Adjusting the CV: I really have to believe it now

2023-05-25 15:45:24

Adjusting your central heating boiler and your radiators: it sounds technical, so difficult, and therefore something to postpone for a while. But now that I want to replace my central heating boiler with a heat pump in the autumn, I can no longer avoid it. However, the bonus is considerable: 30 to 40 percent gas or energy savings is no exception.

Central heating systems in the Netherlands are often not properly adjusted. And mine is no exception. The gas-fired central heating boiler usually heats water to a generous 80 degrees Celsius, while water at 60 degrees also heats the radiators just fine, but with the help of much less gas. And the same amount of water flows through all radiators, while a smaller radiator with much less water gets just as hot as a large radiator that has to pass a lot of water.

‘On safe’ may be unnecessarily expensive

Now that I want to switch to a heat pump this year, I need to know how powerful that pump should be. A rough estimate can be made if you know how many cubic meters of gas you burn each year. In my case I end up with a heat pump of 4.5 to 7.5 kW, which is the amount of heat that can be delivered in the house.

If I want to play it safe and opt for the 7.5 kW version, I will pay a little more when purchasing and the power consumption will also be higher. If 4.5 kW were enough for me, that 7.5 kW would be a waste of money and bad for my energy consumption.

The same amount of hot water flows per hour through this small radiator in the bathroom as through a three times larger radiator in the living room. That makes the central heating inefficient and costs 15 to 20 percent extra in gas.Image Vincent Dekker

So now I have to see if I can heat my house with less cubic meters of gas. Then I know for sure that the 4.5 kW heat pump will be sufficient. I have already fully insulated, so now it is really time to adjust the boiler and radiators.

Cooler central heating water

As far as the boiler is concerned, I already took a big step last year. Earlier I described here that I experimented with cooler water flowing from the boiler to the radiators. The temperature is very easy to set yourself. The water was heated to 70 degrees with me and I tested at 50 degrees. The house warmed up quickly. Then tried 40 degrees, but no, that was too little. It has been at 45 degrees since February and that still works. Making water 20 degrees less warm can save up to 20 percent on gas! So I got that profit.

Less water to small radiator

The second saving trick is a bit more complicated. You will do this by ‘water-side adjustment’. You then limit the amount of water that flows through a radiator per hour. With a central heating boiler, the return water must be at least 20 degrees colder than the supply water. If the difference is smaller, the boiler is less efficient.

If you let the same amount of water flow through a large radiator as through a small radiator, then the water that comes out of the small radiator is much less cooled than what comes out of the large radiator. If the water temperature drops from 50 to 30 degrees on the large radiator, it may only drop to 45 degrees on the small radiator. The two streams of water mix to form water of roughly 38 degrees that flows back to the central heating boiler. And that is only 12 and not 20 degrees colder than the supply temperature. The CV runs inefficiently.

Proper adjustment better than hybrid heat pump?
Heat pump specialist Patrick Schimmel thinks that properly adjusting your boiler and radiators is smarter than purchasing a hybrid heat pump, in which you combine a small heat pump with a gas central heating boiler. “Such a hybrid system may save you 40 to 50 percent gas, but it does cost extra electricity. In that case, you may save 10 to 20 percent in energy. Balancing saves 30 to 40 percent gas and costs no extra electricity. If you let a good plumber do the adjustment work, it will cost you regarding 1000 euros. A hybrid heat pump costs a few thousand euros. In short: you save more energy for less money. And you can skip the hybrid heat pump and switch directly from gas boiler to full heat pump in a few years.”

So you have to let less water flow through the small radiator so that that water also cools down to 30 degrees. That is the water-side adjustment. I was very apprehensive regarding this, because it is expensive: it can easily take a plumber a day to adjust all the radiators in the house. But as it turns out: there are dynamic radiator valves, from Danfoss and Heimeier, among others, that a handy do-it-yourselfer can install himself. On YouTube you will find various clear explanation videos regarding it. I dare.

They will save me regarding 15 to 20 percent in energy. That would be 150 to 200 cubic meters of gas, were it not for the fact that I will soon no longer be burning gas. But because of the better adjustment, plus the savings from the supply temperature reduced to 50 degrees, I can already say that a 4.5 kW heat pump will be enough for me!

In his weblog ‘Vincent wants sun’, Vincent Dekker highlights innovations and developments in the field of green energy, close to and far from home. More episodes at Trouw.nl/vincentwilzon. Vincent now also has a podcast, including regarding heat pumps – listen to it via this link or look it up through the known channels.

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