Fuel, Heat and Why Thermal Savings Are the Big Money

Most energy-saving conversations in Malaysia start with electricity — chillers, motors, LED lighting, maximum demand. That is where the meters are visible and where the earlier parts of this course focused. But walk into a food factory, a glove plant, a rubber processor or a hotel laundry and you will often find a second, larger river of money flowing out the door: fuel burned to make heat.

This part turns to the thermal side of a facility. It is less glamorous than the electrical side, harder to see, and frequently where the biggest ringgit savings hide. By the end you will understand boiler efficiency, know how to compare any two fuels fairly, and see why a single boiler project can be worth roughly ten times a solid electrical one.

Two energy bills, not one

A typical process plant pays for energy in two currencies:

- Electricity, metered in kilowatt-hours, running motors, pumps, fans, lights and controls.
- Fuel, usually natural gas, diesel, LPG or biomass, burned in a boiler or furnace to produce steam, hot water or direct heat.

To compare them we need one ruler. The bridge is the unit conversion you met in Electricity Fundamentals: 1 kWh = 3.6 MJ. Since a gigajoule is 1,000 MJ, one GJ equals about 278 kWh of energy. Heat and electricity are both just energy — the trick is to stop measuring one in litres and the other in units, and put everything into joules.

If units like kW versus kWh still feel slippery, the ground-up explainer in Power vs energy: kW and kWh explained is worth five minutes before you go further.

Boiler efficiency: where your fuel actually goes

A boiler's job is to move the chemical energy in fuel into your steam or hot water. It never manages all of it — some heat escapes up the flue, some radiates off the shell, some leaves in the blowdown. What lands in the steam is the useful part.

Boiler efficiency (η) is simply:

$$\eta = \frac{\text{useful heat output}}{\text{fuel energy input}}$$

If you burn fuel worth 100 units of energy and 80 units end up in your steam, your boiler is 80% efficient. The other 20 units heated the sky.

Rearranging gives the question a plant manager actually asks — how much fuel do I need to burn?

$$\text{Fuel required} = \frac{\text{steam demand} \times \text{enthalpy}}{\eta}$$

Here enthalpy is the heat energy carried by each kilogram of steam — the concept comes straight from Cooling Fundamentals, where heat, enthalpy and heat exchangers are built up from scratch. For a boiler, it is roughly the heat needed to turn feedwater into steam at your working pressure.

Worked example. A plant needs 5,000 kg of steam per hour. Each kilogram carries about 2,760 kJ of useful heat. The boiler runs at η = 80%.

Useful heat rate = 5,000 kg/hr × 2,760 kJ/kg = 13,800,000 kJ/hr = 13.8 GJ/hr.

$$\text{Fuel required} = \frac{13.8}{0.80} = 17.25 \text{ GJ/hr}$$

If that fuel is natural gas carrying about 38 MJ per normal cubic metre (Nm³), that is 17,250 MJ ÷ 38 = 454 Nm³/hr. At RM3.00/Nm³, this boiler burns about RM1,362 of gas every hour it runs. Over 6,000 operating hours a year, that is roughly RM8.2 million in fuel. Suddenly the electricity bill for the feedwater pump looks like small change.

The efficiency lever: a little η buys a lot of fuel

Because fuel required sits underneath efficiency in the fraction, small efficiency gains release large fuel savings. The clean way to size an upgrade is:

$$\text{Fuel Saved} = \text{Useful Heat} \times \left( \frac{1}{\eta_{\text{old}}} - \frac{1}{\eta_{\text{new}}} \right)$$

Worked example — 80% to 88%. Suppose the same plant delivers 21,000 GJ of useful heat per year, and an economiser plus burner tune-up lifts efficiency from 80% to 88%.

$$\text{Fuel Saved} = 21{,}000 \times \left( \frac{1}{0.80} - \frac{1}{0.88} \right)$$

$$= 21{,}000 \times (1.2500 - 1.1364) = 21{,}000 \times 0.1136 = 2{,}386 \text{ GJ/yr}$$

Convert to gas: 2,386 GJ = 2,386,000 MJ ÷ 38 MJ/Nm³ = 62,800 Nm³/yr of gas you no longer burn.

