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Calculating Indoor Temperature and Humidity Loads

Indoor climate is influenced by

  • sensible and latent heat from persons, lights, machines and electrical equipment and industrial processes
  • pollution and gases from persons, building materials, inventory and industrial processes

The most important sources influencing the indoor climate may be summarized to

  1. sensible and latent heat from persons
  2. sensible heat from lights
  3. sensible heat from electric equipment
  4. sensible heat from machines
  5. latent heat from evaporation from water surfaces
  6. evaporation from polluting fluids
  7. miscellaneous loads

1. Sensible and latent heat from persons

Sensible heat from persons are transferred through conduction, convection and radiation. Latent heat from persons are transferred through water vapor.

The sensible heat influence on the air temperature and latent heat influence the moisture content of air.

The heat transferred from persons depends on activity, clothing, air temperature and the number of persons in the building.

2. Sensible heat from lights

Heat transferred to the room from the lights can be calculated as

Hl = Pinst K1 K2         (1)

where

Hl = heat transferred from the lights (W)

Pinst = installed effect (W)

K1 = simultaneous coefficient

K2 = correction coefficient if lights are ventilated. (= 1 for no ventilation, = 0.3 - 0.6 if ventilated)

The table below can be used to estimate heat load from lights. (The manufacturers datasheets should be checked for details)

Installed effect (W) Illumination (lux)
200 400 600 800 1000
Incandescent lamp             38             75           110            145            180
Fluorescent tubes             15             25           36             48
             60

Normal illumination of rooms:

Office Activity Illumination (lux)
Normal work 200
PC work 500
Archive 200
Drawing work, normal 500
Drawing work, detailed 1000

3. Sensible heat from electric equipment

Heat transferred from electrical equipment can be calculated as

Heq = Peq K1 K2         (2)

where

Heq = heat transferred from electrical equipment (W)

Peq = electrical power consumption (W)

K1 = load coefficient

K2 = running time coefficient

4. Sensible heat from machines

When machines runs heat may be transferred to the room from the motor and/or the machine.

If the motor is in the room and the machine is on the outside - the heat transferred can be calculated as

Hm = Pm / hm - Pm         (3)

where

Hm = heat transferred from the machine to the room (W)

Pm = electrical motor power consumption (W)

hm = motor efficiency

If the motor is belt driven and the motor and belt is in the room and the machine is on the outside - the heat transferred can be calculated as

Hm = Pm / hm - Pm hb         (3b)

where

hb = belt efficiency

If the motor and the machine is in the room - the heat transferred can be calculated as

Hm = Pm / hm         (3c)

In this situation the total power is transferred as heat to the room.

Note! If the machine is a pump or a fan, most of the power is transferred as energy to the medium and may be transported out of the room.

If the motor is outside and the machine is in the room - the heat transferred can be calculated as

Hm = Pm         (3d)

If the motor is belt driven and the motor and belt is outside and the machine is in the room - the heat transferred can be calculated as

Hm = Pm hb         (3e)

5. Latent heat from evaporation from water surfaces

Evaporation from open vessels or similar can be calculated as

qm = A (x1 - x2 ) ae         (4)

where

qm = evaporated water (kg/s)

A = surface area (m2)

x1 = water content in saturated air at water surface temperature (kg/kg)

x2 = water content in the air (kg/kg)

ae = evaporation constant (kg/m2s)

The evaporation constant can be estimated

ae = (25 + 19v)/3600         (5)

where

v = air speed close to the water surface (m/s)

The temperature in the water surface will be lower than the temperature below the surface.

The temperature can be calculated as

t1 = t2 - (t2 - t3) / 8         (6)

where

t1 = temperature in water surface (oC)

t2 = temperature below the surface (oC)

t3 = wet bulb temperature in the air (oC)

The heat for evaporation can be calculated as

He = qm / (x1 - x2) (h1 - h2)         (7)

where

h1 = enthalpy in saturated air (J/kg)

h2 = enthalpy in air (J/kg)

6. Evaporation from polluting fluids

The flow of a polluting fluid can be calculated as

qf = 22.4 qe / M T / 273         (8)

where

qf = flow of the fluid (m3/s)

qe = evaporated fluid

M = molecule mass of the fluid at 0 oC and 101.3 Pa (kg/mole)

T = temperature (K)

7. Miscellaneous loads

Carbon dioxide - CO2

Carbon dioxide (CO2) concentration in "clean" air is 575 mg/m3.

Huge concentrations can cause headaches and the concentration should be below 9000 mg/m3.

Carbon dioxide are produced by persons during the combustion. The concentration of carbon dioxide in the air can be measured and used as an indicator of air quality.

Activity Respiration per person
(m3/h)
CO2 generation per person
(m3/h)
Sleeping 0.3 0.013
Sitting, relaxed 0.5 0.02
Working, moderate 2 - 3 0.08 - 0.13
Working, heavy 7 - 8 0.33 - 0.38

Smell

Product Smell Limit
(mg/m3)
Ammonia Sticking 0.5
Carbon disulphid Aromatic, little sticking 2.6
Chlorine Sticking 0.06
Chlorate phenol Medical 0.18
Ether Geranium 0.069
Prussic Acid Bitter almond 1
Hydrogen sulphid Rotten egg 0.26
Ozone Little sharp 0.096

  Heat, Work and Energy

Tutorial to heat, work and energy - essentials as specific heat and specific heat capacity

Heat

Heat energy is transferred as a result of a temperature difference. Energy as heat passes from a warm body with higher temperature to a cold body with lower temperature.

