ᐅ Experiences with split air conditioning units in defrost mode?

Hello,

I have an open-plan living and dining area on two levels with about a 1m (3 ft) height difference. In the living room, there is a gas tile stove that does not shut off when a certain temperature is reached. For the past three years, we have used a Fujitsu air conditioner to heat both rooms. A curtain separates the stairwell/hallway, so we are heating a space of about 40m² (430 sq ft) or approximately 100m³ (3,530 cu ft).

The problem is that the Fujitsu frequently defrosts (on one rather unfavorable day, it defrosted 16 times within 14 hours!). During defrosting, cold air flows into the room, which is uncomfortable.

I have looked into this and would like to replace the Fujitsu with another brand or model. Mitsubishi, Panasonic, or Daikin have been recommended by a technician. No air conditioning unit can defy the laws of physics, but there are ways to minimize or work around this issue. It is important to me that NO cold air enters the room during the defrost mode. From what I have seen from the AkkuDoktor, Panasonic units also blow warm air into the room during defrost mode (of course, not comparable to normal heating operation, but the room does not cool down).

I have deliberately not mentioned specific models because I am seeking unbiased user experiences. In the worst case, a model with an integrated electric heating element might be an option (I know this reduces efficiency, but comfort is more important in that case).

I have already tried many things (fan heater, radiator, infrared panel in front of the sofa), but all were only suboptimal.

KlimaRolle schrieb:

The problem is that the Fujitsu often defrosts (on one admittedly unfavorable day, 16 times in 14 hours!)

This "problem" occurs on unfavorable days for every heat pump owner. It’s not unusual—just more or less frequent.

KlimaRolle schrieb:

During defrosting, cold air flows into the room.

That is necessary, as heat must be extracted from the indoor air to defrost outside. Similar to a heat pump that uses warm heating water.
It usually doesn’t last long and doesn’t really cool down the room—only the indoor air temporarily.

KlimaRolle schrieb:

From Akkudoktor, I saw that Panasonic also blows warm air into the room during defrost mode (of course not comparable to normal heating operation, but the room does not cool down).

I am not familiar with such a device. I only know of Panasonic systems where, if there are two outdoor units, the waste heat from the first unit is used to defrost the second unit, or if you have a combined heat pump. In that case, the heated domestic hot water from the DHW tank is used during defrosting.
Normally, either a) heating elements are used as a drip pan heater so that the defrost water does not freeze again immediately, or b) the indoor fan is completely or almost completely switched off.
I have only known it to be the case that you ALWAYS get cool air inside—but ideally only in very small amounts.

Maybe a true air conditioning professional in the forum can better assess this very specific desired situation.

Unfortunately, the Fujitsu can take up to 15 minutes to defrost in the worst case, and the temperature before defrosting is reached again after 30 minutes.

Manufacturers claim that units designed specifically for heating handle this better, such as Nordic, Heavy, or Heatcharge models. I am curious whether this is just marketing or if they actually perform better.

Panasonic Heatcharge supposedly has a heat storage system that activates during the defrost cycle. A commenter on Akkudoktor mentioned that it contains an electric heating element.

For me, it doesn’t matter how they solve it, as long as the room does not cool down significantly or only slightly.

KlimaRolle schrieb:

Panasonic Heatcharge reportedly has a thermal storage system that activates during the defrost cycle. A commenter on Akkudoktor mentions that it includes an electric heating element.
For me, it doesn’t matter how they solve it, as long as the room either doesn’t cool down or only cools down slightly.

There is no electric heating element. And also no perfect solution for you. But if it performs better than before, at least that would help you. You should try to see the unit operating live somewhere. Because Panasonic already limits its operation to ensure the room temperature will definitely drop.
I’ve gathered some information about the devices for you. Under unfavorable conditions, you will still face the same issue—perhaps less severely than before.
However, I only know the theory and nowhere from practical experience. Please also check with other HVAC specialists.

Thanks for the information. I will take a look at the device. If it defrosts less, that would be an improvement.

I’m curious to see if there is any feedback on Daikin or Mitsubishi units. I believe Daikin advertises a “tray heating” feature. I’m not sure if that improves the defrosting behavior.

Alternatively, a second unit could be considered. Hopefully, both defrosting at the same time is rare. But ideally, one unit should be enough. When low humidity leads to few or no defrost cycles, the air conditioning is very comfortable and heats the room well.

KlimaRolle schrieb:

I think Daikin advertises a tub heating system. No idea if it improves the performance.

No, it only heats the tub to prevent the defrost water from refreezing immediately and blocking the drain.