At RM3.00/Nm³, that is:

$$62{,}800 \times \text{RM}3.00 \approx \text{RM}188{,}000/\text{yr}$$

An eight-point efficiency gain — the difference between a tired boiler and a well-kept one with heat recovery — is worth roughly RM188,000 a year on this single plant. And there is a free bonus: at a natural-gas emission factor of 2.2 kg CO₂/Nm³, avoiding 62,800 Nm³ also avoids about 138 tonnes of CO₂ a year, carbon you can later monetise when we reach the carbon-pricing parts of this course.

Compare fuels on RM/GJ, never on price per unit

Here is the mistake that costs Malaysian plants real money: comparing fuels by their sticker price. "Gas is RM3.00, diesel is RM3.50 — gas is cheaper." That reasoning is broken, because a cubic metre of gas and a litre of diesel do not contain the same amount of energy.

The only fair comparison divides price by energy content:

$$\text{RM/GJ} = \frac{\text{price per unit}}{\text{energy content per unit}}$$

Run every candidate fuel through it:

Now the picture is honest. Diesel, the most expensive per litre, is also the most expensive per usable joule. Gas and LPG are close. And biomass — palm kernel shell, a Malaysian by-product — is dramatically cheaper per GJ, which is exactly why so many local mills and processors burn it despite the extra handling and ash. The lesson: never let a per-litre or per-tonne price make the decision. Convert to RM/GJ first, every time.

Why gas prices move — and why efficiency is your hedge

Malaysian industrial natural gas is not priced in a vacuum. It tracks the Malaysia Reference Price (MRP), a formula tied to global liquefied natural gas (LNG) markets. When LNG spikes — a cold winter in Asia, a supply shock in Europe — the MRP follows, and your boiler's fuel line item climbs with it, often faster than any electricity tariff.

You cannot control the MRP. You can control how many cubic metres you burn to make the same steam. That is why the thermal playbook is always the same three moves:

1. Efficiency — economisers, better burners, insulation, tuning.
2. Heat recovery — capture flue gas, blowdown and condensate heat before it escapes.
3. Fuel switching — move to a cheaper RM/GJ fuel, such as biomass, where the process allows.

Every one of these shrinks your exposure to a price you do not set.

Thermal savings dwarf electrical savings

Now the headline. Earlier in this course we celebrated an electrical win: fitting a variable-speed drive (VSD) to a pump to trim its energy. A good VSD project on that pump saves about RM13,750 a year — real money, worth doing.

But look at what we just calculated on the thermal side. A boiler upgrade costing roughly RM180,000 returns about RM188,000 a year in avoided fuel. That is not a little better than the electrical project — it is well over ten times the annual saving:

$$\frac{\text{RM}188{,}000}{\text{RM}13{,}750} \approx 13.7\times$$

This is not because the VSD is a bad project. It is because in a fuel-intensive plant, the thermal system moves an order of magnitude more energy — and money — than the motors do. When you triage a facility, the electrical opportunities are visible and satisfying, but the thermal opportunities are usually where the capstone-sized savings live. Follow the biggest energy flow, not the most obvious one.

Seeing the thermal side clearly

The reason thermal savings get overlooked is simple: heat is harder to see than electricity. There is no equivalent of the electricity meter hanging on every steam line, so fuel waste stays invisible until the monthly gas bill arrives. Continuous monitoring of chilled-water and thermal energy flows — the kind Cobler's CobiNeural platform does across energy, indoor air quality, water and chilled water — turns that invisible river into numbers you can act on, so an efficiency slide shows up as a trend, not a surprise. And when you are ready to put ringgit against the electrical half of the picture, the maximum demand calculator sizes the tariff side.

The takeaway

Your facility has two energy bills, and in fuel-intensive plants the thermal one is usually bigger. Measure boiler efficiency as useful heat over fuel input; size upgrades with Fuel Saved = Useful Heat × (1/η_old − 1/η_new); and compare every fuel on RM/GJ, never per litre or tonne. Because efficiency sits underneath the fuel-required fraction, a few points of η release enormous volumes of gas — which is why a RM180,000 boiler upgrade returning ~RM188,000/yr beats a solid electrical project many times over. Chase the biggest energy flow, and the thermal side will usually point you to the real money.

Next up — Part 7: Turning Savings Into a Number — Payback and Simple ROI — where we take these annual savings and start putting them through the first financial test every project must pass.