Our next rig

[avanti]

Here's a summary of the heating and air conditioning system:

Cabin heating is via a standard Rixen's Espar hydronic furnace fueled by gasoline from the chassis tank. The current generation of Espars have built-in high-elevation adaptation. Also, the standard Ford standpipe was replaced by the correct Espar unit, which apparently improves performance at high elevation. Unfortunately, this requires dropping the tank, rather than using the convenient access port that can be ordered with the Transit. The glycol can also be heated using a 120VAC heating coil in the expansion tank. This useful for saving fuel when shore power is available.

As in most Rixen's systems, the glycol loop feeds both a water/air heat exchanger for air heating, and a water/water flash-plate heat exchanger to produce instant, on-demand hot water. There are warm-air ducts under the refrigerator and in the bathroom.

The Rixen's controller is also capable of controlling a second, independent glycol loop. This is typically used to provide under-floor radiant heating. In our case, however, it is used to heat the tanks and exposed plumbing under the van to achieve true 4-season operation. More on this in a later section. The controller also supports a bluetooth app which runs diagnostics and clears codes. It is not needed for normal operation.

Here is the Rixen's plumbing, located under the bed, just behind the driver's side wheel well:

IMG_5869.jpeg

The two tempering valves control the temperatures of the DHW and the anti-freeze loop.

Air conditioning is provided by a 24V Pro-Air ducted split system, with compressor and condenser mounted underneath the van, and the evaporator/air-handler mounted in the large rear center cabinet above the rear seats. There are four cold-air ducts: two pointing down to the seats/beds and two facing forward. The system is very quiet, and both the compressor and the fan can run at very low speeds for extremely quiet, low-power maintenance cooling.

The controllers for the heat and A/C are currently separate panels:

IMG_5875.jpeg

I plan to integrate them into a single, automatic control system using the van's automation system. Unfortunately, neither controller is designed for external control, so it is going to be a reverse-engineering project. Once this is done, the physical panels will be redundant and I will likely remove them for a cleaner look. In anticipation this, I had CMI construct a filler panel which will conceal the holes from the controllers.

[GeorgeRa]

Thank you for the update.

I wish to know how a fuel standpipe can result in a better performance in high elevation.

Glycol in hydronic system varies from 150-175F. How did you prevent the few gallons aluminum Rixen tank to act as a major heat source inside especially in summer days.

Is your Rixen blower operating in proportionally variable mode?

[avanti]

Originally Posted by GeorgeRa

Thank you for the update.

I wish to know how a fuel standpipe can result in a better performance in high elevation.

The OEM standpipe is much larger in diameter than the correct Espar one. In the presence of the sudden suction pulses from the dosing pump, this leads to cavitation, which leads to bubbles in the fuel, which leads to flame-outs. It is the same phenomenon that occurs when people use too-large (or insufficiently rigid) fuel line in their installations. I can confirm the latter from personal experience, since it was done by Great West and caused no end of problems until I got it sorted. The phenomenon occurs even in diesel, but is worse both with petrol and at altitude. I suspect this mistake may be a source of the rumor that gasoline Espars don't work well at elevation.

Glycol in hydronic system varies from 150-175F. How did you prevent the few gallons aluminum Rixen tank to act as a major heat source inside especially in summer days.

Well, we'll see if it is an issue. There isn't a lot of choice in a Transit, since it needs to be a high point and there is just no space in the engine compartment. The whole setup is in a closed compartment, which I guess could be further insulated. Worst case, I could vent through the floor with a small fan.

Is your Rixen blower operating in proportionally variable mode?

Dunno. I am kind of treating both controllers as black boxes, since I plan to replace them eventually. My custom setup certainly will.

[GeorgeRa]

Originally Posted by avanti

The OEM standpipe is much larger in diameter than the correct Espar one. In the presence of the sudden suction pulses from the dosing pump, this leads to cavitation, which leads to bubbles in the fuel, which leads to flame-outs. It is the same phenomenon that occurs when people use too-large (or insufficiently rigid) fuel line in their installations. I can confirm the latter from personal experience, since it was done by Great West and caused no end of problems until I got it sorted. The phenomenon occurs even in diesel, but is worse both with petrol and at altitude. I suspect this mistake may be a source of the rumor that gasoline Espars don't work well at elevation.

