Suggestions please, as ducted heat pump won't heat below +4C in Tasmania

Home Improvement
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Dirt and mould in the outside units such as at the exchanger, valve stuck, icing of the outside exchanger, low gas, faulty thermostat can be most of the major reasons for failure to warm. It would be worth getting the units checked and if needed serviced. Exchanger fans may also be faulty, this will mean inefficient exchange of heat energy.

As most are aware, in heating mode the outside exchanger’s role is to “cool the outside air” (adsorb the heat from the outside air), the inside exchanger releases that heat. As it gets colder outside the exchange becomes less efficient, but at temps even several degrees below zero the exchange should be still very good. In cooling mode the role is reversed, heat is adsorbed by the inside exchanger and heat is released to the outside.

When in heating mode, the outside exchanger should be blowing air colder than the outside air temperature,. While the unit is actively trying to heat inside air to the set temperature the outside fan should be blowing a reasonable amount of volume of cold air, as it gets closer to the desired temperature inside, the volume of air movement outside should reduce considerably.

Most units are designed to work even at temperatures of around -15 C. Most refrigerants used in domestic units such as R-32 have very low boiling points (temps below -30 odd C (R-32 is around -52 C). So at -15 C there is enough difference that a unit should still heat well. Daikin manufacture R-32 and use R-32 as the refrigerant in their units.

Daikin rate their units to work at the following temps

Outdoor Operating Range Cool (°CDB) -10 to 46
Heat (°CWB) -15 to 18

Heat pump hot water systems rely on this same heat exchange system to heat the water in the tank by adsorbing heat from the outside air (they try to cool the outside air :grinning_face:). They release the adsorbed energy into the water causing it to get hot. The house is no different to this process.

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43

We looked at heat pumps few years ago to replace our gas fired hydronic boiler. Our house requires a minimum of 30kw. While heat pumps struggle as the temperature goes down, did your retailer/installer do the sums on how many kw your house needs to stay warm, eg is it on the heat pumps or the size (number in your case) of heat pumps?

What are your heat pumps ‘driving’? Is it ducted? Underfloor water? Hydronic?

Or do you mean split systems where the largest are roughly 10kw and would usually heat and cool a decent sized room? Since Daikin rates split systems capacity at 7C they should perform close to specification at say 4C.

Other questions noting what @grahroll posted

  • are whatever your heat pump driving putting out warm or hot air, and at what temperature?
  • have you asked your installer/service agent if this is as expected?
  • are the filters cleaned?

For reference we have a 9.3kw Cora and even on -2C mornings it will pump out significant warm air noting our main heat is hydronic but sometimes we just want a faster warmup so turn on the split as a booster for a while.

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44

Thank you for your very well thought out answer. The units are new so I presume not mouldy etc, but I will see if I can get them checked. They shut down when it is cold outside. They just stop. Sometimes it feels as if they are blowing cold (probably just blowing).

The coldest it gets here is -4.

I think the installers have to be honest and tell people that heat pumps just don’t warm like proper heaters or fires. I really miss the central heating of my youth. Our grandchildren in Germany have the luxury of real heating powered by the local cattle farmer! Australia needs to take heating and cooling seriously.

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Thank you Phil. I don’t know if the installer did the sums. The bloke walked in and said “Yeah, you need this one”. Then when we said it was useless he came back and put another one in to the other side of the house. We also spent 4 grand putting fans into the ceiling to reverse blow the hot air down. They are useful for the 3 days a year we get 30 degree heat and we switch them the other way.

The “heat” pumps are the ones that stick high on the wall with huge motor things (sorry for the technical jargon here) outside, that blow cold air out.

Things are not helped by my husband constantly turning the heatpumps off at night to “save”, so in the morning the place is like a tomb. (I often think of using the oven to make a beef Wellington, ha) I get a medical heating subsidy to help with the cost (tiny) and we have solar but without a battery. I use electricity when the sun is shining, one appliance at a time. Our bills are relatively low and non existent in summer and we build up a healthy credit for winter. Solar panels were the best thing we have ever bought with double glazing coming in a close second.

The advertising for “heat” pumps is misleading to say the least. Even when working at their best they don’t really warm like central heating does. It might be cheap - but it ain’t warm when you need it.

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If your units are stopping this is not an ordinary operation. If on heating mode and at the temps you describe, the units should be warming the house interior properly. The Daikin units are designed to properly operate in heating mode down to an outside temp of -15.C. This seems to be an indication of a failure of some component in the units. Reverse cycle air cons are heat pumps, they can just switch operation between at least heating and cooling, they may also dehumidify, and just operate in fan mode.

