Heater Comparison - What's the best way to heat an EV?
By John Wayland
December 6, 1997
Hello to All,
With Fall firmly entrenched, and an overnight low in the Portland area near freezing, I thought it would be a good time to do an EV heater comparison test. Some may remember, that about this time last year, there was a string of discussions about EV heaters. There were lines being drawn between those of us that preferred electric type heaters, and those that preferred fuel-fired heaters. The general take I got from that lively discussion, was that those who live in areas with severe winter conditions felt that the only suitable EV heater was a fuel-fired type, and that those who lived in areas with occasional sub-freezing temperatures but generally mild winters, were happy with the heat produced by electric type heaters.
In this test, I wanted to do two things. First, I wanted to simply compare liquid-heated systems to ceramic-heated systems. And second, I wanted to see just how much heat could be made from ceramic heaters using different air flows and element configurations, so as to determine if electric heaters in Evs could crank out as much, if not more heat than the heaters found in modern ICEV's. Therefore, this is a two part test.
The first part is just the basic comparison between existing Evs equipped with either a liquid-heated system or ceramic-heated system. The second part, are the results from my experimenting with different configurations of air flow and ceramic type heater elements.
Before I move onto the tests, I want to make my feelings on Evs heaters known from the start. As some who know me might suspect......I already had a strong opinion and preference as to which type of EV heating system was best. Personally, I find gas-fired heaters in Evs offensive, and in contradiction with the whole basic premise of ZEVs. And as to the heated-liquid type heaters, I also have a problem with them, too, as I will explain.
I like to take the positive aspects of Evs, and exploit them whenever possible, especially when it comes to comparisons being made between Evs and ICEVs. For far too long, Evs have been ridiculed by the naysayers, for both real and perceived shortcomings.
So if there is an area where we can show that Evs are superior to ICEVs, shouldn't we embrace it? If not for helping to change the image of the EV, I would think that one would want to do it for the obvious improvements at hand.
One of those areas used to be a lack of acceleration and overall power. But 200 mph race-prepared Evs, and the tire-smoking performance of hot street Evs from Alan Cocconi's high tech Civic to 77 year old Dick Finley's Renault, are now blowing away that perceived shortcoming. I feel the same way about the 12 volt electrical system in Evs, too, and that's why I entered into the fray over whether or not to use a DC to DC converter in an EV. For me, it is just another area where the EV can excel over and ICEV.
In the early days of Evs, we didn't have DC to DC converters so readily available, and the performance of the headlights, wipers, ventilation blowers, etc. in our battery powered vehicles didn't measure up to what was the standard in ICEVs. But the tables are turned now, when we pull up next to that ICEV at the stop light at night, and when their lights dim with the slow engine idle, our DC to DC equipped Evs have lights that stay crisp and bright! Another plus for Evs, is their near silent operation, when compared to the noisy ICEVs. That's why I've rallied so hard against motor controllers that needlessly induce a high-pitched squeal into the otherwise serene EV.....why
deliberately throw away what most people find to be a unique advantage? The same is true, in the heater department. Heater warm-up time is another area
where our Evs should be superior to the ICEVs. As ICEV owners shiver, waiting seeming forever for the infernal combustion engine to warm up, we have the ability to have instant heat in our Evs. But I have wondered about these liquid-warmed EV heaters for some time now, as to how they would compare to the heaters in ICEVs, as well as to the ceramic type EV heaters. It's my contention, that there is no good excuse to have to wait for heat in an EV. So now, with my biases clearly stated from the beginning........on with the tests!
Having a US ElectriCar S-10 conversion, a US ElectriCar Ford Escort conversion, a Jet Industries ElectraVan, the E-car '65 Mustang EV, and the Datsun EV all in my possession at the same time, made it really convenient for conducting the heater comparisons. Three of the EV heaters were tested in an informal way, that is, I did not use meters and other test gear. Instead, I just simply had the opportunity to use the vehicles, and in the process, experience how the heaters performed. But with the other two Evs, I collected accurate data. I also set up a heater unit for bench testing, and experimented with using dual ceramic heater elements.
