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    Firstly is it MHRV or MVHR....?

    Whichever one it is I seem to be getting wildly different cost estimates, anything from a couple of £k to £10k...! Can someone please point me in the general direction of a product that does what it says on the tin...?

    (ie the tins says it recovers more heat than it loses and its not too noisy and doesn't breakdown much..)

    It's just HRV "Heat Recovery Ventilation" or ERV "Energy Recovery Ventilation" (for those systems that also exchange humidity between the air streams. At least, that's what it's called over here - the "M" bit is a given :)

    As for your price quotes, that's quite insane to be quoted £10k - I assume that must also include a heat pump? Even so, that's more than we paid for a full GSHP installation here in Montreal.

    Posted By: James Norton(ie the tins says it recovers more heat than it loses and its not too noisy and doesn't breakdown much..)

    It can't recover more heat than it loses - did you mean recover more heat than is *uses*? They all should do that - but *only* if you have an airtight house in the first place. If you don't, then it's a waste of time/money.

    Over here the systems are available in big box hardware stores for around Can$700 or less - but not including the ducting (not that that is expensive). I have no idea how much an HVAC contractor charges to install - we had ours installed in the new house as part of the overall HVAC installations and it wasn't a separate line item as HRV systems are mandated by code over here anyway.

    As for noise, ours isn't noisy - but it's in the mechanical room of the basement - the air flow is silent as far as I can hear. As for reliability, it's just a synchronous AC motor so should last for as long as the bearings last.

    Paul in Montreal.
    • CommentAuthorCWatters
    • CommentTimeDec 10th 2008
    We got quotes for our system back in 2005 so info is a bit out of date. System was for a 3300sqft 5 bed 3 bath house. Came at £2600 for the kit and £1600 for installation so about £4200 total installed. Other quotes were as high as £6000. Some of the more expensive quotes assumed two small heat exchanger units rather than one big one. Not sure why. The single unit we installed works fine.

    Main problem we had was with the positioning of the room vents. The installers put the ducts in the corners of the room and later after plastering we found we couldn't fit the grills as they were too close to the wall. Think very carefully where they should go - for example if the vent is in a corner that makes it difficult to build a floor to ceiling wardrobe on two walls.
    • CommentAuthordocmartin
    • CommentTimeDec 10th 2008
    Just been,today, for my free course for installers with a Dutch company with a third of the market over there. I hasten to add that the UK headquarters are in Burton on Trent! The HRU 4 MVHR for a house of up to 175 M2 is just under £1000 for hard wired controls and £1100 approx for the remote control version. Amateur installation would appear to be simple and straightforward, especially for a newbuild with appropiate planning from an early stage. Apparently I-beams can be a problem as one is only allowed to make a single hole of 125mm diameter; the makers recommend rigid ducts of 150mm diameter or flat 240 x 60 neither of which are allowed.
    This unit is DC, EC motors with a specific fan power of 0.5 w/l/sec, i.e. scores very high on SAP Q. Inlet ducts to habitable rooms are recommended to be sited near windows; apprently grilles near corners often have wardrobes etc placed in front of them
    Posted By: Paul in MontrealIt can't recover more heat than it loses


    you are quite right "more than it uses" was what I meant. Good to know that my suspicions about £ insanity were correct. Have looked into it a bit more since posting I'm seeing common things in nearly all from the sub £1k to the '£insane'.

    Seem to be two main types (see pics):
    1. smaller unit with two pull-out filters (cheaper)
    2. big metal box

    All with:
    DC motor
    Option for 'summer bypass' (whatever that is)
    Quoted efficiencies of 90% (although occasionally quoted as 95% or are they all 90-95 really on margins for error and user control..?)
    Crazy multi line graphs that are supposed to demonstrate performance... leaving me none the wiser.
    Some with flexible ducting some with rigid which I assume is better but is it worth it, could I use flexible to get round tricky corners...?
    Counter flow heat exchanger (...?)

    I guess with all we discuss on this forum its about how high you climb up the hyperbola of cost vs performance I s'pose... but anything I should look out for to avoid getting a real lemon?

    Also what about running the inlet ducting underground for pre heat...? good idea / diminishing return...?


    Installers course eh...? fancy a new customer? 2 new builds next spring /summer, posi-joists rather than I-joists...

    SAP Q, would that be appendix Q? and is it something I can use to compare units...?


    Has any one heard anything about the 'PAUL' units supplied by GBS...? I suspect top notch performance but big price tag...?

    Type 1
    Type 2
    • CommentAuthorEd Davies
    • CommentTimeDec 11th 2008 edited
    Posted By: James NortonOption for 'summer bypass' (whatever that is)

    If a) the inside of the house is warmer than ideal and b) the inside is warmer than the outside (e.g., at night time in summer) you might want the ventilation but not the heat exchange.

