ᐅ Reversible air-to-water heat pump vs. air conditioning unit with heating function

Hello everyone,

This is my first post here, and when it comes to house building, I am a complete beginner. I will likely have several questions for you in the future regarding the planning and construction of a solid masonry bungalow.

My first question has been on my mind since the beginning of the planning process:

What are your experiences or opinions about a reversible air-to-water heat pump with active cooling compared to an air conditioning system with heating function for the entire house?

I have read many reports on this topic, but every option has its pros and cons. My main concern is which solution is truly the most effective for cooling indoor temperatures during summer when outside temperatures reach around 40°C (104°F), especially with wall thicknesses of 30 to 36.5 cm (12 to 14.5 inches).

I have read that a ground-source (geothermal) heat pump is generally the most efficient, but it is more expensive to install than a reversible air-to-water heat pump. However, based on my experience in the USA (Florida), I am very impressed with an air conditioning system that also provides heating. So, I am uncertain whether a reversible air-to-water heat pump can cool indoor air just as effectively.

A few days ago, during a planning meeting on a day with 39°C (102°F) outside temperature, the representative from my masonry construction company said right away, “You really notice the air conditioning at these temperatures.” That comment surprised me somewhat because everyone usually wants to sell you the KfW construction standard and the most sustainable solution. In my opinion, it won’t help much if, for example, I end up sitting in the bungalow at 30°C (86°F) room temperature when it’s 35°C (95°F) outside, just because I have an air-to-water heat pump.

I would really appreciate any brief replies or shared experiences because practical experience means more to me than any reports or sales pitches promoting the latest technology.

Best regards

The cooling effect of a heat pump system is inherently limited, whether it is a ground-source (brine-water) heat pump or an air-water heat pump. Only the floor is cooled, but no moisture is removed from the room air. If you cool down thoughtlessly, you will encounter condensation problems. That is why dew point sensors are installed to interrupt cooling in time. So, you should not expect miracles.

If you seriously consider cooling, equip some rooms, for example living rooms and bedrooms, with an air conditioning system.

I am not sure how efficient or cost-effective heating with an air conditioner in winter can be...

If necessary, you may need to install both systems: heating and, in some rooms, an additional split air conditioning unit.

In any case, make sure to plan external shading for windows, especially on the south and west sides!

@hendi1908

You are describing the same thing in green. Both are heat pumps and operate on the same principle. The only difference is the medium that is ultimately heated or cooled—once water and once air.

With a reversible air-to-water heat pump, you could also cool the air. Or with the so-called “air conditioner,” you could heat water. Of course, this wouldn’t be very productive or efficient, but it would work since it’s essentially the same device and principle. Even in Florida.

However, there is a big difference in effectiveness because the heat exchangers and other components are designed for the specific medium they interact with. That is why there are distinctions such as air-to-air heat pumps or air-to-water heat pumps. (A ground-source heat pump is also a heat pump, but the energy transported to the house comes from the ground and returns there during cooling mode.)

To answer your questions: If you want effective and noticeable cooling, nothing beats an air-to-air heat pump designed specifically for that purpose (as is common in Florida). On the other hand, using air for heating here in cooler climates is less optimal, so you need a “proper” heat source (gas, air-to-water heat pump, ground-to-water heat pump, etc.).

Of course, you could also combine systems, including thermal mass activation and ceiling cooling, but that involves different costs and challenges.

@Daniel-Sp @Mycraft

First of all, thank you for your quick and really informative answers.

So, do I understand correctly that an air conditioner is basically an air-to-air heat pump, or am I mixing things up?

As a layperson, I’ll try to explain it this way. I currently live in an older apartment building with an oil heating system, and I have had a split system installed in the bedroom afterwards.

I have read that air-to-water heat pumps can only raise the temperature by about 6°C (11°F), and the cooling sensation they provide is quite different. Now I’m concerned that if I install an air-to-water heat pump with cooling capabilities, with an outside temperature of 39°C (102°F), the rooms will become unbearably hot. Or am I miscalculating given wall thicknesses of 30–36.5 cm (12–14 inches)? I only know that some acquaintances who built houses have installed split units anyway despite having heat pumps and external shading because they couldn’t achieve proper cooling in summer. I definitely want to avoid that. Also, I don’t want the indoor unit of the split system to be visible on the wall.

