Process heat — the energy used to heat materials in manufacturing, food processing and other industry — is one of New Zealand’s larger sources of industrial emissions, largely because much of it comes from coal and natural gas.
It is also one of the more tractable, because the engineering is understood and the electricity system has a high renewable share.
Temperature determines the options
The single most useful framing is what temperature the process actually requires.
Low temperature (roughly below 100°C) — space heating, hot water, some washing and drying. Heat pumps are generally the answer. They deliver several units of heat per unit of electricity, which makes them cheaper to run than direct electric resistance heating by a wide margin.
Medium temperature (roughly 100–200°C) — much food processing, drying and sterilisation. High-temperature heat pumps and electric boilers are options, and biomass is well suited.
High temperature (above 200°C) — cement, glass, some metals and chemical processes. Harder to electrify with current technology, and where biomass, and in some cases hydrogen, are being considered.
The common finding on assessment is that processes are frequently run hotter than they need to be, because that is how the plant was set up. Establishing the actual required temperature is the first engineering task and it sometimes changes the answer entirely.
Do the efficiency work first
Replacing a boiler that is heating an inefficient process just electrifies the waste. The sequence that produces the best economics:
- Reduce demand — insulation on pipework and vessels, fixing steam leaks, eliminating unnecessary heating, better controls and scheduling.
- Recover heat — heat exchangers capturing waste heat from exhausts, condensate and process streams. Frequently the highest-return intervention available and routinely overlooked.
- Optimise the existing system — correct sizing, sequencing of multiple units, and turndown capability.
- Then change the fuel.
Plants that do this in order frequently find the replacement heat source can be substantially smaller and cheaper than the one they were about to install.
The fuel options
Electricity. Heat pumps for low and medium temperature, electric boilers where heat pumps do not reach. The constraints are electrical capacity at the site and the cost of network upgrades, which can exceed the plant cost. Talk to your lines company early.
Demand charges matter as much as energy cost. A process drawing large power in short bursts can attract charges that undermine the economics, which makes load management and thermal storage part of the design rather than an afterthought.
Biomass. Wood chip, pellets and residues. Well suited to medium and higher temperatures, and effectively a drop-in replacement for coal in many boiler applications. The constraints are fuel supply security, storage and handling space, and local air discharge consent conditions.
Geothermal, where the resource exists, which in New Zealand means specific locations.
The economics
Model the full picture rather than fuel cost per unit of energy:
- Capital cost including electrical or fuel handling infrastructure.
- Network connection or upgrade cost, which for electrification is frequently the largest single item.
- Operating cost including demand charges.
- Maintenance, which differs substantially between technologies.
- Carbon cost avoided, since fossil fuel use carries an ETS cost embedded in the fuel price.
- Downtime during changeover, which for a continuous process can dominate.
EECA runs programmes supporting decarbonisation projects, including co-funding in some cases. Criteria and availability change, so check current programmes directly rather than relying on older summaries.
Doing the assessment properly
An energy audit or process heat assessment by someone experienced in the sector is the right starting point. It should establish actual temperature requirements, map where heat is used and lost, quantify recovery opportunities, and model options against real site constraints.
The engineering capability for this work exists in New Zealand, including in Taranaki where the process and mechanical engineering base built around the gas industry transfers directly.
The wider system context
Electrifying process heat adds load to a system already growing from transport electrification and data centres. That interacts with generation build and network capacity, and it is why grid connection lead times matter to industrial projects.
EECA publishes energy efficiency and decarbonisation material and data, MBIE publishes energy statistics, and the Electricity Authority publishes market data at emi.ea.govt.nz — all under open licences.
