What's going on with our UFH!?

[Andehh]

Checking how our UFH and ASHP performed with the recent cold snap, and our heatmiser app is showing some really odd behavior...  Per attached pics. The tiled rooms are hit harder then those carpeted, I'd almost suggest closer to the manifold the bigger the drop.

 

What is causing these large drops? Could it be defrost cycles? Anything I can do to soften this happening, as it is really slowing down the warming up of the house.

 

Edited November 30, 2023 by Andehh

[Andehh]

To add to the above, we have a lot of zones throughout the house, but they are all being operated together....ie all open for 2 x 4-5 hour periods a day.

[Alan Ambrose]

OK suggest this is either your HP cycling or the UFH blending valve closing off as the water is too hot.

 

You can see from the graph that Heatmiser is 'calling for heat' but something else is shutting off the heat supply for a bit - presumably until whatever it is has cooled down enough and then it starts up again.

 

Suggest close observation of the manifold, actuators, mixing valves etc and the HP itself. Also checking what temperature the blending is set to. Looks like the cycle is about an hour? A temperature probe / thermal camera and a voltmeter might help.

[ProDave]

Those graphs confuse me.  If the set temp is 16 degrees and the actual temp is fluctuating around 17 degrees, why is it even calling for heat?

 

Are those room temperatures?  If so I can't believe the room temperature goes up and down so rapidly, so I would be looking at some other local heat source confusing the thermostat.  Is it near a fridge for instance and the heat from the back of that influencing the thermostat?

[billt]

I guess that the set temperature (dashed line)is 21 degrees during the heating period. The 16 degrees in the top line is probably the current set temperature.

 

That's a good idea about a local heat source. If it was the heat pump defrosting the shape would be the inverse of that. Fairly long period of high temperature, dropiing for a few minutes during the defrost time.

[Alan Ambrose]

>>> why is it even calling for heat?

 

The dashed line is your programmed heating schedule - it says 'heat up from 16 to 20 degrees please from 3-7am, then don't heat after 7am unless it drops below 16'. If you check the profile for those rooms you should find that that's what is set. This is the basic operation of any typical timed programming device and is described in the manual.

 

>>> Are those room temperatures?

 

Depending on which thermostats and sensor set-ups you have - most likely room temperatures. You can add floor sensors and/or remote wired or wireless room sensors to the standard room temperature display - so it depends on your set-up. Ask you installer maybe?

 

>>>  I can't believe the room temperature goes up and down so rapidly, so I would be looking at some other local heat source confusing the thermostat

 

It does look a bit rapid, but I've found it is surprisingly sensitive. Yes, you're seeing desired temperature (dashed line) and actual temperature (reddish graph) together with an indication of whether Heatmiser thinks it has called for heat (hence the red colour). If the call for heat somehow doesn't switch the heat source on, say, due to a fault or you light the log fire (which Heatmiser doesn't know about) then the actual temperature won't necessarily reflect the expected behaviour of the programmed temperature - i.e. slowly catching up with the programmed temperature.

 

 

 

  

Edited November 30, 2023 by Alan Ambrose

[Alan Ambrose]

Some examples:

 

(1) Electrically heated kitchen floor with floor sensor following programmed morning cycle. Yeah, it's bang-bang (i.e. on/off) control with a 0.5 degrees dwell and 10 minute 'output delay'.

(2) Wet UFH on frost standby (will heat if temperature drops below 12 degrees). Log fire keeping the place warm - each bump is someone adding a new log or two.

(3) Electrically heated area following program. (Outside temperature is quite cold and therefore takes ages to warm up.)

Edited November 30, 2023 by Alan Ambrose

[JohnMo]

6 hours ago, Andehh said:

Checking how our UFH and ASHP performed with the recent cold snap, and our heatmiser app is showing some really odd behavior...  Per attached pics. The tiled rooms are hit harder then those carpeted, I'd almost suggest closer to the manifold the bigger the drop.

 

What is causing these large drops? Could it be defrost cycles? Anything I can do to soften this happening, as it is really slowing down the warming up of the house.

 

Couple of observations.

 

Set back is very large for a heat pump, for it to cope your flow temps will be way higher than you really need. You normally set it back a couple of degrees only.

 

For heat to spike that much you either have the temperature reader way to close to the heat source or it's direct electric heating. Reading close to source as above reply.

 

The thing is, are you are trying to flow way to hot for the heat pump and it's just cycling on and off, as it can't dump the heat quick enough.

