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Post by the light works on Oct 17, 2021 13:26:35 GMT
now that the cold season is coming around, I'm reminded of the old question of whether it warms the cabin up faster to crank the heater to max, or to leave it lower to allow the engine to warm up more; and it occirred to me to think that with newer more fuel efficient cars, there is less (or no) engine waste heat for heating the cabin.
the first generation Sprinter van dealt with this by having a diesel burning heat exchanger to supply cabin heat. but I wondered if it might be more efficient to redesign the Aircon to be a true heat pump; or if it would be better to add electric heat strips to the climate control.
the biggest advantage to a fuel burning heat exchanger is that it converts the fuel directly to heat, which is the most efficient conversion, but the disadvantage is it may not transfer the heat to the cabin as efficiently as it produces it. also if the car no longer uses fuel for propulsion, you're pretty much out of luck.
the biggest advantage of the heat pump is that moving heat from one place to another is more efficient than manufacturing heat - but the disadvantage is that the most likely place it will pull heat from is the engine coolant, and that might keep the engine below optimum temperature for longer.
the advantage of the electric heat strips is they have a fast response, and don't pull heat from the engine to work, but they do place additional load on the engine. however, that might help the engine reach operating temperature quicker, which means they would spend less time in operation than the other options.
obviously, none of us have the time and tech to do the actual experiments, but what are your thoughts?
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Post by rmc on Oct 17, 2021 17:32:18 GMT
now that the cold season is coming around, I'm reminded of the old question of whether it warms the cabin up faster to crank the heater to max, or to leave it lower to allow the engine to warm up more; and it occirred to me to think that with newer more fuel efficient cars, there is less (or no) engine waste heat for heating the cabin. the first generation Sprinter van dealt with this by having a diesel burning heat exchanger to supply cabin heat. but I wondered if it might be more efficient to redesign the Aircon to be a true heat pump; or if it would be better to add electric heat strips to the climate control. the biggest advantage to a fuel burning heat exchanger is that it converts the fuel directly to heat, which is the most efficient conversion, but the disadvantage is it may not transfer the heat to the cabin as efficiently as it produces it. also if the car no longer uses fuel for propulsion, you're pretty much out of luck. the biggest advantage of the heat pump is that moving heat from one place to another is more efficient than manufacturing heat - but the disadvantage is that the most likely place it will pull heat from is the engine coolant, and that might keep the engine below optimum temperature for longer. the advantage of the electric heat strips is they have a fast response, and don't pull heat from the engine to work, but they do place additional load on the engine. however, that might help the engine reach operating temperature quicker, which means they would spend less time in operation than the other options. obviously, none of us have the time and tech to do the actual experiments, but what are your thoughts? Blower on... feel wind.. if cold, blower off. Repeat every couple of minutes |
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Post by the light works on Oct 17, 2021 20:04:40 GMT
now that the cold season is coming around, I'm reminded of the old question of whether it warms the cabin up faster to crank the heater to max, or to leave it lower to allow the engine to warm up more; and it occirred to me to think that with newer more fuel efficient cars, there is less (or no) engine waste heat for heating the cabin. the first generation Sprinter van dealt with this by having a diesel burning heat exchanger to supply cabin heat. but I wondered if it might be more efficient to redesign the Aircon to be a true heat pump; or if it would be better to add electric heat strips to the climate control. the biggest advantage to a fuel burning heat exchanger is that it converts the fuel directly to heat, which is the most efficient conversion, but the disadvantage is it may not transfer the heat to the cabin as efficiently as it produces it. also if the car no longer uses fuel for propulsion, you're pretty much out of luck. the biggest advantage of the heat pump is that moving heat from one place to another is more efficient than manufacturing heat - but the disadvantage is that the most likely place it will pull heat from is the engine coolant, and that might keep the engine below optimum temperature for longer. the advantage of the electric heat strips is they have a fast response, and don't pull heat from the engine to work, but they do place additional load on the engine. however, that might help the engine reach operating temperature quicker, which means they would spend less time in operation than the other options. obviously, none of us have the time and tech to do the actual experiments, but what are your thoughts? Blower on... feel wind.. if cold, blower off. Repeat every couple of minutes and if you have to leave the car idling for a half hour to generate enough heat to defrost the windshield? |
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Post by rmc on Oct 17, 2021 21:12:55 GMT
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Post by GTCGreg on Oct 17, 2021 22:16:41 GMT
Even high efficiency gasoline engines will have plenty of waste heat to properly heat the cab of a typical car. Engines with exhaust driven turbocharges are the most thermodynamically efficient engines bet even those have plenty of waste heat. It's a requirement of the thermodynamic OTTO cycle that is used for all IC gas engines that heat must be removed from the cycle for it to operate. The maximum efficiency of the OTTO cycle is less than 60%. That means that at least 40% of all energy put into the engine ends up going out the radiator.
