Electric (vegtherm or other) versus coolant heat FPHE

For discussing the modifications needed for diesel vehicles to run with 2 tank veggie oil conversions.

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Electric (vegtherm or other) versus coolant heat FPHE

Postby SunWizard » Wed Mar 05, 2008 3:26 pm

I did some calculations based on 100watts of power so its easy to scale up, and this is the highest amount of temp. gain you could get out of a 100 watt filter wrap (bigger than most), because it assumes no heat loss and 100% efficiency. Size of the filter makes no difference when no heat loss assumed.

Here are the numbers if you want to compute it yourself: 1 watt = 3.4 BTU/hour. 1 BTU raises 1 pound VO by 1F per hour. So 100w=341BTU/8 pounds/gal=42.6F/3gph=14F gain. The 3gph is based on 15mpg and driving 45mph as a simple average fuel consumption for a Ford truck, and will be higher on the freeway, such as 5gph which makes the heat gain only 8.5F (looped return.)

Note that the most common filter wraps are only 60 watts or ~1/2 this size and there will be some heat loss.

These same numbers can be used to compute the max. temp gain of a inline VO heater like a vegtherm, they are 200 watts, so double the above numbers, between 16 and 28F gain depending on speed. The actual numbers will be less than this since there will always be some heat loss.

You could also use these figures as best case heat gain for injector line heaters, glow plug heaters, any type of electric heat.

As a comparison, as long as you have a working thermostat at 180F, with a FPHE (flat plate heat exchanger) I get at least 160F no matter how cold it is out. So at 0F outside, you are getting 160F gain compared to a 10F gain with electric wrap. This is the difference with a 50,000 BTU FPHE versus 341 BTU wrap for about the same price.

Note: I used the values for water, no heat loss, and 100% efficiency to keep the analysis simple. After you take account of the issues of VO has about half the specific heat of water, poor heat transfer efficiency and heat loss, you end up with close to the same results as for my simplification. I have determined this by pumping my VO over an electric heater element (known watts) in a pipe and measuring the temps of the VO in and out at varied flow rates.

The only accurate method is to measure your actual VO temps with your electric heater since it will vary somewhat based on the surface area of the heat element versus flow versus insulation. A infrared thermometer is useful for this as long as you measure the VO temp on a wide enough metal section of line that is not attached to the heat source.
Last edited by SunWizard on Wed Mar 19, 2008 12:30 pm, edited 3 times in total.
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Postby Cumminscanuck » Thu Mar 06, 2008 10:40 am

Great information Sun, I've never done the calculations so this puts things very much in perspactive fro me. I'm fitting a FPHE and a Vegtherm Mega. I had also intended fitting Injection Line Heaters but there is not sufficient room because of the clamps that hold the lines in place. Based on your findings, it would seem that the ILH's were not really necessary anyway.
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Postby hheynow » Thu Mar 06, 2008 2:42 pm

I like over kill. I have a FPHE, Vegtherm Mega and 70 watt 12v filter wrap heater. The system works OK without the filter wrap but since my Vormax is under the truck the filter sees cold ambient temps. IMO the filter wrap aids in water separation and lessens fuel restriction on fat laden oil at WOT. I'd never consider eliminating the Vegtherm. Granted the FPHE transfers more BTUs to the oil ONCE HOT but sometimes immediate electric heat is just as valuable in its own way.
Last edited by hheynow on Thu Mar 06, 2008 3:15 pm, edited 1 time in total.
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Postby Cumminscanuck » Thu Mar 06, 2008 2:57 pm

I forgot to add that I also have a coolant heated filter in the engine bay.
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Postby Jake Palmer » Fri Mar 07, 2008 7:44 am

I agree that an FPHE offers fantastic heat, and I think they make homemade heat exchangers (like the one in my samurai) or even HiH obsolete.

However, I personnally won't convert a car without a vegtherm. For me, it means switching to VO 3kms earlier on my daily commute, which is a means I'm doing 1/3 more of my commute on vegetable oil.

Plus, it guarantees good heat. I'm using a VegSensor on my e300d, so the Vegtherm will probably kick in & out to just maintain perfect heat.
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Postby Welder » Sat Mar 08, 2008 5:00 am

I've been loitering around biofuels forums for about 3 or 4 years now and have been gleaning knowledge from experienced SVO greasers all the while.

