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Room Sensible Heat Ratio (SHR) Calculator

Reference: ASHRAE Fundamentals

💧 HVAC

Free sensible heat ratio calculator. Find the room SHR from sensible and latent cooling loads and the required supply air temperature and airflow for correct dehumidification (ASHRAE).

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📋 ASSUMPTIONS & BASIS

ASHRAE Fundamentals

Design criteria, governing codes and assumptions.

ℹ About This Calculator

The sensible heat ratio (SHR) is the share of the cooling load that is sensible (temperature) rather than latent (moisture). It sets the slope of the room process line on the psychrometric chart and therefore the supply air condition needed to hold both temperature and humidity. This calculator finds the room SHR from the sensible and latent loads and helps you check the supply air temperature and airflow so the coil dehumidifies correctly.

Comfort applications typically run SHR around 0.7-0.85; spaces with many people, ventilation air or moisture sources have lower SHR and need deeper coils or colder supply air to remove humidity. If the airflow is set only by the sensible load, a low SHR space can end up warm and humid. Match the coil apparatus dew point and supply condition to the room SHR line, and confirm with a psychrometric analysis.

Sensible Heat Ratio Method

ASHRAE Fundamentals

Step 1 - Total cooling load = sensible load + latent load (kW).
Step 2 - SHR = sensible load / total load.
Step 3 - A lower SHR means more latent (moisture) load, needing colder/drier supply air.
Step 4 - Required supply airflow = sensible load / (1.2 x 1.006 x (room temp - supply temp)).
Step 5 - Pick a supply temperature that meets both the sensible airflow and the latent (dehumidification) demand.

Worked Example

A room has a 12 kW sensible and 3 kW latent load. Total = 15 kW, so SHR = 12 / 15 = 0.80. Airflow to carry the sensible load with a 24 °C room and 13 °C supply is 12 / (1.2 × 1.006 × 11) ≈ 0.90 m³/s, and the 13 °C supply must also be dry enough to remove the 3 kW latent load.

Using SHR in Coil Selection

The room line

Plotting the room condition and the SHR slope on the psychrometric chart shows the supply condition the coil must deliver. The steeper the latent demand, the further the supply point drops in both temperature and moisture.

Sensible airflow vs latent demand

Airflow is usually set by the sensible load and the room-to-supply temperature difference, but the chosen supply must also sit low enough on the chart to remove the latent load. In low-SHR spaces this pushes the coil to a lower apparatus dew point.

Watch ventilation and people

Outdoor air and occupancy add most of the latent load. Where these are high, expect a low SHR and design the coil and supply air accordingly, or add dedicated dehumidification.

Frequently Asked Questions

What is sensible heat ratio (SHR)? +

SHR is the sensible cooling load divided by the total (sensible plus latent) load. It describes how much of the cooling job is lowering temperature versus removing moisture.

Why does SHR matter for AC design? +

It sets the slope of the room process line and hence the supply air temperature and humidity needed. Ignoring a low SHR leaves a space humid even when the thermostat is satisfied.

What is a typical room SHR? +

Comfort spaces are often 0.7 to 0.85. Densely occupied, high-ventilation or high-moisture spaces are lower and need more dehumidification.

How does SHR affect supply air temperature? +

Lower SHR (more latent load) needs colder, drier supply air and a lower coil apparatus dew point; higher SHR can be met with warmer supply air and more airflow.

What if I size airflow on sensible load only? +

In a low-SHR space that can leave the latent load unmet, so the room stays humid. The supply condition must satisfy both the sensible and latent demand.