Sensible Heat Factor – SHF, RSHF & GSHF

SHF,RSHF & GSHF are elements used in heat load calculation & which affects the psychrometric properties of the air.

SHF – Sensible Heat Factor

• The thermal properties of air can be separated in to latent & sensible heat.
• The term sensible heat factor is the ratio of the sensible heat to total heat, where the total heat is the sum of sensible & latent heat

RSHF – Room Sensible Heat Factor

The room sensible heat factor is the ratio of room sensible heat to the summation of room sensible & room latent heat. this ratio can be expressed as:

• The supply air to the conditioned space must have capacity to offset simultaneously both the room sensible & room latent heat loads.
• The room & the supply air condition to the space may be plotted on the standard psychrometric chart & this point can be connected by straight line 1-2.
• This line represents the psychrometric process of the supply air within the conditioned space & is called the room sensible heat factor line

• The slope of the RSHF line illustrate the ratio of sensible to latent loads within the space & it is shown in figure as ∆h_S (sensible heat) & ∆h_l (latent heat).
• Thus if adequate air is supplied to offset these room loads, the room requirements will be satisfied, provided both the dry bulb & wet bulb temperature of the supply air falls on this line.

GSHF-Grand Sensible Heat Factor

The 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.

• Air passing through the conditioning apparatus increase or decrease in temperature and/or moisture content.
• The amount of rise or falls is determined by the total sensible & latent heat loads that the conditioning apparatus must handle.
• The condition of the air entering the apparatus (mixture condition of outdoor & return room air) and the condition of the air leaving the apparatus can be plotted on the psychrometric chart & connected by straight line 1-2.
• This line represents the psychrometric process of the air as it passes through the conditioning apparatus & is referred as the grand sensible heat factor line.

• The slope of the GSHF line illustrate the ratio of sensible & latent heat that the apparatus must handle & it is shown in figure as ∆h_S (sensible heat) & ∆h_l (latent heat).