to a vapour, and cools the air. The coil also removes moisture from the air, which is why DX coils both cool and dehumidify.Browse our range of Cooling coils and HVAC products to see configurations built for different capacities and applications.How Does a DX Cooling Coil Work?A DX coil works as one part of a vapour-compression refrigeration cycle. Here is the process step by step:Compression: The compressor raises the pressure and temperature of the refrigerant vapour.Condensation: In the condenser, the hot refrigerant rejects heat and becomes a high-pressure liquid.Expansion: The liquid passes through an expansion device, such as a thermostatic expansion valve (TXV) or electronic expansion valve (EEV). Its pressure and temperature drop sharply.Distribution: A refrigerant distributor splits the flow evenly across the coil circuits.Evaporation: Inside the coil tubes, the cold refrigerant absorbs heat from the air and evaporates.Return: The low-pressure vapour returns to the compressor, and the cycle repeats.Sensible and latent cooling: The coil surface runs below the air’s dew point, so water vapour condenses on the fins and drains away. This removes latent heat (humidity) along with sensible heat (temperature), which is important in humid climates.Main Components of a DX Cooling CoilTubes: Usually copper, carrying the refrigerant.Fins: Aluminium or copper plates that increase the heat transfer surface area. Fin density is measured in fins per inch (FPI).Headers and return bends: Connect the tubes into circuits.Distributor: Feeds refrigerant evenly to every circuit. Poor distribution lowers capacity and can cause icing.Expansion valve (TXV/EEV): Controls refrigerant flow based on superheat.Casing and drain pan: Support the coil and collect condensate.Types of DX Cooling CoilsBy constructionCopper tube, aluminium fin: The most common option. It is cost-effective and performs well in general comfort applications.Copper tube, copper fin: Better corrosion resistance. It suits coastal, industrial or chemically aggressive environments.Coated or epoxy-coated coils: A protective layer extends coil life in corrosive conditions.By circuitingFull circuit: One refrigerant circuit serves the whole coil. It is simple and suits steady loads.Split or face-split circuit: Separate circuits serve different parts of the face. This gives better part-load performance and humidity control.Row-split / interlaced circuit: Circuits are interleaved so that even at part load, refrigerant contacts the full airflow. This improves coil utilisation and reduces freeze-up risk.By applicationComfort cooling coils: For offices, malls and hotels.Process and precision cooling coils: For data centers, labs and manufacturing.Dehumidification coils: Designed for deep cooling and tight humidity control.For custom configurations, see our product catalogue.Applications of DX Cooling CoilsDX coils are used wherever a compact, self-contained cooling solution is needed:Air handling units (AHUs) and packaged units in commercial buildingsCleanrooms and pharmaceutical facilities needing precise temperature and humidity controlData centers and server rooms requiring reliable, continuous coolingCold storage and food processing facilitiesHospitals, hotels, malls and officesIndustrial process cooling and dehumidificationDX Coil vs Chilled Water CoilFeatureDX CoilChilled Water CoilCooling mediumRefrigerant (evaporates in coil)Chilled waterSystem complexitySimpler, no chiller plantNeeds chiller, pumps, pipingBest forSmall to medium capacityLarge buildings, high capacityTemperature controlStaged or variable compressor controlValve modulation, very preciseInstallation costGenerally lower for small systemsHigher upfront, efficient at scaleRefrigerant chargeLarge charge in the coil circuitMinimal in the coilRule of thumb: DX is usually the better fit for small to medium loads and standalone systems. Chilled water tends to win in large central plants.Advantages and LimitationsAdvantagesCompact and fast to installHigh heat transfer efficiency, since there is no secondary fluid loopLower first cost for small and medium systemsGood dehumidification performanceLimitationsNeeds careful refrigerant distribution and controlRisk of freezing if airflow is low or the coil is dirtyRefrigerant leaks and charge limits need attentionLess suited to very large capacitiesHow to Select the Right DX Cooling CoilCheck these factors before buying:Cooling capacity (TR or kW) and the sensible heat ratio (SHR)Air flow and face velocity, to avoid moisture carryoverFin density (FPI) and the pressure drop it createsRefrigerant type, such as R410A, R32 or R454B, and compatibility with your systemCircuiting for part-load controlMaterial and coating, based on environment and air qualityOperating conditions, including entering air temperature and humidity (for India, design for local high-humidity conditions)Not sure what to specify? Visit the Airtree HVAC homepage to contact our team, or view our range.Key TakeawaysA DX cooling coil cools air by evaporating refrigerant directly inside its tubes.It combines sensible cooling and dehumidification in one component.Material, circuiting and fin density should match the application and environment.DX suits small to medium systems, while chilled water suits large central plants.Frequently Asked Questions1. What does DX mean in a DX cooling coil?DX stands for direct expansion. The refrigerant expands and evaporates directly inside the coil to cool the air.2. Is a DX coil the same as an evaporator coil?Yes. In a refrigeration circuit, a DX coil is the evaporator coil. The term “DX” highlights that refrigerant, not water, is used.3. What is the difference between a DX coil and a chilled water coil?A DX coil uses evaporating refrigerant. A chilled water coil uses water cooled by a separate chiller.4. Why does a DX coil freeze up?Common causes are low airflow, a dirty coil or filter, low refrigerant charge, or faulty expansion valve control.5. Which refrigerants are used in DX coils?Common options include R410A, R32 and R454B, depending on the system design and regulations.6. Where are DX cooling coils used?They are used in AHUs, cleanrooms, data centers, cold storage, hospitals, hotels and commercial buildings.

