Keeping our cool under way

We just finished installing a mini-split, high-SEER air conditioner in our pilothouse, now that we've stopped in one place long enough to get it delivered. This post will be exclusively about the installation of this air conditioner and how it came about, so if you are not interested in such things you can just skip past it. I'll return to our normal travelogue in my next post.


The new air conditioner in operation, during testing. "62" is the current setpoint, the lowest available. When powered down, the louver door on the bottom closes completely; it can oscillate, if desired, when operating.

One of the great things about a nomadic existence is that we can choose to follow temperate weather, staying comfortable year-round without breaking the bank on the energy budget. But if you have followed us for any length of time, you'll know that we've sometimes chosen a different path, for one reason or another. In the bus, that was often due to our volunteer work with the American Red Cross, which had us driving into tropical storms, and heading into the sweltering heat of summer in the south during hurricane season.

The reasons are more mundane on the boat. At seven miles an hour, it's not possible to just zip away to cooler climes on a whim. And without being able to do the river system of the central US by starting in the Great Lakes and slowly working south, due to Vector's height, if we wanted to do them at all we had to start north from Mobile in June. That inevitably put us in heat and humidity unlike any we've heretofore experienced on the boat.

When we designed the bus, more or less from scratch, we had the luxury of designing in some highly efficient and flexible climate control systems. We deliberately set things up so that we could run an air conditioner directly from the batteries if needed, for example to keep the bedroom cool overnight without running the generator. On the road, with the massive 7.5kW alternator spinning, we could run two air conditioners and still have juice left over for charging the batteries. It was a great system, and, frankly, we were spoiled by it.

The boat came to us as a completed work. While I personally would have made some different design choices during construction, we deemed most of the existing systems to be livable "as is" (and had we not, we would have passed on this boat). What we've done instead is to make incremental improvements over time, mostly DIY, that have made life easier. One such project, a fairly major one, was to upgrade the electrical system fairly early on, increasing alternator capacity from 1,560 watts to 2,640 watts (still a far cry from the bus, with three times that amount), and inverter capacity from 3,000 watts to 4,000 watts.

One of the hopes we had for that upgrade was that it might allow us to run at least one of our four air conditioners on the inverter, if not from batteries alone, then at least when the alternator was spinning. Sadly, this proved not to be the case. The inverter simply could not start both the massive seawater pump, which supplies all four units simultaneously, plus one air conditioner, admittedly an older and less efficient type than are available today.

There are lots of ways to solve this problem. One would be to simply run the generator whenever we need air conditioning, even under way. Fuel and maintenance included, that costs anywhere from $2 to $4 per hour, depending on fuel and lube prices. This summer alone we will be under way some 500-600 hours, and having an air conditioning solution that can also run on batteries will reduce generator hours at anchor as well. So, while running the generator is the simplest solution, and even the cheapest in the short term, it's not the best answer in the long haul.

We might also have replaced the large seawater pump with smaller individual pumps, one of which the inverter might be able to start along with a single AC unit, and/or replaced one or more air conditioning units with more efficient models. These solutions would also require changes to the seawater plumbing, the unit mounting, and possibly the refrigerant piping, and when we added up the potential costs it was prohibitively expensive. Also in the cost-prohibitive category was an electrical upgrade, adding an extra inverter so that the pump and the AC unit could be separated across two different inverters.

We opted instead to do some creative engineering, adapting technology that has been cooling apartments in the far east for decades and has recently reached US shores as a more efficient alternative to whole-house air conditioning: the mini-split heat pump. These have been available here for a decade or so in 230-volt models, as those are more or less the same units used in Asia. More recently, 120-volt models have also become widely available. An additional advantage of installing such a system is that it can be used when the boat is out of the water, unlike the built-in system we already have.

Regular readers may remember that we bought a "portable" 120-volt air conditioner in Panama City a few weeks ago, as a "proof of concept." Before making permanent changes to the boat, including drilling some very large holes through walls and weather decks, we wanted to have some confidence that a relatively small unit in the pilothouse would keep us comfortable enough under way to minimize the need for the generator, and also that the inverter and alternator would be able to start and sustain such a system indefinitely under way.


Mr. Roboto, sitting on the pilothouse settee and blowing hot air out the window.

