ᐅ Is the heating system oversized?

Saruss schrieb:
Heat pump? That’s a gas heater!

Sorry, misread that. It should be the same anyway.

Jochen104 schrieb:
Then adjust the heating curve on the heat pump (lower the supply temperature) until only your desired temperature is reached. That way, it works properly, and your heat pump only uses the energy it actually needs. Although, from my layman's estimate, the heat pump might be oversized.

But if the flow rate is set to maximum in all rooms and thus all 11 heating circuits are open, doesn't the heating system end up working "too hard"? It has to supply water to all the heating circuits, right? That would be 11 times 2 liters per minute flow, a total of 22 liters per minute (5.8 gallons per minute), and running 24 hours a day...?

Also, doesn’t that defeat the purpose of my temperature-controlled room sensors... since the heating is always on...? I thought I set the room temperature and then the controller manages it accordingly.

For example, as I currently have it set to 20°C (68°F):

> Too cold > controller opens the flow until 20°C (68°F) is reached again
> Too warm > controller stops the flow until the temperature falls below 20°C (68°F)...

This means that once the target temperature is reached in the house, the flow is only open in a few rooms at a time. The boiler can’t modulate down to such a small heat demand (because it has a minimum output of about 7 kW)... so the heat exchanger heats up too quickly, causing the boiler to turn off (when the maximum set supply temperature is reached)... and then turn on again (it cycles), resulting in only short bursts of heating and slow warming of the rooms.

The system behavior with this setup is, as mentioned, predictable.

Honestly, I was surprised by the 7 kW minimum output you mentioned. The heating system is definitely oversized / too powerful for a 140 sqm (1507 sq ft) house of modern construction/insulation. Last year, even at -12°C (10°F), I never needed 7 kW. At most, 4.5 to 5 kW for a short time, then back down to 3.3 kW.

With proper sizing and flow temperature, your controllers would intervene easily, if at all necessary. Such drastic on/off regulation only happens because too much power is sent to the flow line and the flow temperature is set too high.

In my personal opinion, the solution consists of three options:
a) Let the system cycle more frequently (--> significantly shortens lifespan)
b) Replace the system with a smaller one (unlikely, but you can try, warranty as already discussed in the thread)
c) Install a buffer tank for the heating flow (also covered by warranty, of course).

Best regards
Thorsten

Basti2709 schrieb:
Also, doesn’t this kind of defeat the purpose of my temperature-controlled room sensors, since the heating is always running...? I thought I set the temperature in the room and the controller would take care of it…

For example, right now I have it set to 20°C (68°F):

> Too cold > Controller opens the flow until 20°C (68°F) is reached again
> Too warm > Controller stops the flow until the temperature drops below 20°C (68°F) again…

This way, once the target temperature is reached in the house, flow is only open in a few rooms > the boiler can’t modulate down accordingly (because it has about a 7 kW minimum)....resulting in the heat exchanger warming up too quickly and the boiler shutting off (reaching the maximum set flow temperature)…and then turning on again (it cycles), meaning the rooms are only heated in short bursts / slowly.

An example of how I understood it as a layperson:

Your version:
You’ve now reached 20°C (68°F) in your rooms. The valve closes. But the heating system doesn’t “know” that (it’s presumably controlled by outside temperature and return temperature) and continues pushing 45°C (113°F) water against the closed valve.
Although no heating energy is delivered to the room, the 45°C (113°F) warm water in your underfloor heating continues to warm the room further. After some time, the floor starts losing heat over a few hours, the room slowly cools down, and eventually your temperature controller notices the temperature has dropped below 20°C (68°F). So, the valve opens again.
In the meantime, your heating system detects from the warm return water that the energy is not being used and stops heating. Then, when colder water starts coming back from the previously closed circuits, the heating system kicks back on. It has to heat the return water, estimated at about 20°C (68°F), back up to 45°C (113°F) supply temperature and pumps it again into your system. The floor warms first, then the room slowly warms up, and eventually your controller notices it’s over 20°C (68°F) again and closes the valve. However, you still have 45°C (113°F) water in the floor that keeps heating the room… and the cycle starts all over again.

My version:
The heating runs continuously and circulates warm water according to the supply temperature as set by the heating curve (currently about 30°C (86°F) supply at −4°C (25°F) outside temperature). The water returns at about 27°C (81°F), the heating system warms it up by 3 degrees, and keeps it circulating.

You can calculate for yourself which version causes the heating system to cycle more, which uses more electricity, and which keeps the rooms more evenly warm.

Saruss schrieb:
According to the Energy Saving Ordinance, I have an ht of 0.285. What is it for you?
That also explains why everyone says to do a heat load calculation and not just rely on Energy Saving Ordinance documents.
However, aside from that, the calculation contains many assumptions that aren’t actually accurate; starting with generic thermal bridge values, it states "windows with Uw <1.00" (we are really well below that in reality), perimeter/basement insulation is 0.035 instead of 0.038 insulation.
I calculated using the actual materials, dimensions, etc. from the project plan for the construction site, based on the tenders, so it was of course more precise.

0.30 is not the best. We have, however, also changed a few details – better insulated roof, much better basement windows with one completely removed, floor insulation removed but compensated with more insulation on the slab, better front door...

Estimated final value around 0.28... but that would not affect the heating system by 3 kW, so I am sticking with the 8 kW heater, since we also need a lot of hot water.

I might have the calculation updated with the new values.