Fun Fact----Unit Conversions for Heating Energy and Methods for Energy Savings Calculation

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This post was last edited by “Hasty Passerby” on October 23, 2018, at 09:12. Some basic knowledge—Conversion of units for heating energy and methods for calculating energy savings: 1. A series of terms such as energy, energy consumption, heat consumption, and thermal energy have the same meaning and units in the field of heating. There’s no need to worry about how to express them. However, when these physical quantities are considered together with factors like time and space, the calculations become complicated. Therefore, when performing calculations related to heating, it’s essential to understand the meaning of these physical quantities; there’s no need to concern oneself with the derivation process. By eliminating certain conditions, the calculations can be simplified. 2. There are three common units for measuring heat; it is important to know which unit is most frequently used and in what contexts it applies. These units are as follows: (1) Joule (J), Kilojoule (KJ), and Gigajoule (GJ). They are widely used in engineering calculations and are part of the International System of Units. It is commonly used in practical operations such as thermal calculations, heat metering, and heat testing; it is also the unit primarily expressed in standard and regulatory technical documents such as charts and graphs. However, other units of export and engineering* conventions are intertwined, making such a unit less convenient for thermal calculations today. (2) Watt (W), kilowatt (KW), megawatt (MW) – these are engineering-derived units that are commonly used in heating systems. For example, the heat capacity of hot water boilers can be 7MW, 14MW, 29MW, 56MW, etc. The boiler capacities of 10t, 20t, 40t, 80t, etc., which are often mentioned, correspond to the designed output of steam boilers with similar capacities. In engineering, thermal metering instruments for hot water boilers and heat exchange stations, as well as design calculations, estimations, and heating performance indicators related to HVAC systems, are widely used. (3) Car, Kcal... are calorie units that have been phased out, but are still used in engineering, especially in many technical books; for example, the standard calorific value of coal is given as 7000 KCal. 3. When calculating and estimating heating indicators, I recommend 4 basic conversion formulas. The results obtained from these calculations may have some errors, but they are still accurate enough. If an exact calculation is required, one must consult the relevant chart manuals: (1) 1W = 0.86 Kcal, 1 Kcal = 1.163 W ； (2) 1 ton of saturated steam = 0.7 MW = 2.5 GJ = 600,000 Kcal ； (3) 1 kg of standard coal = 7000 Kcal = 29300 KJ ； (4) Thermal equivalent: 1 Kcal = 4.1868 KJ ； 1W = 3.6J (the thermal equivalent is a conversion formula, not a physical relationship, and is commonly used in thermodynamic calculations). 4. Key energy-saving indicators for heating in the Beijing area (over a 4-month heating period): (1) First stage of energy savings: Building heat consumption of 31.6 W/m2, coal consumption of 25.1 kg of standard coal/m2 ； (2) Second step of energy saving: Building heat consumption is 20.6 W/m2, and coal consumption is 12.4 kg of standard coal/m2 ； (3) Third step: Energy savings – The thermal energy consumption of the building is 14.65 W/m2, while the coal consumption is 8.82 kg of standard coal per m2. Note: The key energy-saving target for Beijing in the first phase is to reach the best level achieved before the year 2000. When other regions use this as a reference, they first convert the indicator values for these 4 months into an equivalent value. In northern regions where the heating period lasts 6 or 7 months, assessment indicators are set based on that duration; monthly assessments are recorded temporarily, and the final energy-saving performance is determined at the end of the period. 5. Examples of calculations for evaluating energy consumption indicators: (1) Example 1: Our heating company established guidelines for evaluating energy-saving performance at 8 steam-water heat exchange stations located in a development zone in Hohhot in 2010. The local heating period lasts for 6 months; annual reports on energy consumption during these three consecutive heating periods were compiled. Through data analysis and cost calculations, the initial target for steam consumption per square meter at each heat exchange station was set at 160 Kg of steam/m2 throughout the entire heating period. It is known that the local design area heat index is 65 W; steam is metered at each station, the steam is saturated steam, and the operating pressure is less than 0.6 MPa. What is the equivalent amount of standard coal per square meter during the heating period? What is the heat equivalent per square meter during the heating season? Which energy-saving indicator is closer to that in the Beijing area? Solution: A, 0.16×0.7=112000W=130256Kcal ； B: 130256/7000 = 18.608 Kg of standard coal; this value is close to Beijing’s first-step energy-saving target. When calculated over a period of 6 months, it becomes 18.608×6/4 = 27.9 Kg of standard coal ； C, 112000w/180d/24h=25.9w/m2. (Well below the design value) Regarding the determination of coal consumption metrics, an analysis from a technical perspective is necessary; at the same time, the price of fuel must also be taken into account. The establishment of energy-saving targets involves identifying the break-even point in energy management from a techno-economic standpoint, so as to truly find ways to save energy – there should be no manipulation of numbers. It is meaningful to calculate the steam production cost and pipeline losses when setting steam consumption targets. (2) Example 2: In another hot water boiler room of our company, no meters for measuring the heat supply are in use. The coal consumption target for the 6-month heating period has been set at 43 Kg of coal per m2. The lower calorific value of coal is 5400 Kcal. What is the equivalent coal consumption per square meter during the heating period? What is the heat consumption per square meter during that period? And what is the equivalent amount of standard coal? Solution: a) 43 × 5400 = 232200 Kcal = 270049 W ； b, 270049/700000=0.385t(saturated steam) ； c, 270049w/180d/24h=62.5W/m2, 6 months ； d, Equivalent standard coal: 43×5400/7000=33.2 Kg. (If the coal consumption index per square meter is determined based on standard coal during the heating period, it is this calculated value; however, it may not necessarily have practical significance.) This example illustrates the importance of measurement in all physical and quantitative aspects that fall within the scope of assessment, such as heat metering, fuel metering, electricity metering, and water metering. By means of statistical measurements, it is possible to enhance energy-saving assessments and analyses, and to take timely and effective corrective actions; this avoids waiting until after the heating period has ended to discover through calculations that energy consumption has exceeded limits, resulting in production losses. When setting coal consumption targets, it is necessary to take the coal price at that time into account; the target set after an increase in coal prices should determine whether it represents the break-even point. Conversion summary: Energy conversions: 1 GJ = 277.778 KW; 1 KW = 0.0036 GJ; 1 KW = 1000 W; 1 W = 0.0001 horsepower; 1 horsepower = 9809.5 W = 9.8095 KW; 1 kcal/h = 1.163 W = 0.0012 KW = 0.0001 horsepower; 1 cal/s = 4.1868 W = 0.0042 KW; 1 W = 1 J/s = 1 A·V = 1 m²·kg/s². Unit explanations: GJ – gigajoule; kcal – kilocalorie; Cal – calorie; S – second. The heat consumption in buildings is always expressed in ‘watts’. Heat calculations are all expressed in gigajoules. Early units used in our country: Kcal (thousand calories), Cal (calorie); 1 Kcal = 1000 Cal. Unit for measuring thermal energy: KW