Indoor Temperature and Humidity Loads
Calculate sensible and latent heat from persons, lights, electric equipment, machines, evaporation from water surfaces, polluting fluids and miscellaneous 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
- 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 on the moisture content of the 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 disulphide | Aromatic, little sticking | 2.6 |
| Chlorine | Sticking | 0.06 |
| Chlorate phenol | Medical | 0.18 |
| Ether | Geranium | 0.069 |
| Prussic Acid | Bitter almond | 1 |
| Hydrogen sulphide | Rotten egg | 0.26 |
| Ozone | Little sharp | 0.096 |