Fancy MVHR functions?

[puntloos]

1/ I'd love to extract hot air away from (&HRecover/reuse it, ideally), and cold, dry air onto 

  - Computer (electrical) cupboard

  - Ceiling mounted projector

  - Fridge/Freezer?

  - Gas fireplace (decorative mainly)

 

2/ I'd love to put dry, heated air into

  - Airing cupboard

  - Clothes storage.

 

3/ STRONG air in kitchen/garage in particular for fire/smoke/fumes

 

My questions:

 

1/ Can any MVHR do this by default, or do I need a special setup? 

2/ Will MVHR be able to do this all the time, or will it only produce hot air when it's actually cold outside, and will it only produce cold air when it's hot out?

3/ Any other thoughts/ideas?

Edited September 2, 2019 by puntloos

[ProDave]

You don't want your house mvhr linked into the garage.

[SteamyTea]

8 hours ago, puntloos said:

I'd love to extract hot air away from (&HRecover/reuse it, ideally), and cold, dry air onto 

This is more a job for air conditioning rather then MVHR.

 

MVHR works on the little and often principle.

 

[Jeremy Harris]

8 hours ago, puntloos said:

2/ I'd love to put dry, heated air into

  - Airing cupboard

  - Clothes storage.

 

 

MVHR does not deliver dry, heated, air normally.  Unless there is some form of post-heating in the supply ducting then MVHR delivers air that is always cooler than the room air in cool weather.

 

8 hours ago, puntloos said:

3/ STRONG air in kitchen/garage in particular for fire/smoke/fumes

 

 

Definitely an extremely bad idea.  Apart from kitchens being an extract room, with a specified extract rate in the regs, there is a very serious fire issue with supplying fresh air to a room (or garage) that may well be the initial seat of a fire.

[jack]

9 hours ago, puntloos said:

2/ I'd love to put dry, heated air into

  - Airing cupboard

 

We have a drying cupboard (or will do when I get around to finishing it) in our utility room. It has an MVHR extract above it, and the door will be ventilated at the bottom to allow airflow.

 

It's also beside the plant room. I've left provision for a fan to blow warm air from the plant room into the bottom of the airing cupboard, but to be honest, I doubt I'll bother using it given how effective unheated air is at drying things. 

 

 

[Jeremy Harris]

Similarly, we have a drying area in the utility room, and I fitted an MVHR extract into the ceiling above one of those hoist up clothes racks.  Works extremely well, and dries stuff very quickly:

 

 

 

[puntloos]

1 hour ago, JSHarris said:

Similarly, we have a drying area in the utility room, and I fitted an MVHR extract into the ceiling above one of those hoist up clothes racks.  Works extremely well, and dries stuff very quickly:

 

Very nice, I guess even "cold" airflow works better than only natural air movement!

 

3 hours ago, JSHarris said:

 

Definitely an extremely bad idea.  Apart from kitchens being an extract room, with a specified extract rate in the regs, there is a very serious fire issue with supplying fresh air to a room (or garage) that may well be the initial seat of a fire.

3 hours ago, ProDave said:

You don't want your house mvhr linked into the garage.

 

I was purely thinking on demand though. It's a fair point that I hadn't thought about that you could, well, fan the flames.. but if the issue is smoke or noxious fumes, being able to turn the fans up to 11 sounds like a very helpful idea..

 

3 hours ago, JSHarris said:

 

MVHR does not deliver dry, heated, air normally.  Unless there is some form of post-heating in the supply ducting then MVHR delivers air that is always cooler than the room air in cool weather.

I'm thinking some system where indeed MHVR is the main source of comfort in the house, but when needed (perhaps triggered by heat sensors, or by 'the projector turning on" the more extreme functionalities switch on. 

But I also seemed to recall you mentioning 'running the MHVR in reverse' or something.. 

 

3 hours ago, SteamyTea said:

This is more a job for air conditioning rather then MVHR.

 

MVHR works on the little and often principle.

 

 

OK so my idea is not practical? Or are there ways to have "all the air types" (cold, normal, heated) available at all times on demand that are not insane?  ?

 

I think the dream would be to have the MHVR be the main system, but having AC be available as backups that can kick in if there's a short term demand for more. Is this doable/feasible? 

