Comparison between brine heat pump and gas heat pump

Gas: Gas condensing compact unit with 150-liter stratified storage tank + controlled residential ventilation with heat recovery + solar domestic hot water heating - Vaillant auroCOMPACT VSC S 146/4-5 150 or 206/4-5 150 - 150 liter stratified storage tank including integrated solar utilization in the unit - Vaillant auroTHERM VFK 145V - Vaillant recoVAIR 260 or 360 (central supply and exhaust air)

Many questions have already been answered.

Regarding the system above. - Don’t expect too much from solar domestic water heating. Conventional collectors only work with direct sunlight. The alternative – vacuum flat tube collector – which also works with diffuse light, has about double the collector costs. Depending on the number of residents, you have hot water energy costs of about 0.40–0.70 cents/day. The payback period of such a system is therefore very long. Especially since electricity for the circulation pump is also added. However: With a gas condensing boiler you do need solar thermal.

- The 150 L storage tank is (much) too small. In my opinion, 300 liters is the minimum. If you have more than 2 residents, 400 liters makes sense. The system mentioned here, in my opinion, does not even function adequately for 2 people, as the storage volume is far too small. I have a 300 L stratified storage tank. In winter, it is naturally only heated in the upper area by gas. That’s about 150 L that get really warm. That gets tight with a somewhat larger bathtub. I can’t imagine sitting in a tiny puddle of hot water if I only had a 150 L stratified storage tank...

There are many calculations. Based on current (!) energy and equipment prices, the TOC (Total Cost of Ownership, meaning energy costs + capital costs + ...) over 20 years with a gas condensing boiler is somewhat lower than with an air-water heat pump. However, the differences are rather marginal.

The brine heat pump: For that, you need the corresponding conditions. For example, I couldn’t do it at all; it simply doesn’t work here. If it works: Here you have decent annual performance factors (COP). Assuming energy prices continue to rise, it is definitely worth considering if planned long-term (20 years). Of course, you are very efficient here, reduce direct energy costs, but have higher capital costs.

A 5 kWp photovoltaic system facing south or a 2*3 kWp east/west setup is certainly a very good choice for a single-family house. Especially in combination with the heat pump. Even here, amortization is a long-lasting affair. Without a battery or heat pump, you generally have about 25–30% self-consumption. The rest is fed into the grid, with declining remuneration. When you’ve built, the price is surely around 11.5 ct/kWh. A battery or a heat pump (hot water in summer) increases the self-consumption rate, which makes sense. In my opinion, you should aim for a self-consumption/autonomy rate of >45%, preferably 55% or more. Photovoltaics on the single-family house these days – if it is to make sense – means: Use as much electricity yourself as possible, draw as little as possible.

The manufacturers mentioned are all reputable companies producing quality products. In my view, there is nothing against these systems (except the mentioned undersized hot water storage tank).

Best regards Thorsten