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Tuesday, July 2, 2013

Diesel Heating System

This post a a bit of an historic memoir looking back at a topic that consumed most of my time from shortly after we contracted the N60 until about a month ago.  It's another subject that you would think would be easy, but ended up being another exercise in landing the boat on the moon.  The subject is heating the boat in cold weather.

When we contracted the boat we included the optional air conditioning system.  It is what's known as a reverse cycle system which means that it can both heat and cool.  You may be familiar with heat pumps in houses?  It's the same thing.  When cooling the boat, the system is moving heat from the boat's interior and dumping it in the ocean water.  When heating the interior, it is pulling heat out of the ocean water and dumping it in the boat.  But there is a little twist.  When the ocean water temp gets too low - somewhere in the 40's - there is no longer enough heat in teh ocean water for the system to extract and it shuts down.  But wait, there is a solution for that.  Each air handler (there is one in each living space) also has an electric heater coil that can be used when the water is too cold.  We figured this system would meet our needs so we signed on the dotted line and went off to enjoy the xmas and new years holidays.

But as I read more about other boats, I started to think our system wouldn't be enough, or at least was sub-optimal.  We plan to do a fair amount of high-latitude cruising where heat will be essential, and where the water temps can be quite low.  One guy had run up through the Canadian Maritimes and his heat crapped out on him.  Later he discovered that the system was fine and that he had just encountered water that was too cold.  We were up in the same area last summer and regularly saw water temps in the 30's and 40's, and that was in July!

Another worry was that running the heat would mean running the generator, and in colder climates it would mean running it all the time.  That's not our favorite was to cruise, and seems particularly nutty while underway when the main engine is producing gobs of waste heat and dumping it in the ocean.

And this is why many boats have hydronic heat, which is just a fancy word for circulating hot water heat like you find in many homes.  It's also commonly known as diesel heat since the main heat source is a boiler that burns diesel.  By the way, diesel and home heating oil are the same thing, plus or minus some additives, so these boilers are really no different in principal than a home oil boiler.  And, with a little bit of engineering and forethought, the system can be linked to the main engine and utilize the waste heat to warm the boat without having to fire the boiler.  That means free heat while underway.  And even when running off the boiler, the electric load is light so you don't need to run the generator.  Plus, it's a much more efficient use of diesel.  A generator is around 20% efficient when you look at the energy content of the fuel consumed versus the electric power available to heat the boat.  Most of the energy goes out the exhaust pipe and out the cooling system as heat.  A boiler, on the other hand, is about 85% efficient, i.e. 85% of the energy content of the fuel burned ends up as heat in the boat rather than heat dumped in the ocean.  It all sounds like a much better fit for our cruising plans.

All this convinced me we should add diesel heat, so the question became how and what kind.  PAE offers a wide range of "standard" options, all of which are engineered, priced, and ready to include with the check of a box.  The reverse-cycle air conditioning system is an example, but unfortunately diesel heat is not, so it becomes a custom option of one sort or another.  Some of these customizations PAE will engineer and build, and others they turn to various industry suppliers and specialists to provide.  Diesel heat falls into this later group.

Step one involved getting a proposal from an outfit in So. Cal. that PAE regularly works with.  The turn around time was good and within a week or two I had a sketch of a system design and pricing.

In parallel, I started talking to other boat owners, collecting names of suppliers and recommendations, and started calling the vendors who came most highly recommended.  This first big thing I discovered is that there are two findamentally different approaches to designing an AC+heat system for a boat.  The first appraoch is to build two independent systems, one the heats and one that cools.  With this approach I would proceed with the AC system currently planned, and build a completely independent and separate heating system.  The proposal that I had in hand was for this type of an independent system.  The second approach is to build an integrated system with a single set of air handlers in each room, and run either hot or cold water through the loops to heat or cool as needed.  Water chillers would cool the water, and a diesel boiler and/or engine heat would heat the water.

