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Calculating Indoor Temperature and Humidity Loads Calculating sensible and latent heat from persons, lights, electric equipment, machines, evaporation from water surfaces, polluting fluids and miscellaneous loads Sponsored Links

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. 2. 3. 4. 5. 6. 7.

sensible and latent heat from persons sensible heat from lights sensible heat from electric equipment sensible heat from machines latent heat from evaporation from water surfaces evaporation from polluting fluids 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)

Illumination (lux) Installed effect (W) 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

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

Smell


Product

Smell

Limit (mg/m3)

Ether

Geranium

0.069

Prussic Acid

Bitter almond

1

Hydrogen sulphid

Rotten egg

0.26

Ozone

Little sharp

0.096

Calculating Indoor Temperature and Humidity Loads  

The heat transferred from persons depends on activity, clothing, air temperature and the number of persons in the building. 1. Sensible and...

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