Hybrid heat pumps minimize emissions and overall costs

The energy transition aims at reducing CO2 emissions. In existing residential houses with gas heating, how could such a reduction best be reached when switching to a heat pumping solution? This has been studied for a standard Dutch setting.

The typical Dutch residential house is heated by gas with a condensing boiler and with medium insulation. The study compared a shift from the condensing boiler to either a conventional all-electric heat pump, or to a hybrid heat pump running on electricity or gas. The first alternative includes both air-source and ground-source heat pumps. The hybrid heat pump is an air-source heat pump combined with a condensing boiler. In order to make a valid comparison, costs for both generation, transmission and distribution of the energy was taken into account, as well as the cost for appliances.

More heat pumps leads to more electricity used
The drawback of an all-electrical heat pump is that it loses efficiency when the outdoor temperature drops – which is also when the heating need peaks. Therefore, more electricity will be used to reach a certain level of indoor comfort, compared to periods with higher outdoor temperatures. And this affects both electricity costs and emissions. With nation-wide deployment, it would also require investments in the electricity infrastructure: transportation, distribution and power generation.

With a hybrid heat pump, the energy carrier can be varied, allowing for further reductions in costs and/or emissions. For example, when heat pump performance is poor due to low temperatures, or when the emission factors of the available electricity are poor, gas may be used. And electricity may be used when the availability of clean electricity is good.

Six scenarios compared regarding economy and environment
In the study, the three heating options were combined with two insulation options: medium and high levels of insulation, giving a total of six scenarios, with the “condensing boiler, medium insulation” scenario being the base line. Compared to this, the lowest overall costs would be for the scenario “hybrid heat pump, medium insulation”. In comparison, the “all-electric heat pump, medium insulation” scenario would more than double the costs, mostly due to the investment needs in electricity infrastructure in order to meet the increased peak load.

Regarding CO2 emissions, all five scenarios led to a reduction compared to the base line. The largest decreases were for the two scenarios with heat pumps and high insulation. This is not surprising, as emissions decrease together with energy use. Comparing the two scenarios with the same level of insulation shows that hybrid heat pumps led to more reductions than the alternatives in both cases.

It is also relevant to compare the reduction cost per unit CO2. The study shows that the lowest cost per ton of CO2 reduction is for the “hybrid heat pump, medium insulation” scenario, followed by the “hybrid heat pump, high insulation” scenario. This indicates that at markets that today are highly reliant on gas for heating, a wide-spread deployment of hybrid heat pumps would be an attractive alternative, both from an economic and an environmental perspective.

Piet Nienhuis, Gasunie, the Netherlands

This text is shortened by HPC.

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