    Counter flow heat exchanger (...?)

    This just means the outgoing air flows through the heat exchanger in the opposite direction to the incoming air so that the nearly warmed incoming air is heated the last little bit by the warmest outgoing air and the coolest outgoing air is used for the initial heating of the cold outdoor air as it comes in. To get more than 50% efficiency you have to use something of the sort.

    Also what about running the inlet ducting underground for pre heat...? good idea / diminishing return...?

    If the ground around the ducting is to ever be warmed then you need to run air through the duct which is warmer than the ground. This runs the risk of condensation and hence mould.
    Thanks for that Ed, so w/ regard to the heat exchanger, there all pretty much of a muchness?

    Posted By: Ed DaviesIf the ground around the ducting is to ever be warmed then you need to run air through the duct which is warmer than the ground. This runs the risk of condensation and hence mould.

    was thinking the other way round ie the warming up sub zero winter incoming air taking advantage of warmer winter ground temperature so the heat exchange doesn't have to do as much:
      Untitled-1 copy.jpg
    • CommentAuthorstephendv
    • CommentTimeDec 11th 2008
    Posted By: James NortonPS
    Has any one heard anything about the 'PAUL' units supplied by GBS...? I suspect top notch performance but big price tag...?

    Some of the Paul models are certified by the Passivhaus Institute - and seem to be a very popular choice for passivhauses in Germany (they're referenced in a many projects). Very pricey yes.
    • CommentAuthorstephendv
    • CommentTimeDec 11th 2008
    Posted By: James Norton Good to know that my suspicions about £ insanity were correct. Have looked into it a bit more since posting I'm seeing common things in nearly all from the sub £1k to the '£insane'.

    Not just £, Euro too. I was quoted around 2600 Euro for units from Germany (Paul and also Innoair) both certified by the PHI. The more reasonably priced (sub 2000 Euros) were from Ubbink, Helios and Ventaxia.
    • CommentAuthorAdrianHunt
    • CommentTimeDec 11th 2008
    "posi-joists rather than I-joists..."

    That's partly why I've used Posis, but be careful if they're not all the same length, as the struts don't line up!
    Itho are near the top of the Sap q database, and don't seem as expensive as some, so I think they'll get my vote. (fairly soon before the plunging £ increases the price!)
    What are posi-joists? Why not just use engineered floor trusses? They have plenty of space to run pipes, ducts, wires and what have you. Plus they use less material then either regular joists or I-joists.

    Paul in Montreal.
    Posi joist
      Untitled-1 copy2.jpg
    Thanks James - they look like engineered trusses buy use metal webs between the top and bottom chords rather than wood. Lots of space for ducts and the like though!

    Paul in Montreal.
    Posted By: Paul in MontrealLots of space for ducts and the like though!

    Pre-cisely ! :smile:

    Are posi-joists much more expensive than a solid wood joist sized to take the same loading?
    I am interested in getting more headroom on the ground floor by using more joists of a smaller size and I like the idea of being able to run services through the Posi-Joists.
    Can they be cut to length or do you need to get them manufactured the length you want? (uneven stone walls)
    Oops, just had a quick google and they have trimmable ends! thats one question answered.
    • CommentAuthorandy500
    • CommentTimeDec 12th 2008
    I fitted ours to an existing house (with first floor completely in bits at the time tho').
    We have a Stork MHVR 90 (Greenwood/Starkey Systems in the UK) - DC motors, pullout filters, infinitely variable speed as DC but with three basic settings - each programmable as to extract and supply speeds etc, timer boost pullcords next to the showers. MHVR90 is dutch I think, seems well made compared to some of the plastic stuff I've seen at shows.
    Our original quote did have two of the main units, but they had one ex-display, removed from a show house, so we got just the one unit 'cheap', and it's perfectly fine, apart from some plaster spatters on the case. Two grand, for everything inc about 12 extract/supply terminals. I'm guessing installation would be a lot of £££, but it's not rocket science, as long as you have a design and plan to work to.
    I'd recommend the spiral wound rigid metal ducting - cut with an angle grinder, and all 90 degree/tee/jointing pieces have a rubber seal, so in theory you don't need duct tape (actually ally foil tape is best). Flexi-duct is supposedly noisier, can reduce airflow a bit due to lack of a smooth bore, plus if you are entertaining the possibility of having mice at some point...
    Ours is all rigid, then a foot or so of flexi to each ceiling outlet. Main in/out from outside to the main unit is flexi insulated with foil and rockwool - tricky to work with as it's so bulky, but stops condensation in the unheated loft void area.
    If I did it again, I'd do the underground air inlet - 20 degC air in summer and winter for free is too good to pass up on, and could be done with any system, provided underground access is feasible from the main unit.
    From a personal K.I.S.S viewpoint, I wouldn't get a unit with the rotating heat exchanger, no matter how efficient they claim it is - just looks a bit Heath Robinson, plus there's an extra motor and a drivebelt to go wrong.
    Overall, highly recommended, and there's not much I can say that about - no bathroom mould in existing mouldy bathroom at all in 2+ years, no open windows needed unless it's august and 30 degrees outside, no winter stuffiness (2 of us have asthma), no draughts, it's quiet (can *just* hear it in the bedroom at night, like a gentle breeze outside, unless it's on boost), and it sucks well on boost - bathroom mirror can stay clear even when the shower door is opened.
    Of the two you've pictured, ours is a 90 degree tilted version of type 1.
    • CommentAuthordocmartin
    • CommentTimeDec 14th 2008
    With regard to "heat exchangers are all basically the same"; I remember a post by Paul in Montreal about quoted surface areas of heat exchangers. Most manufacturers/ sales teams can't, or won't, supply this information. Paul in M gave examples that ranged from 17 to 50+ m2 surface area. waiting to hear from Itho about the surface area of the HRU4; when on the installation course initial indications that area is in the higher end of the range above.

