Calculation for the right mini split size. Is 24.000 BTUs enough?

I need a mini split for keeping the temps in my rooms right. Is for the following setting 24.000 BTUs enough?

I have two sealed rooms (flower and motherplants), total 16.7 x 12.2 x 8.5 feet (1731 cubicfeet) (5.10m x 3.70m x 2.6m) which are side by side and have between air circulation by a big fan and ducting.

The stuff I need an AC for:

4x 600/750 Watt double ended HID
1x 200 to 400 HID light for vegetation
1x 750 watt dehumidifier
1x water cooled propane co2 generator (I could place the water reservoir outside of the room)
1 x 100 Watt clone light
some small pumps and fans

So in total around 4250 Watts (maybe a little bit extra for some pumps and fans) if running flowerlights at 750 Watts. Mostly I will run them at 600Watts. That would be 600Watts less and result in total 3650Watts.

Good would it be, if the unit can heat also.

How many tons should I get? I did read that it is better to split the load on two small units, but I don't think I will do that.

I need the unit to be quiet, because it is not common here to have ACs. It will be behind the building at a wall which is you can't see from the walking paths. Are stronger units louder or more silent?

When is an unit too big? Can you get it too big?

How reliable are the different brands?

I did that there are units where you don't need an HVAC guy because the lines are preloaded or whatever. Is this usually the case? Probably will need to do it myself.

with DE lights, you need at least 4500 btu for each 1000 watts. if that helps

and that 4500 is a bare min. I would go 5500 each just so they are not working so hard. your 24k unit is more than enough. you are right though splitting the load helps a lot.

I can't help with tonnage but I can tell you that my cheap 12000BTU is running really quiet. You can barrely notice it's running when you are outside...

It's not common that the hoses are preloaded if you buy at a specialised place. You need to borrow of rent a vaccum pump and put the system under vaccum before you open the valves and the hoses usually don't come with the machine you have to buy them separately cut them to length and flare them. You better hire someone who know what he's doing for this type of unit.

Some big surface store like home Depot will sell unit with quick connect and the hose are preloaded. I can't tell if they are reliable... Since I know no one who ever buy them.

ok. stuff got a bit more complicated, as proprietary owner doesn't want me to install an outdoor unit. So I was thinking about doing a work around. Maybe some pro is reading here too? Ok here is what I was thinking:


I know the idea of putting an outdoor condenser unit inside sounds unsound but I was thinking to put the outdoor unit into an insulated box (inside one of my rooms). This insulated box would have two fans, which are each matched with the cfm rating of the condenser unit and pull air into and out of the box (from and to outside of the building).

I was looking at some of the mini splits and it seems that you can find outside units from mitsubishi which move around 2000 cfm.

I was thinking about using two fans (ruck etamaster 355 Ruck 3320m³/h) which are each able to move around 2000 cfm.

Each fan uses at maximum load around 250 Watts of power. Considering a mini split has a COP rating of over 1, I think that even with the extra energy use of the fans I would come cheaper (energy wise) than anything else what would be possible in my place.

Can I build in another room an insulated box which contains the condenser unit and this box is connected to ducting which inputs air (from outside of building) and ducting which outputs air (also to outside of the building)? I know that the condenser needs big amounts of air, so I would install two fans which are each able to move around 2000 cfm of air. I would install one fan for pulling air from outside, pushing the air into the box and then another one pulling the air out of the box and pushing them outside. The fans were chosen under the assumption that most mitsubishi condenser units (in the range of power that I need) are able to move around 2000 cfm max each.

If I could use such a design, I would need to add 500 Watts total for the two fans. I think like that I would still be more energy efficient than other solutions. Maybe only one fan would also be sufficient, then I would only need 250 Watts extra. I am only able to use some indoor solutions and unfortunately geothermal pumps or swamp cooler are not possible. I know it is a bit problematic to find such device if you need a 2 to 3 ton unit.

So what do you know, would such a setup work? I have not enough knowledge and experience in HVAC, that is why I need to ask a pro.

So far I have some concerns:

- Are the outdoor condenser units working with variable fan speeds, and is it a problem if my inline fans blow directly onto the condenser unit? Maybe the airstream of the inline fans, messes with the heating or cooling process of the condenser unit. Also has fast moving air some sort of own effect in temperature (e.g. cooling through windchill)? If it would be the case that direct air has some detrimental effect on efficiency of the unit, I probably could use some sort of wind baffle like it is offered by Mitsubishi (https://www.pinterest.de/pin/469500329886926899). What do you think?

