I'm afraid that you have been misinformed about the Freeze Stat function. To quote from the Ecodan manual.
Freeze stat function *1 - An operational function to prevent the water circuit from freezing when outdoor ambient temperature drops.
Flow t - The target outlet water temperature at water circuit when operating in Freeze stat function. *2
Outdoor ambient temp. - Minimum outdoor ambient temperature which freeze stat function will begin to operate, (3–20ºC) or choose**. If asterisk (**) is chosen freeze stat function is deactivated. (i.e. primary water freeze risk)"
*1. When the system is turned off, freeze stat function is not enabled.
*2. Flow t. is fixed to 20°C and unchangeable.
As you have correctly stated, the defrost cycle is performed to remove ice formation from the Evaporator coils at the rear and side of the heat pump unit, but this process must be carried out whether the ambient temperature is above or below the Freeze Stat setting, and even if the Freeze Stat function is disabled.
The Freeze Stat function is to prevent the water circuit from freezing, not to prevent the Evaporator from icing up.
Obviously you can disregard the information I have provided should you wish to do so.
*1. When the system is turned off, freeze stat function is not enabled.
I have to say it is increasingly clear to me that this freeze stat thing is just another pointless manufacturer gimmick that allows them to charge ever high prices for stuff you just don't need. Now that @transparent has triumphantly lowered the tone, I feel able to say it is a heat pump equivalent of a farting bracket in a faux-luxury car.
Back in the real world, there are two similar but not at all the same problems that need to be solved:
(1) at low ambients, typically around 0 to 5 degrees C, the chilling effect of a running heat pump on its surroundings causes frozen condensation to build up on the coils. This is a bad thing because it interferes with heat transfer and impairs efficiency.
(2) if, for whatever reason, the heat pump is off, meaning no heat is being generated, the circulating fluid in the system can freeze, leading to burst pipes (just like any other frozen burst pipe), which is bad news.
Both problems involve freezing, but in other respects they are very different, in particular in relation to whether the heat pump is in a running state or not. This means the solutions are different.
In case (1), because the heat pump is running, there is in practice no realistic risk of the circulating fluid freezing. There is simply no need for a freeze stat function (which is why the majority of heat pumps don't have one). Instead, when it detects icing up of the coils, it goes 'into reverse', and instead of pumping heat from the ambient air into the house, it pumps heat from the house into the outside air, and in the process melts the ice. It is in effect doing what an air conditioning unit does, but because we don't want air conditioning, we want heat, it becomes what I have called a heat thief, stealing heat from your house to achieve the defrost. Regular defrosts (clearly visible in my monitoring data, see posts passim) are detrimental to both overall heating performance (room temps) and efficiency.
Case (2) is where a freeze stat could be useful (just like I used to have a frost stat connected to my oil boiler: if the temp fell below 7 degrees, the boiler fired, regardless of any timer settings, useful for example if I was away and had the heating off, and a cold snap happened). But there is a major problem with the Mitsubishi freeze stat, which I have quoted from @derek above: When the system is turned off, freeze stat function is not enabled. Which makes it useless. Something that is not enabled doesn't do anything. It will also be 'not enabled' ie useless on the other obvious case when the heat pump is unavoidably off, during a power cut.
The standard solutions to case (2), circulating fluid freezing and damaging the system because the heat pump is off, are either to add antifreeze (glycol) to the circulating fluid, or to install antifreeze valves. Neither solution (sic) is problem free, on balance I currently incline towards the use of glycol, though there is a case for not using it, because having only water circulating means (a) better heat transfer and (b) much simpler draining down and topping up (householder can do it, no need for an expensive engineer visit). But I also don't like the idea of antifreeze valves dumping the circulating water, and leaving the system in a non-functional state until positive action is taken. Other domestic pipes will probably also freeze, and cause extensive damage...
Conclusion: Mitsubishi have included a farting bracket in their heat pump. It has no real world practical use.
