ᐅ Is a buffer tank useful for a heat pump?

RotorMotor schrieb:

“Robust” against planning errors?
Certainly not robust against high consumption.

Correct, robust against planning errors. I already mentioned that a buffer tank does not increase efficiency.

RotorMotor schrieb:

“For one,” but where is the “for the other”?
And the “for one” is really quite irrelevant.

That is actually an important point: the heat pump must be able to get rid of its heat during operation. With low supply temperatures and a small temperature difference between supply and return, the system must be designed for a volume flow adapted to the specific heat pump model. This is all feasible, but if the hired heating installer does not put in enough effort, a system without a buffer tank can, in the worst case, fail to work reliably. That is the only point I wanted to make.

RotorMotor schrieb:

A 1000L tank is of course quite extreme. Additionally, many heat pumps operate at only half their efficiency at 45°C (113°F) compared to 35°C (95°F).
You could say this helps reduce cycling even more.
Whether it is worth doubling the electricity consumption though, I find very questionable.

My example was obviously formulated unclearly. I was not referring to specific temperatures in the example, but trying to provide a roughly understandable example of the heat energy needed to raise the temperature of 1000L (264 gallons) of water by 10°C (18°F). Perhaps it lacked sufficient context. I think further discussion on this point will not be helpful here.

For a system without a buffer tank, it is important to me that the heat pump is modulating and by no means oversized at the same time. From my perspective, it can even be sized smaller than the calculation suggests, as long as it is sufficient for domestic hot water production (depending on the system).

Typical heating demand calculations based on building element values do not consider solar gains, internal heat from occupants and appliances, nor the building’s time constant—that is, the heat storage capacity of the materials used in the building (e.g., heavy structure).

One must also keep in mind that the calculation considers the worst-case scenario. In the event of noticeable undersizing, the house does not remain cold throughout the year but might be a bit cooler indoors only for a few days every five years or so.

I took the time to calculate this as accurately as possible for a house of 475m² (5113 ft²) and arrived at 9kW as a sufficient size. However, 12kW was installed because the heating installer refused to install the smaller unit. The actual annual values are very close to those originally calculated and suggest that 9kW would have been enough.

jx7 schrieb:

The repair appointment was initially canceled because Enrgi insisted on advance payment and said they could only come once the money had been received. Since the transfer couldn’t be completed that quickly, the appointment was canceled again for the time being.

What kind of clowns are these? This is the factory service department of a heat pump manufacturer, not a small independent heating technician, right?

CC35BS38 schrieb:

What kind of clowns are these? This is the factory customer service of a heat pump manufacturer, not a small independent heating engineer, right?

German distributor for the Spanish heat pump brand "Ecoforest"

And you are seriously still considering repairing the unit after all this hassle?

Rübe1 schrieb:

And you’re seriously still considering repairing the unit given this whole situation?

Option 1:
€4,800 service appointment from Energie:
- Compressor replacement
- Check heating system for faults (check dirt traps in heating circuit/brine circuit, temperature sensors, bypass valve)
- Optimize hydraulic balancing (significantly less heat reaches the upper floor compared to the ground floor when all individual room controllers are open)
- Optimize configuration (limit maximum speed, possibly increase hysteresis?, possibly night setback?)
- Increase pool heating time from 15 minutes per hour to 30 minutes per hour
If the repaired and optimized heating system still cycles frequently, install a buffer tank for approx. €2,000

Option 2:
Installation of a new brine-to-water heat pump from a major brand
- 30% subsidy
- Price around €20,000

Currently, I do not have an offer for retrofitting a buffer tank.

The lowest current quote for installing a new brine-to-water heat pump is €34,000 (which would be €23,800 after the subsidy).

If prices stay like this, we will decide to repair.

If we receive an offer of €18,000 for a new heat pump (which would be €12,600 after the subsidy), we will go for a new heat pump.

We are still uncertain about the exact price point that separates the two options.

How would you decide? Considering the €4,800 repair cost (plus possible additional cost for installing a buffer tank) and the frustrating issues with Ecoforest, how much would you be willing to spend on a new heat pump?

(1) After the appointment with Enrgi, the issue with the cycling was resolved. In the last 24 hours, there were only two cycles lasting 3:21 hours and 2:07 hours, respectively.

The following measures were taken:
- ERR all set to maximum (previously not sufficient to fix the problem)
- Inverter replaced
- Software update
- Power output adjusted from 3-12 kW to 2.5-7.5 kW

(By the way, the bypass valve was completely closed.)

(2) After the software update, the options for scheduling programs are now very limited. I can only activate/deactivate the entire heat pump, but not specific operating modes (heating, cooling, domestic hot water, pool).

The only type of scheduling is based on the heating limit in spring/fall. Contrary to my assumption, this is not based on a 24-hour average but on the current temperature. This means that in spring/fall heating only occurs at night when the temperature is below 12°C (54°F). If the temperature during the day is above 12°C (54°F), heating is turned off. I consider the limitation of heating times during the transitional seasons an advantage, but the heat pump could operate during the day using self-generated solar power, while at night I have to buy electricity.