How to use the constant temperature and humidity load calculator
A precision environment room has to hold temperature and humidity inside a narrow band at the same time, so unlike ordinary comfort cooling the load has to be split into sensible and latent parts from the start. Enter equipment heat, lighting density, occupancy, outdoor air quantity and the indoor and outdoor conditions, and this calculator separates internal and outdoor air load into sensible and latent, then reports the total cooling load, the moisture removal rate and the sensible heat factor.
Humidity ratio is derived from temperature and relative humidity. The same relative humidity holds far more moisture at a higher temperature, which is why summer outdoor air arrives carrying more than twice the water content of the conditioned room and why the outdoor latent term often dominates the answer.
Watch the sensible heat factor. When it is low, the coil has to cool the air well past the room set point to strip out moisture, and the space overshoots cold. The usual answers are a reheat coil, a desiccant wheel, or reducing outdoor air and adding energy recovery so the latent load never arrives.
These figures cover internal gains and outdoor air only. Envelope conduction, solar gain through glazing, infiltration and duct heat gain are not included, so use a full load calculation and a mechanical engineer's review before selecting equipment.
Frequently asked questions
Sensible load lowers dry bulb temperature while latent load condenses moisture out of the air. A precision room has to hold both temperature and humidity inside a narrow band, so the ratio between the two decides the coil selection and the dehumidification strategy.
A low SHF means latent load dominates, so the air has to be cooled well below the room set point to wring out moisture and the space ends up too cold. That is why low SHF designs add a reheat coil or a desiccant wheel, or cut the outdoor air quantity and add an energy recovery wheel.
Summer outdoor air often carries more than twice the moisture of the room air, so its latent load climbs fast. Bringing in only the minimum required ventilation and recirculating the rest is the most reliable way to cut operating cost in a precision room.