Air-to-water heat pump sizing in new construction

Isn't that what is always done?

I think that is the core issue. It deviates from the standard and is new – like the heating load calculation. You don't make money with tedious details, especially when it has to be done twice – as in our case.

Additionally, our general contractor is still afraid of cracks in the plaster and the resulting warranty issues.

Hello everyone,

we are also currently in the process of deciding on an air-to-water heat pump, but I am a bit overwhelmed because the offers vary greatly.

Our single-family house (KfW55) + granny flat and basement apartment will have a total of about 290m² of heated space. According to the Energy Saving Ordinance, the heating demand is 0.276 W/(m²K). According to my calculation, that would be 8kW. If I assume 6 people x 0.25kW for hot water, that adds another 1.5kW, so a heat pump with 9.5 - 10kW should be sufficient.

Where is my thinking wrong? One provider offered me a 14kW Daikin 3M heat pump. Did he simply ignore my Energy Saving Ordinance and assume a too high heat demand, or am I missing something?

My second question concerns the buffer tank: One provider says that a 100l buffer tank is sufficient because the underfloor heating already stores a lot of water, another says that 500l are needed to keep the cycling low. I would really appreciate your assessment.

Best regards

14 sounds way too big. 500l buffer tank anyway. Best you calculate it yourself on the heat pump consumption database Energy Saving Ordinance heating load.

I have entered my parameters on the page and come to 8.2 - 8.5kW. So that is already clarified. Thank you very much :)

What should I do regarding the buffer tank? We have planned individual room control. How large should the buffer tank be designed?

What should I do regarding the buffer tank? We have planned individual room control. How large should the buffer tank be designed?

Normally, a buffer tank is not installed at all. What you need is a hot water tank for potable/shower water supply (in whatever manner). That has nothing to do with a buffer tank.

A hot water storage tank (TWS 400 liters including 2 heat exchangers) was offered in addition to the buffer tank. That is clear to me and also fits. I will address the buffer tank again.