 

 

[SteamyTea]

I worked at the RNIB head office in London. They had zoned heating, air conditioning and lighting.

Was an expensive system, ticked all the boxes for a charity, except one.

It was useless.

[Jeremy Harris]

There are some fundamental points about the way MVHR works, and what it can and cannot do, that are probably worth making:

 

1.  A normal MVHR system only changes the air in the house about once every 2 to 3 hours.  The air flow rate is low, and barely perceptible if you place your hand over one of the terminals.

 

2.  The low air flow rate means that MVHR cannot move much heat, as air has a pretty low heat capacity.

 

3.  With a normal MVHR (i.e. one that does not have any additional means to heat or cool the supply air to the house) the fresh air supply to the house will always be cooler than the temperature of the air in the house, in cool weather.

 

4.  It is possible to heat a passive house with an MVHR system that has some form of post-heating system built in to the fresh air supply ducting, but it will never be a lot of heat.  For example, our MVHR has an internal air-to-air heat pump, that can heat the fresh air supply, but even running at maximum it can only supply about 1.5 kW of heat, to the whole house.  This is OK for a very low energy passive house, and it's also an expensive way to provide heat (in terms of capital cost).

 

5.  If opting to heat a passive house with some form of duct heating built in to the MVHR system, then the response time will be slow, unless the MVHR ventilation rate is significantly increased, just because the MVHR only changes the air in the house every two to three hours normally.

[puntloos]

1 minute ago, SteamyTea said:

I worked at the RNIB head office in London. They had zoned heating, air conditioning and lighting.

Was an expensive system, ticked all the boxes for a charity, except one.

It was useless.

 

OK, so how do I untick that box?

 

Seriously though can you be a bit more specific? Obviously offices can be poorly designed with pretty much everybody except the janitor being uncomfortable. 

 

But my system would be for example:
 

1/ on-demand low cooling duct (where a tiny bit of cold air can hit some sensitive equipment - the projector, a PC, the fridges maybe. Ideally the AC on, but in 'powersave' mode) 

2/ on-demand high cooling (If things get beyond the MVHR's capabilities - climate change?) - just turning on the AC and blasting the results into all rooms evenly

3/ on-demand heating (I'm still not clear if MVHR can do this? How do you heat your house if it's a surprisingly long winter?)

4/ boost heating 

 

Clearly I think I'm just thinking of how a car works, where you can control the various outputs in various places, and internally there's standard outside air, heated air and cooled air.. 

Can't we replicate this in a house?

[puntloos]

6 minutes ago, JSHarris said:

There are some fundamental points about the way MVHR works, and what it can and cannot do, that are probably worth making:

 

1.  A normal MVHR system only changes the air in the house about once every 2 to 3 hours.  The air flow rate is low, and barely perceptible if you place your hand over one of the terminals.

 

2.  The low air flow rate means that MVHR cannot move much heat, as air has a pretty low heat capacity.

 

3.  With a normal MVHR (i.e. one that does not have any additional means to heat or cool the supply air to the house) the fresh air supply to the house will always be cooler than the temperature of the air in the house, in cool weather.

 

4.  It is possible to heat a passive house with an MVHR system that has some form of post-heating system built in to the fresh air supply ducting, but it will never be a lot of heat.  For example, our MVHR has an internal air-to-air heat pump, that can heat the fresh air supply, but even running at maximum it can only supply about 1.5 kW of heat, to the whole house.  This is OK for a very low energy passive house, and it's also an expensive way to provide heat (in terms of capital cost).

 

5.  If opting to heat a passive house with some form of duct heating built in to the MVHR system, then the response time will be slow, unless the MVHR ventilation rate is significantly increased, just because the MVHR only changes the air in the house every two to three hours normally.

 

Thanks @JSHarris - this is great info, I think I had most of it 'here and there' but it's good to get the whole picture, thanks for taking the time to explain.

 

 

So your passive house will not be heated 'actively' in strong winters? Is this a worry? I imagine bad winters haven't happened since you built.. 

 

 

As I said below I think in "most cases" I would want to design my house to indeed be MVHR/passivhaus style. But funds permitting I do want to have engineered a solution (even if the actual AC unit isn't installed yet, or sits idle most of the time) that can respond to extreme cases. I would indeed be very tempted to install super powerful fans into the system for 'those cases'

 

The 'cooled air supply to devices' thing sounds nice, but really is only a nice to have - perhaps as a freebie..

