A Cooling Unit’s Total kW Does Not Specify Its Sensible Duty

What the cooling coil removes

Sensible cooling reduces the air’s dry-bulb temperature. Latent cooling addresses the energy associated with removing water vapour: moisture condenses when air encounters a sufficiently cold coil surface. A coil can therefore remove heat through a temperature change and through condensation. These are components of heat removal, rather than two interchangeable descriptions of the same duty.

Vertiv’s eight-page precision-cooling white paper, marked SL-24642/(R03/10) and copyright 2017, describes electronic equipment as producing sensible heat without producing humidity. That is useful context for the IT contribution. It does not establish zero moisture-removal duty for the whole room. The room requirement needs its own assessed basis.

For one stated rating point and boundary, total cooling capacity = sensible capacity + latent capacity. A total therefore answers how much heat the unit can remove across those components together. It does not say how much of that total is available for lowering air temperature.

References: [CS1][TR1][EP1]

Read sensible-heat ratio with its denominator

Sensible-heat ratio, or SHR, is sensible capacity divided by total capacity at the same conditions and boundary. EnergyPlus’s DX-coil documentation illustrates the discipline: its gross rated SHR uses gross sensible and gross total capacities together, with supply-fan heat excluded from both.

Multiplying total capacity by SHR recovers sensible capacity only when that ratio belongs to that total and rating point. A ratio taken from another condition or a different gross/net basis cannot supply the missing sensible figure. A higher SHR describes a larger sensible share of the stated total; the absolute capacities still need comparison with the required duties.

References: [EP1]

SC-227: both offers say 20 kW, but one misses sensible duty

SC-227 is an original fictional comparison. Stipulate concurrent capacity figures for two room-cooling offers at identical stated conditions and the same net boundary. Offer A has 20 kW total capacity, comprising 16 kW sensible and 4 kW latent. Offer B also has 20 kW total capacity, comprising 19 kW sensible and 1 kW latent. No real product is assigned to either offer.

Separately stipulate a requirement on that same basis: 18 kW sensible and 0.5 kW latent, totalling 18.5 kW. These inputs are explanatory assumptions, not a room assessment, product rating or test result.

For A, 20 kW exceeds 18.5 kW in total, and 4 kW exceeds the 0.5 kW latent requirement. But 16 kW is 2 kW below the sensible requirement. Passing the total comparison has hidden a component shortfall. The larger latent figure cannot simply be reassigned to sensible duty at this stipulated rating point.

For B, 19 kW exceeds 18 kW sensible, and 1 kW exceeds 0.5 kW latent. B clears these two arithmetic comparisons. A’s SHR is 16/20 = 0.80; B’s is 19/20 = 0.95. Neither ratio is a universal target or proof of efficiency.

The capacity figures are not a prediction of the heat and moisture actually removed as loads change. B’s arithmetic result completes no site selection, humidity-control assessment, redundancy evaluation or air-distribution assessment. It establishes only what follows from the supplied component capacities and requirements.

Keep the entering air and fan-heat boundary attached

Air entering the coil has both a temperature and a moisture state. Airflow determines how much air passes through the exchanger and also forms part of its performance basis. ASHRAE’s terminology identifies entering wet-bulb temperature, entering dry-bulb temperature, outdoor dry-bulb temperature and airflow among parameters affecting gross sensible and total capacity. A capacity split at one point is consequently not a fixed allocation for every condition.

Condensation explains why the moisture state matters: temperature reduction and moisture removal are coupled through the coil’s thermal conditions. Trane’s 2000 Engineers Newsletter discussion shows that maintaining dry-bulb temperature alone can still leave insufficient moisture removal. A satisfactory temperature figure does not establish the latent duty.

Gross and net add another distinction. Fan heat can use part of the coil’s sensible removal before cooling is available to the room. ASHRAE’s net-capacity definitions account for a manufacturer-assumed fan-heat rate, which can differ from the actual installed fan. Retain the offered unit’s stated treatment rather than applying an assumed correction. The manufacturer’s applicable performance data must place the requested sensible and latent duties on the same basis.

References: [AS1][TR1]

The DSE page makes the labels visible

Vertiv’s public Liebert DSE page, checked October 20, 2026, presents separate Total Nominal Capacity and Net Sensible Capacity headings in its Model Specifications Overview. Those are different labels, even though both columns express capacity in kW as well as kBtuh.

Use that page to recognize the distinction. The headings alone do not establish a matched basis for subtracting the columns and calling the difference latent capacity. The offered configuration and applicable rating conditions still need to accompany the manufacturer’s figures. Neither fictional SC-227 offer represents a DSE product.

References: [CS2]

Cooling kW does not specify electrical input or annual energy

A cooling-capacity kW is a rate of heat removal. Electrical-input kW is the rate of electricity consumed by the stated equipment boundary. EnergyPlus treats the quantities separately when defining cooling coefficient of performance as cooling capacity divided by electrical input. SHR instead divides one thermal component by a thermal total.

Annual electricity use, expressed in kWh, requires electrical input over time. Equal total cooling capacities in SC-227 therefore establish neither equal electrical demand nor equal annual electricity use. The example supplies no input-power figures, operating profile or energy comparison.

References: [EP1][DE1]

Resolve the cooling comparison before physical IT planning

The useful supplier response is applicable performance data or a selection report identifying the offered configuration, common rating conditions, gross/net treatment and corresponding sensible and latent capacities. It should address the separately stated duties, rather than replace them with one larger total. When these inputs are missing, the offer comparison remains unresolved.

Use the related CDU capacity guide for liquid-circuit conditions, flow and approach temperature, and the airflow guide for actual volume and air mass. Those subjects do not establish the room unit’s sensible and latent duties.

Leviathan’s Physical Infrastructure Planning & CAD service addresses agreed rack layouts, cable pathways, point-to-point schedules, labels and planning records. Authoring capability and outputs are confirmed per engagement. Cooling selection, HVAC work, thermal-performance approval and licensed facility engineering belong to the customer’s appointed specialists outside this scope.

For the physical IT planning inquiry, share the equipment list, current rack and cable plans, requested documentation outputs and responsible reviewers. Identify which cooling requirements are resolved and which still await their owners. The linked service and project inquiry support a discussion of that physical documentation scope, requirements and availability.