We have done test on the fastest way to raise the temperature in the patient compartment of ambulances. We found that running the blower on its highest speed will raise the temperature the fastest even when starting with a cold engine. The problem with that is with all the air movement, you get a wind chill effect so it feels colder, but it will still raise the temperature the fastest. So if you want to heat your car's cabin the fastest, set the bower to the highest setting, direct the air out the dash vents, turn on the recirculate option if it can be used in heat mode, and above all, do not turn on the defroster. When the defroster is turned on in most cars, it also turns on the AC compressor. The idea is to use the AC to dehumidify the air to clear the fog from inside the windows. While this is fine for defogging the windows, you will get less heat while the defroster is running.
Some of our ambulance HVAC systems also can provide electric heat. These are mainly used when the ambulance is connected to shore power but if the ambulance has an on board self-contained genset, it can be used for supplemental electric heat. Electric heat derived from the vehicles 12 Volt system is pretty much useless. At 12 Volts, it just takes too much current to get any useful heat. Save the 12 Volt heaters for your heated seats. Those 12 Volt heaters like the one RMC linked to are garbage. They draw about 10 Amps at 12 Volts. That's 120 Watts for a heat output of about 400 BTU. About the same as you would get lighting a candle.
As for heat pumps, Tesla is the only car manufacture that I know of that is using heat pump technology. They use it as part of their overall thermal management system for the batteries, motors and cabin HVAC. It would make sense for other electric vehicle manufactures to also use heat pumps for cabin heat. Maybe they do, I just haven't heard of them doing so.
As for Diesel engines, we have found that we often just can not get enough heat from a Diesel to heat the back of the ambulance. We either have to use auxiliary fuel fired heaters or supplemental electric heat if the ambulances has an on board generator.
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Post by the light works on Oct 17, 2021 23:23:46 GMT
Even high efficiency gasoline engines will have plenty of waste heat to properly heat the cab of a typical car. Engines with exhaust driven turbocharges are the most thermodynamically efficient engines bet even those have plenty of waste heat. It's a requirement of the thermodynamic OTTO cycle that is used for all IC gas engines that heat must be removed from the cycle for it to operate. The maximum efficiency of the OTTO cycle is less than 60%. That means that at least 40% of all energy put into the engine ends up going out the radiator. We have done test on the fastest way to raise the temperature in the patient compartment of ambulances. We found that running the blower on its highest speed will raise the temperature the fastest even when starting with a cold engine. The problem with that is with all the air movement, you get a wind chill effect so it feels colder, but it will still raise the temperature the fastest. So if you want to heat your car's cabin the fastest, set the bower to the highest setting, direct the air out the dash vents, turn on the recirculate option if it can be used in heat mode, and above all, do not turn on the defroster. When the defroster is turned on in most cars, it also turns on the AC compressor. The idea is to use the AC to dehumidify the air to clear the fog from inside the windows. While this is fine for defogging the windows, you will get less heat while the defroster is running. Some of our ambulance HVAC systems also can provide electric heat. These are mainly used when the ambulance is connected to shore power but if the ambulance has an on board self-contained genset, it can be used for supplemental electric heat. Electric heat derived from the vehicles 12 Volt system is pretty much useless. At 12 Volts, it just takes too much current to get any useful heat. Save the 12 Volt heaters for your heated seats. Those 12 Volt heaters like the one RMC linked to are garbage. They draw about 10 Amps at 12 Volts. That's 120 Watts for a heat output of about 400 BTU. About the same as you would get lighting a candle. As for heat pumps, Tesla is the only car manufacture that I know of that is using heat pump technology. They use it as part of their overall thermal management system for the batteries, motors and cabin HVAC. It would make sense for other electric vehicle manufactures to also use heat pumps for cabin heat. Maybe they do, I just haven't heard of them doing so. As for Diesel engines, we have found that we often just can not get enough heat from a Diesel to heat the back of the ambulance. We either have to use auxiliary fuel fired heaters or supplemental electric heat if the ambulances has an on board generator. I think the fire department ambulance has an electric heater that runs off shore power, but I'm not sure if it also uses an engine driven generator to power it. ambulances would be a good comparison platform, except I doubt you have enough different models sitting around to comparison test. I guess Tesla is a pretty good gauge of what Elon deems the most efficient overall system for an electric, it still leaves the question of whether it would be the best solution for a car that will ultimately be able to use waste heat. |
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Post by wvengineer on Oct 21, 2021 20:26:08 GMT
With a IC car (gas or diesel), you will always have waste heat from the engine that can be used for cabin heating. The one exceptions I can think of are cars like a Yugo or Classic VW Bug. The Yugo was too cheap to include a heater and the Bug was an air cooled engine that didn't have a ducting setup to blow engine air into the cabin. Bugs had a option for a gas fired heater.
Today, there is no production ICE car that doesn't use waste engine heat for cabin heating.Hybrids do get interesting. They Chevy Volt and Nissan Leaf both have heat pump systems to supplement the engine waste heat, but it does take a chunk out of battery life.
