MVHR Decisions...what to do?

[Thorfun]

Hi all,

We're at the stage with our building control/timber frame design drawings where we could really do with an MVHR design. We're building a large house with a basement and a room above a double garage. total internal floor area is approx. 450m2 (including the double garage, so about 405m2 habitable space). I have roughly calculated the volume to be 1150m3 (we have a high vaulted entrance hall, and the room above the garage is also vaulted and our basement has 2.9m high ceilings) and using the resources I've found on here and from the reading I've done I've calculated that I need a max flow rate of approx 440m3/h.

 

Sizing Decision

I have received multiple quotes, all but one have come back with a 2 x unit system which I really want to avoid. None of those have given any calculations to prove that a single unit cannot deliver what is required. The one quote that came back (from PaulScotland) with a single unit design also gave calculations which I've put below and shows that I'm not a million miles off on my initial calculations and that I've over specified my requirements if their calculations are to be believed.

 

 

They have suggested a Zehnder Comfoair Q600 (https://www.bpcventilation.com/zehnder-600-unit) which seems to fit the bill. one of the 2 unit quotes specified 2 x Q350 units and when questioned about using a single Q600 the response was (in red):

 

"1. You’ve calculated that the boosted ventilation rate is 510m3/h. Is there a specific reason you didn’t specify the Zehnder Q600 model that can deliver 600m3/hr in one unit rather that 2 separate units? The Q600 isn’t large enough, as the fan duty would be at 85% at boost – this is against Zehnder’s own guidelines. At a push we could do it, as we design to very low pressure drop, but I’d prefer to lower the fan duty."

 

They didn't tell me how they got to 510m3/h either (and also said that the total floor area was 470m2 so not sure how they got to that unless they included our sunken courtyard) and that is way more than my calculations and PaulScotland's.

 

Anyway, first decision that I need help with is, do you think that the single unit will be enough and should I trust the one company pushing a single unit or the 4 other companies pushing a 2 unit system? and does the response to my question in red above hold water?

 

Design Decision

 

now I also need to make a decision on how to/who to design the system and the duct runs and positions. 

 

a couple of the quotes came back with individual costings for design work. one at £650 (PaulScotland) and the other at £1100 (Enhabit)! is it really that hard to design that it can cost that much? I'm tempted to design it myself but I'm concerned about making a mistake as it won't be something that's easy to fix afterwards if I do. would it be worth paying someone to design the system so then at least if it doesn't work as designed I have someone to go back to? but then, if I fit it myself to their design they could just say it was installation error as I didn't get them to design it?

 

for those members who have designed their own MVHR system, what software did you use? was the effort worth the saving or was it a time consuming nightmare that would be best left to the professionals? I am tempted to pay for the design and then buy the materials and fit it myself so I can spend some of the savings from fitting on the design. but I'm just unsure.

 

Cooling Decision

 

I have made a decision on this one (thanks to all those others that contributed on the various other threads on this subject) and have decided that I will run pipes from the ASHP to the MVHR unit and cap them off. then if after a year or so of living in the house our external shading isn't stopping solar gain sufficiently I will have the option to install a duct cooler/fan coil type unit at that point.

 

Unit Decision

 

Now, if the single unit is feasible and a 600m3/h unit will do the job then I have to decide what unit to get. the Zehnder one looks good but then the Vent Axia Sentinel Kinetic High Flow unit might also suffice. (https://www.bpcventilation.com/vent-axia-kinetic-highflow-r-h). But then there are also the Komfovent R-700 units which are a bit bigger so might be better as they would give a bit more headroom (https://www.bpcventilation.com/domekt-r-700-v).

 

Anyone got any recommendations for a unit of the size I require or are they all pretty much on an even keel? the unit will be in the plant room in the basement so I'm not overly concerned about noise but our plant room is 1.2m x 3.1m so size could be an issue as we would need to fit the DHW, UFH and other hardware in there (although we do have a separate 'comms' room for networking, automation, electricity equipment etc).

 

 

Sorry about the length of this post and I hope that the lovely folk on this forum can give me some advice on the decisions that I need to make.

 

 

[Conor]

You will need two units. The building control requirement of 0.3 ACH is the absolute minimum you want to work at and those units will be running at high speed to meet that. You really want to run at 0.5 ach and have the fan speed curve in the middle of the range, so there's the capacity for decent boost rate. so you'll need a much higher capacity unit. I'm just under 300m² gross floor area and borderline if I can get away with just one unit- looking at the zehnder Q600 and komfobent 700.