    James, yes Appendix Q of SAP; I have yet to do my own installation and then my Daughter's. With the other aspects of my extensive refurb and 'new' garden, I will be overwhelmed till at least Summer 2010!
    • CommentTimeDec 15th 2008
    This is another type of system (declaration - I import this stype of system)

    I have posted this to highlight some an alternative approach to the mono-box solution as these systems are compromised for convenience

    Important features of a modular approach are:

    Dedicated duct to each room - easier to balance, less noise cross transfer and lower air speeds
    Ability to swap fan units (easy maintenence and introduction of new technology)
    LARGE heat exchanger - big cross section, big surface area and lower air speeds.

    Lower air speeds are very very important as this sifnificantly reduces air resistance throughout the system leadin to very low power fans being required

    Low air speeds over the heat exchanger also allow it to work in-situ rather than just in a laboratory...
      hrv background.jpg

    So basically there's a fan in each if the little black and red boxes, which each serve one or two rooms? Low/mid/high price...?

    • CommentTimeDec 15th 2008 edited
    Costs - 1500-3000 for one-offs (one to two systems - large homes, say 350+ are often better split into zones as the ducting gets ridiculous)
    For high volumes we can get under £100 including ducting (largest site is 45 systems)

    The answer to the original question is:
    If Designers included HRV provision from day one and builders khew how to install it then I would not have to inlcude design and support costs - the systems would then become off the shelf items.
    At the moment though - most systems are badly designed and badly installed - we inspect systems on a regular basis when we perform air tightness testing.

    - We have measued 90% efficiency on this system in-situ.

    - I have also tested lots of diffenret ducitng options on a BS EN compliant test rig (not jus the the BRE standard configuration), so I do know what happens when you move away form Part Q.

    - PVC flexible ducting should be banned.
    - Semi rigid Aluminium works very well and has a fire rating
    - A tight bend is equivalent to approx. 6m of straight duct in terms or reducing measured air flow
    - Flat channel ducing does not (on our tests!) provide the equivalent air flows claimed.

    For small units (mainly flats) I do specify other manufacturers system and I have also specified different systems in the same large house, being carefull to balance each zone

    This image may be slightly clearer
    - The red fan (and ductng) is extracting from wet rooms (Kitchen, Bathroom and a WC in the entrace area) and on to the heat exchanger
    - The blue fan supplies cold air to the heat exchanger
    - The green distribution unit (no fan) and ducts feed air to the living rooms.
    - Ducting runs are underneath insulation (at least 150mmm)
    - The gray ducting is insulated.
      Plot 4 plan 2.jpg
    • CommentAuthorTuna
    • CommentTimeJan 23rd 2009
    Just to ressurrect an old thread, has anyone come across the Vortice Prometoe? Looks like a nice unit, well designed, wireless remote and apparently efficient - at an apparently good price..

    • CommentAuthorTuna
    • CommentTimeOct 28th 2009
    Yes, bought it and have it partially installed. Does seem to be good kit, but won't know for another month or so - connections to outside and power have yet to be applied.

    One thing I will say is that these are big units and the arrangement of ducts near the unit takes a lot of space. The inlets and outlets to the unit are never quite in the order or position you want them in. Nothing insurmountable, particularly if you have them in loft space, but for smaller houses or room in roof designs where the unit is 'inside' the occupied envelope, it's something you have to allow for. This isn't a criticism specific to the Prometeo unit, but something worth noting.

    In our case, it would have helped to have a much bigger utility room or separate machine room downstairs to accommodate thermal store, vent unit and so on - another 4 sqm at least.
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