This is something I hope to avoid on the principal that if your DHW is kept at 50 with a 10 degree margin, and not on a timed setting, it shouldn’t take so long to get up to temperature from 40 to 50, and although the pump will have to kick in to heat it more frequently than in higher ambient temperatures, it will not have to be on for long periods to do so.
You shouldn't need to raise the temp of DHW as high as 50°C
The safety devices now fitted as standard to prevent scalds are set to 42°C by default. That's the maximum likely to be required for washing up. Shower units with hot & cold supplies usually have a default of 31.5°C
It's a waste of energy to take the storage tank higher than you're ever going to need.
The lower the Leaving-Water-Temperature of the heat-pump, the greater is the efficiency.
You should be able to set the controls such that the pump is not 'kicking in'. Slow and steady is the way to run it. Avoid on-off cycling.
@transparent at the moment the water is needing to be reheated only every 15 hours. It is taking 15 hours for the water temperature to fall below 45. And then it falls towards 40 only for about an hour. So at the moment the pump is only “kicking in” every 15 hours. Hardly on-off cycling. Slow and steady, in fact. I am talking about winter. I will of course review the temperature at that point. For info, at this temperature the water is as I like it to be. Cooler would not suit me. At the end of the day these systems have to serve us, not vice versa. The flow temperature at the moment is very low, as it should be.
I have an Ecodan that replaced storage heaters and I've gone from using about 20,000 kWh for heating and HW to about 7000. A medium sized bungalow with radiators and now at about 21 deg daytime and 17 at night. I'm very pleased as most of it is/will be paid for by RHI. Not as cold as where you are but rural Lincolnshire can get quite chilly. BTW I don't care much about COP; I'm more concerned about using less energy. It's not necessarily the same thing.,
A few points based on yours.
Freeze stat doesn't seem to use a lot of power and only happens (for me) at night when the heating is off. It just keeps the pumps running and kicks in if the flow gets below a certain temperature. It's not all wasted because when my heating starts at 5am it hits the ground running as it were.
The main issue at low temps, as well as reduced efficiency, is defrosting; this can drain a lot (20% or so) of power and the hotter you ask your ASHP to run the worse it gets. DHW is particularly vulnerable because even if your DHW is set to 43 deg, the ASHP will heat the flow to 50 or 55 to achieve that. You can get into a bit of a vicious cycle if the DHW takes excessive time to heat because your radiator flow/room temp drops a lot and struggles to catch up.
Auto adaptation is good but it does tend to bump up the flow temp, especially if heating up the house after a set back. You can limit the effect of this in the settings if you want. (I do)
You said you can't get energy delivered/consumed. I could get this on the FTC6 console before I had Melcloud (I still can actually). It's easy for the installer to mess up dip switch settings so that this won't work.
If you have any Ecodan specific questions why not start another thread? There are a few of us here who have them and quite a bit of knowledge.
@kev-m Thank you very much for this. What you say about consumption confirms my better expectations. Re the Freeze Stat function, what you say ‘ It just keeps the pumps running and kicks in if the flow gets below a certain temperature’ implies that it’s necessary for the flow to stay above a certain temperature to avoid the freeze stat kicking in. Until I get to winter, I won’t know how the flow temperature performs. At the moment it is unbelievably low. It is probably possible to find the energy usage settings on the FTC controller display but I am still at the ‘nervous’ stage so it will take me a while to go in there and explore. Also, the FTC control display is in the most stupid position possible almost. Low down on the wall in a narrow cupboard!
This was last December’s temperature record summarized (for rainfall please read ‘snow’….) It’s always hard to think of winter here when it is still Flaming June….
@kev-m Thank you very much for this. What you say about consumption confirms my better expectations. Re the Freeze Stat function, what you say ‘ It just keeps the pumps running and kicks in if the flow gets below a certain temperature’ implies that it’s necessary for the flow to stay above a certain temperature to avoid the freeze stat kicking in. Until I get to winter, I won’t know how the flow temperature performs. At the moment it is unbelievably low. It is probably possible to find the energy usage settings on the FTC controller display but I am still at the ‘nervous’ stage so it will take me a while to go in there and explore. Also, the FTC control display is in the most stupid position possible almost. Low down on the wall in a narrow cupboard!
