ASHP / Underfloor heating issue

[Benpointer]

Hi all,

 

We've just got back from a weekend away to find our ASHP-underfloor-heated house rather cold (17C versus thermostat settings of 20-23C in various rooms).  Obviously it's cold outside (-0.9C at present) but we've never had this before and our system has been in 12 years.  It's a Mitsubishi Ecodan 8.5kW pump.  

 

Both the ASHP and the underfloor heating appear to be on.  The UFH is showing demand from all zones as you would expect.   The ASHP is in Heating Eco mode and has the target water temp set to 43C.  Checking the power use of the ASHP with my Emporia monitoring I see that it is cycling between no power and full power (c.2.6kW) every 10 minutes or so, as follows: 

 

 

Here's a cycle in second intervals:

 

 

Over the same 10 minute cycle the actual water temperature rises from 27C to 46C and then falls rapidly back again to 26-27C once the ASPH stops.

 

It feels like the problem may lie with the UFH circulation rather than the ASHP.  As I say, we had the system for 12 years without issue and we've been able to keep the house nice and warm through previous snaps.

 

If anyone has got any ideas about what the issue is, I'd be grateful. 

 

Thanks

[Benpointer]

PS, just to say Emporia shows the Ecodan is drawing an average of about 1.1kWh each hour, so our COP adjusted 8.5kW ASHP is more like a 3kW heat pump at the moment, which is clearly not enough to keep even our well-insulated bungalow (c180m2) warm.

[JohnMo]

Is you circulation pump ok?

[Radian]

Is it able to breathe properly? Evaporator coils full of ice?

[Benpointer]

54 minutes ago, JohnMo said:

Is you circulation pump ok?

Well I think so but I am not sure  how I would tell for sure?  There appear to be two circulation pumps, one on the out and one on the return.  I do have a plumber coming out to look at the issue tomorrow but he is not an ASHP expert - I am hoping he will either give the UFH a clean bill of health or spot and resolve the issue. 

 

32 minutes ago, Radian said:

Is it able to breathe properly? Evaporator coils full of ice?

Again, I am not sure how to tell for certain.  The side and back look frosty for sure but not, as far as I can tell, full of ice.  Here are a couple of photos:

 

(Thanks for the replies btw!)

 

 

 

[PhilT]

11 minutes ago, Benpointer said:

The side and back look frosty for sure but not, as far as I can tell, full of ice

From your photos it looks like it's in a defrost cycle, are you able to watch it every time the power drops (lots of steam etc.)? Mine shows a similar flow temperature drop on defrost, but occuring no more than twice an hour in the small frosty hours at -5degC. If yours is defrosting that often there may be something wrong with it.

[jack]

Can you tell whether the water from the ASHP is getting into the UFH manifold? You might get cycling like this if TMV on the manifold isn't letting water past properly or the pump on either the manifold or in the ASHP itself isn't working properly (although I think most ASHPs will throw an error code if the internal pump isn't working properly).

 

Might also be a blockage or restriction somewhere - is there an inline filter/strainer you can check?

[Benpointer]

2 hours ago, jack said:

Can you tell whether the water from the ASHP is getting into the UFH manifold? You might get cycling like this if TMV on the manifold isn't letting water past properly or the pump on either the manifold or in the ASHP itself isn't working properly (although I think most ASHPs will throw an error code if the internal pump isn't working properly).

 

Might also be a blockage or restriction somewhere - is there an inline filter/strainer you can check?

I am going to try to see if I can get the ASHP to run without interruption in Hot Water mode, rather than UFH, in an attempt to rule out blockages in the UFH circuit.  Normally we don't use the ASHP for HW because, reasons, but it is connected for HW.  (We use solar HW and an immersion for HW).

 

Just need to persuade Mrs. P. it's ok to dump 100l of 65C water to get the thermostat to trigger ASHP HW heating (!)

Edited December 13, 2022 by Benpointer

[JohnMo]

why dump water just pull out the thermostat? or thermostat probe

[Benpointer]

14 minutes ago, JohnMo said:

why dump water just pull out the thermostat? or thermostat probe

Doh!  Yes should've done that! 🤦‍♂️

 

Anyway, there wasn't much above 55C in the top of the tank; I duly dumped it.  

 

And hey presto the ASHP ran consistently at 3.5 kW draw for 20 mins without a problem heating the water.  I did notice some build up of frost on the back of the ASHP but to be expected, I guess.  Seem to prove the issue is not with the ASHP itself.

 

So...   On further investigation there is a mixer valve on the UFH heating circuit (photo below), presumably to ensure the flow to the floor is not too hot.  It was set to MIN. (When? Did I do that in the summer to 'save money' - I don't remember doing so).  

 

I have now set mixer valve to MAX and the ASHP has been running uninterrupted since(!), showing 41C target and 41C actual flow temp.   So that's progress.

