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Sunday, 4 January 2015

HVAC HEATING LOAD CALCULATIONS



We have seen the basic concept of HVAC in our previous post "Heating ventilating and air conditioning (HVAC)" and we have also discussed the cooling load calculations by considering one example in my previous post "HVAC cooling load calculations".

Now it’s time to start our discussion over heating load calculations, let us understand how we should go for calculating the heating load for designing the correct HVAC system. 

Let us consider how we will calculate the cooling load calculation for HVAC system .Before starting the calculation of Cooling load , I will suggest to look previous post "Heating ventilating and air conditioning (HVAC)" for better understanding the concept of cooling load calculations. 

Heating Load Calculations

Calculation of heating load means heat losses through a various components of building as mentioned below in figure.
  1. Walls
  2. Roofs
  3. Windows
  4. Doors
  5. Exposed floors
  6. Basement walls
  7. Basement floors
  8. Duct loss
  9. Infiltration
  10. Ventilation
Now we will find equations to calculate the heat losses as mentioned below in table.

Sr. NO.
Heating Load sources
Calculating equation
1
Ceiling, Roofs, glass & walls
q= UA Δ t
2
Walls below grade
q= UA Δ t
3
Above grade floors

4
Infiltration & ventilation air

Sensible
q s= 0.018 Q Δ t

Latent
q t= 80.7 Q ΔW


Let us consider area of each room (Ft2)
                             
 Description
Living room
Master bed room With attached bath room and closet
Bed room I
Bed room II
Kitchen
Total
West Wall
91
152



243
Partition
192
0



192
Roof
480
458
156
156
240
1490
West door
21
0



21
East wall

0
88
88
135
311
South wall

192
0
80

272
West glass
35
24



59
East glass




14
14
Shaded glass
13
13
13
13
11
63
Total area
834
839
257
337
389
389

Remarks- Let street b/w master bedroom and simple bed room is 5ft wide
We have counted bedroom master and bedroom I and II , kitchen individual so now calculation that we  have done earlier will be changed in excel file.

Let us consider about the guidelines in order to calculate the heating load

  1. First we should select /chose weather conditions of outdoor design for example wind   speed, temperature and directions.
  2. Selection of indoor-air temperature that should be maintained in each location
  3. Temperature of attached garage & unheated-spaces might be calculated with the help of outdoor ambient temperature.
  4. Selection of coefficients of heat transfer for inside walls, outside walls, glass, non basement floors, and ceilings.
  5. Calculation of net applicable area of floors, walls, windows & ceilings
  6. Calculation of heat losses due to transmission for roofs, walls, glass, ceiling
  7. We can calculate heat losses with the help of equations of heat losses.
  8.  Determination of heat losses from basement
  9. Determination of associated energy with cold air across the window, outside doors, building construction materials
  10. Total heating load will be the summation of energy associated with infiltration of cold air and transmission heat losses for roofs, walls, glass, and ceiling.

Heating Load Calculations


This blog is basically based on the process for calculating the Heating load calculations for HVAC system.

Image courtesy : Google

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