MJNewton

Having picked up a Titon HRV1.25Q Plus Eco for a price that was too good to pass on I now find myself with slightly less controllability than the Xpelair Natural Air 180 unit previously planned for. Specifically, the Titon's humidity-controlled boost function is based on an absolute threshold rather than rate-of-rise, and its summer bypass has fixed thresholds that cannot be adjusted at all. All along I have been planning on employing a Pi Zero to monitor system temperatures and control boost and setback flows, and so I have decided now to bring humidity-controlled boost and summer bypass within its scope also. The former can piggyback the existing boost input but with the bypass being internally controlled I have had to pinpoint on the control PCB where to tap into to influence (actually take over) this function. What I would like the panel's input on is the control logic for these features in case there's something I haven't considered (or just got plain wrong!). Humidity-Controlled Boost I am attracted to rate-of-rise control on the assumption that it'll ride out seasonal variations better whilst also being more sensitive and reactive to genuine need. To achieve this control I think I need to consider: Inputs: Extract (i.e. from rooms) humidity Outputs: Boost Settings: Rate-of-rise threshold ($rateofrise), time period ($timeperiod), when to turn off again ($deactivatethreshold) Control Logic: 1) If the humidity rise over $timeperiod exceeds $rateofrise activate the boost. 2) Continue with boost until the humidity falls to $deactivatethreshold. This sounds reasonable I think? What should $deactivatethreshold be though? The pre-rise humidity value, or at least something near it in case the background humidity has risen slightly in the meantime? My starting figures are likely to be something like 5% for $rateofrise and 5 minutes for $timeperiod. Incidentally, I was planning on taking measurement every five minutes so that'll be the minimum boost time period. Summer Bypass From what I have read it seems that summer bypass works better in theory than in practice but I like the idea of it and given the Titon has the capability I may as well make use it. As per the previous process I think I need to consider: Inputs: Extract (i.e. from rooms) temperature, Intake (i.e. from outside) temperature, time of day(?) Outputs: Summer bypass, boost(?) Settings: Room temperature threshold ($roomtempthreshold), Outside temperature minimum ($outsidetempmin), quiet time ($quiettime), when to disable bypass again ($deactivatethreshold) Control Logic: 1) If the temperature of the air being extracted from the rooms exceeds $roomtempthreshold and the outside temperature is at least $outsidetempmin then activate the summer bypass (unless the outside temperature exceeds the room temperature). 2) Additionally (and optionally?), with the bypass active also activate boost unless we are within $quiettime (e.g. at night). 3) Continue with the bypass active (and, optionally, boost) until the room temperature falls below the $deactivatethreshold. Typical figures might be 22C for $roomtempthreshold, 15C for $outsidetempmin, 2300-0700 for $quiettime and 18C for $deactivatethreshold. Thanks for reading this far. Should I be considering a different approaches? Is there anything I should/could consider?

Not the most popular posts this one! ? Nevertheless, I thought I'd follow up with my conclusion in case it is food for thought for others that may find themselves in a similar quandary. What I have decided to do is *not* put a vent at the top of the top stairwell. The reason being is that my planned flow rates (on boost) for the top floor are: en suite extract 8 L/s, master bedroom and dressing room supplies 5.8 L/s each. Thus, there should be a net positive supply (11.6 compared with 6) which should therefore result in air flow out through the stairwell thus in turn eliminate the dead spot I was concerned about. Of course, this theory is wonderfully simplistic but it's all I can go on until the system is installed at which point I could always add a vent if need be or, most likely, just live happily with the as-planned system!

I'm a bit confused about this bit. Whilst supply and extract complement each other functionally they nevertheless operate completely independently with their own fan and air ways. I would therefore not expect adhustment of a supply vent to change the noise levels heard from an extract vent. Perhaps though, the fact this is happening is a big clue as to what the issue might be? (Not sure what though!) Incidentally, have I understood you correctly that there is only a single supply and extract vent at the moment? If so, it could well be that the minimum speed of the unit is still far exceeding the airflow that you want/need passing through the vents. An anemometer would be useful, and will be required anyway come balancing time.

