Aquahot System

[edroelle]

I wanted to kick around an idea and get some of your thoughts. 

I am semi-familiar with the Aquahot system and the Webasto burner.   But, does anyone have a photo of the construction behind the Webasto burner, the location of the 1500 watt electric coil, and the way the heat is transferred from the domestic hot water to the circulating antifreeze solution?

I am able to keep the coach warm down to about 50 degrees with the 1500 watt electric coil heating the domestic hot water and the antifreeze solution which circulates through the heat exchangers in the coach.   I would like to be able to use park electricity to heat the coach when temperatures are lower, and still maintain the 110 volt capability.

My thought is to install a small 10 gallon water heater or an instant water heater in the antifreeze return line before the Aquahot.   I would wire the secondary heater to the opposite 110 volt leg of the incoming service.

Any thoughts would be appreciated.

Ed Roelle
Flint, MI

[wg4t50]

Ed, My Aqua Hot system running only on the 120 volt heater, works OK down into the 40's, however I also use a 1500 watt electric air heater sitting in the living room area when have parked in the garage, With this setup it works well.  When on the road / outrside, I simply turn on the diesel burner and enjoy.
You can Google Aqua Hot, and find good info / service into, I have found the very best info is from Roger Berke, a certified Aqua Hot parts & service source.
Roger Berke
Mobile 916 214 6518
Email:  roger.berke@qmail.com

Good luck

[rv_safetyman]

Ed, I wanted to update my efforts to keep my bus above freezing this winter using both a radiant electric heater and the Aqua-Hot.  You can see my update at the end of this thread:

http://www.busconversions.com/bbs/index.php?topic=22056.0

Some of that information might help with your thought process.  As you will see, I use a combination of radiant electric heater and the stock Aqua-Hot.

Your idea to add an electric water heater in series with the Aqua-Hot boiler essentially adds a second 110v electric element into the boiler system.  Aqua-Hot has a version with two elements to address the marginal heating of a single element.

The only possible issue I see with your approach is how the system will accommodate the added expansion of the antifreeze.  I suspect that will be taken care of by the pressure cap/overflow tank, but you might need a larger overflow tank.

You mention wiring the second element on the opposite leg.  Works fine on 50 amp service, but on a 30 amp post, they are essentially on the same leg.

I am in the process of wiring a separate outlet in the coach for the heater.  It will be wired conventionally with the exception that the source will be a male plug.  That male plug is then plugged into an outlet in the bay (non-inverter outlet).  The reason I am doing that is to allow me to "cheat" on a 30 amp post.  I will use the 30 amp service to feed the normal coach loads and sneak an extension cord to a 15 amp outlet on the post for just the radiant heater.

As has been noted, most folks with Aqua-Hots use an auxiliary radiant heater for their interior heat.  Most get away with that heater and a bit of supplement from the Aqua-Hot (on electric only).  Radiant heaters are great in that they allow you to focus the heat on the area where you are located at the time.  That way you don't have to heat the whole bus to a certain comfort level.

Not sure that this answers your question, but it might give you something to "chew on".

Jim

[gumpy]

Ed,

The Aquahot consists of a 15 gallon steel tank which has a custom burner fixture welded into it. The Webasto head is mounted to this fixture, and the burner basically shoots it's flame
into the center of the 15 gallons of coolant. There are fins in the burner chamber which collect the heat and radiate it to the coolant, to heat the 15 gallon reservoir.

Domestic hot water is produced on demand. The 15 gallons of coolant are maintained at 180 degrees. There is 130 feet of 1/2 inch copper tube wrapped around the coolant reservoir,
and sealed to the tank with a thermo-conductive paste material of proprietary composition. I experimented with some fiberglass filler compound once, and I think it would work very well
for this purpose. 

The electric element is installed into the end of the reservoir, just as it would be in a household water heater. Nothing special. It's electrical circuit contains a 190 degree thermoswitch,
which gives it priority over the diesel heater when plugged in, simply by heating the water hotter than the diesel thermoswitch, so the diesel burner doesn't turn on when plugged
in unless the temperature drops due to excessive heat loss, such as you will get heating the coach.

It is not possible to heat the coach using only the electric element (well, maybe if ambient is 50 degrees).  I can, however, keep my water bay from freezing by using only the electric
element, which I activate using a thermocouple relay that I've attached to my system that is set at 34 degrees activation.

Hope this is not too confusing. If so, email, or ask more specific questions that we can hash through.

Sorry, I don't have photos. The Aquahot is enclosed in an insulated stainless enclosure. I have not had a need to dismantle that. I did get a tour of the factory, though, and have re-plumbed
my aquahot, so I do have a pretty good understanding of how they are put together.

craig

[Sean]

Ed, as promised in our off-line chat, I am chiming in here, but it looks like several others have beat me to it, so I don't have that much to add.

... does anyone have a photo of the construction behind the Webasto burner, the location of the 1500 watt electric coil, and the way the heat is transferred from the domestic hot water to the circulating antifreeze solution?

There is an exploded view in the manual available from Aquahot's web site.  Craig did an excellent job of explaining it as well.  A minor correction -- heat normally only transfers from the coolant to the domestic water.

I am able to keep the coach warm down to about 50 degrees with the 1500 watt electric coil heating the domestic hot water and the antifreeze solution which circulates through the heat exchangers in the coach.

Again, just to be clear -- the electric element is immersed directly in the coolant reservoir and heats the coolant.  The coolant, in turn, heats both the coach and the domestic water.

I would like to be able to use park electricity to heat the coach when temperatures are lower, and still maintain the 110 volt capability.