Both of the US ElectriCar Evs have warmed liquid heaters. These are designed so that the EV converter can leave the stock automotive heater cores in place. With the original ICE, heated engine coolant was circulated by the water pump through the heater core. But in this system, a small tank of liquid is electrically heated, and circulated through the heater core via a
small 12 volt pump. On the surface, this seems like a neat way to go, since it allows the EV builder to leave the basic heater/defroster system untouched, and after mounting the main heating unit under the hood, a simple hook up of two hoses and a few wires is pretty much all there is to it.
In contrast, the remaining three Evs, the ElectraVan, the Mustang, and my Datsun have ceramic element type heaters. In the Mustang and my Datsun, the element simply replaces the stock heater core. This type of EV heater requires a little more effort to install, since the stock heater needs to be disassembled and modified. The ceramic element is not the same size and shape as the old liquid core it replaces, so one must fabricate an air baffle to force the intake air through the element, not around it. There is also a little more temperature control and electrical work to do as well. Usually, when employing this type of EV heater, the old core is discarded. But the one from my Datsun made its way back into the car this past Summer, and now serves duty as the mini-radiator for the car's liquid-cooled Auburn Kodiak speed controller. Some on the list, have suggested using the waste heat from the controller cooling system to supplement the EV heating system, but I have
found that in powering up my light weight Datsun, the controller stays cold most of the time, so there is very little usable heat available.
The ElectraVan was originally equipped with a fuel-fired heater, very similar to those that were used in some air-cooled Vws. The previous owner hated it because of the smells that emanated from it, because it had a wimpy blower motor with virtually no defroster effect, and because of the fact that the ElectraVan (a supposedly emmissions-free EV) still relied on gasoline. Last Fall, she had E-car remove it, and install a system we designed ourselves, using a ceramic element, new ducting and deflection flaps, and a robust squirrel cage blower. But before we installed the new unit, we spent some time with the fuel-fired heater. We had to agree with her, that it was an inadequate, smelly and unacceptable way to heat an EV. I will admit, that these fuel-fired heaters do not normally smell like this example did, but they all still require some kind of petrolium-based fuel (usually gasoline) and exhaust pollutants into the air.
I have had the opportunity to use the heaters in the ElectraVan, the Escort, and the Mustang, but I did not actually compare them side by side. These are also the three Evs where I did not use any test instruments, nor obtain any hard data as to the performance of the heaters. But I did use all three Evs when it was less than 40 degrees outside, and offer the following observations.
The US ElectriCar Ford Escort is a wagon model, and is a 120v EV, using ten Trojan 5SHPs for the battery pack. The heater is a warmed-liquid type. In the late evening, the temperature outside was somewhere between 35 and 40 degrees, as I went outside to move the vehicle. I turned on the heater, and set the fan speed on 'low'. I waited and waited, and finally, after what seemed like three minutes or so, began to feel the air from the vents change from cold, to 'luke warm'. After maybe six minutes, the vent air was what I would describe as 'warm but not hot', but at least the interior of the car was beginning to get comfortable. I took the Escort out for about a 15 minute drive, and the heater's air eventually warmed a little more, but it never approached the kind of 'hot' heat that one is used to in a modern ICEV. I found the heater to be unacceptable.
The ElectraVan's heater uses a single ceramic element, with a pretty healthy blower drawing its air through the element. The system runs off of 108v, courtesy of 18, T-105 Trojan batteries. I have used the heater in this EV on many occasions, including days where the outside temperature was in the low 30's. It produces heat instantly, and can get the ElectraVan uncomfortably 'hot' inside. On the low speed setting of the blower, the air exiting the heater is so hot, that it is uncomfortable to keep your hand close to the vents! But, when the blower is on the high speed setting, the element cools down to the point where the exiting temperature is 'very warm', but not 'hot'. In short, the heater works very well, and does a good job of warming the interior of the small microvan.
