Mitsubishi settings for DHW and Home Heating

[roadrunnerAlgarve]

I have a Mitsubishi ASHP (PUHZ-SW120YHA) plus Hydrobox (EHSC-VM20UK) installed by one contractor and a DHW tank installed by another, at a later date. The DHW tank was completed in June and foolishly, I did not check both heating and DHW working together.

I do not have a Mitsubishi room thermostat, but have Tado Smart thermostats on almost all radiators.

I am including a photo of the FTC5 panel.

I hope that the small tank temperature icon to the right of the tap, is reading the DHW tank temperature, although there is a small difference to the actual tank thermometer reading.

What I am uncertain about is the “Target temperature” setting.

Before installation of the DHW tank this was set at 55C and it maintained the buffer tank at this set temperature

This target temperature has three options: Target Flow; Target Room and Compensation Curve, I.e.

Which of these settings must I select to control the temperature in the buffer tank?

(“Target Flow” seems to be the only one that allows me to set a temperature of, say 55C)

The Mel Cloud app confuses things further by showing a set “Set temperature” of 22C and a “Room temperature” of 24C.

How can the system possibly know the room temperature with out a Mitsubishi room 'stat?

If I try to increase this setting, it just changes it to some figure around the 22C

 

[PhilT]

Yes the icon you mention is the dhw temp. 55 is very high. I use 42 but each household has different requirements. 

 

Your radiator heating circuit is set at target flow temp of 55 which is a test setting and generally not used for day to day space heating. It needs to be set with either a weather compensation curve or at target room temp mode. At this time of year a radiator circuit flow temp should read around 35 to 40 on Melcloud, rising to max 50 only when outside temps drop below zero.

 

Room temp of 24 looks like a fixed dummy number presumably because you have no room stat connected?

 

To get the most efficient operation you really need a Mitsu remote controller/room stat.

 

 

[GLPinxit]

Forgive me if I've misread the first paragraph of your post but you seem to be concerned that you can't heat your hot water at the same time as you heat the house. This is exactly how my Ecodan works and as far as I know everyone else's does too. (And it is a bit annoying on a very cold day when the radiators go cold because the hot water heating has come on.)

[JamesPa]

1 hour ago, GLPinxit said:

Forgive me if I've misread the first paragraph of your post but you seem to be concerned that you can't heat your hot water at the same time as you heat the house. This is exactly how my Ecodan works and as far as I know everyone else's does too. (And it is a bit annoying on a very cold day when the radiators go cold because the hot water heating has come on.)

... correct, and every other heat pump or fossil fuel boiler that features weather compensation or indeed operation at low flow temperature.  It's unavoidable if you want to do either of these. 

 

WC has been mandatory in Germany (and probably several other eu countries) for a long while so it's nothing new.  

 

Think about the best time to heat water for you and maybe reprogram accordingly.  

 

 

Edited November 1, 2023 by JamesPa

[roadrunnerAlgarve]

Thank you very much for all the responses. However, it makes me realise that I just took so much for granted with the contractor that insalled the ASHP.

For example, as I recall, the system was left with what is now clear, was a 55C target flow temperature and I (wrongly) understood that the buffer tank was being controlled at that temperature. Consequently the radiators were heated at 55C as opposed to the circa 65-70C from the old gas boiler.

There was no Mitso room thermostat and the Tado Smart TRV's seemed to do a good job in controlling individual room temperatures.

I feel rather sceptical that I will get sufficient heat with a radiator flow temperature of 35to 40 although I recognise that using compensation may deal with this.

Equally, I can't see how a Mitso remote controller can work with the multiple Tado Smart TRV's other than setting it at a higher temperature than I would ever need in e.g. the lounge.

I would appreciate comments on the above before posting separately on DHW, but I would just make it clear that I recognise the need for timing DHW heat input at a different time to space heating. At the moment, I have DHW heating times of 04:30 to 6:00 and 14:30 to 17:30 and will see how that works

 

[roadrunnerAlgarve]

A small addition to the above.