Great - thank you.

Thanks everyone for the replies. I did spot some isolation hangers like the following: ..but they seemed surprisingly pricey and not all that readily available. I'll look to make a DIY equivalent with whatever I can lay my hands on, perhaps exhaust hangers as some have mentioned. For isolating the unit from the ductwork I believe semi-rigid aluminium ducting like that below is what's generally used and so presumably is flexible enough to perform this function well? Is there any issue siting this so that it acts as right-angle bend between the MVHR unit and the ducting? Or am I better using a solid (smooth) right-angle bend and then using a short length of the semi-rigid to connect straight with the ducting? I might be over-thinking things and it really doesn't matter either way...

Ah I see. Finger's crossed it is primarily the fact that it is running unpiped. I am sure that others that have installed MVHR units have run them prior to installation (I know I will be - I won't be able to help but fire it up!) and so should be able to comment about this. I see that inline silencers/attenuators only cost tens of pounds and so that could be worthwhile as a matter of course anyway. What unit have you got?

Sorry to hear (no pun intended) about your noise issues Crofter. This has got me worried about my planned MVHR installation now. May I ask you to elaborate on what the issues are? Given your proposal to move vents I take it this means that the noise is coming from these, or have you not actually got as far as siting any vents yet?

I am considering options for mounting a Xpelair Natural Air 180 MVHR unit on the block wall inside the loft space with particular regards for vibration-transmitted acoustic isolation. Firstly, I should ask if others do consider it necessary to even be thinking about this? If it is, any recommendations on the best approach to take? The unit is ~20kg and not only has rear mounting holes but also some on the side that are intended to be used if installing in a kitchen cupboard. I am contemplating using a couple of gallows-style wall brackets from which the unit could hang on springs attached to battens on the side of the unit. I figure this would isolate it well in terms of vibration transmission whilst still being within the range of movement that could be accommodated by short flexible ducting lengths mating to the rest of the system. One difficulty with this approach is knowing what springs to buy as all the ones I see online have absolutely no information useful for me to apply Hooke's Law that I had much practice with at school! Any comments/suggestions?

I am planning a retrofit installation of an MVHR system to our "2.5 storey" (i.e. the top floor is half in the roof space) 2007 house, and the current plan for the system layout is here. I am wondering whether to fit a ceiling vent at the top of the top-floor stairwell (indicated on the drawing by the blue question mark) to help reduce the effects of stratification? Certainly in the summer months a fair amount of heat collects up there and is much warmer than the lower floors and so some active cooling (or at least freshening) of that air could be advantageous. Whilst I haven't noticed an obvious temperature differential when the heating is on during the colder months I can't help but feel that there must be warm air sitting up there. With MVHR I'm thinking I might end up with something of a 'dead spot' in this location as there is no obvious air pathway between a supply and extract vent from what I can tell without the inclusion of a vent. Might it therefore be worthwhile? If so, supply or extract? I am leaning towards supply given it's more of a living space than a wet room, however extract could be beneficial based on the fact that in the winter I could be recovering some of the heat up there, and in the summer could be extracting it out of the house (with the bypass on hence no recovery). What does the panel think? Happy to receive comments on any other aspect of the proposed design too.

Do you have a link to what the PH rates are?

Apologies Lizzie; it was not my intention to come across as critical. Perhaps my wording was poor. My point wasn't aimed towards you, but rather the marketing of show tickets (generally building related), in particular that they are sold by one hand of event organisers and yet given away by the other. It just made me wonder if all that many people actually do end up paying as I see more offers for free tickets than paid. I suppose at the end of the day they just want footfall, paying or not, otherwise exhibitors won't be willing to pay to attend.

I'm not sure if all that many people actually pay to visit these shows as there seems to be an abundance of routes to free tickets available online. Here's an example for a number of upcoming shows.

