Chilled water loop temp adjustment

In the past you could shut down one or two compressors manually to get less cold air, if this is what you want.

This is pretty normal on a looped system I am afraid. But you can adjust the fan speed locally to get it more even, or..?

I think he's trying to say that the air conditioners or air handlers rather in the upper decks cannot keep the temperature where it is set with the additional cooling demand needed and he wants to lower the temperature of the chilled water temperature set point on the chiller system.

The chillwater system I use will not allow lowering of the lower setpoint of the chillwater circuit because doing so will lead to freezing the fancoils, and then things will really get warm.

Make sure the water circuits are completely bled of air.
Make sure the fan coils are clean.

Beyond that, your choices are to reduce the heat load by tinting windows, using shades, or increase the cooling capacity by retrofitting larger fancoils, or using multiple fancoils.
We had good results by optimizing the airflow to and from the fancoils. Your manual should detail how much cross sectional area is needed for intake and exhaust based on the size of your fancoil. If the airhandling capacity of your ducting is not matched to the cpacity of the fan coil you are in essence throttling down the fan coils.

It is also helpful to know the Delta-T (change in temperature) from the intake of the fan coil to the output. An inexpensive and easy way to quantify this is to "borrow" the instant read meat thermometer from the chef.

Hi C4ENG

It might help if you could post the temp of your current set up. Going below 8 is a bad idea and below 6 is stupid. Investigate also if your compressors have a separate freeze protection - the comment about freezing in fancoils is incorrect, but you can easily knacker your evaporators which would be annoying. Goes without saying that you should have glycol in the mix.

Also try calling Jesse at Beard Marine Savannah, he's a pretty helpful sort.

The freezing of the fancoils is an occurence I was warned of by the manufacturer of our chillwater system.
And, wouldnt glycol make the problem worse as a glycol mix has a lower heat capacity than straight freshwater?

Freezing the fancoils is the least of the problems. The chilled water will freeze in the evaporator, not the fan coils unless you are operating one outside in the arctic.

The loop is chilled in the evaporator and only gets warmer as it travels away from there. Freezing the evaporator will likely destroy the chiller. The only thing worse I can think of is having an evaporator tube fail and dump refrigerant and oil into the chill loop and put loop water into the compressor.

Glycol has about 80 percent of the heat transfer capacity of pure water, so if heat transfer is the major concern then you have to increase the volume by 20 percent to produce the same heating/cooling capacity.

What really makes the difference is that a 60/40 mix of glyco/water will prevent the water from freezing down to -70F. That will protect your system far more than it will hurt your cooling capacity.

Makes a lot of sense.
I had been warned not to lower the setpoint because the airflow through the fancoils could be blocked by the condensation on the fancoils freezing up ... a phenomenon I have seen in residential applications using direct expansion systems when the weather outside wasn't hot.
The danger of freezing the chillwater circuit in the evaporator seems far more likely, though our system does have a freeze protection thermostat.
Marmot, what recommendations would you make to the original poster?

Don't mess with anything if you don't know what you are doing. Don't assume you know more about the system than the manufacturer, and find a source for sunshades or something else to reduce the heat load in the affected spaces.

Another band-aid might be to turn off the fans in spaces that can live without cooling for a few hours in the hottest part of the day.

What we don't know is if this is a new problem, one that has developed over time or if its always been that way and is a design fault. This is a cue ...

The idea of turning off fans in other spaces makes the assumption that the limiting factor is the heat absorption capability of the chiller circuit. If the chillers were showing very long run times, I would assume this is the case. More likely though, is that there isnt enough fan coil capacity for the spaces that are warmer?

If the delta T of the air flow across the coils in the hot compartment is high then that is a reasonable suggestion. If it is not very great then it might be because the chill water was warmed as it picked up a lot of heat on the way up there. Or the chill water might not be cold enough to start. Has the boat always had this problem or is it a symptom of global warming?

The coils could be dirty, the fans might be dirty, something might be blocking the air inlet or outlet, there is still a lot of information missing.

Hi,

If it is a chilled water system where there are any steel sections in the system flakes of corrosion might well be stuck in those stupid little 3 way valves preventing the opening or closing fully ( they are a bypass valve in reality that allows chilled water to bypass the coil when the temp setting is higher)

I have dealt with similar problems over the years and have found that often the core issue is that the whole system is the absolute minimum size and that to eliminate it one must upgrade the air handlers often the chillers and sometimes the piping.

The project that I am just finishing up now we added another complete chiller unit, installed 3 new air handlers on the upper deck. We discovered when the system was originally designed they did not take into account cooling of the electrical space ( 15 cubic meters ) the upper deck day head ( 12 cubic meters ) and they had assumed the same thermal load per cubic meter in the wheelhouse as the other spaces not taking into account the greenhouse effect of the windows.

We also added a fresh air plant to the system so that rather than pumping warm moist air into the boat we have cool dry air supplied to all cabins.

The fact that your chillers are able to reach their set point of 8.5 tends to indicate that the issue is with the air handlers - rather than your compressors being undersized. Going down to 6 degrees will help but it is the lowest temp you can use, there is a risk of local freezing in the evaporator. I don't think this two degree drop will make the difference you're looking for.

If the air handlers are older you might first try acid cleaning them - accumulated crap on the fins might not be visible but makes a huge difference to performance. I'm afraid I can't remember the figures but its surprising how much even 0.1mm of dirt makes to efficiency. When I joined my last boat the entire interior was warm solely due to every air handler having mildly dirty fins. An acid clean soon turned the boat to an ice box.

Re engineering the system is a last resort to the problem and yes an acid flush may well solve the problem. But if the air handlers are undersized and the chiller is sized per the requirements of the system it will get down to temp regardless. By installing an additional air handler the chiller may or may not be able to handle the extra load.

In calculating A/C for a yacht there are many factors and some builders do not allow for tropical conditions. The brand mentioned in the O.P. was Condaria which to me indicates it is most likely an Italian built boat. I have observed first hand that some builders from this region do at times underspec the equipment installed.