The transfer of energy as a result of the temperature difference alone is referred to as heat flow. The Watt, which is the SI unit of power, can be defined as 1 J/s of heat flow.

Other units used to quantify heat energy are the British Thermal Unit - Btu (the amount of heat to raise 1 lb of water by 1oF) and the Calorie (the amount of heat to raise 1 gram of water by 1oC). Units of energy used may be calorie (cal), Joule (J, SI unit) or Btu. For comparing units, check the unit converter for more information!

Calorie is defined as an amount of heat required to change temperature of one gram of liquid water by one degree Celsius.

1 cal = 4.184 J

Specific Enthalpy

This is the term given to the total energy, due to both pressure and temperature, of a fluid (such as water or steam) at any given time and condition. More specifically it is the sum of the internal energy and the work done by an applied pressure.

The basic unit of measurement is the joule (J). Since one joule represents a very small amount of energy it is common to use kiloJoules (kJ) (1 000 Joules).

Specific enthalpy is a measure of the total energy of a unit mass. The unit commonly used is kJ/kg.

Heat Capacity

Heat Capacity of a system is the amount of heat required to change the temperature of the whole system by
one degree.

Specific Heat

Specific heat is the amount of heat required to change temperature of one kilogram of a substance by one degree. Specific heat may be measured in kJ/kg K or Btu/lboF. For comparing units, check the unit converter for more information!

Specific heats for different materials can be found in the Material Properties section.

Since enthalpy of a fluid is a function of its temperature and pressure, the temperature dependence of the enthalpy can be estimated by measuring the rise in temperature caused by the flow of heat at constant pressure. The constant-pressure heat capacity - cp - is a measure of the change in enthalpy at a particular temperature.

Similarly, the internal energy is a function of temperature and specific volume. The constant volume heat capacity - cv - is a measure of the change in internal energy at a particular temperature and constant volume.

Unless the pressure is extremely high the work done by applied pressure on solids and liquids can be neglected, and enthalpy can be represented by the internal energy component alone. Constant-volume and constant-pressure heats can be said to be equal.

For solids and liquids

cp == cv

The specific heat  represents the amount of energy required to raise 1 kg by 1oC, and can be thought of as the ability of a substance to absorb heat. Therefore the SI units of specific heat capacity are kJ/kg K (kJ/kg oC). Water has a very large specific heat capacity (4.19 kJ/kg oC) compared with many fluids.

  • Water is a good heat carrier!

Amount of Heat Required to Rise Temperature

The amount of heat needed to heat a subject from one temperature level to an other can be expressed as:

Q = cp m dT         (2)

where

Q = amount of heat (kJ)

cp = specific heat (kJ/kg.K)

m = mass (kg)

dT = temperature difference between hot and cold side (K)

Example Heating Water

Consider the energy needed to heat 1.0 kg of water from 0 oC to 100 oC when the specific heat of water is 4.19 kJ/kg K:

Q = (4.19 kJ/kg.K) (1.0 kg) ((100 oC) - (0 oC))

    = 419 (kJ)

Work

The amount of mechanical work done can be determined by an equation derived from Newtonian mechanics

Work = Force x Distance moved in the direction of the force 

or 

W = F l       (3)

where 

W = work (Nm, J)

F = force (N)

l = length (m)

Example - Work done by Force

The work done by a force 100 N moving a body 50 m can be calculated as 

F = (100 N) (50  m)

  = 5000 Nm (J)

 

Work can also be described as the product of the applied pressure and the displaced volume:

Work = Applied pressure x Displaced volume

The unit of work is joule, J, which is defined as the amount of work done when a force of 1 newton acts for a distance of 1 m in the direction of the force.

1 J = 1 Nm

Energy

Energy is the capacity to do work (a translation from Greek-"work within"). The SI unit for work and energy is the joule, defined as 1 Nm.

Moving objects can do work because they have kinetic energy. ("kinetic" means "motion" in Greek).

The amount of kinetic energy possessed by an object can be calculated as

Ek =1/2 m v2         (4)

where

m = mass of the object (kg)

v = velocity (m/s)

The energy of a level position (stored energy) is called potential energy. This is energy associated with forces of attraction and repulsion between objects (gravity).

The total energy of a system is composed of the internal, potential and kinetic energy. The temperature of a substance is directly related to its internal energy. The internal energy is associated with the motion, interaction and bonding of the molecules within a substance. The external energy of a substance is associated with its velocity and location, and is the sum of its potential and kinetic energy.