But I would have to also say, that if this same heater was installed in a more regular sized vehicle with a lot more interior space to heat, it might not be enough to keep up with severe Winter temperatures.
The 65 Mustang EV has the identical battery pack as is used in the Escort, that is, 120v worth of Trojan 5SHP batteries. But the Mustang's heater is more like the one in the ElectraVan, as it uses a single ceramic element. But unlike the draw-through design of the ElectraVan, the Mustang heater uses a blow through system, where the element is downstream from the output of the blower fan. We mounted the ceramic unit inside the heater plenum, in the exact position where the Mustang's original liquid heater core used to reside. At the time, we wondered if we should have used two elements, do to the large internal volume of the interior of the old Mustang, but we went with the single unit, in an effort to conserve battery power. As with the ElectraVan, the heat is instant with no waiting. The Mustang's blower moves a good amount of air, and when set to the highest speed, it overcomes the single ceramic element and the heater produces only 'tepid' temperatures. But with the blower set to the low speed position, the element produces 'very warm' air, and the heater does a pretty good job. In the Mustang application, the ceramic element is being run at 120v, where in the ElectraVan the same brand element is being run at a lower 108v. It seems that the heat output in the Mustang is not quite as good as with the unit in the ElectraVan......we're still scratching our heads on this one.
OK...next up, are my Datsun and the US ElectriCar S-10. In contrast to the previous 'seat of the pants' tests, I used time vs temperature measurements in this side by side comparison. The comparisons between these two Evs and their heaters were made on the same chilly 38 degree morning. I even got up earlier than usual, to make certain I could test both vehicles, before the temperature began to rise, as I wanted the ambient temperature to stay the same for each test. So at 4:30 AM....out I went, into the dark, cold, foggy morning, with my watch, a flashlight, and one of my wife's meat thermometers.
I did not wear a coat, as I wanted to be able to feel the effects of the heaters.
The first up, was the US ElectriCar S-10 truck. This vehicle has a 312v battery pack consisting of 52 Genesis batteries in a series/parallel arrangement. The heater is a warmed-liquid type, that interestingly, is not linked with the liquid-cooled AC motor/inverter package. The meat thermometer that I used for the test is calibrated in 5 degree increments, from 50 degrees, up to 550 degrees. I inserted the long 'probe part' of the thermometer into the center dash vent, and clipped the gauge end of the thermometer to the vent's louvers so that I could easily read the gauge. Since it was only 38 degrees inside the truck, the gauge was pinned at the bottom limit of 50 degrees at the beginning of the test. I powered-up the truck, selected the highest heat temperature, and turned the blower fan on low. Then I waited, and waited some more. Two minutes into the test, I was shivering from the cold and the gauge was still pinned at 50 degrees........I could still see my breath in the cold cab! At three minutes, the gauge still read 50 degrees. At four minutes, the gauge needle finally began to move off of 50 degrees, and I could feel that the air from the vent was warming. At five minutes, I read 60 degrees (readings rounded up to the nearest 5 degrees), and could no longer see my breath in the cab, but boy, was I cold! At six minutes, the air from the vent finally felt like the heater was waking up, and the gauge confirmed that notion with a reading of 75 degrees. At seven minutes, there was 90 degrees of warm air flowing out of the vents, and the cab was becoming more comfortable, but far from warm inside. From that point, the vent temperature never got any hotter than 90 degrees, and when I cranked the blower to the highest speed, the temperature fell to 70 degrees. I found this heater, like the one in the Escort, to be totally unacceptable, and couldn't imagine anyone being stuck in a Minnesota snow storm and being
able to keep warm.
