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Old 07-15-2015, 04:54 AM   #41
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Truma Combi uses a very high efficiency sealed combustion burner so most European users just leave it in boiler standby mode when on the road for instant hot water. The Combi's heating mode yields far higher combined cycle efficiency than standard open combustion RV furnaces so overall propane usage is generally lower. And the small coaxial cowl vent allows flexible installation while avoiding cutouts in the van sidewall.

On demand water heaters do have the advantage of "endless hot water", but most Class B's don't have the huge fresh and grey water tanks necessary to take advantage of that.
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Old 07-15-2015, 12:27 PM   #42
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Do you think it really saves water? Every one I've encountered, you have to run the water a bit for it to activate.
You're right.
The wasted water is probably a wash...clearing whatever is in the hot water pipe.

I should have just said it saves propane needed to heat the unused hot water.
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Old 07-15-2015, 01:06 PM   #43
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You're right.
The wasted water is probably a wash...clearing whatever is in the hot water pipe.
Some people install solenoid-controlled hot-water recirculation loops in their rigs. You press a button and a few seconds later you have hot water without wasting any water at all. I used to think that this was a bit much, but I've though it over and it really is pretty simple and effective. I am going to add one to my Espar-based demand hot-water system. Would make sense in a tank-based system as well.
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Old 07-15-2015, 02:35 PM   #44
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Truma Combi uses a very high efficiency sealed combustion burner so most European users just leave it in boiler standby mode when on the road for instant hot water. The Combi's heating mode yields far higher combined cycle efficiency than standard open combustion RV furnaces so overall propane usage is generally lower. And the small coaxial cowl vent allows flexible installation while avoiding cutouts in the van sidewall.

On demand water heaters do have the advantage of "endless hot water", but most Class B's don't have the huge fresh and grey water tanks necessary to take advantage of that.
I do like the idea of smaller cutouts, and the space savings of just one unit, but I'm not sure that overall LPG use will actually be lower in our application. I'm not interested in "endless hot water". I am interested in not heating water that doesn't need to be heated.

From what I understand, the Combi is best when you want to hold more or less constant house temperature, so that any energy leaking out of the water reservoir simply applies to heating the house, especially if you expect to want warm water often during the day. That's not what we expect will be our operating mode.

If the unit is just used as a furnace, then the real question is which device has a more efficient heat exchanger. I didn't see any Truma data regarding this, nor did I find any for the Suburban NT16 we have planned.
Similar goes for using the Combi in water only mode. I didn't see any data on tank insulation and heat loss. edit: I just noticed the efficiency data in the Truma user manual. Now if only I can get that info for the NT16

We expect to mostly NOT be in Annie during daylight (unless we're driving..in which case being in Annie is probably a good idea). When we are driving, Annie's heater and thermoses will be adequate.

We will be using hot water only a few times a day, like washing dishes or our hands & faces.

We generally won't need warmed water in the middle of the night.

So, we usually won't need much heat during the day, and we we sleep fairly cold.
When we do want heat, like waking->breakfast, returning from a rainy day hike, or dinner-> lounging time, we'll probably want the heat to come up quickly. The Truma must take some of the available LPG energy to just warm water that we might not want. So all other things, like heat exchange efficiency, being equal, the Truma is likely to heat the house more slowly.

All in all, I think our choice of separate units is best for our uses. I could end up being entirely wrong...hopefully not too badly.

Stan
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Old 07-15-2015, 02:39 PM   #45
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Some people install solenoid-controlled hot-water recirculation loops in their rigs. You press a button and a few seconds later you have hot water without wasting any water at all. I used to think that this was a bit much, but I've though it over and it really is pretty simple and effective. I am going to add one to my Espar-based demand hot-water system. Would make sense in a tank-based system as well.
This seems like an interesting idea. How does it work?
Does it have some additional pump system to circulate the water through the water heater and lines?