Clo-Clothing and Thermal Insulation

 The insulation of clothes are often measured with the unit "Clo", where

1 Clo = 0.155 m2K/W

  • Zero (0) Clo corresponds to a naked person
  • One (1) Clo corresponds to a person wearing a typical business suit
Clothing Insulation
Clo m2K/W
Underwear - pants Pantyhose 0.02 0.003
Panties 0.03 0.005
Briefs 0.04 0.006
Pants 1/2 long legs made of wool 0.06 0.009
Pants long legs 0.1 0.016
Underwear - shirts Bra 0.01 0.002
Shirt sleeveless 0.06 0.009
T-shirt 0.09 0.014
Shirt with long sleeves 0.12 0.019
Half-slip in nylon 0.14 0.022
Shirts Tube top 0.06 0.009
Short sleeve 0.09 0.029
Light blouse with long sleeves 0.15 0.023
Light shirt with long sleeves 0.20 0.031
Normal with long sleeves 0.25 0.039
Flannel shirt with long sleeves 0.30 0.047
Long sleeves with turtleneck blouse 0.34 0.053
Trousers Shorts 0.06 0.009
Walking shorts 0.11 0.017
Light trousers 0.20 0.031
Normal trousers 0.25 0.039
Flannel trousers 0.28 0.043
Overalls 0.28 0.043
Coveralls Daily wear, belted 0.49 0.076
Work 0.50 0.078
Highly-insulating coveralls Multi-component with filling 1.03 0.160
Fiber-pelt 1.13 0.175
Sweaters Sleeveless vest 0.12 0.019
Thin sweater 0.20 0.031
Long thin sleeves with turtleneck 0.26 0.040
Thick sweater 0.35 0.054
Long thick sleeves with turtleneck 0.37 0.057
Jacket Vest 0.13 0.020
Light summer jacket 0.25 0.039
Smock 0.30 0.047
Jacket 0.35 0.054
Coats and overjackets and overtrousers Overalls multi-component 0.52 0.081
Down jacket 0.55 0.085
Coat 0.60 0.093
Parka 0.70 0.109
Sundries Socks 0.02 0.003
Thin soled shoes 0.02 0.003
Quilted fleece slippers 0.03 0.005
Thick soled shoes 0.04 0.006
Thick ankle socks 0.05 0.008
Boots 0.05 0.008
Thick long socks 0.10 0.016
Skirts, dresses Light skirt 15 cm. above knee 0.01 0.016
Light skirt 15 cm. below knee 0.18 0.028
Heavy skirt knee-length 0.25 0.039
Light dress sleeveless 0.25 0.039
Winter dress long sleeves 0.40 0.062
Sleepwear Under shorts 0.10 0.016
Short gown thin strap 0.15 0.023
Long gown long sleeve 0.30 0.047
Hospital gown 0.31 0.048
long pajamas with long sleeve 0.50 0.078
Body sleep with feet 0.72 0.112
Robes Long sleeve, wrap, short 0.41 0.064
Long sleeve, wrap, long 0.53 0.082

An overall insulation or Clo value can be calculated by simply taking the Clo value for each individual garment worn by the person, adding them together. The mean surface area of the human body is approximately 1.7 m2.

Heat Index

 he heat index is a measure how an average person perceives temperature and humidity and how it affect the human body to cool it self.

Heat Index in degrees Fahrenheit

The heat index can be calculated as

tHI = -42.379 + 2.04901523 t + 10.14333127 φ

    - 0.22475541 t φ - 0.00683783 t2 - 0.05481717 φ2

    + 0.00122874 t2 φ + 0.00085282 t φ2 - 0.00000199 (T φ)2         (1)

where

tHI = heat index (oF)

t = air temperature (oF) (t > 57oF)

φ = relative humidity (%)

heat index diagram fahrenheit

Apparent Temperature Heat Stress Index (oF)
Relative Humidity
(% RH)
Temperature (oF)
80 85 90 95 100 105 110 115 120 125 130 135 140
0 78 82 87 911) 94 97 100 103 105 107 108 110 110
5 78 82 86 90 94 98 102 106 110 114 117 121  
10 78 82 86 902) 95 100 105 110 116 121 128    
15 78 82 86 91 96 102 108 115 122 130      
20 79 82 86 91 97 104 112 121 130 140      
25 79 82 87 93 100 108 117 127 138        
30 79 83 88 94 102 112 122 134 148        
35 80 84 89 96 106 116 129 143          
40 80 84 91 99 109 121 136 152          
45 80 85 92 102 114 127 143            
50 81 86 95 1053) 118 134 152            
55 81 88 97 109 124 141              
60 82 89 100 113 129 149              
65 82 91 103 118 136                
70 83 93 106 123 143                
75 84 95 109 1284)                  
80 84 97 113 134                  
85 85 99 117                    
90 86 102 122                    
95 86 104                      
100 87 107                      
  • T(oC) = 5/9[T(oF) - 32]

Sunstroke and heat exhaustion:

1) Caution - Fatigue is possible with prolonged exposure and/or physical activity

2) Extreme Caution - Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or physical activity

3) Danger - Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity

4) Extreme Danger - Heatstroke/sunstroke is highly likely with continued exposure

Heat Index in degrees Celsius

heat index diagram celsius

 

Clothing, Activity and Human Metabolism

Human metabolism at low and high activity with different levels of clothing

 

Human Activity Clothing
Comfort temperature
Relative air speed Heat transferred from person to surroundings
Convection Radiation Latent vapor Total
(Clo)1) (oC) (m/s) (watt) (watt) (g/h) (watt) (watt)
Sitting still Naked 28.8 < 0.1 36 38 40 27 102
30.1 0.3 47 29 40 27 102
30.7 0.5 51 24 40 27 102
31.4 1.0 57 20 40 27 102
0.5 26.2 < 0.1 36 37 42 28 102
27.4 0.3 47 28 42 28 102
27.9 0.5 50 23 42 28 102
28.5 1.0 56 19 42 28 102
1.0 23.3 < 0.1 36 35 44 30 102
24.5 0.3 45 27 44 30 102
25.0 0.5 50 22 44 30 102
25.6 1.0 55 17 44 30 102
1.5 20.7 < 0.1 36 34 46 31 102
21.8 0.3 45 26 46 31 102
22.3 0.5 50 21 46 31 102
22.8 1.0 55 16 46 31 102
Medium activity Naked 24.4 < 0.1 59 65 115 77 204
26.2 0.3 76 51 115 77 204
27.1 0.5 83 44 115 77 204
28.2 1.0 93 35 115 77 204
0.5 19.9 < 0.1 60 63 120 80 204
21.6 0.3 76 48 120 80 204
22.4 0.5 83 41 120 80 204
23.3 1.0 92 33 120 80 204
1.0 15.3 < 0.1 60 59 123 83 204
16.9 0.3 76 45 123 83 204
17.7 0.5 83 38 123 83 204
18.6 1.0 91 30 123 83 204
1.5 10.9 < 0.1 62 57 126 84 204
12.5 0.3 77 43 126 84 204
13.2 0.5 83 36 126 84 204
14.0 1.0 91 29 126 84 204
High activity Naked 22.1 0.3 107 67 192 129 306
23.4 0.5 117 60 192 129 306
24.9 1.0 130 48 192 129 306
0.5 15.7 0.3 108 64 198 133 306
16.8 0.5 119 55 198 133 306
18.2 1.0 130 44 198 133 306
1.0 9.3 0.3 110 59 202 135 306
10.4 0.5 120 51 202 135 306
11.7 1.0 131 40 202 135 306
1.5 3.2 0.3 113 56 205 137 306
4.2 0.5 122 47 205 137 306
5.4 1.0 131 37 205 137 306

