Making my webasto more efficient?

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
Summary:
The air intake for my webaster water heat exchanger is under the floor. If I duct air from the room it is warming, it'll make it more efficient right?

Full story:
I have a water heating Webasto. An old DW80. It is amazing at heating the hot water in our calorifier but only average as an air heater. Currently my heater pumps water around the boat to 4 separate heat exchangers in 4 cabins. The air from these each exchangers is frankly only warm... not hot.

I have insulated all the ducting and insulated all the water pipework from the Webasto to the heat exchangers. However the heat exchangers themselves are ofer in lockers or under the floor in cold locations near a bare hull. If i change one of the heat exchanges to a car heater type, which allows me to duct the air INTAKE then it would allow me to suck already warmed air back through the heat exchanger.

My point being... warming cold air and pumping it into the cabin space must be a lot worse than cycling air that your already warming in the cabin and leave the air under the floor boards and in lockers, cold.

Right?
 

scruff

Well-known member
Joined
2 Mar 2007
Messages
1,171
Location
Over here
Visit site
The colder air from outside will be drier than air warm moist air from the cabin so require less energy to heat. It will also reduce condensation.

There could be a way of utilising a heat exchanger on the exhaust to pre-warm intake air. Need to ensure you aren't pumping exhaust back into cabin mind...
 

Daverw

Well-known member
Joined
2 Nov 2016
Messages
2,761
Location
Humber
Visit site
If you not sure what people are taking about when they mean outside air is drier, next time your in your car put you heating on in recirculating mode, see how quickly you cannot see out your windows.

Yes the downside of heating outside air is more fuel but a drier boat.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
I appreciate the outside air thing but my webasto doesnt take air from the outside even in its current format. It's a water heating webasto not an air heating webasto. I'm assuming the latter draw air from outside? I've never used one so I wouldnt know.
 

pcatterall

Well-known member
Joined
2 Aug 2004
Messages
5,431
Location
Home East Lancashire boat Spain
Visit site
I appreciate the outside air thing but my webasto doesnt take air from the outside even in its current format. It's a water heating webasto not an air heating webasto. I'm assuming the latter draw air from outside? I've never used one so I wouldnt know.

Yes some misunderstanding of your question. You are not warming cold air from outside but warming cold air from inside.
In the worst case cold air from the hull. The debate about recirculating cabin air using air heaters is another matter ( but I know I usually recirculate the air in my car and that the Eber manual shows a recirculating set up for their cab heaters)
 

pvb

Well-known member
Joined
16 May 2001
Messages
45,603
Location
UK East Coast
Visit site
I appreciate the outside air thing but my webasto doesnt take air from the outside even in its current format. It's a water heating webasto not an air heating webasto. I'm assuming the latter draw air from outside? I've never used one so I wouldnt know.

It doesn't matter what sort of heater it is, the general consensus view is that simply re-heating the air inside the boat encourages the build-up of condensation, which is why most air heaters draw the air to be heated from outside.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
It doesn't matter what sort of heater it is, the general consensus view is that simply re-heating the air inside the boat encourages the build-up of condensation, which is why most air heaters draw the air to be heated from outside.

For me its impossible to duct all the air blowers from an outside feed. I could install more radiators in the boat. I have two already wired into the webasto circuit in addition to the matrix air blowers. But a radiator is still going to do the same thing. Heat air already in the cabin.
 

scruff

Well-known member
Joined
2 Mar 2007
Messages
1,171
Location
Over here
Visit site
If I now understand correctly, your system is closer in set up to a domestic central heating system than a more common blown air heating system?

You say it heats the water in the calorifier fine to hot temps, but does not effectively distribute the heat around the boat?

What condition is the water pump in? Could it also be that there is high pipe friction in the water system? Could you try draining the system down, disconnecting the rads and try blowing down the distribution pipes - see if there is a blockage / sediment build up?
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
If I now understand correctly, your system is closer in set up to a domestic central heating system than a more common blown air heating system?