In Ipswich we reach temps around what you experience, on heating mode the house is always kept “toastie”. I would raise a formal complaint about the faulty operation with Daikin.

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That would be a ‘split system’ in ‘jargon’ :slight_smile:

I second there is something wrong. Turning ours on in the cold of morning around 0C may take 2-3 minutes to start generating heat but they have never shut down and always warm the house as expected.

I second that because what you describe is not how they should work. However your retailer ‘owns’ the problem under Australian Consumer Law. Daikin units are specified at 7C and at -15C their efficiency drops off so roughly 50-60% of capacity at that limit, but still should be generating noticeable heating.

A call to Daikin might be fruitful, but if not you will need to resolve this by sending a formal Letter of Complaint to your retailer and installer, and cc Daikin. There are myriad links to relevant information and how to’s by using the Community search tool for ‘Letter of Complaint’.

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These units appear to be your first experience with split systems (aka heat pumps). No offence intended but have you read the remote control manual cover to cover to be sure you know all the functions and features, and that everything has been set correctly, as you expect? These remotes can be confusing for a new user. Even after having ours for years I need to reference that manual on occasion to remind myself how to set various functions.

A note on Daikin operation - in heating mode when the unit thinks the room is at the set temperature the inside unit will start cycling off and on to maintain that temperature, and that is normal.

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We have seven Daikin splits systems (6 roof mounted and one mounted at ground level). The user guides state they will work efficiently to at least -10°C as they have a defrost system to ensure the external unit doesn’t freeze up at lower temperatures. Where we are in Tassie, it gets to -6°C, but regularly nights in winter as between -2°C and 4°C. The split systems work well and haven’t had any issues in 5 years, apart from water getting into the isolating switch adjacent to the roof mounted external unit.

First thing to do is make sure the unit is on the heating function. It is shown as a :sun: on the control. Set the temp to say 20°C and turn on. Don’t use the ‘A’ setting.

If it fails to heat, the next option is to turn off power to the unit to reset it. This is done by going to the switchboard and turn off the circuit breaker for the aircon. Check by returning to the internal fan that lights are off and the control doesn’t work. Then turn the circuit breaker back on. See if this fixes the problem.

If this doesn’t work, it is then likely a fault with the unit or its installation. Call the installer and see if they have any more troubleshooting you can do. If they don’t, they might need to inspect and run fault codes to see if the unit has a fault. They can also check the thermostat, defrosting function etc is working. If it is a fault, either the unit or from its installation, this will be covered by the warranty/consumer guarantees.

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Most inverter based units do not cycle off, they just drop to their lowest possible capacity. If they are cycling off this means they are generally overpowered for the area, so even at minimum power they are heating or cooling too much and so cycle like the old style non inverter units do to control temps. This cycling is very inefficient and why inverters are preferred, switching on and off generally consumes a noticeably higher amount of power as the motor uses more energy to start the compressor.

Old style fridges are an example, they draw more current initially to start the compressor, then they’ll run at maximum until set point is reached then they switch off. Newer inverter fridges do not actually stop, they just drop to their lowest point of operation if the set point has been reached and as things warm up the inverter unit increases power in steps to maintain set point rather than running at maximum. If the old style has to cycle a lot, then a much larger electricity bill is to be expected than if an inverter one is able to just drop to minimum. If an inverter unit has to go to maximum all the time, it will not be cheaper to run or if it has to cycle on and off all the time will be a similar outcome.

From Daikin on heating cycle operations

Thermostatic control in heating (indoor unit):

Thermostat off: delta t >/= +2.5°C or delta t >/= 0.5°C continues for 1 minute (this means the temp has reached one of those points above the set point)
Thermostat on: delta t </= -0.5°C (this means the unit will start if the temp drops this much below set point)

Where the thermostat is located can affect how the temp is the room is sensed and thus affect operation.

The fact that it cuts out is either a fault somewhere or in heating mode the unit is functioning as a single speed compressor. This non inverter type operation on heating has been noted with at least some Daikin inverter units such that in heating mode they don’t step down the power and instead cut off. Still if the room is cold, then stopping shouldn’t be observed, it should run until set point is reached and then stop.

Another thing is the vanes should be pointed down when in heating mode, they should not be in wave mode. If the sensor is picking up return air temp, and it is vented upwards, the sensor in the unit could be picking up a “false” high temp as the return air sensor may be picking up the expelled air temp instead of what the room is actually at.

@Oldduck perhaps you could supply the model numbers and we can possibly find the stepping points for cooling and heating operation. My cousin who is a refrigeration and AC mechanic may also be able to give me some advice about your units and expected operation.