1) Clo is used to measure the thermal insulation of clothes - 1 Clo = 0.155 m2K/W

 

 

Indoor Design Conditions – Industrial Products and Production Process

Recommended indoor temperature and humidity for some common industrial products and production processes...

Recommended design conditions should provide employees with a comfortable and healthy indoor work environment together with optimal condition for the production process. Unfortunately this is obvious not always possible. Often it may be necessary to make special arrangements shielding employees from the production environment.

The table below can be used to indicate design conditions - temperature and humidity - for some common production processes.

Industry Process Temperature Relative humidity
oC oF
min max min max %
Abrasives Manufacturing 26 26 79 79 50
Ammunition   21 21 70 70 40
Bakery Flour storage 16 26 61 79 55-65
Production 23 26 73 79 40-70
Billiard Room   23 24 73 75 40-50
Bowling Center Bowling alleys 23 24 73 75 50- 55
Billiard rooms 23 24 73 75  
Bread Flour and powdered storage 21 27 70 80 60
Fermentation 27 27 80 80 75
Retarding of Dough 0 4 32 40 85
Final Proof 35 49 95 120 85-90
Counter flow Cooling 24 24 75 75 80-85
Brewing Hop storage -2 0 29 32 50-60
Yeast culture room         80
Candy Chocolate Pan supply air 13 17 55 62 55-45
Enrobed room 27 29 80 85 30-25
Chocolate Cooling Tunnel supply air 4 7 40 45 85-70
Hand Dippers 17 17 62 62 45
Molded goods cooling 4 7 40 45 85-70
Chocolate Packing room 18 18 65 65 50
Chocolate finished stock storage 18 18 65 65 50
Centers tempering room 24 27 75 80 35-30
Marshmallow setting room 24 26 75 78 45-40
Grained marshmallows drying 43 43 110 110 40
Gum drying 52 66 125 150 25-15
Sanded Gum drying 38 38 100 100 25-40
Gum finished stock storage 10 18 50 65 65
Sugar pan supply air 29 41 85 105 30-20
Polishing pan supply air 21 27 70 80 50-40
Pan rooms 24 27 75 80 35-30
Nonpareil Pan supply air 38 49 100 120 20
Hard candy cooling tunnel air 16 21 60 70 55-40
Hard candy packing 21 24 70 75 40-35
Hard candy storage 10 21 50 70 40
Caramel rooms 21 27 70 80 40
Ceramics Refractory 43 66 110 150 50-90
Molding room 27 27 80 80 60-70
Clay storage 16 27 60 80 35-65
Decalcomania production 24 27 75 80 50
Decoration room 24 27 75 80 50
Cereal Packaging 24 27 75 80 45-50
Cheese Curing Cheddar 7 13 45 55 85-90
Swiss 16 16 60 60 80-85
Blue 9 10 48 50 95
Brick 16 18 60 65 90
Limburger 16 18 60 65 95
Camembert 12 15 53 59 90
Clean rooms   21 27 70 80 40-60
Distilling Grain Storage 16 16 60 60 35-40
General Manufacturing 16 24 60 75 45-60
Aging 18 22 65 72 50-60
Fruit Storage Apples -1 4 30 40 90
Apricots -1 0 31 32 90-95
Grapefruits (California) 14 16 58 60 85-90
Grapefruits (Florida) 10 10 50 50 85-90
Grapes (Eastern) -1 0 31 32 85
Grapes (Western) -1 -1 30 31 90-95
Lemons 14 16 58 60 86-88
Oranges (California) 4 7 40 44 85-90
Oranges (Florida) 0 1 32 34 85-90
Peaches and Nectarines -1 -1 31 31 90
Plums -1 0 30 32 90-95
Citrus fruits 3 4 38 40 90-95
Fur Storage -2 4 28 39 25-40
Drying 43 43 109 109  
Gum Manufacturing 25 25 77 77 33
Rolling 20 20 68 68 63
Stripping 22 22 72 72 53
Breaking 23 23 74 74 47
Wrapping 23 23 74 74 58
Hospitals Operating, Cystoscopic and fracture rooms 20 24 68 76 50
Patient rooms 24 24 75 75 40-50
Intensive care unit 24 24 75 75 40
Administrative and service areas 21 27 70 80 30-50
Leather Drying 21 49 70 120 75
Storage, winter room temperature 10 16 50 60 40-60
Lenses (optical) Fusing 24 24 75 75 45
Grinding 27 27 80 80 80
Libraries and Museums Normal reading and viewing rooms 21 23 70 74 40-50
Rare manuscript and Storage Vaults 21 22 70 72 45
Art Storage Areas 18 22 65 72 50
Matches Manufacture 22 23 72 74 50
Drying 21 24 70 75 60
Storage 16 17 60 62 50-55
Meat and fish Beef (fresh) 0 1 32 34 88-92
Beef (frozen) -23 -18 -10   90-95
Fish (fresh) 1 2 33 35 90-95
Fish (Frozen) -23 -18 -10   90-95
Lamb and Pork (Fresh) 0 1 32 34 85-90
Lamb and Pork (Frozen) -23 -18 -10   90-95
Mushrooms Sweating out period 49 60 120 140  
Spawn added 16 24 60 75 100
Growing period 9 16 48 60 80
Storage 0 2 32 35 80-85
Paint Applications Oil paint spraying 16 32 60 90 80
Drying oil paints 15 32 59 90 25-50
Brush and spray painting 15 27 59 81 25-50
Pharmaceuticals Manufactured powder storage and packing area 24 24 75 75 35
Milling room 24 24 75 75 35
Tablet compressing and coating 24 24 75 75 35
Effervescent tablets and powders 24 24 75 75 20
Hypodermic tablets 24 24 75 75 30
