Monitoring AC water pressure?

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wkearney99

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Feb 17, 2018
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Location
USA
Vessel Name
Solstice
Vessel Make
Grand Banks 47 Eastbay FB
Anyone had any success setting up monitoring for the freshwater supply for HVAC?

We've got a single intake/outflow setup for our four compressors. 3 of which are split systems, and the last one is an all-in-one. It's the last one that's a problem. The sea strainer got congested, but not enough for the first 3 systems to present errors. It was only the last unit that threw an error. It's on about 6' of hose to/from the main manifold. Pressure can drop just enough for that last one to fail.

I'm wondering about maybe putting something on the manifold to track/monitor the pressure, and alert me if it drops into a certain range. As in, don't alert if it stops (because, yeah, the AC system is off). Only alert if it's dropping into a low range. That'd help give me a heads-up that something's likely amiss.

I've got a Maretron FPM100 that I could use for this.

I'm wondering what PSI range this stuff runs. It's a Dometic setup, but I don't have the specific part numbers handy.
 
Can you look at your water pump specs?
 
Your manifold may be the problem. It should have an inlet that is centered with the separate outlets, one center, one left, one right. If you have a branch on a branch you will have uneven flow. I had this problem. Reconfiguring the manifold solved the uneven flow I had.
 
Not sure how yours is plumbed. I experimented with mine running through all 3 units in series, and found that the last unit couldn't handle the elevated coolant temperature. In redoing my system, I increased pump size, plumbing size, and added PVC valves to reduce water flow to the nearest units and increase flow to the farthest. My boat has a much larger external and internal strainers to extend time between cleaning.

As far as an alarm warning system, a simple addition to your Maretron system would be to add a water temperature sensor to the discharge hose after the 4th air conditioner. I'm assuming the system has configurable alarms for temperature. Plan to tee the line with the water going through the run of the tee and the sensor in the bull.

Ted
 
You could give it a try, but I think it's unlikely to work. The raw water plumbing is open ended, so the only pressure is water head and pipe resistance. So I think the pressure difference between running and not running will be very small, and even smaller between running properly and not properly.


But you never know, and if you decide to try it I'd be very interested to hear how it goes. A flow sensor would more typically be used for something like this where the water flow spins a paddle wheel of some sort. I think Maretron might even have such a thing. Actually here's what they say refer you to for a sensor https://www.gemssensors.com/search-...itches-Sensors/family/Electronic-Flow-Sensors
 
The all-in-one and its direct plumbing might be fouled. When was the last time it got serviced and cleaned? As mentioned these are not water-pressure sensitive systems, it all about flow.
 
As Twistedtree said,
The pressure will depend on the pump and the resistance to flow (head).

Flow is what you want to measure. Most small (<50') boats HVAC heat pumps require 3 to 4 GPM for each unit.

Hope this helps
 
If it a Dometic unit, you can easily add their optional water-out temperature sensor which will monitor the temperature at the outlet hose connection. If it exceeds the temperature you select in the control unit setup, it will shut down the system and indicate a Pump Sentry fault or PPP error. Ideally, this should happen before an HPF fault occurs which is technically harder on the compressor. An added advantage to monitoring outlet temperature is that in the event the water flow is adequate, but the condensing coil is beginning to clog, you will be alerted to the fact so that you can clean/flush the coils.
 
I believe that the rate of water flow not only cools the coils but also keeps the outlet clear of buildup to a degree. Imagine how much debris will get gently washed away at 3GPM vs 1GPM. So, as pointed out, maybe a larger pump is required for multiple units and long runs.
An alarm is a good idea and it can be powered from a point on the HVAC circuit so it only works when the pump is working. As the OP pointed out, if the unit isn't on, we don't want the alarm functioning.
 
Excellent points, from everybody, I'm going to look into the flow rate question. I'll be at the boat today and I'll get some pictures and model numbers
 
I believe that the rate of water flow not only cools the coils but also keeps the outlet clear of buildup to a degree. Imagine how much debris will get gently washed away at 3GPM vs 1GPM. So, as pointed out, maybe a larger pump is required for multiple units and long runs.
An alarm is a good idea and it can be powered from a point on the HVAC circuit so it only works when the pump is working. As the OP pointed out, if the unit isn't on, we don't want the alarm functioning.

That was my feeling about using a range as a threshold for the alarm. As in if it's below a certain point we really don't care because the unit is either off or we already know there's an error. So knowing a sweet spot would be the key, the question is whether or not whatever we use to monitor it is capable of bracketing a range like that. I don't know if the maretron units do this or not
 

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