Hydronic Heat, Hot water, and Engine Pre-heating

Alloy

Well-known member
Hi TDI

Thanks for the explanation. I've added more of my $0.02.

- The HW tank is a heat exchanger. What does the preheater do?
----The pre-heater is a more efficient transfer agent than the hot water heater when using glycol as the heating agent. When you are running off-grid (using hydronic coils only, it should provide more efficient overall heat transfer to the water and therefor support a higher volume of flow (better shower) and the process should take less time to reach temperature. I'll simplify if this isn't the case.

>>I've not found a need to rapid heat the HW. It takes about 45 min to bring our propane 12gal (6gal on a previous trailer) tank to 60C (140F) temp which we get 5 showers from. Once up to temp it sits for hours so I've added a layer of 1" EPDM.

>>Locating the heat exchanger on the outlet of the HW tank will make it "on demand".


- Why circulate through the expansion tank?
---- The expansion tank serves three purposes; first - heat expansion, second - keeps system air-free once bled, third - it increases the volume of glycol in the system by almost double, allowing the glycol to cool sufficiently before cycling back through the furnace. If the glycol temperature is too close to the output heat temperature of the furnace, it can trip the furnace shutdown. This is especially important when the summer loop is running and only the hot water is being heated.

>>The Espar B5WS with a low side of 1500W may be a better choice Hot water returning to the boiler means there is no demand on the system, heat (cab heaters) exchanger(s) are too small, plumbing is not sized correctly or the boiler is too big. Creating heat loss makes the system less efficient. Have you looked at a sealed system with an air trap to remove oxygen with oxygen barrier PEX



- Overflow isn't needed if the expansion tank is sized correctly.
---- You are correct. The expansion tank needs to vent. I'm using the overflow tank to maximize the volume of glycol in my small expansion tank (1.5 litres) and in the small van, I don't have room for an expansion tank outside my camper and I really don't want to smell the expansion gas which will be vented outside where the tiny overflow lives. As I tune the system, I expect some things to change a bit...

>>Expansion tank(s) with a rubber bladder.


- A domestic water loop and a heating loop each controlled by a separate circulation pump is another possible layout.
---- Not sure I understand. Diagram has separate pumps for water circulation, glycol circulation, and anti-freeze circulation. Do you mean combining the glycol and water loops and just run water?

>>Separating the domestic water from the cab heating with a circ pump for each zone.



- Why the mixing valve on the sink?
---- The glycol coming out of the furnace can heat the water in the water heater up to 80°C (176°F) at steady state. The mixing valve will ensure any water coming out of either the sink or the shower is below 120°F

>>The hotter the system runs the greater the loss. For 50C running the system (if possible) at 60C is better.


- Filtering water coming out of the tanks will become an issue as the filter(s) plug up.
---- There is an external sediment filter (cleanable) preventing any water in the system having particles over 10 microns. This significantly helps the other filter's lifespan. The other filters handle smaller particles, carbon, and metals. I also have an optional ultraviolet filter for microbes for use in foreign countries. The system was built to ensure purified water from the shower or sink. I built the van for a Patagonia trip and water will be an issue in many of the countries, even when showering as I will be filling my tanks sometimes from rivers and lakes.

>>A FW pump is 40-60psi. The pressure drop through the filters gets to be an issue, especially for showers. We filter the water going into the tanks to 1 micron then add Pruorgen. This keeps the sediment (I've removed tanks with a crud build up on the bottom) out of the tank. Our tanks are slopped to a 3/4" bottom drain so no water left in the tanks.


- How many watts will the system draw with the engine off?
---- Furnace at 37 watts high (should only run a short time at this speed) and 12 watts on low. Each pump is 16 watts and the fans connected to the cabin heaters run 1.8 watts each. I have 200 watts of solar and 300 aH of house batteries to get me through...

>>Those are great numbers for the cabin heaters. Something with 2 speeds may recover the heat faster after the van doors are open.

- Will FW tank heating be needed?
---- Mine will be in the main heated cabin so I just need to ensure that the interior does not freeze. I'm a bit concerned about my diesel fuel in really low

>>Will the Espar run on Kerosene or a mix of?
 

TDIVan

New member
Received the two electronic valves to control the water heater loop and the summer loop. These have four allen-head bolts where the motor drive can be removed in case of failure and replaced with a manual lever.
IMG_3492.jpgIMG_3493.jpg

The shower fixture coming from England next week. it will mount to the exterior of the van and when the rear hatch is lifted, it will attach there. Imagine unlimited warm showers
bullfinch-showerpoint.jpg
Here is the flow-restrictor when you have to run from stored water. It goes between the shower head and the hose.
restrictor-valve.jpg
 

TDIVan

New member
Hi TDI

Thanks for the explanation. I've added more of my $0.02.

