Reversible Air-Water Heat Pump vs. Air Conditioner with Heating Function

Hello everyone,

this is my first post here and I am a complete beginner when it comes to house construction, or rather, I will definitely have some questions for you in the future regarding the planning and construction of a solid bungalow.

My first question has been occupying me since the beginning of the planning:

What is your experience or what do you think about a reversible air-water heat pump with active cooling compared to an air conditioning unit with heating function for the entire house?

I have already read many reports about this, but there are advantages and disadvantages to everything. I am really only interested in which solution is most effective for cooling the room temperature in summer at temperatures around 40 degrees with a wall thickness of 30 to 36.5 cm?

I have read that a ground-source heat pump would actually be the most effective, but it is more expensive to purchase than a reversible air-water heat pump. However, since my experience with an air conditioning unit with heating function in the USA (Florida) was very impressive, I am in doubt whether a reversible air-water heat pump can cool the indoor air just as well.
A few days ago, during the planning meeting at 39 degrees outside temperature, the representative from my solid construction company said as the first sentence, "You really notice the air conditioning at these temperatures." That statement surprised me a bit, because of course everyone wants to sell you the KfW construction method and the most sustainable solution. In my opinion, it does not help if afterwards (exaggerating) I sit in the bungalow at 35 degrees outside temperature with 30 degrees room temperature and can say that I have an air-water heat pump.

I am very happy about any response or experience, no matter how short, because experience values are more important to me than any reports or statements from salespeople who always think the newest is the best.

Best regards

The cooling effect of a heat pump system is inherently limited, whether it is a ground-source heat pump or an air-to-water heat pump. Only the floor is cooled, but no moisture is removed from the room air. If you cool down naively, you will have a problem with condensate. That’s why dew point monitors are installed, which interrupt the cooling in time. So don’t expect miracles. If you are seriously considering cooling, equip some rooms, for example living and bedrooms, with an air conditioning system. How well and budget-friendly you can heat with an air conditioner in winter, I don’t know... Possibly you need to install both, heating and additionally a split air conditioning system in some rooms. In any case, at least think about external shading for the windows on the south and west sides!

You are describing the same thing in green. Both are heat pumps and both operate in the same way. Only the medium that is ultimately heated or cooled is different. Once water and once air.

So you could also cool the air with the reversible air-water heat pump. Or heat water with the so-called "air conditioner". Of course, this is not really productive or efficient, but it would work. Because it is the same device and the same principle in each case. Even in Florida.

But of course, there are huge differences in terms of effectiveness. Because the heat exchangers etc. are designed for the medium to be acted upon, and that is why there is the distinction between air-to-air heat pump or air-to-water heat pump. (Ground-source heat pump is also a heat pump, only the transported energy towards the house comes from the ground and returns again in cooling mode).

But to answer your questions: If you want effective and noticeable cooling, nothing beats an air-to-air heat pump that is explicitly designed for this purpose. (Just like in Florida). Conversely, heating with it here in our latitudes is suboptimal and you need a "real" heat source (gas, air-to-water heat pump, ground-water heat pump, etc.).

Of course, you could also combine it and provide concrete core activation and ceiling cooling, but this brings other sums and problems.

First of all, many thanks for your quick and really informative answers.

Have I understood correctly that an air conditioner is basically an air-to-air heat pump, or am I mixing something up here?

I will try to explain it as a layman. At the moment, I still live in an old building apartment and have an oil heating system here, and I have retrofitted at least a split unit from Daikin in the bedroom.

Regarding air-to-water heat pumps, I have read that they can handle a maximum of 6 degrees, and the cooling sensation is completely different. Now I am concerned that if I have an air-to-water heat pump installed that can also cool, I will melt inside the rooms at 39 degrees outside temperature. Or am I miscalculating with a wall thickness of 30-36.5 cm? I only know that a few acquaintances who built have installed split units despite having heat pumps and external shading because they have no chance to cool in summer. However, I no longer want that. The split unit should not be visible on the wall at all.