Well, we'll see if it is an issue. There isn't a lot of choice in a Transit, since it needs to be a high point and there is just no space in the engine compartment. The whole setup is in a closed compartment, which I guess could be further insulated. Worst case, I could vent through the floor with a small fan.


Dunno. I am kind of treating both controllers as black boxes, since I plan to replace them eventually. My custom setup certainly will.

I designed my 6.5 liters coolant tank which is usually ¾ full so my D5 hydronic system operates at about 5 liters. Lower volume could give you lower stored energy capacity to help in these hot summer days. As long the heater rod is submersed the system should operate fine. A level sensor could help to monitor lower level.

For hot water operating on minimum volume (Espar plus flat plate heat exchanger) bypassing Rixen tank could work. I have seen an operating bench top prototype of D5 with a flat plate heat exchanger working OK.

[avanti]

Thanks.
I tried to order a float valve, but Rixen's only offers it on their larger units. Guess retrofitting one shouldn't be too hard.

[GeorgeRa]

Originally Posted by avanti

Thanks.
I tried to order a float valve, but Rixen's only offers it on their larger units. Guess retrofitting one shouldn't be too hard.

I used reed switches based level sensor, both reed and capacitive good to 185F.
Ultrasonic could be a good option if you find one with OK minimum distance to fluid.

https://kus-usa.com/product/sss-ssl-sender/
https://kus-usa.com/product/capacita...el-sensor-cls/

[avanti]

The design of the van had three main goals:

1) Reliability
2) Comfort and convenience
3) Élan

Of these, reliability was #1. By "reliability" we don't primarily mean saving money on repairs, but rather minimizing the likelihood that the van will let us down in a way that would spoil a trip. We probably would never have replaced our Legend except that the Sprinter chassis did not meet this goal. We have high hopes that the gasoline Transit will be both more reliable and easier to get repaired in the field.

This kind of reliability doesn't mean that nothing ever breaks. But it does mean that when something important breaks, there should be some kind of work-around that allows the trip to continue. This is where redundancy comes in. We tried hard to build in as much redundancy as practical given the constraints of a B-van. Here are the main ones:

Electrical
There are several imporant redundancies built into the electrical system:
--The main storage is implimented as two 24V lithuim batteries wired in parallel. If one should fail, we could proceed at half-power on the other one.
--Although the system is native 24 volt, all of the essential consumers (lights, Espar, macerator, video, heating pads, automation etc) are on a 12V bus. This bus can be fed from two sources: (a) a 100A 24->12V converter or (b) a 60A power feed (CCP1) from the chassis auxiliary battery. So, if the main power system were to fail completely, the van would still be livable. A simple manual switch chooses between these two modes.
--The refrigerator and freezer normally each run at native 24VDC, but can also accept 12VDC. Each has a 3-position switch (off/24V/12V), so that they can run during a system failure. They also automatically run at 120VAC when shore power is present. Also, the fact that the fridge and freezer have separate compressors adds another level of redundancy.
--The vehicle engine charges the main batteries via a DC-AC-DC setup, in which a 175A power takeoff (CCP2) from the engine is used to power a dedicated 2500A inverter, which is fed via an automatic transfer switch to the vehicle's shore power circuit. This means that both shore power and engine power are available as backups for 120VAC should the main inverter fail.

Dual Dump
As has been discussed at length on this list, macerator systems can be easily provided with a back-up gravity dump in case of macerator failure. All of our vans have been so-equipped, including this one.

Heat
The main Espar hydronic cabin heater has a built-in 120VAC heating coil, so that hot water and limited heat can be producted should the Espar furnace fail. This can be powered by (a) shore power; (b) the main batteries/inverter; and (c) via the engine DC-AC-DC inverter. We also carry a small "cube" ceramic heater as an additional backup.

Automation
Although the vehicle makes extensive use of Home Assistant for automation purposes, the system is designed such that no "essential" function is dependent on it. For example, although the main LED lighting in the van is normally controlled via the automation system, it is configured so that the basic ON/OFF switches continue to operate even if the entire vehicle network goes down.

Tank Heat
As a true 4-season van, the outside tanks can be heated either via conventional 12VDC heating pads and/or by the secondary Espar hydronic loop.

Battery Heat
The biggest downside to lithium batteries is the fact that there are temperature limits below which they cannot be charged, used or even stored. So, battery heating must be considered a critical function. As described above, the main batteries can be heated either from ambient air from the van (usually heated via the Espar), and/or via the dedicated 12V battery heating pads. Especially problematic is a cold-start of the system in frigid weather in the absense of shore power. In this case, the procedure would be to switch the van to the engine 12V source, idle the engine, and use the resulting power to operate the Espar and the battery heating pads.

[GeorgeRa]

Thank you for the update. Our van is not as complex as yours but my wife, not being directly involved in design, needs some help in operating different appliances or lights. Ability to operate the van by both of us should be considered under the reliability umbrella. All CBs and switches are labeled and I have a printed and laminated cheat sheet. Sometime it is a useful refresher for me and in case of me being predisposed she can follow instructions.
It has the following key sections:

• On the road
• Camping - electrical with shore power
• Camping – electrical on batteries
• Water fill
• Extended storage

[avanti]

Originally Posted by GeorgeRa

Thank you for the update. Our van is not as complex as yours but my wife, not being directly involved in design, needs some help in operating different appliances or lights. Ability to operate the van by both of us should be considered under the reliability umbrella.

Totally agree. In our first van, doing something like using a hair dryer required turning on the inverter, which required going down something like three levels on a geeky inscrutable menu tree. It was awful. So, when designing the Legend, I was very careful to have big, labelled switches to do important stuff:

Control Panel lights.JPG

This was a big success. I am hoping that Home Assistant will let me do even better, since I will have complete control of the menu system.

[Arlo]

Thanks, Avanti, for your great posts on the new van. Is the macerator somehow protected from freezing, or would you just run some antifreeze through it during winter travel (or switch to the gravity dump)?

[avanti]

Originally Posted by Arlo

Thanks, Avanti, for your great posts on the new van. Is the macerator somehow protected from freezing, or would you just run some antifreeze through it during winter travel (or switch to the gravity dump)?

Yes, the hot glycol line runs parallel and proximal to the macerator to prevent freezing. I will probably add a wrap of insulation to contain the heat. All the other outside pipes (there aren't many) are similarly protected. The goal is for everything to "just work" while winter camping. Of course, for winter storage I will winterize by blowing out the freshwater pipes and adding a bit of antifreeze to the dump lines. As I will show later, the tanks are very robust and will not need any special winterization beyond draining.

[avanti]

The van uses a conventional black-tank toilet system with the usual three tanks. The black tank is mounted above the floor of the bathroom, forming a pedestal for a low-profile porcelain toilet. I would have preferred a combined black/gray tank, but in the Transit's limited space, it made more sense not to waste the space under the toilet.

The Transit's undercarriage presents significant space issues when positioning undercarriage tanks. Many DIYers throw up their hands and go with interior tanks. This was not an option we were willing to consider. We spent ages shopping for commercial tanks that fit the available spaces, but none met our capacity goals. So, we decided to go with custom-designed fresh and gray tanks fabricated in 16 gauge 316 Stainless Steel. It turned out that there was enough left-over material to do the black tank as well, so all three tanks are stainless. Here are the CAD drawings of the three tanks:

tanks.png

tanks-exploded.png

The exploded drawings show internal anti-slosh baffles and also heating tubes which connect to the anti-freeze glycol loop. The tubes are continuous with no internal fittings, so I am comfortable with the safety, although I am mulling over switching to propylene glycol just for the extra safety. The capacities of the tank are as follows: Fresh-30 gal; Grey-20 gal; Black-11 gal. The tanks mount on either side of the van near the front. The fresh tank is on the passenger side and the grey tank is on the driver's side. Here is a finished tank:

Fresh Tank.png

and here it is installed:

IMG_6241.jpeg

For tank level sensing, I would normally have used See-Level capacitive sensors, but they do not work on metal tanks, so we needed to find an alternative. We found an interesting product from an Australian company called Safiery. They make a pressure-based sensor that determines the tank level by the fluid pressure at the bottom of each tank:
https://www.safiery.com/tank-level
They interface directly to the Victron tank level module. They are quite precise and provide a continuous measure with no moving parts. They look like they should be pretty robust.