Oct 29, 2026

How to Calculate Dehumidifier Capacity for an Industrial Space

Quick answer: Dehumidifier capacity is the moisture entering your space every hour, plus a safety margin. Add up the water brought in by outside air, people and process work, then multiply by 1.15 to 1.25. Compare that figure, in kg of water per hour, with a unit's rating at your own room conditions.Excess humidity does real damage in industrial buildings. It rusts machined parts, cakes powders, puts condensation on packaging, grows mould on stored goods and causes static problems in electronics. In a pharma area it can push a batch out of specification. A dehumidifier only helps if it matches the load it actually faces.An undersized dehumidifier runs around the clock and never reaches its set point. An oversized one costs more to buy and, in some designs, cycles badly. Sizing it properly takes a tape measure, a psychrometric chart and about twenty minutes. This guide walks through the method, with a worked example for a plant in Delhi NCR.Step 1: Set the conditions you need to holdDecide the indoor temperature and relative humidity (RH) your product or process needs. Then find the worst outdoor condition at your site. In North India that is the monsoon, often 32 to 35 °C at 70 to 80% RH.SpaceTypical target RHPharma packing and coating30 to 50%Electronics assembly40 to 60%Food and packaging40 to 55%Metal and machinery storage40 to 50%Treat these as starting ranges. Your product specification or applicable standard always overrides them.Next, convert each condition into a humidity ratio, which is grams of water per kg of dry air. A psychrometric chart or any online calculator does this in seconds. The gap between outdoor and indoor values is the water every kilogram of incoming air carries into the room.Step 2: Add up the moisture loadFour sources matter.Outside air. This covers leakage through doors, gaps and openings, plus any fresh air you supply on purpose. It is usually the largest share. For leakage, a rough planning figure is 0.25 to 0.5 air changes per hour in a reasonably tight building, and 1 or more where loading doors open often.People. Allow about 0.05 to 0.15 kg/h per person, depending on how hard they work.Process. Open tanks, washing, steam, wet products and drying all add water. Get these numbers from your process team, because this is the load most often forgotten.Building ingress. Vapour passing through walls and roofs is small in insulated rooms. In an uninsulated shed it can be significant, so raise your margin there.The outside-air load uses this formula: Load (kg/h) = airflow (m³/h) × 1.2 × humidity ratio difference (g/kg) ÷ 1000Step 3: A worked exampleTake a packing hall measuring 20 m × 15 m × 5 m, which is 1,500 m³. The target is 24 °C and 50% RH, a humidity ratio of 9.3 g/kg. The monsoon outdoor condition is 32 °C and 70% RH, or 21.1 g/kg. The difference is 11.8 g/kg.SourceBasisLoad (kg/h)Air leakage0.5 air changes per hour, 750 m³/h10.6Fresh air600 m³/h supplied8.5People20 people at 0.1 kg/h2.0ProcessWashing area, from process team3.0Subtotal 24.1With 15% margin24.1 × 1.1527.7The hall needs roughly 28 kg of water removed per hour. Since 1 kg of water is about 1 litre, that is close to 670 litres per day. These figures are illustrative, so use your own airflow and process data.Step 4: Check the rating at your conditionsBrochure ratings are usually quoted at a warm, humid test point such as 30 °C and 80% RH. At 24 °C and 50% RH the same machine can remove well under half as much. Ask the manufacturer for output at your design condition, not the headline number.If fresh air is pre-treated in an air handling unit, the load on the room dehumidifier falls. Our guide on what an air handling unit is explains how a cooling coil and fan section handle that job.Step 5: Plan placement and controlsSizing is only half the job. Put the unit where it can draw from the dampest part of the room, and make sure its airflow reaches every corner so no dead zones form. Seal gaps and fit strip curtains or air curtains at loading bays to cut the leakage you just calculated. Mount the RH sensor away from the unit's outlet and from doors, so it reads the room and not a local draught. Condensate from a refrigerant unit needs a proper drain, and a desiccant unit's regeneration exhaust should be ducted outside.Refrigerant or desiccant: which type fits?Refrigerant (condensing). Cools air below its dew point so water condenses on a coil. It suits rooms above about 20 °C that need 45 to 60% RH, and it uses less energy per kg removed.Desiccant. Draws moisture into a rotating wheel, which is dried with heated air. It holds 20 to 40% RH and works in cold rooms where a coil would frost.The packing hall above, at 24 °C and 50% RH, normally suits a refrigerant unit. Had the target been 30% RH, a desiccant unit would be the safer choice.Sizing mistakes to avoidUsing average weather instead of the peak monsoon condition.Ignoring loading bays, shutters and doors that stay open.Leaving process moisture out of the total.Trusting the nameplate figure instead of output at room conditions.Skipping RH sensors and controls, so the unit cannot hold the set point.Frequently asked questionsHow do I calculate dehumidifier capacity for a factory? Find the humidity ratio difference between outdoor and indoor air, multiply it by the air entering per hour, and add people and process moisture. Apply a 15 to 25% margin. The result is in kg/h.How many litres per day is 1 kg/h? About 24 litres per day, because 1 kg of water is roughly 1 litre. Our example load of 28 kg/h works out to around 670 litres per day.Is a bigger dehumidifier always better? No. Oversizing raises purchase and running cost and can make some units cycle on and off. A 15 to 25% margin over the calculated load is usually enough.Can I size a dehumidifier from floor area alone? No. Floor area gives only a rough idea. The load comes from air leakage, people and process moisture, so two rooms of the same size can need very different capacities.Which type should I use for 30% RH? Use a desiccant dehumidifier. Refrigerant units struggle to hold humidity that low, especially in cooler rooms.Get your space sizedIf you would rather have an engineer check the numbers, send your room dimensions, target RH and process details to AirTree HVAC. You can see the full dehumidifier and air handling range on our products page, and find more HVAC guides on the AirTree blog.