[Andehh]

Thanks all, ill add some more details here:

 

We have a large bungalow, lot of windows but good insulated. Ait tightness of 2.2,  160mm PIR in floor & ceiling, 150mm dri therm 32 full fill cavities. Every bit of insulation double checked during installation by myself. It isn't great by buildhub standards/passive, but it is well insulated vs your average new build.

 

Samsung Gen6 12kw ASHP, supplying Joules spec UFH throughout with Heatmiser controls. We have c20 zones of UFH (as 6 bedrooms, 3 bathrooms, large kitchen & lounge with multiple loops etc). It is over zoned but it is all controlled together, controlled as all on & all off during cosy periods. This is why 16 degrees during night to keep all zones ''off'' then boosted to 21 degrees during the 2 x Cosy periods/an hour either side of them.

 

Heating periods right now are 3 am to 8am and 11am to 4pm, with 1 hour DHW first thing & last thing within Cosy periods.... all on via 21 degree temp then all off via 16 degree set back. House holds the heat pretty well loosing 2 degrees over night with the -3 deg temps.

 

Flow temperature right now is 32 degrees out of ASHP, supplying two manifolds. No blending valves on the manifolds, flow rates between 1 and 2L/min.

 

All stats are next to sockets in each room, with UFH below carpets in most rooms. MVHR is on & used throughout.

 

After the day today, this si what it looks like...again showing the heating on & hooting off periods....

 

 

Edited November 30, 2023 by Andehh

[ProDave]

All graphs are showing a step in temperature at roughly 02:00 when it is not heating, what happens then?  The step is a similar size to the other steps later on when it is heating.

[Andehh]

No idea at all! i'm struggling to even imagine what it is. 

 

We have MVHR going, and do notice in the morning when some bedrooms are opened the temps really jump as the central corridor retains more heat then the rooms with big windows coming off of it.

 

The fact it is shown in both the Master Bedroom & Kitchen...opposite ends of the house & different MVHR is even more perplexing....

 

Also shows up in kids bedrooms...

 

 

Edited November 30, 2023 by Andehh

[Andehh]

For what its worth, the whole system has been performing pretty well & normally up until the temps dropped this week.

 

Some of the kids bedrooms don't heat up as much as I would like, but they are small rooms, with very high ceilings & carpeted so not unexpected -vs- tiled rooms! Big kitchen has always heated up around 1 degree an hour for October/early November without any issue etc

 

Checked out energy usage so far today and it looks to be around 36kWh for the day to sar, which for nearly 9.5 hours of a 12kw ASHP operation seems remarkably low! Also a flow temp of 32 degrees after a few hours of operation also seems too low....!?

Edited November 30, 2023 by Andehh

[markocosic]

Sketch a schematic of WTF is actually fitted. There must sure;y be some buffer or secondary circulation pump etc for this kind of thing to be going on.

[Andehh]

Thanks Mark, I will do that!

 

In the meantime I had a long chat with Joules (supplying & who spec'd it all) on the performance of the system & struggle we have in actually getting the house to warm up sufficiently & some odd temp drops we see.

 

They have proposed that with us starting the heating across the FULL ''cool'' house at 3am during -3 degree temps, what is probably happening is the ASHP runs at full whack to pump heat into the house....and because -3 degrees it runs into defrost cycle reasonably quickly. However, due to a cool house & very low flow temps when the defrost cycle kicks in & the ASHP pulls the flow back/uses the UFH temps (which are every low) to defrost the defrost takes longer to run, before the system then restarts and heats the house. At this point the zones are now cold (because defrost cycle drawn back out what little heat) so the ASHP goes into full whack mode....and frosts up. It then reveres & what little heat it has put into the house....is pulled right back into a prolonged defrost period. We have a 50-60mm screed over a full 275sqm bungalow so lower retained heat capacity. We therefore end up in a vicious cycle, created by quite a 'cool' house in the first place.

 

They have recommended we turn it off over night & run it for the course of the day tomorrow & weekend during the warmer periods of the day, to see if this is enough to break the cycle and get real warmth into the slab & house.

 

There is a logic in this, however the really short & odd spikes are unusual all the same, and are possibly caused by the above behaviour!?!?!. They only appeared/appear during the really cold spots (and flatten out when the day warms up). Heatmiser possibly being very sensitive (which it is, I can detect when kids open their door in the morning based on the change in their room temp!!) could be picking this all up due to the 50mm screed acting quite quickly to the change in temps from defrost cycles?

 

If a ''turned off'' ASHP freezes up/detects its frozen (or was frozen when the heating turned off)...... would it still kick in a defrost cycle?