Colloids 21 21 70 70 30-50
Caught drops 27 27 80 80 40
Glandular products 24 24 76 76 5-10
Ampoule manufacturing 24 24 75 75 35-50
Gelatin Capsules 24 24 76 76 35
Capsule storage 24 24 76 76 35
Microanalysis 24 24 76 76 50
Biological manufacturing 24 24 76 76 35
Liver extracts 24 24 76 76 35
Serums 24 24 76 76 50
Animal rooms 24 27 75 80 50
Small animal rooms 24 26 75 78 50
Paper Binding, cutting, drying, folding, gluing 15 27 59 81 25-50
Storage of paper 15 27 59 81 34-45
Storage of books 18 21 64 70 38-50
Plastics Manufacturing areas thermosetting molding compounds 27 27 80 80 25-30
Cellophane wrapping 24 27 75 80 45-65
Photographic Development of film 21 24 70 75 60
Drying 24 27 75 81 50
Printing 21 21 70 70 70
Cutting 22 22 72 72 65
Plywood Hot pressing, resin 32 32 90 90 60-70
Cold pressing 32 32 90 90 15-25
Printing Binding 21 21 70 70 45
Folding 25 25 77 77 65
Pressing, general 24 24 75 75 60-78
Plate making 24 27 75 80 max 45
Lithographic press room 24 27 76 80 43-47
Letterpress and web offset rooms 21 27 70 80 50
Paper storage, letterpress 21 27 70 80 43-47
Paper storage, multicolor sheet feed lithography 24 27 76 80 50-55
Raw Material Storage Nuts, insect 7 7 45 45 65-75
Nuts, rancidity 1 3 34 38 65-75
Eggs -1 -1 30 30 85-90
Chocolate, flats 18 18 65 65 50
Butter -7 -7 20 20  
Dates, figs 4 7 40 45 75-65
Corn Syrup         90-100
Liquid sugar 24 27 75 80 60-50
Rubber-dipped goods Cementing 27 27 80 80 25-30
Dipping surgical articles 24 32 75 90 25-30
Storage prior to manufacture 16 24 60 75 40-50
Laboratory, ASTM standard 24 24 75 75 50-55
Textile Cotton, carding 24 27 75 81 50
Cotton, spinning 15 27 59 81 60-70
Cotton, weaving 20 24 68 75 70-80
Nylon, production 27 27 81 81 50-60
Rayon, spinning 21 21 70 70 85
Rayon, twisting 21 21 70 70 65
Silk, spinning 24 27 75 81 65-70
Silk, weaving 24 27 75 81 60-70
Wool, carding 24 27 75 81 65-70
Wool, spinning 24 27 75 81 55-60
Wool, weaving 24 27 75 81 50-55
Tobacco Cigar and cigarette making 21 24 70 75 55-65
Softening 32 32 90 90 85
Stemming and strigging 24 30 75 86 70
Filler tobacco casing conditioning 24 24 75 75 75
Filler tobacco storage and preparation 26 26 78 78 70
Wrapper tobacco storage and conditioning 24 24 75 75 75

 

People and Heat Gain

Heat Gain from Occupants in Air Conditioned Spaces - in btu/hr

The table below indicates the sensible and latent heat loss from people. The values can be used to calculate heat loads handled by air conditioning systems.

Typical Application Sensible Heat
(btu/hr)
Latent Heat
(btu/hr)
Theater-Matinee                             
                       200                         130
Theater-Evening                        215                         135
Offices, Hotels, Apartments
                       215                         185
Retail & Department Stores                        220                         230
Drug Store                        220                         280
Bank                        220                         280
Restaurant                        240                         310
Factory                        240                         510
Dance Hall                        270                         580
Factory                        330                         670
Bowling Alley                        510                         940
Factory                        510                         940
  • Tabulated values are based on 78oF for dry-bulb temperature
  • Adjusted total heat value for sedentary work, restaurant, includes 60 Btu/hr for food per individual (30 Btu/h sensible and 30 Btu/h latent heat).
  • For bowling figure one person per alley actually bowling, and all others as sitting (400 Btu/h) or standing (550 Btu/h)

Cooling Loads – Latent and Sensible Heat

Latent and sensible cooling loads to consider in design of HVAC systems

The design cooling load (or heat gain) is the amount of heat energy to be removed from a house by the HVAC equipment to maintain the house at indoor design temperature when worst case outdoor design temperature is being experienced. There are two types of cooling loads:

  • sensible cooling load
  • latent cooling load

The sensible cooling load refers to the dry bulb temperature of the building and the latent cooling load refers to the wet bulb temperature of the building. In the summer, humidity influence in the selection of the HVAC equipment and the latent load as well as the sensible load must be calculated.