I am looking for a set of lift and slide aluminium 'patio' doors and was wondering if anyone had any recommendations, or indeed non-recommendations! In case it's relevant, the opening will be around 3.8m W x 2.1m H and I'm wanting either triple panel with centre opening (if possible) or quadruple panel with two centre openers. Lift and slide is preferred on the assumption that this would provide easier sliding and potentially better weather proofing, and also that they can be locked in a semi-open state to prevent the nipper from escaping. A low threshold would be preferred but it doesn't have to be flush. I've been looking at products from Kawneer, Reynaers, Real, Sunflex, Kloeber, Air, Smart and no doubt numerous others but it is difficult to narrow the selection down. I am sure it doesn't help that my search has been pretty much all online and I haven't had opportunity to see most of them in the flesh yet - perhaps that's when I'd be in a position to rule some out based on aspects such as width of sight lines and cost; both of which I am keen to keep reasonably low! There may even be others differentiators that I hadn't considered; even just taking a liking to some subtlety of design on one over another. I am in Wiltshire and any recommendations on suppliers/fitters would be welcome too as whilst the current plan is to go for supply-only I am mindful of the potential benefits of supply-and-fit either to avoid or aid the resolution of any problems.

Without closed-loop control I would expect the supply and extract rates to become unbalanced over time by virtue of the filter fouling rate being different, assuming that the fresh air and exhaust filters tend to be removing different types and quantity of particulate matter (eg. pollen and other outdoor air detritus for the former; dust, lint and dead skin for the latter?). Of course, regular filter changes will help mitigate this but flow resistance will inevitably have increased prior to this happening.

During further research into constant volume fans I stumbled across this article written by someone at the Passive House Institute on the benefits of automatic long-term balanced operation through the use of them. They do seem a very worthwhile feature so unless I find some other aspect of the Xpelair unit to discount its selection I think I'm going to go with it. There is a caveat in the article about the extra benefits of calibration once in the installed state so I will endeavour to compared the measured total flow rate of each terminal with that measured by the unit to see if any permanent offset adjustment is warranted (and/or indeed just to see how accurate the measurement and control really is).

I am looking to see what MVHR units could suit our 120m² house and am being drawn towards the Xpelair Natural Air 180. One feature that seems to set it apart from others in this price bracket (~£1k) is the use of constant volume fans. These, if my understanding is correct, are fans with a known relationship between RPM, current draw and flow rate thus enabling closed-loop control of actual flow rate in real time despite varying external factors. Sure enough the controls for trickle, boost and purge rates on this unit are all set in m³/hr rather than RPM or %power. This sounds like a useful feature to have, not only for initial commissioning to make the whole-house supply vs extract rates balanced but to also help ensure the desired performance levels remain constant over time despite gradual filter fouling, varying wind pressures etc? I am assuming that the ability of the unit to keep supply and extract rates balanced may also aid efficiency if (or, rather, given!) my house is likely far from airtight by helping minimise pressure-induced air ingress/egress via routes other than the MVHR? I am wondering what the panel's views are of constant volume fans and whether they are a worthy differentiator between competing products or am I better off remaining focused on other aspects of a unit's specification e.g. efficiency, noise etc? Does anyone have experience of the Xpelair 180 in particular?

I recognise that your suggestion is a compromise out of necessity, but I've been wondering about how careful one must be with siting of supply terminals assuming there is a risk that moving air - even warm air - can have quite a cooling effect on people beneath/near them? I seem to recall one installation manual stating a need to avoid siting them over beds and seating areas, presumably for this reason. Could you (and/or of course any others with MVHR) comment on how 'draughty' supply terminals actually are in practice?