The House heating is now set on "Compensation Curve" and the buffer tank thermometer (about 15cm from top of tank), was reading 32C before heat pump started at 18:00 and it is now 34C and the heat pump has stopped running. Only a small demand (3 towel rails) Outside temperature is 18C.

What is switching the heat pump?

[JohnMo]

40 minutes ago, roadrunnerAlgarve said:

Outside temperature is 18C.

The warm south, currently 7 here, been that hot all day mixed with continuous rain.

[JamesPa]

1 hour ago, roadrunnerAlgarve said:

For example, as I recall, the system was left with what is now clear, was a 55C target flow temperature and I (wrongly) understood that the buffer tank was being controlled at that temperature. Consequently the radiators were heated at 55C as opposed to the circa 65-70C from the old gas boiler...

Radiators must be sized according to flow temperature and ashp flow temperatures for space heating are almost always 55c or less.  Sometimes this requires rads to be replaced, but often existing rads are oversized so only some or even none need replacing.  The installer should have done these calcs annd if he didnt then he is bad. It's quite possible yours were already large enough for 55c but your installer should definitely have done the calcs.

 

In the shoulder season even lower flow temps are fine provided the design is correct.  That's how wc works, matching flow temps to demand.

 

TRVs (smart or otherwise) are generally deprecated as a control mechanism for ashps.  The way to set them ashps up is to balance the rads so the rooms end up at the right temp then use trvs as temperature limiters only, ie they shut off relatively rarely to deal with eg solar gain.  So basically set them a degree or two higher than the desired temp and, over a period if months, adjust the wc curve so that it gives the right temp at most outdoor temp conditions.  It's a different way of working which, once you get it right, many deem more comfortable. 

 

I still have gas and have recently turned my flow temp down to 55c resulting in a much more comfortable environment because the boiler is working less hard for longer, much like an ashp does.  I have changed about half my rads (as I am preparing for ashp).  The ones i havent changed are fine at 55, ie they were previously oversized, some of the ones I changed are now oversized at 55 because I designed them for 45c in prep for ashp.

Edited November 1, 2023 by JamesPa

[JamesPa]

52 minutes ago, roadrunnerAlgarve said:

The House heating is now set on "Compensation Curve" and the buffer tank thermometer (about 15cm from top of tank), was reading 32C before heat pump started at 18:00 and it is now 34C and the heat pump has stopped running. Only a small demand (3 towel rails) Outside temperature is 18C.

What is switching the heat pump?

Most likely the heat pump has shut down because the return temp exceeds the flow temp (+ some margin) that the weather comp curve determines is correct for the current outdoor temp.  That's basically how they work.

Edited November 1, 2023 by JamesPa

[PhilT]

55 minutes ago, JohnMo said:

The warm south, currently 7 here, been that hot all day mixed with continuous rain.

Algarve presumably

[roadrunnerAlgarve]

Yes it is the Algarve. I only came to the conclusion that the original contractor was bad when it was too late and that is why I chose not to use him again. However, my main mistake was in choosing Mitsubishi, because the support and I suspect, knowledge is non existent.

I suspect the rads will suffice as they are the rather large cast aluminium ones and not  the pressed steel ones used frequently in UK. They are all on one circuit, upstairs and downstairs and I want different temperatures in some rooms, hence the Tado TRV's.

What I am wanting to do is optimise what I have, but it sounds as though I will have to wait until colder weather before I can get any meaningful results.

[JamesPa]

1 hour ago, roadrunnerAlgarve said:

They are all on one circuit, upstairs and downstairs and I want different temperatures in some rooms, hence the Tado TRV's.

Heatgeek advocate, with some logic, not over zoning (because it's ineffective and inefficient) and balancing rads for equal (or desired) room temp when left 'open loop'.  

 

A slightly refined version applicable to a two storey house with bedrooms upstairs, is to operate open loop downstairs (balanced for temp) and use trvs upstairs.