This was last December’s temperature record summarized (for rainfall please read ‘snow’….) It’s always hard to think of winter here when it is still Flaming June….
your flow temperature is higher than mine and so you would expect a lower COP, which is the case
Correct. This was a known compromise at the design stage: having a small old listed cottage, with low ceilings and in particular low window sill heights, I have limited wall space for radiators. I selected the largest K3s that would fit without looking painfully ugly and even so they were on the small side and that meant a high LWT to get the rooms to design temps. I accepted this would reduce efficiency because the alternative, radiators so large they obscured windows and/or ruined the visual appearance of the room was not an option as far as I was concerned. Having a solid ground floor and in places virtually non existent first floor underfloor space was also a factor, running additional piping for extra rads was not a simple solution. One of the prices I pay for living in an attractive old building is having higher heating bills, it just a case of that's the way the cookie crumbles.
Likewise, ultra-insulation isn't going to happen in buildings like mine. I have insulated the loft where I can, but some of the roof space is too narrow to fit any insulation, as the first floor rooms extend into the roof space:
I am adding secondary glazing, but it is a lengthy process because nothing is square or level in the majority of windows, many of which are very loose fitting cast iron casements in very old oak frames. The secondary glazing is PET-G sheets held in place with magnetic strips, and they are as much about draft reduction as anything else. They do make a noticeable difference, but clearly fall short of ultra efficient modern triple glazing.
The key point is that I as the owner am prepared to tolerate higher heater bills as part of the cost of living in an old characterful building. No doubt when the UK becomes a Chinese satellite state (as will happen before too long), such foolish individualistic notions will be ridiculed and I will get a negative social credit/carbon score and be ordered in the name of the common good to clad my house with 500mm polyurethane foam on pain of deportation, but until that day arrives, I shall carry on just as I am.
Very roughly on an average April day I was using about 1 cubic metre of gas (approx 10kWh) and about 3kWh of electricity when my heat pump was doing an equivalent job.
I don't have past daily data for oil consumption, only annual use, but using that, I can see that I used about the same number of kWh in of oil as I do now of kWh in of electricity (of the order of 11,000kWh pa) to do an equivalent job. That last phrase, to do an equivalent job, is absolutely key to understanding the paradox. What happened in practice is I simply set up my heat pump to 'do an equivalent job' by which I mean achieve the same comfort levels, and because of the nature of heat pumps 'doing an equivalent job' ie maintaining the same comfort levels, this meant 24 hour running. When I tried even just a small overnight setback, the house took many many hours to regain the design temp, only just about getting there by 2100 the following evening:
In contrast, I could run the oil heating on a timer, and do an equivalent job ie achieve the same comfort levels, because the oil boiler could recover from a setback in an hour or so. I can't remember the exact timing, but it was something like on for 0600 to 1000 and 1600 to 2200, with the thermal mass of the building being just enough to maintain comfort during the middle of the day. If I am right about the timer settings, which I think I probably am, then the oil boiler was running for less than half the time the heat pump runs, 10 hours a day instead of 24 hours a day. Sure, it would have delivered more heat per hour on average than the heat pump when it was on, but the fact it was off doing nothing for 14 hours a day meant it delivered considerably less heat per 24 hours than the heat pump, yet it 'did an equivalent job' of providing the same comfort level, because the house was at a comfortable temperature when I was around to notice it, even if during the night the house cooled down (but I didn't mind or even notice, being tucked up in bed).
The bottom line is that, to do an equivalent job, a relatively low powered heat pump has to be on 24 hours a day, to keep up the 'heating momentum', because if it is allowed to slow (cool) down, is takes forever to speed (warm) up again. An oil boiler, on the other hand, has plenty in reserve, and can get back up to speed after a slow down with ease. As a consequence, I end up heating the house when in all other respects I don't need to, during the overnight period and middle of the day, and it is this that accounts for the heat pump's higher delivered (energy out) heat.
Putting it another way: on one level, the oil boiler and heat pump did/do and equivalent job, that is, kept/keep me at the same comfort level, but on another level, they aren't doing an equivalent job, the heat pump keeps the house at the same temp 24 hours a day, whereas the oil boiler only heated the house when it needed to be heated. And, just as to be expected, the former requires more delivered energy than the latter.
The takeaway for prospective heat pump owners is this: be aware that converting to a heat pump may well require you to change the way you heat your house, and as a consequence, you may not see the predicted savings on heating bills. It won't always be the case, but it is always a possibility.
Midea 14kW (for now...) ASHP heating both building and DHW
I am probably the only one, but I find all this stuff about freeze stats confusing. In normal but cold conditions, surely a heat pump will be running all the time, because that is how they are designed to work, meaning the circulating water is always comfortably above freezing temperatures, making a freeze stat redundant. The only time when freezing is a real risk is during a power cut, at which point a freeze stat is useless, because there is no power. Frost protection then has to be achieved in other ways, eg antifreeze solution or antifreeze valves. Perhaps someone can enlighten me...