That's alright - I'd got everything I required, and your query was on-topic by virtue of the aesthetics angle. :-) Regarding the cold space, others with more knowledge will chime in I'm sure if I've got this wrong, but my understanding is that the performance and efficiency of an MVHR is indeed affected by external heat loss/gain, and consideration must also be given to avoiding condensation forming. You should therefore ensure that duct runs and the unit itself are well insulated when located outside the thermal envelope of the building - I don't imagine this is all that difficult to achieve within a loft space using conventional loft insulation though.

@Onoff You will also likely see (or hear!) the benefit of reduced noise by siting the MVHR unit within the loft space.

[Apologies for those that got a half-complete notification - I somehow submitted without having finished] Thanks everyone for the welcome, and indeed the comments/suggestions. Addressing some of the key points raised: Terminology - Yes, if I've found one thing with MVHR it is the variety of terms in use often interchangeably! I am seeing manifolds and plenums being swapped around; and valves, terminals, grilles, vents (and now 'ceiling holes'! ) all being used. Here am indeed talking about, well, the ceiling holes (that's arguably the least ambiguous term given its uniqueness!) System Type - I am intending on using the HB+ system with the central manifold-based flow restrictors (based on your previous discussions/experiences with them JSHarris) and accept that initial balancing is going to be a bit of pain. Having performed a 20-stage iterative balance of our wet central heating system, taking around 6 hours to complete, I've got the determination (and OCD?!) to see something like this through though! It may well end up something of a hybrid system of different suppliers where possible/compatible and I *might* make my own manifolds to suit my specific needs (and budget). Something worth mentioning is that this will be a retrofit installation and whilst it will be performed alongside a new extension it does mean I can afford to be a bit more focused on some of the arguably less(er) important aspects! As you say, Ian, a complete self-build must mean any available time is highly competed for and so I could well understand that subtleties of vent aesthetics are justifiably low down the list! The fact that I am retrofitting means that wherever possible I shall be wanting to install from the below-ceiling side (just to be clear: the ducting will be in the ceiling void; it is just which side I'll be primarily working from!). For this reason I may well end up fabricating my own plenums that I can fix from beneath using a 63/75mm-to-125mm adaptor and 125mm right-angle rigid bend as all plenums I've seen are very much fit-from-above or at first fix. I think I'll be able to do all this from underneath (I've done similar before with an inline shower extractor fan) given the right terminal type (particularly the ones with a collar that is screwed to the ceiling hole edge. The Conus air valve is not one I'd come across JSHarris but could be just the ticket given how slimline it is and depending on how easily I can attached it to a non-HB+ plenum. Am I right in assuming that there's no distinction between supply/extract with that particular type? The type Lizzie has also sound very interesting, but my desire for (expensive) aesthetics is unfortunately sometimes countered by my thrifty-Northern roots so I might have to avoid looking too much into that option!

Hi everyone, My first post here so let me start off with a big thank you to past contributors to MVHR discussions - the archives have been invaluable in getting me up to speed with the nuances of numerous aspects of system design and have even provided answers to questions I didn't know I had! I note a number of names were on the ebuild forum too on which I have also been trawling the archives of. One aspect I haven't read much (anything?) about is aesthetic considerations of the room supply/extract valves. I see that there are numerous options available, most of which are subtle variations on the same theme, but I am sure some must look better 'in the flesh' than others not least given that there appears to be quite a range of costs. I was wondering if anyone had any particular recommendations? I think quality and subtlety of finish would likely pass the wife test (the judging criteria of which is, naturally, only to be disclosed once I am past the point of no return with cutting holes!). I wondered if something like the acoustic offerings from Alnor might fit the bill by virtue of them being fairly plain looking and obviously air vents. I think I am perhaps nervous of the commercial look of a conventional valve having seen them in many an office environment? Of course, perhaps it is more that I am over thinking this and once the novelty and focus on MVHR has worn off any valve will blend in to the surroundings along with everything else. Incidentally, I am planning on using HB-type semi rigid ducting and balancing flows at the manifold end with restrictors; non-adjustable ceiling valves would therefore also be acceptable if this gives any more choice. Mathew