2 Hot water in series

[Aussiecoach]

Hi

I recall reading TomC has two hot water systems in series, the last being powered by the inverter for hot water whilst going down the road. What is the advantage of having the two in series and when stopped I guess you would need to power both, is that so?

Thanx
glen

[prevosman]

The question raises more questions in my mind. For example, why 2, and not just one of greater capacity. Why run it from an inverter? Is there any reason why a HW tank with an engine coolant heat exchanger is not considered?

I used one of these http://www.htproducts.com/literature/lp-13.pdf and modified it so I can thermostatically control a solenoid valve so when the water temp reaches the electric heater set point when heating with engine coolant the flow of coolant stops. As you can see these are available in a range of capacities and the insulation quality is so good you are still drawing hot water from it days after turning off the engine.

I have it set up so if I am not running the engine I can use the internal electric water heater powered with shore or generator power, but also via the engine coolant lines I can heat it by running the Webasto.

Jon

[Jeremy]

I used one of these http://www.htproducts.com/literature/lp-13.pdf

That is the exact equivalent to what I have bought for my bus (not installed yet). My engine doesn't have a block heater, so I saw another advantage of this set up as giving me the option of pre-heating the engine using shore power, rather than having to burn diesel in the Webasto.

A simple electric-only heater (or even two in series) is a much cheaper and easier installation though. Just to confuse things, I've actually also bought a small electric-only water heater which I plan to install downstream of the calorifier - my logic being that my calorifier is very big (75 litres I think), and if the water in that is cold I'm not going to want to heat up that large tank when I only need enough water to do the washing-up.

Jeremy

[prevosman]

Jeremy, I like the concept of using it as a block heater however heat loss through the lines becomes critical It will take a lot of mass and a fast recovery electric heater to bring an engine block up to a relatively warm temperature and the coolant lines need to be well insulated to prevent the loss of heat.

I can say with conviction these HW heaters should never be installed without a means of controling the water temp when heated via engine coolant. After driving we were getting temps approaching 200 degrees so now it is controlled to maintain 130, a much safer HW temp for us. If you install it to warm up the engine, you should consider a circuit that allows you to regulate the temperature without preventing you from using it to heat the block.

[Jeremy]

I understand what you are saying; looking at the information that you linked to about the Super Stor product, it seems that it has a thermostat which prevents the electric element making the water too hot, but there is no temperature regulation when the water is being heated by the heat exchanger - so scalding water could come straight out of your taps or shower. Hence your clever modification to cut off the flow of 'incoming heat' from the heat exchanger when the water in the tank reaches the required temperature.

My device is a SureCal, which is a bit different in that it has an adjustable thermostat on the hot water output, which mixes the hot water coming out with the cold water going in - so the temperature of the water going to the taps is regulated regardless of whether it is heated by the electric element or the heat exchanger. Restricting the temperature of the output water, rather than the temperature of the water in the tank, effectively increases the capacity of the tank - in simplistic terms, a 1 gallon tank filled with water at 100 degrees will deliver 1 gallon of 100 degree water to the taps. A 1 gallon tank filled with water at 200 degrees will deliver 2 gallons of 100 degree water to the taps. (By the way, talking about water at 200 degrees seems very strange to me, as I was taught that it boiled at 100 degrees!).



On the block-heating aspect - I understand what you mean about needing a fast-recovery electric heater to do the job. I'm hoping that brute force will work instead - in other words, that having 75 litres of hot water available should be enough to heat the engine block by a few degrees, even if no 'reheating' is done at all. I might be wrong about that though. Regarding insulation - as it happens my calorifier will plumb into the engine coolant lines where they feed the 'bus heat' heating matrices, which are halfway down the bus and above the bay where the calorifier will be mounted. The lines from the matrices to the engine are already insulated

Jeremy

[prevosman]

I replaced the HW heater that came with the bus with the one I linked to for several reasons. The first was not SS and it had a 175 PSI limitation. The pressure relief valve was only 75 PSI. When it was in essence overheated via engine coolant it created excess internal pressures and it dumped water out the releif valve until the valve wore itself out. Some owners who experienced the same thing went to Lowe's or Home Depot and bought a replacement valve but did not recognize that the original releif valve was 75 PSI, and now they were installing a 175 PSI valve. That cured the dumping of excess pressure, but it ended up with a number of tanks bulging at the ends due to excessive pressure.

There is a check valve in the system to prevent HW from back flowing into the cold water via the cold water supply line so the tank bulged because there was no place for pressure to go until the relief valve opened if someone used the wrong pressure valve.

