Single Room MVHR

[Onoff]

The time has come!

 

Currently I have no ventilation in the bathroom other than the window. 

 

The original plan was to use a wall mounted, single room Ventaxia but tbh I think they are bloody ugly!

 

 

It was @Ferdinand's recent thread that put me onto one of these:

 

 

I can mount this up in the loft which is pretty much a blank canvas. But where to put the vents as in there are 4. There's two go outside as I understand it and I guess they just have to be a certain distance apart. Planning those in the soffit.

 

But the two inside???

 

In the interests of keeping some symmetry I was thinking maybe one vent where the green Post-It is high up on the wall behind the rainfall head. It'd go through that tile into the void behind the mitred corner then up through the ceiling to the unit in the loft. I fancy the challenge!

 

 

Then the 4th vent, maybe in the ceiling outside the bathroom, again where the green Post-it is? This room is next to be gutted much as bathroom was, as in ceiling replaced,  floor dug down etc:

 

 

(Temporary bathroom door btw).

 

Or inside the bathroom?

 

 

Big question, the MVHR unit and pipes in the loft: The loft is cold and uninsulated. Do the unit and ducts need to be "lagged"?

 

Thanks

Edited April 10, 2019 by Onoff

[Carrerahill]

I am going to be doing exactly what you describe above, my plan is to return the warm fresh air into the loft bedroom or the upstairs hall - it is my understanding that having only the extract in the bathroom this will negatively pressurise it, drawing air in from the hall and thus ensuring that the bathroom air is being circulated, if you put the return into a smallish room like that you are going to create a fairly balanced situation and the extract side of the system may not be as efficient.

 

You also then get the benefit of the warm air returning into the house freshly somewhere you might actually want it.

 

I am going to do a kitchen unit and a bathroom unit.

 

 

Edited April 10, 2019 by Carrerahill

[Ferdinand]

@Onoff

 

It seems to be a really complicated way to deal with ventilation for a single bathroom. ?

 

An alternative .. if the problem is an ugly unit with the through the wall one ... is to just put it in a small cupboard with a louvred door, as I did with one of mine.

 

That will save you at least 4 pipes, and a half-octopus in the loft.

 

Or would that not fit in with the design? ?

 

Ferdinand

 

 

 

 

 

[Onoff]

1 hour ago, Ferdinand said:

half-octopus in the loft.

 

?

 

In the cupboard...I'm listening. We have a cupboard though it's on two internal walls. What sort of unit were you thinking?

 

Would it mean a long 4" pipe out to the soffit?

 

Rather than a louvre door how about a vent in one of those tiles above the door? Or the top full tile above the loo on the cupboard side?

 

 

 

 

(Tbh I'd still rather make than buy!)

[Ferdinand]

2 hours ago, Onoff said:

half-octopus

 

Indeed. It is in the mind as I am having a third of half of an octopus for tea, having had the other two-thirds of the half with a friend the other week.

 

It is all the fault of the octopus sellers of Whitstable, who refuse to deal in portions smaller than a semi-Octopus, which do not work for individual light lunches. Given the musicality of Canterbury Cathedral, they should at least be familiar with demi-semi-quavers, and therefore be willing to sell me a demi-semi-octopus ie one tentacle. plus a slice of mantle. Alas, not.

 

Tasty octopus, though.

 

3 hours ago, Onoff said:

I'm listening.

 

I was referring to the first unit you display, which is a through-the-wall item ie one 100mm hole, and you think is plug-ugly. The first one I installed back in 2012 put into a backless cupboard carcase with a louvred wooden door and mounted slightly off the wall. and was therefore invisible. 

 

That might be less trouble than a cephalopod in your loft.

 

But it would require an external wall, which may be scarce.

 

Ferdinand

 

 

 

 

 

 

 

[Ed Davies]

7 hours ago, Onoff said:

In the interests of keeping some symmetry I was thinking maybe one vent where the green Post-It is high up on the wall behind the rainfall head. It'd go through that tile into the void behind the mitred corner then up through the ceiling to the unit in the loft. I fancy the challenge!

 

Wouldn't it be less of a challenge to just put it in the ceiling, above the Post-It or maybe a bit further away from the shower head?

[Onoff]

4 minutes ago, Ed Davies said:

less of a challenge

 

Where's the fun in that? ?

 

 

[Onoff]

Well fair play to Susan ?:

 

https://www.gumtree.com/p/plumbing-central-heating/heat-recovery-unit-fully-working-home-made-unit-size-80cm-x-70cm-x-33cm/1336403114

[ProDave]

1 hour ago, Onoff said:

Well fair play to Susan ?:

 

https://www.gumtree.com/p/plumbing-central-heating/heat-recovery-unit-fully-working-home-made-unit-size-80cm-x-70cm-x-33cm/1336403114

Well that's basically all that is at the heart of my Mitsubishi unit.

[Onoff]

2 hours ago, ProDave said:

Well that's basically all that is at the heart of my Mitsubishi unit.

 

Shouldn't there be a condensate drain somewhere on the diy one?

 

What would improve the efficiency or is the Correx heat exchanger the limiting factor? Would encasing in pir improve efficiency?

[ProDave]

7 hours ago, Onoff said:

 

Shouldn't there be a condensate drain somewhere on the diy one?

 

What would improve the efficiency or is the Correx heat exchanger the limiting factor? Would encasing in pir improve efficiency?

The Kingspan / Mitsubishi Lossnay units like mine don't have a condensate drain.  Just a core similar to that made of waxed paper, and some fans. The case is mostly lined inside with polystyrene mouldings to give a smooth airflow path around the various components.

 

I don't know how it manages when just about every other mvhr does have a condensate drain but it doesn't fill up with condensation.