[Thorfun]

16 minutes ago, Conor said:

You will need two units. The building control requirement of 0.3 ACH is the absolute minimum you want to work at and those units will be running at high speed to meet that. You really want to run at 0.5 ach and have the fan speed curve in the middle of the range, so there's the capacity for decent boost rate. so you'll need a much higher capacity unit. I'm just under 300m² gross floor area and borderline if I can get away with just one unit- looking at the zehnder Q600 and komfobent 700.

but 0.3ACH for 1150m3 = 345m3/h, right? and on the Q600 specifications it shows a flow rate of 350m3/h @ 100Pa is in the recommended working point (unless I'm reading that chart all wrong that is! which is possible, I did get an 'E' in my A-level physics).

 

 

and then the Komfovent R-700 has an even higher flow capacity. maybe if I insist on having a single unit I need to look at commercial units?

[Thorfun]

I've just realised that the PaulScotland calculations don't include the room above the garage which is 7m x 7.4m (approx) and contains a shower room and vaulted ceiling. I will go back to them and ask why they excluded those rooms as that could make the difference on their calculations.

[Dan F]

We have 310m2 and a caclulated boost rate of 370m3/h and will be using the Q600.  My understanding is that the Q600 is good up to around a 460m3/h boost rate.

 

If you need an even larger unit there is this model:  https://www.bpcventilation.com/airflow-adroit-dv245 (930m3/hr!)

 

(I personally would favour one unit over two..)

Edited August 18, 2020 by Dan F

[Thorfun]

1 hour ago, Dan F said:

We have 310m2 and a caclulated boost rate of 370m3/h and will be using the Q600.  My understanding is that the Q600 is good up to around a 460m3/h boost rate.

you'll have no issues with the Q600 from what I can tell. it does state that it's max ventilation rate is 600m3/h but maybe above 460m3/h it becomes too inefficient?

 

1 hour ago, Dan F said:

If you need an even larger unit there is this model:  https://www.bpcventilation.com/airflow-adroit-dv245 (930m3/hr!)

that's a beast of a machine, and around the same sort of size and cost as the commercial ones on the BPC website. e.g. https://www.bpcventilation.com/freetime-smart-zone-1500 which is 1500m3/h @ 200Pa but I'm not clever enough to know what difference that figure @200Pa makes over the domestic figures quotes @ 100Pa.

 

1 hour ago, Dan F said:

(I personally would favour one unit over two..)

great minds think alike. ? 

[dpmiller]

have you tried BPC for a design quote?

[Nickfromwales]

I've just sepcified 2x Brink 325's where a 400 would 'just about do it', but the difference in strangling the ducts back to one unit would make for a less-than-pleasant-to-live-with solution. Instead I opted for 2 parallel setups strategically sharing the whole house config and then the ducts to atmosphere ( 160mm for the 325's ) will be T'd together to give 2x 180mm ducts to atmosphere. One is set to be at 60% duty and the other to 40% so I know there's ample headroom for efficient boost ( still not maxing the units out ) and the system will be very quiet in operation to boot. The issue about 1 big FO unit being run to the hilt is noise ( audibility at the terminals to be precise ) so decide if you can deal with noise in the bedrooms and whether or not that was a wise decision....

[Thorfun]

17 minutes ago, dpmiller said:

have you tried BPC for a design quote?

yes. gave me 3 options all of which were 2 x unit designs.

[Nickfromwales]

3 minutes ago, Thorfun said:

yes. gave me 3 options all of which were 2 x unit designs.

Writing.................................................wall...

[Thorfun]

4 minutes ago, Nickfromwales said:

I've just sepcified 2x Brink 325's where a 400 would 'just about do it', but the difference in strangling the ducts back to one unit would make for a less-than-pleasant-to-live-with solution. Instead I opted for 2 parallel setups strategically sharing the whole house config and then the ducts to atmosphere ( 160mm for the 325's ) will be T'd together to give 2x 180mm ducts to atmosphere. One is set to be at 60% duty and the other to 40% so I know there's ample headroom for efficient boost ( still not maxing the units out ) and the system will be very quiet in operation to boot. The issue about 1 big FO unit being run to the hilt is noise ( audibility at the terminals to be precise ) so decide if you can deal with noise in the bedrooms and whether or not that was a wise decision....

Hi @Nickfromwales. thanks for this and I definitely don't want noisy MVHR in the bedrooms, or any rooms tbh, but....on a normal flow rate on the Q600 would the noise be perceptible? it's not like the Q600 will be maxed out at that level of ventilation?

