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• JFE - Advantages of decentralized Gas Heating

HEATING VALUE

The heating value of gas is the quantity of heat produced by complete combustion of one m3 of gas in reference conditions defined in standard EN 437.
This can be expressed in two forms:
• Either in Lower Heating Value (LHV): In this case, the latent heat contained in water vapor of combustion products is considered as lost (in the chimney).
• Or in Higher Heating Value (HHV): One recovers heat from this water reduced to a liquid state

Conversion of units

Standard EN437 uses the "mega Joules per cubic meter" for all gases.

The "kilo Watt hours per cubic meter" is more commonly used for G20 and G25 gases: 1 kWh/m3 = 3,6 MJ/m3

In the case of the G31 gas at 15°C and 1013 mbar: 1MJ/kg = 1,87 MJ/m3

We retain the following orders of magnitude
• For the G20 : Hs = 1,11 x Hi
• For the G25 : Hs = 1,11 x Hi
• For the G31 : Hs = 1,09 x Hi

ENERGY

Definitions of the Calorie
The calorie (cal symbol) (from the Latin calor, "heat") is a unit of heat energy defined (calorie at 15°C) like the amount of heat (or heat energy) required to raise the temperature of one gram of water from 14.5 °C to 15.5 ° C under normal atmospheric pressure (1 atm or 101,325 kPa).

Several units are used to express the energy
• Calorie (Cal): Thermal origin unit
• Joule (J): Mechanical origin unit
• Watt hour (Wh): Electrical origin unit

Conversion of units
• 1 kWh = 3,6 MJ=860 kcal
• 1 cal= 4,18 J

POWER

Horsepower is the amount of energy expended during a time unit.

ABSORBED POWER

Also called "heat flow" is the power absorbed by the unit at the level of its gas supply (inlet). This power can be expressed in kW (HHV or LHV). The power of a device expressed in HHV is about 10% higher than that expressed in LHV.

MEASUREMENT OF ABSORBED POWER

Simplified formula of the measurement (identified from a gas meter) of the power absorbed by a unit at the level of its gas supply:

With :

Q_LHV : Heat flow (LHV) (kW)

LHV : Lower Heat Value of Gas (MJ/m3)

T : Gas Température (°C)

p : Gas pressure (mbar)

V : Volume measured by the meter during the period « t » (m³)

t : Duration of the V Volume measurement « V » (s)

This formula can be used to determine the caliber of a gas meter according to the power of connected devices.

POWER OUTPUT

Expressed in kW, it is the power transmitted in the form of heat by the device and that contributes to heating (output of the device).

The heat is transmitted under the form:

• of convection (moving air): air volume heating 
• and of radiation: ground surface heating
  

COMBUSTION YIELD

The losses are mainly losses of heat at the level of evacuated smokes and that do not contribute to heating.

CHIMNEY CONNECTION

Examples :

• Radiant panels are A type
• Tubes and unit heaters can be either type B or C (see type A in some cases)

Type A assembly:

• This assembly can be accepted if there is no possibility of connecting the device (and provided that it is designed for this)
• Requires adequate air renewal or use of mechanical extractions

Type B assembly:

• This assembly is not recommended in the case of a building in depression
• There should be a sufficient air renewal to feed combustion air apparatus

Type C assembly:

L’appareil de chauffage est certifié « CE de type » avec le terminal que nous vendons. L’utilisation d’un autre type de terminal fait perdre la certification de l’appareil.

GAS SUPPLY PRESSURE

The devices are designed to operate in the reference conditions below.

The pressure regulators allow the adaptation of the pressure to the nominal value of the devices.

An operation beyond these limits is a hazard for the device and persons.

Conversion of units:

• 1 mbar = 100 Pa
• 1 bar =10 m EC (height of water column)

SPECIFIC HEAT OF THE AIR

Q_{(kJ) =} m . c . dT

Q_(kJ) : Energy required to raise a mass in temperature (kJ)

m : Mass to raise in temperature (kg)

c : Specific mass heat (kJ/kg/K)

• Air = 1 kJ/kg/K

• Water = 4,18 kJ/kg/K

dT : Température elevation (K or °C)

V : Volume (m³)

Case of dry air:

• Density of dry air: 1 m3 of dry air weighs 1.25 kilograms => Q_(kJ) = 1,25 x 1 x V x dT

• The same formula expressed Wh => Q_(Wh) = 0,34 x V x dT