 

Which strategy is best depends on your system, house and pattern if use, but keeping it simple is a good general guide.

 

And you are right that to tweak the adjustment of heating systems it helps if it's cold outside!

[PhilT]

12 hours ago, roadrunnerAlgarve said:

it sounds as though I will have to wait until colder weather before I can get any meaningful results.

how cold does it get in the Algarve approx?

Are the TRV's connected to the Miitsu controller? Not sure I understand how that would work - I have just one room sensor connected to the controller

Edited November 2, 2023 by PhilT

[roadrunnerAlgarve]

It very rarely gets below -2C /-3C now and even that doesn't last long. When we came to live here 18 years ago, it would get to -5C and for longer periods. 

The Tado TRV's are only controlled from the Tado app. Most of the rads are individually controlled but the lounge has two rads and these are combined on one Tado room thermostat. In view of the spurious Mitsubishi room temperature it would be good to feed in this signal to the heat pump, but I wouldn't think that is a goer.

There is only my wife and I in the house with the lounge and 3 bedrooms on the upper floor. These 3 bedrooms very infrequently used when family, living elsewhere in Europe, visit us (normally in summer!).

Downstairs is the master bedroom and a family room/ office.

In the colder periods we have lounge and kitchen at say 22-23C in the evening and 19C in the day. Upstairs bedrooms are at 19C. Downstairs bedroom is at 19C during the day and 22C in the late evening.

The Tado TRV's were brilliant with the old gas boiler and I cannot imagine how I could achieve the same results without them.

[sharpener]

4 hours ago, roadrunnerAlgarve said:

In view of the spurious Mitsubishi room temperature it would be good to feed in this signal to the heat pump, but I wouldn't think that is a goer.

 

Wouldn't have thought so. But did the Tado provide a "call for heat" signal to the boiler, and if so can you connect it to the HP so when all the rooms are up to temp it cuts out?

 

I plan a similar set up with an existing Honeywell Evohome TRV network (with the necessary output) and Vaillant HP (with the necessary input) so I think it could be made to work. The TRVs will be set as overtemp limits as in practice I expect the WC will do the heavy lifting controlwise.

[roadrunnerAlgarve]

2 hours ago, sharpener said:

But did the Tado provide a "call for heat" signal to the boiler,

You have reminded me that there was an additional WiFi relay device that switched the boiler according to chosen timer settings. So the Tados only had a function when the timer setting was "On" and the boiler running.

That unit was discarded when the boiler was scrapped.

What I would like to find out is where the displayed room temperature comes from, when there is no Mitso room thermometer!

 

[PhilT]

Is room temp reading 24 all the time? If you have no room stat connected to the controller that is probably just a dummy number. All of my parameters that have no device/connection read 25 all the time on MELCloud

[sharpener]

On 02/11/2023 at 17:03, roadrunnerAlgarve said:

You have reminded me that there was an additional WiFi relay device that switched the boiler according to chosen timer settings. So the Tados only had a function when the timer setting was "On" and the boiler running.

That unit was discarded when the boiler was scrapped.

What I would like to find out is where the displayed room temperature comes from, when there is no Mitso room thermometer!

 

 

That sounds like the equivalent of the Honeywell BRD91. Shame, you might have been able to benefit from incorporating it.

[roadrunnerAlgarve]

Night temperatures are going down so I am trying Weather Compensation, but not promising results so far.

I have looked at YouTube videos but the display and available controls on my unit are not the same and I can only change the lower temperature and most times it returns to -32!

Photo attached.

What am I doing wrong, please? 

[sharpener]

On 05/11/2023 at 09:50, roadrunnerAlgarve said:

most times it returns to -32

 

Is that the OAT reading? Have you got a proper OAT sensor fitted and is it working? You could check it with e.g. gentle application of a hair dryer.

 

WC curve looks vaguely plausible but I would expect no heating at 16C not 35.

[JohnMo]

On 05/11/2023 at 09:50, roadrunnerAlgarve said:

What am I doing wrong, please? 

