Heat Pump Limit?

[Cybr.Myk]

I'm the guy who had asked. I was also wondering about the dogs - so I got my answer.

My dog’s name is Queen Cleo’paw’tra. Not sure if your user name has anything to do with your dog or not.

 

[Cleo-n-Company]

My dog’s name is Queen Cleo’paw’tra. Not sure if your user name has anything to do with your dog or not. View attachment 636980

It does 100%

Cleopatra is our oh-so-beloved 12 year old Standard Poodle

She has always enjoyed riding in the Model S because of the low step-in

 

[STS-134]

doesnt the patent state the existence of two resistance heaters in heating mode 3?

Looks like this design does have a few issues with efficiency, if this guy is correct about how it works.

First, there's a heating mode that he calls "Heating 1" in the first video that he describes between 6:15 and 7:45 where the radiator is the source of heat, and sends heat directly to the chiller. This is the most efficient mode. The batteries get heated only by the drive unit.

But this system appears to be incapable of the following heat flow:
- Heat sourced from radiator (which goes directly to the chiller)
- Heat sent to cabin condenser AND liquid cooled condenser for heating up the batteries and cabin quickly and efficiently, when the outdoor temp is say at 0°C and the batteries are at the same temperature

The issue is that when the system connects the liquid cooled condenser and batteries in the same glycol loop, the chiller is always between the two, and the batteries are always after the chiller. It apparently cannot run in "split system" mode with the radiator and chiller in one circuit and the liquid cooled condenser and batteries in the other. In such a scenario, it would be forced to run the drive unit inefficiently in order to heat the batteries but as we know, this is basically like running at COP=1 and is far less efficient than using the heat pump.

Next, look at "Condition 9", discussed between 7:30 and 8:30 in this video (the same one you posted above):

This is the mode where the batteries, drive unit, and atmosphere all supply heat to the cabin via the heat pump. But why is the radiator last in the loop, just before the chiller? The atmosphere has to be warmer than the refrigerant coming out of the batteries and drive unit, right? Otherwise this flow wouldn't work. But why don't we put the radiator FIRST in the loop after the chiller? This allows the coolant to absorb the maximum amount of heat from the atmosphere first, before taking heat from the batteries and drive unit. Why cool off the batteries more than necessary?

The final issue is with "Condition 15" or "Cooling 3" which he describes between 4:30 and the end of the video in the third video in the series:

This mode only works well when it's not too hot outside. But let's take an example of a very hot day. Let's say it's 45°C outside and we want to chill the batteries to around 25-30°C. What's the temperature of the glycol coming back from the radiator? Well it's at least 45°C, right? It cannot be cooler than the atmosphere. But we're sending that glycol directly to the chiller?!? This is like one of those inefficient portable AC units with the hose going out the window which no longer operates as an entirely split system because it requires direct intrusion from the hot side to the cold side (via cracks in the building where hot outdoor air replaces the cool indoor air that was pushed into the hose and expelled through the window). I think he may have missed an operating mode here? Assuming the drive unit can take temperatures of 45-50°C without any issues (is this possible?), it would be far more efficient to operate the system like in "Condition 14" or "Cooling 2" (discussion of that mode starts at 3:20) with the liquid cooled condenser, radiator, and drive unit in one loop and the batteries and chiller in the other, with the exception that the cabin condenser is inactive and the cabin evaporator is used. In this way, the heat from the cabin and batteries (from the cabin evaporator and chiller) are rejected via the LCC and radiator, and after cooling off via the radiator, the still warm glycol can take some heat from the drive unit (which I'm assuming can tolerate being much hotter than the batteries) before picking up more heat via the liquid cooled condenser and rejecting it via the radiator.

 

[STS-134]

Looks like this design does have a few issues with efficiency, if this guy is correct about how it works.

First, there's a heating mode that he calls "Heating 1" in the first video that he describes between 6:15 and 7:45 where the radiator is the source of heat, and sends heat directly to the chiller. This is the most efficient mode. The batteries get heated only by the drive unit.

But this system appears to be incapable of the following heat flow:
- Heat sourced from radiator (which goes directly to the chiller)
- Heat sent to cabin condenser AND liquid cooled condenser for heating up the batteries and cabin quickly and efficiently, when the outdoor temp is say at 0°C and the batteries are at the same temperature

The issue is that when the system connects the liquid cooled condenser and batteries in the same glycol loop, the chiller is always between the two, and the batteries are always after the chiller. It apparently cannot run in "split system" mode with the radiator and chiller in one circuit and the liquid cooled condenser and batteries in the other. In such a scenario, it would be forced to run the drive unit inefficiently in order to heat the batteries but as we know, this is basically like running at COP=1 and is far less efficient than using the heat pump.