 

[SteamyTea]

A lot of it has to do with the volume of air you need to shift. In a car this is easy as it is small, and the noise is masked.

A house is very different.

If you really want to control each room, then you need to have a water based heater/chilled in each input duct, and each room will need an extract duct.

As well as individual control for each room.

Then you will need 2 separate systems, one to heat and the other to cool.

Large ductwork as well as separate fans for each room.

Fun system to design, install and commission.

Would get a really fat user manual too.

[Jeremy Harris]

16 minutes ago, puntloos said:

 

Thanks @JSHarris - this is great info, I think I had most of it 'here and there' but it's good to get the whole picture, thanks for taking the time to explain.

 

 

So your passive house will not be heated 'actively' in strong winters? Is this a worry? I imagine bad winters haven't happened since you built.. 

 

 

As I said below I think in "most cases" I would want to design my house to indeed be MVHR/passivhaus style. But funds permitting I do want to have engineered a solution (even if the actual AC unit isn't installed yet, or sits idle most of the time) that can respond to extreme cases. I would indeed be very tempted to install super powerful fans into the system for 'those cases'

 

The 'cooled air supply to devices' thing sounds nice, but really is only a nice to have - perhaps as a freebie..

 

 

 

We don't use the MVHR for heating at all, only for a small amount of supplementary hot weather cooling (the air-to-air heat pump within the unit can heat or cool).  Our heating is by UFH on the ground floor, run from an ASHP.

 

The capacity of our heating system is significantly greater than the house will ever need, as it a larger than needed ASHP became available at the right price.

 

The cooling capacity of a single supply duct from the MVHR, when in active cooling mode and running at a normal ventilation rate, is less than 100 W, so just about enough to offset the heat produced by one person in that room.

[puntloos]

14 minutes ago, SteamyTea said:

A lot of it has to do with the volume of air you need to shift. In a car this is easy as it is small, and the noise is masked.

Fair, although the noise would (perhaps?) hopefully be mostly in the plant room(garage? loft?) rather than in the specific room in question?

 

Quote

A house is very different.

If you really want to control each room,

Probably only a few rooms though. Livingroom, 2 bedrooms, maybe an office?

 

Quote

 

 

then you need to have a water based heater/chilled in each input duct, and each room will need an extract duct.

Do you mean this: http://www.coolingandheatingsolutions.com/brochures/water_chillers_Mini-Chiller-Range.pdf ?

Why not something more like this - an AC-Heater-Cooler: https://www.amazon.com/EdgeStar-AP14001HS-Portable-Conditioner-Dehumidifier/dp/B003PCSR82

 

Quote

As well as individual control for each room.

Not unusual nowadays obviously.

 

Quote

Then you will need 2 separate systems, one to heat and the other to cool.

Large ductwork as well as separate fans for each room.

Fun system to design, install and commission.

Would get a really fat user manual too.

 

So far, naively I'm sure, it doesn't sound insanely pricey. You'd need the chillerheater type device, perhaps x3 - and "clever ducting" and some sensible control system...

[puntloos]

10 minutes ago, JSHarris said:

 

 

We don't use the MVHR for heating at all, only for a small amount of supplementary hot weather cooling (the air-to-air heat pump within the unit can heat or cool).  Our heating is by UFH on the ground floor, run from an ASHP.

 

The capacity of our heating system is significantly greater than the house will ever need, as it a larger than needed ASHP became available at the right price.

 

The cooling capacity of a single supply duct from the MVHR, when in active cooling mode and running at a normal ventilation rate, is less than 100 W, so just about enough to offset the heat produced by one person in that room.

 

Ah funny I forgot anbout UFH. Of course. I don't think I need any powerful heating in most cases. It just seemed mildly helpful if the air was already available (e.g. perhaps the exhaust from that AC...)

[PeterW]

14 minutes ago, puntloos said:

Fair, although the noise would (perhaps?) hopefully be mostly in the plant room(garage? loft?) rather than in the specific room in question?

 

Nope - noise of the unit is incidental and the noise comes from either the air flow through the  vent cowls (exhaust and supply) which is a function of air speed and vent gaps, or transmitted down the ducts. This can be sorted by using inline silencers. 