I next, put my Datsun's heater to the test. I had pulled the Datsun out from the shop earlier, before I ran the test on the S-10. I also turned off the shop heat the day before, in anticipation of doing the heater tests the next day, and I wanted the car to be as cold as the ambient air. When a had backed the Datsun out of the shop, I ran both the windows down, so that the car would be as cold as the S-10 that had been outside.The Datsun has a 144v battery bank of 12 Optima Yellow Tops, and the heater uses a single ceramic element, identical to the elements in the ElectraVan and the Mustang heaters. The heater uses a blow through design, and has a two speed fan that puts out a pretty good air flow. Getting into the cold car, I ran the power windows up and placed the thermometer's probe portion into the driver's-side defroster vent. I could easily see the gauge face from my position in the driver's seat, as the dial needle was once again pinned to the 50 degree position. I switched on the ignition, selected the defrost position, and turned the heater on with the fan set to low. Within 30 seconds, the needle of the gauge had moved to indicate 70 degrees, and by the time one minute had elapsed, there was 90 degrees of warm air flowing from the defroster vents. At two minutes, there was nice, hot, 135 degree air and the interior of the Datsun was becoming very warm. The heater stayed at 135 degrees with the fan set to 'low', so I switched it to 'high'. On the Datsun's heater, there is not a whole lot of difference in air flow between the low and high speed settings of the fan, as the 'low' speed is more like most car's fans on 'medium'. The temperature dropped to 120 degrees with the fan blowing its maximum. The Datsun, like the ElectraVan, has a relatively small interior volume for the heater to warm, so the single element does a very good job. But in all honesty, I thought that the heaters in my ICEVs were still more powerful, so I decided to go measure one of them as well.
At the Wayland home, the family 'ride', is a '93 Subaru Legacy all wheel drive wagon. This is a car that specializes in being very capable in Winter driving extremes, so it comes as no surprise that it has a killer heater/defroster system. It has an outrageously powerful blower fan, that moves huge amounts of air. In fact, the air from just one of the five dash mounted vents, is about half of the volume produced by the entire output of the fan in my Datsun! I warmed up the Sube, and took it out for a short drive to bring it up to full temperature. Returning back to the home base, I inserted the thermometer's probe into one of the dash vents, and set the heater fan to the lowest position. I also kept my foot on the accelerator, to keep the engine at 1800 rpms, to ensure an adequate liquid flow through the core. Just as I had suspected, the heater in the Sube was indeed, more
powerful than any of the single element electric heaters. The temperature peaked at 160 degrees with the fan on the lowest setting, and dropped to 140 on the hurricane setting! Keep in mind, this heater is almost overkill for most situations, as I usually drive in the middle of Winter with my window down and the heater cranked to full, and stay warm and toasty. But, in areas where the temperature goes below zero, I would imagine that this is just what is needed.
Now, it's time for part two of this heater test, where I experimented with the ceramic elements in a setup on the test bench, in my shop. As I have stated earlier, the heat was turned off, so the shop was real cold! I left it that way and also left the overhead door open, so that the bench test would simulate how the experimental heater would work in a vehicle out in the cold.
After realizing that in severely cold areas, a single element EV heater may not be up to the task, and certainly after having compared the ceramic heaters to a powerful ICEV heater, I wanted to see how much heat I could get from a ceramic-based EV heater, and at what kind of current draw. I have a beefy, 12 volt squirrel cage blower motor that is from a large ICEV, that is about eight inches in diameter and blows about the same amount of air, that the blower in the Sube does. You can feel the wind from this thing clear across my 24 foot shop! I set it up on the bench with three different speed settings, to simulate the blower in a modern vehicle, and ran it off of a power supply. I next, took two ceramic elements and stacked them, one on top of the other, in a sandwiched array, between two halves of a venturi/baffle arrangement. The sandwich was positioned so that it completely covered the air intake of the monster blower, making a neat, draw-through type heater. Using 10 gauge wires and a heavy duty relay with a capacitor for arc suppression, I rigged the setup to run off of a stack of 12 fully-charged Optima Yellow Tops in series, at 144 volts. I also had it configured so that I could use a single element, or both at the same time. For testing measurements, I again used the meat thermometer, placed a short distance from the output section of the blower. I also had a DVM connected to the terminals of the elements to measure the applied voltage, as well as a digital clamp current meter on the positive power lead. I made a chart the night before, so that I could record the test results, and plot the amps, volts, and ultimately the watts needed, for whatever temperatures I obtained.