* farting bracketn. A device to the left of the clutch pedal found in luxury vehicles which enables the driver to lift one buttock and let one go without taking his attention of the road. Roger's Profanisaurus Rex, Dennis Publishing, 2005.
Midea 14kW (for now...) ASHP heating both building and DHW
@derek-m I am not disregarding any information. I came on this forum to get information and thank you for the input.
Please feel free to correct me if I am wrong in assuming this: the refrigeration coils (and/or the Evaporator) contain fluid. This fluid contains water and is presumably part of the ‘water’ circuit.
I am not the only person getting this ‘wrong’. Mitsubishi are also deluded. Mitsubishi definition:see screenshot
I will now leave the forum and rejoin it with a suitably male user name.
@amanda1 several of us are trying to politely put you on the right track, there is no misogyny here, I think I was quite polite in my previous posts.
the "defrost" youtube that you linked to is what the heat pump has to do to de-ice the evaporator when it has iced up. icing up happens on cold damp days when the heat pump is working hard. it happens with all brands of heat pump. This has nothing to do with the "freeze stat setting" and as derek-m and I and others have re-iterated, it happens when the heat pump decides it wants to - there is no setting for you to control when or whether "defrosts" happen.
I note that you refer to a comment that "In the meantime, either the immersion heater or some other secondary heating system will kick in to provide heating for your house". The "will" in there is incorrect. It's a may. In some system designs, there may be an immersion to come on for heating at this time. in other system designs, there is not such a backup heater, the system just waits for the defrost to complete. Its worth pointing out that IF the system is spending too long in defrost mode AND you have an immersion backup heater that runs in thatsituation, you are effectively spending most of your time running the CH on an electrical resistance immersion at a COP of 1.0. which is obviously going to be expensive. That might be the issue you are getting.
additional: when I refer to immersion above I mean an resistance heater in the CH circuit. NOT an immersion on the hot water tank (which you probably also have)
@amanda1 - I regularly bang on about compressorgate, not whether it will happen, but when it will happen. All big manufacturing industries are on the make (its their function, its called capitalism for a reason), and the temptation to indulge in cooking the books, obfuscation, hyperbolic marketing, and all the other sins that manufacturers and marketeers are prone to, must be overwhelming at times. Perhaps just consider the freeze stat as yet another farting bracket included to persuade you to buy their brand of heat pump.
Probably the biggest con in the industry is the universal practice, endorsed by those goons at MCS, of quoting heat pump performance based on ideal conditions, and burying the fact that when the chips are down, or rather the icicles are appearing on your compressor, and you really need some heat, the performance will be no where near the rated output.
Midea 14kW (for now...) ASHP heating both building and DHW
@cathoderay Thanks. I now have masses of information on both the Freeze Stat function and the Cold Weather Protection function and the defrost process, and I will save all this for future reference. There’s zero chance of my ASHP being switched off or in holiday mode in winter this year - firstly because the Holiday mode is so bloody complicated that I can’t be bothered just now to find out how to set it, and secondly because I want to see how this thing performs in a winter season when I am in the house and requiring heat from it. If I did go away I think I would just leave it running as if I was in the house anyway! So there is little danger of the heating not being on at all during a sub zero snap.
I will have to wait until December to really find out how much difference sub-zero temperatures will make to consumption. There’s no point in my trying to change the mode of operation to weather compensation until then - as it is at the moment the ASHP is in auto adaptive mode (ie Terminator mode - it is Intelligent 😱) and it’s using hardly any electricity whilst still delivering DHW and heat when I need them. Many people on here talk about a standby consumption of 2.5kWh a day, and my Ecodan appears to be consuming about 4 to 5 kWh a day (including heating the hot water every 15 hours or so and occasionally heating the house to 19C) out of a total of 9 kWH a day on average. (Melcloud says 4.4kWh in the kast 24 hours with Standby accounting for 92.4% of the last 24 hours). This is peanuts compared to the 40kwh a day I was using the day before the Ecodan was installed. December and January are going to be expensive months, they always have been, but I am fairly confident that they will be less expensive than previously.