 

I'm not totally out of the woods yet though as the ASHP is still only drawing about 1.0 kW.  

 

My assumption at this point is that there is a flow issue with the UFH that prevents the 41C water getting to the floors at a sufficiently high rate, thus the ASHP is not having to work very hard to keep the UFH water at 41C.

 

Not quite sure the where to go next.  There's a Boiler Buddy which has never been cleaned to my knowledge so that may be worth looking at (albeit, it's on the ASHP circuit so would affect both UFH an DHW if that was the issue).  There's a dedicated pump for the UFH circuits but if that had failed, I assume we'd have no heating at all.

 

The lad the plumbing firm sent round was not much use btw - scratched his head then called his boss, who suggested the ASHP might need re-gassing (why?)

 

Photo of the UFH mixer valve, now set to MAX:

 

 

[jack]

4 hours ago, Benpointer said:

The lad the plumbing firm sent round was not much use btw - scratched his head then called his boss, who suggested the ASHP might need re-gassing (why?)

Whatever you do next, it should not in any way involve this plumbing firm!

[Benpointer]

15 hours ago, jack said:

Whatever you do next, it should not in any way involve this plumbing firm!

Very limited choice round here (north Dorset) but yes, I take your point.  

 

If anyone can recommend a good plumbing firm that knows something about underfloor heating and ASHPs near Shaftesbury, that would be great but it seems the vast majority of firms don't have experience of ASHPs and UFH.

[jack]

1 hour ago, Benpointer said:

If anyone can recommend a good plumbing firm that knows something about underfloor heating and ASHPs near Shaftesbury, that would be great but it seems the vast majority of firms don't have experience of ASHPs and UFH.

 

Keep posting. I think the BuildHub hive mind has solved most of the ASHP and UFH problems that have been posted over the last couple of weeks.

 

I've never seen this sub-forum so busy. I think a lot of people are suddenly finding in this cold snap that their ASHPs perhaps haven't been installed or commissioned as well as they should have been.

[Radian]

1 minute ago, jack said:

I've never seen this sub-forum so busy. I think a lot of people are suddenly finding in this cold snap that their ASHPs perhaps haven't been installed or commissioned as well as they should have been.

 

Too true Jack. It's looking bad but I guess we've got a selection effect going on here. I've only seen one member posting up about how well his ASHP is doing but that doesn't mean he's the only one with a correctly installed system.

[Dave C]

35 minutes ago, Radian said:

 

Too true Jack. It's looking bad but I guess we've got a selection effect going on here. I've only seen one member posting up about how well his ASHP is doing but that doesn't mean he's the only one with a correctly installed system.

 

Just to back that up ... I've had no real problems with my system: the only tweaking I've been doing is seeing how much I can adjust the WC curve down, because the installer set everything up with a default certainly-hotter-than-required curve. Which I suppose at least ensures your house gets warm enough so isn't the worst possible issue, even if ideally they'd have spent the time to get things better.

[jack]

1 hour ago, Radian said:

Too true Jack. It's looking bad but I guess we've got a selection effect going on here. I've only seen one member posting up about how well his ASHP is doing but that doesn't mean he's the only one with a correctly installed system.

 

Well mine's working fine, more or less!

 

I do think it could work more efficiently. Ideally I'd like to be able to change the flow temperature based on time of day or a trigger, so I can turn the temperature up when there's off-peak or solar power available, and run it cooler when energy is expensive.

[jack]

1 minute ago, Dave C said:

Just to back that up ... I've had no real problems with my system: the only tweaking I've been doing is seeing how much I can adjust the WC curve down, because the installer set everything up with a default certainly-hotter-than-required curve. Which I suppose at least ensures your house gets warm enough so isn't the worst possible issue, even if ideally they'd have spent the time to get things better.

 

Yes, I've been doing some tweaking of this too.

 

I'm getting very frustrated with the controller that came with my ASHP. Setting the timer is a hideous experience. For example, it isn't clear exactly how the timer periods work. You basically program in a series of events, each of which is either "on" or "off". For each "on" event, you select whether it's DHW or UFH. The "off" event doesn't refer to the mode.

 

It isn't clear whether setting UFH "on" from midday say, then DHW "on" from 14:00, results in the DHW setting overriding the UFH setting (in which case a single "off" event is all that's required to end both programs), or the DHW setting "nesting" within the UFH setting (in which the first "off" ends the DHW setting and the ASHP returns to UFH until the next "off" trigger).

 

I don't really have the time (okay, the patience!) to experiment with this but knowing the details would make a difference to how I program it.

[Luke1]

1 hour ago, jack said:

 

Well mine's working fine, more or less!

