Room based ventilation control

[kris2lee]

I have one ventilation specific project in my mind and I would like to hear some suggestions about what specific hardware and software the forum users would use for that.

After renovation, our house is planned to have a central ventilation with heat recovery (i.e. air blows into living rooms (living room, bedrooms) and is taken out from sanitary rooms (kitchen, bathrooms)).

My idea is to install CO2 sensors into each living room and rH sensors into sanitary rooms and control the amount of needed ventilation based on sensor data. Now it does mean that when one room has increased CO2 or humidity production it does mean that ventilation rate has to be increased. But it would be increased for whole operation because only central unit fans can be controlled. This will cause more noise and will also increase the used energy (due fan power usage and increased heat loss).

I think that the last one is not a big concern when the size of investment is considered but the noise problem is really important to me and I really want enough fresh air into the rooms that are occupied - this is the reason for the ventilation after all.

One option is commercially available VAV (variable air volume) valves. But they are expensive. Really expensive. I need about 10 of them so this would cost me more than my ventilation unit.

So I plan to buy all together by my self. Stuff I need is the following:

1) ventilation valve (this is not a problem, I can get it from the ventilation supplier),
2) variable position motor to control the valve (Belimo is expensive and is not an option but I did locate some reasonably priced products so this is also not a big concern I belive (and hope)),
2) air volume sensor (I have some ideas but more ideas are welcome),
3) 2 analog inputs (one to read air volume sensor and another to read motor position feedback),
4) 1 analog output to control the motor position.

Ideally one valve hardware should not cost more than 100 euro (without VAT) but 120-130 euro may still be acceptable. Products with CE certification are preferred but I'm probably not too picky.

I see that the system should be separated into 3 logical units. Room sensor reading, air volume control and central control unit. Central control is needed because ventilation intake and outtake air volumes has to be synchronized and central ventilation unit fans has to be controlled.

My current idea is to use KNX CO2 and rH sensors and realize other sensor reading and motor control with Wago products for example but I'm open to any idea.

Kris

[kris2lee]

I like to add more background information. Now I'm not the expert in the ventilation fiend and following notes are made by common sense and by observing the ventilation design process.

Each room ventilation is limited by its projected ventilation rate what is defined by normal occupant count in the room and desired air quality. Persons activity has be also considered. When in sleep, the CO2 production is quite minimal but will increase rapidly with slight activity.

When ventilation is designed then room occupant count is considered. For example when you have child room then I would advise to design needed ventilation for at least two persons (children are not always alone in the room but may be there with friend, parent etc.). For living room I would suggest also considering possible cast count. It is usually considered unnecessary to design room ventilation for maximum activity. For example bedrooms are designed for low activity.

When needed ventilation rate is known then pipe sizes are calculated based on that. This does not mean that higher than designed ventilation rate is not possible but it will cause more noise for example because air has to move faster in the pipe and will create more vibration.

Central unit ventilation rate is calculated by summing together individual room ventilation rates.

CO2 concentration is measured in ppm (part per million). Outside CO2 concentration is around 350-400 ppm. Suggested CO2 concentration for office work is 850 ppm almost everywhere in the world. This is the CO2 concentration above what people usually start to feel air as stuffy . This is of course personal. For private sector this does differ from country to country. When room CO2 concentration is set for example to 850 ppm then this means that this should not go over that figure. It could be lower when room is ventilated but is not occupied.

As ventilation is designed for maximum possible capacity then there is quite big overhead. When you have a normal size family but at day you stay at home alone then to keep your room well ventilated whole house is ventilated unnecessary. When everyone is at home and is staying in the living room then bedrooms are unnecessary ventilated or when everyone is sleeping then living room is unnecessary ventilated and so on. This will open room for quite measurable possibility to keep ventilation rate as low as possible.

Kris

[drmacchi]

Hi Kris, yours is a big project ! . I'm planning a ventilation system too, not as hard as yours, and i'd like to do some notes (i'm not an expertise in ventilation, but i read a lot...)
1) you say "heat recovery" . Does your ventilation system perform a >70% heat recovery? there are many products , but you should choose the recovery unit with almost this performance.
My home is already built, so i can not add a central system, and i had to use some standalone devices with heat recovery (double exchange) in some rooms : bedroom, bath, kitchen etc . My devices 5 units E100SX do perform 70% heat recovery and 70 mc. flow rate

http://www.forclima.it/download/catalogo_2010.pdf

So flow rate is another important feature to evaluate. You want CO2 and HR% sensors, but you should provide enough "flow rate" to satisfy your needs.