To the original question on the most efficient way to heat the cabin, On newer cars built to the PZEV standard (partial zero emission vehicle), the emissions control system is based on the engine being at running temp. The catalytic converter works poorly at ambient tempt. Because if this, the car will automatically use a fast idle until the engine gets up to temperature. Once it engine is warmed up and the cat is at operating temperature, it will reduce idle speed to save fuel while idling.
For me, even on a very cold morning (0f or lower), even if start driving as soon as I start the engine, the temp gauge is starting to creep up within about 2 miles of easy driving and I am starting to get some heat out of the system.
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Post by GTCGreg on Oct 21, 2021 21:00:21 GMT
The one exceptions I can think of are cars like a Yugo or Classic VW Bug. The Yugo was too cheap to include a heater and the Bug was an air cooled engine that didn't have a ducting setup to blow engine air into the cabin. Bugs had a option for a gas fired heater. The early VW bugs (and microbus) did have a cabin heater, sort of. You could open a vent that would divert engine cooling air into the cabin. You could also direct some of the luke-cool air onto the windshield. It worked about as well as you would expect, which was not very well at all. My 61 microbus also had a gas heater. One day I pulled the knob to start it and heard a loud explosion. I looked in the driver side mirror and saw a big hole in the side of the bus with black smoke billowing out of it. The was the end of the heater. |
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Post by wvengineer on Oct 21, 2021 23:56:44 GMT
As for Diesel engines, we have found that we often just can not get enough heat from a Diesel to heat the back of the ambulance. We either have to use auxiliary fuel fired heaters or supplemental electric heat if the ambulances has an on board generator. Interesting that a Diesel engine would not be able to supply enough waste heat to a back. I would think a diesel would have no trouble producing enough hot coolant to heat an ambulance and then some. Is it a matter of engine design or is the heating system is sized for a single row cab and not a 500+ ft^3 work area? |
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Post by the light works on Oct 22, 2021 0:57:43 GMT
With a IC car (gas or diesel), you will always have waste heat from the engine that can be used for cabin heating. The one exceptions I can think of are cars like a Yugo or Classic VW Bug. The Yugo was too cheap to include a heater and the Bug was an air cooled engine that didn't have a ducting setup to blow engine air into the cabin. Bugs had a option for a gas fired heater. Today, there is no production ICE car that doesn't use waste engine heat for cabin heating.Hybrids do get interesting. They Chevy Volt and Nissan Leaf both have heat pump systems to supplement the engine waste heat, but it does take a chunk out of battery life. To the original question on the most efficient way to heat the cabin, On newer cars built to the PZEV standard (partial zero emission vehicle), the emissions control system is based on the engine being at running temp. The catalytic converter works poorly at ambient tempt. Because if this, the car will automatically use a fast idle until the engine gets up to temperature. Once it engine is warmed up and the cat is at operating temperature, it will reduce idle speed to save fuel while idling. For me, even on a very cold morning (0f or lower), even if start driving as soon as I start the engine, the temp gauge is starting to creep up within about 2 miles of easy driving and I am starting to get some heat out of the system. the car may get heat within a couple miles, but we use heated seats in it. the truck takes 5 miles or more to start showing heat. it's that first bit of mileage I'm thinking of. |
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Post by the light works on Oct 22, 2021 0:59:32 GMT
As for Diesel engines, we have found that we often just can not get enough heat from a Diesel to heat the back of the ambulance. We either have to use auxiliary fuel fired heaters or supplemental electric heat if the ambulances has an on board generator. Interesting that a Diesel engine would not be able to supply enough waste heat to a back. I would think a diesel would have no trouble producing enough hot coolant to heat an ambulance and then some. Is it a matter of engine design or is the heating system is sized for a single row cab and not a 500+ ft^3 work area? I'm guessing in the case of the ambulances, it's the size of the heater. but diesels take a long time to get up to temperature, so if they're running short trips, it may never catch up. |
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Post by GTCGreg on Oct 22, 2021 2:43:18 GMT
As for Diesel engines, we have found that we often just can not get enough heat from a Diesel to heat the back of the ambulance. We either have to use auxiliary fuel fired heaters or supplemental electric heat if the ambulances has an on board generator. Interesting that a Diesel engine would not be able to supply enough waste heat to a back. I would think a diesel would have no trouble producing enough hot coolant to heat an ambulance and then some. Is it a matter of engine design or is the heating system is sized for a single row cab and not a 500+ ft^3 work area? The Federal specification for ambulances (KKK-A-1822) requires the heating system in the patient compartment of an ambulance to be able to heat the interior of the ambulance from 32ºF to 68ºF within 30 minutes of starting with a cold engine and running it at high idle (1600RPM max). We have found that no matter how big a heater core we put into the ambulance, and even using a coolant boost pump, some diesel engines just can't produce enough heat to meet the spec. Once the engine is under load and the vehicle up to temperature, the engine usually has no problem maintaining the temperature. It's just that if a customer insists that the ambulance meets the full KKK spec, we have no choice but to put in an auxiliary fuel fired heater. |
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