ASHP control improvements

[Itrium]

Hi Everyone,

 

I have just moved into a new build 3 bed terrace-house which is heated by a 5 kW Ecodan ASHP, total floor area about 60 sq.m. Heating is UFH with a separate circuit in each room with its own neoStat thermostat, I guess this is to comply with building regs even though the smallest room is only 2 sq.m giving a total of 9 thermostats.

Each circuit is fed through a manifold with electric actuator. The Ecodan is fired up when any of the thermostats call for heat. Ecodan flow temperature is controlled using the compensating curve method with the FTC5 controller.

 

This is my first experience of heat pump technology and it all seems mindlessly complicated for such a small dwelling. I would be interested to hear your answers to a few questions about the system.

 

I was advised by the installer to run the heating 24/7/365… does this mean there should be pumps working all the time or that the system should turn on if a thermostat calls for heat?

 

The controller has a potentially expensive to run legionella prevention cycle. I have seen unvented HW cylinders with uncovered header tanks (including the occasional dead bird!) for years with healthy occupants… is this legionella prevention some health and safety scheme gone mad or jobs for the boys?

 

Looking at the thermostats, it is quite possible for a single small circuit to be left active and calling for heat. Surely running a very lightly loaded ASHP will give excessive cycling on and off? Looking at the error log, I see several U1 error codes indicating an overheating Ecodan.

 

I would like to improve and simplify the heating with the option of easily returning it back to its original state if there are warranty issues. It should be possible to use the auto adaptive flow control by using a thermistor sensor in the main living area which contains the kitchen, lounge and dining. There is a kosher Mitsubishi temperature sensor for about £100 but a 5k thermistor off ebay should do fine for a few pence connected with some bell wire.

 

In my opinion, only the 3 bedrooms would benefit from thermostats. The intention is to disconnect and remove all the actuators except for the bedroom ones. Also, the call for heat function needs removing from the remaining thermostats. Thus the auto adaptive controller does the bulk of the temperature control with the bedrooms set to a lower temperature.

 

Finally, switch off the legionella prevention and run the DHW as cool as possible to give a good shower.

 

This leaves me with a system where the main living area has the optimum temperature control with the ability to have cooler bedrooms. Any fine tuning can still be done by adjusting water flow rates on the manifold.

 

On paper, this sounds to me a far more sensible approach to what is already installed but I would appreciate comments from more experienced members.

[ProDave]

What you have is pretty good.  Most of what you need is understanding how to best use it.

 

Individual room thermostats is normal on UFH, if you think about it, not much different to normal radiators having a thermostatic valve so stop one room getting too hot.  So keep those and set them to temperatures that suit you, usually lower in the bedrooms than the living room for example.

 

The only thing I would do is ADD a time switch or programmer so you can set the times that the heating comes on and goes off.  It will depend on how well insulated the house is whether turning it off at night works or if the house cools down too much in winter meaning it takes too long to get warm in the morning.  This timing function may be possible with the controller supplied with the heat pump but I don't know your unit, perhaps someone else can comment?

 

Regarding the hot water, most of us find 50 degrees (or in my case 48 degrees) is plenty hot enough and we don't run a legionairs cycle.  You should be able to turn that off.

 

 

[joth]

> I was advised by the installer to run the heating 24/7/365… does this mean there should be pumps working all the time or that the system should turn on if a thermostat calls for heat?

 

No the pumps shouldn't be running constantly, just that it should be able to call for heat at any time. Really shouldn't have to be 24 hours a day, but I expect their point is not to let the house get cold when out etc, and expect to heat up in half an hour when back.

The FTC does have a timer built in which is fine if you don't want it running specific times, e.g. while sleeping

 

Legionella cycle is disabled in the menu. Long press menu button -> DHW

 

9 room stats for a 60m2 does sound very complex! Not what I'd install from scratch, but now you have it it'd be worth seeing if you can make it work as needed. Sounds like the main thing is it calling for heat with too few actuators open.  I'm controlling my ecodan via loxone and it's trivial to set it to only call for heat to the ASHP when some minimum % of rooms have a requirement for it, but with a wiring centre that doesn't generally seem supported so the easiest first step maybe to just remove the actuator from the largest living area loop, that way that is always there as a heat sink for the ASHP at least.

 

[SteamyTea]

Is there a buffer tank installed?

Turn off the legionella cycle, it is pointless.