You say it heats the water in the calorifier fine to hot temps, but does not effectively distribute the heat around the boat?

What condition is the water pump in? Could it also be that there is high pipe friction in the water system? Could you try draining the system down, disconnecting the rads and try blowing down the distribution pipes - see if there is a blockage / sediment build up?

Well you could be right here. I think my pipes are smaller than they should be looking at the old DW80 Webasto specs. I agree this could well be the main issue. Replacing all the pipework for a larger diameter would be a massive undertaking.

The radiators do get hot but perhaps there is simply not enough flow to feed the heat exchangers with enough water to blow hot enough.

Another option is get a heat exchange with more exchange matrix and a smaller fan. For example I have a matrix heater linked into my engine circuit and it blows really slowly.... but it has some many little exchange plates that the air is really hot and so it works fantastically. What do you think?
 

lw395

Well-known member
Joined
16 May 2007
Messages
41,951
Visit site
I suspect you eberbasto is thermostatic, and the problem is not getting heat into the water at the heater, it is getting the water away from the heater to the matrices, and heat out at the matrices.

Start by measuring the temperature of the water leaving the webasto, the temperature of the water at the matrices and the returned water temperature, then you might know what's going on.
It's possible the water is just circulating around the calorifier and not heating the matrices properly.
It's possible the matrices are not big enough.
You can get 12V circulator pumps.
You could try restricting the flow to the calorifier if it's in parallel with the matrices.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
I suspect you eberbasto is thermostatic, and the problem is not getting heat into the water at the heater, it is getting the water away from the heater to the matrices, and heat out at the matrices.

Start by measuring the temperature of the water leaving the webasto, the temperature of the water at the matrices and the returned water temperature, then you might know what's going on.
It's possible the water is just circulating around the calorifier and not heating the matrices properly.
It's possible the matrices are not big enough.
You can get 12V circulator pumps.
You could try restricting the flow to the calorifier if it's in parallel with the matrices.

Good advice... how might i measure the temp of a pipe? A simple digital surface temp meter?

You could be right about the calorifer... I currently have a system to switch a value and it gives me the option of Calorifier .... or Calorifier and Matrices.... But I don't have the option of matrices only. I'll check if it is parallel or series and see what I can do.
 

TopBanana

Member
Joined
14 Aug 2017
Messages
152
Location
Poole, Dorset
Visit site
Old thread I know, but did you sort this out? I'm in the midst of installing a hydronic heating system like yours. It sounds like flow might have been short circuiting through the calorifier, necessitating a balancing valve?
 

Daverw

Well-known member
Joined
2 Nov 2016
Messages
2,761
Location
Humber
Visit site
pressure drop across calorifier is going to be less than the heater matrix so will need balancing, no different to your central heating at home.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
Old thread I know, but did you sort this out? I'm in the midst of installing a hydronic heating system like yours. It sounds like flow might have been short circuiting through the calorifier, necessitating a balancing valve?

I think you might be right. I haven’t sorted it yet as I’ve been in the Canary Islands with the boat and only using it to head the calorifer which works well.

However I’m going up to Svarlbard next year to this winter I’ll be looking to sort this issue.

I will firstly simply block the pipe to the calorifier and ensure only water circulated via the heaters and see if this helps. But I think you’re right that the water short circuits to the hot water tank which then tricks the thermostat in thinking it is already hot. At least I hope it is that as it is a good system otherwise.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,800
Location
Bristol
Visit site
That's a good idea for diagnosing it. You might find your heater is coking up due to the frequent cycling.
Yeah potentially
That's a good idea for diagnosing it. You might find your heater is coking up due to the frequent cycling.

Yeah potentially. Although that wouldn’t account for my radiator getting hot initially and then cooling down. I do have a Webasto heater metrix pipes into the engine which works well so I may rig that into the webasto system and see what the difference is.
 
Top