Hydronic Heating plumbing question

[bcboomer]

I can't afford a plumber so I'm here again for some free advise
I'm putting in an Espar hydronic heater and also looping in the engine cooling system so I can heat when motoring as well as with the furnace.
I was trying to figure out where to put 2 selector valves to choose which heat source to use. My concern was having them both accessible but then thought about just using 4 check valves to allow either source without worrying about getting 1 valve wrong and starving the furnace of return flow.
I'm using Sea-Tech 1/2" CTS fittings.
Does anyone know why this would not work?

[sailorchic34]

In theory your idea will work fine. The problem is check valves will fail at some time and then bad things will happen.

But, there is a way to do it with out selector valves or check valves. Plum your hydronic heater as you would normally do it. Then on the discharge (hot) side of the espar heater (I'm assuming the heating pump is before the heater), you make two tee connections about 12" apart on the main loop. The first connection after the heater will be the return back to the engine. The second tee after the heater will be the hot line from the engine. YES both supply and return from the engine connect to the same line. Don't connect closer then 12" or further then 24". ~12" is perfect for proper mixing.

Then have a spst switch to power the hydronic pump (not the furnace when the engine is running.

What happens is the heater pump runs when you want heat from the engine. It circulates water through the off espar heater. But with the engine running you have engine heated water injected into the loop.

You could tie the thermostat into the pump to control temperature. Probable need a dpst switch for that.

On a larger boat, one could add a water to water heat pump/chiller and use the hydronic loop for cooling.

This is a simple type of a primary/secondary system, where the engine is primary and espar loop is secondary. The engine loop being side arm. No selector valves and no check valves required. With the engine off no water flows through the engine loop as the pressure is the same (well near enough) that no flow diverts to the engine loop. Only really need to disable the esper heater from firing when the engine is on, which could be via N.C. relay on the engine key circuit..

Unless you add a pump to the engine loop (which you really don't want to do) there will not be enough head in the engine loop to pump water around the hydronic loop. By using side stream injection, you use the main heating pump for circulation and the engine pump is just pumping via a low head bypass/ decouple point between the two tees.

Simple and Easy Peasy

I'm an engineer, I can do this.....

Edit: After pondering a few minutes, I would upside the 1/2" pipe between the two tees to 3/4". 1/2" is pretty small and we want to reduce head loss at the decouple point. Decouple point is what the pipe between the two tees is called in engineering speak :-). We're decoupling the pumps, which eliminates all that messing about with check valves and selector valves.

[bcboomer]

Thankyou, thankyou

That is exactly what I was looking for. I'll sit down in the morning and rework my fitting order. (Fresh Water Systems.Com seem to have the best price/availability for SeaTech)

My Westerbeke W46 has a "Flow control" in the coolant circuit which I think improves the flow to the heater circuit. I have no idea how much flow there is but would that upset your design? Or would it just give a little boost to the Espar pump?

The switch sounds like a good idea although an Espar dealer told me the hot engine coolant would tell the heater to pump but not fire. A switch sounds safer.
Thanks again for your help.

[Oliver L.]

bcboomer, sailorchick,

I would recommend keeping the systems separate. If you have anything happen in the hydronic system, your engine coolant will drain and you will be without propulsion - which could be disastrous.

A small brick type heat exchanger between the two tees will work exactly the same way, but it will be just one hose more on your engine.

Despite the fact that I have two engines I kept my heating/cooling loop separate for exactly that reason...

Oliver

[Racer86]

Just to confuse you a little more, they do make 3 way ball valves. You can control 2 circuits with one valve. Put one on supply's and one on returns.

[seasick]

I like the idea of potentially being able to circulate the Espar stream through the engine to preheat it on extremely cold days. Keeping the two streams completely separate may be the safer option though.

[sailorchic34]

Originally Posted by Oliver L.

bcboomer, sailorchick,

I would recommend keeping the systems separate. If you have anything happen in the hydronic system, your engine coolant will drain and you will be without propulsion - which could be disastrous.


Oliver

A very good point.

Here's a link to one on amazon. One think to watch for is pressure drop, but for the small flow rates we're working with it should be fine.

http://www.amazon.com/B3-12A-Stainle...HEAT+EXCHANGER

[W3GAC]

All of the hydroponic marine heaters I know specify 3/4" hose. Indeed they are rather specific about the specs/ material of the hose. Recommend going on their web site for full run down of requirements/ reasons. Regarding running though engine... of course the worse thing of direct run through engine and not another heat exchanger, if not done properly or inadvertent wrong valve closed is engine over heating/ shut down/ maybe engine damage.