I would like it the same way in my bungalow because I simply love the cooling performance of a split unit, but I don’t want the split unit to be visible in the room. You probably know this from houses/hotels, etc., that only have ventilation shafts above the room door. I want such a shaft above the room door in every necessary room of my bungalow as well. Ideally, I want to be able to control the temperature (cooling supply) individually in each room, or alternatively have an electronic display in the living room through which I can control it for the individual rooms.
That means this would then be an air-to-air heat pump, and I would simply need completely normal radiators for the winter as well? What is best used as the "real" heat source (oil/gas/...)? Is this still up to date in a new bungalow? Do I then absolutely need underfloor heating or not?

So I understood correctly that an air conditioner is basically an air-to-air heat pump or am I mixing something up now?

You understood that completely right. Your current Daikin system in the apartment is also an air-to-air heat pump. Heat pumps just sell better when you call them by their proper name. Because as soon as the average builder hears the word "air conditioner," they usually turn red.

But if you package it and throw around technical terms, many are willing to install the same devices as a heating source. Because then suddenly it is considered environmentally friendly.

I read that air-to-water heat pumps can only manage up to 6 degrees and that the cooling feeling is completely different.

You can't say that so generally. It can be 2-3 degrees but also sometimes 6; it’s just that at 35°C outside you still have 29°C inside. The performance is very limited because the wrong medium is acted upon and no dehumidification takes place. But it is precisely the humidity that makes the environment feel too warm. Here, a floor heating cooling combined with the air-to-water heat pump simply cannot achieve anything. Additionally, hardly any convection occurs and the warm air simply remains where it is. Because, as is well known, heat rises. Of course, the floor gets colder that way, but the living area of the person is usually not near the floor.

I only know that a few acquaintances who built [such systems] have now installed split devices despite heat pumps and external shading because they have no chance of cooling in summer.

That's how it is. A lot of factors have to come together, and you need a lot of shading—ideally also natural shading through trees in addition to the artificial measures on the house—to have a pleasant and cooler indoor climate in modern houses without active cooling. Physics cannot be tricked.

The split device should not even be visible on the wall.

Then you just use something else. The well-known wall-mounted indoor units are only one option to cool the air inside the house. There are also ceiling cassettes or duct units to make the whole thing as inconspicuous as possible.

I would like to have such a duct above the room door in every necessary room of my bungalow.

Those are duct units and it gets very, very expensive and complicated (and also unnecessary) if you want that in every room. But yes, the customer is king and you can build everything the way you want. It is then also quite similar to the USA with a central climate/ventilation system that maintains the entire house at the desired temperature through large ventilation ducts.

Ideally, being able to control the temperature (cooling supply) individually in every room.

That is possible, but as I just said, it gets very, very expensive and is basically unnecessary in a single-family house.

Does that mean that this is then an air-to-air heat pump and I simply also need completely normal radiators for the winter?

No one needs radiators nowadays anymore. Surface heating systems, meaning underfloor heating, are significantly more efficient and economical if it’s a permanently inhabited home.

What do you best use as a "real" heat source (oil/gas/...)? Is this still contemporary in a new bungalow?

You use what is best for the house. Depending on how high your heat losses are, the suitable heating source is selected. For example, if you only need about 4 kW to heat, it makes no sense to rely on gas, etc. For 8-10 kW (and more), gas is not a bad choice.

We don’t know exactly what kind of building you are planning. The wall thickness says hardly anything. That’s only one parameter of many.

I basically find the topic interesting as well. But be careful not to let yourself be too guided by the current situation in your planning! These are the 2 weeks of extreme heat in the year. If in 3-4 weeks continuous rain at 15 degrees is forecast, you will definitely want a heated conservatory. And around Christmas, a fireplace with enough space for a large Christmas tree in the living room is the most important thing.

Despite climate change, we are not in Florida with 6 months of heat per year. A reversible air-to-water heat pump makes sense if it doesn't cost too much extra. But it won't work miracles and rather cools the feet with underfloor heating. For us, it makes more sense on hot days to pay attention to sensible external shading and ventilation behavior.