Dan F

Which ASHP is this? What is hysteresis? My understanding is that with a target flow temp of 23C and a 7K hysteresis (as an example) with an open loop system the ASHP is going to run until flow temp reaches 30C and then shut down. Is this how yours behaves, or does it do something different e.g. mark-space ratio. I assume you much have hysteresis much lower than 7K? Otherwise, if flow temp does have to ramp up to 30C before ASHP shuts down, this risks temperature fluctuations and possibiity to overshoot.

It's not marketing (and I haven't seen it mentioned in marketing materials), it's a control strategy that is important to control cycling when heating load is less than minimum output. Without an integral-based control mechanism how would ASHP control cycles? Using simple hystersis would result in more temperature swings impacting efficiency and comfort AFAIU..

I know various people, including a Vaillant-approved installer, who have had to purchase and install their own replacement boards! What kind of "persuasion" was required? Is the new board already installed now? (make sure they move your cooling resistor over, and don't take it away with the old board. if you have one installed)

You don't have to disable anything, this is all automatic. We have UFH on ground-floor and Comfopost on first floor. (not a great idea as boosting MVHR to increase first-floor cooling brings in more warm air on ground floor) If you have UFH and/or fancoils on both floors there is no reason to install Comfopost no. In our case installing UFH on first-floor wasn't justified and given the cacluated cooling load was so low we felt that fancoils weren't justfied either. The comfopost was more of an insurance than anything else. What we realised living here though is that bedroom temperature can be quite important for some people to sleep well, and controlling bedroom temperature would have been very easy and effective with fancoils, but much harder with comfopost where you need to run it for extended periods of time and maintain the whole first-floor at a lower temperature.

2.8kw cooling is actually a fair amount for a very insulated house in the U.K, assuming you have shading/overhangs. Our calculated cooiing load was <1kW from what I remember. The thing is, and I didn't realise this at the time, those numbers are based on: - Water temp of 7C which isn't particulatly efficient. - Air temp of 28C But post-MVHR air temperature is never 28C assuming you keep internal temperature under control. If external temperature is 41C, internal temperature is 21C and MVHR efficency 90% you are looking at closer to 23C. And, if post-MVHR temp is 23C and not 28C cooling power is only 75% of what is quoted. On top of that, you can't really compare cooling power of Comfopost with cooling power of fancoil if you need run mvhr on boost to increase cooling, as it's cooling warmer incoming air, not air at existing room temperature. A simpler approach to stopping first-floor heating up via MVHR on all but the very hottest days is to turn MVHR to minimum during the day on very hot days. Not as effective, but lot simpler..

I have one. They are useful for ensuring MVHR doesn't gradually heat up the house when external termperature is high, but I wouldn't recommend for "active" cooling and if I was doing this again I'd definitly opt for fancoils instead. That said, because we have automatic external blinds and cooling load is very low we aren't in a rush to install fancoils and Comfopost does help keep first floor temperatures more comfortable than if we didn't have it installed. If we didn't have the external blinds though, it would be a different story. You do have to run the comfopost fairly constantly for this work though, and I've gradually adjusted circuit flow temp to ensure this doesn't cause ASHP to cycle like mad. I've put a Loxone automation in place to automatically turn on comfopost circuit when MVHR is delivering warm air to bedrooms, and boost if required.

Yes, any venetian blinds. We got them supplied with windows and control them via Loxone. Our are https://www.roma.de/, but AFAIU they don't sell into the U.K directly. Check with your window supplier as it simplifies things if you get them via then. Also, need to consider recess in construction for blind-box if you want them hidden.

Don't ask them for a price. Tell them it doesn't work as designed and you want it fixed under warranty.

It's the heat pump board that matters, so your unit has the bug and: i) The default -60º min behaves like -30º min ii) It ignores any attempt to change the value, eg. to -100º min, This is bad news for over-sized systems and for systems like ours where adjusting this makes sense. See https://energy-stats.uk/vaillant-arotherm-firmware-351-06-07-problems-energy-integral/\ I had Vaillant switch mine out FoC, but I don't think anyone else has had any sucess.

Exactly. Main reason to keep hysteresis at 7K or to keep the integral start at -60 ºmin is comfort (or any limits you need to consider for the flooring type if open loop). But in a system like ours, this isn't a concern. Using -120º will have a direct impact on the amount of cycling when demand < min power and in turn a small impact COP. Adjusting the hysteresis probably want make any difference in practice, but no harm in increasing. This brings me to another question though, do you have buggy firmware that doesn't allow this to be configured, or newer one?