Factors that influence to the sensible cooling load

  • Glass windows or doors
  • Sunlight striking windows, skylights, or glass doors and heating the room
  • Exterior walls
  • Partitions (that separate spaces of different temperatures)
  • Ceilings under an attic
  • Roofs
  • Floors over an open crawl space
  • Air infiltration through cracks in the building, doors, and windows
  • People in the building
  • Equipment and appliances operated in the summer
  • Lights

Notice that below grade walls, below grade floors, and floors on concrete slabs do not increase the cooling load on the structure and are therefore ignored.

Other sensible heat gains are taken care of by the HVAC equipment before the air reaches the rooms (system gains). Two items that require additional sensible cooling capacity from the HVAC equipment are:

  • Ductwork located in an unconditioned space
  • Ventilation air (air that is mechanically introduced into the building)

Sensible Heat Load and Required Air Volume Chart

Sensible heat load - heating or cooling - and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below:

Sensible heat and required air volume

Factors that influence to the latent cooling load

Moisture is introduced into a structure through:

  • People
  • Equipment and appliances
  • Air infiltration through cracks in the building, doors, and windows

Other latent heat gain is taken care of by the HVAC equipment before the air reaches the rooms (system gain).

Latent Heat Load and Required Air Volume Chart

Latent heat load - humidifying and dehumidifying - and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below:

Latent heat and required air volume


 

HVAC Terms

Definition of some common HVAC industry terms - absolute humidity, pressure, temperature and more

 