The portable unit, which we nicknamed "Mr Roboto," has been doing a fine job of that, and we consider the experiment a success. Thus it was time to take the next step, installing a permanent solution that would not take up a full seat on the pilothouse settee, have a Rube-Goldberg hose hanging out the window attached to a piece of cardboard, or require us to empty a condensate tank every other day.

Mr. Roboto is a 10,000 BTU/hr unit, which was adequate if not stellar. For the permanent solution, we opted to go up to 12,000 BTU/hr, which we felt was still within the capability of the inverter to start. This is also the largest size mini-split system available in 120 volts, and had components small enough for us to mount in the limited space we had available. We picked a slightly older heat pump model from HighSeer, aka Parker Davis HVAC Systems, who sells under the Pioneer brand name. It was just $699 complete, freight included, on Amazon.

One key feature of this model (and many like it) is that it is a "DC inverter" system. The incoming line voltage is rectified to DC, which then feeds a high-frequency inverter circuit that in turn drives the compressor. This allows motor speed to be efficiently varied and allows for a "soft start" under software control. Without this feature, our house inverter would have more difficulty starting the unit up. We were not looking for a heat pump type -- air conditioning was the primary goal -- but most units on the market seem to fall into this category, so it was just a bonus for us.

As the name implies, the system is split into two parts, connected by refrigerant lines. The smaller part goes inside the living space, mounted on the wall, near the ceiling. The larger part goes outside, and while an optional wall-mount bracket is available, it is generally intended to be bolted to a pad on the ground. Finding a suitable spot for this outside unit was one of the biggest challenges of the project.

We knew right away that the inside unit would need to go on the forward-facing pilothouse wall, above the settee. That meant removing a nice bookshelf that was installed there by the previous owner, and relocating the books thereon, many of which were also purchased by the previous owner. About half what was up there was obsolete, and we found other homes for the rest. I was able to remove the shelf without destroying anything other than the bungs that covered the mounting screws. It's a very nice shelf, and we're going to see if it will fit above the master berth instead.


I forgot to photograph the shelf before removal. This old photo was the best I could find.

With that decision made, we next needed to determine how to get the refrigerant lines from there to the flybridge deck, where the outside unit would be installed. The two choices here were to route the lines on the surface of the wall, then up through the ceiling onto the deck, or else drill a 2.5" hole in the wall behind the unit for them to come out the back. We wanted a cleaner finished look, so we opted for the big hole in the wall, making the installation a firm commitment (although we've covered similar holes elsewhere by hanging art over them).


The inside unit mounted. Again, I neglected to first photograph the hole I had to make in the wall, just above and to the left of the small light fixture.

The wall has an interstitial space nearly 2" across, large enough to run the pipes. But bending the copper pipes to run them up through the wall is risky, connecting them to the rest of the line set would be a challenge, and insulating the connection nearly impossible. Plus, I'd have to drill a 2" hole through the deck, from above, dead-center on the wall. That hole would be on a part of the deck exposed to weather, so I'd need to use a gooseneck, or seal the hole some other way.


Inside the galley cabinet, with freshly drilled hole in the top. You can see light coming from the hole in the deck above. The silver stuff is the insulation around the existing flexible AC duct.

We chose instead to drill all the way through the wall into a galley cabinet. That would give me plenty of room to bend the pipes gently, make the connection, and insulate it. It would also let me come up through the deck inside the flybridge settee, a bit more sheltered from the elements and also out of sight, with a convenient place to hide the excess refrigerant lines and cables. If we centered the unit on the wall, my hole would come out in the wrong cabinet and we'd have to go through two cabinets, taking up precious space in both. We elected to offset the unit to port so that the lines would come out in the correct cabinet. I was, however, able to run the condensate drain line down through the wall, and connect it to an existing condensate drain under the pilothouse settee.


Hole in the 3/8" aluminum deck plate, inside the settee. Also shown is the PVC fitting I used to protect the hole from water entry and the pipes from chafe.

Fortunately, that cabinet already has a large AC duct in it, so it was already partly unusable and unsightly inside. The upper galley cabinets are wall-mounted, with a gap between their tops and the ceiling, so I had to drill a hole in the top of the cabinet to match the one I drilled in the deck under the flybridge settee. I also had to carefully notch the vinyl-covered ceiling panel to fit once the pipes were in place.


