What are best practices on hydronic heat and domestic hot water?

belfert · July 06, 2009, 01:59:53 PM

I have a Proheat heater I will soon be installing. I also have a Marine type water heater with heat exchanger.

What are the best ways to hook these up? If I leave the Proheat on I believe it circulates coolant all the time and only heats when the coolant gets cool enough. This seems like it would drain the battery when boondocking. I've considered an aquastat, but not sure how I would hook that up electrically.

Any comments?

belfert · July 07, 2009, 10:27:02 AM

Any suggestions?

buswarrior · July 07, 2009, 03:35:50 PM

You have lots of options, that may be why we're all timid to respond!

You can use the circ pump of the proheat to run everything, you can have a hot loop from which other pumps feed circuits, you can control the proheat via thermostat, or let it run and control the circuits with thermostats.

You can plumb directly to your engine system, you can run an isolated system, you can have some form of heat exchanger between the two. You can divide up the existing system and run it in sections.

You can plumb the generator coolant in as another source of free heat, you can plumb it so the engine coolant gives you free heat, you can choose to do neither.

You can have a hot water tank heat exchanger of a billion different kinds, you can get the free electricity at the campground to heat the hot water tank and use that to circulate backwards.

The way you design it will be right, the way everyone else designs it will be not right for you!

I'm still trying to make up my mind how to change mine.

clear as mud?

happy coaching!
buswarrior

belfert · July 07, 2009, 03:59:36 PM

I'm asking specifically about dealing with the domestic hot water, not the rest of the system. I think I have a handle on the rest of the system.

I'll be boondocking 99.9% of the time so I'll only have electricity to heat water when the generator runs. I'll trying to find a reasonably simple way to not have to run the heater all the time just to heat domestic water. Even just the circulating pump on the heater will draw down the batteries.

I'll also heard about using a flat plate exchanger for continuous domestic hot water for less fuel, but not a clue how that would work.

NewbeeMC9 · July 07, 2009, 09:28:07 PM

Quote from: belfert on July 07, 2009, 03:59:36 PM

.....I'll be boondocking 99.9% of the time so I'll only have electricity to heat water when the generator runs. ......

why not just use waste heat from the generator if this is the case

you could run the gen coolant through a flat plate HX on one side and water on the other side

WEC4104 · July 07, 2009, 09:52:23 PM

If I understand Brian's goal, he is looking for available domestic hot water with a minimal reliance on electricity (generator or battery). Running the generator will produce surplus heat, or electricity he could turn into heat, but that is not what he is seeking. I think he is looking for is an efficient diesel fired solution that doesn't suck amps. Do I read this correctly?

John316 · July 08, 2009, 04:50:01 AM

If you are looking for a diesel fired system, how much do you want to spend. We didn't do Aquahot for the obvious reasons. WAY too expensive. We then looked at Oasis, and they have a cleaner system for much less. The only problem is it still costs.

I will let you know how installation goes. Ours is in transit right now....

God bless,

John

Sean · July 08, 2009, 05:46:14 AM

Brian,

We manage this by making hot water only when we need it.

When we are on the road, waste heat from the engine makes its way into the hydronic system, and we have a tank full of hot water when we stop. That lasts us until bed time.

When we are dry camped, we will either run the Webasto or the generator for 40 minutes each night to make hot water, which will get us through the day's dishes and showers.

The rest of the day, it will be luke-warm, which is good enough for hand washing. But we definitely do not run the Webasto full-time unless it's cold enough outside to be needing domestic heat.

HTH,

-Sean
http://ourodyssey.blogspot.com

belfert · July 08, 2009, 07:02:11 AM

To be clear, I already have a Marine water heater with heat exchanger. I also have a Proheat diesel coolant heater. I run the generator at least once a day to charge batteries and more often when A/C is needed. Right now, the electric element in the water heater is always on and powered when the generator is running.

I'm trying to figure out the best way to turn the diesel heater on/off as domestic hot water needs to be heated. I could turn on the diesel heater and it will circulate coolant continuously and turn on/off as needed, but that would probably burn a fair bit of battery.

I'm not super concerned about battery life as I can just recharge with the generator, but I don't want to waste battery power either.

Maybe the best solution would be to just use the generator when I need hot water and forget about the cost and hassle of getting the water heater to turn on the diesel heater when hot water is needed. I only use the bus twice or three times a year anyhow and it might be cheaper to burn diesel in the generator.

buswarrior · July 08, 2009, 08:42:57 AM

Combine your electric element with scavenging the generator coolant heat to the heat exchanger, and you've got a quicker recovering set-up, and shorter run time?

The Proheat, besides being an electrical drain, also casts off a fair bit of wasted heat. The generator rigged that way above might even use less fuel, degree for degree into the water heater, depending on the burn rate of your model of Proheat. And do some charging at the same time?

Lots of fun with the variables!

happy coaching!
buswarrior

Sean · July 08, 2009, 01:01:30 PM

Quote from: belfert on July 08, 2009, 07:02:11 AM
I'm trying to figure out the best way to turn the diesel heater on/off as domestic hot water needs to be heated. I could turn on the diesel heater and it will circulate coolant continuously and turn on/off as needed, but that would probably burn a fair bit of battery.