Oct 26, 2026

Ceiling Suspended vs Floor Mounted AHU: How to Choose the Right One

A ceiling suspended AHU hangs from the slab above the false ceiling, so it suits buildings with little plant room space. A floor mounted AHU stands on a plinth in a plant room and suits large airflows and heavy-duty use. Choose by space, airflow, filtration and servicing access.Most AHU quotations begin with a capacity figure, but the first real decision is simpler: where will the unit sit? Put it in the wrong place and you pay for it every year, in noise complaints, awkward filter changes and ducting that runs further than it should.This guide compares the two layouts we are asked about most, the ceiling suspended AHU and the floor mounted AHU, and gives you a short set of questions to settle the choice for your own building.What Each Type IsAn air handling unit does the same job in both layouts. A fan moves air through filters and a cooling coil, sometimes a heating coil or humidity section, and sends it into ducts. What changes is the housing and how it is supported.A ceiling suspended AHU is a compact unit hung from the slab on rods or brackets, usually inside the false ceiling void. A floor mounted AHU is a larger modular unit that sits on a base frame or plinth, normally in a dedicated plant room, and can be built from several sections joined in a row.When a Ceiling Suspended AHU Makes SenseThe main reason to choose a suspended unit is space. If the building has no spare plant room, or the plant room was given to something else during design, hanging the AHU above the ceiling frees that floor area for rent or use.It fits well in offices, hotels, malls, hospitals and other commercial buildings where each floor or zone has its own unit. Airtree's Ceiling Suspended AHU covers 700 to 12,000 CFM, can be supplied with or without treated fresh air, and can include double-skin panels and access doors for maintenance.The trade-offs are real, though. Capacity tops out lower than a floor mounted unit, the structure above must carry the weight, and servicing happens overhead. Filter and coil access needs a proper service panel in the ceiling and enough clearance to work.When a Floor Mounted AHU Makes SenseA floor mounted unit is the workhorse for large airflows and demanding air quality. Because it stands on the ground, it can be longer, taller and heavier, with room for extra sections such as multi-stage filters, a heat recovery section, a humidity section and large coils.That is why it shows up in pharma plants, hospitals, laboratories, airports and clean rooms. Airtree's Floor Mounted AHU is built for high air volumes and critical applications, and can be configured for return air, fresh air or treated fresh air.The cost is floor area. You need a plant room, a plinth, clear space around the unit for coil pull-out and filter access, and a duct route into the building. In return, servicing is easier, because technicians work at floor level with the unit's full length in front of them.Ceiling Suspended vs Floor Mounted AHU: Side by SideFactorCeiling suspendedFloor mountedInstallationHung from the slab, above the false ceilingOn a plinth in a plant roomFloor areaNone usedNeeds a plant roomAir volumeSmall to mid-size (Airtree: 700 to 12,000 CFM)Mid-size to very largeSections and filtrationPossible, but limited by unit sizeMore sections, more room for fine filter stagesServicingOverhead, through access panelsAt floor level, full accessNoiseClose to occupied rooms, needs careKept