  • ABSOLUTE HUMIDITY - The weight of water vapor in a given amount of air.
  • ABSOLUTE PRESSURE - Pressure measured with the base of zero.
  • ABSOLUTE TEMPERATURE - A temperature scale expressed in degrees oF or oC using absolute zero as a base. Referred to as the Rankin or Kelvin scale.
  • ABSOLUTE ZERO - The temperature at which molecular activity theoretically ceases. -456.69 oF or -273.16 oC.
  • AIR CONDITIONING - The process of controlling the temperature, humidity, cleanliness and distribution of the air.
  • AIR, Standard Conditions - Conditions at which capacity ratings for air conditioning equipment is rated.
  • AMBIENT - Refers to the temperature surrounding a body or unit under test.
  • ATMOSPHERIC PRESSURE - The weight of a 1 unit column of the earth's atmosphere.
  • BIMETAL - Two metals with different rates of expansion fastened together. When heated or cooled they will warp and can be made to open or close a switch or valve.
  • BOILING POINT - The temperature at which the addition of any heat will begin a change of state from a liquid to a vapor.
  • BRITISH THERMAL UNIT (BTU) - The amount of heat necessary to change the temperature of 1 pound of pure water 1 degree Fahrenheit (oF).
  • CAPILLARY TUBE - A refrigerant control consisting of a small diameter tube which controls flow by restriction. They are carefully sized by inside diameter and length for each particular application.
  • CENTIGRADE - A temperature scale with the freezing point of water 0 oC and the boiling point 100 oC at sea level.
  • CHECK VALVE - A valve designed to permit flow in one direction only.
  • COMPRESSION - The reduction of volume of a vapor or gas by mechanical means.
  • COMPRESSION RATIO - The ratio determined by dividing the discharge pressure, in PSI (Pa), by the suction pressure in PSI (Pa).
  • COMPRESSOR - A mechanical device used to compress gases. Three main types - reciprocating, centrifugal and rotary.
  • CONDENSATION POINT - The temperature at which the removal of any heat will begin a change of state from a vapor to a liquid.
  • CONDENSING MEDIUM - The substance, usually air or water, to which the heat in a condenser is transferred.
  • CONDENSING UNIT - The portion of a refrigeration system where the compression and condensation of refrigerant is accomplished. Sometimes referred to as the 'high side'.
  • CONDUCTION - The transfer of heat from molecule to molecule within a substance.
  • CONTACTOR - An electromagnetic actuated relay. Usually used to refer to the relay which closes the circuit to a compressor.
  • CONVECTION - The transfer of heat by a moving fluid.
  • COOLING ANTICIPATOR - A resistance heater (usually not adjustable) in parallel with the cooling circuit. It is 'on' when the current is 'off", adding heat to shorten the off cycle.
  • COP - Ratio of work performed or accomplished as compared to the energy used.
  • CUBIC FEET PER MINUTE - A common means of assigning quantitative values to volumes of air in transit, usually abbreviated CFM.
  • CYCLE - The complete course of operation of a refrigerant back to a selected starting point in a system.
  • DENSITY - Mass or weight per unit of volume.
  • DISCHARGE LINE - A tube used to convey the compressed refrigerant vapor from the compressor to the condenser inlet.
  • DISCHARGE PRESSURE - The pressure read at the compressor outlet. Also called head pressure or high side pressure.
  • DRY AIR - Air which contains no moisture vapor.
  • DRY BULB TEMPERATURE - Temperature read with an ordinary thermometer.
  • EFFECTIVE TEMPERATURE - An arbitrary concept which combines into a single value the effect of temperature, humidity, and air movement as sensed by the human body.
  • ENTHALPY - Total amount of heat in one pound (kg) of a substance calculated from accepted temperature base, expressed in BTU's per pound mass (J/kg).
  • EQUIVALENT LENGTH - That length of straight tubing which has the same pressure drop as the fitting, valve or accessory (of the same nominal size) being considered.
  • EVAPORATIVE COOLING - The cooling effect of vaporization of a liquid in a moving air stream.
  • EVAPORATOR - A device in which a liquid refrigerant is vaporized. Some superheating usually takes place.
  • EVAPORATOR SUPERHEAT - The actual temperature of the refrigerant vapor at the evaporator exit as compared to the saturated vapor temperature indicated by the suction pressure.
  • EXTERNAL STATIC PRESSURE - The sum of the static and velocity pressures of a moving air system at the point of measurement.
  • FAHRENHEIT - A temperature scale with the freezing point of water 32 oF and the boiling point 212 oF at sea level.
  • FEET PER MINUTE - A term assigned to a velocity of a moving air stream, usually express FPM.
  • FILTER-DRIER - A device that removes moisture, acid and foreign matter from the refrigerant.
  • FLASH GAS - Instantaneous evaporation of some liquid refrigerant at the metering device due to pressure drop which cools the remaining liquid refrigerant to desired evaporation temperature.
  • FREEZING POINT - The temperature at which the removal of any heat will begin a change of state from a liquid to a solid.
  • GAUGE PRESSURE - Pressure measured with atmospheric pressure as a base.
  • HEAT - A form of energy causing the agitation of molecules within a substance.
  • HEAT EXCHANGER - A device for the transfer of heat energy from the source to the conveying medium.
  • HEAT FLOW - Heat flows from a warmer to a cooler substance. The rate depends upon the temperature difference, the area exposed and the type of material.
  • HEAT OF COMPRESSION - The heat added to a vapor by the work done on it during compression.
  • HEAT OF THE LIQUID - The increase in total heat (Enthalpy) per pound of a saturated liquid as its temperature is increased above a chosen base temperature. (Usually - 40 oF for refrigerants).
  • HEAT TRANSFER - The three methods of heat transfer are conduction, convection and radiation.
  • INCHES OF MERCURY - Atmospheric pressure is equal to 29.92 inches of mercury.
  • LATENT HEAT - Heat that produces a change of state without a change in temperature; i.e., ice to water at 32 oF or water to steam at 212 oF.
  • LATENT HEAT OF CONDENSATION - The amount of heat energy in BTU's that must be removed to change the state of one pound of a vapor to one pound of liquid at the same temperature.
  • LATENT HEAT OF FUSION - The amount of heat energy, in BTU's required to change the state of one pound of a liquid to one pound of solid at the same temperature.
  • LATENT HEAT OF MELTING - The amount of heat energy, in BTU'S, that must be removed to change the state of one pound of solid to one pound of liquid at the same temperature.
  • LATENT HEAT OF VAPORIZATION - The amount of heat energy in BTU's required to change the state of one pound of a liquid to one pound of vapor at the same temperature.
  • LIFT - To elevate a fluid from one level to a higher level.
  • LIQUID LINE - A tube used to convey the liquid refrigerant from the condenser outlet to the refrigerant control device of the evaporator.
  • MANOMETER - A tube filled with a liquid used to measure pressures.
  • MBH - One MBH is equivalent to 1,000 BTU's per hour.
  • MEAN TEMPERATURE DIFFERENCES - The mean of difference between the temperature of a fluid receiving and a fluid yielding heat.
  • MELTING POINT - The temperature at which the addition of any heat will begin a change of state from a solid to a liquid.
  • MERCURY MANOMETER - Used to measure vacuum in inches of mercury.
  • MICRON - A unit used to measure high vacuums. One micron equals 1/25,400 of one inch mercury.
