ᐅ Sizing of Hot Water Storage Tanks

Hello everyone,

Our house, which we will build next spring, will be equipped with an air-to-water heat pump, a centralized mechanical ventilation system with heat recovery, and underfloor heating.

The living area (ground floor/upper floor and an office in the basement) is about 180 sqm (1937 sq ft).

At the moment, I am giving some thought to the size of the hot water tank – according to the construction company, a tank with a volume of 200 liters (53 gallons) is included.

Currently, there are two of us, but we are planning to have two children, so eventually there will be four of us.

Is a 200-liter (53-gallon) hot water tank sufficient for four people?

The system offered is a Tecalor 403 SOL (we have not planned a solar panel on the roof, but the pipes for it will definitely be pre-installed up to the roof as preparation).

Best regards,
Dirk

Hello,

Doc.Schnaggls schrieb:
.....Currently, I am thinking about the size of the hot water storage tank – according to the construction company, a tank with a volume of 200 liters (53 US gallons) is included......The offered system is a Tecalor 403 SOL

What is the heating load according to DIN EN 12831?

Doc.Schnaggls schrieb:
.....(we have not planned a solar panel on the roof, but the piping for it will definitely be installed as a pre-installation up to the attic)..

Economically, that will not be viable!

Best regards

€uro schrieb:
What is the heating load according to DIN EN 12831?

Thanks for the quick reply!

I don’t have a detailed heating load calculation yet—we haven’t signed a contract so far.

Why do you think the system without a solar module for domestic hot water heating is not cost-effective?

What I forgot to mention earlier: From the start, we will install a photovoltaic system with 8 SolarWorld SW255 poly modules (1.96 kWp) on the roof.

Since we will mostly generate our own electricity for operating the heat pump with this setup, I didn’t consider an additional solar module for domestic hot water heating strictly necessary.

Best regards,
Dirk

Doc.Schnaggls schrieb:
...I don’t yet have a precise heat load calculation – we haven’t signed a contract yet.

Without a heat load calculation and the demand for domestic hot water, it’s basically impossible to select an appropriate heat source.

Doc.Schnaggls schrieb:
...Why do you think the system is uneconomical without a solar module for domestic hot water heating?

I meant that a solar thermal system is uneconomical. Moreover, "pre-installations" for this usually require a buffer tank, which often reduces efficiency.
Well-designed systems (without solar thermal) can operate without a buffer tank!

Doc.Schnaggls schrieb:
...What I forgot to mention earlier: From the start, we’re installing a photovoltaic system with 8 SolarWorld SW255 poly modules (1.96 kWp) on the roof.

Fundamentally a good approach. However, I would dimension the system based on the actual energy demand for heating and domestic hot water.
Another positive side effect: Raised photovoltaic modules reduce cooling load during the summer heat period.

Doc.Schnaggls schrieb:
..., I didn’t really think an additional solar module for domestic hot water was necessary.

Correct. Therefore, no solar air source heat pump is needed.

Best regards,

Thanks again for the quick reply!

€uro schrieb:
Without a heating load calculation and the domestic hot water demand, it’s basically impossible to select a heating system.

I can understand that. Our house will be a prefabricated home, but individually designed. The manufacturer offers two air-to-water heat pump systems: one for a living area of up to about 140 sqm (1500 sq ft), and the other for up to about 210 sqm (2260 sq ft). Once we have the exact heating load calculation, I will compare the data more specifically. Thanks for the tip!

€uro schrieb:
By solar thermal system, I meant it is uneconomical. Also, “pre-installations” for this usually require a buffer tank. Often a killer for efficiency.
Well-designed systems (without solar thermal) manage without a buffer!

OK, so my opinion wasn’t entirely off. I’ll reconsider whether the pre-installation even makes sense.

€uro schrieb:
Basically a good approach. However, I would coordinate the system sizing with the actual energy demand for heating and hot water.
Another positive side effect: Raised photovoltaic modules reduce cooling load during hot summer periods.
Correct. Therefore, no air-source solar heat pump is needed.

OK, then I will take another close look at that once I have detailed information. A photovoltaic system can certainly be expanded or downsized without much trouble.

Best regards,

Dirk

Doc.Schnaggls schrieb:

OK, I will take a closer look at that as well once I have detailed documents. A photovoltaic system can certainly be easily expanded or reduced in size.

During the planning phase, adjustments to the photovoltaic system are still possible. Once it is installed on the roof, changes are no longer as easy or cost-effective to implement (such as changing the inverter, redesigning the string layout, or the number of trackers).