My control system will be rather simple and only based on HR% : i have some oregon sensors (temp, HR%) that will be read by RFXCOM , and these values are managed by Homeseer wil will turn on/off the E100sx with some X10 modules.

if you need some infos for CO2 sensor, please check this topic too : http://www.domoticaforum.eu/viewtopic.p ... co2#p43237

2) How much energy will your system need? i know that central system are really hungry of energy.

Best regards.
Lorenzo

[kris2lee]

Hello,

Hi Kris, yours is a big project !

Yes indeed. Pipework is designed by ventilation design bureau. I also have a friend who does build ventilation systems but he does not know automation part.

you say "heat recovery" . Does your ventilation system perform a >70% heat recovery? there are many products , but you should choose the recovery unit with almost this performance.

I plan to use the unit from Helios. Like this http://www.heliosventilatoren.de/mbv/kw ... k_0310.pdf
They claim that it will recover up to 90%. They also have units that are claimed to recover over 90% but they do not have such nice control options. I figured out that the first kind of units are actually made by finnish company Vallox. They have remote control unit that is working over RS485. They have also gateways into KNX and LON. I thought that when I get the maschine I will first try to figure out what exact protocol they are using before I go to the gateway route.

These control options are actually the reason I favor these units. I have not found anything better yet (does not mean it does not exits, just I have not found it).

My home is already built, so i can not add a central system, and i had to use some standalone devices with heat recovery (double exchange) in some rooms : bedroom, bath, kitchen etc . My devices 5 units E100SX do perform 70% heat recovery and 70 mc. flow rate

So is ours but we did tear it appart and planned the place for the ventilation pipes. Do you plan to route the air from the cooker hood trought this unit?

So flow rate is another important feature to evaluate. You want CO2 and HR% sensors, but you should provide enough "flow rate" to satisfy your needs.

Flow into the living rooms is planned as 8,3 - 10 l/s per person in the room. For example our bedrooms flow rate would be 20 l/s. Living room flow rate would be 66,4 l/s (8,3 l/s, 8 persons - consider cast). In total it would be about 130 l/s what will make about 468 m3 in hour. I think that this is a lot, much more than usually suggested for the house of this size (about 120 m2) but after I made calculations I do not see how it would be reasonable to have less. It would be possible to reduce the total flow rate using the dynamic flow control I have in mind but the price difference between lower flow rate units was less than 10% so I dont see meaning in this.

How much energy will your system need? i know that central system are really hungry of energy.

Planned unit will consume from 32 W to 286 W (from minimum power to full power) when running. So actually it would use considerable amount of energy when running all the time at maximum power.

Kris

[John]

Kris,

A very nice solution. I was also thinking about this option, but i have my doubts.In case the valve is not working properly how do you repair. If you don't have a fixed ceiling this will not be a problem but the most houses (also mine) do have a fixed ceiling.

John

[drmacchi]

Hi Kris , if i were you, i would go for a photovoltaic system that could help you with energy bill. Here we say "if you have done 30, do 31 !"

[kris2lee]

In case the valve is not working properly how do you repair. If you don't have a fixed ceiling this will not be a problem but the most houses (also mine) do have a fixed ceiling.

This is good question. I must thank the designer who designed my ventilation system (pipework). I told them that I want to have valves and they found quite nice solution. Ventilation unit is in the basement. There are also valves for the first floor. Our house does have another two floors (one is actually extended attic). Now for those two floors the pipes run to the attic (what is left from it) where all the other valves are and then run down into the rooms. There is also one separate valve in the second floor bathroom where false ceiling was needed but it was needed anyway.

So all the valves are accessible. But you can actually run the pipes below the ceiling (let them be visible). Many modern architects do that. Or when you run them inside the wall then you can left some hatch so you could still access the valve. Sure thing is that you have to make them accessible.

One more note. After every valve there is small silencer because air going through the valve will create more noise. This is actually another thing that will make this solution more expensive because you could have minimum two silencers.

[kris2lee]

John,

I was also thinking about this option, but i have my doubts.

Did you do any research on what devices to use?

Kris

[John]

Kris,

I stopped my research because in our situation it is no option to place the controlled valves.

John