Next, look at "Condition 9", discussed between 7:30 and 8:30 in this video (the same one you posted above):

This is the mode where the batteries, drive unit, and atmosphere all supply heat to the cabin via the heat pump. But why is the radiator last in the loop, just before the chiller? The atmosphere has to be warmer than the refrigerant coming out of the batteries and drive unit, right? Otherwise this flow wouldn't work. But why don't we put the radiator FIRST in the loop after the chiller? This allows the coolant to absorb the maximum amount of heat from the atmosphere first, before taking heat from the batteries and drive unit. Why cool off the batteries more than necessary?

The final issue is with "Condition 15" or "Cooling 3" which he describes between 4:30 and the end of the video in the third video in the series:

This mode only works well when it's not too hot outside. But let's take an example of a very hot day. Let's say it's 45°C outside and we want to chill the batteries to around 25-30°C. What's the temperature of the glycol coming back from the radiator? Well it's at least 45°C, right? It cannot be cooler than the atmosphere. But we're sending that glycol directly to the chiller?!? This is like one of those inefficient portable AC units with the hose going out the window which no longer operates as an entirely split system because it requires direct intrusion from the hot side to the cold side (via cracks in the building where hot outdoor air replaces the cool indoor air that was pushed into the hose and expelled through the window). I think he may have missed an operating mode here? Assuming the drive unit can take temperatures of 45-50°C without any issues (is this possible?), it would be far more efficient to operate the system like in "Condition 14" or "Cooling 2" (discussion of that mode starts at 3:20) with the liquid cooled condenser, radiator, and drive unit in one loop and the batteries and chiller in the other, with the exception that the cabin condenser is inactive and the cabin evaporator is used. In this way, the heat from the cabin and batteries (from the cabin evaporator and chiller) are rejected via the LCC and radiator, and after cooling off via the radiator, the still warm glycol can take some heat from the drive unit (which I'm assuming can tolerate being much hotter than the batteries) before picking up more heat via the liquid cooled condenser and rejecting it via the radiator.

So I found the patent on the heat pump. It does describe 15 operating modes but these seem to just be examples. I don't think they are a collectively exhaustive list of operating modes, i.e. there are operating modes that are not described in the patent. For "Condition 15" or "Cooling 3" mode, the patent says:

FIG. 29 is a schematic diagram illustrating the vehicle thermal management system of FIG. 10 configured in a third cooling mode to provide quieter HVAC cabin pull-down. The third cooling mode 3000 improves the cooling power to noise ratio during HVAC cabin pull-downs. During HVAC cabin pull-downs, e.g., cooling a cabin after a long soak in the sun on a hot day, there is typically quite a lot of noise coming from the external fan 324 and the compressor 214. The vehicle heat pump system 202 architecture provides an opportunity to use the battery system 106 as a heat sink in order to reduce external fan noise and also compressor 214 RPM/noise. Instead of rejecting all of the liquid cooled condenser 224 load to ambient, some of that load could be delivered to the battery system 106 (if sufficiently cool). This would immediately reduce the external fan 324 speed/noise, lower the discharge pressure, increase the refrigeration specific cooling power, and therefore also reduce the compressor 214 speed/noise. The cabin condenser 216 is not operational. The 3-way valve 230 routes all of the refrigerant to the drive train liquid-cooled condenser 224. The radiator 236 rejects part of the load, and the rest of the load goes to the battery system 106 via the 5-way valve 208 (series).

So it's basically used when pulling down the temperature of the cabin quickly, and it's done to reduce compressor noise. It's not meant for extended use. I think it's likely that it does have the ability to operate like in "Condition 14" or "Cooling 2" mode described in that third video, except with the cabin evaporator working instead of the cabin condenser.

The general rules seem to be:
1. Any two sections can be connected in a glycol loop by themselves: chiller + batteries, batteries + drive unit, drive unit/LCC. The rest will then be in a separate loop. Or, all of the components can be included in one giant loop
2. If any condenser is active, at least one of the two evaporators must be active (in other words, if the compressor is pushing heat to a condenser, it needs to source it from at least one of the evaporators, and if it's pulling heat from the evaporators, it needs a sink to dispose of it).

I think there are also operating modes that do not use the compressor. For example, if the cabin requires neither heating nor cooling, the system can connect the drive unit to the radiator and simply run the drive unit pump, to cool the drive unit without any use of chillers or condensers. It can also cool both batteries and drive unit without the use of the compressor as well by connecting components in the proper way via the octovalve and running the appropriate pumps. Given that the name of the game is efficiency, it's likely that it does this if for example it's 15°C outside, the sun is providing proper cabin temperature without any use of the heat pump, and the batteries and drive unit can be cooled via the radiator with pumps alone (and possibly a radiator fan, if the vehicle isn't moving).