There is no such thing as “the cold” - a crash course on heat transfer.

Shift your perspective: the chamber is not keeping the cold in – it’s keeping the heat out.

1.      There is no such thing as THE COLD. Cold is a relative term that relates to the negative temperature delta between something of lower temperature relative to something of higher temperature. While ice water is cold to a human, ice water is boiling relative to liquid nitrogen. To sound educated in cryotherapy – you must start thinking, and talking, in terms of heat.

2.      Heat and temperature are NOT the same. Heat is known as an extensive property of matter contrasted by an intensive property of matter (e.g. temperature, pressure, etc.). Extensive properties can be added together, intensive properties cannot. I like to use this analogy, “if it’s 70F on one side of the room, and 70F on the other side of the room… it’s not 140F in the room. But if there is 70 joules of heat on one side of the room, and 70 joules of heat on the other – there is 140 joules of heat in the room”. Rather intuitively, when an object receives heat it’s temperature increases, and when an object loses heat it’s temperature decreases. It’s like the transfer of money. The more money (heat) you have the richer (warmer) you are, and vice versa. Two baseballs at different temperatures have different amounts of heat content in them. All mass has heat unless it is at absolute zero (-459.67F) – which is impossible to get to. Even deep space only gets to -455F.

3.      Heat is energy. It’s important to realize that energy, and therefore heat, is NEVER destroyed/lost – it merely transfers from mass to mass. Let’s consider your left hand and your right hand. You take your left hand and stick it into ice water for 10min. The heat from your left hand is being sucked from it by the water. Because of this, the temperature of your hand decreases and the temperature of the water increases. Heat is being transferred between the two. Now you remove your hand from the water and hold your other hand. One hand is cold and one hand is warm. This is important: heat ALWAYS transfers from higher temperature to lower temperature. The heat from your warm hand is transferring into your cold hand, warming it. Conversely, because the heat content of your warm hand is decreasing, the warm hand is becoming colder. The larger the difference in temperature between two masses, the more heat is being transferred per second.

4.      There is no heat transfer when objects are at the same temperature. It’s called thermodynamic equilibrium and it’s important when we talk about windchill. Let’s come up with rather silly analogy. Say it’s 110F outside and really windy. You leave a metal spatula near the hot stove. Heat transfers from the stove to the spatula, raising its temperature. You notice and pull the spatula away – the spatula is 110F. You throw it outside into the 110F air, thinking to cool it off. I don’t care how hard the wind is blowing outside – that spatula is NOT changing temperature. Remember that bit about heat always transferring from hot to cold? Both the air and the spatula are the same temperature. Neither one is warmer than the other. They will both remain the same temperature until it starts cooling off outside.

5.      Conduction, convection, and radiation. There are three ways heat is transferred. Conduction happens when masses are in contact with each other. It is a highly efficient mode of heat transfer. You can conduct heat into air despite air being a non-physical object, but extremely poorly. Conduction to air only happens when the air is very still (no flow) which it practically impossible. If the air begins to flow, we convert into the second mode of heat transfer – convection. Like your convection oven at home, by applying flow to a fluid it will improve the rate of heat transfer. Like blowing on a hot cup of tea instead of just letting it sit there. Lastly, radiation is a very weak form of electromagnetic heat transfer and exists at all time between all object above absolute zero – don’t worry about radiation 😊 it’s not really important in the context of this crash course.

How does this apply to Electric Cryotherapy?

1.      Your cryotherapy system is acting like a heat vacuum. The air is convecting the heat away from the clients body, lowing the temperature of their skin while warming the air. Like a convection oven in reverse.

2.      We can literally trace the heat output of the user all the way from their skin to the air, into the evaporator, through the refrigerants, and all the way up to the condenser on the roof where it is rejected to atmosphere. It’s all part of the vacuum. The CryoDyson.

3.      The chamber is not keeping the cold in – it is keeping the heat out. The goal is to have as little heat content in the air as possible, so the air is the coldest it can be. The colder the air, the faster the heat transfers from the client’s skin. You will see this in terms of session duration.

4.      If the chamber is not cold enough for the client, they can increase windchill (convection) inside the chamber. More convection = more heat transfer.

5.      It’s important to note that more wind does NOT mean colder air temperature. The air temperature remains the same, the RATE OF HEAT TRANSFER increases. Here is a simple windchill calculator: Wind Chill Calculator (weather.gov). What it is calculating is something called “effective temperature” meaning the temperature of STILL AIR required to equal the amount of heat being transferred by highly convective air (windchill).

6.      Because the system is so cold, it will instantly nucleate (freeze) water vapor in the air. You will see this as fog coming from the machine. It is NOT producing water, simply freezing/condensing the vapor content already present in the air.

7.      We put off a lot of water vapor as human. Both from perspiration and especially from respiration. The average human emits half to a full liter of water from their breath each day. Let’s keep that water moisture out of the system because the consequent ice can clog the evaporator. Have your clients wear a mask. It’s more comfortable for them to breathe and helps maintain the performance of your system.