- I live in a climate where in winter we can get temperatures as cold as -5 Fahrenheit. It happens rarely but it can happen. That situation means that I would need a unit which would work also in these kind of temperatures. Mitsubishi offers Hyper Heating units which work in these temperature ranges. Unfortunately it seems that the Mitsubishi 2 to 3 ton units which support Hyper Heating are almost only twin systems (have two fans), which would mean a combined airflow of 3600cfm. To provide 3600cfm of air with my inline fans to the insulated box where the condenser unit would be in, I would need to buy much stronger and much more expensive inline fans. So I only know the Mitsubishi units so far, but maybe somebody of you know the product range of the other quality brands. Does somebody know a unit which is capable to work in low temperature settings and has a cfm rating of around 2000cfm? Other option would be if somebody knows strong inline or other fans which would be able to do 3600cfm and are actually not that expensive.

- also what do you think, would I need two or one of these inline fans? I mean suffice how much would such a condenser unit have postive influence on the static pressure. Would the outdoor unit be a resistance or an noticeable aid in pulling air for one fan in such a setup?

So that is the situation. What do you think?

I'll try my best to answer but i dont know if my english is good enough lol.

I think this could work but you need to exange the air of that room fast enough so it match the outside temperature closest as possible.

I would use two fan, if you use only one of the same rating as the unit, i dont think it will be strong enough. The fan on the unit has barrely no restriction...air flow directly thru the condenser. In you room the fan has to pull air thru a passive intake before pushing it out, thats why i would use 2.

Another thing is the fan size... 12inch fan is only about 1100cfm. I dont know how you would discretly hide a bigger intake+exhaust than a 12inch.... Its massive!

Wouldn't be easier to use two 12000btu portable unit? (The ones who has 2 duct intake+exhaust, the one with only one duct are crap)

Can you give me a link to a good portable unit? Are they able to heat also? How is the efficiency/COP rating of these kind of units?

Actually the building is some sort of industrial building and there was some kind of AC solution still inside. It has two air chimeys. They serve only for exhausting air. Or maybe you pull air into them. One of these chimneys has its opening directly to my room. Also there was a big old fan in that room with a big opening in the wall. I removed that fan. It was so fucking heavy. Even with two persons we amost couldnt handle that box. So I have already big openings for air intake and exhaust. Actually there are also big electric controlled dampers built into that building.

Actually I would use these fans (https://www.ruck.eu/ventilatoren/rohrventilatoren1/rohrventilatoren-ec-motor/emix-ec/emix-355-ec-11?productFrequency=50&filterFrequency=50&filterErP=conform). They are 14 inch (355 mm) and without pressure drop the are rated aorund 1950 cfm (3320m³/h). I will get two of them for around 1100 bucks total. If I need to go bigger the price will jump up a lot with that manufacturer. But the units would get much much stronger too. Also I couldn't find any other brand which was as cheap as this manufacturer, while providing quality.

In principle my whole idea sounds possible, but I am not sure if something unwanted efficiency wise might happen. And I need to know that before I spent the money and buy all that crap and install it

I

Sam&Max said:

Can you give me a link to a good portable unit? Are they able to heat also? How is the efficiency/COP rating of these kind of units?

Actually the building is some sort of industrial building and there was some kind of AC solution still inside. It has two air chimeys. They serve only for exhausting air. Or maybe you pull air into them. One of these chimneys has its opening directly to my room. Also there was a big old fan in that room with a big opening in the wall. I removed that fan. It was so fucking heavy. Even with two persons we amost couldnt handle that box. So I have already big openings for air intake and exhaust. Actually there are also big electric controlled dampers built into that building.

Actually I would use these fans (https://www.ruck.eu/ventilatoren/rohrventilatoren1/rohrventilatoren-ec-motor/emix-ec/emix-355-ec-11?productFrequency=50&filterFrequency=50&filterErP=conform). They are 14 inch (355 mm) and without pressure drop the are rated aorund 1950 cfm (3320m³/h). I will get two of them for around 1100 bucks total. If I need to go bigger the price will jump up a lot with that manufacturer. But the units would get much much stronger too. Also I couldn't find any other brand which was as cheap as this manufacturer, while providing quality.

In principle my whole idea sounds possible, but I am not sure if something unwanted efficiency wise might happen. And I need to know that before I spent the money and buy all that crap and install it

Click to expand...

