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Canada's timeline to end sales of petrol-powered cars advanced to 2035

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kalvado:

--- Quote from: jakeroot on July 13, 2021, 10:30:30 PM ---
--- Quote from: kalvado on July 13, 2021, 09:39:04 PM ---As far as I remember, typical dual function household units cannot go below water freezing temperature. One if reasons, besides refrigerant properties, would be ice formation in the radiator. Unlike liquid water, ice cannot just drip down.

--- End quote ---

Could you not reverse the refrigerant process to melt the ice formation? If it's radically below freezing, I could see this becoming very inefficient, but I think it's still possible.

--- End quote ---
Can you run an AC in a car when outside temperature is below 0? Sure, most countries would consider it legal. Make sure driver has an extra layer of warm coat available.

You can always solve issues by over engineering, but things could get complex, expensive and inefficient.
Heat pumps take advantage of high transfer efficiency over small temperature differences. When temperature differences are not so small, benefits of heat pump may be more difficult to actually implement, especially for the places like Winnipeg (this is Canadian forum, right?) where hot days in summer require real AC, and cold winters present challenges due to freezing coolant and oil becoming too viscous to start ICE. I really wonder what the gas formulation is for those conditions.
I can imagine quite a few tricks to be implemented, but things like twiceh-a-year major system service for reconfiguration may be too much to ask from an average driver.

Duke87:

--- Quote from: kalvado on July 13, 2021, 09:39:04 PM ---As far as I remember, typical dual function household units cannot go below water freezing temperature. One if reasons, besides refrigerant properties, would be ice formation in the radiator. Unlike liquid water, ice cannot just drip down.
--- End quote ---

Ice formation won't occur unless the coils get below the dew point of the surrounding air. Fortunately in most climates it tends not to be that humid when it's cold.

When it comes to functional limitations of heat pumps, in practice there are two of them:

1) As temperatures outside drop, the rate of heat loss through the walls of your building (or car) increases and the maximum rate at which a heat pump can pump inside decreases. So even once you factor in the effects of things like sunlight and people's body heat, a point will come where the heat pump can meet some but not all of the demand and you need to turn to another heat source (typically electric resistive heaters in the air handler) to pick up the slack.

2) As temperatures outside drop, the efficiency of a heat pump drops. There comes a point where the ratio of heat energy moved to energy consumed (this is known as a Coefficient of Performance, or COP) drops below 1. Once this happens, even if the heat pump is still capable of meeting the demand for heat, you are better off shutting it off and switching over to resistive heat.

So it becomes a question of at what point do you hit one of these two limitations. With older heat pumps it often was around freezing, but there are newer heat pumps that are perfectly capable of running in heat pump mode lower than that. Indeed, we have a heat pump at our home and the resistive heater doesn't start to kick in and help until the temperature drops below about 20 outside.


--- Quote from: jakeroot on July 13, 2021, 10:30:30 PM ---Could you not reverse the refrigerant process to melt the ice formation? If it's radically below freezing, I could see this becoming very inefficient, but I think it's still possible.

--- End quote ---

That's counterproductive since you'd be pulling heat from inside to do this. This problem is more effectively resolved with resistive heating elements on the coils. That's how your freezer does it.

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