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Webasto Thermotop C Delta T Query


system 4-50
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I've had a webasto Thermotop C professionally installed but with me doing the water side, the radiators etc.  I had intended to include a car heater blower that I've bought from Car Builder Solutions but am somewhat flumoxed by the Webasto instruction manual.  Despite blower boxes and a fan-assisted warm air heater (I assume these are the same sort of thing?) being shown in many of their plumbing diagrams, their Plumbing Section, Water (Hints & Tips) has the following:

"Blower Boxes"

"Try to avoid installing blower boxes as they are not really suitable for use with these types of heater.  The problem is that nobody manufactures a blower box specifically for hot water applications.  The technology is derived from air-conditioning where it is desirable to have a long winding flow across the matrix to evaporate all the gas and to dehumidify the cabin.  To use this same technology for heating will never work effectively as we need a buffer of water at each end of the matrix so there is parallel flow across the whole of the matrix and therefore a small delta-T (the temperature difference between the flow and return).  With the standard air-conditioning derived units the delta-T will be unacceptably large by the time the liquid has exited the matrix because of the distance the liquid has to travel."

Can anybody help with:

Q1. Does my car heater matrix & fan constitute a blower box to be avoided, or is there a difference?

Q2. Why is a big delta-T bad?  Surely that is what we are trying to achieve ie a big transfer of heat out of the pipework into the cabin?

Q3. What have I misunderstood?

 

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34 minutes ago, system 4-50 said:

I've had a webasto Thermotop C professionally installed but with me doing the water side, the radiators etc.  I had intended to include a car heater blower that I've bought from Car Builder Solutions but am somewhat flumoxed by the Webasto instruction manual.  Despite blower boxes and a fan-assisted warm air heater (I assume these are the same sort of thing?) being shown in many of their plumbing diagrams, their Plumbing Section, Water (Hints & Tips) has the following:

"Blower Boxes"

"Try to avoid installing blower boxes as they are not really suitable for use with these types of heater.  The problem is that nobody manufactures a blower box specifically for hot water applications.  The technology is derived from air-conditioning where it is desirable to have a long winding flow across the matrix to evaporate all the gas and to dehumidify the cabin.  To use this same technology for heating will never work effectively as we need a buffer of water at each end of the matrix so there is parallel flow across the whole of the matrix and therefore a small delta-T (the temperature difference between the flow and return).  With the standard air-conditioning derived units the delta-T will be unacceptably large by the time the liquid has exited the matrix because of the distance the liquid has to travel."

Can anybody help with:

Q1. Does my car heater matrix & fan constitute a blower box to be avoided, or is there a difference?

Q2. Why is a big delta-T bad?  Surely that is what we are trying to achieve ie a big transfer of heat out of the pipework into the cabin?

Q3. What have I misunderstood?

 

Plumb it in to your calorifier loop on the return line, and only use it when the engine is running.  All the massive delta-T drop will do is stop warming the canals and rivers.

 

If you add it to the CH circuit, it will steal so much heat from your radiators that the manufacturers recommend against it, so don't bother using it with the Webasto unless you really want to. :D  You will gain heat at the expense of Webasto system life, which is a bad solution.

 

Q1. Yeah but, no but! If the matrix is fed by waste engine heat that will otherwise go in the canal/out of the car radiator, use it at will.  Otherwise note the add it to the calorifier loop output comment.

 

Q2.  The Webasto wants to maintain a central heating loop at a mostly constant temperature.  Stealing most of the heat part way down is not what they are designed to do, so they need to work harder than they expect.  This is probably better for them than cycling on and off too often, but not recommended.

 

Q3. Cost of Webasto system damage vs Cabin heating!

 

 

 

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What a right load of old techno-babble written by the manufacturer. The real problem is blower boxes as you propose require a truly vast heat input in order for the air from them to actually FEEL hot to the user putting their hand in front of the warm air output. The Webasto gets the blame and they then have to field the guarantee call so to avoid this they made up a load of old twadde to back up their instruction not to use warm air boxes. 

 

Bear in mind the whole 5kw output from your Webasto can easily be soaked up by your scrap car heater. Have you looked up its specification?

 

Q1 Yes

 

Q2 because it starves the other heat emitters of heat 

 

Q3 how power hungry even small warm air blowers are...

 

 

 

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Obviously it depends on the size of the “blower box” but we have a 1.7kw one installed on the step to keep steerer’s tootsies warm. https://www.kurandamarine.co.uk/kalori-heater-matrix/heater-matrix-units/kalori-silencio-fai-kk12014081-kalori

In our case, run from the calorifier loop.

 

But the heating power consumed obviously depends on the fan speed, so on a slow speed it will output a lot less than 1.7kw, the air will feel hot and the deltaT will be low. Even on fast fan though, on ours the air feels fairly hot.

 

The deltaT can be controlled by adjusting the fan speed and water flow so I don’t see any system as being problematic provided the above parameters are reasonable.

Edited by nicknorman
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The blower is:

QUIET HEATER  Yes - only 46db noise output  - you can hardly hear it. Requires hot water feed from your engine.

Supplied as shown below so it's ideal for maybe a secondary heater in the back of a limo, van or motorhome. 

12½" (320mm) wide x 6" (152mm) high x 5" (125mm) front to back. Heat output 5.5 KW.

Maximum air flow 250 m³/hr. Simple plumbing - 15mm inlet and outlet. High efficiency copper core matrix with aluminium fins.