As a layperson, the technical details of what happens due to various settings being changed are less important to me than the impact those changes might have on electricity consumption or on the correct functioning of the ASHP. But the technical details are still helpful.
@transparent Yeah I’d like to see the context of that. Context is everything. The phrase “knowlege expert” can be used in different ways. You and I both know that I am not a “knowledge expert” on anything to do with ASHPs. You could be using me as a disparaging example of someone who THINKS they are a knowledge expert. But I would like to point out that I do NOT think that. I am not a knowledge expert. I am a learner. Just like many of the people who are ASHP owners, I am a layman. I don’t know the technical vocabulary but I do know that to use these things effectively some grasp of the principles of operation and of the settings is essential.
These things don’t lend themselves to simplification for the layman. Good luck to anyone trying to explain them to older people in draughty sub-standard housing in the Highlands (of which there are many) who are scared of the internet and don’t have a broadband connection, a router, or any understanding whatsoever of how to control their heat pump. And good luck to anyone trying to explain them to people who have had gas central heating (and there are some of those people on this forum) and who have no real experience of the cost of using electricity.
For example - (Anecdote Alert:) in my village (sorry, but I do live in Brigadoon…) the conversation at the chip van recently regarding heat pump installation ran along the lines of “they take your back boiler out, you know” “yes, you can’t have your stove/fire/whatever”. For them, that was the bottom line. Because of high-handedness, because of councils having these systems installed without any previous educational campaign. Which would have to be door to door by the way, not online.
Grant funding for ASHPs is intrinsically discriminatory because to get it you have to first know it is there and you have to be OK with the internet. So there’s a whole bunch of folks in the middle ground who would benefit from this kind of system becayse they have antiquated heating systems, but they aren’t on “passport benefits” and are scared of computers and so they can’t access the funding.
Finding some way of educating people (this is something I do claim to be a knowledge expert on, by the way, education) - firstly as to how ASHPs work and the DIFFERENCE in operation from old systems is crucial. Explaining that switching it on and off as needed is not a good option and explaining that you can’t dry your clothes on the radiators. Secondly, ONE clear straightforward explanation of the likely consumption, in terms of electricity bills rather than in terms of KWh is needed. This is the thing that I have had the most difficulty in getting a straight answer on. The classic response is “It depends….”
“It depends” is not good enough. Yes I know it does “depend” on a number of variables. But ASHP promoters and manufacturers need to start to reduce the number of variables. There needs to be an effective scale of exemplars of typical costs in different types of property, from ultra efficient new-builds through to 60s council properties. It needs to be visual not with loads of text.
And in the meantime, rather than throwing ASHPs indiscriminately into every house, the government should focus some funding into working with energy companies to develop special tariffs, possibly means tested, that subsidise those people who are currently in fuel poverty but who will be making the transition from gas, oil or storage heaters to ASHPs.
And there should be a high quality national training scheme for ASHP engineers.
in terms of electricity bills rather than in terms of KWh is needed. This is the thing that I have had the most difficulty in getting a straight answer on. The classic response is “It depends….”
kwh needed is the only unit that can be calculated or estimated by a system designer. although we've had a lot of debate here about how accurate (or not) the various methods used are. they have to start there, display that (perhaps with a range due to the aforementioned lack of accuracy ), then multiply by price per unit , which also has a range based on time, geography, type of contract). I do sometimes read discussion on other forums about "my electricity bill is x00 per month" - but how much use was that for ? that has to be the start point.
And in the meantime, rather than throwing ASHPs indiscriminately into every house, the government should focus some funding into working with energy companies to develop special tariffs, possibly means tested, that subsidise those people who are currently in fuel poverty but who will be making the transition from gas, oil or storage heaters to ASHPs.
totally agree, I've posted on this before. On the rough working assumption that gas is 1/3 of the price of electricity, and a heat pump is 3x the efficiency of gas, you come out run-cost neutral. BUT if the HP isn't a well designed or installed system , or if it has to run at a high LWT due to the nature of the property or climate, then that 3x efficiency could be lower. Also , because heat pumps work at best efficiency if on all the time , that might well mean in a leaky house that was previously run on fossil fuels with "the least amount of heating-on-time that the owner could tolerate", the total amount of heat needed may end up being higher.
so the way to remove the risk of "cost a fortune to run" is for the electricity tariff, at the very least when used for ASHP heating, to be lowered, either for all, or means tested as you say.
