ᐅ Fresh water station and buffer tank: a technically better choice?

face26 schrieb:

How much of the photovoltaic power can the heat pump use? And when is the energy needed again? Are there losses until then? And what if the sun isn’t shining? Who heats the buffer then?
The calculation isn’t that simple.

The buffer isn’t just heated but "overheated." For example, my underfloor heating is currently running at 33°C (91°F). When the sun is shining, the system overheats our buffer tank as much as possible, so in the end, the buffer might reach around 45°C (113°F). The heat pump then switches off in the evening until the temperature drops back down to 33°C (91°F). This means on good days, I can heat through the entire night without using expensive electricity from the grid. Of course, there are losses here as well, but you have those with any energy storage. Only, a buffer tank costs me just a fraction of a typical battery storage system.

It has to be considered individually whether this makes sense or not.

So how do the 45 degrees get into the buffer tank? The heat is generated by the heat pump. Sure, using electricity from photovoltaics, but that costs you at least the feed-in tariff you don’t receive. Also, your heat pump has to operate at less efficient higher temperatures; otherwise, you won’t store anything in the buffer. This means you get a worse coefficient of performance (COP) when heating the buffer compared to not doing it at all. And yes, the stored excess temperature is lost again through thermal losses. Additionally, you have higher initial costs because your buffer tank is larger and therefore more expensive than if you only had one for domestic hot water or water heating. And again, who heats your buffer to the required temperature when the sun isn’t shining? You have to heat the full 1000 liters (about 264 gallons) instead of just 500 liters (about 132 gallons), for example.

No one said you should compare this to a battery.

What I mean is, there are more factors that need to be considered in the calculation. In my opinion, a heating buffer tank (in conjunction with heat pumps, pellets, etc., is different) is rarely an efficient solution. It’s better to store 1-2 degrees of excess heat in the tons of screed and manage it together with the photovoltaics so that heating occurs during the time when the sun is most likely shining... simpler and, in most cases, more efficient.

But there’s plenty of information about this online, especially in the already mentioned forum.

face26 schrieb:

There you also have to heat up 1000 liters instead of just 500, for example.

In that case, you obviously need to use a stratified buffer tank. The buffer tank cost me almost nothing, so it was worthwhile for us. As I said, you have to calculate on a case-by-case basis.

What I think is nonsense is overregulating the underfloor heating. During the day, the rooms already warm up further from the sun, so overheating the underfloor heating is counterproductive for comfort.

face26 schrieb:

And again, who heats your buffer tank to the required temperature when the sun isn’t shining?

So basically, throughout the entire winter using expensive electricity from the grid. And in summer, when the photovoltaic system is producing well, you don’t even need the buffer tank. face26 explained that well.

Grantlhaua schrieb:

In this case, you definitely need a stratified buffer tank. The buffer tank barely cost me anything, so it makes sense for us. As I said, you have to calculate on a case-by-case basis.

However, in 99% of cases, that is not true, so this argument only helps those who also get such a tank "for free."
That does not change the other arguments, which carry much more weight.
It’s simply the case that combined with a properly sized heat pump (especially a modulating one), it makes little sense in 95% of cases, even with photovoltaic systems.

Grantlhaua schrieb:

What I think is nonsense is overruling the underfloor heating system. During the day, rooms already warm up due to solar gain, so overheating the underfloor heating is counterproductive to comfort.

You forget the time delay until the energy reaches the room when the sun is no longer shining, but that doesn’t matter—it’s not the main factor anyway.

And a layer buffer can also cause hydraulic problems.
Since the average consumer has to pay for the storage, the simplest solution is to store the photovoltaic electricity in the screed and sell any additional surplus.