 

I do think it could work more efficiently. Ideally I'd like to be able to change the flow temperature based on time of day or a trigger, so I can turn the temperature up when there's off-peak or solar power available, and run it cooler when energy is expensive.

 

My Nibe SMO 20 controller has the functionality to do this.

I can schedule either a change in the room temperature, or an offset to the curve for up to 3 schedules. So in essence 4 schedules if you include the standard WC curve setting. (And this can be different on each day if you really want!)

 

I have been using this to ramp up the flow temperatures over night whilst I have cheap 5p/kWh electricity! 

 

It can also integrate PV information, and offset the heat pump curves in similar ways I believe, however I've not looked into this because I don't have PV yet...

 

The Nibe controls sound significantly better than many of the controls on other heat pumps on this forum. Yet no one generally considers controls when purchasing a unit.

[jack]

38 minutes ago, Luke1 said:

 

My Nibe SMO 20 controller has the functionality to do this.

I can schedule either a change in the room temperature, or an offset to the curve for up to 3 schedules. So in essence 4 schedules if you include the standard WC curve setting. (And this can be different on each day if you really want!)

 

I have been using this to ramp up the flow temperatures over night whilst I have cheap 5p/kWh electricity! 

 

It can also integrate PV information, and offset the heat pump curves in similar ways I believe, however I've not looked into this because I don't have PV yet...

Wow, it sounds like you can do most if not all of what I'd like to be able to do with mine.

 

39 minutes ago, Luke1 said:

The Nibe controls sound significantly better than many of the controls on other heat pumps on this forum. Yet no one generally considers controls when purchasing a unit.

 

I didn't get as far as looking at controls, to be fair. When I looked into Nibe 7-8 years ago, I'm not sure it was even possible to buy them retail, or if it way, they were way more expensive than the equivalent power Panasonic. They also didn't (at least on the published figures) perform as well.

I'd certainly be thinking a lot harder about controls if I were buying today.

 

I'll eventually get around to looking into whether the optional controllers from Panasonic offer better functionality than I can get with the one that was in the box.

[PhilT]

4 hours ago, jack said:

I think a lot of people are suddenly finding in this cold snap that their ASHPs perhaps haven't been installed or commissioned as well as they should have been.

OMG I really hopes hope it's not a lot, but I know what you mean. One of the main learnings for me is just how much the defrost and ramping back up compromises the nominal power of the unit. Mine takes 20 minutes to get back up to the flow temperature at which it cut off for a defrost cycle. Nine defrosts so far today between 5am and 4pm. To a lesser extent, but same principle, the extent to which hot water breaks need to be taken into account when doing calcs purely for heating.

Edited December 14, 2022 by PhilT

[SteamyTea]

Interesting the comments about the controllers.

I seem to remember that with the Carrier units, a second controller, called Command Module (very space age, very American, in 1967) was needed to set the things up properly.

I think @joe90 has one.

 

What is probably needed is another communication standard to supersede all the others. 

I am not sure how many physical parameters an ASHP actually has that can be changed.

Flow Temp 

Return Temp

Flow Rate

Flow Pressure

Refrigerant  Flow Temp

Refrigerant Return Temp 

Refrigerant Pressure 

Compressor Speed 

Fan Speed 

External Loop Flow Rate

External Loop Flow Temp

External Loop Return Temp 

External Loop Pressure

Room Temp Sensor

External Temp Sensor 

Valve Position Sensors (2 to 5 maybe)

Safety Cutouts (2 to 3)

 

So that is about 20.

Then the reliable software to run and report it all.

 

Amazing it works at all.

 

 

 

 

 

 

[joe90]

2 minutes ago, SteamyTea said:

I think @joe90 has one.

I do and it’s so complicated to use, I don’t!!,!. Another forum member also had one and he helped me to try but in the end I just use a room stat like he did. 🤷‍♂️

[joe90]

Spookily enough I think mine is playing up a little, DHW tank is demanding heat, pump starts as does the ASHP but the ASHP stops after a while and the pump (not in the ASHP) continues to pump, looking like it’s pumping the hot water back around a stopped ASHP so loosing heat not giving it. Will have a poke around in the morning.

[jack]

1 hour ago, SteamyTea said:

What is probably needed is another communication standard to supersede all the others.

 

Many of these units will have the capacity to communicate via the Modbus protocol, but manufacturers (perhaps unsurprisingly) don't like users being able to access/change too many parameters other than via the more advanced controllers that you can buy for an eye-watering premium.

[SteamyTea]

2 minutes ago, jack said:

Many of these units will have the capacity to communicate via the Modbus protocol

'Many' is not good enough. Really has to be all.

I often think that technology is often self serving. Just because something can be done, it does not mean that it has to be done.

Good engineering standards are all that is really needed, and those are based on basic physical properties. 

It is those basic properties that often get lost, and often misunderstood.