Replacement MVHR central Unit - Confused !

[TimCx]

Hello all, I have read many of the threads in this forum but I still have a couple of questions !

 

I am having to replace my MVHR central unit as it has failed. The house has a floor area of about 250m2 on 2 floors but is slightly unusual in that the living space is upstairs and the bedrooms etc are downstairs. The house is 11 years old and very well insulated but not passive. I will not be replacing the ducting just the central unit.

The MVHR unit currently installed was manufactured by a company called 'Ventalutior' but they ceased trading some time ago, I have very little information about the unit but it seems very small its 560 wide*500 tall*260 deep (mm) I have no flow rate information at all. The whole system was commissioned and signed off in 2011.

Upstairs the house has:

kitchen, lounge/diner, study, hallway and utility room (with extract vent) and 2 toilets. The kitchen has extract vent and also a separate cooker hood that is not connected to the MVHR system.

And downstairs:

5 bedrooms (1 with E/S) 2 separate bathrooms (one is shower only) a hallway and a plant room (which has an extract vent as we use it for drying clothes).

 

I am confused is sizing the replacement unit, going by the floor area and the required rates for the number of rooms I think I need a very large unit but the existing one is small. Maybe the regulations have changed a lot since 2011?

 

I have a few questions that I would appreciate some help with:

1) What size unit should I be looking at and how do I calculate this? I have seen the building regs but I am confused by the 0.3ls required for each m2 against the room rates, are there any tools that can help with this?

2) Can you recommend any good quality manufacturers for the replacement unit, Mitsubishi Lossnay and Vent Axia have been mentioned by a friend.
3) Is it worth paying to get a unit with humidity sensors and do they negate the need for boost switches (as in current system) for the bathrooms and utility room. 

4) Are there any 'must haves' for MVHR systems, the current unit has nothing but I would like to be able to monitor the new one on my computer if possible but this is not essential.

 

Thanks in advance

[Bonner]

Building regs have two measures, one for ‘wet’ rooms and one for whole house. Do the sums and see what comes out. As a guide, my place is 280m2 and I have installed a 350m3/hr unit but not tested or signed of yet! 

[PeterW]

19 hours ago, TimCx said:

What size unit should I be looking at and how do I calculate this? I have seen the building regs but I am confused by the 0.3ls required for each m2 against the room rates, are there any tools that can help with this?

Yes there is a spreadsheet somewhere on the forum - let me see if I can find it. The 0.3l/s only works as  a baseline figure, there are lots more minimum calcs you need for all the kitchens, WC, wet rooms etc

[TimCx]

35 minutes ago, PeterW said:

Yes there is a spreadsheet somewhere on the forum - let me see if I can find it. The 0.3l/s only works as  a baseline figure, there are lots more minimum calcs you need for all the kitchens, WC, wet rooms etc

Ah I did see mention of a spreadsheet but I didn't find it. Any links would be appreciated.

[JohnMo]

Use the attached will give you good starter for ten.

 

You need your floor area in m2 for a start.  Your flow into the house has to match the flow going out.

 

Your inlets and outlets are already in place, so an easy reference for number of inlets and outlets.  Inlet in dry rooms extract in wet rooms.  Boost rate at 20% above normal flow. Humidity sensors are ok, but you end having to change the settings for summer and winter.  So boost switch in wet rooms and kitchen are ok.

 

Size MVHR unit at 50-100% bigger than your flow required, so unit is running almost silently.

 

I have Titon MVHR units which seem ok.

 

[TimCx]

Thanks for the info.
I have now calculated the floor area and m3 for all rooms, my hallways and stairs do not have any vents but they account for about 25m2 of floorspace and about 75m3 of volume, I saw a comment somewhere that these areas are not included in calculations, does that mean they should be removed from all calculations or are they required in for example the 0.3ls m2 minimum for floor areas?

[JohnMo]

Hallways and corridors and stairs are part of the ventilated floor space, you may not supply air directly to these areas, but they have to be included.