OK. You've made my head hurt. We need WOT. Meanwhile just set it to comfort 72 (or 22C) and don't worry about it.
LL
LL
How does engine heating work?
It occurred to me today, when running HOLD for heat, that this is more complicated a question than it seems.
There must be 4 different temperatures (at least 4), go with me here and see where it ends up:
A - the temperature at which the heater blend valve to cabin shuts off coolant from the engine block (as coolant cools)
B - the temperature at which the engine blend valve opens (as coolant warms)
C - the temperature at which the thermostat to/from the front radiator closes (as coolant cools)
D - the temperature at which the thermostat to/from the front radiator opens (as coolant warms)
Obviously, A<B and C<D.
It's not obvious if B<C.
It's also not obvious that these temperatures are fixed, though I'd guess at least C and D are.
I'll explain why this is significant.
Say you get into your cold Volt with the intention of heating the cab up with the engine in HOLD. You don't put the electric heating on. As the engine warms up, first it passes temp A and nothing happens, it is still warming up. Then it passes temp B and the valve to the cabin matrix opens and engine coolant flows around the matrix and delivers heat.
A must be some reasonable difference to B because if A and B were the same temperature, almost as soon as you turn the engine off, the valve would close and you'd be back with cold through the matrix. There must be some margin at which the engine heats up past A before opening B, and then allows the engine block coolant to cool down, back to A.
If A is too high, then you end up wasting warm coolant in the engine block, but if A is too low then if you turn the electric heating on you'll end up warming the engine block up with the electric heater.
You want D to be a good bit higher than B if you are engineering it for efficiency. You want to be able to warm the engine coolant up past B (so you can heat the cabin with the engine off, all the way back to A) but if D weren't much higher than B then you may end up wasting useful cabin heat out of the front radiator.
Let's say you have been running the engine for a while and gone all the way to D and now the engine is being cooled by the front radiator. You turn the engine off. What happens now? As the coolant cools, the system is still wasting heat out of the front radiator, because the thermostat won't close until it drops to C. But is it an electronic thermostat, and as soon as the engine stops the thermostat closes at D (or more)?
If the thermostat stays open all the way down to C, then that's just wasted heat that could have gone into the cabin.
Am I anywhere close to figuring out fine details of the heating system? There are some behaviours here that would help improve my efficient use of HOLD if only I could know.
For example, if D was very high, then it would make sense to run the engine for some time after reaching B (the start of getting cabin heat) right up to just under the thermostat temperature, then turn the engine off. This would give the maximum ratio of coolant heat into the cabin, and probably means the engine also ran more efficiently as it would have had less stop-start.
But if the engine reaches D almost as soon as it has reached B, then the most efficient approach would be to turn HOLD off as soon as you feel heat coming through.
Also, if the blend valve from the engine coolant operates only when that coolant is warmer than the electric heated side, then if you are using both electric and engine heating, it would make sense to try to avoid using electric heating any time towards the end of the journey because then the engine coolant circuit will stay 'open' and you can draw off as much of the engine heat as possible. If you electrically heat up the circuit on the cabin side and it causes the blend valve to close, then you'd have wasted the residual heat in the block.
Has GM thought about all of this, or is it a more 'dumb' and wasteful system?
What are the temperatures A, B, C & D?
... and you thought you knew how engine heating worked!!!
There must be 4 different temperatures (at least 4), go with me here and see where it ends up:
A - the temperature at which the heater blend valve to cabin shuts off coolant from the engine block (as coolant cools)
B - the temperature at which the engine blend valve opens (as coolant warms)
C - the temperature at which the thermostat to/from the front radiator closes (as coolant cools)
D - the temperature at which the thermostat to/from the front radiator opens (as coolant warms)
Obviously, A<B and C<D.
It's not obvious if B<C.
It's also not obvious that these temperatures are fixed, though I'd guess at least C and D are.
I'll explain why this is significant.
