ᐅ Alternative to Proxon air-to-air heat pump?

Heizungsbau76 schrieb:

I think most people here have misunderstood the Proxon air heating system. It is not an air-to-air heat pump! It is a standard ventilation system with heat recovery using a crossflow heat exchanger that transfers up to 85% of the heat from the exhaust air to the supply air. The reheating (which compensates for heat losses) is done by small electric heating elements in the ceiling supply air outlets in the rooms. This allows each room to be individually, quickly, and easily temperature-controlled. Ideally, the electricity needed should be provided by a photovoltaic system. A heat pump is not used at this stage.

The claim that air is a poor medium for heat transport doesn’t hold here. Yes, air has a lower specific heat capacity than, for example, water, meaning that to transport 1W of heat, more air must be "moved" than water. The ventilation system already does this, which is why air heat transport is calculated in cubic meters per hour (cbm/h) rather than liters per hour. Secondly, the heating elements deliver heat exactly where it is needed, so transport losses are essentially nonexistent.

The idea that radiators or underfloor heating heat the room better is also incorrect. If a room requires 100W/h of heat, you need to deliver those 100W there, regardless of the method.

In fact, you feel the warm air directly on your body. This means the system responds much faster than a water-based heating system. A radiator needs time to heat up itself and then transfer the heat from the hot water to the room air and surrounding surfaces before you can feel it, so it is slower than air heating. Underfloor heating is even slower, as it has basically no convection and even heats the entire screed. In addition, both water-based heating systems stir up dust inside the house, whereas the air heating system filters it out.

The only heat pump component of the Proxon system is used for domestic hot water heating via an exhaust air heat pump. This unit is connected downstream of the ventilation system’s exhaust air duct. The air leaving the house, which has already transferred about 85% of its heat to the incoming fresh air via the crossflow heat exchanger, is further cooled to extract more energy, which is then transferred to the domestic hot water using heat pump technology. This approach is actually very clever because instead of blowing exhaust air at, for example, 10°C (50°F) outside in winter, you also recover the last remaining usable energy.

It’s similar to a condensing boiler, where exhaust gases—the byproduct of combustion—are cooled so much by a downstream heat exchanger that almost all energy is extracted, and the gases must be mechanically exhausted rather than rising naturally up the chimney. Here, a heat exchanger is installed "behind" the ventilation system.

Now it’s easier to understand why Proxon systems often produce condensate. Of course, this should not happen uncontrolled but be routed through a condensate drain connection! Warm air can hold more water vapor than cold air. When warm indoor air, which contains a relatively high amount of moisture (from cooking, showering, perspiration), passes over cold incoming fresh air to recover heat, condensation will inevitably form. Therefore, filters, the condensate tray, and condensate drain should be cleaned regularly.

From my perspective, this type of system makes a lot of sense because it combines the nowadays essential ventilation system with an affordable heating system, as long as the entire setup is properly coordinated (for example, with a dedicated photovoltaic system and battery) and correctly adjusted.

Just like with a water-based heating system, ventilation and ventilation heating require hydraulic balancing. All supply air vents need to be set according to the room to ensure the appropriate airflow, similar to setting radiator valves. This is done using an electronic vane anemometer with a funnel, which is placed over each duct connection.

Heizungsbau76 schrieb:

I think most people here have misunderstood the Proxon air heating system. It is not an air-to-air heat pump! It’s a standard ventilation system with heat recovery through a crossflow heat exchanger that transfers up to 85% of the heat from the exhaust air to the supply air. The reheating (essentially compensating for losses) is done by small electric heating elements located in the ceiling outlets of the supply air in the rooms. This allows each room to be individually, quickly, and easily controlled in terms of temperature. Ideally, the required electricity should be supplied by a photovoltaic system. A heat pump is not used here at all.

The idea that air is a poor medium for heat transfer doesn’t really apply in this case. Yes, air has a lower specific heat capacity compared to, for example, water, meaning you have to move more air volume to transfer 1 watt than you would with water. The ventilation system does this anyway, which is why air heat transfer is measured in cubic meters per hour (cbm/h) rather than liters per hour. Secondly, the heating elements are right where the heat is needed, so heat losses during transport are practically nonexistent.

The claim that a radiator or underfloor heating heats the space better is also incorrect. If a room requires 100 watts per hour of heat, you have to deliver those 100 watts, no matter how.

The fact is, you directly feel the warm air on your body. This means the system responds much faster than a water-based system.

A radiator first has to heat up itself and then transfer the heat from the hot water to the room air and surrounding surfaces before you can feel it, so it’s slower than an air heating system.

Underfloor heating is even slower, as there’s no convective component and the entire screed has to be warmed up. Additionally, both water-based heating types stir up dust in the house, whereas the air heating system filters it out.

The only heat pump component in the Proxon system is used for domestic hot water heating via an exhaust air heat pump. This is connected behind the exhaust air duct of the ventilation system. The air leaving the house, which has already transferred up to 85% of its heat to the fresh air through the ventilation’s crossflow heat exchanger, has more heat extracted by the heat pump to utilize the energy and deliver it to the domestic hot water system using heat pump technology. This is actually very clever because instead of blowing exhaust air out at around 10°C (50°F) in winter, even the last bit of usable energy is recovered.

Similar to a condensing boiler, where exhaust gases — essentially combustion byproducts — are cooled so much by a downstream heat exchanger that almost all energy is extracted and they can’t rise up the chimney on their own and thus need to be forced out, here there is an additional heat exchanger "behind" the ventilation system.

This also explains why Proxon systems often produce condensate, which, of course, should not be uncontrolled but drained properly through a condensate drain connection!

Warm air can hold more water vapor than cold air. So, when warm room air with a relatively high water vapor content (from cooking, showering, sweating) passes over the cooler incoming fresh air to recover heat, condensate formation is inevitable! That’s why filters, condensate trays, and drainage should be cleaned regularly.

From my point of view, such a system makes a lot of sense because it combines the ventilation system, which is now essential, with a cost-effective heating system — provided the entire system is properly coordinated (for example, its own photovoltaic system with battery) and balanced.

Just like with a water-based heating system, the ventilation/ventilation heating system requires a "hydraulic" balancing. All supply air vents must be adjusted according to the room’s needs to ensure the exact proper airflow, just like radiator valves. This is done with an electronic vane anemometer with a funnel, which is placed over the respective vent connection.