Back on with the "recirculated heat for a bus" idea...

bigger duct is to meet volume required i e number of take offs etc, fan speed and size give velocity but if you have a smaller duct then the fan doesnt need to be as big or as fast . no?

 

sorry what i mean is if the duct is smaller and the fan ie at idle is running slower it will send air at same velocity , bit like hoover nozzle in reverse .

 

If it worked better with smaller pipes, why didn't VW make them smaller? It would have been cheaper. I think too much resistance, so with extra fannyage to overcome that why not?

 

on type four they put a separate fan in , so they realised something was not good . I think putting an aux fan is the way to deal with the prob but still think if you took two ducts to the front you would get more control of your air , both temp and pressure , ie for demisting and individual heat etc. dampers hand or cable operated could be fitted ,also you could control air to the back too by having tee offs with damper to rear under seats say . Its just me zed the way i look at it and think it just seems a bit all or not much if you get what i mean, but its 40 years old so who cares really. I get on ok with what ive got i just open windows n stuff .

 

second thoughts the germans are always right

 

If you decrease the duct size then to transfer the same volume of air you have to increase the flow rate ie faster fan to achieve the same pressure. If you have a given volume of air and you reduce the duct size then you will increase the velocity (venturi effect) but reduce the pressure. (counter intuitive).

to that end the transfer pipe would be of an appropriet size to allow a volume of air to pass into it that is appropriate to the heat source producing it. to increase the velocity this may then be constricted in size at the outley to produce a "jet" of hot air for demisting etc.

That said - I put it to you that it was indeed Miss Scarlet in the Dining room with the lead pipe.

Lemon entry my dear Watson, lemon entry!

 

basically the fan size isnt changing......... the fan speed on a type 1 i governed by the engine speed so if you reduce the speed of the engine it doesnt produce so much air and if you have a small duct going into a big duct the velocity drops to a fart at the other end especially at a low speed and more so if you have leaks at the joints etc. IF you had two separate small ducts the air speed would be maintained down each duct and so more than a fart at the end even if the speed of the engine dropped. and obviously if you had a small nozzle or grille the velocity would increase ie at the screen or where ever."thats my point really" .

If you have a large vent duct and not a big enuff fan it wont work efficiently . Also if its rectangular and at more than 3 to 1 aspect ratio then , you need to put splitters in the duct to make it work with more efficiency, A rectangular duct doesnt work as well as a round duct because air runs down the duct in a circle /vortex off of the fan and the corners of a rectangular duct dont actually carry hardly any air , hence this is why they prefer to use circular ducts but in tight ceiling spaces this is not always possible because the diameter has to be bigger so being deeper and taking up more ceiling void depth. The ideal then would be flat oval duct but this is much more expensive to make and not as versatile. Flexible duct is also much less efficient than ridgid duct ,and using more than 1 mtr of flex is not recommended in ventilation systems because of the increase in resistance. That all said most of us use their buses in the summer so who gives a fcuk

 

And for winter you've got Mr Eberspacher ...

 

In essence: you work out what Cubic metres per minute (m^3/min) is necessary to produce sufficient air pressure at the end of the duct...the volume is fixed...the pressure is variable according to the size of the duct...so a fan capable of transferring 100 m^3/min (volume) will produce X kg/cm^2 (pressure) through a duct of Y cross sectional area....the velocity (m/sec) that the air travels through the duct is determined by the nature of the duct/frictional losses etc. So using two smaller ducts (equal to the cross sectional area of one larger duct) will produce more pressure for a given Volume

Colonel Mustard in the Drawing room with a piece of rope...

BUT as @Dicky has rightly pointed out...the actual heat output will be dependent on having velocity and volume tailored to maximize the transfer of heat from the exchangers to the air that passes over it...which is a factor of the total surface area (cm^2) .
So convective heat transfer
W/m2K = X kg/cm^2 x m^3/min
--------------------------- x l (where l is the length of duct) - frictional loss
cm^2

= warmth

Simples!

Alternatively, wear thermals

 

For noisy propex heaters....Make 'em smaller of course

originally developed for weed growers who don't want to arouse suspicion

 

I'm no expert, but that seems like cobblers to me.

 

Right
Ive now lined my flexible heater tubes with egg boxes - that should work to attenuate the sound. Just off for a blast down the M1 to check it out!

 

Assuming you grow your own:
Herbmeister's third Law of Non-linear Psychoses states:
"The coefficient of perceived intrusion (cpi) from unattenuated HVAC systems is inversely proportional to the quantity of product consumed"

 

What was the question?

 

you might need to look at the heat losses and body heat and hot air breathed inside the bus too

 

plenty oF hot air around here matey!

 

been doing vent for 30 years i no nothing

 

Surely if your door seals are very good and your going on a long journey you will eventually suffocate with this set up

 

only if you neglect to operate the vacuum regulator