# SENSIBLE HEAT FACTOR (SHF) CLASS NOTES FOR ENGINEERING

**SENSIBLE HEAT FACTOR (SHF) **

**CLASS NOTES FOR ENGINEERING**

## Sensible means due to temperature

## difference. Consider both sensible and

## latent heat loads in air conditioning.

## Remove these in the same ratio in which

## added. Suitable sensible heat factor

## makes air conditioning enjoyable.

### There are many types of sensible heat factors.

**(a) ROOM SENSIBLE HEAT FACTOR (RSHF)**

**RSHF=RSHL/(RSHL+RLHL) =RSHL/TRHL**

**where RSHL is room sensible heat load**

**RLHL is room latent heat load **

** TRHL is total room heat load**

#### Example – Room Sensible Heat Factor – RSHF

**The sensible heat gain in a room is 40 kW while The latent heat gain is 16 kW.**

**The Room Sensible Heat Factor will be:**

**RSHF**** = (40 kW) / ((40 kW) + (16 kW)) = 0.71**

**(b) Effective room sensible heat factor = ERSHF **

** =ERSHL/(ERSHL+ERLHL)**

**(i) Effective room sensible heat load = ERSHL**

** Outside air sensible heat load = OASHL**

**ERSHL= RSHL+ BPF. OASHL **

**Where BPF = By pass factor **

**Assume BPF=0.1or 0.15 if not given**

**(ii) Effective room Latent heat load = ERLHL**

**ERLHL=RLHL+BPF .OALHL**

**(iii) OASHL=Volumetric flow rate of ventilated air x density (t**_{dbo} – t_{dbi})

_{dbo}– t

_{dbi})

**(iv) OATHL= Volumetric flow rate x density (h**_{ODC} — h_{IDC})

_{ODC}— h

_{IDC})

**OALHL=OATHL—OASHL**

**OR**

**OALHL = Volumetric flow rate x density (w**_{ho} –w_{hi})x LH of water

_{ho}–w

_{hi})x LH of water

**(c) DIFFERENT CALCULATIONS REQUIRED **

**(i) AIR VOLUME CALCULATION**

**Dehumidified supply air volume=V**_{s} (m^{3}/s)= ERSHL/(ρc_{p}(t_{rdbt}—t_{ADP}))

_{s}(m

^{3}/s)= ERSHL/(ρc

_{p}(t

_{rdbt}—t

_{ADP}))

**t**_{rdbt is the room dry bulb temperature }

_{rdbt is the room dry bulb temperature }

**t**_{ADP is the Apparatus Dew Point temperature}

_{ADP is the Apparatus Dew Point temperature}

**(ii) Outside air flow rate= V**_{o }(m^{3}/s)=number of occupants x 0.10 m^{3}/s

_{o }(m

^{3}/s)=number of occupants x 0.10 m

^{3}/s

**Where 0.10 m**^{3}/s fresh air required per person per second (assumed)

^{3}/s fresh air required per person per second (assumed)

**(d) Grand sensible heat factor =GSHF*** *

* *= Total sensible heat factor

*= Total sensible heat factor*

** = GSHL/(GSHL+GLHL)**

**GSHL=RSHL+OASHL**

**GLHL= RLHL+OALHL**

**GRAND and total are the same thing.**

**(e) Apparatus Dew Point (ADP) is the Cooling coil (Evaporator) temperature. Determine it It can in the following ways:**

**(i) Apparatus Dew Point (ADP) is the point where ERSHF line meets the saturation curve. Draw ERSHF line from the room condition (IDC condition) parallel to the ESHF line**

** (ii) Apparatus Dew Point (ADP) is the point where OAGSHF line meets the saturation curve. Draw OAGSHF line from the mixture condition parallel to the OAGSHF line**

*(iii) *Apparatus Dew Point (ADP) is the point where OASHF line meets the saturation curve. Draw OASHF line from the outside design condition (ODC condition) parallel to the OASHF line

*(iii)*Apparatus Dew Point (ADP) is the point where OASHF line meets the saturation curve. Draw OASHF line from the outside design condition (ODC condition) parallel to the OASHF line

**There is a SHF scale on the psychrometric chart. There is a standard point 27**^{0}C with 50 % RH. This standard point is often reference point or reference circle or alignment circle.

^{0}C with 50 % RH. This standard point is often reference point or reference circle or alignment circle.

**Use a reference point for the sensible to latent heat ratio lines. Taken out of heat from the room is in the same ratio (SH/LH) in which added. This makes room conditions comfortable.**

**Draw a reference line joining the RSHF to the alignment circle. SHF LINE is a line joining the SHF on the scale and an alignment point on the chart***.*

*.*

* *Room Apparatus Dew Point (RADP) is the point where RSHF line meets the saturation curve. Draw RSHF line from the room IDC condition parallel to the SHF line.

*Room Apparatus Dew Point (RADP) is the point where RSHF line meets the saturation curve. Draw RSHF line from the room IDC condition parallel to the SHF line.*