ᐅ Ground source heat pump primarily used for cooling – does that make sense?

Dear Forum,
we are building our first house. I am a layperson, not very technically inclined, and apparently looking for a solution that doesn’t quite follow the usual standards. Usually, there are good reasons for that, which I don’t fully understand yet. That’s why I’m posting my question here and hope for your expertise.

For our new build, I am mainly looking for a cooling option using surface heating systems (underfloor and ceiling heating), as I don’t want an air conditioning system nor exposed pipes inside the house (which is also why I don’t want a mechanical ventilation system). I guess I am a very old-fashioned person: I open a window and it gets cold, I turn the radiator and it gets warm, I light a fire and it gets hot. I understand that this might be a disaster in terms of efficiency, but automatic/central controls and linkages, for example using an outdoor thermostat with underfloor heating in all rental homes we have lived in so far, always lead me to bypass them somehow by keeping about one-third of the windows tilted open almost all the time (which makes the formal energy efficiency completely pointless). Probably, my perception of temperature is very subjective and fluctuates more than the actual measured temperature. In general, all modern well-insulated new builds feel way too warm to me, and I’m a fresh-air enthusiast who loves open windows! Unfortunately, I also don’t find that a mechanical ventilation system gives a subjectively comparable effect to frequent airing by opening windows wide.

Now to the question: since I mostly find the temperature bearable only in the basement during summer, we are considering installing a cooling option. Since air conditioning and mechanical ventilation are out of the question, the only remaining option seems to be a heat pump with cooling function, which we would of course also use for heating. We plan to drill ground probes (geothermal probes) and most likely install underfloor and ceiling surface heating.

My main concern is that even if we install a modern heat pump, we might not use or benefit from the technology properly. Our focus is not primarily on a specific energy efficiency level. If we omit mechanical ventilation, it seems there might be risks of condensation and mold? Then I would keep windows open permanently as before (which does not bother me personally), but of course, this would cause huge energy waste, as the automated heating, cooling, and heat pump would constantly be working against my “manual interventions.”

Does it make sense to install a geothermal probe and brine heat pump mainly for cooling under such ventilation behavior and without mechanical ventilation?

Many thanks, and please don’t be too harsh right away. Maybe in the end I will come to accept the apparently modern and energy-efficient full setup of heat pump plus mechanical ventilation — or we will put electric heaters or coolers in individual rooms as needed, or... or?

Good luck!

Fixmalfertig schrieb:

Presumably, my perception of temperature is very subjective and fluctuates more than the actual measured temperature.

When building a house, you specify the desired room temperatures for heating. With a properly adjusted heat pump, you won’t need to change settings for colder or warmer for the next 10 years.

Fixmalfertig schrieb:

Unfortunately, I also don’t find that a controlled ventilation system has a subjectively comparable effect to frequent airing by opening windows briefly.

That is unfortunately only subjective.

Fixmalfertig schrieb:

If you leave out the controlled ventilation system, it seems that there could be risks of condensation and mold?

Is that because the house is airtight or because you want to cool in summer?

Fixmalfertig schrieb:

Then I would have permanently open windows as before (which personally doesn’t bother me), but of course that causes huge energy waste if the automated heating, cooling, and heat pump are constantly working against my “manual adjustments.”

The heating runs in winter, not in summer. So you can open the windows as much as you want in summer. In winter, it certainly causes massive energy waste if the temperature is set incorrectly. But that is due to planning, not the heat pump.
If you want to cool in summer, you won’t open windows and let warm air in. Cooling usually means it gets about 2°C (3.6°F) cooler. If windows are open all the time, there will be no cooling effect.

Fixmalfertig schrieb:

Many thanks and please don’t dismiss everything outright. Maybe in the end, I will opt for the apparently modern and energy-efficient complete setup with heat pump plus controlled ventilation system and “get used” to it.

That is actually the ideal option. Just make sure to have it planned and calculated by an engineering firm—not to have the heating installer just build a system based on their usual rough estimates.
Otherwise, there are other options depending on your budget. Keywords include concrete core activation, chilled ceilings, cooling sails, or similar.

Thank you for your response.

Yes, we have an engineering firm that could calculate and design this for us—once we know exactly what we want.

nordanney schrieb:

Is it because the house is airtight or because you want to cool in summer?

From what I’ve read so far, it seems both are issues: too high humidity in airtight houses and also a too-low water temperature in the cooling circuit, which could cause condensation.

The first issue could be addressed with a controlled ventilation system or theoretically through manual ventilation.
Regarding condensation during cooling—I’m not sure how to prevent that or what is needed to avoid mold growth (probably no cooling of the water below 16°C (61°F)? But if condensation still occurs, what then? Presumably, ventilation is needed in that case?).

So, if I don’t have a controlled ventilation system, but I do have surface cooling and heating in an airtight house, does that leave me no choice but to open the windows? Which would likely greatly reduce the efficiency of heating, cooling, and the heat pump?

Has anyone here installed a heat pump for cooling and heating without controlled ventilation and can share their experience?

nordanney schrieb:

There are of course other options depending on your budget. Keywords are thermally activated building systems, chilled ceilings, cooling sails, etc.

I understood that these systems still somehow need cold water to generate the cooling effect, so a heat pump would presumably be required upfront? Or can thermally activated building systems, chilled ceilings, and cooling sails work without a heat pump? For us, only a heat pump with ground source probes would be an option.

Many thanks and have a nice evening!

The problem with cooling through the floor or surface cooling is that it does not dehumidify. Dehumidification accounts for a large part of the cooling effect.
Also, you can only cool minimally due to the dew point.
Surface cooling on ceilings is more effective but also does not dehumidify.
In a modern (airtight) house, I would always install a controlled ventilation system with heat recovery.
If you want effective cooling, the only option is an air conditioning system.
Are you even allowed to do a deep borehole? It is prohibited in some areas.
Installing a temporary solution just for cooling makes no sense.

Thanks Rick, yes, we are allowed to do a deep drilling, that wouldn’t be a problem. But strictly for heating purposes, we wouldn’t even need it since there is geothermal energy available in the street. Only if we want to cool using the heat pump as well, we would need our own borehole. So it’s quite a lot of effort just for cooling. And from what I’m reading here, it actually doesn’t make much sense without controlled ventilation since the cooling effect is limited and there are risks of moisture buildup. The roof structure so far also suggested that you could actively cool with the heat pump, using it reversibly. But apparently, that is not really the case? Why exactly? Because of the risk of dew point issues?

@Fixmalfertig Several aspects need to be considered here.
Mechanical ventilation with heat recovery always makes sense in new houses because they are so airtight. Otherwise, natural ventilation is often not sufficient anymore...
For cooling, mechanical ventilation with heat recovery only helps at night using the bypass. Such a system always dehumidifies to some extent. To cool through the air, the airflow rate must be significantly higher. That is possible but requires a more specialized setup, which we have, for example.

Cooling through the floor can lower the temperature by a maximum of 2-3 degrees Celsius (3.6-5.4°F), but it often results in cold feet due to the dew point issue. Using ceiling panels and similar systems can achieve more cooling, but they do not provide dehumidification, which would have a stronger effect.
Since you already have a heating system, this does not make sense at all. It costs a lot for little impact. Do yourselves a favor and install a proper air conditioning system instead. It is cheaper and will deliver the results you want.