@gary Thanks, will do as suggested.  

Neil

@johnmo Evening, we do open three sets of double glass doors to outside most mornings for the fresh air.  It seems to be the ASHP continually cycling at any temp under 30 degs, still learning.

Thanks,

Neil

Going back to your -39 issue, this a glitch in the software running on the FTC, which is slightly surprising given that yours is a new installation, but should disappear if the FTC software is updated. I don't know if this is something you can do yourself, ours was done by a Mitsi engineer when they came to fix something else.

The temperature it reads is from a thermistor in the control display unit, so unless that is in a place that is useful to measure and you want to use it to run in Room Temp mode it is superfluous.

What do your timers control? Particularly the HW one you have trouble with. I can only presume you have a pumped hot water loop and it is that pump which the timer operates. In which case you need it on to enable you to draw hot water - but that will come at an efficiency cost on the HW side of things.

@harriup Hi, thanks for the reply, I do indeed have two timers, one for water loop and another for heating, both need to be on to access each commodity respectively.  It's a bit annoying that all this kit is installed which isn't necessarily required reading the forums.  My thermistor  which was reading -39 fixed itself, which I'm now assuming to be the software update you mentioned, my FTC is located within the control room with the water tank and UFH manifolds so very warm and not where I'd like the temp measured.  Is there a setting I need to alter to ensure this isn't the case?  My biggest problem is the house is just too warm, typically between 22-23 degs despite turning the heatmisers down to 19.5 in each room we use.

I feel I have more to learn,

Thanks,

Neil. 

Using Auto Adapt/Room Temperature mode, where the FTC decides on operational temperatures and running periods, requires an internal temperature measurement. Unfortunately there is no way to provide this via third party connections – it requires a Mitsubishi remote unit, a thermistor on cable run to wherever you need it that is plugged into the FTC board or the thermistor in the FTC display itself, which is really provided as a last resort so that the AA mode works come what may. But most people's display unit is not in a suitable location! But as you don't need AA mode it is not something that should be of concern.

I say that because while it is usefully responsive to changes in room temperature when using radiators (as I do) I have the impression that that is a hindrance with underfloor heating due to the lag between heating the core of the floor and heating the air in the room. Which is the problem you are having.

Are you familiar with the principle of base temperature for buildings, and degree days? (A rabbit hole of data for sure.) Basically, given that you will have some heat loss from the HW supply into the house, along with the addition of heat from electrical appliances, heat from human and animal habitation, and, not least, solar gain, the outside temperature at which you have to start your heating system is lower than might be supposed. It is quite possible for a well insulated house like yours that no additional heat is required until the OAT falls into the low teens. So at the moment you might only need to add heat to your slab for a couple of hours in order to maintain a desirable IAT (I know that this is a strategy that some people use – just a few hours of low-cost electricity put heat into the floor slab overnight and that is enough to see them through the rest of the day).

As you are not using flow temperature as a variable to control heat input the only one you have is time. You could simply adjust the time the heating runs for, but obviously that would need constant tweaking as the seasons change. You can use the thermostats in addition to any time restrictions but think of them not as setting the temperature you would like now but as controlling the effects of the lag you get with underfloor heating, ie lower them until the house stops overheating due to the additional heat in the floor.

@harriup Hi, Solar gain is definitely an issue for us on sunny days, we have a lot of glass south facing particularly the bedrooms and lounge.  I've been running the constantly on and low temp WC for a while now and it's basically just too warm.  I was hoping the low and slow approach for us would give efficiency and low consumption as I've seen this approach has worked for many on the forum but it seems we will have to do the timed approach which I believe is bad for efficiency!

I've put the bedroom heatmisers at 18.5 but they were showing 22.0 last night.  My partners not happy, and she's from Florida originally.

Opinions welcome.....

I wouldn't place efficiency at the top of the list – you have to get to an understanding of how your house works themally and how the heating system works with your particular house in order to heat it effectively and judiciously. Once you are at that point you can tweak for efficiency, whether that is consumption- or cost-based. At the moment you might be putting too much heat in, but doing so efficiently, therefore not consuming as little as you could get away with.

I don't understand your comment about a timed approach being bad for efficiency. Yes, the pump itself is more efficient with lower flow temps, and more efficient with longer, steady runs than a series of shorter ones. But, though I don't have a UFH myself, I believe that is what you will tend to get anyway. A larger capacity to absorb the output of the pump allows for lower flow temp which will then also mean less need to break output down into shorter bursts.

Solar gain has to be worked around though. It might be enough on its own to keep large parts of your house warm enough down to quite low temperatures outside. I would suggest that you try limiting the runtime so you are not adding any heat to the floor overnight, then you are not doubly heating areas if the IAT is also being raised by the solar gain the following day. If there is no or little solar gain then that is the point that the room thermostat setting should be triggering input from the pump. It will be trickier if some parts that get no solar gain then get cold - a matter of adjusting flow rates in zones, probably?

It is a tedious job but you might find it informative to look at MelCloud regularly and see when and how long for the heat pump is running, how the on/off points relate to the internal temps (though they won't be recorded on there) and the external temps. Understanding what the pump is actually doing is important to guide you in how to adjust what you change.

@harriup Afternoon, My timed approach comment was the understanding that on/off was not as beneficial as slow/steady with heat pump permanently running.  As you say, it's going to be a case of continuous tweaks and seeing what happens.  It's a full time job.

Thanks,

Neil.

Posted by: @harriup

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I wouldn't place efficiency at the top of the list – you have to get to an understanding of how your house works themally and how the heating system works with your particular house in order to heat it effectively and judiciously. Once you are at that point you can tweak for efficiency, whether that is consumption- or cost-based. At the moment you might be putting too much heat in, but doing so efficiently, therefore not consuming as little as you could get away with.

...

I cannot emphasise how much I agree with this. The number of times in my professional life when I've had to explain why "efficient" and "effective" are not the same thing is incredible.

You could, of course, make your heating system incredibly efficient just by turning it off but obviously it would in no way be effective at that point. @harriup's absolutely right to suggest you focus on effectiveness first and then tweak the efficiency within that envelope. This forum and others like it are littered with threads in pursuit of optimal efficiency and most at some point will contain a post from someone reminding everyone that the primary goal of maintaining a comfortable level of heat still has to be met.

That's not, I hasten to add, suggesting, @ngillam, that you have lost sight of any of this; just giving a big thumbs-up to @harriup.

@majordennisbloodnok Afternoon, agreed.  I'm more than willing to sacrifice efficiency to make it cooler.  I could run it and open the windows, just doesn't make sense.  I just want to learn about options and seem to enjoy tinkering with settings but want to avoid annoying my other half, it's defiantly too warm on the lowest flow temp on the slow steady approach, I'm going to switch to timed this week and see what happens.

Neil

Hello Gary,

Hope you're well.  remember you mentioning flow temps and reducing flow.......do the images of my UFH mean anything to you?  We're still running too hot, typically 23-24 degrees and running at 15KWH per day.  I've noticed red lights go out on heatmisers for rooms that are the coldest...what does it mean, the heatmisers in each room are set high but feel the flow rates need tweaking?

 Thanks,

Neil.

The lights going out means those UFH circuits have closed off as the thermostats that are controlling them have been satisfied, if the rooms are too cold then the thermostats are set too low for those areas.