Measuring and calculating the actual heated air output from the diesel heater.
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- เผยแพร่เมื่อ 27 พ.ย. 2024
- It's something I've been meaning to do for a while and a question from a viewer spurred me on.
Let me know if my method and maths are actually doing the thing.
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Only thermodynamic power equation you'll need:
Mass_flow_rate x specific_heat_capacity at constant pressure x (outlet_temperature - inlet_temperature).
For bulk flow velocity to mass flow rate assume constant density and use: air density at sea-level. Mass flow rate = density x velocity x flow area.
Incompressible flow assumption valid as is very very subsonic.
Use 1005 J/kg/K for specific_heat_capacity at constant pressure.
This is a zero dimensional calculation and is very relivent here.
Great channel as alway!!
Thanks David. There’s no reason to try and be any more precise than you’ve already done, because as you said, everybody’s setup is different. As long as you’ve got a ballpark estimate, that’s good enough. I’m certainly happy with the output of my 2kwatt heater in my transit camper. It keeps us roasting in sub zero weather. Keep up the good work! kind regards, K33F
Enjoy your Diesel heater videos .I have learned alot .Thanks David keep them coming 👍
Nice work, thanks for doing the tests! Your numbers make sense to me and match what I've calculated with my setup. 80-85 percent efficient makes sense because they don't continually generate condensate. That is usually 85 and above.
So I bought a 5KW model from some seller on Amazon and from day one I wasn't overly impressed by the heat output. Picked up an anemometer to measure the flow rate and plugged the values into the conversion websites uses here in this vid to discover to my horror, the advertised 5KW power output fell way way short. In fact, I got a measly 2.27KW for a flow rate of 9.4m/s with an input temp of 22C and output temp of 60C. To get anywhere close to 5KW, that output temp would need to be 106C , or the flow rate would need to more than tripled!
What really annoyed me was the seller trying to fob me off saying TSD-2 on the model/rating plate merely meant the unit was a split type (i.e. heater and fuel tank not in the same housing). When looking at the operator manual which gave physical dimensions of the 2/5/8KW models, it was readily apparently the "5KW" model I was sent fell short of the overall length by almost 100mm. To add insult to injury the supplied remote wasn't supplied with a battery and the manual made no mention of what was needed. Assumed it was a regular 23A 12V 'car alarm remote' type battery it didn't fit. After hours of searching, discovered there's a marginally smaller 12V, the A27 which worked a treat, albeit sourced over a week or so later from the heater arriving.
Left a scathing review on the item and returned for a full refund.
wat a knob
Good to hear from you, was getting worried after the storm.
Thanks David! If you've not already got a Marine Engineer's sheepskin on the wall I should send you mine. If you ever get a chance check out the Wallas diesel heaters from Finland. They have a few nuances that the bus heaters don't. The exhaust goes out the top (handy when the ocean is down,) and preheats the combustion air in a double walled flue pipe resulting in warm not hot exhaust gas and no need for flue insulation. The igniter is a glow wire and runs nearer 5A of 12 V dc on startup. I've run them for 20 years now on the boat I live aboard and am just starting to experiment with a toolbox portable China bus heater for fun. My suspicion is the Wallas runs a higher efficiency just based on the similar fuel pump and very low operation frequency but it's hard to beat 100%!.
I'd like to see inside a Wallas heater now. :)
@@DavidMcLuckie I'd take mine apart and share a video except (1) I have a face for radio and voice for the silent movies, (2) I despise video editing, and (3) the damned thing is running great at the moment and if i mess it up a new one is $$$!
Great information David ...gives me a rough idea of what mine will be using in the van 3 3l ph high, 1 4l ph low...ish! Thanks
yeah , i tidy my workshop once a year , whether it needs it or not .. as for your calculations NFI , but nice colours on the whiteboard
I know it's been a year for this video but I couldn't take my eyes off the melted plastic bottle of fuel at the exhaust lol. Great video though as I just bought one of these to suplament a 14k electric furnace that would not keep up with 25 F outside. Best it could do was 62 F inside and with one of these in a 1000sq foot room the furnace actually cycles and the temp stays at 70 F. Also this is just with the heat blowing in an the unit outside with the air intake pulling in that 25 F temp. Very nice and I am going to fully plumb it in so it intakes the warmer air inside. Might be able to turn off the expensive 35 USD a day, yes 35 a day at below freezing, furnace. Thanks for the videos and looking at tuning the thing now.
Near for you looks perfect to me. I just say that the room felt warmer. Excellent video. !:- )
I don't know how you could make this better without expensive test equipment
Very good David. The results shows that little energy relative to the energy of the hot air outlet is lost through the exhaust. Perhaps around 14% loss. 86% efficiency is better than running a diesel engine to supply electrical power to, say a radiator. At best you would get 50% efficiency, more likely to be closer to 30% efficiency as a guess.
But you also get electricity 😁
@@MickeyMishra from the exhaust Mickey? Yes, you can get some electricity from the heat of the exhaust but that will come from a proportion of the waste energy, again at best 50%, more likely much less of this - at best you will recover 5% improving the overall efficiency from 86% to 91% - mind you these are very optimistic guesses!
@@MiniLuv-1984 Exactly and SPOT ON!
Also i saw someone who removed the disel pump, and used a switch and gravity fed the disel heater it apered to work would be cool to see what the pros and cons are, also porting the intake exhaust for better performance 🧐
Thanks David, great work, would be great to see the % efficiency
Only thing I'd say is your air mass calculator seems to be using the density of air at 0°, at 70° air is 20% less dense which will be reflected in your final figure. This is all at sea level, so if you want an even more accurate figure then you need to figure out the barometric pressure at the time of the experiment.
I think you may have a higher measured/calculated air quantity than actual due to the bend in the duct.
You had the anemometer on peak, but if there is more concentrated flow on one side than the other, this will skew the results.
You could straighten the duct and take a reading, use that in the calcs.
The temperature rise may be slightly lower with a straight duct due to increased flow.
But then those things could offset each other and still end up with the same results!
Great information, thank you!
Repeat it several times at the same settings to get an average. Then you can give us an estimated % efficiency
Thanks for this! Understanding the air volume and temperature change will help in deciding the size of the heater for the volume of the space you want to heat. 😃 Thanks for all the brain food you serve up.😀
Hullooooo! Question for you, Sir? I bought the supposed "8K" heater. I'm finding that there's not much difference in heat output above the 3.6 fuel setting - just uses far more fuel. Do I need to tune this thing? If so, how would you suggest? Note: I've noticed that my fan seems lazy - it speeds up when I increase fuel, but soon reverts to slower speed. I believe heat is being wasted out the exhaust and not exchanged due to this - do you concur? How do I make the fan run faster, more of the time?
Your videos are great as always. It would have been an interesting add on to see what is the heat output of the diesel exhaust. Might have been an interesting sanity check, as the two heat outputs should be roughly equal to some (lower) percentage of theoretical output of a perfect diesel burn which you calculated already.
I haven't come up with a way to accurately measure the waste heat from the exhaust. My anemometer will melt. :)
@@DavidMcLuckie yes you would have to try to measure the intake side instead but I'm guessing it would be hard to get a good seal to get an accurate reading
Hi, when I first purchased my 5kw heater it worked well straight out of the box brilliant, after a month or so core temperature seems to be dropping 150c at max output and 105c low power idle.
Am I right in thinking it's getting coked up and coke is acting as an insulation. Also starting to smell of diesel. Any thoughts.
Looks like my workbench, is it contagious? as I bought a heater after watching this channel for years
Sadly yes. All my workbenches now look like this.
I often wonder how high the output would be if you joined 2 heaters together. Heater Centipede style.
maybe I should get out more ;)
Hello David, thanks a lot for your videos! I finally made the decision to buy one of these magnificent engineering marvels. However, since I own an old VW Bus that has "historical value" I'm rather hesitant cutting a hole in the floor of my bus. I'm wondering if it's enough to only cut a hole for the exhaust so the fresh air intake will use cabin air. I assume it will work that way but do you reckon it will have any impact on the Diesel heaters performance? Maybe you could run a test? Thank you :-)
Not so much on the heaters performance as a heater exactly but it does have a negative effect on the temperature. The reason you don't use cabin air for combustion is that you have to replace that air from outside once it's been burned and gone out the exhaust. So you are taking cold air from outside into the cabin, burning it and sending it out the exhaust. Instead of just purely heating the circulating air in the cabin. Some people do it deliberately to keep the air in the cabin 'fresh' at a slight loss to heating performance.
