Posted by: @s_gatorator

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Hi @cathodeRay , aren't all of the cycles in your chart defrost cycles? The clue I'm seeing is in the OAT graph, which has a small spike just after the compressor stops, presumably due to your outside temperature sensor being near the external unit and it getting some heat from the warm air at the end of the defrost cycle when the fan restarts. I have the same think on ours.

Of the charts that I posted on 17/01/2025 at 8:46 am, the first two are normal cycling, the second two are defrost cycles. The way I identify defrost cycles is the LWT falls below the RWT.

The OAT spikes are indeed down to the sensor being, in my (Midea) case, inside the main case, meaning it is really the AIT (air intake temperature) rather than the true OAT. In normal cycling, when running, the unit exhausts cooler air, which lowers the OAT/AIT, when it is off the OAT/AIT recovers a bit with a small spike visible. In defrost cycles, this spike is more marked as the unit, as you say, exhausts warmer air. We've had quite a lot of discussion about the problems of using AIT rather than OAT on other threads, because of course it is the OAT which is actually the IAT that the weather compensation curve uses. The OAT being actually the AIT also complicates assessments of heat loss, because the rest of the house is sitting in the true OAT rather than the AIT, and finally, the local slightly cooler air around the heat pump has at least some detrimental effect on performance. My heat pump by the way isn't in a so called cold well, but it is 1ft in front of a wall, and inevitably some of the air drawn in at the rear comes from the cooler air in front of the unit. Some heat pump brands do have true OAT sensors, placed away from the unit, but many don't. 

Posted by: @s_gatorator

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If the temperatures are lower, as in Europe, the moisture freezes out of the air and it looks like frosting does not occur below -7C or above 5C (quick internet search). Otherwise, here, I agree, it's a problem.

This is indeed what one hears. One wonders whether there is a sort of tinkling of breaking ice as the moisture drops out of the air at -7 degrees. More seriously, -7 to +5 degrees is really quite a large range, there must be places in Europe where the OAT is within that range for some if not much of the time. I wonder what happens there?

Posted by: @cathoderay

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Of the charts that I posted on 17/01/2025 at 8:46 am, the first two are normal cycling, the second two are defrost cycles. The way I identify defrost cycles is the LWT falls below the RWT.

Ah! OK, that's interesting, thanks @cathodeRay, I stand corrected. NIBE have a separate OAT sensor. I now know about Air Intake temperature sensors!

Another way I can see defrost cycles is the evaporator temperature, which goes positive.

Posted by: @cathoderay

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More seriously, -7 to +5 degrees is really quite a large range, there must be places in Europe where the OAT is within that range for some if not much of the time. I wonder what happens there?

That's a very good question. I wonder if anyone on the forum has an idea, an interested contact, or experience of living the ASHP in such temperatures

Posted by: @s_gatorator

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I now know about Air Intake temperature sensors!

That is indeed what they are, though Midea calls readings from it the Outdoor ambient temperature. As ambient is in practice rather vague (does it mean immediate surroundings, or just surroundings? And surrounding what? The heat pump? The building?), and on top of that given ambient temperature is often used interchangeably with outside air temperature, there is a recipe for confusion. As a result, someone on this forum, maybe @jamespa, used the unambiguous term Air Intake Temperature to name the variable.

Posted by: @s_gatorator

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I wonder if anyone on the forum has an idea, an interested contact, or experience of living the ASHP in such temperatures

I echo this!

Posted by: @s_gatorator

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I wonder if anyone on the forum has an idea, an interested contact, or experience of living the ASHP in such temperatures

We need to be on the lookout for a person with a name that sounds vaguely Eastern European or Scandinavian.

@editor might know someone.

@transparent I'm actually working on a podcast episode along these lines and will start looking for homeowners in the next couple of weeks with surnames ending in "wicz" and "ski" 🤣

Great! 😆 

I'd also been keen to attract here some people who might later play a part in rebuilding Ukraine.
There's a lot of content on the Forum which would allow them to provide heat and light in locations which may only have intermittent power for years to come.

They don't need to replicate the energy supply system as it was before,
nor in the style we have here in UK.

It would a lot cheaper/quicker to create community clusters which can use multiple sources of energy when they are available, including micro-hydro which is more abundant in winter.

That would provide them with systems that are more resilient to outages.

@editor Don’t forget you have lady readers too so include “ska” for the married ladies. 😉 Regards, Toodles.

Vaillant's comment about de-icing is:

It is hard to say how often a de-icing cycle will take place as it depends on several things…
• The humidity of the air
• The amount of energy being taken out
• The period of time the energy is being taken.
The de-icing cycle will happen more often when the outside air temperature is around 2.5°C but will happen less often when the air temperature is below 0°C, as there is less water in the air.

From page 4 of

Posted by: @johnr

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but will happen less often when the air temperature is below 0°C, as there is less water in the air.

Of course, that should be a key thing, warmer air can hold more water than cooler air. But in practice my heat pump seems to do much the same defrost activity (duration and frequency) at -4 degrees (0600-0900) as it does at 0 degrees (1800-0000): 

Do any Vaillant owners have similar charts for their heat pumps?

@cathoderay Ditto my Grant ASHP, During last week's cold spell it spent much of each day frosting then clearing, even down to -6C which was the lowest temperature we reached in West Oxfordshire. But then I know my overall installation was done far from optimally in terms of the kWh used at any OAT.

Mike

@cathoderay & @transparent I have attempted to measure start up current spikes but don’t have high speed monitor devices. The monitor on our battery system monitors at once per 5mins which isn’t a fast rise but that’s not an adequate resolution. The octopus mini samples at one per min and shows a steady rise, so for me there is no fast switch on issue.

@judith - thanks. Can you get leaving and returning water temperature at one minute intervals? That would let us see frequency and duration of defrosts on a Vaillant if you can get a chart covering a defrost period.