As Jim said, most folks simply add portable electric heaters for this purpose.  We don't have an Aquahot, just a Webasto, so we have no way to heat the coolant loop electrically.  Instead, we have electric toe-kick heaters in addition to the hydronic fan-coil heaters.  We use a marine DHWH which has both an electric element and a hydronic coil. Still, in sub-freezing temperatures, we need to run the Webasto periodically even when plugged in, as it is the only source of heat in the bays.

My thought is to install a small 10 gallon water heater or an instant water heater in the antifreeze return line before the Aquahot.

As Jim said, Aquahot has an option for a second electric element.  I don't know if this can be retrofitted to single-element units, but it would be worth asking Aquahot.

Another option would be to remove the existing element and see if it is a common size.  You might be able to replace it with a 3,800-watt, 240v element, and install a 240v SPDT relay that would wire it across both legs when 240v is available, and just to one leg when it's not.  That would give you plenty of heat on 240v, but you'd have to live with just 950 watts on 120v.  The 950w would probably give you decent DHW, but you might find the burner firing up under high demand.  It would not be enough to keep the burner from firing if the fan-coils start calling for heat.

Your idea to install a water heater in the return line would also probably work, but having an extra water heater more or less defeats the entire idea of having an Aquahot instead of separate boiler and tank.  The extra heater will also have no effect on DHW availability other than when the fan-coils are operating.

I would wire the secondary heater to the opposite 110 volt leg of the incoming service.

Good idea, but again remember Jim's caution -- when using a 50-to-30 dogbone, this will end up on the same leg as the other one.  Here again a 240v relay could be used to ensure it is only engaged when you are on true split-phase service so that it is not overloading your system when on 30a.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[prevosman]

Ed,

If you use a conventional, but small sized electric HW heater such as the types used in the marine and RV industry such as these http://www.htproducts.com/literature/lp-13.pdf they will have a 120 volt electric heating element. Connect it to your water supply (HW into the Aqua hot HW heater) so it supplies either hot or cold water depending on if you have it on and run the Aquahot coolant through it's coils from the heater return lines.

The HW tank water contents will be the heat source to warm the coolant when required and it will be the equivalent of adding more wattage to the Aquahot heating element.

Just wire it on the other leg from the Aquahot heater element and if you have 50 amp service or the generator running you are good to go. But as a comment, we have two electric toes psace heaters we use when we don't run the heat pumps or the Webasto and sometimes they aren't enough. There is no substitute for the BTu's of the Webasto.

[Sean]

If you use a conventional, but small sized electric HW heater such as the types used in the marine and RV industry such as these http://www.htproducts.com/literature/lp-13.pdf they will have a 120 volt electric heating element. Connect it to your water supply (HW into the Aqua hot HW heater) so it supplies either hot or cold water depending on if you have it on and run the Aquahot coolant through it's coils from the heater return lines.

So just to be clear, you are proposing he buy a very expensive marine water heater, of the type you'd need if you had no Aquahot at all but just a diesel boiler, in order to supplement the Aquahot, one of whose claimed benefits is that you will not need one of these expensive hot water heaters.  Correct?

No matter, though, because:

The HW tank water contents will be the heat source to warm the coolant when required and it will be the equivalent of adding more wattage to the Aquahot heating element.

Actually, this does not really work.  I speak, here, from experience, because we do exactly this with our system.  We have no Aquahot, just a Webasto, a pump, and a thermal/expansion tank.  Therfore we use an 11 gallon Seward marine water heater for our domestic hot water.

On those rare occasions when we are parked someplace with a power outlet, and the temps drop down to the freezing range, we'll turn the Webasto system pump on, just to take a little heat from the DHWH and circulate it through the system to keep the bays from freezing.

The heat exchanger in one of these marine water heaters is designed for unidirectional use.  It works well in that direction, but not in reverse.  The coolant moves through the coils much too quickly to absorb much heat from the domestic water.  The coolant loop will never even get warm enough for the aquastats to start the fans, despite a hot water temperature setting of 180 degrees.

So while this would take the DHW load off the Aquahot (as would even a cheap residential DHWH), it's not going to contribute significantly to the domestic heating ability of the hydronic loop.  Plumbing a regular DHWH into the coolant system itself, as Ed originally proposed, would be far more effective, and lots cheaper.

FWIW.

I don't care for Aquahot units, for a variety of reasons.  But if this were my system, I'd replace the 1500w 120v element with a 3800w, 240v element and a relay, as described above, and add a couple of portable electric heaters for those times on 120v-only service.  Also FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[Gary W]

Here is a picture of the end unit of my Aqua Hot, you can see the electric element.


Gary

[edroelle]

Thank you for all the inputs and photo.

I asked Aquahot about adding a second 110 volt heater.   Their response was to replace the whole unit @ $9000 !!

Jim, we currently use 2 radiant heaters to supplement the Aquahot, but thought having another heat coil in the coolant line would give better temperature control and be safer. 

Craig, your description with the photo helps me visualize the construction.   Quite a complex assembly.   I HAD thought the 110 volt heating element was in the DHW rather than the coolant.   

Sean, a friend did install a 240 volt coil and that works well.   I would like to avoid compromising in the 110 volt operation down to the 950 watts.    In winters we have 50 amp but many other times we are limited to 30 amps or less.    Also, my intent would be to utilize the extra water heater only when 50 amps was available.    A negative to my plan when on 30 amps, I would be heating that extra 10 gallons of stored coolant when circulating in the heating mode.

Jon,   I found out that my toe space heaters had been found to be a fire hazard – the brand was Cadet if I remember right. 
   
Gary, it looks like from your photograph that there are more water and coolant lines but I understand much better.

Thanks again,
Ed Roelle