 

[Itrium]

Thanks for these replies. Legionella cycle definitely gets turned off. I like the idea of just removing the main living area actuator for starters, it probably accounts for about half the heating load and would always give a good water flow through the ASHP. There is no buffer tank on this system.

Has anyone tried the auto adaptive flow control on the FTC5?  A controller that sets the flow temperature according to room temperature as well as outside temperature should be more responsive than a simple on/off signal from a thermostat. I suppose this could be Mitsubishi hype?

[Tez1982]

Hi, I have a very similar installation, with stat in each room. I am Interested to find out how you ended up running the system for best efficiency. And what settings you ended up with for weather compensation low end and high end?  

[JohnMo]

Does your unit have an outside air sensor?  If it has, has it been setup to run in weather compensation mode, hence the installer saying to run 24/7/365.  If it hasn't could one be installed?

 

If you are in weather compensation mode the thermostats should only come into play to limit the room temp, so should be set slightly higher than you would like the room temp.  If the rooms are routinely getting to hot, and removing the call for heat, the weather compensation curve needs lowering, so you are putting less heat in to the floor.

 

You can fine tune individual room temps by tweeking the flow rates of individual circuits, lower flow rate equals cooler floor/room.  But don't do this until you have the weather compensation curve set correctly.

 

Night setback should be 1 or 2 degrees only.  Other wise you use too much energy trying to recover the next morning.

[JohnMo]

1 hour ago, Tez1982 said:

Hi, I have a very similar installation, with stat in each room. I am Interested to find out how you ended up running the system for best efficiency. And what settings you ended up with for weather compensation low end and high end?  

What someone has set the curve to look like my not suit you, I may like a 19 degC temperature you may like it 21.  This and the thermal properties of the different houses, will give different requirements for the curve.  But your curve should be a straight line.

 

All the ones I have seen start at 20 degC outside temp, and 20 degC flow temp.  Then it's a matter of finding a cool day, move the thermostats out the way (set at max), let the heating run for 24 hrs, if house is cold increase curve angle upwards, if to hot vise versa.  Once your house gets to the temp you want, bring the thermostats back to just above the normal house temp as limit stops.

 

 

[Tez1982]

Looks like my gradient starts at 15degrees outdoor temp with a flow temp of 30 degrees and ends up at -2degree outdoor temp at 40 degree flow temp. I guess if I wait for a cold day then set all the stats to max for 24hrs, if the bungalow is still cold, I would up the gradient so there's a higher flow temp and if it's too hot I reduce the gradient so there's a lower flow temp!? 

I don't think the mitsubishi FTC-5 has a set back mode unfortunately so I have it programmed off during bedtime hours..

I was considering buying a mitsu wireless control stat. Then running the system in room temp(auto adaption) mode. I think this sets the flow temp. In conjunction with the room temp and outdoor temp. automatically so the curve is set automatically. I could remove the actuators from all the UF heating loops in the main living area i.e. lounge,kitchen and family room then just use the bedroom stats as limiters. Would this be a good approach for better efficiency. The manual recommends to run in this mode,but with my current setup the auto adaption is not available. 

[Roby]

Hi folks,just started using weather comp on my ecodan,I don't have a separate stat in the house just the one fitted in the FTC with trvs on the rads.Question is ,what controls the indoor temp,do I need to fit a separate stat?

[JohnMo]

The indoor temperature is controlled in the following ways.

 

Water flow temperature, this needs to be set so trv are not closing down flow, keep reducing flow temp until you have most the house the temperature you want, say 19-20 degrees.  Some room like bedrooms may be warmer than you require so reduce the flow through the radiator or UFH loop.  If a room is colder than you require up the flow.

 

If when it gets colder the house is getting to warm your temperature curve needs making more shallow, not getting hot enough it's needs to be steeper.

 

Think the FTC is fitted room compensation, you may need to switch that of for a couple of days while you get the target flow temps set up.

 

WC is matter of balancing heat put into the house, with the heat escaping. 

 

Trvs set out of the way at max while you set things up.  Once set up your trv should be set at a couple degrees above you normal room temp.

 

You need to set a night time set back also a couple degrees cooler than your day temp.

 

 

[Roby]

Many thanks for your reply,trying to get my head round this and get it set up before winter .One more question.If I get this set up will it mean the pumps and the outside unit will run all day and night,what, if anything will tell them I have no demand for heat.

