Grand Sensible Heat Factor is the ratio of the total sensible heat to the grand total heat load that the conditioning apparatus must handle, including the outdoor air heat loads. This ratio is expressed as:

GSHF = grand sensible heat factor

TSH = total sensible heat

TLH = total latent heat

GTH = grand total heat

The air which is passing through the AHU coil increases or decreases the temperature and/or the moisture content. The amount of rise or fall is determined by the total sensible and latent heat load that the conditioning apparatus must handle. The condition of the air entering the apparatus (mixture condition of outdoor and returning room air) and the condition of the air leaving the apparatus is plotted on the psychrometric chart as shown below.

GSHF Line is plotted between mixture conditions to supply air leaving condition from apparatus. The slope of the GSHF line represents the ratio of sensible and latent heat that the apparatus must handle. GSH is projected on the enthalpy lines to estimate the ∆hs (grand sensible load) and RLH is projected on the enthalpy lines to estimate the ∆hl (grand latent load). Grand total load (GTH) is the enthalpy difference between the mixed air condition and the supply air condition.

Notes

1. The RSHF line in Figure -1 is the line sloping between room condition and the supply air temperature whereas the GSHF line in Figure – 2 is the line sloping between the mixture condition and the supply air temperature.

2. The Apparatus dew point (ADP) is the coil surface dew point temperature required to accomplish a cooling/dehumidifying process.