Tonight, just before registering here, I almost bought one of those Vegsensors for a Vegtherm had I bought a couple years ago, but I didn't buy it because I wasn't sure how accurrate it would be in switching off the electric heat. I mean, I know the Vegtherm is designed to be self limiting based on the oil flow rates' heat sink action acting against element resistance (or something like that), but because the sensor appeared to be surface mounted, I wasn't sure how well it could react to what's happening inside the heating tube.

I was wondering if anyone had tested thoroughly these things out? (I know their cheap, but if they cut power prematurely, they are devaluing the Vegtherm. OTOH, if they don't react in time, scorched fuel may result)
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Postby SunWizard » Sat Mar 08, 2008 9:30 am

Jake Palmer wrote:I agree that an FPHE offers fantastic heat, and I think they make homemade heat exchangers (like the one in my samurai) or even HiH obsolete.

However, I personnally won't convert a car without a vegtherm. For me, it means switching to VO 3kms earlier on my daily commute, which is a means I'm doing 1/3 more of my commute on vegetable oil.

Plus, it guarantees good heat. I'm using a VegSensor on my e300d, so the Vegtherm will probably kick in & out to just maintain perfect heat.


How do you determine when to switchover? On my truck I switchover as soon as the coolant guage starts to move, which is 140F. And once it starts to move it hits 180F in <1 minute. Using this method, my VO is always between 160F-180F (perfect heat in my book) even right at switchover, because the FPHE is so much heat, and coolant temp is so well regulated. (As long as you have a good working thermostat, which is very important even running on D2.)

If I switched over any sooner, I think I would be breaking the accepted wisdom of "only switchover when the engine is warmed up". I think hot VO into a cool engine is not good, and the VO would probably be greatly cooled in the IP and lines even if you got it hot before them with a vegtherm. And cool VO into a cool engine is worse.
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Postby 240Volvo » Sat Mar 08, 2008 11:17 pm

Interesting data, SunWizard, and many thanks for all of your labors on this general subject and for this new site.

I just want to point out that the use of electrical heat applied in Elsbett's systems is not to achieve the ideal heat, but to melt any gelled oil in the filter and increase initial viscosity. They combine that with FPHE.

Of course I don't really belong in this thread with my system, just wanted to add that thought.

Carry on!
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Postby canolafunola » Sun Mar 09, 2008 11:20 am

I think electric heat is a waste of money and causes more harm than good. You should not switch to VO until the engine is up to temp and once your engine is up to temp, electric heat is not needed. If you switch before the engine is up to temp thinking the electric heat will be sufficient you will probably end up with engine problems down the road.

I have experimented with glow plug heaters. First one was made with brass fittings. I was always careful to run in only with adequate fuel flow. After 10,000 miles I disassembled it and found small pieces of poly on the brass and also carbon on the glow plug. These small particles are constantly being emitted and where do you think they go? Next, I built a glow plug heater out of Teflon, used it for 10,000 miles and disassembled. No more poly on the Teflon surfaces but expectedly found carbon on the glow plug. Tissue paper that I used to wipe the internal passages of the Teflon cylinder was black with carbon. Where else do you think the carbon went? I got what I needed from the experiment and have since decommissioned the glow plug heater.
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Postby Welder » Mon Mar 10, 2008 1:41 am

Unless you were using a coolant heated filter, I don't think there'd be much option except electrically heated filters.

Some people swear by heater hose wraps, while others think they're a PITA.

I built a custom coolant heated filter, but shelved it after deciding I didn't like the Goldenrod/BaldwinB10AL style filter element I had built it around. Maybe someday I'll resurrect the project again using another element.
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Postby Burbarian » Mon Mar 10, 2008 2:12 am

At the risk of sounding like a total idiot (note that I AM a total idiot, but sometimes don't want to sound like one): What about an electrically heated FPHE?

When you pull into your garage or driveway at night, plug in your diesel vehicle. Standard procedure in cold climates with the block heater, yes, but you might take it one step further. A timer can activate an hour before your regular departure time and turn on an aux water pump and a thermostat regulated electrical resistive heating element in a tube on one branch of your coolant heater line. This will circulate heated coolant through your engine, the FPHE, the coolant heated filter, the HIH/HOH, etc. Come time to bid the wife farewell and head out to bring home the bacon, unplug the vehicle as usual. Only this time it is already at operational temperature. Just turn the key and off you go running immediately on VO, liquefied swine, what have you.
Note that this can be adapted to alternate heat sources like a solar heat storage system, domestic hot water tank, etc. by using quick connect fittings with valves plugging into an inline heat exchanger. Of course if you are starting cold in winter time from someplace without a power outlet, then it's regular 2-tank procedure.

