Advice required
Hi all, just about to commit quite a bit of money in fittings and hose on my camper heating system, and what to run it by everyone to see if I have got it right, or if there is something I've missed. I want to leave the OEM system as intact as possible, so as not to cause and future cooling problems. I'm about to get some 3/4" stainless steel braided PTFE hose (SSBH) made up, two are 4.5m long, and the third is a 1.0m long. These are the hoses that connect the whole system together, they are not cheap, another bit of overkill but they have to thread their way under the truck and hard lines are too difficult (I tried) , and rubber just won't last and I don't want to replace them ever.
A brief description of the whole system first.
Water Cooled Turbo
OM352A engine has been a new water cooled turbo, and I need to plumb that in to the lines that feed the cab heater. The line coming off the top of the engine / water pump is the pressure line, and the one coming off the bottom of the water pump is the suction line. I have put a T into the top line going to the cab heater, and the return from the turbo goes into the main waterpipe coming from the bottom of the radiator. The Garret manual says I should connect the return of the turbo as low in the cooling system as possible, and on the return/suction side of the radiator to get a thermo-syphon effect after shut down to help cool the turbo. The hoses are near vertical the way I have plumbed them and you can't get a lower spot so it should be good. These hoses are only 10mm, that's what is specified, and I have used a silicone coated rubber hose supplied with the the turbo.
Webasto 90ST 9kw diesel heater. (90ST)
To provide a water supply to the 90ST, I put another T in the top pressure line going to the cab heater. That is feed line to the 90ST which has it's own water pump. It will normally only be running when the engine is not running, but either way, it will have enough pressure to pump water to the back of the truck through around 4.5M of SSB 3/4" PTFE hose.
Electric Booster Pump ( EBP)
In series with the 90ST, I have a Davies Craig Electric Booster pump. When the engine is running, I don't think there will be enough flow through this line to provide enough heat to the camper, especially if the cab heater is used. The EBP flows 15l per minute, and is designed especially for this. When the engine is running and we want to send the coolant to the camper, the EWP will provide the pressure to push it down the lines, a 10m circuit in total. Should it prove not to be needed, then I can always leave it switched off, or take it out.
Camper Heating System.
I have decided to go with all manual valves, I was thinking of using motorised valves but it was a bit complex and I didn't think it was worth the hassle, and I don't think I have enough space either.
The camper heating system consists of the a 20 litre calorifier to provide hot water for shower. washing up etc. This is the main circuit that will be normally open to ensure we have hot water for showers etc. Most of the time it will run off engine heat. The calorifier has an 800W electric heating element as well, so we can heat up the water from shore power if necessary. The feed to this has a 1/2" valve to control flow.
So that the priority will be the camper heater when we want it to be, a 3/4" valve controls the flow into the two 5kW fan driven heat exchangers plumbed in series. We should be able to sort out a how much we open this valve to provide just enough heat, without cooking us and everything in the cabinet. The heat exchangers have two fans each, the fans draw air into the compartment from outside (through an air filter) and blow it into the camper. The fans will be thermostatically controlled, so they switch on an off automatically in the low speed mode, I only want to run the fans at the low speed setting, as it is very quiet at that speed. I can manually override the fans to full speed if required. At full speed then fans will suck in 500m3 per hour, so at half speed, it should still be a reasonable amount of air to help control condensation.
http://www.kalori.com/produit.asp?idpr=24
Finally, there is a 1/2" Stainless steel pipe loop, 2m long inside the rear compartment where the water tanks are. This is to provide some heat into this area to stop the tanks from freezing up in cold weather. I'm not sure if this is necessary, but I have done it anyway. A 1/4" valve limits the flow to this circuit when it is opened. This is also something we can set the ball valve to a certain angle to limit flow.
The return line from the camper is another 4.5M long 3/4" and returns to the main suction line at the bottom of the water pump. The water then enters the engine block, warming it up or at least stopping it from freezing.
Pipe Routing
The hot water pipe from the 90ST to the camper run right alongside the diesel fuel lines feeding the engine and the 90ST itself. I have done this that it might help with the diesel waxing in cold weather. I can run a small Facet pump that I use to prime/bleed the system and it will pump fuel around the supply circuit, through the filters, the fuel pump and back to the tank. Not sure if this is required, but it is an option to help keep the main fuel tank warm. The plan is to cable tie the supply and return fuel lines to the hot water feed pipe from the 90ST.
Both the SSBH hot water feed and return lines run next to the grey water tank. I'm not sure at this stage whether they will be in direct contact as I have not designed the grey water tank yet, but could possibly even run it through the tank itself if required, Since we don't want the tank to get very hot, the alternative is to run a loop from the return line through the tank and use a three way valve to control the flow. I have not decided on this and could be that just having the touching the tank will be enough, it depends on how cold it gets I suppose.
Problems I can see.
First one is that the when the 90ST is running, I suspect the there may be a short circuit through the turbo instead of the engine block. The pipe is pretty small in comparison to the ones through the engine block, so this may not be a problem and the water will not be hot enough to do anything to the turbo, but it may limit the effectiveness in pre-heating the engine.
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Second is that the Cab heater is out of the loop when the 90ST is running. Apart from some complex three way valving and a load of pipes, I can't see how to fix that, I don't think it is a major problem not having the cab heater working when the engine is not running.
Finally, will heating up the diesel be a problem in hot weather? I suspect we may even get the diesel in the tank up to water temp on a long run in high temps, but maybe not. It this is a problem, then I could separate the fuel lines away, and only cable tie them together when we go to colder climates.
When the fans are not running on the heat exchangers, there may be quite a bit of residual heat inside the cabinet itself. Not too much of a problem but the main 220V inverter lives in that cabinet as well, and it doesn't like working above 50 degrees. I will insulate all the pipes running to the heat exchangers to limit this, and there will always be some air flow due to the hot air inside the cabinet rising and flowing out, but it will be pretty warm inside there. I might have to rig up sometime to turn one of the fans on if it gets too hot inside there.
The compartment with the calorifier and the manifold is in it is going to get hot, it also house the Shurflo water pumps, if it is too hot, I can move them into the boot, but would prefer to keep them where they are. I will lag the manifold and all the pipes in that compartment, but heat will always escape and there is no ventilation in that one yet, maybe I should cut a hole to allow the hot air to enter the boot area. The manifold lives under the calorifer, and it is a tight squeeze to get the pipe in, and I needed a few unions to make sure I could get it in and take it out again.
Don't worry, the pipes don't look that bad now, but it is a pretty small space for lot of piping under there, especially 3/4" stuff.