You have a point, portable unit are less efficient than a window or a mini split unit. I have a portable 8000btu and i think a window 5000btu can perfrom pretty close to it.

I did not know you were in a industrial building... 14inch duct going out of the roof is pretty normal in a industrial local!!

I cant predict how exactly this will be efficient. Im not an refrigeration engineer, i work in that domain but im more a eletromecanical technician. I think if the air exange of that room is good i cant see why the effiency will not be close to an outside unit, if you ignore the power consuption of the extra fans (you have to consider if you need two of these fan, this about the same power consuption of a 1Ton unit itself)! You have one advantage running it inside tho : you will never have the sun directly pointing at the unit!

What is the size of the room the unit will be in?

Thing is that I have only one big room available. In this room I did built my flower and motherplants room. These two rooms share a common wall and ducting with a 2000cfm fan will recirculate the air between those rooms.

So in this big room with my two grow rooms I still now need to incorporate my AC solution. I was thinking not to waste more than one and a half square meter for my mini split in a box. (Do you think this will be a problem? E.g. maybe the airflow will be restricted because of the mini split in such a small box?) The box would need to be insulated with rockwool or something, so I will not have problems with the temperature difference between outside and inside air. E.g. when I try to heat the flower and mother room but then I pull cold air into the big room through my box, then heat exchange between my box and the bigger room will have negative effect on the heating in the mother and flower rooms (as everything is in one big room).

Why are you asking about the room size the unit will be in?

So I was thinking and investigating more about the the mini split in a box solution:

I realized that the fan of the outdoor unit of the mini split will operate at different speed RPM (revolutions per minute). This would mean that it would make sense to match my EC inline fans rpm with the rpm of the outdoor unit. The ec fans air volume output is a linear function of rpm and as it seems you control that by controlling voltage in the range of 0-10 Volts.

To match the rpm of the outdoor unit with the rpm of the inline fans, I would need to find out the rpm of the outdoor units fan. I was thinking by doing that by measuring the voltage of the fan of the outdoor unit. Then I would send that value to some controller which would adjust the voltage setting for the inline fans. Like that my inline fans would not work always on full speed.

What do you think? Would that work? Or do you think it is better to measure Amps of the fan?

Actually I am also really wondering how fast the fan of the outdoor unit will usually run. I mean what determines its speed? I was trying to find some graphs which show the usual fan speed of such a unit over the course of a day, but couldn't find anything. I am wondering about that because I am trying to estimate the overall efficiency of my system. E.g. if the fan speed is linear with the overall power consumption of the compressor then I can calculate the energy efficiency rating for the whole system including my 500 Watts of inline fans. But if the fan speed of the outdoor unit is not linear with the compressor then I can't do that. Somehow I have the feeling that if the relation is not linear, the whole system would be less energy efficient because maybe the fan of the outdoor unit would often run fast when the compressor doesnt have much to do. that would cause my inline fans also to waste energy??? Maybe I am just thinking too much...

I think 1.5x1.5m is really too small. It with create so much turbulence in the airflow I don't think the condenser will work properly. I was thinking something way bigger like maybe 3x3x3 so the unit can work freely like it's outside and you had to exange that amount of air each x minutes based on the heating capacity of the condenser. Let say the consenser raise the 3x3x3 room temp 1° in 5min, you know you have to at least exange total amount of air (~1000cubic feet) each five minutes. I don't think you need to match precisly the speed of unit's fan, just exange that air often enough so the room temps don't exeed outdoor temp.

If you think you really need to match that speed, don't read current, it won't tell you that much, output voltage will tell you which rpm it is running if it's a variable speed controller. Sometime the fan has 2-3 speed and each speed has it's wire on the motor. It's doable but it will be really hard to find some componant that do specifically this.

But I don't think it's necessary. I think you could only turn the fans down with a relay hook up on the unit's fan .

Probably I will not have that space. I could place a wind baffle so the inline fans would not blow directly into the compressor (if that could be a source of problem). The inline fans would have a rating of around 1950cfm running at full speed with ideal static pressure situation.

If I use two fans I will hopefully counteract any pressure problems even when using a small box.

How do you think will the air turbulence be problematic for the compressor? What is your reasoning?

By relay hookup you are refering to measure the output voltage? Actually what is output voltage in the case of a fan, and where to measure that. Googling didn't help much. Can you shortly explain?

