Calculating Indoor Temperature and Humidity Loads
Indoor climate is influenced by
The most important sources influencing the indoor climate may be summarized to
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.
Heat transferred to the room from the lights can be calculated as
Hl = Pinst K1 K2 (1)
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)|
|Fluorescent tubes||15||25||36|| 48 ||60|
Normal illumination of rooms:
|Office Activity||Illumination (lux)|
|Drawing work, normal||500|
|Drawing work, detailed||1000|
Heat transferred from electrical equipment can be calculated as
Heq = Peq K1 K2 (2)
Heq = heat transferred from electrical equipment (W)
Peq = electrical power consumption (W)
K1 = load coefficient
K2 = running time coefficient
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)
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)
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)
Evaporation from open vessels or similar can be calculated as
qm = A (x1 - x2 ) ae (4)
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)
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)
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)
h1 = enthalpy in saturated air (J/kg)
h2 = enthalpy in air (J/kg)
The flow of a polluting fluid can be calculated as
qf = 22.4 qe / M T / 273 (8)
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)
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 |
|CO2 generation per person |
|Working, moderate||2 - 3||0.08 - 0.13|
|Working, heavy||7 - 8||0.33 - 0.38|
|Carbon disulphid||Aromatic, little sticking||2.6|
|Prussic Acid||Bitter almond||1|
|Hydrogen sulphid||Rotten egg||0.26|
Heat, Work and Energy
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
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 of a system is the amount of heat required to change the temperature of the whole system by
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.
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)
Q = amount of heat (kJ)
cp = specific heat (kJ/kg.K)
m = mass (kg)
dT = temperature difference between hot and cold side (K)
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)
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
W = F l (3)
W = work (Nm, J)
F = force (N)
l = length (m)
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 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)
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.
The insulation of clothes are often measured with the unit "Clo", where
1 Clo = 0.155 m2K/W
|Underwear - pants||Pantyhose||0.02||0.003|
|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 with long sleeves||0.12||0.019|
|Half-slip in nylon||0.14||0.022|
|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|
|Coveralls||Daily wear, belted||0.49||0.076|
|Highly-insulating coveralls||Multi-component with filling||1.03||0.160|
|Long thin sleeves with turtleneck||0.26||0.040|
|Long thick sleeves with turtleneck||0.37||0.057|
|Light summer jacket||0.25||0.039|
|Coats and overjackets and overtrousers||Overalls multi-component||0.52||0.081|
|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|
|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|
|Short gown thin strap||0.15||0.023|
|Long gown long sleeve||0.30||0.047|
|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.
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.
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)
tHI = heat index (oF)
t = air temperature (oF) (t > 57oF)
φ = relative humidity (%)
|Apparent Temperature Heat Stress Index (oF)|
|Relative Humidity |
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
Clothing, Activity and Human Metabolism
|Human Activity||Clothing ||Comfort temperature ||Relative air speed||Heat transferred from person to surroundings|
|Sitting still||Naked||28.8||< 0.1||36||38||40||27||102|
|Medium activity||Naked||24.4||< 0.1||59||65||115||77||204|
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 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.
|Bowling Center||Bowling alleys||23||24||73||75||50- 55|
|Bread||Flour and powdered storage||21||27||70||80||60|
|Retarding of Dough||0||4||32||40||85|
|Counter flow Cooling||24||24||75||75||80-85|
|Yeast culture room||80|
|Candy||Chocolate Pan supply air||13||17||55||62||55-45|
|Chocolate Cooling Tunnel supply air||4||7||40||45||85-70|
|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|
|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|
|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|
|Peaches and Nectarines||-1||-1||31||31||90|
|Hospitals||Operating, Cystoscopic and fracture rooms||20||24||68||76||50|
|Intensive care unit||24||24||75||75||40|
|Administrative and service areas||21||27||70||80||30-50|
|Storage, winter room temperature||10||16||50||60||40-60|
|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|
|Meat and fish||Beef (fresh)||0||1||32||34||88-92|
|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|
|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|
|Tablet compressing and coating||24||24||75||75||35|
|Effervescent tablets and powders||24||24||75||75||20|
|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|
|Photographic||Development of film||21||24||70||75||60|
|Plywood||Hot pressing, resin||32||32||90||90||60-70|
|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|
|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|
|Tobacco||Cigar and cigarette making||21||24||70||75||55-65|
|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
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 |
|Latent Heat |
|Offices, Hotels, Apartments ||215||185|
|Retail & Department Stores||220||230|
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:
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.
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:
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:
Moisture is introduced into a structure through:
Other latent heat gain is taken care of by the HVAC equipment before the air reaches the rooms (system gain).
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: