Radiant Heating/Cooling

[drew.ward]

Hi Everyone,

I'm working on the multi-year process of getting my dream job going. I'm hoping in about 3-5 years to be operating tourist charters out of Puerto Vallarta. I've been doing research and there seems to be a strong market there for short day trips and such.

For my plan to work I'd be looking at refitting a larger powered yacht and also living aboard. I'm not worried too much about the logistics of power versus sail for liveaboard purposes as this boat won't really be doing too much long-distance travel (at least not for several years). It's also a bit of a training vessel for me as it will allow me to learn some of the intricacies of the sea while not having to take the plunge directly from land to sail (my only sailing experience was in college racing 420's).

In Puerto, it looks like the money is on a big power yacht making short fishing/snorkeling/beach excursion trips. Also though I'm going to have to provide a fairly high level of comfort to compete. Basically, higher than I'd need for myself.

The boat that I'm looking at is an older 100' steel yacht. It's a mechanically sound vessel with a decent layout and all the rest. It does not however have an HVAC system installed. Being (1) steel, and (2) Mexico, I''m thinking keeping a hundred feet of boat cool is going to be an issue.

I remember my old apartment in Mexico used to turn into a virtual microwave oven. Because the money is going to be coming from providing a comfortable environment to the customers, I want to include cooling in the planing. Right now it's still in the stage of looking at the viability of purchasing this boat (basically how much is it going to cost me in the end).

I have to redo the insulation and all on this boat and as such will be treating a lot of the surfaces. I've been thinking about the viability of a radiant cooling/heating system. These are the ones you see in newer houses where liquid is circulated through a series of tubes embedded in the walls or floor providing passive heating or cooling.

For a boat I am envisioning the following system:

A trailing intake tube weighted down to draw cool water from below the boat. A small DC pump to bring that water up to an insulated holding tank.

The cold water would be held in the storage tank only for a short while as it would be constantly cycling back out through an exhaust. Basically it's just holding temp, not volume.

On the flooring surface of the boat (and possibly some of the larger exposed hull areas) I would install these tubes. I'm probably going to use an artificial product that looks and feels like natural stone tiles for much of the flooring (looks real but is resin based and weighs very little and is flexible enough to deal with expanding and contracting metal). These also conduct heat about the same as a tile floor would. So with no cooling system they would just provide enough of a temperature barrier to keep the metal from burning feet. But with cooling would provide a comfortable surface. Also, with the cost of teak going through the roof it comes out being cheaper.

The tube-cooling system is mechanically very simple: you simply evenly disperse the liquid throughout and use a circulating pump strong enough to keep things moving properly. It uses either water mixed with anti-freeze or a special liquid. The water never leaves this system but only cycles through it.

What I am thinking is that all I would need were two main heat exchangers for the system. One for cooling would simply draw cooling effect from the cold ocean water, and the other could be tied in to draw heat from the engines' and gen set's cooling systems for warmth in cooler climates.

This system probably won't provide all the heating and cooling I would need. But, It should take care of 30-50% of it. If anything it should take the edge off of HVAC expenses with very little energy usage.

I'm doing some other design mods to the boat to ensure natural airflow at least in the public areas of the ship. This will take care of some of the cooling as well.

The nature of the charter's I'm planning are motor somewhere, sit for a while, motor somewhere, sit for a while, etc. So I don't want to have to run the engines / gens all the time. I can include the cost of diesel in my business plan during cruising, but when we're just sitting I have a hard time justifying burning all that fuel just for cool air.

So what do you guys think of this, would it likely work? I know this is a longer post than most, and that most of you don't deal with the issues associated with a larger vessel, but I'd appreciate your opinions from a systems/engineering standpoint.

To me it just seems that cooling the boat is more logical than cooling the air in the boat. And even though this is a large power vessel, I would rather do some work up front and have a more efficient vessel with a lower cost of long-term operation.

Let me know what you guys think...

[GordMay]

I don’t think a Hydronic Radiant Cooling system will be effective in a high temperature & high humidity climate.

Radiant cooling systems generally operate with 65 degree F fluid, installed in large surface areas (usually embedded in concrete mass), and don’t work well in a higher Relative Humidity (think “condensation” above 40%R/H).

See also the previous discussion “chilled water air conditioning” at:
http://www.cruisersforum.com/forums/...ning-6174.html

[Pblais]

For heating I think you can be OK but not cooling. Gord points to the threads we have already on this subject. Cooling takes more energy than heating due to the removal of humidity as well as basic cooling. Hot air rises so a warm floor works and feels nice. It won't work in reverse as well. My guess is you couldn't tell it was even on if it was really hot and humid. The temperature difference in the water isn't that much to provide serious cooling. If the water was 60 F then it might have a chance to work and if the water was that cold you wouldn't need it.

[drew.ward]

I actually hadn't thought of the humidity factor. It is usually around 80% + down there. Oh well...it was an idea.

[Boracay]

One of the problems that I have experienced as I rebuild Boracay is that I did not enjoy my time on the boat as much as I had expected.

I thought about this for quite some time and then I remembered an experiment that I had done in my flat to improve ventilation.

I hung bits of cotton thread from the top of each window so that I could see where the airflow was greatest.

The result of this experiment was that if I want airflow and ventilation I should open the windows.

I did the same on Boracay. I opened most of the portholes and hatches and had an immediate improvement in the internal environment.

So my suggestion is that you should forget about fancy cooling systems.

If you want airconditioning then install airconditioning.

If you want a pleasant environment inside the boat then make sure that your rebuild includes a means of leaving hatches and portholes open almost all the time, possibly with wind scoops.

Just don't locate the hatches over the bunks.

[Ex-Calif]

I am all for out of the box thinking but every "cruising" boat over 60 feet that I have been on had a huge freaking engine room with a dedicated genset that ran all the time and provided icy cold air in the cabins.

At some point in boat size you just close you eyes and pay your bills.

[GordMay]

At 80% relative Humidity, it's a tough nut:
Assuming an ambient temperature of 80 deg.F, the dewpoint temperature is about 73 degrees F.
At 90 deg. F ambient, the dewpoint goes up to about 83 deg. F.