Pressure differential wouldn't be an issue. If the turbulence the two ec fan create while blowing too close to the unit it will disturb natural flow of the condenser fan and it would not work properly.

Imagine the air the goes out of the machine goes straight back inside because of turbulence. If a had to do this I would at least line in the exhaust fan directly right in front of the condenser fan and even try to install like some sort of funnel and for the intake fan make try to make some baffle with many hole to diffuse the air equally across the box.

I know portables are less efficient but maybe you better use 3x 12 000btu portable than a 24000 + two huge fan. It will be less assle and it may consume the same power as the big unit plus two fan.

I don't know the size of your operation but before trying to cool the room, is there a way to decrease the heat generated so you can use a normal portable AC? Like venting your lamp if it's not already done or changing HID to LED? COBs emit a fair amount of light without dissipating much heat.

A relay is kind of an electrical switch. It's the same thing you have on the wall to turn on the light but instead of you switching it on and off with your finger, it's an electrical current that energise a coil and mimic the action of your finger, there is many option available for the coil voltage input 5, 6, 12, 24, 36 Vdc, 24, 120, 230 Vac

You would jump the two wire from the unit fan (probably 230vac) and bring them to the relay coil, on the output of the relay you plug the in line fan. Unit fan is On = Inline fan On

Sam&Max said:

Thing is that I have only one big room available. In this room I did built my flower and motherplants room. These two rooms share a common wall and ducting with a 2000cfm fan will recirculate the air between those rooms.

So in this big room with my two grow rooms I still now need to incorporate my AC solution. I was thinking not to waste more than one and a half square meter for my mini split in a box. (Do you think this will be a problem? E.g. maybe the airflow will be restricted because of the mini split in such a small box?) The box would need to be insulated with rockwool or something, so I will not have problems with the temperature difference between outside and inside air. E.g. when I try to heat the flower and mother room but then I pull cold air into the big room through my box, then heat exchange between my box and the bigger room will have negative effect on the heating in the mother and flower rooms (as everything is in one big room).

Why are you asking about the room size the unit will be in?

So I was thinking and investigating more about the the mini split in a box solution:

I realized that the fan of the outdoor unit of the mini split will operate at different speed RPM (revolutions per minute). This would mean that it would make sense to match my EC inline fans rpm with the rpm of the outdoor unit. The ec fans air volume output is a linear function of rpm and as it seems you control that by controlling voltage in the range of 0-10 Volts.

To match the rpm of the outdoor unit with the rpm of the inline fans, I would need to find out the rpm of the outdoor units fan. I was thinking by doing that by measuring the voltage of the fan of the outdoor unit. Then I would send that value to some controller which would adjust the voltage setting for the inline fans. Like that my inline fans would not work always on full speed.

What do you think? Would that work? Or do you think it is better to measure Amps of the fan?

Actually I am also really wondering how fast the fan of the outdoor unit will usually run. I mean what determines its speed? I was trying to find some graphs which show the usual fan speed of such a unit over the course of a day, but couldn't find anything. I am wondering about that because I am trying to estimate the overall efficiency of my system. E.g. if the fan speed is linear with the overall power consumption of the compressor then I can calculate the energy efficiency rating for the whole system including my 500 Watts of inline fans. But if the fan speed of the outdoor unit is not linear with the compressor then I can't do that. Somehow I have the feeling that if the relation is not linear, the whole system would be less energy efficient because maybe the fan of the outdoor unit would often run fast when the compressor doesnt have much to do. that would cause my inline fans also to waste energy??? Maybe I am just thinking too much...

Click to expand...

you would just need to bring in enough air for the condenser to remove the heat.a constant fresh supply should suffice. you could put a duct on the air discharge and duct that out.if it goes up. even better.
an a/c unit is heat transfer. it collects it in the evap, refrigerant absorbs it and takes it to condenser to remove it. Most new condensers have power mngmt that controls fan speed according to heat load. if demand is low. speed of fan will be low.

Yes but in a small box like this you don't even meet the minimum distance required between the unit and the wall, I doubt it will properly work at 100%. It something to investigate in but it's a fair amount of money to test it.

I may investigate more in a commercial portable unit http://www.americoolllc.com/products.htm

Perhaps like this one http://www.americoolllc.com/products/wpc-5000

It may a be a bit pricier than a mini split but it's designed to do exactly this.

