**2. Performance parameters of biomass cookstoves**

In biomass cookstoves, conversion of chemical energy into thermal energy takes place due to combustion of solid biomass. The parameters which affect performance of biomass cookstoves are of two types *viz*. thermal parameters and emission parameter includes emission factor of different pollutants. The thermal performance parameters include fire power, efficiency, specific fuel consumption and turn-down ratio. The emission performance parameters include emission factor of a pollutant (g/kg or g/kJ or g/MJ) or indoor concentration of a pollutant (ng/m<sup>3</sup> or μg/ m<sup>3</sup> or mg/m<sup>3</sup> or g/m3 ) [9].

The amount of thermal energy produced (kJ) per unit time (s) is known as fire power (kW). Mathematically fire power is defined as follows:

$$\text{Fire power (P)} = \frac{\text{mass of fuel burnt} \times \text{Calorific value of fuel}}{\text{Time taken for complete combustion of fuel}} \text{ kJ/s or kW} \qquad (1)$$

Fire power is the total amount of energy available for cooking the food per unit time. The energy actually used for cooking the food will be very small as compared to that of the fire power due to various losses. **Figure 1** shows energy balance for a biomass cookstove. Out of the total energy available in the form of fire power (a), some of the energy is absorbed by the cookstove body in the form of an internal energy and some energy is lost form the cookstove body to the surroundings through convection, radiation and to the ground through conduction (b). Heavier cookstoves absorb more energy in the form of the internal energy. Hence, traditional cookstoves as well as modified biomass cookstoves made of mud and brick are found to have

**Figure 1.**

*Schematic of energy balance of a cookstove [9]. [Reprinted from Renewable & Sustainable Reviews, Vol. 41, Sutar K. B., Kohli S., Ravi M. R. and Ray A., Biomass cookstoves: A review of technical aspects, 1128–1166, 2015, with permission from Elsevier.].*

poor efficiencies as compared to the metal biomass cookstoves. Some of the energy in the fire is absorbed by the pot and the pot contents (c). During this transfer of energy, some of the energy is lost to the atmosphere with flue gases and some energy is lost in the form of direct radiation and convection (d). Vessel walls also lose some heat to the atmosphere in the form of convection (e). From the top portion of the pot, there will always be evaporative (f) and convective energy losses (g).

From **Figure 1**, it is clear that actual energy used per unit time for cooking the food (Pu) = {(c)�[(e) + (f) + (g)]}/t. Now, thermal efficiency (η) of biomass cookstove is defined as the ratio of actual energy used by the pot and the pot contents for cooking the food per unit time to the fire power available due to combustion of fuel. Mathematically, thermal efficiency is defined as follows:



*USEPA: United States Environmental Protection Agency, CPCB: Central Pollution Control Board, ppm: parts per million, ppb: parts per billion, ng: Nano gram, and B[a]P: Benzo(a)Pyrene.*

#### **Table 1.**

*WHO guidelines for indoor air quality [15] and ambient air quality standards for USA [16] and India [17].*

*Energy Efficiency, Emissions and Adoption of Biomass Cookstoves DOI: http://dx.doi.org/10.5772/intechopen.101886*

Specific fuel consumption (SFC) is the mass of dry fuel required (g) to produce a unit output. Here, the unit output is a mass of water remaining in the pot at the end of the test (kg). SFC is expressed in terms of g/kg [14]. Turn down ratio is the ratio of maximum and minimum power between which the cookstove can be operated satisfactorily [9].

Emission factor (g/kg or g/kJ or g/MJ) of a particular pollutant is mass of that pollutant emitted (g) per kilogram of the fuel burnt or per kJ or per MJ of energy released during the cooking task [9]. Indoor concentration of a particular pollutant (ng/m<sup>3</sup> or μg/m3 or mg/m<sup>3</sup> or g/m<sup>3</sup> ) is defined as the amount of exposure of that pollutant (ng or μg or mg or g) to the user per m<sup>3</sup> of the air in the room or cooking space [9].

According to WHO guidelines [15], carbon monoxide (CO), particulate matter of size less than 10 μm (PM10) and of less than 2.5 μm (PM2.5), nitrogen dioxide (NO2), formaldehyde, naphthalene, benzene and polycyclic aromatic hydrocarbons (PAH) are found to be major indoor air pollutants. Considering global warming potential of these pollutants, it is very important for the researchers to know the safer limits of these pollutants in ambient air as recommended by the national and international agencies. **Table 1** report WHO guidelines on indoor air pollutants resulting from combustion of fuels and also ambient air quality standards set by United States Environmental Protection Agency (USEPA) for USA [16] and by Central Pollution Control Board (CPCB) for India [17]. For a given pollutant, with increase in averaging time, values of its safe limit decrease. For example, as per WHO guidelines, permissible limit of exposure to CO emissions for 1 hour is 35 mg/m<sup>3</sup> , for 8 hours it is 10 mg/m3 , and for 24 hours this limit is 7 mg/m<sup>3</sup> .