Your curve is all wrong and not easy to manipulate for small changes in temp. 

 

Your lowest flow temp needs to start at a meaningful temperature, you are unlikely to have the heating on above 15 so start there. Same with the end point.

 

So start the slope at 15 deg OAT and finish at say -5.

 

Start flow temp say 28 deg, end flow temp say 35 or 40.

 

Now get a pen and paper.

 

Set all the thermostat out the way say 23 degs. Set the heating on 24/7.

 

With pen and paper monitor outside temp and house temp over the next couple of days see what's happening to room temps. If house is getting colder when it's getting colder outside increase the end point of curve up one degree at a time. If gets too warm decrease the end point.

 

It's a bit of faff but worth doing. This will give you a decent baseline to work from.

[sliderule]

I have FTC6 but I'm sure it's the same. The "Room Temperature" is using a thermistor inside the little FTC box. So it shows the temperature of wherever that is mounted - usually on the FTC Electrics box, which is often mounted on the Domestic Hot Water Cylinder. The little box can be located 10 metres away with a long cable which might be enough to put it into a living room, but unless you are going to use Auto Adaptation (is it available on FTC5?), there's no point. Just ignore it and use Weather Compensation which is very good, but takes a lot of patience to optimise. Be careful not to set it too low or your HP will be cycling on and off frequently which reduces the life of the (expensive) compressor and heat exchangers. Cycling also reduces efficiency and raises energy consumption. I see you have a buffer tank which should reduce cycling. However, if you set the WC too high, your HP will go to a higher power level, also costing money. To adjust the WC, look at the YouTube video  https://youtu.be/-983aLzVZ_I?si=guJZxm1B8xbrnAL-

Mitsubishi Weather Compensation Adjustment, by Mark Sawyer. With mine, I have a MELCloud app which shows me when it's cycling, and a Smart meter which shows the approx power level. Mitsubishi sell a power energy monitor but I think you need the MELCloud app to use it.

As others have said, you don't want your radiator trvs to be turning on and off too much, which could also cause cycling, better to balance down the rads (turn down the flow valves) in all the rooms where you only need background heating, so they heat a little, all the time the heating is on, and set the trvs a little higher. In the main living room, if there are trvs, set them to max, and rely on the room thermostat which I assume is connected to the FTC to stop operations when heat is not required. If you have good house insulation (!!) it's cheaper to run the ASHP most of the time at the lowest flow temperatures you can, without much cycling. I hope your heat pump has been sized correctly because they are often too high powered which will cause them to cycle. However they do have variable speed compressors to adjust the power required.

There are lots of helpful videos on YouTube.

Good luck.

[roadrunnerAlgarve]

On 09/11/2023 at 15:55, sharpener said:

Is that the OAT reading? Have you got a proper OAT sensor fitted and is it working?

Thanks Sharpener, but I don't know if there is an outdoor temperature sensor. The FTC5 is mounted in my pump room which will be at ambient so a sensor inside the panel would give reasonable results.

[roadrunnerAlgarve]

On 10/11/2023 at 17:16, sliderule said:

The "Room Temperature" is using a thermistor inside the little FTC box. So it shows the temperature of wherever that is mounted - usually on the FTC Electrics box,

Thanks Sliderule.

The FTC control box is located in the front panel of the Hydrobox and this is mounted in my pump room so will be at near ambient temperature. Ambient temperatures have been significantly below the "Room Temperature" read out so that doesn't seem to fit.

The main living room has two rads, each with TRVs, but these are combined into one Tado thermostat which controls the TRV position and this is not connected to the heat pump.

[roadrunnerAlgarve]

Sorry to show my ignorance again on Weather Compensation.

If I enter the weather compensation 1st screen there are two options with the LHS being presumably for "View" and the RHS for "Edit"

However if you select "View" there is a provision for adjustment of the lower temperature with horizontal arrows.

What is the purpose of this adjustment?

The settings bear no resemblance to those achieved by adjusting the High and Low settings from the "Edit" screen