MVHR Sizing - please check my calcs!

[Conor]

Budget and practical issues now dictate I'll have to settle for a single large MVHR instead of two medium sized ones.

 

The largest Passive House certified (bonus, not a must) is the Zenhder Q600 - capable of up to 600m3/hr at 200pa.

 

https://www.zehnder.co.uk/ventilation-units/heat-recovery-centralised/units-smaller-800-m3h/zehnder-comfoair-q600-st

 

First stupid question - is this  300m3 on inlet and 300m3 on outlet at the same time? Or can it be biased to extract? I can't seem to find that info on the unit.

 

Second, I've calculated my required "normal" extract and supply rates based on the Passive House design guide that gives typical nominal rates for each type and size of room. They then say 33% increase from this figure for boost, and 33% reduction for minimum flow rates. I've also done a sense check against the building control requirement on 0.3ACH. 

 

Is there anything I've missed? I can't quite figure out what flow rate capability I need...

 

 

Edit: I can greatly reduce the extraction requirements - I've planned two 60m3/hr extracts in the kitchen, this can be reduced to one, and a extract in the vaulted hallway as I think it'll gather a lot of warm air and any smells that escape the kitchen through the mezzanine.

Edited October 8, 2020 by Conor

[Thorfun]

I'm sorry I can't help with your questions, but can only tell you what we're planning. we're having the Q600 and are building a basement and two above ground floors for a total of about 440m2. We're using Enhabit to do the design and calculations as I didn't want to make a mistake on it and their price was really quite good for the equipment and so I thought the design fee was acceptable seeing as the total price wasn't much more than I could've bought the equipment myself online!

 

When I was getting quotes I had 2 companies recommend the Q600 and both of them suggested using the larger 90mm ducts to get the air flow required at lower rates and this is what is currently being designed for us by Enhabit.

 

So, maybe you could consider that to assist with your flow rates?

 

like I said, probably not much help but thought I'd comment just in case it does help.

[Conor]

Thanks @Thorfun, I'm thinking along those lines as well. I'm firing off an email to Paul heat recovery, they seem to have the best price on the Q600. I think they charge a £600 design fee that is then mostly deducted from the final bill if they supply the whole system. I'll check out Enhabit as well.

[Thorfun]

Just now, Conor said:

Thanks @Thorfun, I'm thinking along those lines as well. I'm firing off an email to Paul heat recovery, they seem to have the best price on the Q600. I think they charge a £600 design fee that is then mostly deducted from the final bill if they supply the whole system. I'll check out Enhabit as well.

Paul were cheaper on the design fee but more expensive on the unit as the price for the unit on the website is not available if you have them do the design as they include an extra on top for the 'journey' that you'll take together with them and for ongoing support. their website price is just for people who want to do it all themselves.

 

I had both Paul and Enhabit quote and there wasn't a lot between them. in the end, for me it came down to Enhabit being more local to me (London as opposed to Scotland) and I had some really good chats with the guy on the phone and they reduced the design fee quite a bit. Plus they also do ASHP, Solar PV and other bits so I thought that if I went with them then I could maybe get them involved in the other aspects of the build that I'd need help with. I am sure I would've been happy with Paul though if I'd chosen them.

[Thorfun]

all of the above is with the caveat that I haven't actually had the design finished yet nor received any components etc. so my opinion of Enhabit could always change as we progress with it all. 

[Dan F]

23 minutes ago, Thorfun said:

all of the above is with the caveat that I haven't actually had the design finished yet nor received any components etc. so my opinion of Enhabit could always change as we progress with it all. 

 

We've had design by enhabit and happy with the service so far. They are also doing supply and commisioning (but not install).  We also found them to be cheaper than Paul.  Only thing we've noticed is that some of the ducting equipment is other brands and not just Zehnder, so may that be one way they keep their prices low.  Not saying this is an issue though...  (ublink + fitt)

 

Design has be comprehensive and included flow-rates (based on building regs + PH), 3D design and drawings, interaction with frame desginer, advice on gaps needed below each door etc.

 

 

Edited October 8, 2020 by Dan F

[Thorfun]

15 minutes ago, Dan F said:

 

We've had design by enhabit and happy with the service so far. They are also doing supply and commisioning (but not install).  We also found them to be cheaper than Paul.  Only think we've noticed is that some of the ducting equipment is other brands and not just Zehnder, so may that be one way they keep their prices low.  Not saying this is an issue though...  (ublink

 

Design has be comprehensive and included flow-rates (based on building regs + PH), 3D design and drawings, interaction with frame desginer, advice on gaps needed below each door etc.

 

 

supply and commissioning only here as well. our quote states "Zehnder's ComfoTube ducting system" so if we don't get the Zehnder stuff I will see at the time if there's cause for concern.

 

we've had to go for 4 manifolds though, 2 for the basement and then 2 for the above ground rooms. this will apparently help with fitting the 90mm ducts through the service void I have designed as we can send the larger duct from the MVHR unit through the service void to the manifolds above rather than running 15 x 90mm ducts. as well as other reasons that I was told and don't fully understand. I think it had something to do with pressure or air loss in the large manifold? and by having smaller manifolds it will make the system more efficient. something like that. anyway, it's not costing me more so I'm happy to go with their recommendations. ?

[Dan F]

8 minutes ago, Thorfun said:

supply and commissioning only here as well. our quote states "Zehnder's ComfoTube ducting system" so if we don't get the Zehnder stuff I will see at the time if there's cause for concern.

Ours too. But in the intro, rather than the itemized part.

 

To be fair the ublink ducting is needed for intake/exhaust as it's more flexible and will help ensure we can get these through joists.   Although they did supply the same for MVHR<->Manifold internally too.

 

For the internal ducting a initial 50m of a  https://agix.fitt.com/ product has been delivered so far.  Nothing to make me think that it's any worse than the Zehnder stuff, although it has come damaged..

 

 

[Thorfun]

37 minutes ago, Dan F said:

Ours too. But in the intro, rather than the itemized part.

 

To be fair the ublink ducting is needed for intake/exhaust as it's more flexible and will help ensure we can get these through joists.   Although they did supply the same for MVHR<->Manifold internally too.

 

For the internal ducting a initial 50m of a  https://agix.fitt.com/ product has been delivered so far.  Nothing to make me think that it's any worse than the Zehnder stuff, although it has come damaged..

 

 

as long as it's the stuff that is antibacterial I'm sure they all do the same job!