  • MOLLIER CHART - A psychrometric chart. How-to convert between Mollier and Psyhrometric charts?
  • MUFFLER - Device installed in hot gas line to silence discharge surges.
  • OIL SEPARATOR - A device for separating out oil entrained in the discharge gas from the compressor and returning it to the crankcase.
  • PARTIAL PRESSURE - The pressure exerted by any individual gas in a mixture.
  • PITCH - The slope of a pipe line for the purpose of improving drainage.
  • PITOT TUBE - A device comprising a small diameter orifice projecting directly into an air stream measuring total pressure and surrounded by an annular section with small diameter entrances normal to the flow, measuring static pressure; both sections are usually connected to a manometer to indicate velocity pressure.
  • PRECHARGED LINES - Refrigerant line's which are filled with refrigerant and are sealed at both ends. The seals are broken when the lines are installed and the line charge becomes part of the total system charge.
  • PRESSURE DROP - The decrease in pressure due to friction of a fluid or vapor as it passes through a tube or duct or/and lift.
  • PRESSURE - TEMPERATURE RELATIONSHIP - The change effected in temperature when pressure is changed or vice versa. Only used at saturated conditions. An increase in pressure results in a temperature increase. A decrease in temperature results in a pressure decrease.
  • PUMPDOWN - Process of pumping refrigerant out of the evaporator and suction line at the end of the on- cycle by closing a solenoid valve in the liquid line and letting the compressor shut-off by the low pressure control.
  • PSYCHROMETER - A devices having both a dry and wet bulb thermometer. It is used to determine the relative humidity in a conditioned space. Most have an indexed scale to allow direct conversion from the temperature readings to the percentage of relative humidity.
  • PSYCHROMETRIC CHART - A chart on which can be found the properties of air under varying conditions of temperature, water vapor content, volume, etc.
  • QUICK CONNECT - Name given to the end connections on precharged lines which screw on to mated fittings of the outdoor and indoor sections. Tightening the quick connections ruptures the seals on the fittings and the line charge becomes part of the total system charge.
  • RADIATION - The transfer of heat without an intervening medium. It is absorbed on contact with a solid surface.
  • RECEIVER - A vessel for holding refrigerant liquefied by the condenser.
  • REFRIGERANT - A substance which produces a refrigerating effect while expanding or vaporizing.
  • REFRIGERANT CONTROL - A device used to meter the amount of refrigerant to an evaporator. It also serves as a dividing point between the high and low pressure sides of the system.
  • REFRIGERANT DISTRIBUTOR - A device which meters equal quantities of refrigerant to independent circuits in the evaporator coil.
  • REFRIGERANT MIGRATION - The movement of refrigerant through the system to the compressor crankcase during the off-cycle, caused by its attraction to oil.
  • REFRIGERANT OPERATING CHARGE - The total amount of refrigerant required by a a system for correct operation.
  • REFRIGERANT VELOCITY - The rate at which refrigerant is moving at a given point in a system, usually given in feet per minute (FPM).
  • REFRIGERATION - The transfer of heat from a place where it is not wanted to a place where its presence is not desirable.
  • REFRIGERATION EFFECT - The amount of heat a given quantity of refrigerant will absorb in changing from a liquid to a vapor at a given evaporating pressure.
  • RELATIVE HUMIDITY - The percentage of water vapor present in a given quantity air compared to the amount it can hold at its temperature.
  • RELAY - A device used to open and close an electrical circuit. The relay may may be actuated by a bimetal electrically heated strip, a rod wrapped with a fine resistance wire causing expansion when energized, a bellows actuated by expansion of a fluid or gas or an electromagnetic coil.
  • REVERSING VALVE - A device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve.
  • RISER - A vertical tube or pipe which carries refrigerant in any form from a lower to a higher level.
  • SATURATED VAPOR - Vapor in contact with a liquid.
  • SATURATION - A condition of stable equilibrium of a vapor and a liquid.
  • SENSIBLE HEAT - Heat that can be measured or felt. Sensible heat always causes a temperature rise.
  • SIGHT GLASS - A glass installed in the liquid line permitting visual inspection of the liquid refrigerant for the purpose of detecting vapor in the liquid. They also generally have a device included to monitor moisture content of the refrigerant.
  • SLUGGING - A condition in which a quantity of liquid enters the compressor causing hammering and possible compressor damage.
  • SPECIFIC HEAT - The amount of heat necessary to change the temperature of one pound of a substance 10 F.
  • SPECIFIC VOLUME - The volume of a substance per unit of mass; i.e., standard air 13.33 cubic feet per pound. The reciprocal of density.
  • STANDARD AIR DENSITY - 0.075 pounds per cubic foot. Equivalent to dry air at 70 oF and at sea level pressure.
  • STATE CONDITION - Substances can exist in three states - solid, liquid or vapor.
  • STATIC PRESSURE - The normal force per unit area at a small hole in the wall of a duct.
  • STATIC TAP - A means by which static pressures of a duct system may be read directly, usually consisting of a small diameter hole in the side of the duct connected to a manometer.
  • SUB COOLING - Cooling of a liquid, at a constant pressure, below the point at which it was condensed.
  • SUBLIMATION - A condition where a substance changes from a solid to a gas without becoming a liquid.
  • SUCTION LINE - A tube used to convey the refrigerant vapor from the evaporator outlet to the suction inlet of compressor.
  • SUCTION LINE ACCUMULATOR - A device located in the suction line that intercepts quantities of a liquid refrigerant and thereby prevents damage to the compressor.
  • SUPERHEAT - Heat added to a vapor after all liquid has been vaporized.
  • TEMPERATURE - A measurement of heat intensity.
  • THERMISTOR - Basically a semiconductor which has electrical resistance that varies inversely with temperature.
  • THERMOSTAT - A bimetal actuated switch to close and open a circuit to indicate or terminate operation of a heating or air conditioning system.
  • THERMOSTATIC EXPANSION VALVE - Refrigerant control which monitors the flow rate according to the superheat at the evaporator outlet.
  • TON OF REFRIGERATION - The amount of heat necessary to completely melt one ton of 32 oF ice in 24 hours.
  • TOTAL HEAT (Enthalpy) - Total heat energy in a substance. The sum of sensible and latent heat.
  • TOTAL PRESSURE - The sum of all partial pressures in a mixture of gases.
  • TRAP - A depression or dip in refrigerant piping in which oil will collect. A trap may be placed at the base of a suction or hot gas riser to improve oil return up the riser.
  • VACUUM - Any pressure below atmospheric pressure.
  • VAPOR BARRIER - The term applied to an impervious layer of material superimposed upon a layer of insulation. Vapor barriers are always applied on the warm side of the insulation layer.
  • VAPOR PRESSURE - The pressure exerted by vapor.
  • VELOCITY PRESSURE - In a moving fluid, the pressure capable of causing an equivalent velocity as applied to move the same fluid through an orifice such that all pressure energy expanded is converted into kinetic energy.
  • WATER MANOMETER - Used to measure pressure in inches of water.
  • WET BULB TEMPERATURE - Temperature read with a thermometer whose bulb is encased in a wetted wick.