Brian, you are trying to make the Proheat do something is was not designed to do. If you really want the water heater to "be in charge" of starting and stopping the Proheat and its circulating pump, I could design a set of controls to do that, but you still would not have "on demand" hot water -- when the water in the water heater gets cool enough to demand heating, you will now have the Proheat start-up time (about two minutes, IIRC), plus the time for the hydronic fluid to come up to temperature, typically about five minutes, before any heat at all makes it into the water heater. During this time, the water will be getting cooler; worse, it will actually give back some of its heat to the hydronic loop as soon as the circulating pump starts, because the water heater is better insulated than the hydronic lines.

Then, once the water heater stops calling for heat, you will have the Proheat's spin-down time. All told, you will still be running the circulating pump (and losing heat to the environment) a good deal longer than you will be heating water.

This is the reason why we manage the water heater situation manually -- when we know we will need hot water, we start either the generator or boiler as needed. We decide based on battery charge: if the batteries are below 80% and can absorb bulk charge for 40 minutes, we run the generator that long. This gives us hot water (electrically) and also charges the batteries. We'll also take that opportunity to do some other things if we can, like make ice, or vacuum the house, to take advantage of the generator running.

If we don't need to charge batteries, we run the Webasto instead, because it uses (in our case) much less diesel to heat the water -- about half.

Everything about dry camping is a trade-off. The decision about how much tankage to have, how much solar, and how much "stuff" gets left on all the time will all impact how long you can last.

-Sean
http://ourodyssey.blogspot.com

donnreeves · July 08, 2009, 02:32:19 PM

I have a Pro-heat with a marine water heater which gives several options for making hot water. When plugged in we use the electric element in the heater. On the road engine heat circulates through the heat exchanger in the marine unit. When boon docking we can let the Pro- Heat and the water heater's heat exchanger make the hot water, but it takes 2 hours and a lot of cycles of the Pro-Heat to accompish this.I installed an aquastat on the water heater to control the Pro-heat. The best way to make hot water while boon docking is with a flat plate heat exchanger. I installed it on the hot water line comming out of the water heater. Within 3 minutes of firing up the Pro-heat the water temp is 130 degees and is continuous as long as the pro-Heat runs. To sum up, we make hot water on the road with engine heat and the marine water heater. In campgronds we use electric. Boon docking we fire up the Pro-heat when we need hot water and shut it off when we don't. Donn

NewbeeMC9 · July 08, 2009, 02:57:07 PM

Sounds like the easiest thing to do would be run the gencoolant through the HX and seems like you run the gen a good bit when you boon dock. I have seen a small 10 plate added inline after the marine water heater for quicker hw recovery.

by the way, which water heater do you have? do you have a link, model? you too Sean what do you have?

David Anderson · July 08, 2009, 03:22:22 PM

Quote from: belfert on July 08, 2009, 07:02:11 AM
Maybe the best solution would be to just use the generator when I need hot water and forget about the cost and hassle of getting the water heater to turn on the diesel heater when hot water is needed. I only use the bus twice or three times a year anyhow and it might be cheaper to burn diesel in the generator.

Brian, there is some logic to that statement. I have a Webasto system and plumbed where I can bypass all my coach heaters if I want no heat and send all the btu's to the water heater heat exchanger. I do this with a manual 3 way valve (one in, two outs).

If I'm boondocking I usually let the genny heat the electric element in the water heater while I charge the batts. It seems to (though I've not verified) heat the water faster than the webasto. I agree with Sean. Lot's of waste heating the chamber, lines, etc. thus taking longer to heat the water.

Now, like Sean, when on the road I let the webasto system (pump only) scavenge heat from the engine heat exchanger. When I stop for the night I have a full tank of hot water.

David

Sean · July 08, 2009, 03:41:27 PM

Quote from: donnreeves on July 08, 2009, 02:32:19 PM
... we can let the Pro- Heat and the water heater's heat exchanger make the hot water, but it takes 2 hours and a lot of cycles of the Pro-Heat to accompish ...

Wow, Donn, how big is your water heater? We have hot water in only about 45 minutes from our 45,000 BTU/hr Webasto. We have a 11-gallon water heater, which provides all the HW we need -- in five years, we have never run out. Of course, we almost exclusively boondock, so we also take navy showers -- not to conserve heat, but to conserve water and waste capacity. For the same reason, we have valves that recirculate water from the hot side of any tap back to the fresh tank; this lets us step into a nice hot shower (or do dishes) without having to let any water run down the drain first.

I do like your direct flat-plat exchanger system, though. What is the rating of the exchanger?

Quote from: NewbeeMC9 on July 08, 2009, 02:57:07 PM
... by the way, which water heater do you have? do you have a link, model? you too Sean what do you have?

We have the Seaward 11-gallon unit in galvanized finish, model F1100, which we bought at West Marine (who no longer carries Seaward). We also looked at Force-10, but they were more expensive for basically the exact same device.

Quote from: David Anderson on July 08, 2009, 03:22:22 PM
... I have a Webasto system and plumbed where I can bypass all my coach heaters if I want no heat and send all the btu's to the water heater heat exchanger. I do this with a manual 3 way valve (one in, two outs).

I should have mentioned that our hydronics are plumbed this same way.

Quote
If I'm boondocking I usually let the genny heat the electric element in the water heater while I charge the batts. It seems to (though I've not verified) heat the water faster than the webasto.

I can verify this, as well, at least in our case. It's a bit faster, and also gets the water hotter. We have to remember which way we heated the water before we get in the shower...

-Sean
http://ourodyssey.blogspot.com