catalinajack
Guru
The below quote from O.C. Driver (Ted) was from another thread in response to a question I asked. Ted was very gracious with his time trying to help me understand the dynamics. Water flow is important. Taking Ted’s advice, I endeavored to increase the flow as I had always suspected could be much better given from observing the outflow from the three thru-hulls. Here is what I did.
1. A very thorough, multiple-pass acid cleaning of the entire system.
2. Used a plumbing snake from the outside to remove any residual dirt. Lots came out.
3. Replaced the hoses from the pump to the compressors. One was found to have been crushed to half its size.
4. Reconfigured the output manifold on the pump. This change had a dramatic impact on the water flow. See the before and after pictures of the outflow. My guess is that the outflow was doubled.
The manifold was the culprit. The original setup always bothered me. See the before and after pictures. Before the change, the manifold was a “T” off the pump with one side plumbed directly to a compressor with the other side of the “T” to another “T” with two hoses. This resulted (for the five years I have owned the boat) in one-half the water supply going to one compressor and the other half going to the other two, approximately. Instead, I used a cross fitting threaded to the pump with three hose barb fittings. This resulted in a balanced and much stronger outflow. Those extra 90-degree bends in the original setup obviously restricted flow and Ted cautioned such bends indeed would.
I did not replace the raw water feed from the thru-hull to the pump as this would be another major project and one that does not now seem to be a problem. I am very happy with the result. Even with the water temp today at 44 degrees, two of my three units are producing plenty of heat. My aft unit is producing 111 degrees of heat from an input air temp of 69 degrees. My forward unit is producing 103 degrees from 67 degrees. My mid-cabin unit produces 78 degrees from 69 degrees, an increase of five degrees from before improvements. This unit has always been an underperformer (heating and cooling) which will need further investigation.
Quote:
Originally Posted by catalinajack
Ted. Here is the update. The pump is a Dometic/March Model AC-5C-MD nominally rated at 17 GPM/1000 GPH. It feeds three units through 5/8 ID hoses. The raw water supply hose is 3/4. It has one sharp 90-degree sweep and one gradual 90-degree sweep to the sea-cock over about 8 feet of hose. The sea-cock and the pump can be changed to a 1" output.
Ok, this will be easy as I was using this same pump till October. The below link will give you the March spec sheet and flow graph. The curve line on the graph you want to use is AC-5-MD 60HZ.
https://www.defender.com/pdf/502649_March.pdf
From the spec sheet, the inlet is 1". So 3/4" hose isn't doing you any favors. While the outlet is only 1/2", boosting the size to 1" for the manifold will have benefit for reducing frictional line loss. 3/4" hose from the manifold to the AC units should be fine. If you have a run from the manifold to one of the units that is >25', I would do it in 1" and reduce it going into the unit.
To figure head loss, start with the highest water point at the highest AC unit, and guess / measure that point to sea level. On my boat, the pilot house unit is approximately 8' above sea level. So the best I could hope for would be 14 GPM with that pump. That number doesn't take into account frictional line loss. If you have the AC manual, they usually specify a minimum GPM flow measured at the hull discharge. My Webasto 12,000 BTU unit has a minimum requirement of 4 GPM and 5.25 GPM is recommended. So, with 3 units the minimum is 12, recommend is 15.75, and the pump after static head pressure can best case produce 14 GPM. Inspite of my best plumbing practices, I couldn't get above 3 GPM at the stateroom unit which was >25' away from the pump. Finally conceded defeat; switched pumps which included a larger supply hose; and now have >6 GPM at the stateroom unit discharge.
1. A very thorough, multiple-pass acid cleaning of the entire system.
2. Used a plumbing snake from the outside to remove any residual dirt. Lots came out.
3. Replaced the hoses from the pump to the compressors. One was found to have been crushed to half its size.
4. Reconfigured the output manifold on the pump. This change had a dramatic impact on the water flow. See the before and after pictures of the outflow. My guess is that the outflow was doubled.
The manifold was the culprit. The original setup always bothered me. See the before and after pictures. Before the change, the manifold was a “T” off the pump with one side plumbed directly to a compressor with the other side of the “T” to another “T” with two hoses. This resulted (for the five years I have owned the boat) in one-half the water supply going to one compressor and the other half going to the other two, approximately. Instead, I used a cross fitting threaded to the pump with three hose barb fittings. This resulted in a balanced and much stronger outflow. Those extra 90-degree bends in the original setup obviously restricted flow and Ted cautioned such bends indeed would.
I did not replace the raw water feed from the thru-hull to the pump as this would be another major project and one that does not now seem to be a problem. I am very happy with the result. Even with the water temp today at 44 degrees, two of my three units are producing plenty of heat. My aft unit is producing 111 degrees of heat from an input air temp of 69 degrees. My forward unit is producing 103 degrees from 67 degrees. My mid-cabin unit produces 78 degrees from 69 degrees, an increase of five degrees from before improvements. This unit has always been an underperformer (heating and cooling) which will need further investigation.
Quote:
Originally Posted by catalinajack
Ted. Here is the update. The pump is a Dometic/March Model AC-5C-MD nominally rated at 17 GPM/1000 GPH. It feeds three units through 5/8 ID hoses. The raw water supply hose is 3/4. It has one sharp 90-degree sweep and one gradual 90-degree sweep to the sea-cock over about 8 feet of hose. The sea-cock and the pump can be changed to a 1" output.
Ok, this will be easy as I was using this same pump till October. The below link will give you the March spec sheet and flow graph. The curve line on the graph you want to use is AC-5-MD 60HZ.
https://www.defender.com/pdf/502649_March.pdf
From the spec sheet, the inlet is 1". So 3/4" hose isn't doing you any favors. While the outlet is only 1/2", boosting the size to 1" for the manifold will have benefit for reducing frictional line loss. 3/4" hose from the manifold to the AC units should be fine. If you have a run from the manifold to one of the units that is >25', I would do it in 1" and reduce it going into the unit.
To figure head loss, start with the highest water point at the highest AC unit, and guess / measure that point to sea level. On my boat, the pilot house unit is approximately 8' above sea level. So the best I could hope for would be 14 GPM with that pump. That number doesn't take into account frictional line loss. If you have the AC manual, they usually specify a minimum GPM flow measured at the hull discharge. My Webasto 12,000 BTU unit has a minimum requirement of 4 GPM and 5.25 GPM is recommended. So, with 3 units the minimum is 12, recommend is 15.75, and the pump after static head pressure can best case produce 14 GPM. Inspite of my best plumbing practices, I couldn't get above 3 GPM at the stateroom unit which was >25' away from the pump. Finally conceded defeat; switched pumps which included a larger supply hose; and now have >6 GPM at the stateroom unit discharge.
