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Combustion Fan Booster

03/22/2017 9:46 AM

This could be either for mechanical or electrical engineering but is probably a little basic for either.

I have a small diesel combustion device intended to heat water for providing comfort heating and domestic hot water in a vehicle. This has a combustion fan and is designed to operate from sea level to about 4500 feet altitude. Since this is in a vehicle that can transverse any road. (And I mean ANY road which to me means someone has taken at least one vehicle there before). So I would expect it to operate up to 14000 feet or maybe a little more. ( I have taken it to 14000 already. The combustion fan is not large, I believe it pulls about 15 watts max.

The manufacturer of the unit sells a modification that monitors the atmospheric pressure and decreases the amount of fuel delivered to the unit to match the pressure available. That means that the output is far less at higher altitudes than at sea level. The thing is, at the high altitudes, you really need more output not less because it is colder. Therefore the manufacturers solution in unacceptable. I would like to design an input booster that would take a 12 volt squirrel cage fan (I don’t think I will need a very big one, not over 10 watt input) to provide a slight pressurization of the input ahead of the combustion fan, simply raising the input to the equivalent of 2250 altitude. It is my intent to utilize a map sensor from another vehicle I own. (Not the one in the vehicle, but one I bought to cure a check engine light before I found the broken wire). The Sensor was only $7 so it wasn’t worth returning) This should give me a 0-5v output. Since I will only be monitoring the pressure between the two fans, I will set up to maintain about an equivalent pressure to 2250 altitude. I will measure the output on my other vehicle, since I plan to travel soon to a location where an old airport was 2250.

I plan to either make a variable speed drive to control the speed of the booster fan to provide that output pressure to the input of the combustion fan or to use a Raspberry or Arduino if I can. This won’t really need to be very accurate, since, Although the device is designed only to operate 0-4500 feet, my home is at 7500 feet and I have run the furnace at that altitude frequently in the past. I recently rebuilt the unit due to a failed water pump and it looked very good, no soot or damage in the combustion area. Actually, I never operate the heater while the vehicle is in motion, only when camping overnight. At first I will probably simply monitor the MAP sensor and manually adjust a rheostat to try things out.

Please point out any problems you see at my approach. I realize that some of you will not understand what I am proposing and will lead others astray, but that is the nature of forum.

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#1

Re: Combustion fan booster

03/22/2017 10:43 AM

I'd vary the pressure in the hot water tank before worrying about atmospheric pressure changes to your combustion air.........good luck.

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#4
In reply to #1

Re: Combustion fan booster

03/22/2017 12:37 PM

Changing the pressure in the hot water tank would have absolutely no effect on the combustion process which takes place at atmospheric pressure on intake and exhaust.

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#2

Re: Combustion fan booster

03/22/2017 10:57 AM

I don't know if your system will work well as stated, it seems to me you should be concerned with oxygen concentration level principally rather than pressure per se, and a small low wattage fan may not be sufficient on it's own....maybe an oxygen concentrator would help....

"At 12000ft, the standard barometric pressure is 66 kPa (496 mmHg). This means that there is 65% of the oxygen available at sea level"

http://www.altitude.org/air_pressure.php

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#5
In reply to #2

Re: Combustion fan booster

03/22/2017 12:40 PM

Although there is much in error on the internet, actually the percent oxygen content is nearly the same from sea level to 14000 feet. The reason for Oxygen to breath at higher altitudes is the lack of pressure, not oxygen per se.

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#10
In reply to #5

Re: Combustion fan booster

03/22/2017 2:07 PM

Then why do people breathe supplemental oxygen at high altitudes? So what effect do you think adding oxygen to your air intake would have?

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#12
In reply to #10

Re: Combustion fan booster

03/22/2017 2:30 PM

That is because for lungs to properly function under high exertion, the partial pressure (mmHg, kPa, or psi units whatever units), must be substantially the same as at sea level.

The partial pressure is not a percentage. The percentage (ratio of the constituents) of oxygen in air does not vary more than few ppm across the barometric column.

Why not just bring a bottle of NOX, or oxygen and use it with the burner?

Or burn higher silanes (not really, no one on earth could afford such luxury). Although, I think I just invented the perfect market for that synthetic fuel. Campers the world over should love me for this.

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#19
In reply to #12

Re: Combustion fan booster

03/22/2017 4:12 PM

I understand the partial pressure relationship of oxygen at higher altitudes, but the problem as I see it is not the pressure, although that may be a contributing factor, the problem is lack of oxygen....I don't see why you would waste your time trying to elevate the pressure when you could just supplement the oxygen...A tank of oxygen bleeding into the intake of the burner would solve the problem easily....

