ᐅ What happens when the hot water tank is empty?

Created on: 21 Dec 2020 05:07
A
ARPcPro
Hello everyone,
I have a house offer with a "Junkers ground source heat pump STM // including a 185-liter (50-gallon) hot water storage tank."
A bathtub requires about 300 liters (79 gallons) of water to fill.

After using the 185 liters (50 gallons), will I still have immediate hot water?

If not, how long does it take before I can continue filling the bathtub?
G
guckuck2
21 Dec 2020 12:04
hampshire schrieb:

That takes hours – if you want the full temperature from the tank in the bathtub.

Well, maybe not hours after all...
Assuming the tank is really empty, meaning the supply temperature is 15°C (59°F) cold (temperature from the ground loop), and you want to heat a 185-liter (49-gallon) tank to 45°C (113°F).
A heat source with 6 kW heating capacity is used for this.
That takes 80 minutes.

In practice, however, the tank is usually not empty, unless intensive showering is done alongside the bath.
J
Joedreck
21 Dec 2020 13:57
When in doubt, you can install a 24 kW tankless water heater suitable for solar systems in between. It measures the temperature of the hot water and reheats it if necessary. However, for new constructions, I generally consider this the second-best solution.
G
guckuck2
21 Dec 2020 17:24
Most heat pumps have an electric heating element. It can be configured accordingly if the compressor is not fast enough.
ARPcPro22 Dec 2020 05:11
guckuck2 schrieb:

Most heat pumps have an electric heating element. It can be configured accordingly if the compressor cannot heat up fast enough.

Thank you very much for the answers.
The user manual shows that this ground source heat pump SUPRAECO STE 80-1 does not have a heating element.
4.1 Auxiliary heater
The heat pump may be sized to cover the entire demand of the house independently, so that normally no auxiliary heater is required. However, an auxiliary heater can be installed, which only operates in an emergency when the heat pump is not running.
The heat pump may also be sized so that it only covers part of the house demand, requiring an auxiliary heater for colder seasons. In this case, the auxiliary heater also helps in emergencies, for extra hot water, and thermal disinfection.
The auxiliary heater consists either of an electric heater or a mixed option, for example from electric, oil, or gas boilers.
Auxiliary heating is automatically activated by the controller when necessary.
G
guckuck2
22 Dec 2020 09:31
That’s just a checkmark on the order form.

But of course, it’s inefficient.
Y
ypg
22 Dec 2020 09:42
In a household of four people, a water heater that is too small can be an issue. However, it doesn’t have to be if you make sure, for example, not to waste water. I think that’s acceptable. I had about 80 to 90 liters (21 to 24 gallons) in a terraced house – after a full bath and brushing teeth, there was no room left for even a small wash-up.
180 liters (48 gallons) can be sufficient 🙂

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