ᐅ Cooling with a heat pump through underfloor heating?

kati1337 schrieb:

During the summer months, our ventilation system only runs at night. If I run it during the day, no matter how much I shade the windows, I end up pumping warm outside air into the house. Then there is the heat recovery feature in modern systems – it can sometimes be turned off via bypass or summer mode, but it doesn’t help much when it’s 30°C (86°F) outside.
The underfloor heating doesn’t run at all because the heating system is set to summer operation. The air conditioning runs daily, switching on and off, and dehumidifies/cools. I wouldn’t want to live without air conditioning again – it’s quiet and provides real quality of life on the wall.

Can the ventilation system not cool the air somewhat? From what I have read, this is possible. Also, the underfloor heating would be running since it is supposed to cool. It’s clear that temperature control via underfloor heating is nowhere near as effective as an air conditioner. But if you go from outside into a room that is 4°C (7°F) cooler, that’s already a lot gained for little cost.

kati1337 schrieb:

During the summer months, our ventilation system only runs at night. If I run it during the day, no matter how much I shade, I end up bringing warm outside air into the house.

Although this is not directly related to the main topic:

The heat gain from a central mechanical ventilation system with heat recovery activated is minimal!

With an indoor temperature of 23°C (73°F) and an outdoor temperature of 30°C (86°F), the temperature difference is 7°C (13°F).
At 100 m³/h (59 cfm), this results in a maximum of only 250 W if the bypass is active.
With heat recovery at 90% efficiency, only 25 W remain.
This is truly negligible.

Therefore, do not turn off the central mechanical ventilation system in summer, and activate the bypass only at night!

Acof1978 schrieb:

Can the ventilation system cool the air a bit? From what I have read, it is possible. Also, the underfloor heating would be running since it is supposed to cool. It is clear that temperature control via underfloor heating is not nearly as effective as an air conditioner. But it is enough if you enter a room that is 4°C (7°F) cooler from outside. That already achieves a lot for little cost.

We didn’t opt for the cooling function of the system because I had read online beforehand that it can only lower the temperature by 2-3°C (4-5°F) at best, and cold air doesn’t rise either – so you get the cold feet problem. There are systems that combine ventilation with air conditioning. We have a standard central ventilation system without a cooling function. The cooling feature of the heat pump (if we had purchased it) would only cool via the underfloor heating.

When we were building, I considered air conditioning more of a luxury. Now, with the first summer in the house underway, I’m really glad we have it. It is very difficult to keep the heat out of such a well-insulated, new house. Just the sunlight coming through the windows alone heats the house up. You either have to shade so thoroughly that you might as well live in a cave, or you let the light in. The amount of heat energy from 1 meter (3 feet) of window front with sunlight is not to be underestimated – I vastly underestimated this during construction.

Once the warm air is inside the house in summer, it is hard to get it out again without air conditioning. The only thing I can think of is not ventilating during the day and then trying to flush out the warm air by ventilation at night. But in a summer like we had in 2019, the night temperature was often still around 30°C (86°F). It’s really uncomfortable to sleep at those temperatures.

In May, I managed to get the house temperature up to 28°C (82°F) even though the outside temperature was only 18°C (64°F). I hadn’t shaded the windows, and the ventilation system was running without the summer bypass, meaning 98% heat recovery. Over several sunny days, the house kept warming up. We only managed to get rid of the warm air by manually setting the ventilation system to summer mode (some exhaust during the day, higher ventilation rate at night) and cooling down again with the air conditioning units already in May.

RotorMotor schrieb:

This is not directly related to the main topic, but:

The heat input through the central controlled residential ventilation system with activated heat recovery is minimal!

With 23°C (73°F) inside and 30°C (86°F) outside, the delta T is 7 degrees.
At 100m³/h (59 cfm), the maximum heat input is only 250W if the bypass is active.
With heat recovery efficiency at 90%, only 25W remain.
This is really negligible.

So do not turn off the central controlled residential ventilation system in summer, and activate the bypass only at night!

These are calculated values. In practice, we have experienced that you cannot maintain 23°C (73°F) inside the house without air conditioning when it is 30°C (86°F) outside—unless you heavily shade the building like a bunker. In reality, the indoor temperature still rises, and the problem then is that with heat recovery, you can no longer lower the temperature effectively.

kati1337 schrieb:

We didn’t buy the cooling function of the system because I had read in online research beforehand that it can only lower the temperature by 2-3 degrees (if you’re lucky), and cold air doesn’t rise anyway — resulting in the cold feet problem.
There are apparently systems where ventilation is combined with air conditioning. We have a standard central ventilation system, which does not have a cooling function. The cooling function of the heat pump (if we had bought it) would only cool via the underfloor heating system.

When we were building, I considered air conditioning more of a luxury. Now that we’re experiencing our first summer in the house, I’m really glad to have it. It’s very difficult to keep the heat out in such a well-insulated, new house. Just the sunlight coming through the windows raises the temperature inside. You either have to shade the windows so thoroughly that you could live in a cave, or you let the light in. The amount of heating energy that 1 meter (3 feet) of window exposed to sunlight provides is significant; I massively underestimated this during construction.
And once the warm air is inside the house in summer, it’s hard to get rid of it without air conditioning. The only thing I can think of is not ventilating during the day and then trying to ventilate the warm air out at night. But in a summer like we had in 2019, the temperature at night was often still close to 30°C (86°F). It’s really uncomfortable to sleep in those temperatures.

In May, I managed to reach 28°C (82°F) inside the house even though the outside temperature was only 18°C (64°F). I hadn’t shaded the windows, and the ventilation system was running without the summer bypass, meaning 98% heat recovery. Over several sunny days, the house kept getting warmer. We only got rid of the warm air again after manually switching the ventilation system to summer mode (some exhaust air during the day and more ventilation at night) and already cooling down with the air conditioners in May.

You have the problem of underfloor heating temperature control with cold feet. I have the same problem with the air conditioning, similar to in a car, especially with our daughter — colds and so on. Since none of us ever walk barefoot in the house but always wear slippers, the cold feet issue doesn’t occur for us.

But it will all become clear in practice :-)

Acof1978 schrieb:

Even with an enthalpy heat exchanger? Because we will have one of those as well.

You mainly need it during winter. In summer, it’s basically ineffective.

Acof1978 schrieb:

As far as I understand it as a layperson, it can regulate humidity.

Yes, but only if there is an imbalance. If humid air already comes inside, it can’t regulate anything. Humid air goes out -> through the moist enthalpy exchanger -> new humid air comes in. Result in summer -> humidity everywhere. In winter, no, because there is a temperature difference and then the moisture can be regulated and slightly increased through the exchanger, so it doesn’t drop to unexpectedly low levels inside the house.

Acof1978 schrieb:

Can the ventilation system cool the air a bit? As far as I’ve read, this is possible.

No, that’s just marketing talk. Sure, you might bring in slightly cooler air at night but the amounts are negligible. RotorMotor explained it quite well.

Acof1978 schrieb:

Also, the underfloor heating would be running, since it’s supposed to provide cooling. It’s clear that temperature control via underfloor heating is nowhere near as effective as an air conditioner. But it’s enough if you enter a room that is 4°C (7°F) cooler than outside. That already gains a lot for little money.

No, that’s wishful thinking. Underfloor heating for cooling will only make the floor a bit cooler but won’t significantly cool the air inside the house, and above all, the humidity remains. Four degrees is unrealistic, unless the house is in a forest and barely gets any sun.