A Quick Primer on Refrigerants and Phase Changes

Some basics of refrigerants are important because they play a key role in how efficiently your Air Conditioning system works. Proper air conditioning system maintenance includes an examination of the refrigerant load because the right charge is critical to optimized system performance. Phase changes in the refrigerant are what keep you cool. Refrigerants do this task well because that is their purpose. So let’s spend a few minutes to better understand refrigerants and understand their key role in effectively keeping you cool.

A refrigerant is what circulates in a heat pump that delivers hot or cold air by either compressing the refrigerant back into a liquid to deliver energy or allowing the refrigerant to expand by lowering the pressure whereupon it returns to a gas as it is able to absorb the large sums of energy needed to cross the phase change boundary from liquid to a gas.

We discuss the parts of your heating and cooling system heat pump through which the refrigerant circulates here.

We discuss the nerdy side of refrigerants and phase change here.

Basically you can cause a liquid to go through a phase change by changing the pressure or by adding energy to the liquid and causing the temperature to rise to its boiling point. We add energy to water to boil it and cook food. The water does not get hotter than 212 degrees F at sea level barometric pressure. You can boil it hard or simmer. The temp is a steady state temp at the phase change temperature of water at a particular air pressure. All the heat from the burner then is going to turn liquid water to gas, i.e. steam.

Now actual boiling bubbles do play a role in cooking- I figure they play a key role in keeping noodles agitated and separated from sticking; but the water does not get hotter than 212 degrees F, unless you get a pressure cooker where the pressure can be increased and thus raise the boiling point of the water.

Now water boiling on Pike’s Peak is totally different, much lower, because of the lower air pressure. This scientific principle has thwarted more than one cook until they figure out what is happening and how to ameliorate.

Let’s talk a moment about refrigerants

A great refrigerant is a liquid that is a low density liquid but a high density gas. The refrigerant also needs a high latent heat of vaporization. This means it takes a lot of energy to cross the phase change barrier from liquid to gas, which is energy released returned to a liquid. Water, for example, requires 972 btus of energy for each pound of liquid water turned to steam.  Our refrigerant also needs to condense under moderate pressure, so our HVAC systems can operate under less stress. Good refrigerants have many other properties; non flammable, ozone friendly, low toxicity, a lubrication attribute, etc.; but the factors that serve our theme here are the pressure and temperature characteristics and the latent heat of evaporation, which are the key factors in the refrigeration cycle, heat pump cycle whatever you want to call it, that keeps us cool.

A couple of stray points here.

The refrigeration cycle works in reverse to collect heat. This is a trend in the northern states when people want to use fewer fossil fuels and avoid CO – carbon monoxide generation in their homes. Heat pumps work quite efficiently but there are issues, the evaporator coils (we are collecting heat now) can freeze up at low ambient temps because, of course, they take heat from ambient and deliver it to the cozy home. But, in North Texas, heat is the issue and we concentrate our efforts on staying cool.

Therefore our HVAC technology in North Texas concentrates on air conditioning and then natural gas or direct electric heat to fulfill our needs for heating. But heat pumps work well, and there are even small infiltrations of ground source heat pumps which use the heat inherent in the earth to heat and cool homes. Again, we discuss the heat pump and refrigeration cycle here. 

There are other models of heat transfer using the principles of physics, but existing evaporation condensation technology has had years to optimize the space in homes and fits quite nicely generally into the architectures of homes, and so the battle has been to configure refrigerants that do not attack the ozone layer and then get the old and dangerous refrigerants out of the market.

Are you still here?

So not many people made it to the last paragraph of this particular page. If you are still interested in the physics and technology, you can find a variety of resources in Youtube or in google, by using the search terms here plus the more technical terms you will find along the way. I am going to spare you phase diagrams describing heat and pressure for materials in phase change but the wiki covers it well.

Any comments or thoughts? Just leave them below.





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