[Thorfun]

Just now, Nickfromwales said:

Writing.................................................wall...

true and that's why I keep researching. but Enhabit have said they 'could' make the Q600 work and Paul have said the Q600 is fine. Both are reputable MVHR companies, right? BPC and a local company have specified 2 x units. I'm still waiting for CVC to get back to me with what they think.

 

I'm just concerned about balancing 2 x units, plus the maintenance of 2 x units, running of 2 x units etc will be more than a single unit. true or not?

[Nickfromwales]

1 minute ago, Thorfun said:

true and that's why I keep researching. but Enhabit have said they 'could' make the Q600 work and Paul have said the Q600 is fine. Both are reputable MVHR companies, right? BPC and a local company have specified 2 x units. I'm still waiting for CVC to get back to me with what they think.

 

I'm just concerned about balancing 2 x units, plus the maintenance of 2 x units, running of 2 x units etc will be more than a single unit. true or not?

Depends on a well thought out design, and I know the Brink ( which Nick @ CVC will likely suggest ) can run as a balanced, harmonised pair to keep the entire system at equilibrium.

[Thorfun]

Just now, Nickfromwales said:

Depends on a well thought out design, and I know the Brink ( which Nick @ CVC will likely suggest ) can run as a balanced, harmonised pair to keep the entire system at equilibrium.

ok. thanks. I really appreciate your input and I will await a response from CVC before making a decision.

[Dan F]

5 minutes ago, Thorfun said:

ok. thanks. I really appreciate your input and I will await a response from CVC before making a decision.

 

You could also request a quote from GBS (green building store).

[Nickfromwales]

Just don't ask EsaveP..... Harold could fall into a bucket of tits and come out sucking his thumb  

[Thorfun]

7 minutes ago, Dan F said:

 

You could also request a quote from GBS (green building store).

I’ve already had a quote from Enhabit. I thought they were one and the same since the merger?

[Thorfun]

9 minutes ago, Nickfromwales said:

Just don't ask EsaveP..... Harold could fall into a bucket of tits and come out sucking his thumb  

But there’s a photo of David Cameron on their website. Surely that’s a top notch endorsement right there! 

Edited August 18, 2020 by Thorfun
Added emoticon in case people thought I was serious

[Nickfromwales]

1 minute ago, Thorfun said:

But there’s a photo of David Cameron on their website. Surely that’s a top notch endorsement right there! 

Rearrange these letters to form an opinion;

 

fcunigk pisne's pssi pu, rberewy

[Mikey]

Hi @Thorfun, which MVHR unit did you go for in the end?!  Currently going through the same decision making exercise...!

 

 

[Thorfun]

1 hour ago, Mikey said:

Hi @Thorfun, which MVHR unit did you go for in the end?!  Currently going through the same decision making exercise...!

 

 

Zehnder Q600. i didn't want 2 x smaller units and so the company i was using made the Q600 work with regards to flow rates by using 92mm ducting.

[LionessHeart]

@Thorfun - can I ask who you eventually got to do the design of your MVHR? And, if you had someone install it for you (we'll be building in Kent, not too too far from you). Thank you!

[Thorfun]

13 minutes ago, LionessHeart said:

@Thorfun - can I ask who you eventually got to do the design of your MVHR? And, if you had someone install it for you (we'll be building in Kent, not too too far from you). Thank you!

i initially used Enhabit to design our MVHR system but they eventually merged with Green Building Store and the guy that designed it ended up moving to GBS and they took over design and delivery of materials. they also sent someone to install. a great team who were really personable and did, from what i can tell, a great job. i'm sure they'd be worth a shout if you're just looking for an installer. https://www.facebook.com/apexventilation/ . ask for Ben. 🙂

[LionessHeart]

Thank you for that!

 

So you got your MVHR (designed, supplied, installed and commissioned) by the Green Building Store?  As it happens, I'm speaking to GBS about our ASHP, UFH and MVHR as well.... good to know you were happy with their service. Thanks again.

[Thorfun]

6 hours ago, LionessHeart said:

Thank you for that!

 

So you got your MVHR (designed, supplied, installed and commissioned) by the Green Building Store?  As it happens, I'm speaking to GBS about our ASHP, UFH and MVHR as well.... good to know you were happy with their service. Thanks again.

Well, not exactly what I said. It was designed and supplied by Enhabit and GBS took over when they merged with/took over Enhabit. The installers were arranged by GBS but they’re an independent sub contractor. it’s not been commissioned yet as we’re not finished.