So when I gutted and redid my water bay I did a few things. I pulled the old tank (which had not bulged, but was 15 years old) and replaced it with the new SS tank. I then added a second 130 degree F thermostat which controlled a solenoid valve on the coolant line to the tank. Additionally I drilled a very tiny hole in the check valve so if the solenoid valve failed to close and internal water temps got very hot and increased the pressure the excess would bleed through the pinhole in the check valve and be absorbed by the expansion tank on the CW side of the system.

As to heating the engine my coach has an 80,000 BTU Webasto and it is used in very cold temps to not ony heat the coach interior, but can also be used to maintain a warm engine temperature so a cold start is not required. A side benefit is it keeps my HW hot. If I did not have the Webasto I would instead just run my generator prior to engine start for a few hours and use the block heater. I am not shy about running my generator because as long as I have to drag the thing around with me I might as well use it if it makes sense. I'm kind of an energy hog in that I want us to have all the heat, cool and electric we need rather than roughing it. My Boy Scout days are over.

[Joe Camper]

I suppose 1 reason for 2 10gal takns instead  of 1 20 is the failure factor. If 1 goes down you still have hot water.

We have a raritan 20g just 1. I have no clue what pressure relief it has but it does not weep and our tank is slightly expanded so Im guessing it has the wrong one. LOL Been that way before I got it

On a related note if I were starting from scratch with bays with wood floors I would first line the plumbing bay floor with a tray similar to what you put under a washing machine you put on an upper floor of a home. A drain pan for the entire bay floor. I have seen an entertainer coach done with this and it just seemed to be a smart thing to do.

[artvonne]

  While I agree that heat loss in using an electric water heater to heat a big ol Bus engine is significant, almost any electric hot water heater element is double or tripple the wattage of anything normally put into an engine for that purpose. We dont need to heat the engine to operating temperature, and we dont need to be taking a shower and washing dishes while the engine is heating. Its only necessary to heat the engine enough to burn diesel, so anything over 50F should be more than sufficient.

 The reason many like TomC are running everything off inverters, including the water heater(s), is so they have the ability to park for extended periods, dry camp, without needing to run the generator continuously.  By managing power consumption, we can utilize a battery bank to drive all electrical loads through inverters, and need only run the generator intermitently to manitain battery capacity. It should also be pointed out that diesel generators do not last as long running below 50% rated power for extended periods, so using them at full rated power for shorter intervals makes more sense in that regard, however the cost of a battery bank and big inverters is also significant. Using two water heaters..., two shorties fit under the floor in a cargo bay better than a tall skinny one. That extra capacity can allow you to have hot water until you "can" run the generator again.

  Lots of ways to skin a few cats around here.

 

[luvrbus]

Suburan makes a 16 gal for the rv you can have the best of all power sources even the engine and with a pump you can have engine pre heat,SW16DE model Seward has a good heater also electric and engine heat.
Check your marine world good hot water heaters practice there is to overheat the water use a mixer then  a 10 gal hot water heater becomes a 16 gal unit I think it is Attwood that sells one now with that setup


good luck

[Joe Camper]

I recently did a trip thru Texas and OK, last month when it was 100+ every day. This bus had the gen in the plumbing bay. There was a 3 day stretch that we needed to run the gen straight thru.

The cold water coming out of the pipes was so heated that it was too hot with the water adjusted all the way to cold.

How much or little the gen in the plumbing bay played in this problem I do not know but it had to account for some of the problem.

It was a very uncomfortable situation. How would you deal with this?

[artvonne]

  Pass the cold water line past the AC ??

  Thats an interesting thought about the Gen putting heat into the water tank.

[prevosman]

 While I agree that heat loss in using an electric water heater to heat a big ol Bus engine is significant, almost any electric hot water heater element is double or tripple the wattage of anything normally put into an engine for that purpose. We dont need to heat the engine to operating temperature, and we dont need to be taking a shower and washing dishes while the engine is heating. Its only necessary to heat the engine enough to burn diesel, so anything over 50F should be more than sufficient.

 The reason many like TomC are running everything off inverters, including the water heater(s), is so they have the ability to park for extended periods, dry camp, without needing to run the generator continuously.  By managing power consumption, we can utilize a battery bank to drive all electrical loads through inverters, and need only run the generator intermitently to manitain battery capacity. It should also be pointed out that diesel generators do not last as long running below 50% rated power for extended periods, so using them at full rated power for shorter intervals makes more sense in that regard, however the cost of a battery bank and big inverters is also significant. Using two water heaters..., two shorties fit under the floor in a cargo bay better than a tall skinny one. That extra capacity can allow you to have hot water until you "can" run the generator again.