This view shows both holes lined up. You can see the underside of the aluminum deck; I had to remove the yellow fiberglass batt insulation that you can see in other sections of the ceiling, which I notched and replaced later.

We found a spot for the outdoor unit just forward and inboard of the flybridge settee. In this spot all the air intakes for the unit are unobstructed, the settee is still fully usable, and the port helm chair can still swivel 360°. The small aisle between the helm chairs is still accessible. While large and perhaps unsightly, the unit is at a convenient height to use as a cocktail table when using the settee, and Louise is going to make a canvas cover for it for when it is not in use, which will be the vast majority of time. I did have to drill four holes through the weather deck for the mounting bolts.


Outdoor unit bolted in place. To the left is the settee, sans cushion at the moment. The thing to the right with the Home Depot bag flapping over it is the pedestal for the helm chair, removed so I could work behind the unit. The bag is to keep the greased pedestal from soiling my clothes.

I finished off the hole from the galley to the inside of the pilothouse settee with a 2.5" PVC fitting (spigot to FIPT) which I bedded into the deck with butyl tape. It only needs to deflect occasional rainwater that finds its way inside that locker. I also drilled a hole through the forward end of the settee to get the pipes and cables out to the outside unit, and this I finished with a 2.5" PVC 45° elbow, secured from the inside by cementing it to another spigot fitting.


PVC flange in place before running the line set.

With these two holes perpendicular to each other and only about a foot apart, the trick now was to get the pre-terminated 16' copper line set through both holes without kinking it. The line came coiled, and I uncoiled only enough from both ends to reach the respective terminations, then carefully worked both ends into their holes without disturbing the rest of the coil. It was a slow process but I got the lines in without kinking them or even damaging any of the pre-installed insulation.


Excess line set coiled under settee. Pipes exit to the right to the outdoor unit. At rear can be seen the pipes heading down below deck. The Styrofoam block seen underneath the coil is to minimize stress from vibration, rather than having the stiff coil supported only by the ends.

The copper lines are pre-flared and have the flare nuts already installed, ready to mate to the flare fittings on the outdoor and indoor units. HighSeer even provides some flare sealant to put on the connections. I torqued them to just a hair above spec with a torque wrench -- it's really easy to damage copper flare connections if not careful.


Insulated line set coming down from the deck has been connected to the bare copper lines from the indoor unit. The single gray insulation tube shown at right, also pre-installed on the indoor unit, proved inadequate to cover both pipes and connections, so I had to add foam pipe insulation to the exposed portions later.

The refrigerant for the entire system comes pre-installed inside the outdoor unit, which contains the compressor. After making the connections, I pressure-tested them with a can of R-134a I happened to have lying around. This let me use a soap solution to check for leaks before I even evacuated the lines. I bought a cheap venturi-type vacuum pump at Harbor Freight to do the evacuation. While this pump is only capable of about 28"Hg of vacuum rather than the 29+" called for in most HVAC guides, I judged it good enough, especially after blowing the lines out with R-134a. The mini-split actually uses R-410, a more modern, higher-pressure refrigerant.


Behind the outdoor unit, showing the pipe/cable egress from the settee.

My manifold gauges, which I've owned since the days before R-134a and other modern refrigerants supplanted R-12 and R-22, fit easily on the vacuum pump. The newer R-410 systems use a different size fitting, however, and I needed an adapter, also from Amazon. That was the last item to arrive, just in time to evacuate and charge the system for testing before we left for California. Our air compressor, which is sized for "hookah" diving, could not deliver enough air continuously to evacuate the system; I had to make a dozen passes, closing the manifold valve each time the compressor kicked in.


Notched ceiling panel back in place. This 1" section is all that "shows" of the line set indoors, but you have to get your eyeball up above the cabinets to even see it.

I'm pleased to report the system works perfectly, in both cool and heat modes. Our inverter easily starts it, even on batteries. And, surprisingly, it's quiet. So quiet we, at first, did not think it was running. We had to shut down the AC in the rest of the boat to hear it. It was also quite a bit more effective than Mr. Roboto, and even beats the built-in seawater-chilled air conditioner in that room. We're very pleased, and looking forward to testing it under way. We've even already given it a nickname. Meet Meriwether, the Pioneer.