【HVAC Version】Daily Question 20180711 (Short Answer)
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This post was last edited by cy3352 on 2018-7-11 14:37. What does the thermal efficiency of a boiler mean, and how is it determined? Answer: The thermal efficiency of a boiler refers to the ratio of the heat effectively utilized by the boiler to the heat input to the boiler. The measurement methods include the positive balance method and the negative balance method
The thermal efficiency of a boiler refers to the percentage of the heat input from the fuel that is useful heat. There are generally two methods for measuring and calculating the thermal efficiency of boilers: 1. Positive balance method 2. Negative balance method
1. Thermal efficiency = Output heat / Input heat * 100% 2. There are positive balance and negative balance； 3. The determination is carried out in accordance with GB/T10180-2017 Code for Thermal Tests of Industrial Boilers
? Best answer: Boiler evaporation rate and boiler thermal efficiency. 1 ton/hour (t/h) ≈ 60×104 kilocalories/hour (kcal/h) ≈ 0.7 megawatts (MW). There are generally two methods for determining and calculating a boiler’s thermal efficiency: 1. Positive balance method – This is the method in which thermal efficiency is calculated by taking the ratio of the heat utilized by the boiler to the total heat released by the fuel; it is also known as the direct measurement method. The formula for calculating the steady-state thermal efficiency is as follows: Thermal efficiency = Useful heat energy utilized / Total heat energy released by the fuel * 100% = Boiler evaporation rate * (Steam enthalpy – Feedwater enthalpy) / Fuel consumption * Lower heating value of the fuel * 100%. Here, the boiler evaporation rate is determined through actual measurement, in kg/h ； Steam enthalpy – obtained from the enthalpy-entropy chart, kJ/kg ； Feed water enthalpy – obtained from the enthalpy-entropy diagram, kJ/kg ； Fuel consumption — measured actually, kg/h ； Lower heating value of fuel — actually measured, kJ/kg. The above thermal efficiency formula does not take into account the effects of steam humidity, blowdown volume, and steam consumption, and is suitable for a rough calculation of the thermal efficiency of small steam boilers. As can be seen from the above formula for calculating thermal efficiency, a positive balance test can only determine the boiler’s thermal efficiency, but not the various heat losses. Therefore, through positive balance tests, one can only determine the boiler’s evaporation rate and thermal efficiency, but it is not possible to identify the underlying causes or propose improvement measures. 2. Reverse balance method The method of determining and calculating various heat losses in a boiler in order to obtain its thermal efficiency is called the reverse balance method, or indirect measurement method. This method facilitates a comprehensive analysis of the boiler, helps identify various factors affecting thermal efficiency, and suggests ways to improve it. The counterbalanced thermal efficiency can be calculated using the following formula. Thermal efficiency = 100% – the sum of the percentages of various heat losses = 100% – q2 – q3 – q4 – q5 – q6. Here, q2 represents the heat loss due to exhaust gases, in % ； q3——Heat loss due to incomplete combustion of gas, % ； Q4 — Heat loss due to incomplete combustion of solids, % ； q5——Heat dissipation loss, % ； q6——Physical heat loss of ash, %. Most of the time, counterbalance calculations are used to identify the main factors affecting thermal efficiency and address them.
Answer: The thermal efficiency of a boiler refers to the ratio of the heat effectively utilized by the boiler to the heat input to the boiler. The measurement methods include the positive balance method and the negative balance method
The thermal efficiency η1 of a boiler is the percentage of heat output relative to the heat input, that is: ×100%. There are generally two methods for determining the thermal efficiency η1 of a boiler: positive balance and negative balance. Positive balance method: During the testing process, the input heat Qr, the effectively utilized heat Q1, and the fuel consumption B are determined directly; the thermal efficiency is then calculated using the formula ×100% = q1. Counterbalance method: It involves determining various heat losses through thermal balance tests, and the thermal efficiency is calculated using the formula η1=100-(q2+q3+q4+q5+q6)%
Answer: The thermal efficiency of a boiler refers to the ratio of the heat effectively utilized by the boiler to the heat input to the boiler. The measurement methods include the positive balance method and the negative balance method
The thermal efficiency of a boiler refers to the percentage of heat effectively utilized by the boiler compared to the heat input to the boiler per unit of time. There are usually two measurement methods: the forward balance method and the reverse balance method.
The thermal efficiency of a boiler refers to the percentage of the heat input from the fuel that is useful heat. There are generally two methods for measuring and calculating the thermal efficiency of boilers: 1. Positive balance method 2. Negative balance method
The thermal efficiency of a boiler refers to the ratio of the heat effectively utilized by the boiler to the heat input to the boiler. The measurement methods include the positive balance method and the negative balance method
The thermal efficiency of a boiler refers to the percentage of the heat input from the fuel that is useful heat. There are generally two methods for measuring and calculating the thermal efficiency of boilers: 1. Positive balance method 2. Negative balance method