The engineer in me was immediately drawn to the integrated system.  I liked the idea of a single set of pipes run through the boat, and single set of air handlers ducts and vents, and a single set of thermostats and controls.  It seemed simpler and easier to build, but over time I became aware of the downsides too.  The challenges are:

  1. More complicated controls.  Some suppliers said they were never able to get these systems to work well.  Others said I need a $20,000 control system to make it work properly.  This greater expense is probably why integrated systems generally appear only in larger boats where the control system is a smaller portion of the total cost.
  2. Temperature limit problems with equipment.  The chillers typically used have a water temp limit of 140F, but boilers are typically run at 180F.  That means you either need to have a valve bypass system to keep the hot water away from the chillers, or you need to run the boiler at a much lower than normal temperature.  And since the boiler is also typically used as a source for domestic hot water, in the cooling season you will be running both hot and cold water that needs to be directed to the right places, and only the right places.  This is an example of why the control systems get complicated.
  3. Cooling vents are ideally located high up in a room since cold air drops.  This helps mix up the air and create even cooling.  Conversely, heat vents are ideally located low in the room since hot air rises.  With a combined system, you need to favor one system or the other and cannot optimize both.  I've experienced this on our Grand Banks when running the reverse cycle heat.  That system is optimized for cooling with all the vents high up in the rooms.  When heating, there is very distinct stratification of the heat.  Stand up and walk around and it's very warm, but sit down and you are quickly cold again.
The net result is that other that the duplication of certain components, the separate systems let you optimize each.  At the same time I was finding out that it would be much more difficult than ever imagined to find someone to build the stand alone system, let along an integrated system.  Dividing and conquering was sounding wiser and wiser.  I could let the ship yard build the AC system which they can do in their sleep and do it well.  And that system could serve as a backup heating system if I had trouble with the diesel system.  So after much fretting I relented and focused on a stand-alone diesel heat system.

I mentioned that finding someone to supply the heating system turned out to be much harder than I ever imagined.  I'd say it ranks right up there with finding monitors - perhaps even higher.

PAE, for very understandable reasons, wants suppliers for a system like this to provide the whole thing, soup to nuts.  It's the old one-throat-to-choke addage.  They want someone who will design the system, provide sufficient documentation for the yard to build it, supply all the parts, complete the installation at commissioning time, inspect fire and test the system, then stand behind it.  The proposal I had from the outfit in So. Cal. provided all that.  It's no wonder they are a prefered supplier for PAE.

But the more I studied the proposed system, the more concerned I became about its suitability for our needs which will involve some pretty cold places.  And this became more pronounced as I compared it to systems proposed by firms up in the Seattle area.  As an example, the So. Cal. system called for a 50kBTU boiler where the Seattle system called for 85kBTU.  That's a pretty big difference.  I also had at least one boat owner from the Seattle area assert that a 50kBTU system would not cut it up there.  And quite frankly, Seattle is not that cold.  If you want cold, go to Vermont in February.  Fortunately my boat can't, but THAT's cold.

Confused, I decided to try getting to the bottom of things and went to calculate the heat loads for all the spaces in the boat, then compare that against the heater sizes each proposal called for in those spaces, and to look at the total heat load which is what drives the boiler sizing.  Doing this is easier than it sounds.  There are guidelines for how many BTU you need per cubic foot of space, and it's easy to figure out the room sizes from the boat plans.  The results were interesting.

In both propsals there were heaters which were not optimally sized fro teh room, but far more were off on the So. Cal. proposal.  But that's not a huge problem.  After all, that's why we have thermostats.  But it is reflective of the attention paid to creating the design.

Second, both propsals totalled up to the same overall heat load which was about 95k BTU.  Since the per-room heaters tend to be slightly over-sized and compensated for with the thermostats, you would size the boiler to match the room loads or be slightly less.  Something like 85kBTU?  But not 50kBTU.  This was confirmation that the 50kBTU boiler was too small.  And a little research revealed that 50kBTU was as big as that vendor offers.

By this time it was March and I had pretty much decided to go with the Seattle proposal based on the more appropriately sized boiler and better domonstrated knowledge, but wanted to see some examples of these system installed in boats.  I was already signed up for the ABT hydraulics course in California, so decided to make a tour of the west coast visiting PAE in Dana Point to see an example of the So Cal. company's work, take the ABT course, then make a run to Seattle to see an example of their work.  It was time very well spent.

