• Indoor heat gain
• Outdoor heat gain

INDOOR HEAT GAIN

Indoor heat gains are caused by operations in a controlled space as:

a) Sensible heat load from:

- Occupants of space

- Animals (agricultural buildings)

- Electronic equipment (copiers, computers, etc.)

- Mechanical equipment (factories, workshops, etc.)

- Dishes (restaurants, dining rooms. etc.)

- etc.

b) Latent heat load from:

- Habitants of space

- Animals (agricultural buildings)

- Open water surfaces (pools, baths, etc.)

- etc.

OUTDOOR HEAT GAIN

Outdoor heat gains to a space are caused mainly by solar radiation through outer structures as:

- Windows, glassed areas,

- Outer walls,

- Roof

- etc.

and infiltration of warm outside air to the space.

Calculation of heat gain

INDOOR HEAT GAIN

a) Heat production of occupants Q_h

Human body produces heat all the time. Production depends on activity, health, space conditions, etc.

Q_h= n . q

where

n - number of habitants

q - heat production of one person

Chart 1: Heat and moisture production of human body*

* These values are for adult man; adult female production is 85% of adult male.

q_t - total heat production [W]

q_s - sensible heat production [W]

m_w - moisture production [g.h^-1]

b) Heat gain from electronic equipment

Q_el =Sc₁.c₂. P

where,

c₁ - coefficient describes simultaneity of equipments utilization

c₂ - coefficient describes average equipments utilization

Both coefficient are depending on the situation as

• Type of a space (an office, a shop, a workshop, etc.)
• Type and number of an equipment
• Expected utilization
• Value varies from 0 to 1, where 1.0 means all the time and maximum usage of an equipment

P - electric input of equipment

Examples:

c) Heat gain from lighting

The total electric input of lighting is assumed to change into heat gain through radiation and convection.

Q_l = Sc₁.P

where c₁ and P as above

d) Heat gain from electric motors

Assumption that total electric input changes to heat gain.

where

c₁, c₂ as above

N - total output of electric motor [W]

h_m - efficiency of electric motor [-]

e) Heat gain from small fans

During summer season in period with high temperature are often used small electric fans, but fanås motor produces heat. For determination of gain use equation for heat gain from electric motor.

f) Heat gain from dishes

Heat gain from one dish is 5 W and moisture production is 10 g.

- in luxury restaurants is supposed 1 dish per hour for one place

- in ordinary restaurants are supposed 2 dishes per hour for one place

- in dining rooms are supposed 3 dishes per hour for one place

g) Other sources of heat gain

If any surface in the space has its temperature higher than air temperature, than this heat gain should be involved in the total sum.

Q = a.S.Dt_m

where

a - heat transfer coefficient [W.m^-2.K^-1]

• involves convection and radiation
• determination of a is difficult, but for plain surface and natural fluxion is about 10 W.m^-2.K^-1

S - area of surface [m²]

Dt_m - mean temperature different of surface and air [K]

OUTDOOR HEAT GAIN

a) Heat gains through window or glassed area

Q_w = Q_wc + Q_wr

where

Q_wc - convection part of heat gain

Q_wr - radiation part of heat gain

aa) Convection part of heat gain Q_wc

Q_wc = k_w.S_w.(t_ev - t_i)

where

k_w- heat transmission coefficient [W.m^-2.K^-1]

S_w - area of window including frame [m²]

t_ev - outside air temperature in the hour for which calculation is determined [K] (chart 3)

t_i - inside air temperature [K]

ab) Radiation part of heat gain Q_wr

Q_wr = [S_ws.I_s.c_s + (S_w - S_ws).I_s,dif].s

where

S_ws - insolated area of window [m²]

I_s - total solar radiation [W.m^-2] (chart 2)

I_s,dif - diffusive solar radiation [W.m^-2] (chart 2, North exposure)

c_s - coefficient due to air pollution

City centre, industrial zone 0.85

Small city 1.0

Countryside 1.15

s - shading coefficient

S_ws = [A - (e₁ - f)].[B - (e₂ - g)]

A,B - width and height of window [m]

e₁,e₂ - length of shadow on window surface caused by shading system

Picture 1: definition of distances c,d,f,g

c,d,f,g - distance of shading system to window edge - shows picture 1

a - azimuthal angle [deg]

h - height of the Sun above the horizon [deg]

g: North 0 deg

East 90 deg

South 180 deg

West 270 deg

Chart 2: Total solar radiation on a surface (data for 50 degrees of northern latitude)

Note: horiz means horizontal surface

Chart 3: Outside air temperatures t_ev, t_em, t_ey

Chart 4: Azimuthal angle a and height of the Sun above the horizon h [deg]

Chart 5: Shading coefficients

b) Heat gain through opaque outer structures Q_s

Three categories of structures depending on its width:

Light structures d < 0.08 m

Q_s = k_s.S_s.(t_ev - t_i)

Medium structures 0.08 < d < 0.45 m

Q_s = k_s.S_s.[(t_em - t_i)+m.(t_ey- t_i)]

Heavy structures d > 0.45 m

Q_s = k_s.S_s.( t_em - t_i)

where

k_s- heat transmission coefficient of structure [W.m^-2.K^-1]

S_s - area structure [m²]

t_ev - outside air temperature in the hour for which calculation is determined [K] (chart 3)

t_i - inside air temperature [K]

t_em - average outside air temperature for 24 hours [K] (chart 3)

t _ey- outside air temperature in y hours before the hour for which calculation is determined [K] (chart 3)

y - time delay [h]

m - coefficient decreasing temperature variation [-]