Say you get into your cold Volt with the intention of heating the cab up with the engine in HOLD. You don't put the electric heating on. As the engine warms up, first it passes temp A and nothing happens, it is still warming up. Then it passes temp B and the valve to the cabin matrix opens and engine coolant flows around the matrix and delivers heat.
A must be some reasonable difference to B because if A and B were the same temperature, almost as soon as you turn the engine off, the valve would close and you'd be back with cold through the matrix. There must be some margin at which the engine heats up past A before opening B, and then allows the engine block coolant to cool down, back to A.
If A is too high, then you end up wasting warm coolant in the engine block, but if A is too low then if you turn the electric heating on you'll end up warming the engine block up with the electric heater.
You want D to be a good bit higher than B if you are engineering it for efficiency. You want to be able to warm the engine coolant up past B (so you can heat the cabin with the engine off, all the way back to A) but if D weren't much higher than B then you may end up wasting useful cabin heat out of the front radiator.
Let's say you have been running the engine for a while and gone all the way to D and now the engine is being cooled by the front radiator. You turn the engine off. What happens now? As the coolant cools, the system is still wasting heat out of the front radiator, because the thermostat won't close until it drops to C. But is it an electronic thermostat, and as soon as the engine stops the thermostat closes at D (or more)?
If the thermostat stays open all the way down to C, then that's just wasted heat that could have gone into the cabin.
Am I anywhere close to figuring out fine details of the heating system? There are some behaviours here that would help improve my efficient use of HOLD if only I could know.
For example, if D was very high, then it would make sense to run the engine for some time after reaching B (the start of getting cabin heat) right up to just under the thermostat temperature, then turn the engine off. This would give the maximum ratio of coolant heat into the cabin, and probably means the engine also ran more efficiently as it would have had less stop-start.
But if the engine reaches D almost as soon as it has reached B, then the most efficient approach would be to turn HOLD off as soon as you feel heat coming through.
Also, if the blend valve from the engine coolant operates only when that coolant is warmer than the electric heated side, then if you are using both electric and engine heating, it would make sense to try to avoid using electric heating any time towards the end of the journey because then the engine coolant circuit will stay 'open' and you can draw off as much of the engine heat as possible. If you electrically heat up the circuit on the cabin side and it causes the blend valve to close, then you'd have wasted the residual heat in the block.
Has GM thought about all of this, or is it a more 'dumb' and wasteful system?
What are the temperatures A, B, C & D?
... and you thought you knew how engine heating worked!!!
1 - 15 of 15 Posts
Internal coolant merge appears to be around 55C (same as ERDTT cutoff).
External rad opens around 82-85 and closes around 75-78. So with an optimum temp of ~75C, you see why ERDTTs 55-65 is not enough to satisfy EMM.
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B < C.
I have not measured when the mixing valve closes going the other way. Not sure I really could unless there's a PID for the electric heater temp to compare. (which I don't have)
The best you could do is see that engine coolant temp drops more slowly and electric heat starts up.
External rad opens around 82-85 and closes around 75-78. So with an optimum temp of ~75C, you see why ERDTTs 55-65 is not enough to satisfy EMM.
B < C.
I have not measured when the mixing valve closes going the other way. Not sure I really could unless there's a PID for the electric heater temp to compare. (which I don't have)
The best you could do is see that engine coolant temp drops more slowly and electric heat starts up.
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When you have real winter, the AC doesn't run.
If it's warm enough that the AC will run, that's too warm to turn the heat on!
Compressor won't run below freezing or so.
Just blend in outside (cold=dry) air.
Oh, and never use the actual defrost setting.
I just have it on standard auto or foot+window setting. Reduces the times AC comes on vs guarantees it to be on with defrost setting. (If warm enough to compressor to run)
If it's warm enough that the AC will run, that's too warm to turn the heat on!
Compressor won't run below freezing or so.
Just blend in outside (cold=dry) air.
Oh, and never use the actual defrost setting.
I just have it on standard auto or foot+window setting. Reduces the times AC comes on vs guarantees it to be on with defrost setting. (If warm enough to compressor to run)
1 - 15 of 15 Posts