For my bungalow, I would like the same setup because I really like the cooling performance of split systems, but I don’t want the indoor unit to be visible inside the rooms. You probably know houses or hotels where there are only ventilation ducts above the doors. I want a similar duct above the door in every necessary room of my bungalow. Ideally, I want to control the temperature (cooling supply) individually in every room, or alternatively have an electronic display in the living room that lets me control the settings for each room.

Does this then mean that it is an air-to-air heat pump and that I would need additional conventional radiators for the winter? What is the best heating source to use (oil/gas/etc.)? Is that still up to date for a new bungalow? Do I absolutely need underfloor heating or not?

hendi1908 schrieb:

So, have I understood correctly that an air conditioner is basically an air-to-air heat pump, or am I mixing things up?

You’ve understood that perfectly. Even your current Daikin system in the apartment is an air-to-air heat pump. Heat pumps just sell better when they’re called by their proper name. Because as soon as the average homebuilder hears the word “air conditioner,” they usually react negatively.

But once you package it with technical terms, many are willing to install the very same units as a heating source—because then it suddenly seems environmentally friendly.

hendi1908 schrieb:

I’ve read that air-to-water heat pumps can only lower temperatures by about 6 degrees, and that the cooling effect feels very different.

You can’t generalize like that. It might be 2 to 3 degrees, or sometimes up to 6, but the real point is that if it’s 35°C (95°F) outside, inside you’ll still have about 29°C (84°F). The cooling capacity is very limited because the wrong medium is being influenced and no dehumidification takes place. But it’s actually the humidity that makes the environment feel too warm. Here, floor cooling with an air-to-water heat pump can’t do much. Also, there is little to no convection, so the warm air just stays where it is. As we know, warm air rises. Naturally, the floor can become cooler this way, but the occupied zone where people are usually located is typically not at floor level.

hendi1908 schrieb:

I just know that a few acquaintances who built their houses have installed split systems despite having a heat pump and external shading, because they had no chance of cooling in summer.

That’s exactly how it is. A lot of factors have to come together, and you need extensive shading—ideally natural shading like trees in addition to artificial measures on the building—to achieve a comfortable and cooler indoor climate without active cooling in modern houses. Physics cannot be tricked.

hendi1908 schrieb:

The split system should not be visible on the wall at all.

Then you just choose something else. The well-known wall-mounted indoor units are only one option for cooling indoor air. There are also ceiling cassette units or ducted systems that can be installed very discreetly.

hendi1908 schrieb:

I would like to have such a duct above the door in every room of my bungalow where it’s needed.

Those are ducted systems, and it becomes very expensive and complicated (and usually unnecessary) if you want that in every room. But yes, the customer is king, and everything can be built exactly as you want it. It’s also somewhat similar to what’s possible in the USA with a central HVAC system that keeps the entire house at the desired temperature through large ventilation ducts.

hendi1908 schrieb:

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

That’s possible, but as mentioned, it gets very expensive and is generally unnecessary in a single-family home.

hendi1908 schrieb:

Does that mean it is an air-to-air heat pump and that I simply need regular radiators for winter heating as well?

No, nobody really needs radiators anymore. Surface heating systems, like underfloor heating, are much more efficient and economical, especially if you live in the home permanently.

hendi1908 schrieb:

What is the best “proper” heat source to use (oil/gas/…)? Is that still appropriate for a new bungalow nowadays?

You choose whatever works best for your house. Depending on your heat loss, you select the suitable heat source. For example, if you only need about 4 kW for heating, it doesn’t make sense to opt for gas or similar. But for 8 to 10 kW (or more), gas can be a reasonable choice.

We don’t know exactly what kind of build you’re planning. Wall thickness alone says very little, as it’s only one parameter among many.

I find the topic generally interesting as well. But be careful not to let the current situation overly influence your planning! Right now, it’s just the two weeks of extreme heat per year.

In 3–4 weeks, when continuous rain and temperatures around 15°C (59°F) are expected, you’ll definitely want a heated sunroom. And around Christmas, a fireplace with enough space for a large Christmas tree in the living room becomes the most important feature.

Despite climate change, we are not in Florida with six months of heat per year. A reversible air-to-water heat pump makes sense if it doesn’t add too much extra cost. However, it won’t work miracles and is more likely to keep your feet cool with underfloor heating.

For us, it makes more sense on hot days to focus on effective external shading and proper ventilation habits.