I would love to know how mutch watts ouput you will get it you boost up the rmp’s and pulse rate.. that will give more kw’s right? Like to hear from you!
Do they have kilt style coveralls in Scotland? I'm just playing, your earlier videos kinda sold me on the cheap china heater for my truck canopy hunting rig,cheers from western canuckistan
what if you reduced the input air hole up by half, I did and the sensor temp went up by 38C in altitude mode, I'm now thinking of putting a 16ml pump on to replace the 22ml one just to see how that works out
David, based on your knowledge of these heaters and heating in general, would it make sense to purchase a 300CM exhaust pipe and coil it up into a nice circle spiraling downward (condensation) before exiting the HVAC area and blow a fan up through it. Recover the heat going outside with a small 5 watt fan? your thoughts on this including safety.
That's a great idea. The only thing I would do is to tune it again for CO after adding that length of exhaust as it will add a bit of restriction. As far as safety is concerned, other than burning yourself on it there isn't much else. :)
5kw heater is really 3,5kw
thanx for this test video. I wonder dit you ever tested if the amout per hz is wat you used in your calculation. i think the real use per amount of time doesn't go that liniar to the frequenzy of the pomp
Good job! Good enough, and most won't do the math or care! They just want the heater to work; just saying!
Hi David.
Do you know of any additives to keep the glow plug clean and from fouling??
So about 33 pence an hour to get 3.5kw of heating, using heating oil. Compared to electricity at 34 pence per kwh currently (Nov 2022). If you could run these off of used cooking oil you'd be on to a winner! I guess a more accurate way to measure airflow might be to let the heater inflate a large bag?
Thanks. You say these numbers are for the 5KW heater, I wonder what the 8KW unit would produce, higher pulse rate.🤔
I can 'make' it 8KW. But it'll produce enough carbon monoxide to actually cause me to leave the workshop and stand outside until it clears. 8KW heaters don't actually exist.
@@DavidMcLuckie Okay, thanks for that comeback.
I didn't mean for my reply to sound as rude as that. What I meant was there are only two 'sizes' of heater. A 2KW small body and a 4KW large body. Everything else is marketing. I've seen 10KW and 12KW advertised. And some sellers trying to sell the large body as a 2KW as well.
@@DavidMcLuckie thanks again, while i assumed that from your videos, I thought maybe they included a higher pulse rate controller in the 8KW unit.
Steve
@@DavidMcLuckie This is pure gold information for me.
How long do these last on just battery power like a marine battery. Or how many amp hours does one use.
For your typical 110Ah leisure cell, it would power a heater non stop for around 24 hours.
Your the only person I think would test if you can run a 24v heater on 12v just by changing the controller setting. Or vise versa.
There is debate on if the glow plugs are all 12v and given a pwm signal allowing them to be ran on either.
Or perhaps a 24v glow plug will still get hot enough to start the thing since the warm up period before it starts pumping is pretty long.
The only thing not 24V on a 24V heater is the ECU. The fuel pump, fan motor, and glow plug are all 24V.
@@DavidMcLuckie the fan should be pwm controlled so 12v or 24v should just alter the duty cycle for the fan. Fuel pump just being a solenoid might be forgiving with what it does and dosnt accept.
I know 100% the 24V fuel pumps don't work with 12V. I've had two by accident now.
I have one idea, but don't know the math. How about a know volume, heated with a closed loop? So a box connected to both the air in, and air out.
Ideally to do that you'd use a huge box you could put the whole heater in. Then you'd know the volume air inside the box and all you need to do is time how long it takes to heat the air by an amount. There is also a factor of the box radiating heat you'd have to take into account.
I don't have any boxes big enough. And I did google room heating equations but that made my head hurt.
@@DavidMcLuckie well if someone out there can work out the volume of their van and it has some insulation. Wouldn't be mega accurate but would give some real world measurements.
what is the efficiency somewhere around 85-90%?
Bought the 8kw chineese diesel heater thinking it would give an ouput of 8kw.. to bad it’s just marketing i think.. 3,5 kw is not enough for my shed so i’m looking for an idea of boosting it.. is it possible for you to test higher fan speed and pulsrate (outside test) and check how mutch kw you can get by messuring with your wind meter and online calculations? Maby on 7.0 hz or something? 😊
It is a test for the future. But I think we worked out that to get the 8KW we need to use the massive fuel pump and the fan won't spin fast enough for it burn properly.