Either that or just get some chemical heat pouches....of course this could be solved by just getting a warmer sleeping bag, and forget about the heater...

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#21
In reply to #19

Re: Combustion fan booster

03/22/2017 4:21 PM

Funny thing is, I went out to the control room for a drink of water, and we discussed this topic. The first thing the old bull said was, "get a warmer sleeping bag, and a hotter dame". He is a biker, so I had to clean that up just a little bit.

Personally, I don't care how nice the sleeping bag, or the dame is if (1) my toes get cold, or (2) I have to take a shower in a bathroom with icicles hanging off the ceiling.

I totally agree all the man needs is a few more small Oxygen bottles, and a needle valve to introduce it into the flow stream. Blowing air faster past the heat exchanger on this is not a great way to stay warm.

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#25
In reply to #21

Re: Combustion fan booster

03/22/2017 5:40 PM

Round here we just fire up another heater when the girlfriend or wife starts coming up short for various reasons.

If I was the OP I would just buy a high altitude rated freestanding portable propane unit and a long hose and run it off a 20 - 30# bottle or larger RV cylinder located outside.

Or just leave the RV engine running being if you can afford a RV and the fuel it uses you can afford to let it idle all night a few times a year to keep comfortable and unlike a DIY heater hack to get more out of something not designed for the conditions at hand it's far less likely to blow up/burn down and kill anyone.

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#22
In reply to #19

Re: Combustion fan booster

03/22/2017 4:29 PM

A bottle of oxygen would be a very expensive solution, and dangerous too. At my altitude I use a CPAP machine which many here do, that compensates for the lower pressure and is much safer than oxygen. The only people here using oxygen here are those with actual damage to their lungs. A CPAP is simply a blower to increase pressure and can develop over 15 psig at a fairly low wattage if you turn off the humidifier and heater. Mine runs at about 9 psi.

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#24
In reply to #22

Re: Combustion fan booster

03/22/2017 4:56 PM

Well if you have a welding setup the tank refill is cheap ~$15, and if you don't, the tanks are only about $55 new...and if you have medicare you can probably get it for free....I'm curious as to the danger you mention, what do you find dangerous?

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#30
In reply to #19

Re: Combustion fan booster

03/23/2017 5:58 AM

In principle, I suppose you could maintain the oxygen partial pressure constant by increasing the concentration, going up to 100% oxygen when total pressure down to about 0.2bara, 20% of sea level. Don't know whether that would be OK physiolgically, but I'd guess it's been tried.

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#26
In reply to #10

Re: Combustion fan booster

03/23/2017 1:03 AM

Concentrated O2 does not play friendly with open flames. In fact, if the OP is a "flatlander" they are the ones that should be on submental O2, otherwise, they will suffer Hypoxia at 14,000ft. I grew up in the Rocky Mountains and when I get above 12,000ft I defiantly feel it. It can strike you before you realize it.

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#32
In reply to #26

Re: Combustion fan booster

03/23/2017 9:14 AM

Apparently, something has definitely affected you. Oxygen is an oxidizer, not a fuel, damnit! I am a flat lander, and I totally object. I live at 3320 ft. elevation. Have most of my life lived in higher elevations. I had no problems (younger) in the Wasatch and Uinta Mountains, around Mt. Agassiz, and King's Peak around there somewhere, near 14,000 ft. but only the most determined go to the crest.

So when you are above 12,000 you defiantly feel it? Did spell auto-correct bite you in the posterior yesterday? Did you mean to say "definitely feel it?"

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#37
In reply to #32

Re: Combustion fan booster

03/23/2017 12:53 PM

Perhaps an effect of the 'submental oxygen' previously noted.

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#38
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Re: Combustion fan booster

03/23/2017 1:23 PM

Thumbs up vote on that!

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#34
In reply to #26

Re: Combustion fan booster

03/23/2017 10:20 AM

My home is at 7600 feet and the trails I walk out my back door are higher. I have no problem with this altitude. My %O2 in the blood runs about 98% according to a finger monitor. When people come to visit, we have to tell them to wait a couple days before they try anything strenuous. When I reach 14K up in Colorado area, I walk and never run. I tried running a little at 14K and thought I would die.

When we had a friend visit that was having a lot of problems, we told him to practice breathing like he taught his band students (He is a retired high school band teacher) That helped him a lot. My wife struggled with breathing for a time and finally is now able to do well at this altitude.

14K is really tough and I wouldn't want to try sleeping at that altitude without my CPAP but I definitely do not need oxygen supplement. I still can keep my O2 around 95-96 % while awake but need to use every bit of my lungs.