OK......on with the results. The temperature inside the shop, was just shy of 40 degrees....bbburrrr!! (is that how you spell that?). On the first run, I used only one element, and got very similar results to what I had recorded from the heater in my Datsun.
The 'low' speed setting on the test blower is comparable to the 'low' setting in the Datsun (both of which are closer to a medium setting as found in average vehicles), and a temperature of 130 degrees was registered. The voltage at the element was 147.6 and the current draw was at 7.9 amps (1166 watts). The test bench blower when set on 'medium', is more powerful than the 'high' speed setting in the Datsun, and as a result, the temperature registered at 105 degrees. The voltage at the element was 147.3 and the current draw was at 7.5 amps (1307 watts). With the test blower set to 'high' (or gale force), the temperature went to 90 degrees and held. The voltage at the element was 147.0 and the current draw was at 8.2 amps (1205 watts).
OK now, hold on to your hats, because the results from two elements are really impressive! I charged the batteries for about fifteen minutes to bring them back up to where they were at the start of the single element test, and then proceeded, repeating the previous steps, but with two elements running this time. With the 'low' speed setting on the test blower, a temperature of 175 degrees was registered! The voltage at the element was 145 and the current draw was at 14.1 amps (2044 watts). On 'medium', the temperature registered at 155 degrees. The voltage at the element was 144.3 and the current draw was at 15.2 amps (2193 watts). With the test blower set to 'high', the temperature went to 140 degrees and held. The voltage at the element was 144 and the current draw was at 16.9 amps (2433 watts).
To see what a slightly slower fan speed would produce, I reduced the supply to the fan to imitate the 'slow' speed setting found in most vehicles. At this speed, the temperature climbed to an unbelievable 200 degrees! From about a foot away, it hurt to hold my hand in the air stream for more than a few seconds.
I returned to using the 'high' fan speed, and closed the overhead shop door. From ten feet away, I could feel hot air being blasted. In short order, the heater actually started to warm the whole shop!
I came away from my tests with some strong opinions, indeed:
First, I would never recommend a liquid-warmed heater for use in an EV, at least none of the type that US ElectriCar had used. They are totally inadequate in their heating ability, and the extremely long warm-up time is embarrassing and frustrating, when compared to an ICE heater.
Second, the ceramic element type heaters are wonderful, with an instant heat capability.
Single elements draw an average of about 1200 watts, and will affect an EV's range, but for short commutes, it really isn't a problem. In small to medium sized Evs, when driven in moderately cold weather, the single element type heaters work well. They do not put out as much intense heat as the stock heaters of ICEVs, but with their super quick warm up time, (even with a lower output temperature), they warm a cold vehicle faster than the ICEV heater can.
Third, the dual element ceramic heater is awesome! It puts out more intense heat than high output ICEV heaters can. In fact, I wouldn't recommend using the dual elements with the very lowest speed selection of the blower motor, since the intense temperature may melt the plastic vent runners! With both elements cranked on, the wattage consumed is pretty high (about 2200 watts average), but then, there is so much heat available that one would quickly switch back to a lower heat setting. I think that the dual element heater with its super-hot air, would be used for shorter periods of time, and possibly end up consuming less electricity overall. With the dual element heater, ice could easily be melted away from the windshield, then, the lower heat setting could be used.
I hope that this information will be useful for those new Evers in the process of building their first Evs, or for those who are looking to update their existing heat systems.
See Ya......John Wayland