@dockray

I think that I am correct in saying that 'freeze stat' is different from defrosting, but others with an Ecodan may be able to provide more information.

Hot water production and use is very much subjective, and can vary widely from home to home. It will therefore be up to you to decide on the best way to operate your system.

Ecodan owner here. As far as I can tell, Freeze Stat is when the system uses the circulation pump to keep the fluid circulating between the FTC and the HP when it is not calling for heat and it is close to or below freezing. I see it during the overnight set back period when the temperature is sub 3C. That temp can be set from the main controller. Defrost is when the HP clears the ice from the evaporator, usually using heat from the DHW tank via the return pipe.

@abernyte Thanks for the clarification. Can you see both of these happening on MELcloud and if so what am I looking for?

@dockray If you go to reports on Melcloud then Operation Mode you can see a % of Freeze Stat operation in a pie chart.

Defrost can be seen as a 'live' operation in the Control section.

Yes, up to a point. In MelCloud Reports>Operation mode you can see the percentage of time the unit is in the various modes. In Reports>Internal Temperatures when the outside temps are below freezing the return temps will occasionally peak above the flow and that seems to be when it is drawing heat from the DHW tank to defrost.

@abernyte @morgan @derek-m Thank you all. I feel I'm asking, what to most, must seem like very simple questions but when you are new to it everything seems confusing. And electricity is too expensive to not get your head around it all. Thanks for your patience.

@dockray You are very welcome.  Still very much learning myself and I'm easily confused.  I'm aware my system is nowhere near optimum efficiency yet and, like you, appreciate all the help and advice I can get.

Hi, I am very new to all this!

How do I set the warm end of the weather compensation curve when it’s not warm outside?

We’ve got a Mitsubishi Ecodan 8.5kW with UFH (plus 2 radiators on the mezzanine). We live in a newly converted industrial building that is well insulated, it has big windows so we have good solar gain when it’s sunny but we live 400m above sea level on an exposed fell in The Lakes so we have a lot of wind wash.

After commissioning, WC was left set at factory settings. I’ve watched the Heat Geek videos and read lots of threads on here and got the cold end of the curve set when it was minus two outside. We are now down to a flow temperature of 28* at -2 to give us an indoor temperature of 19.5. 

This month the heating COP is 3.4 and the DHW is 2.2. 

Now the weather is beginning to improve I am getting some cycling (but at other times the LWT & RWT appear to be nearly the same) so I’m guessing I need to alter the warm end of the curve or possibly the pump speed?? I've currently got the warm end of the WC curve at 20 degrees with an outdoor temperature of 10 degrees (because that is the highest the outside temperature has got so far) but it’s still cycling when the outdoor temperature gets above 7 or 8* (and I’ve got the room stats capping at 22* whilst I am trying to find the sweet spot, which is higher than I need). 

Our flow temperature seems to be lower than most people’s and I don't want to find I’ve got a low flow temp but something else in the system is working to keep the house warm - if this is even possible? I can’t compare energy usage as we now live in a different part of the country, in a different house, with an ASHP and UFH rather than gas CH and radiators.

I’ve got SO many more questions but I’ll leave it at this for now.

Until a few weeks ago I knew nothing about ASHPs so please go gently and simply with your replies. Thank you in advance.

Apologies for the previous post which was my failed attempt to quote from the original – hopefully it will disappear!
Here are a few thoughts on different bits of the thread:

If your house is so well insulated that the flow temp at -2 only needs to be 28C to maintain internal temperature then surely a 5kW unit would have been big enough? My 8.5 unit is mostly down at the lower end of its output even now when it still not that warm, and it was working at 45C when it was -2.

Though I am no UFH expert, I can't see how the warm end of the curve at 20C can work for heating more than a low-level frost setting. There needs to be a temperature difference for heat to be transferred, if the flow is not a few degrees above slab temperature then it won’t cool, the return temperature will match the flow temperature and the heat pump will eventually turn off. It is possible to set a minimum flow temp of 20C but that is well below the default value of 30.

Are you trying to shower at the same time as the DHW is in operation? Have you restricted the running times of the DHW to two 1.5hr slots? Did you also alter the DHW max. operation time? If you didn’t then what may be happening is that when the tank is very cool you are only getting the default 1 hour of DHW heating before it has a half hour break (to put a bit more space heating in) but then is not able to restart to get up to final temp due to the schedule ending. Give it a longer 90 mins max operation. You could also extend the schedule slots, having them longer is only a problem if the max temp drop is too short and reheat is triggered frequently. But a schedule start does trigger a DHW cycle so you wouldn’t want that starting when the tank is already hot. If you are drawing a shower whilst it is running a heating cycle and it doesn’t have time to complete a reheat of the tank then you also get the disbenefit of the circulation pump mixing the cold inflow with the remaining hot water and making the whole lot tepid.

On MelCloud temp history the times when the flow and return are the same indicate the freeze stat is in operation, or possibly when your slab is not taking any heat out of the flow and the water is just pumping round – when the pumps are off the temps will slowly drop independently of each other. A precipitous drop in flow temp of several degrees would be a defrost – often I see one being done before a pause in operation, though that is not clear from the temperature record alone. The need for a defrost does make the pump push the flow temp up in order to do it but that also makes the flow temp trace look very bumpy, though the rate of energy consumption is pretty consistent.

Posted by: @harriup

↑

Hi, I am very new to all this!

How do I set the warm end of the weather compensation curve when it’s not warm outside?