The need for the heater at 14K is more than just creature comfort, although I do like that, but with a motor home, the domestic water, holding tanks, etc must be kept above freezing unless you wish an expensive repair bill. My motor home is a classic (over 25 years old) gets wonderful mileage (26mpg towing a Samurai) but replacing a tank would involve having a custom unit made which would cost many $$$$.

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#3

Re: Combustion Fan Booster

03/22/2017 12:33 PM

I don't like this approach but what do I know?

As I see it you have at least two problems here. A slight pressurization of air prior to the combustion blower might partially address the first problem of a lack of oxygen to burn the amount of fuel per second. However a larger volume of air will reduce the amount of time the exhaust gasses are in contact with the heat exchanger. Thus while it might allow you to completely burn more fuel per second, less of the heat from the fuel will go into heating water.

To repeat myself, what do I know? ¯\_(ツ)_/¯

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#6
In reply to #3

Re: Combustion Fan Booster

03/22/2017 12:45 PM

Having done much field engineering work from sea level to very high mountains, the increase in pressure was successful in boilers used in the power generation industry. We did have to restrict or shorten exaust stacks at times. Many times this was done because of consulting engineer errors by people not familiar with high altitudes.

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#8
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Re: Combustion Fan Booster

03/22/2017 1:13 PM

So it seems my thoughts aren't completely off base. What do you know.

It sounds like a combination of an added fan and a damper control for the exhaust might fit the bill.

Good luck, just be careful of the possible carbon monoxide levels.

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#9
In reply to #6

Re: Combustion Fan Booster

03/22/2017 2:01 PM

Then you should be aware of the actual pressure differentials between 2000 - 4500 feet and those at 14,000.

Do you think you can generate 4 - 5 PSI static pressure in a combustion system with a 1" dia 6 foot long pipe for an outlet with any 12 volt DC blower fan?

The way I see it for all the possible engineering and redesign of what you have to make it work as yo want where you want I would just buy a high altitude compatible auxiliary heater and use it if and when the main heater you have is showing it can't keep up.

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#7

Re: Combustion Fan Booster

03/22/2017 12:56 PM

I will note that exhaust is about 1 inch and over 6 feet long with a muffler. This makes boosting the combustion fan in my opinion feasible due to the restriction. Also, I will simply be raising the input pressure to 2250 altitude equivalent. The exhaust should not have much effect on the combustion considering how much restriction it has. If it can normally run at 2250 feet it should run at 14000 boosted to 2250.

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#11

Re: Combustion Fan Booster

03/22/2017 2:21 PM

Have you considered over-sizing the fan motor to your furnace, and using a design more like a turbo on an ICE? Only thing is you will not have the other high energy high velocity gas to drive a turbo. So use your raspberry pi or arduino sketch to control pulse width on some pins, and just synthesize a new DC voltage for each elevation from your pressure sensor (MAP).

Or, you could bring an oxygen bottle, and just increase the oxygen partial pressure so the partial pressure in kPa (or psi) matches that at a lower elevation. OR you could obtain some heptasilane fuel (about as rare as metallic hydrogen), because that burns in oxygen and in nitrogen (once it is lit). Heptasilane is about as stable as diesel, and does not spontaneously ignite in air like SiH4 silane does. It has a good heat value also.

If you want to skip the Arduino, and just turn the knob based on what you think the altitude is, why not install another car battery to load the alternator during your drive up? Once there, and the vehicle has shut down, flip a switch that results in the parallel batteries being connected in series, and install a $35 buck converter DC supply from China (or from USA if you could find one), then you can tune in the fan without wastage of electric watts from any dummy load.

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#16
In reply to #11

Re: Combustion Fan Booster

03/22/2017 3:42 PM

I have plenty of batteries for night operation, (4kwh) to run a fan. The heater actually takes an average of a little less than 1KW. Right now I have a 12 volt vacuum cleaner which works poorly as a vacuum cleaner but doesn't pull much of a load pushing through the unit at over 8psi back pressure. At that pressure, the exhaust volume is more than with the combustion fan running. It does look like I might have to damper the exhaust. The vacuum cleaner will take less than 0.35 KWH. As long as I supply enough oxygen, CO shouldn't be a problem, It should be better than in the deprived state, running without the boost. But CO is easy to monitor and I have internal monitors for that anyway.

The biggest problem right now is finding the time to make measurements and try it.

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#17
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Re: Combustion Fan Booster

03/22/2017 3:48 PM

Sure, and good luck. Safety and reliability is key, especially when in remote areas. Help cannot reach you in any "normal" amount of time.

