ᐅ Is the hot water storage tank sufficient?

Hello,

Explosiv schrieb:
...this is about the design of the heat pump and its optimal operating range. The main job of the heat pump is space heating....

That is not necessarily the case. This may apply to an energy saving regulation standard but not to a Passive House. For this reason, a basic analysis (capacity, energy) for heating and domestic hot water is needed.

Explosiv schrieb:
...If the heat pump manages it directly, then with such a poor efficiency that the electricity costs incurred stand in a very unfavorable ratio to the achieved performance...

Therefore, domestic hot water tanks supplied by heat pumps are designed differently compared to those supplied by gas condensing boilers, for example. With proper planning, an electric backup heater is not required for normal operation.

Explosiv schrieb:
...Then the higher investment costs of the heat pump compared to, for example, gas condensing boilers would no longer be amortized, which is already difficult enough in reality...

Noticeably higher investment costs likely apply only to ground source heat pumps with vertical probes. For air source heat pumps, the investment costs are comparable to gas condensing boilers, if you do not forget their connection costs.

Explosiv schrieb:
...Prefer more storage optimized for this type of use, at lower temperatures, rather than a standard storage tank at high temperatures.

That is correct.

Best regards.

kaho674 schrieb:
So the question is, how far can you get with 175L of hot water...?

That probably varies for everyone, but as a starting point, you could look up your last water bill and calculate your average total daily consumption. That will include cold water as well, but at least it gives you a rough idea.

kubus schrieb:
This will vary for everyone, but as a reference you can look up your last water bill and calculate the average total daily consumption. That will include cold water as well, but at least it gives you a rough idea.

If Sunday is the main day for everyone to use the bathroom extensively, then the average won’t mean much.

Hello everyone,
I am bringing this thread up again because I didn’t want to start a new one just for a question.
For our 148 sqm (1594 sq ft) city villa, the construction company is planning a ground source heat pump Weishaupt wwp S6 IDT with an integrated 170-liter (45-gallon) hot water storage tank and a buffer tank. Is 170 liters sufficient for a household of four, or could that be tight?

Dear ZePetrator

We asked ourselves this question as well and discussed it with friends and acquaintances.

The answers vary widely.

You can estimate a solution based on key figures (a) and technical boundary conditions/comfort requirements (b) and coordinate it with your trusted MEP specialist.

a) Key figures
- Water bill from the previous year excluding garden water
assume about 30% of that as hot water demand
=> daily water volume

- Energy consumption for hot water from the previous year
=> daily energy amount needed for heating

- Mornings can get hectic with 4 people if the kids, at a certain age, want to shower longer than 15 minutes ... are there 2 bathrooms available??
=> Peak flow rate in liters per minute that must be supplied

- Bathtub planned?
depending on the design, that means quickly supplying 100 to 250 liters at 42°C (108°F)

b) Comfort
- Should there be a hot water circulation pump?
xx seconds until hot water flows from the tap on the 3rd floor??
=> Plan for standby losses

- How hot should the "cook" have the water from the kitchen tap? (We stopped doing this because it’s too expensive; a small electric kettle runs much cheaper.)
With many small draws, about 80% cold water is "wasted" before usable hot water reaches the kitchen.

- Should the shower water come almost ready to use (about 35°C (95°F)) from the tap, or should the mixing valve/thermostat handle cold water? (see comments in other posts)

- Caution when selecting the control system: during summer operation, some systems/controllers can lose a lot of heat unused through evaporation.

- The 170-liter (45-gallon) tank does not deliver 170 liters of hot water!!
With many small draws, the warm remaining water mixes with the incoming cold water.
Result: mixed temperature for the next draw
and not the initial temperature BEFORE the draw.
This effect also occurs with sophisticated stratified tanks, only it is significantly less pronounced here.
The maximum draw volume is measured during one continuous usage, but that does not correspond to private daily usage patterns.

I hope this brainstorming helps stimulate your family discussion and talks with the MEP planner, so you feel comfortable with the hot water supply later on.

For us (2 adults, 3 growing kids), it worked great after a little adjustment. Our neighbors have about twice the energy consumption for hot water... and they are happy with it too...

Thank you for your response. There are many parameters that need to be considered. We will trust our builder on this. Our hot water consumption is moderate. However, that is always a subjective matter.