Sensible heat ratio
The fraction of total cooling capacity that lowers temperature rather than removes moisture, expressed as sensible capacity divided by total capacity. A load and a coil both carry their own sensible heat ratio, and matching them is what determines whether a system actually dehumidifies the space it cools.
Also called SHR
What is sensible heat ratio in cooling?
Sensible heat ratio is sensible cooling capacity divided by total capacity, for either a building's load or a coil's output. A coil selected on total tonnage alone can carry a different ratio than the load needs, satisfying temperature while under-delivering moisture removal.
Sensible heat ratio: how it works
Total cooling capacity splits into sensible capacity, which changes temperature, and latent capacity, which removes moisture. Dividing sensible by total gives the ratio. Oversizing a coil's sensible capacity relative to a load shortens run cycles, and a shorter cycle spends less time in the steady, moisture-removing phase, pushing the coil's working ratio toward the sensible side regardless of its rated figure.
Where you meet the term
- In a Manual J load calculation, where the load itself carries a sensible heat ratio the equipment has to be selected against.
- In manufacturer expanded performance data, where sensible and total capacity are published together at stated entering conditions and airflow.
- In a complaint that a space feels damp despite the thermostat reading correctly, which is the field symptom of a ratio mismatch.
How to check it
- Compare the load's ratio against the selected coil's ratio. Both figures come from the same kind of calculation, sensible over total, at the same design condition. A coil selected on total tons alone may carry a materially different ratio than the load needs. Technician
- Check airflow against the coil's rated test condition. Airflow above a coil's tested condition raises sensible capacity faster than latent capacity, pushing the working ratio away from what the manufacturer's published figure assumed. Technician
Sensible heat ratio: what it is not
- Matching total capacity in tons does not guarantee a matched sensible heat ratio. Two coils of identical tonnage can split that capacity between sensible and latent in different proportions.
- Adding sensible capacity as a margin does not carry latent capacity along with it. The extra sensible headroom shortens cycles instead, which drags the ratio further toward the sensible side.
Sensible heat ratio questions
What sensible heat ratio should a residential system target?
No fixed figure applies across every building. The ratio a coil should hit comes out of that project's own load calculation, which is the reason a load report has to publish its ratio rather than leaving a reader to infer one from total tons.
Does a variable-speed system fix a ratio mismatch automatically?
It helps, because holding a lower stage keeps the coil wetter for longer, but it does not correct a mismatch created by gross oversizing on the sensible side.
Is sensible heat ratio the same as bypass factor?
No. Sensible heat ratio describes the split between sensible and latent capacity. Bypass factor describes how much entering air passes a coil without contacting its surface at all, which is a separate calculation feeding into leaving air condition.
Where this definition comes from
Written from standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Manual J residential load calculationACCA description of Manual J as the residential load calculation procedure that sizes heating and cooling equipment from the building's construction, insulation, window area and orientation, air leakage, local design temperatures, and internal gains, producing a room-by-room and whole-house load in BTU per hour that equipment is then matched to rather than sized by floor area alone.
- Manual S residential equipment selectionACCA description of Manual S as the procedure that selects specific equipment against a completed Manual J load, using the manufacturer expanded performance data at local design conditions rather than the nominal tonnage on the badge, and applying separate sizing limits to sensible capacity, latent capacity, and heating capacity.