Actually the clearance requirements arent that high. (See picture for example of a unit). Also I think the clearance is needed so the airflow doesn't get restricted or the unit handles stale air. But when I install an inline fan which blows directly air into the unit and another which pulls air out of the unit, then there should be a smooth airflow (considering inline fans are matched in rpm with the units fan). Actually I am not sure why air should go back into the unit if at each end of the box are fans pushing and pulling both in the same direction, leading to quick extraction of air. Do you think the airflow will be that difficult to predict? So far it seems if the fan blades doesn't get forced to blow backwards there is no problem with wind. Other problem with wind would be snow, which could cause too high humidity at the coils and freeze them, but this problem I would not have indoors. So this design could work properly.

With the protable units there would be contact of possibly contaminated air and the unit would exhaust that air outside. So I would also at least need to install a fan with a charcoal filter which pulls the air clean outside. I am not sure if I will come better off like that energy wise. So far I think that in a big box my solution with a mini split would work. Now I need to figure out how small I can make the box so it still will work.

Two other questions:

- Should I push the air into the air chimey and pull it from the other whole in the wall, or is it better to pull the air from the chimney and push it out of the wall opening? Or does it depend if I am heating or cooling with the unit. Because I heard that hot air goes up (better would be to direct it into the chimney) and cool air goes down (pushing it into chimney maybe not so good)?

- Can you tell me what you mean by measuring the output voltage of the compressor fan? If I use a relay would that mean that my ec fans would run at full power always?

Concerning my calculations for cooling, I was using some tutorial from another forum. I guess with 30000 to 32000 btu cooling I would be able to handle everything. Maybe at some time I will change the refelctors that I have for air cooled ones in the summer.But so far here are my calculations:

1. Floor Area of Room

Room Area BTU = L x W x 40 ( H = 8foot + 5btu per foot after that)

Room size: 16.7 x 12.2 x 8.5 feet

Calculation: 16.7 x 12.2 x 42.5btu = 8658.95 btu

If you have a wall that is facing the sun add in for the extra heat
Sun facing wall BTU = L x H x 40

(I have a room in a room. I think I will add one wall.)
16.7 x 8.5 x 40 btu = 5678 btu

2.Equipment
This is trickier to calculate than you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is safer to overestimate the wattage than underestimate it.

Equipment BTU = Total wattage for equipment x 3.5

750 Watt dehumidifier = 2625 btu
30 Watt Pump mother plants = 105 btu
30 Watt Pump return pump to main reservoir = 105 btu
100 Watt propane co2 generator pump = 350 btu
100 Watt heated clone dome = 350 btu
300 Watt recirculation fan = 1050 btu
small fans????

Ballast in room BTU = ballast wattage/2 x 3.5
4x((750/2) x 3.5) = 5.250 btu
(400/2)x3.5 = 700 btu

3.Lighting

Lighting BTU = Total wattage for all lighting x 4

4x750 Watt for flower lights
100 Watt lightning for dome
400 Watt lights for mother plants
= 3500 Watts total

3500x4 = 12000 btu

4.Occupants

Total Occupant BTU = Number of occupants x 400
1x400= 400 btu


5. Total BTU: 37271.95

I was thinking about removing some BTUs
- remove Total Occupant BTU = Number of occupants x 400 = 400 btu
Total BTU: 36871.95

- if flower lights only run at 600 Watts, remove 4x150Watts, 2400 btu
Total BTU: 34471.95

- remove wall that is facing the sun 5678 btu (my room is in a room that is pretty good insulated)
Total BTU: 28793.95

Maybe it is not the best idea to remove BTUs for the flower lights.So I add the 2400 BTUs back.
Total BTU 31193.95


So finally I need something around 30000 - 32000 BTU.

Sam&Max said:

Actually the clearance requirements arent that high. (See picture for example of a unit). Also I think the clearance is needed so the airflow doesn't get restricted or the unit handles stale air. But when I install an inline fan which blows directly air into the unit and another which pulls air out of the unit, then there should be a smooth airflow (considering inline fans are matched in rpm with the units fan). Actually I am not sure why air should go back into the unit if at each end of the box are fans pushing and pulling both in the same direction, leading to quick extraction of air. Do you think the airflow will be that difficult to predict? So far it seems if the fan blades doesn't get forced to blow backwards there is no problem with wind. Other problem with wind would be snow, which could cause too high humidity at the coils and freeze them, but this problem I would not have indoors. So this design could work properly.