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[sailorchic34]

Originally Posted by W3GAC

of course the worse thing of direct run through engine and not another heat exchanger, if not done properly or inadvertent wrong valve closed is engine over heating/ shut down/ maybe engine damage.

With the typical auxiliary heating circuit from the engine if a valve were closed, no flow would happen in the auxiliary circuit. But the primary circuit in the engine will still keep the coolant flowing around the engine. The auxiliary circuit only diverts about 10 percent of the engine flow. Not enough to effect engine heat rejection.

To clarify something from another poster: there would be no flow from the hydronic loop to the engine, so preheating the engine would not be an option. You could add a pump in the engine loop, but that is not recommended as that pump could interfere with the engine cooling pump flow under some conditions. Generally its not good to place two pumps in series with each other, as flow dynamic's can get wonkie. That's why we decouple systems with multiple pumps in different loops.

[sailorchic34]

One further note: the seatech fittings are rated at 180 degrees F at 100 psig. For the esper alone that is fine. But With engine heat being 180-190, your right on the edge of working conditions, which engineers try to avoid.

A heat exchanger would be your friend in this case, as there is an approach temperature that will reduce the actual temperaure to below 180 on the hydronic side. That is with 180 degrees on the engine side, you might only have 170 degrees or so on the hydronic side, which is within the safe working rating.

Esper heaters have a 17,100 btu rating. So 1/2" pex would be fine as flow rate is only 1.7 gpm at 20 degree F delta. Velocity is only 2.3 fps with a pressure drop of 7 feet per 100 feet. For a short runs, say 25' distance from heater to farthest coil, 1/2" would be fine. For longer runs 5/8" or 3/4" would be better.

[witzgall]

Espar makes different heaters with different heating capacities. Each has a specification for the hose sizing. I believe 3/4 is commonly called for.

Chris

Originally Posted by sailorchic34

Esper heaters have a 17,100 btu rating. So 1/2" pex would be fine as flow rate is only 1.7 gpm at 20 degree F delta. Velocity is only 2.3 fps with a pressure drop of 7 feet per 100 feet. For a short runs, say 25' distance from heater to farthest coil, 1/2" would be fine. For longer runs 5/8" or 3/4" would be better.

[Dockhead]

Originally Posted by Oliver L.

bcboomer, sailorchick,

I would recommend keeping the systems separate. If you have anything happen in the hydronic system, your engine coolant will drain and you will be without propulsion - which could be disastrous.

A small brick type heat exchanger between the two tees will work exactly the same way, but it will be just one hose more on your engine.

Despite the fact that I have two engines I kept my heating/cooling loop separate for exactly that reason...

Oliver

I was just going to write exactly the same thing . . .

+1

Plate type heat exchanger.

[sailorchic34]

Originally Posted by witzgall

Espar makes different heaters with different heating capacities. Each has a specification for the hose sizing. I believe 3/4 is commonly called for.

Chris

They make different hot air heaters. But all the hydronic heaters are 17,100 mbh. Ok the D5E goes to 17,700 mbh but that's a minor difference. 3/4" would work for anything. But for short runs 1/2" pex would be fine too. PEX has about 20 ish percent lower friction loss then hose. Plus hose requires insert fittings which reduce the opening at the fittings to about 1/2" For the seatech CTS system 1/2" would be ok. For hose or pex with insert fittings 3/4" would be the way to go.

[Dockhead]

Originally Posted by sailorchic34

They make different hot air heaters. But all the hydronic heaters are 17,100 mbh. Ok the D5E goes to 17,700 mbh but that's a minor difference. 3/4" would work for anything. But for short runs 1/2" pex would be fine too. PEX has about 20 ish percent lower friction loss then hose. Plus hose requires insert fittings which reduce the opening at the fittings to about 1/2" For the seatech CTS system 1/2" would be ok. For hose or pex with insert fittings 3/4" would be the way to go.

Not really important, I guess, but Espar/Eberspacher hydronic heaters come in a variety of sizes: 4, 5, 10, 16kW, etc. Mine is 10kW or 34,000 BTU.

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[sailorchic34]

Originally Posted by Dockhead

Not really important, I guess, but Espar/Eberspacher hydronic heaters come in a variety of sizes: 4, 5, 10, 16kW, etc. Mine is 10kW or 34,000 BTU.

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Ah, I was only going by their %^&*(^ website. I can see their data is somewhat not correct then.

So to the OP, what size is your Esper unit?? It makes a difference.