Our homes need to become a lot more sustainable. Besides insulation, the heat pump is the latest ‘big’ thing when it comes to new construction and renovation projects. But is the heat pump worth the hype?
We asked Michel De Paepe, professor of Thermodynamics and Heat Transfer at the Faculty of Engineering and Architecture, and chairman of EnerGhentIC, the interdisciplinary research community of Ghent University graduates working on energy challenges.
Heat pump technology has been around for a long time. Why is the purchase price still so high?
Michel De Paepe: “I think it’s a perception problem, because what are you comparing it with? A natural gas central heating boiler is not that much cheaper than a heat pump on its own. The most energy-efficient heat pump – the geothermal heat pump – is a lot more expensive because of the drilling. Then you do indeed end up with a high total price, but people can easily spend the same amount on a car or a kitchen without thinking, so our frame of reference is not correct.”
There are different types of heat pump. How do I make the right choice?
“I see that people often choose wrongly. In a passive building with low energy consumption, the air-water heat pump is an interesting choice. For both a total renovation and a well-insulated new building, I would recommend a geothermal heat pump, because you can also use it for passive cooling. That uses less electricity than active cooling with other types of heat pumps.”
Of course, a heat pump consumes electricity. So if you don’t have solar panels, you are simply shifting your energy use from gas to electricity. And your energy bill remains high. So why should you go for that heat pump anyway?
“To get rid of fossil fuels faster. The problem of CO2 emissions is becoming so acute that we need to get it down as soon as possible and ban fossil-fuel boilers. As a society, we absolutely have to tax CO2 emissions higher to make people make that shift. Last winter, we saw people opting for more energy-efficient technologies and insulating, as energy would otherwise become unaffordable. As energy prices fall, that sense of urgency ebbs away. At that point it is up to the government to direct people more through policy. That is lacking, I think, even though we know that energy prices will remain high in the coming years.”
So is the heat pump the most sustainable solution?
“The most sustainable solution is to get your energy consumption down. In Flanders, that still means demolishing or renovating a lot of houses and insulating them better. I principally recommend investing in such measures. A while ago, according to some, I too borrowed more to build a passive house, because I knew I would use much less energy. And that’s true: since February, the heating has barely been on.”
What if I invested in a new gas boiler not so long ago. Should I replace it already?
“No, of course not. If you plan to insulate your house properly, you can work in steps. Our idea – there’s a thesis research on this subject going on right now – is that you should only use your central heating boiler when it’s very cold. As a main heating system, you should invest in an air-to-air heat pump, which is the cheapest kind. You can heat three rooms with one unit. In October and November that sort of heat pump is sufficient for heating, in the coldest months of December and January you should heat with your gas boiler and from February your heat pump should be sufficient again. During that time, you should invest in an energy-efficient home and when that is complete, you make do with just your heat pump and throw out that boiler.”
When is it interesting to make the switch?
“It’s always interesting, you shouldn’t wait. Fossil fuels are going to get more expensive, and the price of electricity is going to go down as more renewable energy comes into the grid. The quicker you switch, the quicker you’ll have a pay back. Above all, think of it as an investment in a low-carbon future for your children. True, you may never recoup the investment in a geothermal heat pump, but we never ask ourselves that question when we buy a car. When it comes to energy investments, we think too much in the short term, whereas this is an investment for the future. With a social and ecological impact.”
What research is ongoing around heat pumps? Can the technology be further refined?
“Every day we see evolutions that make heat pumps the technology of the 21st century. The focus of research today is on making the appliances themselves more sustainable, by adding natural refrigerants, for example. Another trend is integrating the heat pump into the power grid. By adding AI to your thermal storage, your appliance will know when the electricity price is high or low. If the price is low, the AI will instruct the battery to recharge. Then, even with a higher electricity price, you will have heat at a lower price.”
It sometimes feels like the heat pump is really being pushed. Should we fear that there is a lobby behind it?
“There will be companies making money, but the heat pump story is not a hype. It’s a win-win: we all need to move towards climate neutrality and fortunately we have the technology in place that makes that possible. There are alternatives, but they are not enough. We have too little biomass in Europe. You can also make electricity from hydrogen, but for private use that involves too many conversions costing too much energy. From a thermodynamic point of view, that is ‘criminal’ (laughs).”
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