MVHR install in renovated bungalow

[murr_walker]

Hello all, been doing some work on a possible DIY MVHR install in my bungalow in cornwall

 

I have done the calcs etc according to building regs & good practices guides 

 

 

See floorplan below but the building is an 1970's bungalow that has been extended & layout moved around to form 1 large open plan living/dining/kitchen - with the bedrooms & bathrooms in the 'old' part of the house 

 

We are suffering a bit with some mould in the bedrooms - including on interior wall between bedrooms - which suggests it not an insulation issue - i have checked the building for thermal bridges etc and sorted some insulation in the loft - there is good extraction in the bathr

 

My plan is to install a MVHR system to get some air moving in the 'old' part of the house - the front door and 'back' door (bifold door) are in the new part of the house so we have plenty air flow through there with the people coming and going and door open for the dog etc - also as this is where we spend all of our time this part is always warm especially with wood burner (it has its own air supply)

 

MVHR unit will be installed in loft with combined intake/exhaust fitted in North gable wall - radial system fitted in loft for 4 off supply & extracts - all insulated 

 

Extract - kitchen, bathroom, utility, show room     Supply - 3 bedrooms & dinning area 

 

 

 

Looking at a Nuaire Eco 2 - expect to be approx. 55% on trickle & 65% on boost - giving a excess of up to 35% for purge if required 

 

 

 

Appreciate it anyone has any comments of if i have made any glaring errors 

 

thanks!

 

 

 

 

 

 

 

 

 

 

 

[Iceverge]

18 minutes ago, murr_walker said:

Looking at a Nuaire Eco 2 - expect to be approx. 55% on trickle & 65% on boost - giving a excess of up to 35% for purge if required 

 

This might be noisy at 55%. 

 

I'd buy a bigger unit. 30% at trickle is plenty.  No experience of Nuaire. Have you priced filters? Some brands can be expensive. 

 

 

[jayc89]

6 minutes ago, Iceverge said:

 

This might be noisy at 55%. 

 

I'd buy a bigger unit. 30% at trickle is plenty.  No experience of Nuaire. Have you priced filters? Some brands can be expensive. 

 

 

 

So for a 126m3/h house it's best to look for a unit that can support 420m3/h? Which means it runs ~ 30% capacity on trickle? 

[murr_walker]

3 hours ago, Iceverge said:

 

This might be noisy at 55%. 

 

I'd buy a bigger unit. 30% at trickle is plenty.  No experience of Nuaire. Have you priced filters? Some brands can be expensive. 

 

 

thanks for the input _ i should add that the % was worked out at 150pa - i havent yet made any estimates on what the pressure will be 

 

Nuaie eco 2 rated - 

• Airflow performance (high) 324m3/h  90l/s

 

[JohnMo]

A useful table and comparison for different ways to calculate flow rates.

 

Notice you have different flows rate totals for supply and extract, these should be the same (the higher of the two rates), so the house pressure is balanced.  Extracting more than you supply will lead to smoke from your fire coming into the room each time you open the door, or even the flue leaking into the house.  Carbon monoxide leaks can and do kill.

 

You mention only 4 supply, what about the office?

 

If the other two bedrooms are doubles the flow rate needs to be about 11 l/s in those also.

 

Calculate all the flow rates for each room, before you start, then you can do the pressure drop and velocity calcs, to ensure you have enough duct runs to each terminal and size the MVHR unit correctly.

 

 

[murr_walker]

2 hours ago, JohnMo said:

A useful table and comparison for different ways to calculate flow rates.

 

Notice you have different flows rate totals for supply and extract, these should be the same (the higher of the two rates), so the house pressure is balanced.  Extracting more than you supply will lead to smoke from your fire coming into the room each time you open the door, or even the flue leaking into the house.  Carbon monoxide leaks can and do kill.

 

You mention only 4 supply, what about the office?

 

If the other two bedrooms are doubles the flow rate needs to be about 11 l/s in those also.

 

Calculate all the flow rates for each room, before you start, then you can do the pressure drop and velocity calcs, to ensure you have enough duct runs to each terminal and size the MVHR unit correctly.

 

 

 

thanks for the reply, yep i have seen this table - the higher value is is the extract which is on boost and the lower is supply (same as boost when unit isnt in trickle mode)

 

The room labelled office has actually become a store so not a 'habitable' room 

 

The house is 3 people therefore 1 double - 1 single & 1 spare - taking the spare as a single then we are at 33l/s 

 

 

 

My system based on

 

F regs - 3bedrooms 4 people (1 more person that we normally have ) - supply 21 l/s (as above table) or on floor area 29l/s or table 1.3 3 bedroom 31/l/s

Passive house - 3 people - 25 l/s

 

so i have taken my figures as trickle - 31l/s supply & extract  - boost 35l/s supply & extract - is this correct?  they are only different as one is trickle & one is boost 

 

 

does anyone know of a calculator tool to work out flow velocities? - i worked this out but very small numbers, need to review my formulas - aiming for 1-2 m/s in each room 

 

 

 

[JohnMo]

Boost would normally be 25% of trickle rate.

 

Just calculate the internal area, and use below

 

https://www.sensorsone.com/volume-flow-and-area-to-flow-velocity-calculator/

[murr_walker]

1 hour ago, JohnMo said:

Boost would normally be 25% of trickle rate.

 

Just calculate the internal area, and use below

 

https://www.sensorsone.com/volume-flow-and-area-to-flow-velocity-calculator/

boost 25 % of trickle? or 25% higher that trickle?  sorry sturggling with this

 

thanks for the calcualtor - double checked my maths with it and found the error in my forumala - stupid units!

[JohnMo]

25% higher that trickle.

 

 

[murr_walker]

 

from regs my supply (trickle) should be 29 l/s based on area - 31 l/s based on no of bed rooms - extract (boost) should be 35l/s based on wet rooms 

 

therefore my boost should be 13% higher that trickle (35/31 x100 = 112.9%)

 

there is no other way to calculate this as far as i am aware 

 

 

when system is on trickle the regs must be met for the supply sum of each room = 31l/s (ideally distributed sensibly)   - the extract fan speed should be set to match within prob 5% the same sum extract rate (so the air in = air out)

 

when the system is on boost the regs must be met for each extract room (they must match the requirements for each rooms & therefore the sum above)  - the supply fan speed should also be set to match as above 

 

 

correct? 

 

 

[murr_walker]

32 minutes ago, murr_walker said:

 

from regs my supply (trickle) should be 29 l/s based on area - 31 l/s based on no of bed rooms - extract (boost) should be 35l/s based on wet rooms 

 

therefore my boost should be 13% higher that trickle (35/31 x100 = 112.9%)

 

there is no other way to calculate this as far as i am aware 

 

 

when system is on trickle the regs must be met for the supply sum of each room = 31l/s (ideally distributed sensibly)   - the extract fan speed should be set to match within prob 5% the same sum extract rate (so the air in = air out)

 

when the system is on boost the regs must be met for each extract room (they must match the requirements for each rooms & therefore the sum above)  - the supply fan speed should also be set to match as above 

 

 

correct? 

 

 

correction to above extract should be 37 - therefore 37/31*100 = 20%