mvhr zones

[Ozpos]

Hi All and thanks for your experienced knowledge.

 

Could anyone please tell me how are the fans adjusted to accommodate the changes in air volume demand when zones are turned on and off ?

 

Best regards,

Ozpos

Edited November 15, 2023 by Ozpos

[Conor]

Zones are not turned off or on. It's a continuous system. If a high rate is required, fan speeds adjust accordingly and ventilation rates at all outlets / extracts change proportionally. When commissioning, flow rates are set at each terminal at the standard fan setting to what the design requires. This is done by adjusting the aperture at each outlet 

[Ozpos]

Hi @Conor, Thanks for your response.

 

I thought mvhr units run the fans in constant volume configuration such that the air flow is increased if the resistance to flow increases (e.g. due to filter contamination) ?

 

So if I have a zone that is not occupied for certain days in the week then that zone can be restricted with a motorised valve and the air flow reduced to a minimal.  At the same time as turning down the zone surely the fans need to be adjusted otherwise they will try harder to supply the constant volume.

 

Could you please explain more ?

Best regards,

Ozpos

[Conor]

You're over thinking it. You don't want to reduce flow to rooms, the building needs to be continuously ventilated as a whole system. When you shut off a valve, the flow rate just increases at other valves, the fan speed stays the same (generally). You're just adding cost, complexity and work!

[Ozpos]

Thanks but what about systems that have day time and night time zones ?

 

I do not expect to shut off a zone just reduce the flow to standby/holiday mode.  The valves I have seen are proportional.

 

I thought the whole point of zones was one of efficiency ?

Edited November 15, 2023 by Ozpos

[crispy_wafer]

All zones are Preset according to design.  Night time turns the whole system fan down if you want it to!  If you boil a pan/have a shower and raise humidity levels the system boosts to bring levels back into range.  Absolutely no need to change each vent on the fly.  Once it's in, set, monitor, tweak, then forget about it.

[Conor]

It sounds like you are talking about heating rather than ventilation? An MVHR doesn't have zones, air flows through the building from supply point to extract point. That's how they are designed to operate. View it as a flowing stream through your house. Water flowing from bedrooms to bathrooms etc.. if you shit off or reduce one of these points, you mess up the flow through the whole building.

 

You have different flow rate modes for different circumstances. Right now, ours is on a low rate eco mode, to reduce heat loss and drying effect.

Edited November 15, 2023 by Conor

[Ozpos]

What about:https://www.duco.eu/uk/products/mechanical-ventilation/ventilation-units/ducobox-energy-comfort#multi-zone-valve

 

They say:

 

Compact external 2-zone control

With external 2-zone control, the house is divided into a day and night zone.

This zonal control is based on CO2 and humidity. It only provides ventilation where and when needed, in the right amount.

Zonal ventilation ensures maximum energy savings and increases acoustic and thermal comfort.

 

 

 

So I assume as the day zone time ends the zone valve reduces flow and at the same time backs off the fans to compensate.

 

Can anyone else shine a light on how this actually works ?

[JohnMo]

Basically it's similar to their MEV system, the terminals respond to humidity and CO2 and open and close as a response to changes.  The fan speed ramps up and down as required to keep the pressure within system constant. Would assume extracts and supply terminals are linked so the response is, extract opens a suitable supply in the same zone also opens to keep the system balanced.

 

You would expect you just map the system to say terminal A and B are in zone 1 and C and D are in zone 2 etc. then operate a simple time clock or it just does based on where is sees CO2 or humidity. 

 

Reality of saving v cost?

Everyone watching TV in zone one, you go for a shower in zone 2. Both zones operating.

[Ozpos]

Hi @JohnMo, thank you for your response.

 

I am an electronics engineer and always looking to use my knowledge to save cash. I can get hold of co2 and humidity sensors for a couple of quid.  In addition I have built a building control unit using a raspberry pi.

 

Do you know if many mvhr systems can be controlled by an external building management system ?

[ToughButterCup]

What you need @Ozpos, is a visit from @MikeSharp01 . I had a problem with one of my inlets. He took one look at it, grinned and said

 

"You don't need that  one" 

Top bloke.

[SteamyTea]

8 minutes ago, Ozpos said:

I can get hold of co2 and humidity sensors for a couple of quid.

Care to share a supplier.

I have some cheap DHT11s that are rubbish, the DHT22s are better.

CO₂ sensors seem expensive and limited life.

[Ozpos]

No problem but it is a while since I bought some plus delivery is slow.

https://www.alibaba.com/product-detail/SCD40-SCD41-gas-sensor-module-Electronic_1600973791358.html?spm=a2700.galleryofferlist.normal_offer.d_title.2a154649rdSLh0

[JohnMo]

1 hour ago, Ozpos said:

Hi @JohnMo, thank you for your response.

 

I am an electronics engineer and always looking to use my knowledge to save cash. I can get hold of co2 and humidity sensors for a couple of quid.  In addition I have built a building control unit using a raspberry pi.

 

Do you know if many mvhr systems can be controlled by an external building management system ?

If you want to go that route, I would suggest two small MVHR units, one for upstairs one for down.  Wouldn't bother with CO2 as there is supposed to be a strong enough link between humidity and CO2 in a household situation. But if cheap and available why not include.  But would use external sensors (in each room), not internal to the unit, then you can operate in four modes, off, on at minimum set back speed, normal speed, boost. Set threshold something like, humidity, below 41% off, above 41% on at min speed, 45% at normal speed, over 50% boost.

 

You don't need very complex units to do the above.

 

But not really convinced the effort is work it.

Edited November 15, 2023 by JohnMo

[Ozpos]

Hi @JohnMo, thank you for your honesty.  Could you tell me how long you have been involved with mvhr and at what level ?

 

[Adrian Walker]

3 hours ago, SteamyTea said:

Care to share a supplier.

I have some cheap DHT11s that are rubbish, the DHT22s are better.

CO₂ sensors seem expensive and limited life.

True CO2 sensors are expensive, but eCO2 sensors (SPG30) are very good. 

[JohnMo]

1 hour ago, Ozpos said:

Hi @JohnMo, thank you for your honesty.  Could you tell me how long you have been involved with mvhr and at what level ?

 

Designed, installed and commissioned my own system. Have two units, partly to reduce duct lengths on a 25m long house, but also to reduce what boosts and when, I have used coanda effect supply terminals, to further reduce duct lengths.

 

Nothing complex about MVHR, just flows and pressure drops and trying not to overthink stuff that isn't important. Not easy when you read ill informed info everywhere.  Reality is you don't need to boost often, so why bother automating. If you have a shower in a cool bathroom and it's full of steam when you finish, hit the manual boost switch on the way out.  If your cooking smelly stuff, hit manual boost also. That's about the only time ours boosts.

 

My normal flows are now turned down well below (about half) building regs, and humidity floats around 42 to 45% over 24hrs.  CO2 - living room levels average (24 hrs) 521ppm, and max out 630ppm. Our bedroom CO2 levels average (24 hrs) 556ppm with a peak of 665ppm.

 

As I mentioned don't overthink it, keep it simple - let it get on with it. Check the filters every six months, give them a hoover, replace annually, have cone filters in the extract terminals, to keep duct clean.

[SteamyTea]

52 minutes ago, Adrian Walker said:

True CO2 sensors are expensive, but eCO2 sensors (SPG30) are very good. 

Thanks.

Shall take a look at them as I fancy kitting out the house with sensors again.