 

 

Edited November 30, 2023 by Andehh

[Andehh]

So despite heating off from 4pm through to now... I'm still getting these odd bloody spikes!!! And they always seem to start around 1.30 am it seems...

Edited December 1, 2023 by Andehh

[Andehh]

Another room.... Over the course of 24 hours later

[dpmiller]

I wonder if these stats have an accelerator (heater/ some AI copy of) that's massaging the sensor to improve response?

[Alan Ambrose]

>>> I wonder if these stats have an accelerator (heater/ some AI copy of) that's massaging the sensor to improve response?

 

The whole Heatmiser tech set-up is fairly dumb old-school tech although it does have wireless to the hub and an app - otherwise it's a simple set of desired temperature profiles held in software and a relay in each sensor to switch the load. There are settings for each sensor to control the switching (time between call and non-call changes and temperature difference to ignore) - those stop rapid switching. There's also a frost setting and a setting to allow 'pre-heat' warm up to reach desired temperature in advance of the schedule. That's it. This kind of thing (below)...

 

@Andehh - as the designers suggest it's a HP cold weather / defrost thing - can't you get them in to diagnose and fix? Is your house well insulated? If so, the general advice here on BuildHub is to have your heat pump run consistently for long periods to deliver a more-or-less constant internal temperature rather than have it bounce around trying to fit the 16-21 degree swings that it's programmed for right now. Actually a useful experiment would be to change the profile to a constant 20 or 21 degrees for a day or so and see whether it settles down.

 

 

[Super_Paulie]

i think you guys are missing the obvious. 

[Alan Ambrose]

System taken over by prehistoric monsters?

 

Weird bug in software?

 

 

[Andehh]

Found it! it's the MVHR, turned them both off at the mains and all looks to be be resolved after 14 hours.

 

After several hours of research found someone on Facebook who had similar and discussed it bring an anti frost thing the MVHR was doing.

 

Having looked at the MVHR manual (vent axia sentinel) it does say below 0 degrees it does activate frost protection.

 

For now, I'm just happy to have found the culprit.

Edited December 2, 2023 by Andehh

[SteamyTea]

@Andehh

 

Can you do a quick summary.

Something along the lines of:

 

Heating system was unstable

Turned out to be the ventilation system

 

But more detail, and maybe a possible solution.

[Colliox]

Hi Andehh,

 

I haver a similar setup to you. Do you have the Heatmiser Neostst V2? I found them very unstable and each one was calibrated differently. My MVHR was also having a cooling effect on the stats because there is no vent in the stats to allow good airflow. Long story short, I'm going to replace all the heatmiser stats with Joule E91 stats as they are a lot more stable. The only thing is ill loose the App and wifi availability. Also would you not consider to set your stats to the one temperature and forget about them, its a lot more energy efficient than having them on heating periods. You should cut your run hours in half

[JohnMo]

32 minutes ago, Colliox said:

Joule E91 stats

Why would you want a thermostat with 0.5 deg switching hysterisis with UFH, you will end up with room temp swings of about 2 degs. Get something that has a switching hysterisis of 0.1 for way more stable temperatures.

 

Or set your system so the thermostat effectively isn't needed except for extreme temperature swings - solar gain ect.

Edited December 12, 2023 by JohnMo

[Alan Ambrose]

>>> I found them very unstable and each one was calibrated differently.

 

Funny you should say that. I have two set-ups running (in 2 properties) with no real problems for 3 years - one with 14 sensors and one with 10 - including wet and electric UFH, immersions, towel rails and outside sensors. All work fine. There are two small things - (a) the outside sensors are battery and have a shortish range and (2) if I switch off the power to the property completely, the stats end up with the wrong time. I think this may be something to do with my router taking longer to start up than the heatmiser hub - but that's only a guess. Easily fixed once I remember. Also Heatmiser doesn't have a decent user forum and their product guys could be smarter - I've told them a couple of times how I've bodged their system so I can use higher temps on the immersions (their app is limited to 35 degrees) - but they don't listen. The API could be better, although I've not used it in anger. They update the app about once a year instead of every damn week like some apps, which is good. Sure, the temperature reading is from airflow through the stat itself. In one room, stupidly, I put the stat directly above the heating and so it reads high - so for that room we use a separate battery sensor near SWMBO's desk.

 

Are you having a problem with comms to the hub? Have foil back plasterboard or somesuch on internal walls? The stats are supposed to mesh, but I have not actually seen how they do that.

 

Re: 'calibration' - if you want to, you can use the stats' own menus to calibrate. I did, just because I have a Tektronix temperature meter hanging around here. Not sure it's really necessary though.

Edited December 12, 2023 by Alan Ambrose