Vitocal 200-s not reaching target temperature DHW

[aconjaer]

Hi community,

Maybe this question has already been answered, but since I'm not speaking German, I can't check all posts.

I have a Vitocal 200-s heat pump which is also used for the heating of our DHW. However, I've noticed that the heat pump always stops before reaching its target temperature (see image below). In this case, the target temperature is 58°C and the heat pump stops at +- 49°C.

I've checked all parameters, but I'm unable to find the cause of this behaviour.  Can anyone explain to me why this is happening and what I can do to prevent this.

Thanks in advance,

Andreas

[Guennie]

Hi,

The Vitocal 200-A manages a maximum flow temperature of 60°C. 55°C is already very good for the 200-A.

The technology does not allow for more.

How high you really get in the water tank depends on the individual hydraulic design and the maximum flow temperature that can be achieved in the secondary circuit.

In general, it is recommended to set the hot water temperature only as high as necessary.

For example, so that it is enough for everyone to take a shower. If you want to take a bath, you could activate the one-time hot water preparation beforehand, whereby the 2nd setpoint is approached. This is set so that a bathtub filling is achieved.

Regards,

Guennie

[aconjaer]

Hi Guennie,

Thanks for the response.

What I'm trying to achieve is to raise the target temperature when my PV installation is generating excessive power. In this way I try to buffer the heat when there's a lot of sun to use this in the evening.

I can see that heat pump is generating a supply temperature of more than 60°C, which should be enough to get the water tank temperature up to 58°C in my opinion (if you circulate long enough). However, the heat pump stops before reaching its target. What I can understand from your explanation is that the heat pump stops because the max flow temperature is reached in the second circuit? Would it be an option to raise this max flow temperature to achieve higher temperatures in the water tank itself?

Kind regards,

Andreas

[Guennie]

Do you mean the supply line to the hot water buffer has the 60 degrees, only you do not get loaded into the hot water buffer ?
What type and size of hot water buffer you have complained about.

[aconjaer]

Yes, the supply line to the buffer has over 60°C as you can see in the image below (Steektemperatuur = supply temperature). The hot water buffer is a Vitocell 100-W of 300 liter.

[Guennie]

Hi,

ok, I see what you mean. You have the following problem, that the high energy, which you transfer from the heat pump to the storage tank, cannot be transferred fast enough to the drinking water via the heat exchanger pipes inside the storage tank.

Thus you have the problem that the return temperature is also very fast, very high, here is simply at 60 ° C end - more creates the WP simply not. Since the heat pump cannot transfer any more energy into the pipe, the heat pump shuts down.

You must therefore give the water circulating between the buffer and the heat pump more time so that the energy can be transferred to the drinking water. This can be achieved by reducing the speed of the secondary circuit pump during DHW preparation. This reduces the flow velocity and the heating water has more time to transfer its charged energy to the drinking water. At the same flow temperature, the return temperature is colder, thus more energy is transferred to the buffer.

But be careful:

the speed can only be reduced up to a certain point, otherwise the flow will fall below the minimum flow, and then the heat pump will go on fault. It is therefore advisable to have this adjustment made by the heating engineer or the Viessmann technical service.

Regards,

Guennie