Welder: I dispute your claim to having the monopoly on stupid ideas. :D

JohnG: Say, how do you start cold on blend from a remote location that doesn't have an available AC outlet for the block heater? Like if you go overnight ice fishing then have to start up the cold engine the next day?
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Postby SunWizard » Mon Mar 10, 2008 9:13 am

Some people do preheat the VO with electric along with their block heater. And it does shorten the switchover, but mainly due to the block heater. You still have to drive some distance before the engine, mainly the head, piston and cylinders, reach their full temperature. I don't think the extra complexity and energy cost of heating the VO overnight will gain you much if you have a FPHE in your rig since you always get hot enough VO when you have hot enough coolant.
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Postby SunWizard » Mon Mar 10, 2008 9:16 am

240Volvo wrote:I just want to point out that the use of electrical heat applied in Elsbett's systems is not to achieve the ideal heat, but to melt any gelled oil in the filter and increase initial viscosity.

Don't you mean "decrease the initial viscosity"?
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Postby David » Mon Mar 10, 2008 6:22 pm

The one thing I notice the Aussies seem to me more pedantic than the yanks about is the Size of the FPHE's they use.

I notice many yanks seem to think that 10 and 16 plate HE's are adequate (which I tend to believe myself) whereas in oz, mst people would consider a 20 plate HE inadequate and the accepted "standard" is a 30 plate or 2x 20 plates, one before the filters and another as close as possible to the IP.

The guy that does more conversions than anyone else in the country has a standard layout of a 20 and 30 plate HE. There are no conversion Businesses here like in the US.

Few people use electric heating here and those that do tend to favor the home made glow plug type. There are a few that run injection line heaters and fewer still run veg therms but them have concerns about them overheating the oil. :roll:

I think electric heat is a waste of money and causes more harm than good. You should not switch to VO until the engine is up to temp and once your engine is up to temp, electric heat is not needed.


I agree. over a year ago I crunched the numbers with a friend that is in the commercial aircon business and understands all about heat transfer, heat loads, works with heat exchangers on a daily basis and also does a lot of work with heated pools etc. Cut a long one short, he looked up the heat density's ( or whatever it's called ) of veg oil, the transfer rate of various HE"s and the typical ( High end) flow rates of oil in a diesel vehicle. We found Toyota 4wd's appeared to have the highest circulation rates, well above most vehicles so we used that.

With the heat available from the engine, it's estimated circulation rate, ( as from a radiator place we rang) and the flow rate of the oil with its heat take up capacity, we calculated that a 20 plate HE was way overkill to get the oil up to coolant temp.
I have been telling people this for 12 months but still, many seem not to be satisfied and feel that other heating is unnecessary.

Like Sun, we also did a calculation on the heat available from electric heating and although we cam up with a slightly higher number than sun, I was patently clear that with all the other parasitic losses, electric heating was pathetically insignificant.

My friend also commented that the heat from a 20 Plate HE was around the same output as a ducted aircon system would produce that he would typically install to heat an entire house! He remarked how one could imagine taking the heat that was warming all the area of a home and like a magnifying glass in the sun, focusing it on a tiny little stream of flowing oil.

I also fail to understand this obsessive rush to change over to Veg at the soonest possible second. If people are running veg and saving so much on fuel already, cant they afford to burn a bit of dino or Bio to at least let the engine warm up properly? I think the rush to cheat normal processes here is going to cost them a lot more than what they save and what they spend on the devises they think is going to let them avoid spending on a few liters of start up fuel a week.
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Postby John Galt » Mon Mar 10, 2008 8:06 pm

The calcs I did for FPHEs showed the same conclusion. A 12 to 16 plate FPHE rated at 85kBTU/hr puts out as much heat as a medium size house furnace; quite adequate for the job. More is not necessarily better, and an over sized FPHE can actually slow the warm-up time. It's like the faulty logic that thinks turning the room thermostat to maximum warms the room up any faster.

There's no point risking dollars of possible engine damage to maybe save a few cents of diesel.
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