Improving a Webasto water heater output?

[Tim Good]

Question: Will increasing the diameter of the piping up until the heating circuit improve things?

Details:

Ok team... I'm still on with my Webasto and trying to get it to work better prior to a trip to Svarlbard next year. Here are some facts:

1 It's a Webasto DW80 8kw.
2 It goes into my calorifier and then to the heating circuit.
3 It has 15mm pipes but meant to have 22mm. See Webasto DW80 3.jpg
4 It has 4 matrix heat blowers and two radiators. The matrix heaters are clean and dust free. The heater matrix unit are in paralel to the heating circuit, not in series as the diagram depicts.
5 Water temp is meant to get to 68c operating with an emergency shutdown temp of 78c
6 Water temp at the radiators is around mid 60's but at the matrix blowers it is only 43c. All blow 43c equally in all 4 cabins.
7 There is a switch that allows me to select Hot Water or Hot Water & Heat. See Webasto DW80 3.jpg. The two handles open the flow to the heating at "C" and prevent it shot circuiting via "C" "D"

Now... First I appreciate the heaters won't work properly until the calorifier is hot since it is series to the heating circuit but that's ok. So deduct point 2 from the problem as Im testing it with an already hot calorifier.

The water is getting to the right temp as per point 5 as i can measure this in the radiators. .... but I believe I'm meant to be getting perhaps hot air in the upper 50's form the matrix heaters. Now the biggest problem I see is that this heater was intended to be made with 22m pipping, not 15mm. See Webasto DW80 3.jpg. There is 15mm copper pipe coming from Unit which then goes into 15mm white flex tubing which you can see in Webasto Diagram.jpg. So I feel the flow is restricted and therefore the load. I cannot feasibly replace all the pipes in the boat. Its too complex and too difficult.

However I could feasibly replace the 15mm with 22mm from Start > A > B > C > D > E. I.e. the main loop, excluding the heating circuit. The reason is that most of that is going along the boat as 2 main pipes and back again.

If I replaced just that section, would it improve the flow / load on the system and improve the flow to the matrix heaters perhaps? Or since the 15mm pipes still go to the heaters would that basically mean nothing is changed?

Two possible things:
- I don't know the bore diameter in the calorifier
- Even thugh there is a pressure gauge on the photo it is not a pressurised system. The header tank has a drain top at the top of it for starters which is open to the air.

 

[TernVI]

Check the water temperature at the matrices. Not the air temperature.
If it is really only 43degC then your water flow is obviously inadequate.
the air temperature will always be a lot lower than the water temp, unless the air is still.

As well as the pipe diameter, I see 90 degree elbow joints and ball valves. You could try bypassing that and seeing if the flow improves.
The calorifier may be quite restrictive, you could try bypassing it as an experiment. In the long run you could plumb it in parallel, maybe controlled by a water thermostat. I've heard of people using vehicle thermostats.
If you get some Speedfit type plumbing, it's easy to plug and play configurations.
Are you sure it's supposed to run at 68degC? If the water coming back is at say 50degC, you need a lot of water flow to shift 8kW.
I'm sure my eber ran much hotter than that.

 

[rotrax]

I fitted - twelve years ago now - a Webasto Thermotop to a Gibsea 96. We used 15mm speedfit plastic pipe and connectors and had one long slim radiator under the setee berth and two heated towel rails, onr on the end of the galley, the other in the heads.

It was superb.

A clubmember with an Eber and matrix system deep sixed them and went with radiators after being on board with us.

Just saying..................................

 

[TernVI]

On my boat, the eber also heated the engine, like a big old storage heater in the middle of the boat.
Great for keeping the boat dry and warm, but no substitute for a blast of hot air when you want it.

 

[Tim Good]

Just bumping this up again.
Im considering running 22mm pipe from the Webasto uk to the point which the 15mm piles go off to various parts of the boat. That initial run is about 4m.

Would increasing the pipe size on both the to and from feeds, 8m in total, make much of a difference if the pipes going to the heaters remain at 15mm?

 

[mikegunn]

Just bumping this up again.
Im considering running 22mm pipe from the Webasto uk to the point which the 15mm piles go off to various parts of the boat. That initial run is about 4m.

Would increasing the pipe size on both the to and from feeds, 8m in total, make much of a difference if the pipes going to the heaters remain at 15mm?

I had a Webasto wet system on my previous boat and it was superb.
Do you have a dual coil calorifier where the engine cooling circuit is dedicatEd to one coil and the Webasto to the other? If the two circuits are combined you could be spending a lot of energy on warming up the engine’s block.
Mike.

