Controlling MVHR boost

[MarkyP]

I'm planning an MVHR DIY installation in the months ahead, I'm in the process of insulating and flooring the loft conversion at the moment and thinking about what cables I might need to run for controls or switches to the ground floor rooms before the new chipboard floor goes down. It seems the main thing is boost activation when a "wet" room is in use. What is the best approach here? A manual boost switch on the wall? Have boost activated by the light being turned on (in bathrooms)? Or use no switches and instead employ a humidistat in the MVHR unit to trigger boost when humidity reaches a certain level? I like the idea of the latter assuming it would work reliably.

[ProDave]

It depends for a start on what mvhr unit you have and what provision it has for boost and / fan speed control.

 

My own I used immersion heater timer units (which switch  a relay next to the mvhr) so all I needed was a 3 core & earth 1mm cable from the relay box to each mvhr boost switch.

[MarkyP]

I've been looking vent-axia sentinel units which seem to offer a good degree of scope for speed control and boost either at the unit via a humidity sensor, from a wired or wireless controller, or via other external triggers such as light switches.

 

I guess what I'm getting at is why have a boost switch at all if unit or duct installed sensors can trigger boost at a programmed threshold for humidity? 

 

 

[le-cerveau]

I use RH sensors, I have 2 x Brink Renovent Excellent 400 Plus models one for Upstairs one for Downstairs with the options RH sensors fitted into the extract duct just before the unit.

 

The first diagram shows a weeks recordings of the downstairs unit and you can see my mum going into the shower each morning and the MVHR ramping up.

 

The second is an expansion of the first 24 hours:

 This works perfectly for me and allows me to run the system at a lower rate, it ramps up to the Building regs required extract rates. and still has more if required.

 

The house was over warm at this point and I have since corrected the temperature to a more norman 21^oC from 24^oC

Edited November 13, 2018 by le-cerveau

[Roundtuit]

23 hours ago, MarkyP said:

 

I guess what I'm getting at is why have a boost switch at all if unit or duct installed sensors can trigger boost at a programmed threshold for humidity? 

 

Because a humidity sensor can't detect a no. 2, and I think building control requires that you can activate ventilation to dispel odours in such circumstances!  We've put in manual boost switches, but they don't get used to be honest.  The integral humidity sensor in the unit seems pretty good at its job and boosts when showers are on, at a rate proportional to the level of humidity.   I had set a timer to boost for an hour in the mornings when showers where happening, but it really wasn't necessary so I turned it off.

[MarkyP]

7 minutes ago, Roundtuit said:

 

Because a humidity sensor can't detect a no. 2, and I think building control requires that you can activate ventilation to dispel odours in such circumstances!  We've put in manual boost switches, but they don't get used to be honest.  The integral humidity sensor in the unit seems pretty good at its job and boosts when showers are on, at a rate proportional to the level of humidity.   I had set a timer to boost for an hour in the mornings when showers where happening, but it really wasn't necessary so I turned it off.

you cant get a sulphur stat?! 

 

 

[le-cerveau]

9 hours ago, Roundtuit said:

Because a humidity sensor can't detect a no. 2

My MVHR is connected up to all the cisterns and extracts continuously from the bowl. as well as extract terminal(s) in WC wet rooms.