away in the plant roomTypical useOffices, hotels, malls, floor-wise zonesHospitals, pharma, labs, airports, clean roomsSix Questions That Settle the ChoiceHow much air do you need? Work out the airflow for the zone first. Small and mid-size zones suit a suspended unit. Very large halls or whole-wing duties lean toward floor mounted.Do you have a plant room? If you do not, and cannot create one, the decision is already made.How strict is the air quality brief? Clean rooms, operation theatres and pharma areas need several filter stages and tight humidity control, which is easier to build into a longer floor mounted unit.Can the ceiling carry it? A suspended unit puts its full weight on the slab. Ask your structural engineer to confirm the hangers and load before you order.How loud can it be? A unit above a meeting room or hotel corridor sits close to people. Check the noise data and use vibration isolators. A plant room keeps that sound away from occupants.Who will service it, and how? Count the units. Twenty suspended AHUs mean twenty overhead service points, while two floor mounted units mean two. Plan the access panels now.Many buildings use both: floor mounted units in the plant room for large halls and critical zones, suspended units on upper floors where space is tight. A treated fresh air unit can then handle ventilation for either, which matters when you design to ASHRAE 62.1 rates.Common Mistakes to AvoidSizing by tonnage per square foot alone, instead of a proper load calculation.Choosing a suspended unit and forgetting the service clearance around it.Ignoring noise when the unit sits above an occupied room.Placing filters and coils where nobody can reach them, so they never get cleaned. Our guide on cleaning an AHU cooling coil shows what regular access saves you.Treating fresh air as an afterthought. For wider system choices, see our guide to choosing the right HVAC system.Where Airtree Fits InAirtree makes both layouts in Greater Noida, along with Vertical AHUs, Cooling coils and treated fresh air units, so one team can specify the whole air path. If you are unsure which suits your project, share your layout, airflow and air quality needs and the engineers will recommend a configuration.Browse the air handling unit range, see the full products catalogue, or get a quote. If you are weighing AHUs against room-level units, our comparison of AHU vs FCU explains the difference.Frequently Asked QuestionsWhat is the main difference between a ceiling suspended and a floor mounted AHU? A ceiling suspended AHU hangs above the false ceiling and saves floor space. A floor mounted AHU stands in a plant room and handles larger airflows and more sections.Which AHU is better for hospitals? Both are used. Critical zones with strict filtration and humidity control usually get floor mounted units, while lighter-duty areas can use ceiling suspended ones.What airflow does a ceiling suspended AHU cover? Airtree's Ceiling Suspended AHU covers 700 to 12,000 CFM, with or without treated fresh air.Does a ceiling suspended AHU need a plant room? No. It goes above the false ceiling, but it needs structural support, service access and a drain route for condensate.Can one building use both types? Yes. Many buildings pair floor mounted units for large or critical zones with suspended units where space is limited.Keep reading: browse the Airtree blog or the Knowledge Hub for more on air handling and ventilation.

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