The visit to the So. Cal boat confirmed my concerns, and surfaced a few more.  Several of the aux heat exchangers weren't plumbed in the way they should be.  I had also noticed this in the drawing they provided with their proposal, but I chalked it up to a simple mistake that would be corrected on review.  The order that things are plumbed on  aheat loop matters in some cases to ensure you are picking up and dumping heat in the right order.  I asked about it and the guy said they do it both ways with some people prefering one over the other.  On that one I have to disagree.  It's thermodynamics and physics, not opinion and preference.  What they had would work, sort of, but was clearly suboptimal.  I also found a couple of air handlers that had no returns and were relying solely on air leakage around drawers and hatches.  Not good.

The Seattle visit was much more satisfying.  Not only did the drawing that they provided in advance correctly show how everything should be plumbed up, the example boats were well done too.  And I got a little bonus out of the deal too.  I was there over a weekend with time to kill so I took a drive up to Anacortes.  On one of the docks was an N60 - exactly the boat we are building - and there were a few people rummaging around on it.  After a while my staring made them nervous so I said Hi and introduced myself along with my adventure to build a replica of their boat.  Pretty soon Cameron Kemp was my new friend and I was aboard for a trial run to experiment with some autopilot adjustments they had made.  And guess what?  His boat has the exact diesel heat system that I was leaning towards, so I got a tour of that too.

Decision made.  Or at least so I thought.

On return I followed up with the Seattle company to get a complete quote, and to link them up with PAE to be sure it was clear what they needed to do, when, and where.  One of the challenges is that we are commissioning the boat in Dana Point, not Seattle.  There are a lot of people who will say Yes to something, but their actions communicate a different answer.  This turned out to be the case.  They became very difficult to pin down, and when I asked them questions that I expected them to answer, or get the answers, they sent me off to other people to get the answers.  That's not reflective of someone who is going to be the single point of contact to make a heating system come to life.  And PAE was having trouble connecting with him too.  My conclusion was that if the boat were being commissioning in Seattle, he would have been all over it, but that the Dana Point Commissioning was not a deal he was very interested in.  I could understand that, but prefer more direct communications.  No is the prefered answer when you mean No.

At this point I was really getting frustrated.  I had one guy who was stepping up to the plate as needed, but proposing a system that didn't cut it.  Then I had another guy with the right system but an unwillingness to step up to the plate.  Meanwhile, as part of this whole process I had done schematics showing the system the way I wanted it (the samples I had been given were for slightly different boats), I had run all the calculations, and had created a wiring diagram to match the plumbing and place the thermostats where I wanted them.  I had reviewed the whole package with Sure Marine who are the equipment distributor/supplier and who essentially provide all the design services to the installers anyway.  I had also reviewed all the heater placement with PAE and made adjustments at their suggestion.  The system design was 80%-90% done and in hand.  With a little touch up it would be suitable documentation for the yard to build to.

So, I think much to PAE's horror, I told them I was sick of all the running around (not by them, but by others) and that I was going to be the "general contractor" for the heating system.  I would provide the design and documentation, I would field any questions, I would provide the bill of materials along with who to buy from, I would get it all shipped to China, and I would commission it.  I would even buy all the equipment myself rather than doing it through them if they prefered.  After some more back and forth, we had a plan.  After talking to Sure Marine, PAE agreed to use my build plans and buy through Sure.  They also added a few more things that they wanted Sure to supply to make the build easier in China, and Sure was able to do that.  Then PAE give the plans to the yard to get a build quote.  All this got rollup up into a full quote to me with all the appropriate mark ups and mark downs with a satisfactory end number.  The only missing piece is the commissioning, and we agreed that we would select and hire someone at commissioning time to do that work.  Both the So Cal. and Seattle guys are candidates, along with a few others.

In the end I'm happy with the results, though the journey was long and frustrating.  I attribute most of the trouble to commisioning a boat in a location where there is not a wealth of heating experience, but it is what it is.  My other wish is that PAE would make diesel heat one of those pre-engineered, check-the-box options, and obviously offer a truely cold weather capable system.  They do offer an easy path for customers to add diesel heat, but I don't think the product is up to snuff.  And it's otherwise an exercise for the reader to figure out an alternative.

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