What Is Heat Load?

In the field of internal combustion engines, heat load refers to the heat released by a unit of time when a fuel burns in a burner (such as a gas appliance, gas water heater, gas heater, internal combustion engine, or rocket engine combustion chamber). In the burner, the calculation formula is: heat load = fuel consumption * fuel low heating value. The heat load is determined by factors such as the amount of fuel consumed by the main burner.

Sources of urban central heating systems. The heat load of the central heating system mainly includes heat loads such as heating, ventilation, hot water supply and production processes. The heat for heating and ventilation is seasonal heat load, while the heat for hot water supply and production process is mostly annual heat load. Seasonal heat load varies with climatic conditions and varies greatly throughout the year, but fluctuates less during the day. Perennial heat load is less affected by climatic conditions and does not change much during the year, but fluctuates greatly throughout the day, especially for users who need heat throughout the day. ^[2]

Heating heat load

In a certain outdoor temperature in winter, in order to reach the required indoor temperature, the heat supplied by the heating system to the building in a unit time. The heating design heat load refers to the heat supplied by the heating system to the building in a unit time in order to achieve the above-mentioned required indoor temperature when the outdoor temperature is the calculated temperature of the heating outdoor.
When formulating a city or district heating plan or designing its heating system, there is often a lack of accurate raw data. Generally, it can only be estimated by the thermal index method, that is, the thermal index per unit building area is multiplied by the building area to obtain the heating design Thermal load Q (watt). Formulated as:
Q = q _f F
q _f -thermal index per unit building area (W / );
F--building area ()
If the volume of the house is known, the thermal index q _v [W / (m ³ · ° C)] can also be calculated when the indoor and outdoor temperature difference is 1 ° C per cubic meter of building volume:
Q = q _v V (t _n -t _w )

q _v -heat flux (W / (m ³ · ° C)) _;

V--building volume (m ³ );
t _n -indoor calculated temperature (° C);
t _w --Calculated outdoor heating temperature (° C).
The size of the heating heat index qv and qf is related to many factors such as the heat transfer coefficient of the building envelope, the surrounding volume, the tightness or ventilation conditions, the type and shape of the building, and the ratio of the wall and window area, which are usually based on actual engineering statistics From the analysis, you can refer to the information provided by the relevant departments when designing, and choose according to the specific circumstances.

First, the heat consumption of the envelope structure 1. The basic heat consumption of the envelope structure Q _j = A _j K _j (t _R -t _ow )

Q _j- the basic heat consumption of part of the envelope structure, W;
A _j --j The surface area of the envelope structure, m ² ;
K _j --j heat transfer coefficient of part of the envelope structure, W / (m ² * );
t _R -indoor calculated temperature in winter, ;
t _ow -Calculated outdoor heating temperature, ;
-temperature difference correction coefficient of the envelope structure.
2. Additional heat consumption of the maintenance structure (1) The envelope structure with different orientations will receive different amounts of solar radiation. At the same time, the wind speed and frequency will be different in different orientations. Therefore, different vertical envelope structures were modified. The correction rate is:
North, Northeast, Northwest: 0 ~ 10%
East and West: -5%
Southeast, Southwest -10% ~ -15%
South -15% ~ -30%
When selecting the correction rate, the local winter sunshine rate and radiation intensity should be considered. In low areas where the winter sunshine rate is less than 35%, the correction rate in the southeast, southwest, and south direction should be -10% ~ 0, and other directions may not be modified.
(2) Wind surcharge rate For buildings on highlands, rivers, coasts, and open fields that are not sheltered from the wind, and particularly high buildings in towns and factories, the thermal load of the vertical outer structure is increased by 5% to 10%.
(3) The external door additional rate is the cold air that invades when the external door is opened. For external doors that are opened without a hot air curtain for a short time, the basic heat consumption of the external door can be multiplied by the corresponding additional rate. Balcony doors should not take external door attachment rates into account.
(4) Due to the influence of indoor temperature gradient, the height addition rate often increases the heat transfer in the upper part of the room. Therefore, when the net height of rooms in civil buildings and auxiliary buildings of industrial enterprises exceeds 4m, the additional rate is 2% for each additional 1m, but the maximum additional rate does not exceed 15%.
Second, the heat consumption of cold air infiltrating into the gaps between doors and windows Q _i = 0.278L _ao C _p (t _R -t _oh )
Q _i -heat consumption of cold air infiltrating the gaps of heating doors and windows, W;
L--the amount of permeated cold air, m ³ / h;
_ao -air density at the calculated outdoor temperature, kg / m3;
C _p -specific heat of air at constant pressure, Cp = 1kJ / (kg * );

t _R -indoor calculated temperature in winter, ;

t _oh --Calculated outdoor heating temperature, ° C.

Heat load calculation formula

Ventilation heat load

In some civil buildings and factory workshops, foul air is often exhausted and fresh air is introduced outdoors. During the heating season, the heat consumed to heat fresh air is called the ventilation heat load. Generally residential houses only have exhaust ventilation, and do not use organized intake ventilation. Its ventilation heat is included in the heating heat index, and the ventilation heat load is not calculated separately. Ventilation heat load can be estimated using the number of air changes or the ventilation heat index method.

Hot water supply heat load

Use daily heat for hot water. It is generally estimated based on the number of water users, water temperature and water quota.

Production process heat load

It is mainly used for heating, drying, cooking, cleaning and other processes in the production process, or for power equipment of dragging machinery (such as steam hammer, steam pump, etc.). Due to the variety of heating equipment and heating methods, the heat load of the production process is generally estimated based on the measured data or the estimated heat consumption index of the unit output. If there is no measured data, the heat load can be estimated by referring to the previous fuel consumption and boiler efficiency of the factory.

In determining the heat load of the heating system, in addition to the heat load of the various users mentioned above, the heat loss of the heating network should also be added. Since users generally do not use heat at full load and continuous use at the same time, the average heat load value, the maximum heat load value, and the simultaneous use factor of the equipment need to be determined in order to select a heat source and design a heating system.