[SteamyTea]

5 minutes ago, Roby said:

If I get this set up will it mean the pumps and the outside unit will run all day and night,what, if anything will tell them I have no demand for heat

 

There is switched on and ready to go, and switched on and heating.

When in weather compensation mode, the difference between flow and return temperature is what tells the unit when to input more heat.

The room stats are there to set an absolute maximum, and sometimes minimum, temperature.

[Roby]

Excellent,the light has just come on,that's exactly what I needed to know,it now makes a lot more sense ,thanks for your help,have been running on room temp(as advised by the installer) since the installation and have been trying WC for the last couple of days,house is slightly over heated and the reduction in energy consumption has dropped dramatically. Definitely on the  right path. Few more tweaks and all should be good .Thanks guys.will post on my results and findings later

[Roundtuit]

1 hour ago, SteamyTea said:

When in weather compensation mode, the difference between flow and return temperature is what tells the unit when to input more heat.

 

Not the external thermostat?

[JohnMo]

No.  WC basically maintains the return temp.  Target flow/return temp is increased as it colder by taking a reference from the external temperature sensor.

[SteamyTea]

1 minute ago, Roundtuit said:

 

Not the external thermostat?

I don't think so.

Flow [kg/s] x temperature [K] = power [W]

Power [W] x time [s] = energy [J]

 

To heat up stuff you need energy, the faster the energy is delivered, the more powerful the heater, that is the basic of thermodynamics.

There may be many temperature sensors added to a system for control and efficiency reasons, but basically if just two are used on the flow and return, and knowing the flow rate, the energy delivered is then known.  The room thermostat is then just a device to stop overtemperature.

In a very basic system as described above, manual room temperature correction would be initially needed, but once compensation curve is set, then, except in extreme conditions, the system can be left alone.  Room and external temperature sensing can be used to help set that curve automatically and change the rate of thermal delivery to help efficiency, but they are not absolutely necessary to get a functioning system.

 

(bit of a cross post with @JohnMo)

[PhilT]

On 19/06/2021 at 12:44, Itrium said:

Has anyone tried the auto adaptive flow control on the FTC5?  A controller that sets the flow temperature according to room temperature as well as outside temperature should be more responsive than a simple on/off signal from a thermostat. I suppose this could be Mitsubishi hype?

It's a clever feature and seems to work well with my FTC6 and radiator setup but Mitsubishi advise it is not suitable for UFH. At least that's what I interpreted from  their answer to my enquiry; "Auto adaption can only be used with Mitsubishi thermostats. UFH is generally used with third party thermostats so you will need to select the heating mode to fixed flow or weather compensation"

Edited October 16, 2022 by PhilT

[JohnMo]

I would agree adaptive heating with UFH caused my heating to go all over the place, there's to much delay in the floor.

[joe90]

Going back a bit a previous poster here (Jeremy) designed his own adaptive, weather compensating heating control system but after a bit he just used a room stat (like I do) and it worked ok.

[SteamyTea]

1 hour ago, joe90 said:

Going back a bit a previous poster here (Jeremy) designed his own adaptive, weather compensating heating control system but after a bit he just used a room stat (like I do) and it worked ok.

Works when you have a very small variation in heat load per °C external temperature variation (say 100W/°C), probably kills the CoP once the ASHP is outside of it modulation range (say 450W/°C).

[Dave Jones]

you are quite correct zoning is very bad practice as heat will just try and migrate to the colder zone anyway. 

 

Best practice seems to be run it at your comfortable temp day/evening and let it fall back 3 degrees overnight. Set the flow temp as low as your building heat loss allows.

[Roby]

Hi folks, me again been trying out weather comp on my ecodan  8.5kw ashp for the last3/4 days,no matter what I do with the curves I can't get the indoor temp below 24* what's happening?  Power usage is half of what I was using ,which is great,

but just can't get the indoor temp down.Cold end of the curve is 35 @ -3 and warm end is 25 @25. Can't take this one down any further.Why don't they just have one curve??Jesus,one curve, too hot bring it down too cold take it down. Heeeelllp

 

[JohnMo]

Your flow temp is too high.  That why the house is too warm.  You should be able to adjust the curve.  Your start temp needs to drop a couple of degrees.  You may also need the 35 degree also reducing.

[Roby]

Thanks for that ,I'll try this, one at a time,the problems I'm having is that the more I look into the problem the more differing answers I get .I was just worried about bringing the flow temp down too much and it not being sufficient in the colder weather