Wednesday, August 10, 2011

Central Heating in a Boat

I have been having some interesting correspondence with Peter Berry of nb Kelly-Louise regarding narrow boat central heating systems. Peter blogged about it <here>.

Our discussion led to us considering the probable need to ensure the diesel heater output matched the capacity of the radiators. If the output of heater is greater than the capacity of the system to dissipate the heat then hot water will be returned to the heater which may cause it to shut down. Alternatively, if the heater output is less than the capacity of the radiators then the heater might continuously run making the boat too hot. The former might lead to the “coking up” of the burner through frequent cycling whereas the latter is inefficient burning too much diesel.

Peter has a Webasto with an output of 5.2kw. He believes his combined capacity of the radiators on Kelly-Louise is also approximately 5kw so theoretically everything should work correctly.

From what I can understand, his Webasto doesn’t have a thermostat but rather cycles on and off by measuring the temperature of the returning water. I assume a thermostat is built into the burner and measures the temperature of the water rather than the atmospheric temperature in their boat.

We planned on Waiouru having a Hurricane diesel heater and that has a capacity of 7.3kw and I did some calculations on the required capacity of the radiators within the boat.

I’d already decided to opt for finrads; primarily because I didn’t want to use wall space for radiators. The finrads can be placed at floor level. I also wanted small heater panels in the base of the wardrobes to keep clothing dry and warm in winter. My calculations looked something like this:

  • Hurricane Heater output = 7300w
  • Heaters
  • Bedroom Radiators in wardrobes (2) = 1200w
  • Bathroom Towel Rail (1) = 900w
  • Output = 2100w
  • Therefore minimum FinRad capacity = 5200w (7300-2100)
  • Double Finrad capacity per 492mm = 250w
  • Therefore required total minimum length of FinRad = 20 metres

The next problem was to find 20 metres of available linear floor space in a boat that is just over 18 metres long. There is no point in fitting finrads into the back of the galley cabinets, etc. It was immediately obvious the finrads would need to be on both sides of the boat. This has an advantage as it will keep both sides of the boat warm.

So we have planned on finrads in every place where there is open space on the sides of the boat. In addition, I’ve shown a finrad running longitudinally in the storage area under our bed. That will both keep ant thing under the bed dry and warm but also act as a heater whilst we sleep.

I have also considered the consequences of all the radiators being connected on a single ring main. If this were done then it’s possible the first radiator would get very hot working to maximum capacity with very hot water whereas the last radiator would only receive water at a reduced temperature and may not reach maximum capacity. The solution appears to be to create heating zones in the boat; each with their own direct feed pipe from the Hurricane output.

The Hurricane has heating controls for up to four separate space heating zones, each with its own optional thermostat. So we should be able to configure it to maintain different zones of the boat a different temperatures depending upon the time of day.

The 12v DC supply to the Hurricane will be controlled by the Empirbus system. The software program in the Empirbus system will also give us a considerable amount of control over the starting and stopping of the heater. We should be able to send a text message to start the Hurricane if away from the boat and could manage the starting and stopping time of the heater using the timer function within the Empirbus system.

It will be interesting to see if all this theoretical planning can be put into practice.

9 comments:

Bruce in Sanity said...

Hi

All that stuff about Webastos just doesn't apply to the Hurricane, which can cycle on and off without problems, just like your domestic unit can. As long as the Hurricane has enough output to do what you want (and ours is heating a 70 footer very nicely, thank you) you need only an approximate match.

The Hurricane is controlled by the aquastat on the return water temp, a room stat (or stats) for cabin heating, and a cylinder stat for hot water, so *much* more sophisticated than the crude systems used on the Webasto and the like.

Don't forget to put a bit of finrad in the bottom of the airing cupboard.

ATB

Bruce

Tom and Jan said...

Not just the airing cupboard.... Also in the toilet.
A man has to find somewhere warm to hide when the dishes need to be done!

David said...

And don't install the room stat in the engine bay as ours is on Trudy-Ann

David

Tom and Jan said...

Well that's a clever place to install it :-)

Richard said...

Hi Tom and Jan;
My advice to you is that under NO circumstances to allow the hurricane to be switched by anything other than its room stat, cylinder stat,and solenoid valve. There are 3 aquastats within the boiler itself which ensure a high degree of safety, but the boiler needs to be permanently connected DIRECTLY to the batteries via a 25amp fuse only i.e. no switch.
This ensures that when the boiler shuts down, either by no demand from its thermostats, or by yourself, when leaving the boat, then it can safely carry out its "purging" process before switching itself off.
This also part of the warranty from the uk importers Calcutt Boats.
I have just installed one on "Wizard" my 62ft Tug, and am thrilled with it.
Horrified to read your blog, reminds me of when I had a custom built motorcycle built; the builders acted in an almost identical manner, eventually I had to reposess my bike by force, with lots of my supplied equipment having dissappeared!
Hope it all goes well for you .
Wizard.

Tom and Jan said...

Hi Richard,
I assume the owner is able to manually turn the Hurricane on and off and assume this is an electrical switch.
My idea was that the Empirbus system would control this switch. Not that the Empirbus system would overide the integral Hurricane control system.

Dave said...

I'm no boat plumbing expert but your comment about the first radiator being hotter sounds incorrect.In a house all the radiators come off the ring rather than actually being part of the ring. This then allows you to balance the radiators so that the first radiator doesn't take all the heat.

Glad you're blogging positive stuff now. Look forward to seeing pics of the boat as you make progress.

Tom and Jan said...

Dave I think you're right! I had assumed the radiators would be in series. However if there is a ringmain and each heater taps of the ringmain then theoretically they should all get water at the same temperature (apart from heat lost in the ringmain).

I'm not sure if this is only relevant for radiators or is also done for finrads?

Richard said...

The Hurricane can be switched off by the owner, using either the remote panel (part of the kit) or its own master switch, but it is important to realise that this only switces the burner off; the power to the pump and internal aquastats remains on unil the boiler "brain" is satisfied that sufficient residual heat has been removed before safely shutting itself down. The only way the master switch can be switched off is by you ! If the empire bus is used, this can only terminate the 12v power to the boiler, which could be very dangerous and will certainly invalidate any warranty, it can not operate the hurricane's service switch either on the control box, or via the remote switch panel.
You really need to discuss this with Calcutt boats, the importers, their telephone service I have found very helpful.
The theory about the flow and return pipes ( the ring main ) is indeed correct, but the rads closest to the primary heat source(boiler!) will of course get first bite at the available hot water; this is why rads have the lockshield valve at the opposite end to the adjustable temp control valve, to regulate the amount of water and to enable the system to be balanced, so that all rads get the same amount of heat at approx. the same time.
Finally, the finrads are connected straight through in the flow side of the circuit, at least usually; although I have used them many times in the return side to remove some of the surplus heat the water has on its way back to the boiler.
Best of luck; keep positive it will be worth waiting for!
Wizard