ᐅ Is a buffer tank useful for a heat pump?

So you have 170m² (1830 sq ft) of heated floor area with screed.
If you assume 100kg/m² (20.5 lbs/sq ft), that’s 17 tons of “buffer mass.”
If you now add 500 liters (130 gallons), that’s about 3% more.

One might assume that this could extend the heating cycles by 3%.
I can’t imagine that this makes much of a difference.

It’s more important to review all the settings again and also open the valves on the ground floor.

jens.knoedel schrieb:

Actually, the only solution left for a poorly planned heating system is a properly sized buffer tank. With a lower modulation limit of 3kW for the well-insulated house, the heat pump can’t help but cycle heavily, which basically accelerates its aging (think compressor starts).

I would really work with two separate tanks and once the heat pump needs to be replaced, switch to a significantly smaller unit and disconnect the heat pump buffer again.

RotorMotor schrieb:

So you have 170m² (1,830 sq ft) of heated floor area with screed. Assuming 100kg/m² (20.5 lbs/sq ft) load, that’s 17,000 kg (37,480 lbs) of thermal mass. If you add 500 liters (130 gallons) of buffer volume, that’s about 3% more. You might think that would extend the cycling times by around 3%.

I can’t imagine that would make much of a difference.

More important here is to adjust all the system settings again and make sure the valves are fully open on the ground floor.

Hmm, these two opinions seem to contradict each other somehow.

RotorMotor schrieb:

It’s important here to check all settings again and also open the valves on the ground floor.

However, this doesn’t help in autumn or spring when the 3kW minimum output for the house is simply too high. Just like in the last few days. The heating system can’t get rid of its excessively high output.

Basically, I agree with you that a heat pump should run without a buffer tank. But the heat has to go somewhere.

jens.knoedel schrieb:

But that doesn’t help in autumn or spring, when the 3 kW minimum output for the house is simply too high. Just like in the last few days. The heating system can’t get rid of its way too high output.

Basically, I agree with you that a heat pump should run without a buffer tank. But the heat has to go somewhere.

If a buffer tank helps, I’m happy to install one. RotorMotor says it doesn’t help.

>>>

The heat pump shows the following annual balance:
Heating 12,740 kWh
Cooling 1,850 kWh
Electricity 3,180 kWh
Seasonal performance factor: 4.6

I’m currently checking the data from the identical, properly functioning heat pump of the neighbors.

jens.knoedel schrieb:

But the heat has to go somewhere.

Yes, into the 17t (17 tons) of screed. Of course, you need a few cycles per day, but that's not a problem if you use the 17t as a buffer.

jx7 schrieb:

If a buffer helps, I’m happy to install one. RotorMotor says it doesn’t help.

At least physically, the additional 3% mass doesn’t make a difference. However, it could be that the heat pump is poorly configured or can’t be adjusted any better. In that case, using a buffer as a hydraulic separator with its own mixing module can reduce short cycling. But the efficiency will significantly suffer because the heat pump would then have to run at much higher flow temperatures. As I said, start by adjusting the controller first.

jx7 schrieb:

1) The house and heat pump are 7 years old. The heat pump was starting 24 times per day, now the compressor is broken, I have already discussed all of this. One possible solution is a buffer tank. Since I don’t want the discussion to get out of hand and I want to specifically learn something about the topic of buffer tanks, I have formulated the request accordingly.

jx7 schrieb:

Or instead of spending €5,000 on replacing the compressor, would it be better to get a new, better-sized heat pump? What would that cost (9,000–13,000 euros plus installation)? What kind of delivery time should we expect? (So how long could we be without hot water?)

To be honest? Get a heat pump that fits your house.

Your situation is like driving a worn-out car worth €6,000. The engine breaks down, and you put a new engine into the old car that also uses a huge amount of fuel, instead of buying a brand-new car for around €9,000.

Spend €200 for a proper heating load calculation and have a new heat pump installed—brand doesn’t really matter. Even if the initial investment is higher, heat pumps of this size should cost between €6,000 and €9,000 for equipment plus installation (and more than removing the old unit, setting the new one in place, and tightening the fittings isn’t actually necessary).