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Old 07-15-2015, 03:17 PM   #46
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This seems like an interesting idea. How does it work?
Does it have some additional pump system to circulate the water through the water heater and lines?
No. All you need to do is to add a tee in the PEX hot-water feed as close as possible to your faucet. The tee'd out line goes to a solenoid valve and then returns either to the fresh tank or (preferably) to another tee somewhere upstream of the existing pump. You then add a pushbutton switch somewhere near the sink that controls the valve. When you press the button, the valve opens (which, as far as the pump is concerned is the same as opening the faucet). The pump activates and circulates water through the valve and back to the system. Easy-peasy. For the extra credit point, add a thermostatic switch that automatically keeps circulating until the water at the valve is hot.

This is like a $20 project. You can buy the valve on eBay for like $12. The setup looks something like this:

autofill b.jpg
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Old 07-15-2015, 04:45 PM   #47
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I like this!

Stan
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Old 07-15-2015, 06:44 PM   #48
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No. All you need to do is to add a tee in the PEX hot-water feed as close as possible to your faucet. The tee'd out line goes to a solenoid valve and then returns either to the fresh tank or (preferably) to another tee somewhere upstream of the existing pump. You then add a pushbutton switch somewhere near the sink that controls the valve. When you press the button, the valve opens (which, as far as the pump is concerned is the same as opening the faucet). The pump activates and circulates water through the valve and back to the system. Easy-peasy. For the extra credit point, add a thermostatic switch that automatically keeps circulating until the water at the valve is hot.

This is like a $20 project. You can buy the valve on eBay for like $12. The setup looks something like this:

Attachment 2685
If you tee off as you say near a faucet and then tee back in upstream of the pump, after these lines are filled with water, where is the pressure differential that turns on the pump coming from? I think you'd also have to be able to manually turn on the pump when you open the solenoid valve.
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Old 07-15-2015, 06:56 PM   #49
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If you tee off as you say near a faucet and then tee back in upstream of the pump, after these lines are filled with water, where is the pressure differential that turns on the pump coming from? I think you'd also have to be able to manually turn on the pump when you open the solenoid valve.
By "upstream", I mean between the fresh tank and the pump. This is a low-pressure area. The pump will see the pressure differential when the valve opens and turn on by itself.

And, if you somehow don't believe me, then simply drain back into the tank, although this will tend to heat up the water in the tank a bit.
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Old 07-18-2015, 09:12 PM   #50
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Default Installing LPG lines

The LPG line feeds into the van in between the tank's rear mounting assembly and the spring mount.
I punched a 1.125" hole in the van floor, This is large enough to feed a 1/2" black pipe nipple and a rubber grommet.

The nipple goes to a T, which will feed the appliance runs.

There are 3 gas powered appliances, the H2O heater, the furnace, and the cooktop. The H2O heater will be to the left (van rear) of the elbow. The furnace will be forward of the wall frame member shown above. The cooktop will be on the passenger side of Annie, On the counter near the sliding door.

I cut the joists to run the line to the cooktop, cut a length of pipe to fit across Annie, and tried to thread it.

Unfortunately, my ancient 1/2" die's threads were munged, and I couldn't get it to bite into the pipe. So, I took a trip to the not-so-local big box, and had them cut and thread a length. Took the "plumbing expert" 2 goofed/wasted lengths before he managed to cut a proper thread.

I installed the cooktop pipe, and its cut-off valve. The pipe is strapped to pieces of ply which are VHB'd to Annie's floor.

I then installed the feeds to the heaters.

All the appliances will be fed with high pressure flared LPG rubber hose. I'll install the flare adapters when I'm ready to install the appliances. Don't want to ding the flares while doing other stuff. In the meanwhile, temporary plugs will help keep dirt out of the lines.

All the joints will be accessible by easily removable hatches under the cabinetry. The floor under and around the pipes will be insulated with expanding foam. Only the feed-through and the 2 elbows for the cooktop feed will be below my flooring. They will have access hatches as well.
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Old 07-18-2015, 09:14 PM   #51
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Next, I installed the line from the LPG tank to the feed-through. I had earlier attached the line to the regulator assembly.



Next steps will be pressure test, flush and fill the LPG tank. Then do the water runs and resume floor insulation.
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Old 07-26-2015, 11:34 PM   #52
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Default Insulating more floor

The propane lines have been pressure tested. Finding no leaks, I had the tank flushed and filled. I don't have the cooktop installed yet, so I can't claim that we're cooking with gas.