[Ed Davies]

9 hours ago, Onoff said:

What would improve the efficiency or is the Correx heat exchanger the limiting factor?

 

I doubt that the Correx is the limiting factor. Slightly surprisingly, with any reasonable heat exchanger design it's the boundary layer resistances between the air and the exchanger material which dominates; the thermal resistance of the material itself makes very little difference. Some numbers.

[Onoff]

Keen to build a DIY, single room heat exchanger based upon beer cans running through plastic pipe. 

 

It'll be based on this:

 

https://www.instructables.com/id/Air-heat-exchanger-Made-from-soda-cans-and-pvc-pip/

 

The article reckons cans inside 70mm dia pvc pipe.

 

I assume 110mm soil pipe would be too large/inefficient?

[Onoff]

Thinking on these lines:

 

 

With the hot, moist intake just behind the rainfall head:

 

 

[Onoff]

Glued together beer cans for the straight section then maybe some of this where it needs to pass through the branches. Needs the internal diameter to fit snug over a beer can:

 

[Onoff]

Some ventilation 101 please...

 

A 4" bathroom extract fan for instance extracts 15L/s through a 4" duct. There's no restriction per se.

 

First question, does the length of duct impact the efficiency of the extract?

 

The reasoning behind this question then: Taking the screen grab below of a DIY tubular heat exchanger:

 

 

Assuming the "Hot in" is the extract from the (in this case) bathroom, then to still achieve 15L/s would the extract fan need to be more powerful than normal as the surface area of the extract duct is compromised by the heat exchanger tube up the middle?

 

Hope that makes sense!

[ProDave]

Most axial bathroom fans are pathetic with a long run of pipe. you really need a centrifugal fan instead. Ceiling mounted ones tend to be bulky and ugly, so look for in line ones to go in the loft.

[PeterW]

That beer can heat exchanger will just cause condensation and will be about 3% efficient if that.....

 

Just extract the moist air and let the cool air feed in from under the door. 

[Onoff]

32 minutes ago, PeterW said:

That beer can heat exchanger will just cause condensation

 

Why such low efficiency?

[PeterW]

Because you have a tube ... that’s it ..!! Surface area of two tubes, laminar flow, thickness of material etc etc. There is just not enough flow to surface to get anything like any transfer of heat. 

[Onoff]

19 minutes ago, PeterW said:

Because you have a tube ... that’s it ..!! Surface area of two tubes, laminar flow, thickness of material etc etc. There is just not enough flow to surface to get anything like any transfer of heat. 

 

Understood. What if the tube assembly is much longer or are there then other losses?

[PeterW]

2 minutes ago, Onoff said:

 

Understood. What if the tube assembly is much longer or are there then other losses?

 

So.... to get the same surface area of a standard heat exchanger (40sqm) you would need a tube of around 210m long ........

 

I’d fit an ordinary extractor and move on ... 

[Onoff]

For now...my "for now" I'm going to fit a bog standard extractor and not worry about MVHR.

 

I'm still thinking to have the extractor where the green Post It note is, high up on the mitred corner:

 

 

A sparks mate has just fitted one of these. Tbh he went for is based purely on aesthetics. Looks good too to my mind having blue LEDs. Yes, a bit gimicky but it ticks my boxes!

 

 

https://www.ebay.co.uk/itm/Cata-E100GSTH-Grey-Glass-Vent-Extraction-Fan-100mm-With-Humidistat-Timer/272246942762?epid=1138908186&hash=item3f632eac2a:g:~EQAAOSw9VZXPEwX

 

Height wise I'm going to have to have a measure in relation to the rainfall head.

 

If then I punch a 100mm hole through that tile I'm into the "void" behind the mitred corner. Looking back the constrction is thus:

 

Battened and pir'd the walls:

 

 

Pre finsishing the insulation this is how the 3/4" ply goes in the corner:

 

 

There's this sort of a void then behind there:

 

 

The ply  then has the green vcl over it:

 

 

It's then Aqua Pannelled over and tiled:

 

 

If I put a hole through that mitre, into the void, and take flexible duct up through the ceiling in the loft, should I be worried about interstitial condensation forming in the void?

 

Will that vent position be so placed that I can use it later on if I fit MVHR?

 

(Yes it would be easier to stick it on the ceiling).

 

One other question, calcualting the fan size puts it in the mid 90s m3/hr so this fan at 115m3/hr appears OK. My room volume calc took into account the cupboard volume though wher the door will be always shut. Can I ignore the cupboard volume or should I take it into account? There's a nom 10mm gap underneath.

 

 

Cheer

Edited July 1, 2019 by Onoff

[PeterW]

5 minutes ago, Onoff said:

If I put a hole through that mitre, into the void, and take flexible duct up through the ceiling in the loft, should I be worried about interstitial condensation forming in the void?

 

No

 

Just fit it... CT1 (or cheap sealant if it’s coming out in the next 24 months) to the wall and be done with it, but bear in mind you should really have a fall on the duct to an outside vent so any condensation that forms inside runs to the outside not the inside. Bit of fibre insulation around the first part of the duct will help stop it initially. 

[Onoff]

6 minutes ago, PeterW said:

 

No

 

Just fit it... CT1 (or cheap sealant if it’s coming out in the next 24 months) to the wall and be done with it, but bear in mind you should really have a fall on the duct to an outside vent so any condensation that forms inside runs to the outside not the inside. Bit of fibre insulation around the first part of the duct will help stop it initially. 

 

Thanks. The duct will be in an up and over inverted U shape. Up through the ceiling into the loft somewhere NW of the rainfall head pipe. It'll then exit out over that wall plate to a soffit vent much as the soil pipe does. All will change again if I do gable ends instead of these hips:

 

 

Edited July 1, 2019 by Onoff