Equipment SHR Comparison
| Equipment Type | Typical SHR Range | Space SHR | Assessment |
|---|
Sensible Heat Ratio in HVAC Equipment Selection
The Sensible Heat Ratio is a critical parameter in HVAC equipment selection that is routinely overlooked. Getting the space SHR wrong leads to either uncomfortable humidity levels or inefficient dehumidification — both of which significantly impact occupant comfort and energy consumption.
How SHR Affects Equipment Performance
When the space SHR is lower than the equipment SHR, the AC system satisfies the thermostat setpoint (removes enough sensible heat) before removing enough moisture. The result: the space is at the right temperature but too humid. Conversely, if the space SHR is higher than equipment SHR, the equipment runs longer to dehumidify, potentially overcooling the space.
Standard central AC systems have SHR around 0.75–0.80 at rated conditions. Mini-splits and ductless systems, with their smaller coils and higher coil temperatures, often have SHR of 0.85–0.92 — making them poor dehumidifiers in humid climates. This is a critical consideration in Canadian basements and humid-climate regions like southern Ontario. Use this tool alongside the cooling load calculator and latent heat calculator.
Solutions for Low Space SHR
When space SHR is below equipment SHR: (1) select equipment with lower rated SHR — some manufacturers publish SHR data at multiple conditions; (2) add a whole-home dehumidifier in series with the AC; (3) reduce latent loads at the source through better air sealing and ventilation control with ERV; (4) use a two-stage or variable-speed system that runs at lower capacity for longer periods, improving dehumidification. See the payback period calculator to evaluate these options.
Frequently Asked Questions
Mini-split indoor units (heads) have relatively small coils that operate at higher evaporator temperatures than central ducted systems. Higher coil temperature means less condensation (less dehumidification). This results in SHR values of 0.85–0.92 — much higher than central systems (0.75–0.80). In climates like southern Ontario where summer humidity is significant, this means mini-splits alone may not adequately dehumidify without supplemental dehumidification. This is a key limitation to discuss with clients in humid climates.
AHRI Standard 210/240 rates cooling equipment at: 80°F (26.7°C) dry-bulb / 67°F (19.4°C) wet-bulb entering air, with 95°F (35°C) outdoor temperature. This represents a relatively humid indoor condition. If your space is drier (higher SHR) the actual equipment SHR at those conditions may be higher than rated. Manufacturers publish extended performance data showing SHR at various entering conditions — always check this data for humid climate applications.
A dedicated dehumidifier runs its own refrigeration cycle optimized for moisture removal — it reheats the dehumidified air to room temperature (SHR near 0 for the dehumidifier portion). When combined with an AC system, the effective combined SHR can be much lower. The AC handles sensible load while the dehumidifier handles latent load independently. This combination is often used in basements, indoor pools, and commercial kitchens where latent loads are disproportionately high. Size the dehumidifier from the latent heat calculator result.