With the protable units there would be contact of possibly contaminated air and the unit would exhaust that air outside. So I would also at least need to install a fan with a charcoal filter which pulls the air clean outside. I am not sure if I will come better off like that energy wise. So far I think that in a big box my solution with a mini split would work. Now I need to figure out how small I can make the box so it still will work.

Two other questions:

- Should I push the air into the air chimey and pull it from the other whole in the wall, or is it better to pull the air from the chimney and push it out of the wall opening? Or does it depend if I am heating or cooling with the unit. Because I heard that hot air goes up (better would be to direct it into the chimney) and cool air goes down (pushing it into chimney maybe not so good)?

- Can you tell me what you mean by measuring the output voltage of the compressor fan? If I use a relay would that mean that my ec fans would run at full power always?

Click to expand...

You don't see it on the picture but this unit can be installed with a separated intake for condenser, so the condenser is isolated, one duct for intake going outside and one duct for exhaust going outside. In theory there no air from inside going outside and vice versa.

For the relay it really depends how to unit you will chose work. If the fan is a single speed fan (like my unit) you could use the relay method and yes the fan will always be at full blast unless you put a controller on your fan. You said your fan take 0-10v signal if that's the case you don't need a controller, only a potentiometer.

If on the other hand the unit fan is controlled by a drive to generate variable voltage, what you could do is find something that convert let's say 150-230vac to 0-10vdc (I just made that up it as to be measured ) this solution is tricky and maybe nothing exist to do directly exactly this. You may have to build something to accomplish this.

Glenkush said:

You don't see it on the picture but this unit can be installed with a separated intake for condenser, so the condenser is isolated, one duct for intake going outside and one duct for exhaust going outside. In theory there no air from inside going outside and vice versa.

For the relay it really depends how to unit you will chose work. If the fan is a single speed fan (like my unit) you could use the relay method and yes the fan will always be at full blast unless you put a controller on your fan. You said your fan take 0-10v signal if that's the case you don't need a controller, only a potentiometer.

If on the other hand the unit fan is controlled by a drive to generate variable voltage, what you could do is find something that convert let's say 150-230vac to 0-10vdc (I just made that up it as to be measured ) this solution is tricky and maybe nothing exist to do directly exactly this. You may have to build something to accomplish this.

Click to expand...

Oh yeah, in the manual it says that you can install some extra ducting. I am based in europe, so it seems I can't get these devices. I was looking a bit for comparable units here in europe, but couldn't find anything. But it seems like energy efficiency wise considering cooling these portable devices doesn't look too bad on paper. So if I could find a unit which doesn't need a charcoal filter for the exhaust air....

Problematic seems to be the heating. Is there anything comparable to heat pumps considering heating efficiency? I mean is there anything else you can buy which has a COP of more than 1?

Actually I need to start running the room with the lights and see how hot and cold it gets. Also heating season is soon over. Better I start get running and then I decide. I was just hoping I could get a solution which would cover all eventualities. Also I don't want to buy stuff that I don't need later.

Considering the rpm measurment, I was thinking to measure the voltage and then send it to some arduino or raspberry which then calculates and sends the proper signal to my fans. There must be something to send a variable voltage signal I guess.

Sam&Max said:

Oh yeah, in the manual it says that you can install some extra ducting. I am based in europe, so it seems I can't get these devices. I was looking a bit for comparable units here in europe, but couldn't find anything. But it seems like energy efficiency wise considering cooling these portable devices doesn't look too bad on paper. So if I could find a unit which doesn't need a charcoal filter for the exhaust air....

Problematic seems to be the heating. Is there anything comparable to heat pumps considering heating efficiency? I mean is there anything else you can buy which has a COP of more than 1?

Actually I need to start running the room with the lights and see how hot and cold it gets. Also heating season is soon over. Better I start get running and then I decide. I was just hoping I could get a solution which would cover all eventualities. Also I don't want to buy stuff that I don't need later.

Considering the rpm measurment, I was thinking to measure the voltage and then send it to some arduino or raspberry which then calculates and sends the proper signal to my fans. There must be something to send a variable voltage signal I guess.

Click to expand...

Exactly what I was thinking about, these is a way to measure the voltage of the fan with the ADC input of a microcontroller (raspberry don't have ADC input but external modules can be installed) and output a 0-10v signal with a PWM output!!

Forgot to say, voltage has to be isolated and bring down to a safe voltage with a small transformer then transformed to DC with a rectifier so you have a 3.3v or 5v max depending of the voltage the microcontroller can handle