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Good thinking Phil. Not new. We got the first one several years ago. Same problem with cutting out. We were told by installers that they do that. The installers recommended us to buy plenty of fire wood because that was the best heat in their opinion. (Tassie blokes)

Then, as it did not work well, we replaced it for a bigger one and an extra one in the kitchen. They have their own outside motor thingies one near the sitting room the other outside the front of the house. The technician showed us where to put the heating on the remote, the optimal direction, and just leave it there.

Today I set both to 25.5. Temp outside got to 13. The inside temperature was 19. I need a minimum of 22. Maybe I am expecting too much? Should I put it on 30? It doesn’t seem to make a difference except to the blood pressure of the other half who likes to save on electricity.

Happily the better half is lugging wood around today so I will hold off on the Beef Wellington.

I didn’t mention that the sitting room ceiling is high. The kitchen is lower and it warms up better.

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If you have a set point of 25.5 and the room only gets to 19, your unit may be reading the temp at the wrong placement. The unit shouldn’t be cutting off until the temp reading at the sensor reaches around 28 degrees (9 degrees hotter than you experience in the room) or the temp has reached 26 degrees for one minute. It may be reading the temp nearer the ceiling where most of the hot air will be accumulating, rather than at where you are living (lower down in the room).

A fire will feel warmer as the radiant heat is at your level if the units are not reading the temp at the correct level. Some units can have a sensor fitted externally to the unit, and placed in a more appropriate position so room reading is more accurate. If you have a very high ceiling using the fans to circulate the heat off the ceiling may provide a more comfortable outcome and provide a better temp at living level (this will help stop the accumulation of hot air near the ceiling).

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Shouldn’t make any difference if one is trying to achieve 22°C.

A question, do you have good ceiling insulation and are the outlets pointing down to force warm air downwards?

This could be part of the problem. Hot air rises. If the warm air from the heat pump is rising towards the ceiling and the internal thermostat is located in a relatively high position, only the upper air in the room is being heated, not the air down low where you are.

Are these turned on when the heat pump is on? They will be needed since the ceiling is high to ensuring air within the room is mixed and lower air is heated.

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We have two, neither is overpowered, and both cycle on heat not cooling. They are different models about 2 years apart. One is in a large open area, the other in a bedroom.

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That could be a defrost cycle when the fan and heat exchange inside stops working. Outside the unit is heating the evaporator to de-ice the machine. This happens most often when temps outside fall to 0 or below. Sensors detect ice build up and the machine goes into a defrost cycle. A defrost cycle can take up to about 10 minutes until the sensors detect enough heating of the coil (ice melted). The unit does not strictly cease operating, just inside it will be noted that there is no airflow at the unit.

Mitsubishi and a few others do step down and step up power levels when controlling heating and cooling, Daikin has been noted in particular for it’s single mode operation on some models when it comes to heating, I don’t know if this extends to all Daikin models though. Getting model numbers of the outside units should allow finding out the stepping for both heating and cooling cycles. Daikin would also have a defrost mode for their units to defrost the outside coils.

At the moment as I write this, the Daikin Australian site is unavailable, it may be undergoing maintenance.

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Thanks for the comment. My cycling might be caused by the fact I use the Daikin(s) as boosters rather than main heat. It is possible they could get confused by the hydronic main system as that comes up to temperature. It might be interesting to turn the hydronic off one morning and see how the Daikin(s) work on their own.

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Reflects our experience of living in colder places where winter frosts were more common than here in sub-tropical Qld. Multiple brands. Locally we’ve had a few mornings with <5C air temperature, apparent temperature 2C. Which would explain our bedroom AC going into defrost in the wee small hours. Not sure if the Daikin defrost cycle and settings are the same as our MHI or other brands. Also here the Daikin site would not let me in this morning.

@Oldduck what do you do in response to the Daikin Split System (Heat Pump) appearing to shut down? If you do nothing for 10-20 minutes does the unit resume blowing warm air at some later time? It should.

P.S. we have high ceilings (3.2m or around 11feet) in an older all timber cottage. The kitchen is around 35sqm or 15ft x 21ft. To effectively warm the space in winter our norms are consistent with what been posted prior. We run one of the ceiling fans on low speed in reverse to help circulate the air. We set the temperature control to 24C, and the air vanes to blow the lowest down towards the floor. The fan in the unit is set to the middle speed or higher. This helps with the air circulation. We DO NOT run the fan any slower. We may operate the fan at maximum if the room is very cold initially. It’s important to understand that the Inverter powered split system air conditioners power use is not directly controlled by the fan setting. The inverter power is varied in response to the temperature setting. However the fan also needs to operate at a high enough setting to achieve the maximum heat output.

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