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Do you know it could be more than 3 TIMES CHEAPER to produce the same amount of heat through Heat Pumps than through a Diesel Boiler or an Electric Heater? In this video – in order to make a fair comparison – Levelised Cost of Heat or True Cost of Heat in Rupees per kilowatt-hour thermal (Rs./kWhth) is obtained for a variety of commonly used heating sources.

Are you using diesel or LPG for heating water up to 90 degrees C? Now, the government talks about electrification of heat which means replacing diesel or LPG with electricity. But when you are comparing the operating cost of diesel and LPG with electricity, is it even comparable? Let’s find out.

kCal vs kWh

How do we compare the operating costs of diesel or LPG driven hot water generator and electricity? First of all, we have to understand kCal vs kWh. Are they very different from each other? Both are units of energy. 860 kCal is nothing but 1 kWh from units of energy perspective. Now when you are converting kCal to kWh or kWh into kCal what comes into the picture is nothing but the efficiency. In the case of a generator or a power generator, the efficiency of a generator comes into the picture. That’s why people do not compare kCal and kWh that easily. But in a hot water generator, the kCal is converted into heat and in an electricity generator, the electricity consumed in kWh is consumed into water delivery in terms of kCal and that kCal can be easily converted into kWh just by taking kCal and dividing by 860. This is the first thing that we need to understand.

Typical Boiler Efficiency

What is boiler efficiency? What goes into the boiler in terms of kCal supplied, in terms of the fuel’s calorific content gets converted into heat by burning and then gets out as kCal output of the hot water, that is being converted from the cold stage to the hot stage. That’s basically what is happening in the boiler. Then, what is efficiency? Efficiency is in the terms of the losses that take place in the flue gases or any other heat losses that are in an enclosure etc. What is the usual efficiency of the boiler? Boiler manufacturers will say 95% or 90% and whatnot. But boiler efficiency usually is in 70% or 75% range. Particularly if you operate the boiler at the low capacity, the boiler efficiency is more in the 50 to 60% range. Then what is the true kCal delivered as hot water from the kCal input as the fuel? Let’s find out!

Converting Calorific Values to Cost of Heat

So, what are the calorific values of some of the fuels? Here is the table that shows you what are the different calorific values. Now if you take 1 liter of diesel and take the calorific value and divide by 860, that is the number of kWh contained in 1 liter of diesel. Now here is a table that shows what is per kg and per liter calorific value of many of the fuels.

Table Comparing True Cost of Heat from Various Fuels

Now to find the true cost of the energy delivered, multiply the calorific values by the efficiency of the boiler. Let’s assume it as 70%, what happens to the cost? What is the cost per kWh so that you can compare it directly? Nothing else but the calorific value of the fuel multiplied by efficiency divided by 860 and multiplied by the cost of fuel will give you the true cost. So, if you take a diesel-based hot water generator, as you can see the table, that the calorific value of 9400 approximately kCal per liter, it delivers about 11 kWh per liter and if you take only the 60% efficiency, every liter will be able to deliver 6.6 kWh. If you take 66 rupees per liter of diesel – the current diesel price is slightly higher than this – you will find that per kWh price of running a diesel-based hot water generator is 10 rupees. Now is your electricity being as expensive as your 10 rupees per kWh, actually may not be. So, it doesn’t make sense for you to run a diesel-based hot water generator even if your electricity price is directly or anything less than 10 rupees per kWh. But look at the last row – heat pumps!

How do Heat Pumps compare to others?

Heat pumps absorb heat from the atmosphere and deliver more heat for every unit of electricity supplied. For every kWh of electricity supplied, heat pumps are able to deliver up to 3 kWh of heat energy. So, what it means is even if your kWh of electricity, the cost is 10 rupees – since it generates 3 units of energy – per kWh cost of running a heat pump for delivering hot water is less than 3 rupees. So, if you have a diesel boiler, diesel-based hot water generator, or any other fuel, I have made a table that compares all the fuels and their cost per kWh based on these numbers. If you know what your efficiency is, you can work out what is the kWh of delivered heat for your existing hot water generator. 