Yes, thats correct. Yes, hysterisis of 7K will mean compressor comes on at 18C. You ideally want your system designed and installed to never really use the hysterisis though IMO. If your system volume is good, but not very big, it can be a good to increase the hystersis just so that when the compressor comes on (before it dials back to minumum) it doesn't hit the 7K and turn off prematurely. This does however depend on if you have a buffer, are/aren't using mixed circuit and what your emitters are though. In some cases it may not be a good idea to have water 7-15k above target even for a short period of time. In my case I have a buffer + mixed circuits so it only means the buffer gets hotter, the circuits don't. But if you had open-loop with radiators this might not be a good idea.

It targets a flow temperature and adjusts the compressor speed to achieve this, it doesn't target a ΔT. The "Compressor hyster. Heat." is not a target ΔT, but rather the maximum difference between target and actual flow temperature allowed before the compressor shuts down. In a large volume system when heat demand is low (autumn/spring) the primary (or potentially only) mechanism that decides when to turn compressor on/off is the energy integral calculation. This is because the flow temperature never overshoots enough to hit the 7K hysterisis limit. But, with a low-volume system, or one with too many zone controls, the 7k hysteresis will likely be the primary mechanism that controls when compressor turns off.

The aroTHERM works a bit differently. It uses a constant flow rate and varies delta-t between around 2 and 10K.

flow

Do MBC no longer offer this as part of package?

We used a flexible 50 or 75mm pipe in one of the tricky locations where we needed to bring it up through stud-work into the loft, was easier that using rigid waste pipe.

@Alan Ambrose Remeber that the SAP and PHPP calculations are different. One uses internal measurements and one uses external, also the boundary conditions and/or external temps might be different (can't remember). I've seen defaults of 0.040 used as slightly conservative a number for(presumably good spec and well installed) windows and 0.1 used for thresholds. Great installation and this could be less though, and if you have a blind system or poor insulation this could be more, but I think those are good starting points. If rational publish psi values then that will be based on assumptions about the installation situation and fabric make-up, so may not be accurate or valid. Also need to check if rational numbers use SAP or PHPP methodology. Window/doors installation of course aren't the only thermal bridges, you have all the building juntions too. 🙂

There a few commerical products that make them easier to calculate, but none are exactly cheap. If what you need to do is farily limited though, you could potential do them within a trial period. The only low cost (free) approach I know is Therm though, but it takes some time to learn and you need to ensure you use the correct boundary materials and temperatures. Then on top of that you need to caculate thermal bridge psi value seperatly. There is some guideance here: https://peterwarm.co.uk/resources#therm The altnerative approach is to get hold of a book of standard details and use the psi values for these if you are not doing anything really complex/different. Using values taken from standard details is AFAIU acceptable for PH certification if you go down that route, and it's not a requirement to calulate every single bridge.

Also depends what ASHP you have. Some have dew point monitoring which will ensure you can avoid condensation.

Not sure there is much else you can do in terms of filters. I've always wondered if there is a way to detect smoke somehow and temporarily reduce MVHR to away (or turn it off), never looked into it in detail though. Wonder if anyone else has?

Any idea what to look for to know if it works with round back box? What do you look for on the datasheet?

@joth @Thorfun @Rob99 Any suggestions for simple black retractive switches that wouldn't look out of place in room that also uses Loxone Touch Pure and that work with the round (european) plastic back boxes? Either that or some nice looking blanking plates I've realised that we don't need Touch Pure everwhere I've planned, but don't want to fill-in all the locations as i) a simple switch might still be worthwhile ii) some have connections e.g. with door sensors.

Mine bitcoin? Seriously though, don't you get 15p export? It's no a huge amount but if house is already at good temp, hot water tank full and car and batteries both charged, exporting at 15p is as good as anything isn't it?

Sometimes you can tell based on spacer sizes. If the glass is say (3+1+3:/18/4/16/:4 Ar 90%) then you can check the wider spacer is on the outside.

All depends on the fitting you have. Can't you leave the wall-light switch always on, and then control from Lozone? Don't see why it would be an issue with touch switches, although maybe not justified if you don't need switch to also do blinds/curtains or music. I'd start by designing your zones and then decide when a swtich will be needed and where it makes sense for that switch to be. If you play around with it a bit more, I think you'll find it's easier to use the center button to switching between moods, don't think of it as a 5-in-1 light switched. Some moods can be automatics (with precense and/or time of the day, or as part of a scene), typically only some moods are manual.