I still like my oxygen bottle idea, to ensure you keep the BTU count right at the output.

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#18
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Re: Combustion Fan Booster

03/22/2017 4:08 PM

How likely is it that running a back-pressured system that exhaust fumes could leak into the living quarters? Is that really a risk anyone should ever take?

I thought you said this was more like a boiler system anyway, such that any and all exhaust fumes were outside the living quarters. I agree that a flue damper is necessary in the respect that it will result in restoring pressures to nearer sea level conditions.

I can also see that introduction of a small stream of oxygen added to fan output would help with keeping you on the lean side of the burn curve.

Can you also tolerate the noise of the vacuum cleaner blower running all night?

Is there any way to adjust the burner design to better accommodate high altitude operation, still get lean burning with the required BTU output? I should think so, but it all depends on what the thing looks like now, and if there is any room to increase the size of the H-X unit, so longer contact with rapidly flowing gases is possible.

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#23
In reply to #16

Re: Combustion Fan Booster

03/22/2017 4:35 PM

I will correct the reply above. The heater takes less than 1kwh electrical energy for 8 hours. I normally run it about 3 hours over a nights rest stop. The heater output is about 5KW per hour.

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#13

Re: Combustion Fan Booster

03/22/2017 2:34 PM

The design of equipment for high altitude operation involves the balancing of many opposing conditions. While it's true that the percentage of oxygen remains fairly constant, the problem is that the density of the air goes down which means that the volume of oxygen available for combustion goes down as well.

Using a fan to force a higher volume of air through the combustion chamber does increase the available oxygen, but the excess air results in a cooler flame temperature. Restricting the outlet flow to increase the transit time tends to be counterproductive because the combustion products affect the fuel/air ratio resulting in poorer combustion. Large power boilers designed for high altitudes get around this problem by having larger heat exchanger surface areas to capture the lower quality heat before it goes up the stack.

So if you can figure out a way to put a water jacket around your muffler system, you could add an additional 225 sq inches of heat exchanger area (aka an economizer) to your system, but then you run the risk of cooling the flue gas to the point where it might not lift high enough away from the camper...cough, cough...

Messing with combustion stochiometry is never a good idea, especially in tight spaces.

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#14
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Re: Combustion Fan Booster

03/22/2017 2:59 PM

Unless you completely tip the scales by enriching partial pressure of oxygen without increasing nitrogen. Then the lower velocity through the exchange zone will result in better heat output.

Alternative fuel? I don't really think it is necessary, but I suspect one could effectively burn heptasilane at an altitude where diesel might not even ignite.

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#15

Re: Combustion Fan Booster

03/22/2017 3:29 PM

This is a typical graph of differential pressure against volume for a radial squirrel cage:-

From AddA

H is a 9 Watt blower and U a 13 Watt

The left hand axis is labeled in inches of water (InAq) from 0 to 3.15.

You want to create a difference in pressure equivalent to elevations of 2250 feet to 14000 feet

From Wikipedia

Say 60 kPa to 90 kPa

i.e. 30 kPa or about 120 inAq

The increase in volume of air through the burner might achieve what you want, but, don't expect to get that increase in pressure you're looking for.

There's a really good document on fans pressures and altitude at cincinnati fan

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#20
In reply to #15

Re: Combustion Fan Booster

03/22/2017 4:20 PM

You have brought up some significant points, the first of which is the definition of a fan, blower or low pressure compressor, all of which can have a squirrel cage configuration. You have looked up a fan design which was the words I used, and that was in error. What I have experimented with so far could better be referred to as a low pressure compressor. The volume through the heater is quite low also and has the restriction of the intake piping, exhaust piping, muffler, combustion fan, and the combustion itself which creates some back pressure. The actual flow is far less than the 33 CFM in your example and that is for a blower fan, probably used for cooling. I will need quite a different design. It will probably be closer to a vacuum cleaner but may need a custom impeller. I have tried several blowers out so far and a poorly designed vacuum cleaner for 12 volt comes in best. Driving air through the unit it produces 8psi but when I turn on the combustion fan, the pressure actually increases and I shut it off immediately to prevent damage to the heater. I will install a rheostat and see what happens.

Also, although you read it correctly, just so someone else does not make a mistake, The altitude on your graph is for meters so 14000 feet is a little over 4000 on the graph.

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#27
In reply to #15

Re: Combustion Fan Booster

03/23/2017 1:10 AM

Standards only work at sea level. Things change as you climb, density altitude, temperature, humidity ...

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#28

Re: Combustion Fan Booster

03/23/2017 2:56 AM

"... The thing is, at the high altitudes, you really need more output not less because it is colder. ..."