[Arlo]

Very interesting, I’ve never seen custom tanks like that with internal pipes for the glycol loop. While the probability of a leak is no doubt very low, I can relate to considering the use of polypropylene glycol in the loop. I’m curious why you chose that for a custom fresh tank rather than a channel for an external pipe. And what’s the point of the baffles - just mitigating liquid slosh noise?

The pressure-based tank sensors have worked great in my 3-year old ARV. I do an empty-tank recalibration a couple times a year, but it’s not clear that is necessary. Thanks again for the excellent and thought provoking posts!

[GeorgeRa]

I have fresh and grey water custom stainless steel tanks since 2013. They were designed to maintain factory road clearance and volumes are 12 and 14 gallons. Advantages of stainless steel for fresh water is a complete light block preventing algae growth.

I use my hydronic system to heat water in the Isotemp marine water heater which has a seamless SS heating tube inside but I use propylene glycol for safety. In your case you have potential leak in your fresh water tank and flat plate heat exchanger.

I think pressure sensing level sensor for fresh water tank should work unless hard water deposit would change characteristics of the pressure sensor, it is a few inches of water difference. In black and gray tank deposits could be worse. If I would build another van I would repeat reed based Wema sensors.

[avanti]

Originally Posted by Arlo

I’m curious why you chose that for a custom fresh tank rather than a channel for an external pipe. And what’s the point of the baffles - just mitigating liquid slosh noise?

The internal tubes were the recommendation of CMI, although I immediately liked the idea when I saw the proposal. If I were doing it alone, it probably wouldn't have occurred to me and I would likely have copied the ARV "channel" approach. However, the internal tubes clearly have better thermal coupling and I suspect were also easier to fabricate in steel.

The baffles have three purposes: (1) they minimize sloshing, which isn't just a noise issue--it can have significant stability implications, especially on very long tanks like these; (2) they contribute to the structural rigidity of the tanks; and (3) they provided the necessary support for the glycol tubes.

[avanti]

Originally Posted by GeorgeRa

In your case you have potential leak in your fresh water tank and flat plate heat exchanger.

Rixen's uses double-walled heat exchangers for DHW.

It will be interesting to see the longevity of the pressure sensors. They were deliberately located for easy access if needed. (You can see the sensor incorporated into the fresh tank drain in the "installed" picture above.)

[GeorgeRa]

Originally Posted by avanti

...

For tank level sensing, I would normally have used See-Level capacitive sensors, but they do not work on metal tanks, so we needed to find an alternative. We found an interesting product from an Australian company called Safiery. They make a pressure-based sensor that determines the tank level by the fluid pressure at the bottom of each tank:
https://www.safiery.com/tank-level
They interface directly to the Victron tank level module. They are quite precise and provide a continuous measure with no moving parts. They look like they should be pretty robust.

Can you program this sensor for Volume=f(level) for you L shape tank. Nice to see good workmanship in an RV, congratulation.

[avanti]

Originally Posted by GeorgeRa

Can you program this sensor for Volume=f(level) for you L shape tank.

Yes, the Victron tank unit supports that. Don't know whether CMI bothered or not. I will check it out eventually.

Nice to see good workmanship in an RV, congratulation.

Thanks!

[GeorgeRa]

Originally Posted by avanti

Rixen's uses double-walled heat exchangers for DHW.

It will be interesting to see the longevity of the pressure sensors. They were deliberately located for easy access if needed. (You can see the sensor incorporated into the fresh tank drain in the "installed" picture above.)

I read the double wall plate description a while back so I could be wrong. My recollection is that a double wall flat plate heat exchanger will indicate any leak externally but contamination can still occur.

[avanti]

Originally Posted by GeorgeRa

I read the double wall plate description a while back so I could be wrong. My recollection is that a double wall flat plate heat exchanger will indicate any leak externally but contamination can still occur.

I'm no expert, but that isn't my understanding. It is true that such exchangers are designed to leak if one of the barriers (or the gasket) fails (so that the failure is evident), but as I understand it, it would still take two such failures to get contamination.

At any rate Rixen's uses double-wall for DHW, but not for their other exchangers, so they clearly have safety in mind.