 

[Tim Good]

I had a Webasto wet system on my previous boat and it was superb.
Do you have a dual coil calorifier where the engine cooling circuit is dedicatEd to one coil and the Webasto to the other? If the two circuits are combined you could be spending a lot of energy on warming up the engine’s block.
Mike.

No they’re separate. I also removed the calorifier from the circuit as a test yesterday and it didn’t seem to make a huge difference to the temp at the radiators and blowers.

 

[Boater Sam]

If the flow was insufficient due to undersized pipework the heater would short cycle all the time, even from cold after a short time.
I suspect that the fan assist rads are much higher out put than you can achieve with 8kw going in, they are notorious for needing a lot of heat to produce really warm air out. Find out how many kw load you have on the system, the rated input of the rads should be marked on them somewhere.

 

[Tim Good]

If the flow was insufficient due to undersized pipework the heater would short cycle all the time, even from cold after a short time.
I suspect that the fan assist rads are much higher out put than you can achieve with 8kw going in, they are notorious for needing a lot of heat to produce really warm air out. Find out how many kw load you have on the system, the rated input of the rads should be marked on them somewhere.

When you say short cycle, do you mean it throttles back after a short while?

If so then yes that’s what it does. Initially it seems to get to a reasonable temp. 65-68c which is what the manual says it should be. But it seems to throttle back after not too long to around 55-62.

It doesn’t seem much but seems to make a big difference in what the blowers give out. At 55-60 water it’s only about 42c at the blowers. At 68c water it’s more like 53c at the blowers.

 

[Ian_Edwards]

I'd plumb it like this:

I don't think it would take too much work to change the circuit to this configuration, it would allow control of the flow between the calorifier and the matrix heaters. The flow control valves could just be ordinary ball valves or gate valves.
I would also look at the pump, if it's not working well, then the heater will short cycle, it can't remove the heat from the boiler quickly enough.

I still think that the most likely cause is the calorifier causing a thermal short circuit, and can't make out from the posts whether you have managed to check that.

If the system is short cycling and the matrix heater aren't getting hot then they are being starved of heat, either by a short circuit or insufficient flow, the pump isn't up to it, or restrictions in the pipework . Or to look at it another way, the circuit as it is now can't absorb the heat the Webasto can produce.

As a possible reference, my boat has a 10kWatt Eberspacher, calorifier and three 3kWatt matrix heaters, the hot air from the matrix heaters isn't as hot as the hot air from Ebershacer and Webasto hot air heaters I've had on previous boats, but it does keep the boat very warm.

 

[Boater Sam]

When you say short cycle, do you mean it throttles back after a short while?

If so then yes that’s what it does. Initially it seems to get to a reasonable temp. 65-68c which is what the manual says it should be. But it seems to throttle back after not too long to around 55-62.

It doesn’t seem much but seems to make a big difference in what the blowers give out. At 55-60 water it’s only about 42c at the blowers. At 68c water it’s more like 53c at the blowers.

What is "not too long", how many minutes? does it ever lock out with overtemperature?

 

[Tim Good]

What is "not too long", how many minutes? does it ever lock out with overtemperature?

It doesn’t appear to ever go over temp.

Perhaps after maybe 15 mins it starts to cool a little.

Mind you I’m using an IR gun to measure to test temp. It’s fairly accurate on the white radiator but not great on the pipes. I need a thermocouple and decent multimeter.

To test air temp I leave an enamel dinner plate over the hot air outlet for 10 mins and then measure the plate with the IR gun.

 

[pcatterall]

When you say short cycle, do you mean it throttles back after a short while?

If so then yes that’s what it does. Initially it seems to get to a reasonable temp. 65-68c which is what the manual says it should be. But it seems to throttle back after not too long to around 55-62.

It doesn’t seem much but seems to make a big difference in what the blowers give out. At 55-60 water it’s only about 42c at the blowers. At 68c water it’s more like 53c at the blowers.

My original thought! there did seem to be a lot of 'stuff' on an 8kw heater. I guess I would start by experimenting with different stuff on and off to try to get an idea of where the limits are.
It might, at the end of the day, be a case of turning bits on or off as the comfort requirements change through the day.

 

[lynallbel]

It doesn’t appear to ever go over temp.

Perhaps after maybe 15 mins it starts to cool a little.

Mind you I’m using an IR gun to measure to test temp. It’s fairly accurate on the white radiator but not great on the pipes. I need a thermocouple and decent multimeter.

To test air temp I leave an enamel dinner plate over the hot air outlet for 10 mins and then measure the plate with the IR gun.

Some matt/satin paint on the pipes will help the ir gun, slightest shine on any surface you want to measure and all bets are off.