Also, I decided that the H2O runs will all be above the floor. With the tanks now planned to be almost directly above the rear wheels, and with the fresh tank much closer to the H2O heater than in the original layout, it will be straightforward to route the lines without interfering with other stuff.


So now it's time to finish up the floor.


First step is to glue down rigid foam between the van's metal floor ribs. Note that since the metal ribs have tapered sides, the foam doesn't touch the wooden floor joists. We'll add expanding spray foam in the gaps:




The well dressed floor insulator always adheres to this dress code:


Filling in all the little spaces:


Sniffing spray contact cement makes me feel verrry happppiey:
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Old 07-26-2015, 11:35 PM   #53
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Default Installing more floor insulation, continued

They don't lie about expanding foam:


After cutting the excess foam with a scraper blade on my multi-purpose tool, we're ready to put down the second layer of rigid insulation.


But, with all that crawling and bending to cut the foam, my back and knees ache. Besides it started raining and I need to experience this rare event.


So, putting in next layer is put off for a bit.
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Old 07-31-2015, 10:19 PM   #54
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Default More Floor Work

Added the second layer of floor insulation, and foamed the gaps.


Then cut the excess foam.


Cut the clearances in the floor ply for the propane line access, marked where the joists are, so that I can screw things up.
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Old 07-31-2015, 10:20 PM   #55
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Lay down the Reflectix.


Lay down and screw the floor. It's not what it sounds like.


Rinse and repeat.


There's about a 1' section at the rear and end trim to do. Also, I'm going to foam some gaps, and add Reflectix to the wheel wells. That work will wait for a cooler day. I begin to fear that day will never come.
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Old 07-31-2015, 11:31 PM   #56
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Also, I'm going to foam some gaps, and add Reflectix to the wheel wells. That work will wait for a cooler day. I begin to fear that day will never come.
Are you adding any sound deadening material (like FatMat, etc) to the wheel wells and walls?
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Old 07-31-2015, 11:48 PM   #57
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Yes, but it will be a non-standard kind of experiment that we may revisit later.

I have leftovers of a sample can of Daubert V-Damp, which we got for some vibration analysis studies I did at work. Theory says, it doesn't need much to make a difference. So, I dabbed some on the wheel wells. You can sorta see it in the pics. Once it dries, I'll check if it works, and then go from there. It's partly dry now, and tapping on a well sounds less resonant than it did before.

Stan
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Old 08-04-2015, 12:47 AM   #58
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Default Installing the sliding battery tray...A simple project, told in excruciating detail

I finished that last one foot of floor.
Need to make sure that the silicon at the rear edge is well clamped to Annie. Since I am parked outside the workshop, not the garage pantry, I didn't want to pull out the tomato sauce jars I used for the rest of the joists. So I grabbed a broken vise and a broken water pump for the weights.


The floor is finished...except for all the finish work, like vinyl, tile, trim, and/or paint.


So now we can install our first interior thingee. Hint: it's not quite a utility, or a storage tank, or an appliance.
It's the sliding battery tray. Did the first picture above give it away?


The tray will hold 2 4D AGM batteries.
The tray will be mounted on a sheet of 3/4" ply with 1/4-20 bolts and t-nuts. The tray has pre-drilled mounting holes. Holes are drilled in the ply sheet as determined by the tray hole locations. The ply sheet will be mounted to the floor by screw and VHB. We're temporarily leaving the bolts in the ply sheet.


I drilled clearance holes for the bolts in the floor. You can see the four left-side ones here:
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Old 08-04-2015, 12:48 AM   #59
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Putting down the long suffering VHB:


It was suffering from tape worms. I operated to remove them...


Using the bolts in the ply sheet and the clearance holes in the floor as a guide, I mounted the ply onto the floor.


Now it's time to get hammered.
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Old 08-04-2015, 12:49 AM   #60
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Extend the joist location lines to the ply, and screw through the floor and into the joists with a lot of screws.
This should squash the VHB enough to prevent any relapse of VHB tapeworm.


Pull out the bolts, and remount them, but this time with the tray.


And we're done!
The tray is opened:


And the tray is closed:


I am amazed how simply closing the tray also put my tools away.
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