  Lots of ways to skin a few cats around here.

 

I understand about inverters and being able to dry camp, but energy is energy is energy. Usually of the emphasis is on use of batteries for dry camping and if that is the case then it is prudent to do two things. First, make sure there are a lot of batteries, or at least a lot of capacity, and second, due to such reliance on inverters to have at least two inverters in case one of them pukes. Usually loads like a HW tank or ACs or toe space heaters have enough of a current draw to make their use limited. I guess the decision owners need to cosider is the cost of battery replacement if they have a large battery number or capacity, versus the limited cost of running a generator more often. I vote for the generator usage and want less batteries. We RVers rarely use our generators enough anyway.

My inverters (2) have limited dedicated circuits and I admit I am not set up for dry camping, but can do quite well for short periods. My inverter circuits are my forward outlets, rear outlets, TV, microwave, refrigerator, and aux air compressor. That means I can overnight somewhere and not hook up or run a generator. But if I need heat or AC then the generator comes on and stays on as long as I need it, at which time we make ample use of lights and anything else that is going to load the generator. As long as it is running I load it. Unfortunately the trend in store bought conversions is to put in 20KW generators so there is almost nothing I can turn on that even approaches 50% load. With 166 amps capacity available every one of my 4 AC units at about 13 amps is still less than 1/3 the capacity. My HW tank won't draw power after I have been running because it is hot and will remain so unless we start using a lot of HW. We would have to use the electric stove top, the clothes dryer, and the outside BBQ grille to get past 50%

My point is even when being loaded, the way store bought conversions are set up we never make our generators struggle. But we are not alone. Entertainer coaches have even less current draw than motorhome conversions and they have the same size generators. I know for a fact that one nearby company has 20,000 hours on their newest generator and the oldest is at about 37,000. They have not had any work done on the front or back end on those so I think we are going to be OK as long as I do load the generator as much as possible when I do turn it on. A typical load on entertainer coaches is the AC units and maybe the TVs and a microwave. But like all our coaches, once it reaches a comfortable temperature our AC loads drop off to an average of about 30 amps even if the outside temps are approaching triple digits, and much less when the sun goes down.

As far as heating the engine, I used to live in the western NY snow belt and had to start the bus when temps were sub zero. If I got the engine heater to get the engine up to where it was at least warm to the touch, probably in the 40 to 50 degree range I agree that was all that was needed. I usually turned it on the evening before we were leaving on a trip.

[TomC]

I used two 10 gal electric water heaters, one for redundancy (although the heating elements are about $20.00 to replace).  Second-two 10gal water heaters will heat faster then one 20gal (assuming all have the same 1500watt element).  Third, I didn't want to run extra coolant lines to the water heaters for the heat exchanger.  Also, the two water heaters combined were less then $500.00 (still are).  If something happens, most big box stores carry them.  The final one powered through the inverter is usually used for going down the road.  Although-we were parked in front of my friends cabin and only had a 20 amp plug.  I was able to heat one water heater with the inverter and the other with the power cord.  I like the combination so much, I'm using it again on my truck conversion.  In the 17 years I've been using the water heaters, zero maintenance.  I don't thing anyone can say that with a propane, or Aqua Hot type Diesel heater.  Good Luck, TomC

[Aussiecoach]

Hi TomC

Thanx for the detail.

Are they just connected in series, hot output of the first feeds into input of the 2nd then output of the 2nd feeds around the bus?
I guess you just have to make sure the 2nd one is always powered somehow and all is ok.
If you also power the 1st you get twice as much hot water I imagine

Where have you fitted your water pump in this arrangement?

Cheerz
Glen

[TomC]

The way I run the water heaters is I heat the inverter based one first and then turn it off. Then I heat the first water heater and leave it on.  It preheats the second water heater so in essence, the inverter based water heater is just a hot water tank after it is heated.  This gives me 20 gal of hot water (and I don't have the water heated much more then just hot to the touch) and have never run out with two showers and washing dishes.
It is plumbed that my two water pumps (in parallel to increase volume, not pressure) feed the cold water manifold, and the hot water comes off that manifold through the water heaters then to the hot water manifold (I run an individual ball valve per each water appliance).  Even though I used Qest fittings (gasp!), I haven't had any problems.  Not to say I won't. I'm sure I'll have to re plumb it in the future. But with the way I plumbed it, the entire replumbing job shouldn't take much more then a weekend to do.  Until I burst a hose, I'll keep using the bus the way it is.  I don't ever use city water hookup-prefer being on the water pump (can turn off anytime easily) and just filling the tank when needed. Good Luck, TomC