HRV Help - confused

hos

I know this has probably been asked a 1000 times before but we are trying to decide on a MHRV for your new build. It is very well insulated (near passive) & air tight (obviously) single storey. The house is very spread out with pitched roofs & vaulted ceilings in many rooms. I am getting totally confused with what size ducting to use, if we need additional manifolds & what unit or supplier to go with. There seems to be a large variation in cost but is the additional cost worth it. Could some one please PM if we are not to mention suppliers/brands here. Thanks.

Calahonda52

What exact stage is the build at?
Are you designing the system yourself?

The brands are not the issue here yet, we need to figure out is it too late to be even talking about this.
What did the interim Blower door test give as the interim airtightness?

hos

It a double timber frame & this part is nearly complete (at roofing stage). We need to decide on the system (type of ducting, at least) as we are putting in a services zone in the ceiling under the air tight membrane & our timber framer (its being stick built on site) wants to know the depth of this to allow for it. So we are miles away from a blower door test. We are not designing the system ourselves but are confused by all the different advice we are getting from each supplier we speak with. I was hoping some one here could advise me on good systems/reliable suppliers. The house is circa 2600 sq ft.

Calahonda52

What do you mean by double timber frame?
The volume of the house is a design requirement here, rather than just floor area.
Is the attic space above the ceiling outside the airtightness layer?

hos

Hi Calahonda 52,

We had a 100mm timber frame attached to another 100mm timber frame with 100mm space in the middle. Therefore we have 2 timber frames attached by 'ladder type' battens. This set up allows 300mm of cellulose insulation within the walls. Does this make sense? We got the following from one supplier some time back but the house has got slightly bigger since this:
Total floor area = 228m2 x 0.3 l/s = 68.4 l/s. Plus 5 wet rooms - 54 l/s
Volume required on occupancy setting = 68.4 l/s
Volume required on boost setting = 122.4l/s (68.4+ 54l/s) (440.64 m3/h)
There is no attic space. We have a mixture of flat & pitch roofs but are using the full volume of each space. Does this make it clearer?

Calahonda52

Yes, making sense now
So the unit will have to go somewhere, is it single storey?
How are you dealing with all the other services, is there a service cavity inside the internal timber frame.
http://www.housing.gov.ie/sites/default/files/migrated-files/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad%2C1647%2Cen.pdf
Page 18 onwards and the relevant Appendixes will keep you busy tonite.