12:18 i say the same, except i make a halfhearted effort in the Spring x)
Great videos 👍
I don't care about efficiency I care about reliability more than anything especially in an automotive application where you really need to work and so many various conditions and weather types that it's really amazing anything still works after just a few years.
the Chinese are so Advanced. If only America knew this technology on how to make steel that doesn't melt with fuel like kerosene or diesel we could be a superpower one day!
I like learning
Forgive my ignorance, but is a leisure battery a wet cell, AGM , deep cycle?
A 'cheap' leisure battery is normally flooded. A true deep cycle battery is very heavy due to the thickness of the plates. A true deep cycle battery can be any one of those, ie gel, AGM or flooded. Gel are very fragile in terms of charging abuse, because any over charging ie an equalise charge will lift the gel from the plates. AGM are fairly resilient but impossible to replace electrolyte lost from the vale regulator in the event of excessive gassing. The most resilient are large flooded cells used for forklift or old telecom backup systems. However, they do not like being left at a low state of charge for extended periods.
Hope this helps.
Loved it
Try to calculate the heatoutput of the exhaust 🤔
Came here to say exactly this - doing the same calculations on the air intake and exhaust should then highlight where the inefficiencies are and should lead to a more accurate answer (given you're burning a known quantity of diesel with a known calorific value, heat out of the internal and external exhausts should add up)...
The heat lost through the exhaust seems quite a lot. I'm trying to devise a heat exchanger to pre heat the air before it is blown threw the heater.
Being a tight fisted English personage
I'm wanting to know can you use kerosene in these heaters or a mix of kerosene and diesel?
They run fantastically on kerosene.
@@DavidMcLuckie brilliant only ask as we live in a caravan and our main heating fuel is kerosene
Does the fuel consumtion match i live test 1 L Diesel =?
I lack an accurate way of measuring that. I need to get a set of scales.
Sorry if this is slightly off topic, but does anyone know if there is an equivalent glow plug used in combustion engines? It's seems odd to me that the original designer of the heater would make a bespoke plug rather than use a readily available off the shelf part. I cooked my heater and am having to replace the mother board and glow plug. It would be nice in the future to be able to go to a motor factors and get an off the shelf part.
Thanks in advance..
Automotive diesel engines do use glow plugs, but I have no idea if any are compatible.
I imagine that automotive glow plugs are designed to run for short periods of time?
@@MiniLuv-1984 not necessarily, they stay on for roughly the same amount of time. They're normally timed.
Answering my own question, I guess I could take dimensions and compare with a Bosch data sheet.
@@yodab.at1746 Ofcourse, the glow plug in the diesel heater will turn off when it is up to temperature....for some reason i imagined they ran continuously. Thanks!
I don't understand all that mathematic mumbojumbo so does a 8kw heater actually produce 8kw?
No. As 8KW heaters only exist in marketing. But you've given me an idea to see if I can actually get 8KW out of the heater, and find out what it runs like.
Oh you don't want to use my maths, they're awful, I forget what 2+2 is some days... :P
i seen this done before by a mad maths guy but before you can make a guess to kw hrs or btus dont you need a time factor also? i think the other man timed 1 hour for the complete test then he was able to calculate the actual kw/hr and compared that with the energy stored in the diesel that was missing from a full tank. and looking at the specified kw/hr ratings from vevor they said 5000w and 8000w but no time factor so nonsense
Isn’t that ducting 70mm?
A bit like BSP sizes, the regulation size isn't quite the measured size.
Why not calculate heat output in Watts?
Uhh, I did both Kilowatts and Megajoules.
yay
Wow 🧐🙃🤯
So your outlet is 35mm ? My 8k is 75mm
That’s what you entered into your calculations
Radius yes, diameter no.
You know someone is going to say the outlet pipe of the heater is bent, which reduces the air speed.. LOL. Ok it was me that said it but I'm not that anal to care. 😁
You're right. It dropped it by about 2m/s. But it also made it a few degrees hotter than straight out the open heater.
@@DavidMcLuckie If I was the only one to say it, I'm surprised because YT is full of critics and brain surgeons that know everything. LOL. Keep up the great work with your videos mate. I always really enjoy your heater experiments.
we use fahrenheit ! 😑