Two 100mm, two speed axial fans with 400mm fly leads Supplied with wiring, connectors, in-line fuse and rotary control switch.

There are two moulded-in mounting brackets which are ideal for floor mounting but you can easily fabricate some

aluminium angle brackets for other mounting options. Fan motor maximum current 2 amps. Weight 2Kg!!  

QUIET CAR HEATER #HEAT5 

12 hours ago, nicknorman said:

The deltaT can be controlled by adjusting the fan speed and water flow so I don’t see any system as being problematic provided the above parameters are reasonable.

This may be useful.  It is a question of whether I can reduce the number of radiators required, 5.7Kw from the Webasto is a lot of heat, requiring a lot of radiator. 

A further question if I may.  Cycling a Webasto is bad for it, but what does that mean?  Is it cycling between full and half load, or is it cycling between off and some load?

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11 minutes ago, system 4-50 said:

The blower is:

QUIET HEATER  Yes - only 46db noise output  - you can hardly hear it. Requires hot water feed from your engine.

Supplied as shown below so it's ideal for maybe a secondary heater in the back of a limo, van or motorhome. 

12½" (320mm) wide x 6" (152mm) high x 5" (125mm) front to back. Heat output 5.5 KW.

Maximum air flow 250 m³/hr. Simple plumbing - 15mm inlet and outlet. High efficiency copper core matrix with aluminium fins.

Two 100mm, two speed axial fans with 400mm fly leads Supplied with wiring, connectors, in-line fuse and rotary control switch.

There are two moulded-in mounting brackets which are ideal for floor mounting but you can easily fabricate some

aluminium angle brackets for other mounting options. Fan motor maximum current 2 amps. Weight 2Kg!!  

QUIET CAR HEATER #HEAT5 

This may be useful.  It is a question of whether I can reduce the number of radiators required, 5.7Kw from the Webasto is a lot of heat, requiring a lot of radiator. 

A further question if I may.  Cycling a Webasto is bad for it, but what does that mean?  Is it cycling between full and half load, or is it cycling between off and some load?

Good question! Cycling on and off is definitely bad. I’m not too sure about 1/2 to full power, I would guess that’s much less harmful.

 

Anyway, that is certainly one huge heater!

Edited by nicknorman
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Soooo ... Webasto say don't fit it to the system, the forum don't think it's a good idea and even the seller of the blower box says it needs heat from the engine.

 

Wouldn't you be better off fitting it to the engine cooling system and bunging an extra radiator on the Webasto circuit?

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9 hours ago, Mike the Boilerman said:

 

And 

 

 

So.... where is the heat coming from for the rads?

 

 

(and calorifier?)

 

 

However the heat is only dissipated if a/ it’s delivered to the device and b/ it’s expelled from the device by the fan. So reducing the water flow and/or the air flow will reduce the heat output and thus leave some for the other things.

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20 hours ago, Mike the Boilerman said:

 

And 

 

 

So.... where is the heat coming from for the rads?

 

 

(and calorifier?)

 

 

As described above, the heater has 2 fans and 2 speeds, so perhaps 1 fan at the lower speed might give a quarter of the output (other permutations are available).

No calorifier.

21 hours ago, TheBiscuits said:

Soooo ... Webasto say don't fit it to the system, the forum don't think it's a good idea and even the seller of the blower box says it needs heat from the engine.

 

Wouldn't you be better off fitting it to the engine cooling system and bunging an extra radiator on the Webasto circuit?

In order, Webasto discourage but don't prohibit, the forum has not produced a massive turnout yet, and the blower box seller is a car specialist emphasizing that it is a heater using heat from a hot water device, and is not a complete heat source in itself.

Better off?  I have a complex situation balancing numerous requirements from my visitors against for example, the physical space required by radiators, and many other factors.  The more I understand about the way things work, the more likely my final choice is to satisfy most but not all of these.:)

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I used one of these, it works great

 

https://www.t7design.co.uk/products/heating/heaters/1-7kw-panel-mounted-cabin-heater.html

did a post on it in boat building an maintenance, in 2015, but don't know how to link to it.

 

 

 

 

 

 

Edited by Bazza954
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1 hour ago, Bazza954 said:

did a post on it in boat building an maintenance, in 2015, but don't know how to link to it.

Click the icon above the post that looks like three balls in a triangle. Copy the link that pops up. Paste it. 

 

Mike will now come along and say he doesn’t see any posts that look like three balls in a triangle... ;)

So I shall reword it thus:

 

Above the post is an icon that looks like three balls in a triangle. Click it, copy the link, paste the link. 

Edited by WotEver
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1 hour ago, WotEver said:

Click the icon above the post that looks like three balls in a triangle. Copy the link that pops up. Paste it. 

 

Mike will now come along and say he doesn’t see any posts that look like three balls in a triangle... ;)

So I shall reword it thus:

 

Above the post is an icon that looks like three balls in a triangle. Click it, copy the link, paste the link. 

 

 A triangle has three sides. I can only see three balls joined by two lines, making an arrow shape....

 

:P

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2 hours ago, Mike the Boilerman said:

 

 A triangle has three sides. I can only see three balls joined by two lines, making an arrow shape....

 

:P

Have you never heard of a love triangle? That usually has several balls and an arrow shape or two, with a couple of lines (not to be crossed).

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