We’ve got a Mitsubishi Ecodan 8.5kW with UFH (plus 2 radiators on the mezzanine). We live in a newly converted industrial building that is well insulated, it has big windows so we have good solar gain when it’s sunny but we live 400m above sea level on an exposed fell in The Lakes so we have a lot of wind wash.

After commissioning, WC was left set at factory settings. I’ve watched the Heat Geek videos and read lots of threads on here and got the cold end of the curve set when it was minus two outside. We are now down to a flow temperature of 28* at -2 to give us an indoor temperature of 19.5. 

This month the heating COP is 3.4 and the DHW is 2.2. 

Now the weather is beginning to improve I am getting some cycling (but at other times the LWT & RWT appear to be nearly the same) so I’m guessing I need to alter the warm end of the curve or possibly the pump speed?? I've currently got the warm end of the WC curve at 20 degrees with an outdoor temperature of 10 degrees (because that is the highest the outside temperature has got so far) but it’s still cycling when the outdoor temperature gets above 7 or 8* (and I’ve got the room stats capping at 22* whilst I am trying to find the sweet spot, which is higher than I need). 

Our flow temperature seems to be lower than most people’s and I don't want to find I’ve got a low flow temp but something else in the system is working to keep the house warm - if this is even possible? I can’t compare energy usage as we now live in a different part of the country, in a different house, with an ASHP and UFH rather than gas CH and radiators.

I’ve got SO many more questions but I’ll leave it at this for now.

Until a few weeks ago I knew nothing about ASHPs so please go gently and simply with your replies. Thank you in advance.

On reading about your large windows and solar gain - there is usually other times of the day or on exceptionally cold day when large windows - even triple glazed large windows - will be an exceptional drain on your heating. So it will be interesting to see how things will perform in the next few days. Indeed following comment from @harriUp the glazing chilldown may be one reason why the designer proposed an 8.5, to allow for the colder times. 

We have experienced exceptional chilldown in one room where we have triple glazed bifold doors. They cope well down to -2c but from zero onwards there’s seems to be a disproportionate chill effect.

regarding your DHW Cycle it may help if you can arrange a forced DHW Reheat at the start of an hour - eg 10.00 oclock or 3.00 oclock then produce a MELCloud “Hourly Temperature” report for the duration of the DHW cycle. This should give you an indication of performance of the Primary circuit without the influences of a tepid underfloor circuit.

The result may show what’s happening during the heating period - narrowing deltaT, the rising tank temperature and then the falling temperatures, defrost cycle, etc.

To go with this information it would be worthwhile knowing where exactly wher the 2 tank thermistors are located. How close to the top and how close to the bottom.

When you understand the Servicing menu of your  FTC CONTROLLER you may find it useful to get a flow rate during the DHW Cycle at the current pump speed setting, since flow rate along with heat transfer rate has a direct link to understanding why your LWT and RWT will be a certain temperature difference. But that  might be for another time.

hope this is of interest... just ask if you need A better explanation of anything 

@harriup Hi, thanks for taking time to reply. I've reread it many times and think Ive got my head around it. So here goes... 

"If your house is so well insulated that the flow temp at -2 only needs to be 28C to maintain internal temperature then surely a 5kW unit would have been big enough? My 8.5 unit is mostly down at the lower end of its output even now when it still not that warm, and it was working at 45C when it was -2."

They said this was the size we needed following their system design. I was beginning to doubt that I'd got the cold end of the curve right as our flow temperature is so low but the house stayed warm when it was minus 5 last night and then once the sun came out the LWT & RWT have been matching each other today, so I'm guessing the system is not needing any heat due to solar gain. I think its solar gain that has a greater effect on the system than was originally calculated. When it is overcast and windy for a few days the system has to work.

"Though I am no UFH expert, I can't see how the warm end of the curve at 20C can work for heating more than a low-level frost setting. There needs to be a temperature difference for heat to be transferred, if the flow is not a few degrees above slab temperature then it won’t cool, the return temperature will match the flow temperature and the heat pump will eventually turn off. It is possible to set a minimum flow temp of 20C but that is well below the default value of 30."

I'm hoping once it gets to around 10* outside (that is when it started to cycle more than 3 times in an hour) we won't be needing the heating. We live in The Lakes so we won't be able to put that to the test for a while!

DHW

We are waiting until the DHW cycle has finished and it usually reaches target temperature within that time. It is set for 90 mins operation time not 60 ( I learnt that following some cold showers) and is already set to drop 10* before a reheat but I will try setting the DHW cycle for longer than 90 mins to see if that helps.

I'm sure there is cold water being mixed into the remaining hot water somehow. At our old house the remaining water stayed warm for a few hours - here it's a military procedure to make sure we go in one after the other - or like you say, tepid showers. 

MELcloud

Thanks for the descriptions explaining what I can see on the reports, I'm gradually building up a set of notes with info  gained from the threads. I've been merrily looking at the reports but clueless as to what causes the changes 🤔 

Thanks again for taking the time to reply - it's much appreciated.

@sunandair Hi, thanks for the reply. 

"On reading about your large windows and solar gain - there is usually other times of the day or on exceptionally cold day when large windows - even triple glazed large windows - will be an exceptional drain on your heating. So it will be interesting to see how things will perform in the next few days. Indeed following comment from @harriUp the glazing chilldown may be one reason why the designer proposed an 8.5, to allow for the colder times." 

I think you're right. We live in an old industrial building and all the windows are huge but the biggest windows are in the main room which is also double height. But it was minus 6 last night and the house fortunately has stayed warm with a flow temp of 28. Last month we averaged 10kWh a day for heating and 6kWh for DHW. This month it will be more - it hasn't got above 4 degrees outside yet this month.