Saturday, December 27, 2014

Marine Air HVAC - an Aqua-logical wonder of the World

During the process of renovating a sailboat, so many things take longer than expected and cost more than the estimates.  I read about it all the time - browse any sailor's blog, and you'll inevitably read about such-and-such taking 3 times longer than they thought and costing double what it should have.  And while getting our A/C's up and running it did cost a bit more than I would have liked, the fact that we even have a system that functions and operates is a blessing. 

The two 16,000 btu Marine Air condensers
During the survey, we couldn't get it to work, so we weren't sure if we had a few extra boat anchors on board or a bad-ass HVAC system...but lucky for us, it was the latter.  Situations like these are the main reason we got a boat for almost half the going rate - we took a chance on a lot of systems that weren't operational during the initial inspection and rolled the dice that we could get them up and running for a reasonable amount of money.  The watermaker and the a/c system are two great examples of high dollar pieces of equipment that were in-op at the purchase, but only required a small investment and a little work to have perfectly functioning, and important, items on the boat that makes living on one a little easier and a lot more enjoyable.

As suspected, this boat has an extremely expensive a/c system on board.  There are two 16,000 btu "chiller" condensers in the forward starboard locker and five air handlers - one in each cabin and one in the saloon.  The "chiller" condensers are supposedly the more expensive and more energy efficient kinds to have - Shawn over at S.A.L.T. told us that each one would cost around $4k to replace.  And to top it off, each air handler has its own digital thermostat to control the temperature having both a "heat" setting and a "cool" setting as it acts very similar to a household heat pump system.

Digital Thermostat in each cabin and saloon
The saloon control and vent
But here is the cool thing about this system - the condensers work together in a series to chill the fresh water that circulates between all five of the air handlers.  They chill the water down to a cool 48 degrees, but when the water gets down to about 54 degrees, the second condenser shuts down while the first continues to run until it reaches that set temp.  Once it does, it will also shut off and if all of the five zones have reached their set temps, the whole system will shut down until its needed.  But if the chilled water that circulates gets above say 54 degrees, the sea-water pump kicks on and the condensers continue to chill and circulate the water.  So what you can do is turn on the circulator pump a little while before you need it, that way, as soon as the air handler is activated, it will have already pre-cooled the water and cold air blows instantly. The other awesome thing about the system is that each air handler has an extremely strong blower that has three levels of blowing strength.  When I first turn on a particular cabin, the handler blows on high until it gets closer to the desired temperature at which time it slowly decreases strength until the unit shuts off completely.  As we sleep throughout the night, we barely even notice when the unit turns on and off because it only comes on in low strength because it can maintain the desired temp with just activating on low intermittently.  

Part of the control boxes that house system circuit boards
There are also two white control boxes in the condenser locker, and one in each of the five zones throughout the boat.  They house circuit boards and control every aspect of the system.  The ones in the cabins are attached to and control the digital thermostats.

The saloon air handler (before installing a new filter) - each cabin has one of these nicely installed
The odd thing about having only a 3.5 kw generator and such a massive air conditioning system makes a little more sense once we understood the a/c system better.  If we had to, we could run just one condenser and it would have to carry the burden of getting the chilled water down to 48 degrees all by itself - it would take a little longer, but it could eventually do it.  But yesterday, we did a little research - we cranked up the genset and began turning on the a/c system.  It carried the load of both condensers and a few of the air handlers that were powered up with no problem.  Seems that maybe such a small genset might be able to power the whole system if it needed to.  We probably won't ever run the generator all night long just to power the a/c system, but its nice to know that it could if we needed it to.  And while I do have about $1,500 in the repair, I'm told that to install a complete system like this in a boat today would cost in excess of $18k - so its worth keeping this system functioning and operational.  

Here's the break-down:
New circuit board and labor:  $1100
Complete recharge of system with 407c:  $400
Sleeping in a cold cabin on a hot and sticky night:  PRICELESS!!


  1. Nice unit! can't call it small. The admiral gonna love it fo shi, oops sorry Justin. Probably won't need it much in the islands if you've got good ventilation.

  2. We have the same unit and find it excellent. What you didn't mention was that it is a reverse air system taking either the cold or the heat out of the sea water making it more economical and that it can blow warm air as well as cold. We get both extremes so at the moment we have it blowing warm air over winter aboard. It also dries the boat out. Just hope I never need to replace it.

  3. Jim and Kathie - actually its Brandon that didn't approve, Justin just is too busy working on his tan.
    Mark - yeah, that's true - it does Heat and Cool and has a rain-drop that signifies a de-humidified setting I guess - but fo shizzle, wouldn't want to replace any part of the air con-dizzle....oops, sorry, that was for Jim and Kathie.