.

Investigating how you might improve the insulation of the hot water tank, lines and any penetrations/connections, would probably be worthwhile.

If it doesn't loose as much heat, it won't take as much to get it and keep it hot.

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#29

Re: Combustion Fan Booster

03/23/2017 5:58 AM

I find the theory great!!

What sort of electrical power are you going to be using? 12 or 24 volts?

I assume that you are going to use a car engine air volume sensor, which does the exact job you are looking for!! (You will have trouble measuring relative air pressures in other ways I feel.....)

Its called generally a MAF. Look here:-

Air Mass Flow Sensor

I will follow the work with avid interest!!

Do keep us informed....best of luck!!

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#31
In reply to #29

Re: Combustion Fan Booster

03/23/2017 6:19 AM

I forgot:-

Calibration of the fan blades will only be needed once.....also, fine adjustment will be possible with a small simple bit of electronics (PWM) to control the basic "speed/voltage".

After that, it will just run at the speed needed according to the air resistance!! A fun project....

I will follow the work with avid interest!!

Do keep us informed....best of luck!!

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#33
In reply to #29

Re: Combustion Fan Booster

03/23/2017 9:36 AM

Andy, Thanks for your kind words. I had not thought of a MAF. That would probably make things easier and would give better results than a MAP which I had intended to use. The only real problem is that most MAF units are for a much higher air volume and are rather costly. For a one on trial, Somewhere in my junk, I have the same thing, but it was something I was trying out, back in the late 70's for a monitor on one customers (a big customer} that had a process for transformer drying called a "Cold Trap" which involved either dry ice or refrigeration to pull the moisture out of circulated nitrogen in large power transformers. We typically used Vacuum and time to do this, but I tried the MAF type device to monitor the flow. It did work but the customer finally changed methods and I kept the test unit. Now if I can only find it????

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#35
In reply to #33

Re: Combustion Fan Booster

03/23/2017 10:31 AM

I am looking into gas flow measurement ideas also (for my LENR experiment, either confirming or denying the heat balance as something other than unity).

The first mass flow meter I looked at was over $1000. Then I got a quote for a reference standard wet test flow meter in the flow range I need, and it was decked out new at ~$6000, while a refurbished, but highly accurate one (same German OEM) was nearly 3 large.

I saw this on the internet (but got zero response from the maker thus far):

senflow.flowmeters@gmail.com

senflow for liquid or gas measurement

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#39
In reply to #33

Re: Combustion Fan Booster

03/23/2017 2:06 PM

LOL!!

They might be expensive, but I do believe almost any modern Turbo Diesel/Petrol engine has one, so go to the scrapyard........

Even making one, is not beyond a DIYer....

You buy some resistance wire, make a lattice of it in a sturdy air tube.

Pass a DC current through it.

Monitor the current.

Blow air through.

As wire is cooled, current will increase.

Reduce current to a stable level.

The cooling effect (as you apparently already know) is a direct reading of the "amount" of air passing. That is "How many air molecules are passing through and cooling the lattice down?"

As the air gets thinner, the cooling gets less, current drops as the wire heats up.

Then increase voltage to the series DC motor, till the cooling takes place at the required rate.....though as the air gets thinner, it will speed up at the same voltage without adjustment anyway.........

Or a moving vane version might be easier.......

Mass_air_flow_sensor

I have never done this, but that is probably how I would do it!!

Note, never run a series DC motor without a load (fan blades), it might over speed and disintegrate!!

May vacuum cleaners have a universal motor (and a fan), that is basically a series wound motor, that might be adaptable for you......long shot....

If no series wound motor can be found, then you will need a variable speed fan and use PWM to control its speed, as I previously mentioned.

See here:-

Universal_motor

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#36

Re: Combustion Fan Booster

03/23/2017 10:56 AM

It sounds like you are trying to turbocharge your hydronic water heater. Easiest solution is to enclose the unit and blow into the enclosure to develop overpressure and let the optional supplied sensor control the mix. The key is, at 14500 ft altitude, it appears you will need to be able to develop about a 5 psi overpressure in the enclosure to operate as if at sea level. The squirrel cage will not deliver that sort of pressure and volume of flow.

A second issue is pressure sensor location. If the pressure sensor is off in some panel somewhere rather than at the burner air intake or in the burner housing, then pressurizing the burner enclosure won't affect the fuel flow reduction from the optional control.

The last issue is noise. A blower with the power level required will need some attention in noise control.

As an alternative, I would suggest electric radiant floor heat and a quiet generator. The comfort level will be much higher.

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