Pressure Water System Question

[ddsailor25]

I'm installing a pressure water system in our boat. My question involves the hot water tank. We are only going to be heating water by the heat exchanger and was wondering how to regulate the water temperature out of the tank. Our engine is a fresh water cooled engine, so it will run at 180 degrees. With heating the water that hot I don't want to take a risk of burning ourselves. Does someone make a mixing valve to aviod injury?


Thanks,
Dave

[sailorboy1]

What kind of tank is it. My Isotherm has a mixing valve on it that mixes the hot/cold water to regulate the temp of the hot water. I was on their webpage the other day and know they sell them seperate if you need one.

[ddsailor25]

Here is a link to the tank I am looking at. This tank will fit nicely in the area and the heat exchanger hookups are on the front of the tank.

Dave

6 Gallon Water Heater With Front Heat Exchanger

[sailorboy1]

do a search on Defender for the temperature control valve and you should find the answer

[GordMay]

Thermostatic Mixing Valves:

Zurn ➥ Aqua-Gard Thermostatic Mixing Valves - Zurn.com

Watts ➥ What's New - Check out our latest Featured Products and more!

Symmons ➥ Thermostatic Valves - Symmons - the smart choice

[Mule]

I normally use the control at the lavatory or at the shower, so the question I have is why worry about scalding yourself if you pay attention? I am really not trying to be a smart ass, (this time) am I missing something? I must be because these limiting products seem to sell.

[Strygaldwir]

In order to maximize your hot shower time, there could be a temptation to increase the temperature in the tank. This would mean you'd have to use less hotwater in relationship to the cold, resulting in a longer shower. Well, one of the issues with this is the rating of the hotwater tubing to the shower. As the temperature goes up, the pressure that most tubing will handle declines. Some times to the point you can blow the tubing, especially as the tubing gets older.

One possible solution to this dilemma is to mix at the tank and only send cooler water down the tubing. This would allow one to run hotter water in the tank, still providing more showers while not taxing the tubing.

Just a thought

[GordMay]

Originally Posted by Mule

I normally use the control at the lavatory or at the shower, so the question I have is why worry about scalding yourself if you pay attention? I am really not trying to be a smart ass, (this time) am I missing something? I must be because these limiting products seem to sell.

Not everyonme pays proper attention, every time.

Many building/plumbing codes now stipulate that domestic water be delivered to hot water fixtures (usually excluding dish & clothes washers) at no more than 120º F (49C) to prevent scalding, and likewise be stored (tank) at no less than 131º F (55C) to prevent growth of pathogens.

This generally requires that mixing valves (thermostatic or pressure balancing) be installed.

[osirissail]

Wait a minute. On a boat we use the engine fresh water cooling system to pump hot engine coolant through hoses to the water heater. A loop of pipe inside the water heater transfers the heat of the engine to the potable water inside the tank then sends the coolant water back to the engine.
- - There is NO provision for introducing a third "cold" source of water into the engine coolant system. So "Mixing" valves are not usable on a marine heat exchanger hot water tank system.
- - The problem with using engine coolant to heat your hot water tank is there is the strong possibility that you will end up with hot water at the temperature of the engine coolant (180 deg F). This brings up two problems (forget about scalding yourself in the shower) - first the temperature relief valve on the water heater might release dumping hot water from your ships potable water system into the bilges of the boat. I had that problem twice then installed shut off valves on the engine to be able to turn off the engine coolant from flowing through the hot water tank. So now I can self-regulate how hot the water gets by turning the supply valve on or off.
- - Second problem is the extreme high temperature of a tank full of 180+ deg F water on the surrounding boat hull, bulkheads, and wiring is not good for long life, not to mention if you are using poly-butyl piping it will heat dry and fall apart.
- - So what is needed is a simple temperature controlled shut-off valve or metering valve on the supply hose to the hot water heater with a thermostat that can be attached to the tank itself or inserted into the tank. When the water in the hot water tank gets to the temperature you set, the supply line from the engine is shut off. Anybody know where to get those types of valves?

[GordMay]

Originally Posted by osirissail

... There is NO provision for introducing a third "cold" source of water into the engine coolant system. So "Mixing" valves are not usable on a marine heat exchanger hot water tank system...

"Mixing" valves are usable on any marine hot/cold water DISTRIBUTION system.

The water would be stored in the HWT as hot as possible (>131º F), and tempered in the potable water distribution system - not in the engine coolant loop.

[IdoraKeeper]

I have noticed the effect of unrestricted engine coolant circulation during longer runs under power. I am not sure if the hot water tank has been venting or not. On Idora the vent is plumbed to the grey water and I have noticed that line getting warm on occasion. At the very least it could waste fresh water and cause the grey water pump to run. MMMMMMM something to investigate.

Todd

[sailorboy1]

Yes the hot water tank can heat up enough to open the pressure relief, but it's a small amount of water loss.

I normally leave my pressure water pump off unless I need water regularly for a period of time. In this case any pressure in the hot watre tank just goes back to the pressure tank and the relief never opens at all.

[osirissail]

Using a "mixing valve" on the potable water circuit to maintain temperatures at the spigot/shower head is possible but a total waste of money and introduces more complicated machinery into a cruising vessel. Water temperature at the spigots/sinks/showers is regulated by the human who opens the hot and cold water faucets. If the human is too stupid to regulate water temperature while taking a shower or washing in a sink then they should live on land where all the government agencies make sure you cannot hurt yourself due to your own stupidity.
- - The danger of overheated water in a cruising vessel's hot water tank is present when you are using your engine's coolant loop to supply heat to the hot water tank. Diesel engines run at coolant temperatures varying from about 160F to 200F depending upon engine load and age of the engine plus a hundred other problems with keeping the engine from overheating.
- - If while engine coolant is being supplied to the hot water heater - the cruising vessel gets involved in a situation involving the need for prolonged high power / emerg power then it is highly likely that the coolant temperatures will start to climb to and possibly exceed the temperature relief valve setting on the hot water heater. This will open the valve and vent very hot water into and around the area where the hot water heater is located. In my case that is in the Galley area which has happened twice.
- - Subsequently I re-plumbed the relief valve to discharge down a sink drain hose. But still even with the danger of scalding water now diverted to a drain, there still exists the loss of potable water from the tanks down the drain. The amount depends upon whether the potable water pressure pump is left on or is off. The third danger is to the actual plumbing pipes/hoses/tubes around and downstream from the water heater. High temperatures above 140F will harm "plastic" type hoses and significantly weaken them. In the case of polybutyl it takes about one year for the fittings to "cook" and crumble resulting in a lot of water being dumped into the boat's interior before you can turn off the water pump.
- - So the most critical consideration of using the engine coolant system to heat the water in the hot water tank is regulation of tank water temperature. This is done automatically when the AC or DC power is used with the electric heating elements. A non-electrical metering or shut-off valve in the engine coolant supply to the water heater would be a good solution to this problem when using the engine to heat the hot water tank.
- - Additionally, I installed two ball valves on the engine where the coolant is tapped off to go to the hot water heater. These valves can be used to turn off the supply to the hot water heater for temperature protection and - more importantly - to shut off both coolant lines to the hot water heater should a leak or burst hose threaten to drain all the coolant out of the engine. This would - of course - only happen when you are in a emergency situation and need the engine to get your "ass out of a bind," Losing the engine due to a burst coolant hose going to/from the hot water heater would definitely ruin your day.

[goboatingnow]

just run using a proper calorifier and let it rise to engine temp. Thats how all these systems work. You can use a termperate valve to shut off the flow whwn above a certain point (Danfoss and other make them) but it not needed

Dave