Offer validation for air heat pump in a 155m² semi-detached house, year of construction 1982

Hello,

we have a 155m2 semi-detached house built in 1982. The insulation is proper sand-lime brick with an intermediate layer and the windows will also be new next year.
Our 14-year-old Solvis Max Gas has a buffering tank that has rusted through. It still works but the repair is supposed to cost €12,000. Therefore, we are now putting 10 kW peak photovoltaic panels on the roof and removing the solar thermal collectors for hot water.
We had a gas consumption of 19,000 kWh. 48 degrees hot water temperature, all underfloor heating. There is also the heat pocket of an open fireplace connected. We would like to keep this (+ possibly install a new insert in 2-3 years). We get 40% funding.
We also need an additional system separation and would renew the heating circuit distributors to achieve a proper individual room temperature control.
We have now received 2 offers:

1. Vaillant Arotherm plus 105/6 heat pump
- 300l buffer tank for hot water and integration of the fireplace with potable water station
- 200l tank for underfloor heating
- system separation
- new heating circuit distributors (listed at about €5,000 in the offer, but the distributors are still from '82)
- photovoltaic electric heating rod as backup
--> €33,700 4-6 months delivery time

2. Daikin Arotherm 3 H HT with 18 kW and bivalent indoor unit with 500l stainless steel tank
- no system separation, due to stainless steel tank
- backup heater
- 18 kW offered as no on-site appointment has taken place yet.
€38,500

According to my research, Vaillant has the better COP values (about 0.5 better) but we need 2 tanks in the basement and the heat pump next to the front door is larger.
The Daikin could possibly be dimensioned smaller and then become somewhat cheaper.

What would you recommend to me? The 10 kW power should be sufficient, especially if the windows are also replaced, right?
Does renewing the heating circuit valves make sense for individual room control?

I did not want to get any more offers, no one has time anyway...
Many thanks for your assessment!

Best regards,
Christian

What would you recommend to me?

First of all, have a heating load calculation carried out taking into account the new windows. Everything else is just "crystal ball guessing." 19,000 kWh of gas currently costs about €5,000 per year. The question now is how your underfloor heating is designed. The house is "old" and therefore the circuits were probably laid with large spacing and you need a high flow temperature. This also means high electricity consumption for the heat pump. COP over the year maybe 3? So about 6,700 kWh of electricity – that comes to €3,000. So overall a good idea to switch (of course all just very roughly calculated). However, your statement that your house is well insulated is unfortunately wrong. From today’s perspective, one would call it a "catastrophe." Can you do more besides the windows? I am thinking of basement ceiling insulation (if a basement exists) or insulation of the roof or the top floor ceiling. This makes more sense as a first step than any other measure. Because in the end it leads to lower energy consumption, lower flow temperature, and thus a smaller heat pump and lower one-time and running costs. P.S. Depending on your budget, you can also consider renewing the underfloor heating. It is also "old" and certainly not well suited for a heat pump. That is also well and comprehensively subsidized.

Hi How high were the supply temperatures last time at maximum?

More information about the house was good and about the current heating. I don't think the house requires a heating load of over 9kw. It is also unfavorable to keep the water pocket. Both hydraulically and in terms of control, it is complicated. If I then also have 200l buffer storage for the underfloor heating, it makes my toenails curl up.

Hi
What were the maximum flow temperatures recently?

Hello, the flow temperatures were always below 40 degrees. The underfloor heating is embedded in the screed with tiles on top. The roof has little insulation but has a great open roof structure, which I will leave as it is. We also had the energy consultants here, and they didn't find anything serious regarding the basement insulation. And I just like to burn my 2-3 meters of wood per year and enjoy the fire. Of course, the wood heats the air just like the water, but maybe someday there will be a more efficient hydronic stove.
As I said, the old heating system is broken, and I don't feel like installing another overpriced Solvis thing.
The solution with the two buffer tanks isn't bad, one runs at 35 degrees for the underfloor heating and the other at 50 degrees at the top of the tank for hot water.
Daikin has a stratified storage tank, which also worked well with the Solvis.
It's just a question of which system is better and whether individual room control with individual smart home temperature sensors will be useful to me. So far, the problem has always been that the Solvis temperature sensor was placed in the coldest spot in the house while the rest of the house, for example due to solar radiation, was at 27 degrees... I would appreciate further feedback!

We also had the energy consultants here, who didn't notice anything serious regarding the cellar insulation.

Cellar heated or unheated? Insulated cellar ceiling of an unheated and otherwise uninsulated cellar quickly brings about 10% savings in heating costs – pays off in a few years even with DIY.

Hello, the flow temperatures were always below 40 degrees.

Then take a cheap and simple heat pump without water pocket gimmicks and any kind of layered storage tanks.

The solution with the two buffer tanks is not bad, one runs at 35 degrees for the underfloor heating and the other at the top of the tank at 50 for hot water.

No, it is.

The question is which system is better and whether individual room control with separate smart home temperature sensors benefits me.

It does. And that is costs. Ideally, an underfloor heating system is set up (keywords hydraulic and thermal balancing) and then just runs efficiently on its own. Due to the inertia, you can't really control much anyway.