- The HW tank is a heat exchanger. What does the preheater do?
----The pre-heater is a more efficient transfer agent than the hot water heater when using glycol as the heating agent. When you are running off-grid (using hydronic coils only, it should provide more efficient overall heat transfer to the water and therefor support a higher volume of flow (better shower) and the process should take less time to reach temperature. I'll simplify if this isn't the case.

>>I've not found a need to rapid heat the HW. It takes about 45 min to bring our propane 12gal (6gal on a previous trailer) tank to 60C (140F) temp which we get 5 showers from. Once up to temp it sits for hours so I've added a layer of 1" EPDM.

>>Locating the heat exchanger on the outlet of the HW tank will make it "on demand".

>>>> You are correct, on the bench, I'll see how it does for this. having both will give higher volume of hot water but after, will make it more on-demand ;)

- Why circulate through the expansion tank?
---- The expansion tank serves three purposes; first - heat expansion, second - keeps system air-free once bled, third - it increases the volume of glycol in the system by almost double, allowing the glycol to cool sufficiently before cycling back through the furnace. If the glycol temperature is too close to the output heat temperature of the furnace, it can trip the furnace shutdown. This is especially important when the summer loop is running and only the hot water is being heated.

>>The Espar B5WS with a low side of 1500W may be a better choice Hot water returning to the boiler means there is no demand on the system, heat (cab heaters) exchanger(s) are too small, plumbing is not sized correctly or the boiler is too big. Creating heat loss makes the system less efficient. Have you looked at a sealed system with an air trap to remove oxygen with oxygen barrier PEX

>>>> see below

- Overflow isn't needed if the expansion tank is sized correctly.
---- You are correct. The expansion tank needs to vent. I'm using the overflow tank to maximize the volume of glycol in my small expansion tank (1.5 litres) and in the small van, I don't have room for an expansion tank outside my camper and I really don't want to smell the expansion gas which will be vented outside where the tiny overflow lives. As I tune the system, I expect some things to change a bit...

>>Expansion tank(s) with a rubber bladder.

>>>> a bladder-based, closed system was in my first iteration but there were some issues. With 17K BTUs and only 12 litres of fluid in the system, I'd require a one gallon bladder expansion tank. I have not found one that small (I found 2 gallons) but I can't afford the space. With lower hydronic temperatures of 80 decrees C, most smaller euro systems are running a through-system with venting like I have settled on. I decided on the D5SC (5KW) with two modes based on getting to temp quickly, then settling in for steady state operating at the lower level. I considered the D10 too but even at high-elevation with lower efficiency, the D5 will provide sufficient heating.

- A domestic water loop and a heating loop each controlled by a separate circulation pump is another possible layout.
---- Not sure I understand. Diagram has separate pumps for water circulation, glycol circulation, and anti-freeze circulation. Do you mean combining the glycol and water loops and just run water?

>>Separating the domestic water from the cab heating with a circ pump for each zone.

>>>> I think I have a compromise with the design. All three heat sources (120vac, Vehicle Engine, Diesel Furnace) can provide each primary function (Cabin heat, Hot water, Engine pre-heating). Each (or every) primary function can be performed simultaneously depending on the valves and pumps.

Connected to the grid (120VAC)

Scenario: preheat the engine and heat the cabin:

valve #3 NOT water heater bypass
valve #2 Winter loop
Coolant pump: on
Glycol pump on
Waterheater on (Only source of heat)
Diesel Furnace Off

Scenario: heat the cabin only:

valve #3 NOT water heater bypass
valve #2 Winter loop
Coolant pump: Off
Glycol pump on
Water heater on (Only source of heat)
Diesel Furnace Off

Scenario: preheat the engine only:

valve #3 water heater bypass
valve #2 NOT Winter loop
Coolant pump: On
Glycol pump On
Water heater On (Only source of heat)
Diesel Furnace Off

Off-Grid (not connected to 120VAC)

Off-grid, Engine not running

Scenario: preheat the engine and heat the cabin:

valve #3 water heater bypass
valve #2 Winter loop
Coolant pump: on
Glycol pump on
Water heater off
Diesel Furnace On (Only source of heat)

Scenario: heat the cabin and heat water:

valve #3 NOT water heater bypass
valve #2 Winter loop
Coolant pump: off
Glycol pump on
Water heater off
Diesel Furnace On (Only source of heat)

Scenario: heat the cabin only:

valve #3 water heater bypass
valve #2 Winter loop
Coolant pump: off
Glycol pump on
Water heater off
Diesel Furnace On (Only source of heat)

Scenario: heat water only:

valve #3 NOT water heater bypass
valve #2 Summer loop
Coolant pump: off
Glycol pump on
Water heater off
Diesel Furnace On (Only source of heat)

Scenario: preheat the engine only:

valve #3 water heater bypass
valve #2 Summer loop
Coolant pump: on
Glycol pump on
Water heater off
Diesel Furnace On (Only source of heat)

Off-grid Engine running/driving (Only source of heat):

Scenario: heat water only

valve #3 NOT water heater bypass
valve #2 Summer loop
Coolant pump: on
Glycol pump on
Water heater off
Diesel Furnace off

Scenario: Additional heat only (if desired) above normal vehicle heating

valve #3 water heater bypass
valve #2 Winter loop
Coolant pump: on
Glycol pump on
Water heater off
Diesel Furnace off (or on to get lots of heat)

- Why the mixing valve on the sink?
---- The glycol coming out of the furnace can heat the water in the water heater up to 80°C (176°F) at steady state. The mixing valve will ensure any water coming out of either the sink or the shower is below 120°F

>>The hotter the system runs the greater the loss. For 50C running the system (if possible) at 60C is better.

>>>> The hotter the systems operates, the higher the volume. I want the glycol system running at 80 degrees C. I also want the pure hot water system running at 80. The mixing valve prevents my output water temp to shower and sink to be closer to 60 degrees C


- Filtering water coming out of the tanks will become an issue as the filter(s) plug up.
---- There is an external sediment filter (cleanable) preventing any water in the system having particles over 10 microns. This significantly helps the other filter's lifespan. The other filters handle smaller particles, carbon, and metals. I also have an optional ultraviolet filter for microbes for use in foreign countries. The system was built to ensure purified water from the shower or sink. I built the van for a Patagonia trip and water will be an issue in many of the countries, even when showering as I will be filling my tanks sometimes from rivers and lakes.

>>A FW pump is 40-60psi. The pressure drop through the filters gets to be an issue, especially for showers. We filter the water going into the tanks to 1 micron then add Pruorgen. This keeps the sediment (I've removed tanks with a crud build up on the bottom) out of the tank. Our tanks are slopped to a 3/4" bottom drain so no water left in the tanks.

>>>> sounds like a good idea. I hadn't considered hard water issues as we don't have those up in Seattle. I went back and forth with the safety level of water for showering. I'm designing in ultraviolet out of the sink but perhaps I'll revise the shower filtering. Since I am constructing and testing the system outside of the van on a bench. I'll be making mods...

- How many watts will the system draw with the engine off?
---- Furnace at 37 watts high (should only run a short time at this speed) and 12 watts on low. Each pump is 16 watts and the fans connected to the cabin heaters run 1.8 watts each. I have 200 watts of solar and 300 aH of house batteries to get me through...

>>Those are great numbers for the cabin heaters. Something with 2 speeds may recover the heat faster after the van doors are open.

>>>> the cabin heater fans are pretty cheap. I might experiment with two speed fans.

- Will FW tank heating be needed?
---- Mine will be in the main heated cabin so I just need to ensure that the interior does not freeze. I'm a bit concerned about my diesel fuel in really low

>>Will the Espar run on Kerosene or a mix of?

My van is diesel. I generally run some Kerosene through the system every few months to keep it clean. My kitchen stove is a Wallace sealed diesel cooktop. Everything is one fuel in the van and plumbed to my main fuel system. When I get to freezing weather camping, I'll introduce anti-gel additives as necessary.
 

TDIVan

New member
Based on some feedback from @Alloy, I've updated the design to move the pre-heat exchanger in front of the water heater. Steady state it has little improvement but it will heat up the water quicker off grid which would be nice for a more on-demand solution
hydronic-3.png
 

bertn

New member
Great writeup!
I'm new here and just started my van conversion.
Would you guys be willing to give some feedback on my schematic with a simpified setup?

I have installed a D2 diesel air heater for space heating and would like to use my Eberspacher/Espar D5SW for engine pre heat (I'm from Canada and it gets pretty cold here in the wintertime) and for heating a 5 gallon hot water tank when I'm not driving and also would like to heat the hot water tank from the engine coolant heat while driving.

Notes;
*The circulation pump will be connected to a flow switch in the fresh water tank so that when there is not enough water the circulation pump will not be able to run.
*I'm planning to put two solenoid valves in the engine coolant loop so it closes of flow to the engine when I just want to heat up the hot water tank with the D5 and I'm not loosing heat to the engine block.
* blue and red pipes at top of the diagram are the water lines going to shower and sink

Thanks,
Bert
 

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TDIVan

New member
Have my interest peaked. I too have some of those valves. Did you get the waterproof versions? The 12v 3 way has proven really hard to source for us.
Hey,
sorry for the delay, been pretty busy...I did get the supposed waterproof versions. They are expensive $96 US but here is an ebay link: https://www.ebay.com/itm/3-4-NPT-3-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
When they arrived I disassembled the housing and saw that there is a U groove around the housing that would be water-tight if it had an o-ring but I fabricated a solution by topping off the channel with Silicon, fully dryed, then re-attached. Definitely water-tight now...
 

TDIVan

New member
Great writeup!
I'm new here and just started my van conversion.
Would you guys be willing to give some feedback on my schematic with a simpified setup?

I have installed a D2 diesel air heater for space heating and would like to use my Eberspacher/Espar D5SW for engine pre heat (I'm from Canada and it gets pretty cold here in the wintertime) and for heating a 5 gallon hot water tank when I'm not driving and also would like to heat the hot water tank from the engine coolant heat while driving.

Notes;
*The circulation pump will be connected to a flow switch in the fresh water tank so that when there is not enough water the circulation pump will not be able to run.
*I'm planning to put two solenoid valves in the engine coolant loop so it closes of flow to the engine when I just want to heat up the hot water tank with the D5 and I'm not loosing heat to the engine block.
* blue and red pipes at top of the diagram are the water lines going to shower and sink

Thanks,
Bert
Hey, Sorry for the late reply, But if still useful, a couple of things; This is a simplified model so to heat water off-grid, you will need to heat the engine every time you heat water, not terrible but it will take longer to heat. Additionally, anytime you have a closed loop of water, glycol, coolent, whatever, you need to account for thermal expansion. Your hot water loop should have a thermal expansion tank. I have a pint-sized unit for space considerations; an Amtrol ST-1 made for on-demand water heaters. It is a sphere about 4" in diameter and provides about a cup worth of storage. It was difficult to find.
hope this helps
-Delane
 

TDIVan

New member
Any updates on the system?

Sent from my SM-N950F using Tapatalk
Hey,
Sorry for silence, I've been building out a new Van interior. I've staged the system in my shop and have been tuning it. The main observation and adjustment I've made is to add a tiny Amtrol ST-1 thermal expansion tank into the heated water side. Anytime you have a closed fluid system and you heat it, you need to account. This provides about a cup of water expansion without taking up much space. It also makes the water pump happier. I have also added venting to the water supply side, currently 24 gal (4 -6 gal removable tanks). I also increased the size of the glycol accumulator to 24 oz to increase the temperature differential when just heating water off-grid, preventing thermal shut-down of the furnace. With everything in the system compact it was critical to build the system out of the van and test/tune it before installing. Also the one-way valves have a bit too much resistance, I'm a little concerned about the pressure required to keep them open. I've standardized all the pumps in the system to Eberspracher Flowtronic 800 S (800l/h) to limit the spares I carry.
 

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TDIVan

New member
Hydronic heating has it's merits, Many folks like to use passive radiators so there is no moving air, just heat. This method doesn't dry out the cabin like typical air heaters but less than ideal for removing moisture. It would be cool to be able to fabricate a box with a tumbler inside driven by a 12vdc motor and leverage a hydronic radiator to heat it, then have an exterior vent for the humid exhaust air. Basically a small clothes dryer that could dry a couple articles of clothing but not take up much room. Probably a sound investment for winter sports and remove it during summer...
I like the idea!
 

pgeering

New member
Wondering if you have implemented your concept and if so how your real world experience has been. Thanks for an update.
 

mog

Kodiak Buckaroo
TDIVan, great write-up, and a very clear/understandable diagram. (y)

My friend uses the Webasto heater (same style as the Espar) on his truck (17-foot cabin). His system was set-up up a little differently.
His schematic
heating_schematic_s.jpg


And a few more diagrams I have 'collected' (click to enlarge)
motorhome-hydronic-diagram.jpgcutaway.jpgcombitronic_schematic1.jpgD10 2.jpgD10 3.jpgEspar Hydronic10 plumbing.jpgheater configs.jpg
 

pgeering

New member
Thanks mog for all the info. Personally I am not a big fan of running the engine coolant through the entire vehicle.
Therefore planning a heat exchanger combined with a circulation pump inside the engine bay and install the water heater(s) in the back.
Also, nowadays diesels don`t leave much room for these kind of auxiliaries.
 
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mog

Kodiak Buckaroo
Thanks mog for all the info. Personally I am not a big fan of running the engine coolant through the entire vehicle.
Therefore planning a heat exchanger combined with a circulation pump inside the engine bay and install the water heater(s) in the back.
Also, nowadays diesels don`t leave much room for these kind of auxiliaries.
Agreed. My friend was concerned about a 'cabin' issue affecting the engine side which is why he added the valves between the systems (engine circuit and cabin circuit) but a heat exchanger like you plan would be a safer and more failsafe set-up,
 

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