Midea 14kW (for now...) ASHP heating both building and DHW
I think that's right. We have an ecodan and it's serviced by mitsubishi, the engineer turned on our freezestat.
Even if we are not calling for heat the freeze stat kicks in when temp drops below 3c. I think it depends how many power cuts you have we don't get many here but at our old house we had them on a very regular basis.
So really peace of mind as engineer said it would be expensive to fix.
@kev-m Thank you very much for this. What you say about consumption confirms my better expectations. Re the Freeze Stat function, what you say ‘ It just keeps the pumps running and kicks in if the flow gets below a certain temperature’ implies that it’s necessary for the flow to stay above a certain temperature to avoid the freeze stat kicking in. Until I get to winter, I won’t know how the flow temperature performs. At the moment it is unbelievably low. It is probably possible to find the energy usage settings on the FTC controller display but I am still at the ‘nervous’ stage so it will take me a while to go in there and explore. Also, the FTC control display is in the most stupid position possible almost. Low down on the wall in a narrow cupboard!
This was last December’s temperature record summarized (for rainfall please read ‘snow’….) It’s always hard to think of winter here when it is still Flaming June….
It's not quite like that; it's the outside temp that causes Freeze Stat to run (or not). What happens is you set the outside temperature at which Freeze Stat kicks in (or doesn't if you disable it). When that outside temperature is hit, if the flow temp is less than 15 degrees, the ASHP raises it to 20 degrees, stops and repeats. If the flow temp remains at 15 degrees or more, it's just running pumps and monitoring, which uses little power.
How much energy it takes to raise the flow from 15 to 20 degrees depends on how cold it is outside and the heat loss of your house. But any energy used isn't completely wasted; even at 20 degrees flow it's still heating your house a bit.
It's only really needed if you switch your heating off, either overnight or holidays. If the heating is running it's not needed.
@cathoderay You’d think so, but if the coils freeze up then it won’t be able to run - (that’s what actually happened to my neighbour’s pump) - the purpose of the freeze stat is to prevent the coils freezing up. (I think! I’m sure someone will leap in and correct me if I am wrong). The location of my Ecodan is conventional, but in my geographical location there is a significant amount of snowfall, we’re talking more than a foot of snow, frequently, from November to December. Recent winters have been somewhat milder but the snow sometimes doesn’t shift, it builds up, then lingers in big frozen piles, and has to be carted out if the village by tractors. One mile out of the village the grass is green…In 2021 winter on one occasion it took me three hours to uncover my car……so the snow in front of the pump will pile up if I let it, which of course will superfreeze the cold air coming out of the fan, and despite the machine running there is a significant risk that it will ice up. Then there’s the tons of snow that will slide off the roof right on top of the pump if I don’t fix snow guards.
I’ve only had this thing for the month of May so far so I think interesting times lie ahead (and a lot of digging). I do now know that the concentration %of Glycol in the system is 11% so leaving the Freeze stat setting at * will be OK. And someone is coming to double check the level for me. Mitsubishi claim that the Ecodan is particularly good in cold weather, down to -20. We only reached -15 last winter 🥶🥶🥶
@kev-m thanks. My neighbour’s was initially set to 5C. She had it installed late last year and when winter came the defrist cycle on the ASHP was running continuously at first until she discovered this default setting, which is way too high for our average ambient temperatures in December. At the moment, June 6th, we are still regularly getting freezing temperatures overnight. When she had the setting changed to *, the ASHP still worked but it was way cheaper. I think raising the flow temperature may be the problem in ambient temperatures that are below freezing consistently for several days at a time. I am currently not using the Weather Compensation but I am wondering if that will be better or worse regarding the Flow Temperature than the Auto Adaptive Room Temperature mode.
but if the coils freeze up then it won’t be able to run
But isn't that what defrost cycles are for, which are not the same thing as a freeze stat (which from what others have said, kicks in when the circulating water rather than the coils get below a certain temperature)? My confusion is that the primary purpose of a freeze stat is to protect the system when it is off, and in winter/cold weather the only likely reason for the system to be off is a power cut, which means the freeze stat can't do its thing. I can't help wondering if Mitsubishi are peddling a pointless marketing gimmick.
I am sure you have already researched this, but might other countries with cold climates and significant snow build up and high levels of heat pump installations (Scandinavian countries? Canada?) have found ways of managing the snow?