And there should be a high quality national training scheme for ASHP engineers.
I think we're all in violent agreement on this one. existing schemes do not make sure that an install or design is done well, nor do they make sure that aftercare is done properly. unfortunately HP systems are more complex to design, install and aftercare than boilers, so they can't just be "banged in" like a gas boiler would have been.
as a "layman user" you shouldn't need to know what the "freeze stat" setting or any other of the dozens of settings that a HP has, does. your aftercare should take care of that for you. but the practical reality today is that you do need to. (unless you are one of the very very few who've been blessed with finding a superb installer).
I am not the only person getting this ‘wrong’. Mitsubishi are also deluded. Mitsubishi definition:see screenshot
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It is indeed very unfortunate for you to look on their website and be misled by someone's mistake on that page.
This function(freeze protection), under different variations is found in every heating system that has water as a heating medium, for obvious reasons.
The defrost function is found in every heat pump, regardless if it's air to water or air to air(air conditioner)
@cathoderay if freeze protection is a gimmick, I suppose for you, the inverter compressor, the weather compensation, the PWM pump, the reversible valve, the electronic expansion valve, the internet connection, everything is a gimmick. Why did you buy a heat pump, they are a gimmick for a lot of people.
@derek-m I am not disregarding any information. I came on this forum to get information and thank you for the input.
Please feel free to correct me if I am wrong in assuming this: the refrigeration coils (and/or the Evaporator) contain fluid. This fluid contains water and is presumably part of the ‘water’ circuit.
I am not the only person getting this ‘wrong’. Mitsubishi are also deluded. Mitsubishi definition:see screenshot
I will now leave the forum and rejoin it with a suitably male user name.
Ciao.
I don't understand why you would need to change to a male sounding user name.
The evaporator contains only refrigerant gas, no water, which enters the evaporator as a liquid, and as the name suggests, is evaporated back into a gas.
Let me explain how an Air Source Heat Pump (ASHP) works. There may be a schematic diagram within your manual detailing the various components within the system.
As the name suggests, the compressor compresses the refrigerant gas, and in so doing increases both its pressure and temperature. The refrigerant gas discharged from the compressor is directed to the Plate Heat Exchanger (PHE) by the reversing valve. The PHE has the refrigerant gas on one side and the central heating water on the other side. When the refrigerant gas is warmer than the water, thermal energy is transferred from the gas to the water, and in doing so the gas is cooled and starts to condense. The PHE is also referred to as the condenser. The water flowing through the PHE carries the thermal energy to the heat emitters or hot water cylinder.
The refrigerant gas, in liquid form, flows from the PHE to the evaporator via the expansion valves. As the refrigerant gas passes into the evaporator, its pressure is reduced, and it starts to change from a liquid back into a gas. When this phase change takes place it absorbs thermal energy, which is supplied by the evaporator coils and the ambient air flowing around them.
The warmed gas coming out of the evaporator is directed back to the compressor, where the cycle starts once again.
During a defrost cycle the reversing valve changes the gas flow around the circuit, so that the PHE now becomes the evaporator, and what was the evaporator becomes the condenser. Thermal energy is therefore extracted from the water circuit and used to warm the evaporator to melt any ice build up that may have occurred.
If you have any further questions please feel free to ask.
@derek-m Hokay - please could you explain to what part of this process do the terms Flow Temperature and Return Temperature apply? (if they do). And why is it considered more economical for flow temperature to be as low as possible? And what is in those insulated two big pipes connecting the pump to my house - one with a blue lever, the other with a red lever. Is it fluid?
