ᐅ How much buffer storage is needed for around 300 m²? Is installing cooling worth it?

A heat pump is planned for an energy-efficient house 70. The living area is approximately 300 m² (3,229 ft²) spread over 2 floors. It consists of one large apartment and four small apartments. Underfloor heating will be installed throughout.

1.) What size should the buffer tank be? Is 400 liters (106 gallons) sufficient?
2.) Is the extra cost for a cooling function worth it? How many degrees can this roughly lower the room temperature?

Andik81 schrieb:

1.) How tall should the buffer storage tank be? Is 400 liters enough?

Why use a buffer tank at all?

Andik81 schrieb:

2.) Is the extra cost for a cooling function worthwhile? How many degrees can it roughly lower the room temperature?

No, it’s not worth it. Maybe you can lower the temperature by around 3 degrees? It’s not just the cooling function you need, but also humidity sensors in the apartments. Cooling the air naturally causes humidity to rise, which can make the rooms feel very muggy (for example, going from 27°C at 70% relative humidity to 24°C at 83% relative humidity).

jens.knoedel schrieb:

Why use a buffer tank at all?

Isn't it more practical to combine it with a photovoltaic system, for example, for domestic hot water production?

Andik81 schrieb:

Wouldn’t it be more efficient to use this in combination with a photovoltaic system, for example, for water heating?

Buffer tank or hot water tank? These are different things. Or a combination tank?
A traditional buffer tank stores heating water so the heat pump doesn’t have to run as often or as long. In practice, however, a buffer tank often masks poor heating system design and can lead to increased energy consumption.
A hot water tank either stores heated domestic water or uses an integrated heat exchanger to heat the flowing domestic water during use.

Have you already had your heating system planned by a professional?

jens.knoedel schrieb:

Buffer tank or hot water tank? They are different things.

In my question about whether 400 liters (105 gallons) is sufficient for us, I am referring to the heating water buffer tank. Additionally, a 500 liters (130 gallons) hot water tank is planned.

Andik81 schrieb:

My question about whether 400 liters (105 gallons) is sufficient refers to the heating water buffer tank.

Then my first answer applies. It is best to avoid buffer tanks if possible, as they not only incur initial costs but can also increase operating expenses.
If a buffer tank is necessary for hydraulic or other reasons, your professional planner will advise you accordingly and specify the required size.

P.S. Photovoltaics do not play a role in this consideration.