[Jeremy Harris]

The key thing here is to compare the air flow rate from an MVHR supply duct with that from an indoor air conditioning unit.  The normal  flow rate from an MVHR supply terminal would be around 6 to 12l/s.  The normal flow rate through the indoor part of an air conditioning unit would be around 150 to 200l/s.

 

Does this help explain why MVHR isn't that great at moving heat?

[puntloos]

7 minutes ago, JSHarris said:

The key thing here is to compare the air flow rate from an MVHR supply duct with that from an indoor air conditioning unit.  The normal  flow rate from an MVHR supply terminal would be around 6 to 12l/s.  The normal flow rate through the indoor part of an air conditioning unit would be around 150 to 200l/s.

 

Does this help explain why MVHR isn't that great at moving heat?

Yep, I understand it's intended to be a low ongoing flow. I guess the only thing I'm missing from the story is if I can use the MVHR ducting to blast more air occasionally. 

[Jeremy Harris]

1 minute ago, puntloos said:

Yep, I understand it's intended to be a low ongoing flow. I guess the only thing I'm missing from the story is if I can use the MVHR ducting to blast more air occasionally. 

 

 

Not really, as the maximum flow velocity in the MVHR ducts needs to be kept below about 2.5m/s, just to stop it creating too much flow noise. 

[puntloos]

31 minutes ago, JSHarris said:

 

 

Not really, as the maximum flow velocity in the MVHR ducts needs to be kept below about 2.5m/s, just to stop it creating too much flow noise. 

 

Understood. Indeed noise would be bad (ish.. I am not sure I would mind too much if it's incidental, but of course ideally avoided..)

 

I guess the bottom line here is that I need a 'heating/cooling expert" who can design this system, perhaps by selecting the right equipment, building larger or separate ducts etc etc.

 

Anyone on this forum know the price for this added complexity? Is this 'a few bigger ducts and an extra AC unit, set you back 3000 bob and we're done'.. or do we need some industrial designer making this their life work for the coming 6 months..

 

[SteamyTea]

Just now, puntloos said:

'heating/cooling expert"

 

1 minute ago, puntloos said:

the price for this added complexity?

How much you got, then double it, add your birthday, and then a bit for a laugh.

[puntloos]

2 minutes ago, SteamyTea said:

 

How much you got, then double it, add your birthday, and then a bit for a laugh.

 

So 6000 + 1900something and well, a bit is either 1 or 0, but I'll split the difference..

 

7950.5. Doable.

Edited September 3, 2019 by puntloos

[Jeremy Harris]

5 minutes ago, puntloos said:

 

Understood. Indeed noise would be bad (ish.. I am not sure I would mind too much if it's incidental, but of course ideally avoided..)

 

I guess the bottom line here is that I need a 'heating/cooling expert" who can design this system, perhaps by selecting the right equipment, building larger or separate ducts etc etc.

 

Anyone on this forum know the price for this added complexity? Is this 'a few bigger ducts and an extra AC unit, set you back 3000 bob and we're done'.. or do we need some industrial designer making this their life work for the coming 6 months..

 

 

 

You really need to factor in very large duct sizes to make this work.  Warm air heating/cooling systems use ducts that are very much larger than MVHR ducting, typically they will be rectangular and typically be between about 200mm x 200mm up to maybe 200mm x 500mm.   The large duct sizes are needed in order to be able to move the high air volume needed around without increasing the velocity to the point where it starts to get both noisy and cause high duct flow losses.

[puntloos]

5 minutes ago, JSHarris said:

 

 

You really need to factor in very large duct sizes to make this work.  Warm air heating/cooling systems use ducts that are very much larger than MVHR ducting, typically they will be rectangular and typically be between about 200mm x 200mm up to maybe 200mm x 500mm.   The large duct sizes are needed in order to be able to move the high air volume needed around without increasing the velocity to the point where it starts to get both noisy and cause high duct flow losses.

Not sure if it's hard to get such ducts to the first floor, but I think my main concern is the living room anyway, which sounds reasonably doable.

[SteamyTea]

First thing to do is a room/area by room/area heat load calculation, and the associated airflows, for your local weather regime.

That way, if you do get a professional in, they should realise that you know a bit.

If you don't do that, you will never know who is talking sense and who isn't.