LWZ 504 with or without buffer tank

Hello everyone,

I am in the process of equipping our new building with an LWZ 504.
Opinions about buffer tanks vary, I have already noticed that.

I am currently tending to leave the buffer tank aside because we do not necessarily need the cooling function via the underfloor heating (it has worked well without it for the last 30 years) and these "things" generally lower efficiency.
However, I have also read, though not specifically related to Stiebel Eltron, that there are difficulties with some heat pumps when you want to use ERR (which is basically required) but do not have a buffer tank.

What are your experiences and opinions on this?

Best regards,
Roppo

Hello!
We have the THZ 504, identical to the LWZ.
Since we don’t have cooling, no second buffer tank is installed in our system. However, I have already had the wiring prepared in the house for this.
The internal storage for hot water is sufficient for a bathtub and 2 showers; so far, there has been no shortage.

We also have ERR, but at the moment I have all rooms fully open since the flow temperature is still very low. Otherwise, I have reduced a few rooms.

Is the heat pump the only heat source? Then the integrated storage tank is sufficient.

Hi!
We also have a heat pump from StiebelEltron: LWZ304.

For 140m², we don't have an extra buffer storage. ERR is mandatory and therefore installed, but (almost) all are set to "off".

A buffer storage might make sense with a photovoltaic system to store excess electricity as warm water.

Cooling was not really necessary this hot summer. At least if you shade intelligently and turn off the ventilation during the day.

Ok, so if I understand correctly, it is not a problem for Stiebel Eltron to omit the buffer tank, even though there is ERR... We do want to deactivate the ERR, but if you already have a fallback level, it should work as well, I think.

Otherwise, the heat pump is the only heat source, yes. We do have photovoltaics, but we also feed in. Therefore, the electricity is best that is not used in the house.

What options do I have besides underfloor heating cooling with buffer tank to keep the building somewhat tempered in summer? The controlled residential ventilation with HRV, according to my understanding, at best ensures that fresh air is available and the heat is reused – so it has no cooling function whatsoever... which, in summer, can lead to a hot house if the ventilation brings in outside air...

What is a feasible solution there?

Regards

As described, I turn off the ventilation during the day in the "hot" period and switch to "passive cooling airing". This has worked well so far. What happens during passive cooling? There are different options for passive cooling. In the "airing" option, the supply air fan is turned off at night (when the outside temperatures are cooler than inside) and, due to the negative pressure in the house (air is still being extracted through the exhaust fan), cool night air is drawn in through the open(!) windows. This has worked quite well.

Alternatively, there is also the opposite function: exhaust fan off and supply air fan on --> warm air is "pushed" out of the house.

Additionally, one can buy and install a "summer cassette". This has no heat transfer function and prevents the warm indoor air from warming the cool night air. However, the summer cassette must be converted back for winter.

And very important....shade!